Move the libusb source from jumper to external.android-sdk-tools_r12android-sdk-adt_r12

Change-Id: If1f7a5fd668a88a438bd4cc3e44544d14ec4c6ec

12 files changed, 11647 insertions, 0 deletions

diff --git a/libusb/Makefile.am b/libusb/Makefile.am
new file mode 100644
index 0000000..a2be46c
--- /dev/null
+++ b/libusb/Makefile.am
@@ -0,0 +1,21 @@
+lib_LTLIBRARIES = libusb-1.0.la
+
+LINUX_USBFS_SRC = os/linux_usbfs.h os/linux_usbfs.c
+DARWIN_USB_SRC = os/darwin_usb.h os/darwin_usb.c
+
+EXTRA_DIST = $(LINUX_USBFS_SRC) $(DARWIN_USB_SRC)
+
+if OS_LINUX
+OS_SRC = $(LINUX_USBFS_SRC)
+endif
+
+if OS_DARWIN
+OS_SRC = $(DARWIN_USB_SRC)
+AM_CFLAGS_EXT = -no-cpp-precomp
+endif
+
+libusb_1_0_la_CFLAGS = $(VISIBILITY_CFLAGS) $(AM_CFLAGS) -pthread
+libusb_1_0_la_SOURCES = libusbi.h core.c descriptor.c io.c sync.c $(OS_SRC)
+
+hdrdir = $(includedir)/libusb-1.0
+hdr_HEADERS = libusb.h
diff --git a/libusb/Makefile.in b/libusb/Makefile.in
new file mode 100644
index 0000000..34c14b3
--- /dev/null
+++ b/libusb/Makefile.in
@@ -0,0 +1,637 @@
+# Makefile.in generated by automake 1.11.1 from Makefile.am.
+# @configure_input@
+
+# Copyright (C) 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002,
+# 2003, 2004, 2005, 2006, 2007, 2008, 2009  Free Software Foundation,
+# Inc.
+# This Makefile.in is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY, to the extent permitted by law; without
+# even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+# PARTICULAR PURPOSE.
+
+@SET_MAKE@
+
+
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+	sync.c os/darwin_usb.h os/darwin_usb.c os/linux_usbfs.h \
+	os/linux_usbfs.c
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+	while read files; do \
+	  echo " $(INSTALL_HEADER) $$files '$(DESTDIR)$(hdrdir)'"; \
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+	    echo "INSTALL_PROGRAM_ENV=STRIPPROG='$(STRIP)'"` install
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+	-test . = "$(srcdir)" || test -z "$(CONFIG_CLEAN_VPATH_FILES)" || rm -f $(CONFIG_CLEAN_VPATH_FILES)
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+# Tell versions [3.59,3.63) of GNU make to not export all variables.
+# Otherwise a system limit (for SysV at least) may be exceeded.
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diff --git a/libusb/core.c b/libusb/core.c
new file mode 100644
index 0000000..7e4fd24
--- /dev/null
+++ b/libusb/core.c
@@ -0,0 +1,1583 @@
+/*
+ * Core functions for libusb
+ * Copyright (C) 2007-2008 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <errno.h>
+#include <poll.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "libusb.h"
+#include "libusbi.h"
+
+#if defined(OS_LINUX)
+const struct usbi_os_backend * const usbi_backend = &linux_usbfs_backend;
+#elif defined(OS_DARWIN)
+const struct usbi_os_backend * const usbi_backend = &darwin_backend;
+#else
+#error "Unsupported OS"
+#endif
+
+struct libusb_context *usbi_default_context = NULL;
+static pthread_mutex_t default_context_lock = PTHREAD_MUTEX_INITIALIZER;
+
+/**
+ * \mainpage libusb-1.0 API Reference
+ *
+ * \section intro Introduction
+ *
+ * libusb is an open source library that allows you to communicate with USB
+ * devices from userspace. For more info, see the
+ * <a href="http://libusb.sourceforge.net">libusb homepage</a>.
+ *
+ * This documentation is aimed at application developers wishing to
+ * communicate with USB peripherals from their own software. After reviewing
+ * this documentation, feedback and questions can be sent to the
+ * <a href="http://sourceforge.net/mail/?group_id=1674">libusb-devel mailing
+ * list</a>.
+ *
+ * This documentation assumes knowledge of how to operate USB devices from
+ * a software standpoint (descriptors, configurations, interfaces, endpoints,
+ * control/bulk/interrupt/isochronous transfers, etc). Full information
+ * can be found in the <a href="http://www.usb.org/developers/docs/">USB 2.0
+ * Specification</a> which is available for free download. You can probably
+ * find less verbose introductions by searching the web.
+ *
+ * \section features Library features
+ *
+ * - All transfer types supported (control/bulk/interrupt/isochronous)
+ * - 2 transfer interfaces:
+ *    -# Synchronous (simple)
+ *    -# Asynchronous (more complicated, but more powerful)
+ * - Thread safe (although the asynchronous interface means that you
+ *   usually won't need to thread)
+ * - Lightweight with lean API
+ * - Compatible with libusb-0.1 through the libusb-compat-0.1 translation layer
+ *
+ * \section gettingstarted Getting Started
+ *
+ * To begin reading the API documentation, start with the Modules page which
+ * links to the different categories of libusb's functionality.
+ *
+ * One decision you will have to make is whether to use the synchronous
+ * or the asynchronous data transfer interface. The \ref io documentation
+ * provides some insight into this topic.
+ *
+ * Some example programs can be found in the libusb source distribution under
+ * the "examples" subdirectory. The libusb homepage includes a list of
+ * real-life project examples which use libusb.
+ *
+ * \section errorhandling Error handling
+ *
+ * libusb functions typically return 0 on success or a negative error code
+ * on failure. These negative error codes relate to LIBUSB_ERROR constants
+ * which are listed on the \ref misc "miscellaneous" documentation page.
+ *
+ * \section msglog Debug message logging
+ *
+ * libusb does not log any messages by default. Your application is therefore
+ * free to close stdout/stderr and those descriptors may be reused without
+ * worry.
+ *
+ * The libusb_set_debug() function can be used to enable stdout/stderr logging
+ * of certain messages. Under standard configuration, libusb doesn't really
+ * log much at all, so you are advised to use this function to enable all
+ * error/warning/informational messages. It will help you debug problems with
+ * your software.
+ *
+ * The logged messages are unstructured. There is no one-to-one correspondence
+ * between messages being logged and success or failure return codes from
+ * libusb functions. There is no format to the messages, so you should not
+ * try to capture or parse them. They are not and will not be localized.
+ * These messages are not suitable for being passed to your application user;
+ * instead, you should interpret the error codes returned from libusb functions
+ * and provide appropriate notification to the user. The messages are simply
+ * there to aid you as a programmer, and if you're confused because you're
+ * getting a strange error code from a libusb function, enabling message
+ * logging may give you a suitable explanation.
+ *
+ * The LIBUSB_DEBUG environment variable can be used to enable message logging
+ * at run-time. This environment variable should be set to a number, which is
+ * interpreted the same as the libusb_set_debug() parameter. When this
+ * environment variable is set, the message logging verbosity level is fixed
+ * and libusb_set_debug() effectively does nothing.
+ *
+ * libusb can be compiled without any logging functions, useful for embedded
+ * systems. In this case, libusb_set_debug() and the LIBUSB_DEBUG environment
+ * variable have no effects.
+ *
+ * libusb can also be compiled with verbose debugging messages. When the
+ * library is compiled in this way, all messages of all verbosities are always
+ * logged.  libusb_set_debug() and the LIBUSB_DEBUG environment variable have
+ * no effects.
+ *
+ * \section remarks Other remarks
+ *
+ * libusb does have imperfections. The \ref caveats "caveats" page attempts
+ * to document these.
+ */
+
+/**
+ * \page caveats Caveats
+ *
+ * \section devresets Device resets
+ *
+ * The libusb_reset_device() function allows you to reset a device. If your
+ * program has to call such a function, it should obviously be aware that
+ * the reset will cause device state to change (e.g. register values may be
+ * reset).
+ *
+ * The problem is that any other program could reset the device your program
+ * is working with, at any time. libusb does not offer a mechanism to inform
+ * you when this has happened, so if someone else resets your device it will
+ * not be clear to your own program why the device state has changed.
+ *
+ * Ultimately, this is a limitation of writing drivers in userspace.
+ * Separation from the USB stack in the underlying kernel makes it difficult
+ * for the operating system to deliver such notifications to your program.
+ * The Linux kernel USB stack allows such reset notifications to be delivered
+ * to in-kernel USB drivers, but it is not clear how such notifications could
+ * be delivered to second-class drivers that live in userspace.
+ *
+ * \section blockonly Blocking-only functionality
+ *
+ * The functionality listed below is only available through synchronous,
+ * blocking functions. There are no asynchronous/non-blocking alternatives,
+ * and no clear ways of implementing these.
+ *
+ * - Configuration activation (libusb_set_configuration())
+ * - Interface/alternate setting activation (libusb_set_interface_alt_setting())
+ * - Releasing of interfaces (libusb_release_interface())
+ * - Clearing of halt/stall condition (libusb_clear_halt())
+ * - Device resets (libusb_reset_device())
+ *
+ * \section nohotplug No hotplugging
+ *
+ * libusb-1.0 lacks functionality for providing notifications of when devices
+ * are added or removed. This functionality is planned to be implemented
+ * for libusb-1.1.
+ *
+ * That said, there is basic disconnection handling for open device handles:
+ *  - If there are ongoing transfers, libusb's handle_events loop will detect
+ *    disconnections and complete ongoing transfers with the
+ *    LIBUSB_TRANSFER_NO_DEVICE status code.
+ *  - Many functions such as libusb_set_configuration() return the special
+ *    LIBUSB_ERROR_NO_DEVICE error code when the device has been disconnected.
+ *
+ * \section configsel Configuration selection and handling
+ *
+ * When libusb presents a device handle to an application, there is a chance
+ * that the corresponding device may be in unconfigured state. For devices
+ * with multiple configurations, there is also a chance that the configuration
+ * currently selected is not the one that the application wants to use.
+ *
+ * The obvious solution is to add a call to libusb_set_configuration() early
+ * on during your device initialization routines, but there are caveats to
+ * be aware of:
+ * -# If the device is already in the desired configuration, calling
+ *    libusb_set_configuration() using the same configuration value will cause
+ *    a lightweight device reset. This may not be desirable behaviour.
+ * -# libusb will be unable to change configuration if the device is in
+ *    another configuration and other programs or drivers have claimed
+ *    interfaces under that configuration.
+ * -# In the case where the desired configuration is already active, libusb
+ *    may not even be able to perform a lightweight device reset. For example,
+ *    take my USB keyboard with fingerprint reader: I'm interested in driving
+ *    the fingerprint reader interface through libusb, but the kernel's
+ *    USB-HID driver will almost always have claimed the keyboard interface.
+ *    Because the kernel has claimed an interface, it is not even possible to
+ *    perform the lightweight device reset, so libusb_set_configuration() will
+ *    fail. (Luckily the device in question only has a single configuration.)
+ *
+ * One solution to some of the above problems is to consider the currently
+ * active configuration. If the configuration we want is already active, then
+ * we don't have to select any configuration:
+\code
+cfg = libusb_get_configuration(dev);
+if (cfg != desired)
+	libusb_set_configuration(dev, desired);
+\endcode
+ *
+ * This is probably suitable for most scenarios, but is inherently racy:
+ * another application or driver may change the selected configuration
+ * <em>after</em> the libusb_get_configuration() call.
+ *
+ * Even in cases where libusb_set_configuration() succeeds, consider that other
+ * applications or drivers may change configuration after your application
+ * calls libusb_set_configuration().
+ *
+ * One possible way to lock your device into a specific configuration is as
+ * follows:
+ * -# Set the desired configuration (or use the logic above to realise that
+ *    it is already in the desired configuration)
+ * -# Claim the interface that you wish to use
+ * -# Check that the currently active configuration is the one that you want
+ *    to use.
+ *
+ * The above method works because once an interface is claimed, no application
+ * or driver is able to select another configuration.
+ *
+ * \section earlycomp Early transfer completion
+ *
+ * NOTE: This section is currently Linux-centric. I am not sure if any of these
+ * considerations apply to Darwin or other platforms.
+ *
+ * When a transfer completes early (i.e. when less data is received/sent in
+ * any one packet than the transfer buffer allows for) then libusb is designed
+ * to terminate the transfer immediately, not transferring or receiving any
+ * more data unless other transfers have been queued by the user.
+ *
+ * On legacy platforms, libusb is unable to do this in all situations. After
+ * the incomplete packet occurs, "surplus" data may be transferred. Prior to
+ * libusb v1.0.2, this information was lost (and for device-to-host transfers,
+ * the corresponding data was discarded). As of libusb v1.0.3, this information
+ * is kept (the data length of the transfer is updated) and, for device-to-host
+ * transfesr, any surplus data was added to the buffer. Still, this is not
+ * a nice solution because it loses the information about the end of the short
+ * packet, and the user probably wanted that surplus data to arrive in the next
+ * logical transfer.
+ *
+ * A previous workaround was to only ever submit transfers of size 16kb or
+ * less.
+ *
+ * As of libusb v1.0.4 and Linux v2.6.32, this is fixed. A technical
+ * explanation of this issue follows.
+ *
+ * When you ask libusb to submit a bulk transfer larger than 16kb in size,
+ * libusb breaks it up into a number of smaller subtransfers. This is because
+ * the usbfs kernel interface only accepts transfers of up to 16kb in size.
+ * The subtransfers are submitted all at once so that the kernel can queue
+ * them at the hardware level, therefore maximizing bus throughput.
+ *
+ * On legacy platforms, this caused problems when transfers completed early
+ * Upon this event, the kernel would terminate all further packets in that
+ * subtransfer (but not any following ones). libusb would note this event and
+ * immediately cancel any following subtransfers that had been queued,
+ * but often libusb was not fast enough, and the following subtransfers had
+ * started before libusb got around to cancelling them.
+ *
+ * Thanks to an API extension to usbfs, this is fixed with recent kernel and
+ * libusb releases. The solution was to allow libusb to communicate to the
+ * kernel where boundaries occur between logical libusb-level transfers. When
+ * a short transfer (or other error) occurs, the kernel will cancel all the
+ * subtransfers until the boundary without allowing those transfers to start.
+ */
+
+/**
+ * \page contexts Contexts
+ *
+ * It is possible that libusb may be used simultaneously from two independent
+ * libraries linked into the same executable. For example, if your application
+ * has a plugin-like system which allows the user to dynamically load a range
+ * of modules into your program, it is feasible that two independently
+ * developed modules may both use libusb.
+ *
+ * libusb is written to allow for these multiple user scenarios. The two
+ * "instances" of libusb will not interfere: libusb_set_debug() calls
+ * from one user will not affect the same settings for other users, other
+ * users can continue using libusb after one of them calls libusb_exit(), etc.
+ *
+ * This is made possible through libusb's <em>context</em> concept. When you
+ * call libusb_init(), you are (optionally) given a context. You can then pass
+ * this context pointer back into future libusb functions.
+ *
+ * In order to keep things simple for more simplistic applications, it is
+ * legal to pass NULL to all functions requiring a context pointer (as long as
+ * you're sure no other code will attempt to use libusb from the same process).
+ * When you pass NULL, the default context will be used. The default context
+ * is created the first time a process calls libusb_init() when no other
+ * context is alive. Contexts are destroyed during libusb_exit().
+ *
+ * You may be wondering why only a subset of libusb functions require a
+ * context pointer in their function definition. Internally, libusb stores
+ * context pointers in other objects (e.g. libusb_device instances) and hence
+ * can infer the context from those objects.
+ */
+
+/**
+ * @defgroup lib Library initialization/deinitialization
+ * This page details how to initialize and deinitialize libusb. Initialization
+ * must be performed before using any libusb functionality, and similarly you
+ * must not call any libusb functions after deinitialization.
+ */
+
+/**
+ * @defgroup dev Device handling and enumeration
+ * The functionality documented below is designed to help with the following
+ * operations:
+ * - Enumerating the USB devices currently attached to the system
+ * - Choosing a device to operate from your software
+ * - Opening and closing the chosen device
+ *
+ * \section nutshell In a nutshell...
+ *
+ * The description below really makes things sound more complicated than they
+ * actually are. The following sequence of function calls will be suitable
+ * for almost all scenarios and does not require you to have such a deep
+ * understanding of the resource management issues:
+ * \code
+// discover devices
+libusb_device **list;
+libusb_device *found = NULL;
+ssize_t cnt = libusb_get_device_list(NULL, &list);
+ssize_t i = 0;
+int err = 0;
+if (cnt < 0)
+	error();
+
+for (i = 0; i < cnt; i++) {
+	libusb_device *device = list[i];
+	if (is_interesting(device)) {
+		found = device;
+		break;
+	}
+}
+
+if (found) {
+	libusb_device_handle *handle;
+
+	err = libusb_open(found, &handle);
+	if (err)
+		error();
+	// etc
+}
+
+libusb_free_device_list(list, 1);
+\endcode
+ *
+ * The two important points:
+ * - You asked libusb_free_device_list() to unreference the devices (2nd
+ *   parameter)
+ * - You opened the device before freeing the list and unreferencing the
+ *   devices
+ *
+ * If you ended up with a handle, you can now proceed to perform I/O on the
+ * device.
+ *
+ * \section devshandles Devices and device handles
+ * libusb has a concept of a USB device, represented by the
+ * \ref libusb_device opaque type. A device represents a USB device that
+ * is currently or was previously connected to the system. Using a reference
+ * to a device, you can determine certain information about the device (e.g.
+ * you can read the descriptor data).
+ *
+ * The libusb_get_device_list() function can be used to obtain a list of
+ * devices currently connected to the system. This is known as device
+ * discovery.
+ *
+ * Just because you have a reference to a device does not mean it is
+ * necessarily usable. The device may have been unplugged, you may not have
+ * permission to operate such device, or another program or driver may be
+ * using the device.
+ *
+ * When you've found a device that you'd like to operate, you must ask
+ * libusb to open the device using the libusb_open() function. Assuming
+ * success, libusb then returns you a <em>device handle</em>
+ * (a \ref libusb_device_handle pointer). All "real" I/O operations then
+ * operate on the handle rather than the original device pointer.
+ *
+ * \section devref Device discovery and reference counting
+ *
+ * Device discovery (i.e. calling libusb_get_device_list()) returns a
+ * freshly-allocated list of devices. The list itself must be freed when
+ * you are done with it. libusb also needs to know when it is OK to free
+ * the contents of the list - the devices themselves.
+ *
+ * To handle these issues, libusb provides you with two separate items:
+ * - A function to free the list itself
+ * - A reference counting system for the devices inside
+ *
+ * New devices presented by the libusb_get_device_list() function all have a
+ * reference count of 1. You can increase and decrease reference count using
+ * libusb_ref_device() and libusb_unref_device(). A device is destroyed when
+ * its reference count reaches 0.
+ *
+ * With the above information in mind, the process of opening a device can
+ * be viewed as follows:
+ * -# Discover devices using libusb_get_device_list().
+ * -# Choose the device that you want to operate, and call libusb_open().
+ * -# Unref all devices in the discovered device list.
+ * -# Free the discovered device list.
+ *
+ * The order is important - you must not unreference the device before
+ * attempting to open it, because unreferencing it may destroy the device.
+ *
+ * For convenience, the libusb_free_device_list() function includes a
+ * parameter to optionally unreference all the devices in the list before
+ * freeing the list itself. This combines steps 3 and 4 above.
+ *
+ * As an implementation detail, libusb_open() actually adds a reference to
+ * the device in question. This is because the device remains available
+ * through the handle via libusb_get_device(). The reference is deleted during
+ * libusb_close().
+ */
+
+/** @defgroup misc Miscellaneous */
+
+/* we traverse usbfs without knowing how many devices we are going to find.
+ * so we create this discovered_devs model which is similar to a linked-list
+ * which grows when required. it can be freed once discovery has completed,
+ * eliminating the need for a list node in the libusb_device structure
+ * itself. */
+#define DISCOVERED_DEVICES_SIZE_STEP 8
+
+static struct discovered_devs *discovered_devs_alloc(void)
+{
+	struct discovered_devs *ret =
+		malloc(sizeof(*ret) + (sizeof(void *) * DISCOVERED_DEVICES_SIZE_STEP));
+
+	if (ret) {
+		ret->len = 0;
+		ret->capacity = DISCOVERED_DEVICES_SIZE_STEP;
+	}
+	return ret;
+}
+
+/* append a device to the discovered devices collection. may realloc itself,
+ * returning new discdevs. returns NULL on realloc failure. */
+struct discovered_devs *discovered_devs_append(
+	struct discovered_devs *discdevs, struct libusb_device *dev)
+{
+	size_t len = discdevs->len;
+	size_t capacity;
+
+	/* if there is space, just append the device */
+	if (len < discdevs->capacity) {
+		discdevs->devices[len] = libusb_ref_device(dev);
+		discdevs->len++;
+		return discdevs;
+	}
+
+	/* exceeded capacity, need to grow */
+	usbi_dbg("need to increase capacity");
+	capacity = discdevs->capacity + DISCOVERED_DEVICES_SIZE_STEP;
+	discdevs = realloc(discdevs,
+		sizeof(*discdevs) + (sizeof(void *) * capacity));
+	if (discdevs) {
+		discdevs->capacity = capacity;
+		discdevs->devices[len] = libusb_ref_device(dev);
+		discdevs->len++;
+	}
+
+	return discdevs;
+}
+
+static void discovered_devs_free(struct discovered_devs *discdevs)
+{
+	size_t i;
+
+	for (i = 0; i < discdevs->len; i++)
+		libusb_unref_device(discdevs->devices[i]);
+
+	free(discdevs);
+}
+
+/* Allocate a new device with a specific session ID. The returned device has
+ * a reference count of 1. */
+struct libusb_device *usbi_alloc_device(struct libusb_context *ctx,
+	unsigned long session_id)
+{
+	size_t priv_size = usbi_backend->device_priv_size;
+	struct libusb_device *dev = malloc(sizeof(*dev) + priv_size);
+	int r;
+
+	if (!dev)
+		return NULL;
+
+	r = pthread_mutex_init(&dev->lock, NULL);
+	if (r)
+		return NULL;
+
+	dev->ctx = ctx;
+	dev->refcnt = 1;
+	dev->session_data = session_id;
+	memset(&dev->os_priv, 0, priv_size);
+
+	pthread_mutex_lock(&ctx->usb_devs_lock);
+	list_add(&dev->list, &ctx->usb_devs);
+	pthread_mutex_unlock(&ctx->usb_devs_lock);
+	return dev;
+}
+
+/* Perform some final sanity checks on a newly discovered device. If this
+ * function fails (negative return code), the device should not be added
+ * to the discovered device list. */
+int usbi_sanitize_device(struct libusb_device *dev)
+{
+	int r;
+	unsigned char raw_desc[DEVICE_DESC_LENGTH];
+	uint8_t num_configurations;
+	int host_endian;
+
+	r = usbi_backend->get_device_descriptor(dev, raw_desc, &host_endian);
+	if (r < 0)
+		return r;
+
+	num_configurations = raw_desc[DEVICE_DESC_LENGTH - 1];
+	if (num_configurations > USB_MAXCONFIG) {
+		usbi_err(DEVICE_CTX(dev), "too many configurations");
+		return LIBUSB_ERROR_IO;
+	} else if (num_configurations < 1) {
+		usbi_dbg("no configurations?");
+		return LIBUSB_ERROR_IO;
+	}
+
+	dev->num_configurations = num_configurations;
+	return 0;
+}
+
+/* Examine libusb's internal list of known devices, looking for one with
+ * a specific session ID. Returns the matching device if it was found, and
+ * NULL otherwise. */
+struct libusb_device *usbi_get_device_by_session_id(struct libusb_context *ctx,
+	unsigned long session_id)
+{
+	struct libusb_device *dev;
+	struct libusb_device *ret = NULL;
+
+	pthread_mutex_lock(&ctx->usb_devs_lock);
+	list_for_each_entry(dev, &ctx->usb_devs, list)
+		if (dev->session_data == session_id) {
+			ret = dev;
+			break;
+		}
+	pthread_mutex_unlock(&ctx->usb_devs_lock);
+
+	return ret;
+}
+
+/** @ingroup dev
+ * Returns a list of USB devices currently attached to the system. This is
+ * your entry point into finding a USB device to operate.
+ *
+ * You are expected to unreference all the devices when you are done with
+ * them, and then free the list with libusb_free_device_list(). Note that
+ * libusb_free_device_list() can unref all the devices for you. Be careful
+ * not to unreference a device you are about to open until after you have
+ * opened it.
+ *
+ * This return value of this function indicates the number of devices in
+ * the resultant list. The list is actually one element larger, as it is
+ * NULL-terminated.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param list output location for a list of devices. Must be later freed with
+ * libusb_free_device_list().
+ * \returns the number of devices in the outputted list, or LIBUSB_ERROR_NO_MEM
+ * on memory allocation failure.
+ */
+API_EXPORTED ssize_t libusb_get_device_list(libusb_context *ctx,
+	libusb_device ***list)
+{
+	struct discovered_devs *discdevs = discovered_devs_alloc();
+	struct libusb_device **ret;
+	int r = 0;
+	size_t i;
+	ssize_t len;
+	USBI_GET_CONTEXT(ctx);
+	usbi_dbg("");
+
+	if (!discdevs)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = usbi_backend->get_device_list(ctx, &discdevs);
+	if (r < 0) {
+		len = r;
+		goto out;
+	}
+
+	/* convert discovered_devs into a list */
+	len = discdevs->len;
+	ret = malloc(sizeof(void *) * (len + 1));
+	if (!ret) {
+		len = LIBUSB_ERROR_NO_MEM;
+		goto out;
+	}
+
+	ret[len] = NULL;
+	for (i = 0; i < len; i++) {
+		struct libusb_device *dev = discdevs->devices[i];
+		ret[i] = libusb_ref_device(dev);
+	}
+	*list = ret;
+
+out:
+	discovered_devs_free(discdevs);
+	return len;
+}
+
+/** \ingroup dev
+ * Frees a list of devices previously discovered using
+ * libusb_get_device_list(). If the unref_devices parameter is set, the
+ * reference count of each device in the list is decremented by 1.
+ * \param list the list to free
+ * \param unref_devices whether to unref the devices in the list
+ */
+API_EXPORTED void libusb_free_device_list(libusb_device **list,
+	int unref_devices)
+{
+	if (!list)
+		return;
+
+	if (unref_devices) {
+		int i = 0;
+		struct libusb_device *dev;
+
+		while ((dev = list[i++]) != NULL)
+			libusb_unref_device(dev);
+	}
+	free(list);
+}
+
+/** \ingroup dev
+ * Get the number of the bus that a device is connected to.
+ * \param dev a device
+ * \returns the bus number
+ */
+API_EXPORTED uint8_t libusb_get_bus_number(libusb_device *dev)
+{
+	return dev->bus_number;
+}
+
+/** \ingroup dev
+ * Get the address of the device on the bus it is connected to.
+ * \param dev a device
+ * \returns the device address
+ */
+API_EXPORTED uint8_t libusb_get_device_address(libusb_device *dev)
+{
+	return dev->device_address;
+}
+
+static const struct libusb_endpoint_descriptor *find_endpoint(
+	struct libusb_config_descriptor *config, unsigned char endpoint)
+{
+	int iface_idx;
+	for (iface_idx = 0; iface_idx < config->bNumInterfaces; iface_idx++) {
+		const struct libusb_interface *iface = &config->interface[iface_idx];
+		int altsetting_idx;
+
+		for (altsetting_idx = 0; altsetting_idx < iface->num_altsetting;
+				altsetting_idx++) {
+			const struct libusb_interface_descriptor *altsetting
+				= &iface->altsetting[altsetting_idx];
+			int ep_idx;
+
+			for (ep_idx = 0; ep_idx < altsetting->bNumEndpoints; ep_idx++) {
+				const struct libusb_endpoint_descriptor *ep =
+					&altsetting->endpoint[ep_idx];
+				if (ep->bEndpointAddress == endpoint)
+					return ep;
+			}
+		}
+	}
+	return NULL;
+}
+
+/** \ingroup dev
+ * Convenience function to retrieve the wMaxPacketSize value for a particular
+ * endpoint in the active device configuration.
+ *
+ * This function was originally intended to be of assistance when setting up
+ * isochronous transfers, but a design mistake resulted in this function
+ * instead. It simply returns the wMaxPacketSize value without considering
+ * its contents. If you're dealing with isochronous transfers, you probably
+ * want libusb_get_max_iso_packet_size() instead.
+ *
+ * \param dev a device
+ * \param endpoint address of the endpoint in question
+ * \returns the wMaxPacketSize value
+ * \returns LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
+ * \returns LIBUSB_ERROR_OTHER on other failure
+ */
+API_EXPORTED int libusb_get_max_packet_size(libusb_device *dev,
+	unsigned char endpoint)
+{
+	struct libusb_config_descriptor *config;
+	const struct libusb_endpoint_descriptor *ep;
+	int r;
+
+	r = libusb_get_active_config_descriptor(dev, &config);
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"could not retrieve active config descriptor");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	ep = find_endpoint(config, endpoint);
+	if (!ep)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	r = ep->wMaxPacketSize;
+	libusb_free_config_descriptor(config);
+	return r;
+}
+
+/** \ingroup dev
+ * Calculate the maximum packet size which a specific endpoint is capable is
+ * sending or receiving in the duration of 1 microframe
+ *
+ * Only the active configution is examined. The calculation is based on the
+ * wMaxPacketSize field in the endpoint descriptor as described in section
+ * 9.6.6 in the USB 2.0 specifications.
+ *
+ * If acting on an isochronous or interrupt endpoint, this function will
+ * multiply the value found in bits 0:10 by the number of transactions per
+ * microframe (determined by bits 11:12). Otherwise, this function just
+ * returns the numeric value found in bits 0:10.
+ *
+ * This function is useful for setting up isochronous transfers, for example
+ * you might pass the return value from this function to
+ * libusb_set_iso_packet_lengths() in order to set the length field of every
+ * isochronous packet in a transfer.
+ *
+ * Since v1.0.3.
+ *
+ * \param dev a device
+ * \param endpoint address of the endpoint in question
+ * \returns the maximum packet size which can be sent/received on this endpoint
+ * \returns LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
+ * \returns LIBUSB_ERROR_OTHER on other failure
+ */
+API_EXPORTED int libusb_get_max_iso_packet_size(libusb_device *dev,
+	unsigned char endpoint)
+{
+	struct libusb_config_descriptor *config;
+	const struct libusb_endpoint_descriptor *ep;
+	enum libusb_transfer_type ep_type;
+	uint16_t val;
+	int r;
+
+	r = libusb_get_active_config_descriptor(dev, &config);
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"could not retrieve active config descriptor");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	ep = find_endpoint(config, endpoint);
+	if (!ep)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	val = ep->wMaxPacketSize;
+	ep_type = ep->bmAttributes & 0x3;
+	libusb_free_config_descriptor(config);
+
+	r = val & 0x07ff;
+	if (ep_type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
+			|| ep_type == LIBUSB_TRANSFER_TYPE_INTERRUPT)
+		r *= (1 + ((val >> 11) & 3));
+	return r;
+}
+
+/** \ingroup dev
+ * Increment the reference count of a device.
+ * \param dev the device to reference
+ * \returns the same device
+ */
+API_EXPORTED libusb_device *libusb_ref_device(libusb_device *dev)
+{
+	pthread_mutex_lock(&dev->lock);
+	dev->refcnt++;
+	pthread_mutex_unlock(&dev->lock);
+	return dev;
+}
+
+/** \ingroup dev
+ * Decrement the reference count of a device. If the decrement operation
+ * causes the reference count to reach zero, the device shall be destroyed.
+ * \param dev the device to unreference
+ */
+API_EXPORTED void libusb_unref_device(libusb_device *dev)
+{
+	int refcnt;
+
+	if (!dev)
+		return;
+
+	pthread_mutex_lock(&dev->lock);
+	refcnt = --dev->refcnt;
+	pthread_mutex_unlock(&dev->lock);
+
+	if (refcnt == 0) {
+		usbi_dbg("destroy device %d.%d", dev->bus_number, dev->device_address);
+
+		if (usbi_backend->destroy_device)
+			usbi_backend->destroy_device(dev);
+
+		pthread_mutex_lock(&dev->ctx->usb_devs_lock);
+		list_del(&dev->list);
+		pthread_mutex_unlock(&dev->ctx->usb_devs_lock);
+
+		free(dev);
+	}
+}
+
+/** \ingroup dev
+ * Open a device and obtain a device handle. A handle allows you to perform
+ * I/O on the device in question.
+ *
+ * Internally, this function adds a reference to the device and makes it
+ * available to you through libusb_get_device(). This reference is removed
+ * during libusb_close().
+ *
+ * This is a non-blocking function; no requests are sent over the bus.
+ *
+ * \param dev the device to open
+ * \param handle output location for the returned device handle pointer. Only
+ * populated when the return code is 0.
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NO_MEM on memory allocation failure
+ * \returns LIBUSB_ERROR_ACCESS if the user has insufficient permissions
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_open(libusb_device *dev, libusb_device_handle **handle)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct libusb_device_handle *_handle;
+	size_t priv_size = usbi_backend->device_handle_priv_size;
+	unsigned char dummy = 1;
+	int r;
+	usbi_dbg("open %d.%d", dev->bus_number, dev->device_address);
+
+	_handle = malloc(sizeof(*_handle) + priv_size);
+	if (!_handle)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = pthread_mutex_init(&_handle->lock, NULL);
+	if (r)
+		return LIBUSB_ERROR_OTHER;
+
+	_handle->dev = libusb_ref_device(dev);
+	_handle->claimed_interfaces = 0;
+	memset(&_handle->os_priv, 0, priv_size);
+
+	r = usbi_backend->open(_handle);
+	if (r < 0) {
+		libusb_unref_device(dev);
+		free(_handle);
+		return r;
+	}
+
+	pthread_mutex_lock(&ctx->open_devs_lock);
+	list_add(&_handle->list, &ctx->open_devs);
+	pthread_mutex_unlock(&ctx->open_devs_lock);
+	*handle = _handle;
+
+
+	/* At this point, we want to interrupt any existing event handlers so
+	 * that they realise the addition of the new device's poll fd. One
+	 * example when this is desirable is if the user is running a separate
+	 * dedicated libusb events handling thread, which is running with a long
+	 * or infinite timeout. We want to interrupt that iteration of the loop,
+	 * so that it picks up the new fd, and then continues. */
+
+	/* record that we are messing with poll fds */
+	pthread_mutex_lock(&ctx->pollfd_modify_lock);
+	ctx->pollfd_modify++;
+	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+
+	/* write some data on control pipe to interrupt event handlers */
+	r = write(ctx->ctrl_pipe[1], &dummy, sizeof(dummy));
+	if (r <= 0) {
+		usbi_warn(ctx, "internal signalling write failed");
+		pthread_mutex_lock(&ctx->pollfd_modify_lock);
+		ctx->pollfd_modify--;
+		pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+		return 0;
+	}
+
+	/* take event handling lock */
+	libusb_lock_events(ctx);
+
+	/* read the dummy data */
+	r = read(ctx->ctrl_pipe[0], &dummy, sizeof(dummy));
+	if (r <= 0)
+		usbi_warn(ctx, "internal signalling read failed");
+
+	/* we're done with modifying poll fds */
+	pthread_mutex_lock(&ctx->pollfd_modify_lock);
+	ctx->pollfd_modify--;
+	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+
+	/* Release event handling lock and wake up event waiters */
+	libusb_unlock_events(ctx);
+
+	return 0;
+}
+
+/** \ingroup dev
+ * Convenience function for finding a device with a particular
+ * <tt>idVendor</tt>/<tt>idProduct</tt> combination. This function is intended
+ * for those scenarios where you are using libusb to knock up a quick test
+ * application - it allows you to avoid calling libusb_get_device_list() and
+ * worrying about traversing/freeing the list.
+ *
+ * This function has limitations and is hence not intended for use in real
+ * applications: if multiple devices have the same IDs it will only
+ * give you the first one, etc.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param vendor_id the idVendor value to search for
+ * \param product_id the idProduct value to search for
+ * \returns a handle for the first found device, or NULL on error or if the
+ * device could not be found. */
+API_EXPORTED libusb_device_handle *libusb_open_device_with_vid_pid(
+	libusb_context *ctx, uint16_t vendor_id, uint16_t product_id)
+{
+	struct libusb_device **devs;
+	struct libusb_device *found = NULL;
+	struct libusb_device *dev;
+	struct libusb_device_handle *handle = NULL;
+	size_t i = 0;
+	int r;
+
+	if (libusb_get_device_list(ctx, &devs) < 0)
+		return NULL;
+
+	while ((dev = devs[i++]) != NULL) {
+		struct libusb_device_descriptor desc;
+		r = libusb_get_device_descriptor(dev, &desc);
+		if (r < 0)
+			goto out;
+		if (desc.idVendor == vendor_id && desc.idProduct == product_id) {
+			found = dev;
+			break;
+		}
+	}
+
+	if (found) {
+		r = libusb_open(found, &handle);
+		if (r < 0)
+			handle = NULL;
+	}
+
+out:
+	libusb_free_device_list(devs, 1);
+	return handle;
+}
+
+static void do_close(struct libusb_context *ctx,
+	struct libusb_device_handle *dev_handle)
+{
+	pthread_mutex_lock(&ctx->open_devs_lock);
+	list_del(&dev_handle->list);
+	pthread_mutex_unlock(&ctx->open_devs_lock);
+
+	usbi_backend->close(dev_handle);
+	libusb_unref_device(dev_handle->dev);
+	free(dev_handle);
+}
+
+/** \ingroup dev
+ * Close a device handle. Should be called on all open handles before your
+ * application exits.
+ *
+ * Internally, this function destroys the reference that was added by
+ * libusb_open() on the given device.
+ *
+ * This is a non-blocking function; no requests are sent over the bus.
+ *
+ * \param dev_handle the handle to close
+ */
+API_EXPORTED void libusb_close(libusb_device_handle *dev_handle)
+{
+	struct libusb_context *ctx;
+	unsigned char dummy = 1;
+	ssize_t r;
+
+	if (!dev_handle)
+		return;
+	usbi_dbg("");
+
+	ctx = HANDLE_CTX(dev_handle);
+
+	/* Similarly to libusb_open(), we want to interrupt all event handlers
+	 * at this point. More importantly, we want to perform the actual close of
+	 * the device while holding the event handling lock (preventing any other
+	 * thread from doing event handling) because we will be removing a file
+	 * descriptor from the polling loop. */
+
+	/* record that we are messing with poll fds */
+	pthread_mutex_lock(&ctx->pollfd_modify_lock);
+	ctx->pollfd_modify++;
+	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+
+	/* write some data on control pipe to interrupt event handlers */
+	r = write(ctx->ctrl_pipe[1], &dummy, sizeof(dummy));
+	if (r <= 0) {
+		usbi_warn(ctx, "internal signalling write failed, closing anyway");
+		do_close(ctx, dev_handle);
+		pthread_mutex_lock(&ctx->pollfd_modify_lock);
+		ctx->pollfd_modify--;
+		pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+		return;
+	}
+
+	/* take event handling lock */
+	libusb_lock_events(ctx);
+
+	/* read the dummy data */
+	r = read(ctx->ctrl_pipe[0], &dummy, sizeof(dummy));
+	if (r <= 0)
+		usbi_warn(ctx, "internal signalling read failed, closing anyway");
+
+	/* Close the device */
+	do_close(ctx, dev_handle);
+
+	/* we're done with modifying poll fds */
+	pthread_mutex_lock(&ctx->pollfd_modify_lock);
+	ctx->pollfd_modify--;
+	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+
+	/* Release event handling lock and wake up event waiters */
+	libusb_unlock_events(ctx);
+}
+
+/** \ingroup dev
+ * Get the underlying device for a handle. This function does not modify
+ * the reference count of the returned device, so do not feel compelled to
+ * unreference it when you are done.
+ * \param dev_handle a device handle
+ * \returns the underlying device
+ */
+API_EXPORTED libusb_device *libusb_get_device(libusb_device_handle *dev_handle)
+{
+	return dev_handle->dev;
+}
+
+/** \ingroup dev
+ * Determine the bConfigurationValue of the currently active configuration.
+ *
+ * You could formulate your own control request to obtain this information,
+ * but this function has the advantage that it may be able to retrieve the
+ * information from operating system caches (no I/O involved).
+ *
+ * If the OS does not cache this information, then this function will block
+ * while a control transfer is submitted to retrieve the information.
+ *
+ * This function will return a value of 0 in the <tt>config</tt> output
+ * parameter if the device is in unconfigured state.
+ *
+ * \param dev a device handle
+ * \param config output location for the bConfigurationValue of the active
+ * configuration (only valid for return code 0)
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_get_configuration(libusb_device_handle *dev,
+	int *config)
+{
+	int r = LIBUSB_ERROR_NOT_SUPPORTED;
+
+	usbi_dbg("");
+	if (usbi_backend->get_configuration)
+		r = usbi_backend->get_configuration(dev, config);
+
+	if (r == LIBUSB_ERROR_NOT_SUPPORTED) {
+		uint8_t tmp = 0;
+		usbi_dbg("falling back to control message");
+		r = libusb_control_transfer(dev, LIBUSB_ENDPOINT_IN,
+			LIBUSB_REQUEST_GET_CONFIGURATION, 0, 0, &tmp, 1, 1000);
+		if (r == 0) {
+			usbi_err(HANDLE_CTX(dev), "zero bytes returned in ctrl transfer?");
+			r = LIBUSB_ERROR_IO;
+		} else if (r == 1) {
+			r = 0;
+			*config = tmp;
+		} else {
+			usbi_dbg("control failed, error %d", r);
+		}
+	}
+
+	if (r == 0)
+		usbi_dbg("active config %d", *config);
+
+	return r;
+}
+
+/** \ingroup dev
+ * Set the active configuration for a device.
+ *
+ * The operating system may or may not have already set an active
+ * configuration on the device. It is up to your application to ensure the
+ * correct configuration is selected before you attempt to claim interfaces
+ * and perform other operations.
+ *
+ * If you call this function on a device already configured with the selected
+ * configuration, then this function will act as a lightweight device reset:
+ * it will issue a SET_CONFIGURATION request using the current configuration,
+ * causing most USB-related device state to be reset (altsetting reset to zero,
+ * endpoint halts cleared, toggles reset).
+ *
+ * You cannot change/reset configuration if your application has claimed
+ * interfaces - you should free them with libusb_release_interface() first.
+ * You cannot change/reset configuration if other applications or drivers have
+ * claimed interfaces.
+ *
+ * A configuration value of -1 will put the device in unconfigured state.
+ * The USB specifications state that a configuration value of 0 does this,
+ * however buggy devices exist which actually have a configuration 0.
+ *
+ * You should always use this function rather than formulating your own
+ * SET_CONFIGURATION control request. This is because the underlying operating
+ * system needs to know when such changes happen.
+ *
+ * This is a blocking function.
+ *
+ * \param dev a device handle
+ * \param configuration the bConfigurationValue of the configuration you
+ * wish to activate, or -1 if you wish to put the device in unconfigured state
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the requested configuration does not exist
+ * \returns LIBUSB_ERROR_BUSY if interfaces are currently claimed
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_set_configuration(libusb_device_handle *dev,
+	int configuration)
+{
+	usbi_dbg("configuration %d", configuration);
+	return usbi_backend->set_configuration(dev, configuration);
+}
+
+/** \ingroup dev
+ * Claim an interface on a given device handle. You must claim the interface
+ * you wish to use before you can perform I/O on any of its endpoints.
+ *
+ * It is legal to attempt to claim an already-claimed interface, in which
+ * case libusb just returns 0 without doing anything.
+ *
+ * Claiming of interfaces is a purely logical operation; it does not cause
+ * any requests to be sent over the bus. Interface claiming is used to
+ * instruct the underlying operating system that your application wishes
+ * to take ownership of the interface.
+ *
+ * This is a non-blocking function.
+ *
+ * \param dev a device handle
+ * \param interface_number the <tt>bInterfaceNumber</tt> of the interface you
+ * wish to claim
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the requested interface does not exist
+ * \returns LIBUSB_ERROR_BUSY if another program or driver has claimed the
+ * interface
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns a LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_claim_interface(libusb_device_handle *dev,
+	int interface_number)
+{
+	int r = 0;
+
+	usbi_dbg("interface %d", interface_number);
+	if (interface_number >= sizeof(dev->claimed_interfaces) * 8)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	pthread_mutex_lock(&dev->lock);
+	if (dev->claimed_interfaces & (1 << interface_number))
+		goto out;
+
+	r = usbi_backend->claim_interface(dev, interface_number);
+	if (r == 0)
+		dev->claimed_interfaces |= 1 << interface_number;
+
+out:
+	pthread_mutex_unlock(&dev->lock);
+	return r;
+}
+
+/** \ingroup dev
+ * Release an interface previously claimed with libusb_claim_interface(). You
+ * should release all claimed interfaces before closing a device handle.
+ *
+ * This is a blocking function. A SET_INTERFACE control request will be sent
+ * to the device, resetting interface state to the first alternate setting.
+ *
+ * \param dev a device handle
+ * \param interface_number the <tt>bInterfaceNumber</tt> of the
+ * previously-claimed interface
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the interface was not claimed
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_release_interface(libusb_device_handle *dev,
+	int interface_number)
+{
+	int r;
+
+	usbi_dbg("interface %d", interface_number);
+	if (interface_number >= sizeof(dev->claimed_interfaces) * 8)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	pthread_mutex_lock(&dev->lock);
+	if (!(dev->claimed_interfaces & (1 << interface_number))) {
+		r = LIBUSB_ERROR_NOT_FOUND;
+		goto out;
+	}
+
+	r = usbi_backend->release_interface(dev, interface_number);
+	if (r == 0)
+		dev->claimed_interfaces &= ~(1 << interface_number);
+
+out:
+	pthread_mutex_unlock(&dev->lock);
+	return r;
+}
+
+/** \ingroup dev
+ * Activate an alternate setting for an interface. The interface must have
+ * been previously claimed with libusb_claim_interface().
+ *
+ * You should always use this function rather than formulating your own
+ * SET_INTERFACE control request. This is because the underlying operating
+ * system needs to know when such changes happen.
+ *
+ * This is a blocking function.
+ *
+ * \param dev a device handle
+ * \param interface_number the <tt>bInterfaceNumber</tt> of the
+ * previously-claimed interface
+ * \param alternate_setting the <tt>bAlternateSetting</tt> of the alternate
+ * setting to activate
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the interface was not claimed, or the
+ * requested alternate setting does not exist
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_set_interface_alt_setting(libusb_device_handle *dev,
+	int interface_number, int alternate_setting)
+{
+	usbi_dbg("interface %d altsetting %d",
+		interface_number, alternate_setting);
+	if (interface_number >= sizeof(dev->claimed_interfaces) * 8)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	pthread_mutex_lock(&dev->lock);
+	if (!(dev->claimed_interfaces & (1 << interface_number))) {
+		pthread_mutex_unlock(&dev->lock);
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+	pthread_mutex_unlock(&dev->lock);
+
+	return usbi_backend->set_interface_altsetting(dev, interface_number,
+		alternate_setting);
+}
+
+/** \ingroup dev
+ * Clear the halt/stall condition for an endpoint. Endpoints with halt status
+ * are unable to receive or transmit data until the halt condition is stalled.
+ *
+ * You should cancel all pending transfers before attempting to clear the halt
+ * condition.
+ *
+ * This is a blocking function.
+ *
+ * \param dev a device handle
+ * \param endpoint the endpoint to clear halt status
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_clear_halt(libusb_device_handle *dev,
+	unsigned char endpoint)
+{
+	usbi_dbg("endpoint %x", endpoint);
+	return usbi_backend->clear_halt(dev, endpoint);
+}
+
+/** \ingroup dev
+ * Perform a USB port reset to reinitialize a device. The system will attempt
+ * to restore the previous configuration and alternate settings after the
+ * reset has completed.
+ *
+ * If the reset fails, the descriptors change, or the previous state cannot be
+ * restored, the device will appear to be disconnected and reconnected. This
+ * means that the device handle is no longer valid (you should close it) and
+ * rediscover the device. A return code of LIBUSB_ERROR_NOT_FOUND indicates
+ * when this is the case.
+ *
+ * This is a blocking function which usually incurs a noticeable delay.
+ *
+ * \param dev a handle of the device to reset
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if re-enumeration is required, or if the
+ * device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_reset_device(libusb_device_handle *dev)
+{
+	usbi_dbg("");
+	return usbi_backend->reset_device(dev);
+}
+
+/** \ingroup dev
+ * Determine if a kernel driver is active on an interface. If a kernel driver
+ * is active, you cannot claim the interface, and libusb will be unable to
+ * perform I/O.
+ *
+ * \param dev a device handle
+ * \param interface the interface to check
+ * \returns 0 if no kernel driver is active
+ * \returns 1 if a kernel driver is active
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ * \see libusb_detach_kernel_driver()
+ */
+API_EXPORTED int libusb_kernel_driver_active(libusb_device_handle *dev,
+	int interface)
+{
+	usbi_dbg("interface %d", interface);
+	if (usbi_backend->kernel_driver_active)
+		return usbi_backend->kernel_driver_active(dev, interface);
+	else
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+/** \ingroup dev
+ * Detach a kernel driver from an interface. If successful, you will then be
+ * able to claim the interface and perform I/O.
+ *
+ * \param dev a device handle
+ * \param interface the interface to detach the driver from
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
+ * \returns LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ * \see libusb_kernel_driver_active()
+ */
+API_EXPORTED int libusb_detach_kernel_driver(libusb_device_handle *dev,
+	int interface)
+{
+	usbi_dbg("interface %d", interface);
+	if (usbi_backend->detach_kernel_driver)
+		return usbi_backend->detach_kernel_driver(dev, interface);
+	else
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+/** \ingroup dev
+ * Re-attach an interface's kernel driver, which was previously detached
+ * using libusb_detach_kernel_driver().
+ *
+ * \param dev a device handle
+ * \param interface the interface to attach the driver from
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
+ * \returns LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns LIBUSB_ERROR_BUSY if the driver cannot be attached because the
+ * interface is claimed by a program or driver
+ * \returns another LIBUSB_ERROR code on other failure
+ * \see libusb_kernel_driver_active()
+ */
+API_EXPORTED int libusb_attach_kernel_driver(libusb_device_handle *dev,
+	int interface)
+{
+	usbi_dbg("interface %d", interface);
+	if (usbi_backend->attach_kernel_driver)
+		return usbi_backend->attach_kernel_driver(dev, interface);
+	else
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+/** \ingroup lib
+ * Set message verbosity.
+ *  - Level 0: no messages ever printed by the library (default)
+ *  - Level 1: error messages are printed to stderr
+ *  - Level 2: warning and error messages are printed to stderr
+ *  - Level 3: informational messages are printed to stdout, warning and error
+ *    messages are printed to stderr
+ *
+ * The default level is 0, which means no messages are ever printed. If you
+ * choose to increase the message verbosity level, ensure that your
+ * application does not close the stdout/stderr file descriptors.
+ *
+ * You are advised to set level 3. libusb is conservative with its message
+ * logging and most of the time, will only log messages that explain error
+ * conditions and other oddities. This will help you debug your software.
+ *
+ * If the LIBUSB_DEBUG environment variable was set when libusb was
+ * initialized, this function does nothing: the message verbosity is fixed
+ * to the value in the environment variable.
+ *
+ * If libusb was compiled without any message logging, this function does
+ * nothing: you'll never get any messages.
+ *
+ * If libusb was compiled with verbose debug message logging, this function
+ * does nothing: you'll always get messages from all levels.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param level debug level to set
+ */
+API_EXPORTED void libusb_set_debug(libusb_context *ctx, int level)
+{
+	USBI_GET_CONTEXT(ctx);
+	if (!ctx->debug_fixed)
+		ctx->debug = level;
+}
+
+/** \ingroup lib
+ * Initialize libusb. This function must be called before calling any other
+ * libusb function.
+ * \param context Optional output location for context pointer.
+ * Only valid on return code 0.
+ * \returns 0 on success, or a LIBUSB_ERROR code on failure
+ */
+API_EXPORTED int libusb_init(libusb_context **context)
+{
+	char *dbg = getenv("LIBUSB_DEBUG");
+	struct libusb_context *ctx = malloc(sizeof(*ctx));
+	int r;
+
+	if (!ctx)
+		return LIBUSB_ERROR_NO_MEM;
+	memset(ctx, 0, sizeof(*ctx));
+
+	if (dbg) {
+		ctx->debug = atoi(dbg);
+		if (ctx->debug)
+			ctx->debug_fixed = 1;
+	}
+
+	usbi_dbg("");
+
+	if (usbi_backend->init) {
+		r = usbi_backend->init(ctx);
+		if (r)
+			goto err;
+	}
+
+	pthread_mutex_init(&ctx->usb_devs_lock, NULL);
+	pthread_mutex_init(&ctx->open_devs_lock, NULL);
+	list_init(&ctx->usb_devs);
+	list_init(&ctx->open_devs);
+
+	r = usbi_io_init(ctx);
+	if (r < 0) {
+		if (usbi_backend->exit)
+			usbi_backend->exit();
+		goto err;
+	}
+
+	pthread_mutex_lock(&default_context_lock);
+	if (!usbi_default_context) {
+		usbi_dbg("created default context");
+		usbi_default_context = ctx;
+	}
+	pthread_mutex_unlock(&default_context_lock);
+
+	if (context)
+		*context = ctx;
+	return 0;
+
+err:
+	free(ctx);
+	return r;
+}
+
+/** \ingroup lib
+ * Deinitialize libusb. Should be called after closing all open devices and
+ * before your application terminates.
+ * \param ctx the context to deinitialize, or NULL for the default context
+ */
+API_EXPORTED void libusb_exit(struct libusb_context *ctx)
+{
+	USBI_GET_CONTEXT(ctx);
+	usbi_dbg("");
+
+	/* a little sanity check. doesn't bother with open_devs locking because
+	 * unless there is an application bug, nobody will be accessing this. */
+	if (!list_empty(&ctx->open_devs))
+		usbi_warn(ctx, "application left some devices open");
+
+	usbi_io_exit(ctx);
+	if (usbi_backend->exit)
+		usbi_backend->exit();
+
+	pthread_mutex_lock(&default_context_lock);
+	if (ctx == usbi_default_context) {
+		usbi_dbg("freeing default context");
+		usbi_default_context = NULL;
+	}
+	pthread_mutex_unlock(&default_context_lock);
+
+	free(ctx);
+}
+
+void usbi_log(struct libusb_context *ctx, enum usbi_log_level level,
+	const char *function, const char *format, ...)
+{
+	va_list args;
+	FILE *stream = stdout;
+	const char *prefix;
+
+#ifndef ENABLE_DEBUG_LOGGING
+	USBI_GET_CONTEXT(ctx);
+	if (!ctx->debug)
+		return;
+	if (level == LOG_LEVEL_WARNING && ctx->debug < 2)
+		return;
+	if (level == LOG_LEVEL_INFO && ctx->debug < 3)
+		return;
+#endif
+
+	switch (level) {
+	case LOG_LEVEL_INFO:
+		prefix = "info";
+		break;
+	case LOG_LEVEL_WARNING:
+		stream = stderr;
+		prefix = "warning";
+		break;
+	case LOG_LEVEL_ERROR:
+		stream = stderr;
+		prefix = "error";
+		break;
+	case LOG_LEVEL_DEBUG:
+		stream = stderr;
+		prefix = "debug";
+		break;
+	default:
+		stream = stderr;
+		prefix = "unknown";
+		break;
+	}
+
+	fprintf(stream, "libusb:%s [%s] ", prefix, function);
+
+	va_start (args, format);
+	vfprintf(stream, format, args);
+	va_end (args);
+
+	fprintf(stream, "\n");
+}
+
diff --git a/libusb/descriptor.c b/libusb/descriptor.c
new file mode 100644
index 0000000..acd7668
--- /dev/null
+++ b/libusb/descriptor.c
@@ -0,0 +1,719 @@
+/*
+ * USB descriptor handling functions for libusb
+ * Copyright (C) 2007 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "libusbi.h"
+
+#define DESC_HEADER_LENGTH		2
+#define DEVICE_DESC_LENGTH		18
+#define CONFIG_DESC_LENGTH		9
+#define INTERFACE_DESC_LENGTH		9
+#define ENDPOINT_DESC_LENGTH		7
+#define ENDPOINT_AUDIO_DESC_LENGTH	9
+
+/** @defgroup desc USB descriptors
+ * This page details how to examine the various standard USB descriptors
+ * for detected devices
+ */
+
+/* set host_endian if the w values are already in host endian format,
+ * as opposed to bus endian. */
+int usbi_parse_descriptor(unsigned char *source, char *descriptor, void *dest,
+	int host_endian)
+{
+	unsigned char *sp = source, *dp = dest;
+	uint16_t w;
+	char *cp;
+
+	for (cp = descriptor; *cp; cp++) {
+		switch (*cp) {
+			case 'b':	/* 8-bit byte */
+				*dp++ = *sp++;
+				break;
+			case 'w':	/* 16-bit word, convert from little endian to CPU */
+				dp += ((unsigned long)dp & 1);	/* Align to word boundary */
+
+				if (host_endian) {
+					memcpy(dp, sp, 2);
+				} else {
+					w = (sp[1] << 8) | sp[0];
+					*((uint16_t *)dp) = w;
+				}
+				sp += 2;
+				dp += 2;
+				break;
+		}
+	}
+
+	return sp - source;
+}
+
+static void clear_endpoint(struct libusb_endpoint_descriptor *endpoint)
+{
+	if (endpoint->extra)
+		free((unsigned char *) endpoint->extra);
+}
+
+static int parse_endpoint(struct libusb_context *ctx,
+	struct libusb_endpoint_descriptor *endpoint, unsigned char *buffer,
+	int size, int host_endian)
+{
+	struct usb_descriptor_header header;
+	unsigned char *extra;
+	unsigned char *begin;
+	int parsed = 0;
+	int len;
+
+	usbi_parse_descriptor(buffer, "bb", &header, 0);
+
+	/* Everything should be fine being passed into here, but we sanity */
+	/*  check JIC */
+	if (header.bLength > size) {
+		usbi_err(ctx, "ran out of descriptors parsing");
+		return -1;
+	}
+
+	if (header.bDescriptorType != LIBUSB_DT_ENDPOINT) {
+		usbi_err(ctx, "unexpected descriptor %x (expected %x)",
+			header.bDescriptorType, LIBUSB_DT_ENDPOINT);
+		return parsed;
+	}
+
+	if (header.bLength >= ENDPOINT_AUDIO_DESC_LENGTH)
+		usbi_parse_descriptor(buffer, "bbbbwbbb", endpoint, host_endian);
+	else if (header.bLength >= ENDPOINT_DESC_LENGTH)
+		usbi_parse_descriptor(buffer, "bbbbwb", endpoint, host_endian);
+
+	buffer += header.bLength;
+	size -= header.bLength;
+	parsed += header.bLength;
+
+	/* Skip over the rest of the Class Specific or Vendor Specific */
+	/*  descriptors */
+	begin = buffer;
+	while (size >= DESC_HEADER_LENGTH) {
+		usbi_parse_descriptor(buffer, "bb", &header, 0);
+
+		if (header.bLength < 2) {
+			usbi_err(ctx, "invalid descriptor length %d", header.bLength);
+			return -1;
+		}
+
+		/* If we find another "proper" descriptor then we're done  */
+		if ((header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+				(header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
+				(header.bDescriptorType == LIBUSB_DT_CONFIG) ||
+				(header.bDescriptorType == LIBUSB_DT_DEVICE))
+			break;
+
+		usbi_dbg("skipping descriptor %x", header.bDescriptorType);
+		buffer += header.bLength;
+		size -= header.bLength;
+		parsed += header.bLength;
+	}
+
+	/* Copy any unknown descriptors into a storage area for drivers */
+	/*  to later parse */
+	len = (int)(buffer - begin);
+	if (!len) {
+		endpoint->extra = NULL;
+		endpoint->extra_length = 0;
+		return parsed;
+	}
+
+	extra = malloc(len);
+	endpoint->extra = extra;
+	if (!extra) {
+		endpoint->extra_length = 0;
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	memcpy(extra, begin, len);
+	endpoint->extra_length = len;
+
+	return parsed;
+}
+
+static void clear_interface(struct libusb_interface *interface)
+{
+	int i;
+	int j;
+
+	if (interface->altsetting) {
+		for (i = 0; i < interface->num_altsetting; i++) {
+			struct libusb_interface_descriptor *ifp =
+				(struct libusb_interface_descriptor *)
+				interface->altsetting + i;
+			if (ifp->extra)
+				free((void *) ifp->extra);
+			if (ifp->endpoint) {
+				for (j = 0; j < ifp->bNumEndpoints; j++)
+					clear_endpoint((struct libusb_endpoint_descriptor *)
+						ifp->endpoint + j);
+				free((void *) ifp->endpoint);
+			}
+		}
+		free((void *) interface->altsetting);
+		interface->altsetting = NULL;
+	}
+	
+}
+
+static int parse_interface(libusb_context *ctx,
+	struct libusb_interface *interface, unsigned char *buffer, int size,
+	int host_endian)
+{
+	int i;
+	int len;
+	int r;
+	int parsed = 0;
+	int tmp;
+	struct usb_descriptor_header header;
+	struct libusb_interface_descriptor *ifp;
+	unsigned char *begin;
+
+	interface->num_altsetting = 0;
+
+	while (size >= INTERFACE_DESC_LENGTH) {
+		struct libusb_interface_descriptor *altsetting =
+			(struct libusb_interface_descriptor *) interface->altsetting;
+		altsetting = realloc(altsetting,
+			sizeof(struct libusb_interface_descriptor) *
+			(interface->num_altsetting + 1));
+		if (!altsetting) {
+			r = LIBUSB_ERROR_NO_MEM;
+			goto err;
+		}
+		interface->altsetting = altsetting;
+
+		ifp = altsetting + interface->num_altsetting;
+		interface->num_altsetting++;
+		usbi_parse_descriptor(buffer, "bbbbbbbbb", ifp, 0);
+		ifp->extra = NULL;
+		ifp->extra_length = 0;
+		ifp->endpoint = NULL;
+
+		/* Skip over the interface */
+		buffer += ifp->bLength;
+		parsed += ifp->bLength;
+		size -= ifp->bLength;
+
+		begin = buffer;
+
+		/* Skip over any interface, class or vendor descriptors */
+		while (size >= DESC_HEADER_LENGTH) {
+			usbi_parse_descriptor(buffer, "bb", &header, 0);
+			if (header.bLength < 2) {
+				usbi_err(ctx, "invalid descriptor of length %d",
+					header.bLength);
+				r = LIBUSB_ERROR_IO;
+				goto err;
+			}
+
+			/* If we find another "proper" descriptor then we're done */
+			if ((header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
+					(header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+					(header.bDescriptorType == LIBUSB_DT_CONFIG) ||
+					(header.bDescriptorType == LIBUSB_DT_DEVICE))
+				break;
+
+			buffer += header.bLength;
+			parsed += header.bLength;
+			size -= header.bLength;
+		}
+
+		/* Copy any unknown descriptors into a storage area for */
+		/*  drivers to later parse */
+		len = (int)(buffer - begin);
+		if (len) {
+			ifp->extra = malloc(len);
+			if (!ifp->extra) {
+				r = LIBUSB_ERROR_NO_MEM;
+				goto err;
+			}
+			memcpy((unsigned char *) ifp->extra, begin, len);
+			ifp->extra_length = len;
+		}
+
+		/* Did we hit an unexpected descriptor? */
+		usbi_parse_descriptor(buffer, "bb", &header, 0);
+		if ((size >= DESC_HEADER_LENGTH) &&
+				((header.bDescriptorType == LIBUSB_DT_CONFIG) ||
+				 (header.bDescriptorType == LIBUSB_DT_DEVICE)))
+			return parsed;
+
+		if (ifp->bNumEndpoints > USB_MAXENDPOINTS) {
+			usbi_err(ctx, "too many endpoints (%d)", ifp->bNumEndpoints);
+			r = LIBUSB_ERROR_IO;
+			goto err;
+		}
+
+		if (ifp->bNumEndpoints > 0) {
+			struct libusb_endpoint_descriptor *endpoint;
+			tmp = ifp->bNumEndpoints * sizeof(struct libusb_endpoint_descriptor);
+			endpoint = malloc(tmp);
+			ifp->endpoint = endpoint;
+			if (!endpoint) {
+				r = LIBUSB_ERROR_NO_MEM;
+				goto err;
+			}
+
+			memset(endpoint, 0, tmp);
+			for (i = 0; i < ifp->bNumEndpoints; i++) {
+				usbi_parse_descriptor(buffer, "bb", &header, 0);
+
+				if (header.bLength > size) {
+					usbi_err(ctx, "ran out of descriptors parsing");
+					r = LIBUSB_ERROR_IO;
+					goto err;
+				}
+
+				r = parse_endpoint(ctx, endpoint + i, buffer, size,
+					host_endian);
+				if (r < 0)
+					goto err;
+
+				buffer += r;
+				parsed += r;
+				size -= r;
+			}
+		}
+
+		/* We check to see if it's an alternate to this one */
+		ifp = (struct libusb_interface_descriptor *) buffer;
+		if (size < LIBUSB_DT_INTERFACE_SIZE ||
+				ifp->bDescriptorType != LIBUSB_DT_INTERFACE ||
+				!ifp->bAlternateSetting)
+			return parsed;
+	}
+
+	return parsed;
+err:
+	clear_interface(interface);
+	return r;
+}
+
+static void clear_configuration(struct libusb_config_descriptor *config)
+{
+	if (config->interface) {
+		int i;
+		for (i = 0; i < config->bNumInterfaces; i++)
+			clear_interface((struct libusb_interface *)
+				config->interface + i);
+		free((void *) config->interface);
+	}
+	if (config->extra)
+		free((void *) config->extra);
+}
+
+static int parse_configuration(struct libusb_context *ctx,
+	struct libusb_config_descriptor *config, unsigned char *buffer,
+	int host_endian)
+{
+	int i;
+	int r;
+	int size;
+	int tmp;
+	struct usb_descriptor_header header;
+	struct libusb_interface *interface;
+
+	usbi_parse_descriptor(buffer, "bbwbbbbb", config, host_endian);
+	size = config->wTotalLength;
+
+	if (config->bNumInterfaces > USB_MAXINTERFACES) {
+		usbi_err(ctx, "too many interfaces (%d)", config->bNumInterfaces);
+		return LIBUSB_ERROR_IO;
+	}
+
+	tmp = config->bNumInterfaces * sizeof(struct libusb_interface);
+	interface = malloc(tmp);
+	config->interface = interface;
+	if (!config->interface)
+		return LIBUSB_ERROR_NO_MEM;
+
+	memset(interface, 0, tmp);
+	buffer += config->bLength;
+	size -= config->bLength;
+
+	config->extra = NULL;
+	config->extra_length = 0;
+
+	for (i = 0; i < config->bNumInterfaces; i++) {
+		int len;
+		unsigned char *begin;
+
+		/* Skip over the rest of the Class Specific or Vendor */
+		/*  Specific descriptors */
+		begin = buffer;
+		while (size >= DESC_HEADER_LENGTH) {
+			usbi_parse_descriptor(buffer, "bb", &header, 0);
+
+			if ((header.bLength > size) ||
+					(header.bLength < DESC_HEADER_LENGTH)) {
+				usbi_err(ctx, "invalid descriptor length of %d",
+					header.bLength);
+				r = LIBUSB_ERROR_IO;
+				goto err;
+			}
+
+			/* If we find another "proper" descriptor then we're done */
+			if ((header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+					(header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
+					(header.bDescriptorType == LIBUSB_DT_CONFIG) ||
+					(header.bDescriptorType == LIBUSB_DT_DEVICE))
+				break;
+
+			usbi_dbg("skipping descriptor 0x%x\n", header.bDescriptorType);
+			buffer += header.bLength;
+			size -= header.bLength;
+		}
+
+		/* Copy any unknown descriptors into a storage area for */
+		/*  drivers to later parse */
+		len = (int)(buffer - begin);
+		if (len) {
+			/* FIXME: We should realloc and append here */
+			if (!config->extra_length) {
+				config->extra = malloc(len);
+				if (!config->extra) {
+					r = LIBUSB_ERROR_NO_MEM;
+					goto err;
+				}
+
+				memcpy((unsigned char *) config->extra, begin, len);
+				config->extra_length = len;
+			}
+		}
+
+		r = parse_interface(ctx, interface + i, buffer, size, host_endian);
+		if (r < 0)
+			goto err;
+
+		buffer += r;
+		size -= r;
+	}
+
+	return size;
+
+err:
+	clear_configuration(config);
+	return r;
+}
+
+/** \ingroup desc
+ * Get the USB device descriptor for a given device.
+ *
+ * This is a non-blocking function; the device descriptor is cached in memory.
+ *
+ * \param dev the device
+ * \param desc output location for the descriptor data
+ * \returns 0 on success or a LIBUSB_ERROR code on failure
+ */
+API_EXPORTED int libusb_get_device_descriptor(libusb_device *dev,
+	struct libusb_device_descriptor *desc)
+{
+	unsigned char raw_desc[DEVICE_DESC_LENGTH];
+	int host_endian = 0;
+	int r;
+
+	usbi_dbg("");
+	r = usbi_backend->get_device_descriptor(dev, raw_desc, &host_endian);
+	if (r < 0)
+		return r;
+
+	memcpy((unsigned char *) desc, raw_desc, sizeof(raw_desc));
+	if (!host_endian) {
+		desc->bcdUSB = libusb_le16_to_cpu(desc->bcdUSB);
+		desc->idVendor = libusb_le16_to_cpu(desc->idVendor);
+		desc->idProduct = libusb_le16_to_cpu(desc->idProduct);
+		desc->bcdDevice = libusb_le16_to_cpu(desc->bcdDevice);
+	}
+	return 0;
+}
+
+/** \ingroup desc
+ * Get the USB configuration descriptor for the currently active configuration.
+ * This is a non-blocking function which does not involve any requests being
+ * sent to the device.
+ *
+ * \param dev a device
+ * \param config output location for the USB configuration descriptor. Only
+ * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
+ * after use.
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the device is in unconfigured state
+ * \returns another LIBUSB_ERROR code on error
+ * \see libusb_get_config_descriptor
+ */
+API_EXPORTED int libusb_get_active_config_descriptor(libusb_device *dev,
+	struct libusb_config_descriptor **config)
+{
+	struct libusb_config_descriptor *_config = malloc(sizeof(*_config));
+	unsigned char tmp[8];
+	unsigned char *buf = NULL;
+	int host_endian = 0;
+	int r;
+
+	usbi_dbg("");
+	if (!_config)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = usbi_backend->get_active_config_descriptor(dev, tmp, sizeof(tmp),
+		&host_endian);
+	if (r < 0)
+		goto err;
+
+	usbi_parse_descriptor(tmp, "bbw", _config, host_endian);
+	buf = malloc(_config->wTotalLength);
+	if (!buf) {
+		r = LIBUSB_ERROR_NO_MEM;
+		goto err;
+	}
+
+	r = usbi_backend->get_active_config_descriptor(dev, buf,
+		_config->wTotalLength, &host_endian);
+	if (r < 0)
+		goto err;
+
+	r = parse_configuration(dev->ctx, _config, buf, host_endian);
+	if (r < 0) {
+		usbi_err(dev->ctx, "parse_configuration failed with error %d", r);
+		goto err;
+	} else if (r > 0) {
+		usbi_warn(dev->ctx, "descriptor data still left");
+	}
+
+	free(buf);
+	*config = _config;
+	return 0;
+
+err:
+	free(_config);
+	if (buf)
+		free(buf);
+	return r;
+}
+
+/** \ingroup desc
+ * Get a USB configuration descriptor based on its index.
+ * This is a non-blocking function which does not involve any requests being
+ * sent to the device.
+ *
+ * \param dev a device
+ * \param config_index the index of the configuration you wish to retrieve
+ * \param config output location for the USB configuration descriptor. Only
+ * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
+ * after use.
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
+ * \returns another LIBUSB_ERROR code on error
+ * \see libusb_get_active_config_descriptor()
+ * \see libusb_get_config_descriptor_by_value()
+ */
+API_EXPORTED int libusb_get_config_descriptor(libusb_device *dev,
+	uint8_t config_index, struct libusb_config_descriptor **config)
+{
+	struct libusb_config_descriptor *_config;
+	unsigned char tmp[8];
+	unsigned char *buf = NULL;
+	int host_endian = 0;
+	int r;
+
+	usbi_dbg("index %d", config_index);
+	if (config_index >= dev->num_configurations)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	_config = malloc(sizeof(*_config));
+	if (!_config)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = usbi_backend->get_config_descriptor(dev, config_index, tmp,
+		sizeof(tmp), &host_endian);
+	if (r < 0)
+		goto err;
+
+	usbi_parse_descriptor(tmp, "bbw", _config, host_endian);
+	buf = malloc(_config->wTotalLength);
+	if (!buf) {
+		r = LIBUSB_ERROR_NO_MEM;
+		goto err;
+	}
+
+	host_endian = 0;
+	r = usbi_backend->get_config_descriptor(dev, config_index, buf,
+		_config->wTotalLength, &host_endian);
+	if (r < 0)
+		goto err;
+
+	r = parse_configuration(dev->ctx, _config, buf, host_endian);
+	if (r < 0) {
+		usbi_err(dev->ctx, "parse_configuration failed with error %d", r);
+		goto err;
+	} else if (r > 0) {
+		usbi_warn(dev->ctx, "descriptor data still left");
+	}
+
+	free(buf);
+	*config = _config;
+	return 0;
+
+err:
+	free(_config);
+	if (buf)
+		free(buf);
+	return r;
+}
+
+/* iterate through all configurations, returning the index of the configuration
+ * matching a specific bConfigurationValue in the idx output parameter, or -1
+ * if the config was not found.
+ * returns 0 or a LIBUSB_ERROR code
+ */
+int usbi_get_config_index_by_value(struct libusb_device *dev,
+	uint8_t bConfigurationValue, int *idx)
+{
+	int i;
+
+	usbi_dbg("value %d", bConfigurationValue);
+	for (i = 0; i < dev->num_configurations; i++) {
+		unsigned char tmp[6];
+		int host_endian;
+		int r = usbi_backend->get_config_descriptor(dev, i, tmp, sizeof(tmp),
+			&host_endian);
+		if (r < 0)
+			return r;
+		if (tmp[5] == bConfigurationValue) {
+			*idx = i;
+			return 0;
+		}
+	}
+
+	*idx = -1;
+	return 0;
+}
+
+/** \ingroup desc
+ * Get a USB configuration descriptor with a specific bConfigurationValue.
+ * This is a non-blocking function which does not involve any requests being
+ * sent to the device.
+ *
+ * \param dev a device
+ * \param bConfigurationValue the bConfigurationValue of the configuration you
+ * wish to retrieve
+ * \param config output location for the USB configuration descriptor. Only
+ * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
+ * after use.
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
+ * \returns another LIBUSB_ERROR code on error
+ * \see libusb_get_active_config_descriptor()
+ * \see libusb_get_config_descriptor()
+ */
+API_EXPORTED int libusb_get_config_descriptor_by_value(libusb_device *dev,
+	uint8_t bConfigurationValue, struct libusb_config_descriptor **config)
+{
+	int idx;
+	int r = usbi_get_config_index_by_value(dev, bConfigurationValue, &idx);
+	if (r < 0)
+		return r;
+	else if (idx == -1)
+		return LIBUSB_ERROR_NOT_FOUND;
+	else
+		return libusb_get_config_descriptor(dev, idx, config);
+}
+
+/** \ingroup desc
+ * Free a configuration descriptor obtained from
+ * libusb_get_active_config_descriptor() or libusb_get_config_descriptor().
+ * It is safe to call this function with a NULL config parameter, in which
+ * case the function simply returns.
+ *
+ * \param config the configuration descriptor to free
+ */
+API_EXPORTED void libusb_free_config_descriptor(
+	struct libusb_config_descriptor *config)
+{
+	if (!config)
+		return;
+
+	clear_configuration(config);
+	free(config);
+}
+
+/** \ingroup desc
+ * Retrieve a string descriptor in C style ASCII.
+ *
+ * Wrapper around libusb_get_string_descriptor(). Uses the first language 
+ * supported by the device.
+ *
+ * \param dev a device handle
+ * \param desc_index the index of the descriptor to retrieve
+ * \param data output buffer for ASCII string descriptor
+ * \param length size of data buffer
+ * \returns number of bytes returned in data, or LIBUSB_ERROR code on failure
+ */
+API_EXPORTED int libusb_get_string_descriptor_ascii(libusb_device_handle *dev,
+	uint8_t desc_index, unsigned char *data, int length)
+{
+	unsigned char tbuf[255]; /* Some devices choke on size > 255 */
+	int r, langid, si, di;
+
+	/* Asking for the zero'th index is special - it returns a string
+	 * descriptor that contains all the language IDs supported by the device.
+	 * Typically there aren't many - often only one. The language IDs are 16
+	 * bit numbers, and they start at the third byte in the descriptor. See
+	 * USB 2.0 specification section 9.6.7 for more information. */
+	r = libusb_get_string_descriptor(dev, 0, 0, tbuf, sizeof(tbuf));
+	if (r < 0)
+		return r;
+
+	if (r < 4)
+		return LIBUSB_ERROR_IO;
+
+	langid = tbuf[2] | (tbuf[3] << 8);
+
+	r = libusb_get_string_descriptor(dev, desc_index, langid, tbuf,
+		sizeof(tbuf));
+	if (r < 0)
+		return r;
+
+	if (tbuf[1] != LIBUSB_DT_STRING)
+		return LIBUSB_ERROR_IO;
+
+	if (tbuf[0] > r)
+		return LIBUSB_ERROR_IO;
+
+	for (di = 0, si = 2; si < tbuf[0]; si += 2) {
+		if (di >= (length - 1))
+			break;
+
+		if (tbuf[si + 1]) /* high byte */
+			data[di++] = '?';
+		else
+			data[di++] = tbuf[si];
+	}
+
+	data[di] = 0;
+	return di;
+}
+
diff --git a/libusb/io.c b/libusb/io.c
new file mode 100644
index 0000000..1379eb3
--- /dev/null
+++ b/libusb/io.c
@@ -0,0 +1,2308 @@
+/*
+ * I/O functions for libusb
+ * Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+#include <errno.h>
+#include <poll.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/time.h>
+#include <time.h>
+#include <unistd.h>
+
+#ifdef USBI_TIMERFD_AVAILABLE
+#include <sys/timerfd.h>
+#endif
+
+#include "libusbi.h"
+
+/**
+ * \page io Synchronous and asynchronous device I/O
+ *
+ * \section intro Introduction
+ *
+ * If you're using libusb in your application, you're probably wanting to
+ * perform I/O with devices - you want to perform USB data transfers.
+ *
+ * libusb offers two separate interfaces for device I/O. This page aims to
+ * introduce the two in order to help you decide which one is more suitable
+ * for your application. You can also choose to use both interfaces in your
+ * application by considering each transfer on a case-by-case basis.
+ *
+ * Once you have read through the following discussion, you should consult the
+ * detailed API documentation pages for the details:
+ * - \ref syncio
+ * - \ref asyncio
+ *
+ * \section theory Transfers at a logical level
+ *
+ * At a logical level, USB transfers typically happen in two parts. For
+ * example, when reading data from a endpoint:
+ * -# A request for data is sent to the device
+ * -# Some time later, the incoming data is received by the host
+ *
+ * or when writing data to an endpoint:
+ *
+ * -# The data is sent to the device
+ * -# Some time later, the host receives acknowledgement from the device that
+ *    the data has been transferred.
+ *
+ * There may be an indefinite delay between the two steps. Consider a
+ * fictional USB input device with a button that the user can press. In order
+ * to determine when the button is pressed, you would likely submit a request
+ * to read data on a bulk or interrupt endpoint and wait for data to arrive.
+ * Data will arrive when the button is pressed by the user, which is
+ * potentially hours later.
+ *
+ * libusb offers both a synchronous and an asynchronous interface to performing
+ * USB transfers. The main difference is that the synchronous interface
+ * combines both steps indicated above into a single function call, whereas
+ * the asynchronous interface separates them.
+ *
+ * \section sync The synchronous interface
+ *
+ * The synchronous I/O interface allows you to perform a USB transfer with
+ * a single function call. When the function call returns, the transfer has
+ * completed and you can parse the results.
+ *
+ * If you have used the libusb-0.1 before, this I/O style will seem familar to
+ * you. libusb-0.1 only offered a synchronous interface.
+ *
+ * In our input device example, to read button presses you might write code
+ * in the following style:
+\code
+unsigned char data[4];
+int actual_length,
+int r = libusb_bulk_transfer(handle, EP_IN, data, sizeof(data), &actual_length, 0);
+if (r == 0 && actual_length == sizeof(data)) {
+	// results of the transaction can now be found in the data buffer
+	// parse them here and report button press
+} else {
+	error();
+}
+\endcode
+ *
+ * The main advantage of this model is simplicity: you did everything with
+ * a single simple function call.
+ *
+ * However, this interface has its limitations. Your application will sleep
+ * inside libusb_bulk_transfer() until the transaction has completed. If it
+ * takes the user 3 hours to press the button, your application will be
+ * sleeping for that long. Execution will be tied up inside the library -
+ * the entire thread will be useless for that duration.
+ *
+ * Another issue is that by tieing up the thread with that single transaction
+ * there is no possibility of performing I/O with multiple endpoints and/or
+ * multiple devices simultaneously, unless you resort to creating one thread
+ * per transaction.
+ *
+ * Additionally, there is no opportunity to cancel the transfer after the
+ * request has been submitted.
+ *
+ * For details on how to use the synchronous API, see the
+ * \ref syncio "synchronous I/O API documentation" pages.
+ * 
+ * \section async The asynchronous interface
+ *
+ * Asynchronous I/O is the most significant new feature in libusb-1.0.
+ * Although it is a more complex interface, it solves all the issues detailed
+ * above.
+ *
+ * Instead of providing which functions that block until the I/O has complete,
+ * libusb's asynchronous interface presents non-blocking functions which
+ * begin a transfer and then return immediately. Your application passes a
+ * callback function pointer to this non-blocking function, which libusb will
+ * call with the results of the transaction when it has completed.
+ *
+ * Transfers which have been submitted through the non-blocking functions
+ * can be cancelled with a separate function call.
+ *
+ * The non-blocking nature of this interface allows you to be simultaneously
+ * performing I/O to multiple endpoints on multiple devices, without having
+ * to use threads.
+ *
+ * This added flexibility does come with some complications though:
+ * - In the interest of being a lightweight library, libusb does not create
+ * threads and can only operate when your application is calling into it. Your
+ * application must call into libusb from it's main loop when events are ready
+ * to be handled, or you must use some other scheme to allow libusb to
+ * undertake whatever work needs to be done.
+ * - libusb also needs to be called into at certain fixed points in time in
+ * order to accurately handle transfer timeouts.
+ * - Memory handling becomes more complex. You cannot use stack memory unless
+ * the function with that stack is guaranteed not to return until the transfer
+ * callback has finished executing.
+ * - You generally lose some linearity from your code flow because submitting
+ * the transfer request is done in a separate function from where the transfer
+ * results are handled. This becomes particularly obvious when you want to
+ * submit a second transfer based on the results of an earlier transfer.
+ *
+ * Internally, libusb's synchronous interface is expressed in terms of function
+ * calls to the asynchronous interface.
+ *
+ * For details on how to use the asynchronous API, see the
+ * \ref asyncio "asynchronous I/O API" documentation pages.
+ */
+
+
+/**
+ * \page packetoverflow Packets and overflows
+ *
+ * \section packets Packet abstraction
+ *
+ * The USB specifications describe how data is transmitted in packets, with
+ * constraints on packet size defined by endpoint descriptors. The host must
+ * not send data payloads larger than the endpoint's maximum packet size.
+ *
+ * libusb and the underlying OS abstract out the packet concept, allowing you
+ * to request transfers of any size. Internally, the request will be divided
+ * up into correctly-sized packets. You do not have to be concerned with
+ * packet sizes, but there is one exception when considering overflows.
+ *
+ * \section overflow Bulk/interrupt transfer overflows
+ *
+ * When requesting data on a bulk endpoint, libusb requires you to supply a
+ * buffer and the maximum number of bytes of data that libusb can put in that
+ * buffer. However, the size of the buffer is not communicated to the device -
+ * the device is just asked to send any amount of data.
+ *
+ * There is no problem if the device sends an amount of data that is less than
+ * or equal to the buffer size. libusb reports this condition to you through
+ * the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
+ * field.
+ *
+ * Problems may occur if the device attempts to send more data than can fit in
+ * the buffer. libusb reports LIBUSB_TRANSFER_OVERFLOW for this condition but
+ * other behaviour is largely undefined: actual_length may or may not be
+ * accurate, the chunk of data that can fit in the buffer (before overflow)
+ * may or may not have been transferred.
+ *
+ * Overflows are nasty, but can be avoided. Even though you were told to
+ * ignore packets above, think about the lower level details: each transfer is
+ * split into packets (typically small, with a maximum size of 512 bytes).
+ * Overflows can only happen if the final packet in an incoming data transfer
+ * is smaller than the actual packet that the device wants to transfer.
+ * Therefore, you will never see an overflow if your transfer buffer size is a
+ * multiple of the endpoint's packet size: the final packet will either
+ * fill up completely or will be only partially filled.
+ */
+
+/**
+ * @defgroup asyncio Asynchronous device I/O
+ *
+ * This page details libusb's asynchronous (non-blocking) API for USB device
+ * I/O. This interface is very powerful but is also quite complex - you will
+ * need to read this page carefully to understand the necessary considerations
+ * and issues surrounding use of this interface. Simplistic applications
+ * may wish to consider the \ref syncio "synchronous I/O API" instead.
+ *
+ * The asynchronous interface is built around the idea of separating transfer
+ * submission and handling of transfer completion (the synchronous model
+ * combines both of these into one). There may be a long delay between
+ * submission and completion, however the asynchronous submission function
+ * is non-blocking so will return control to your application during that
+ * potentially long delay.
+ *
+ * \section asyncabstraction Transfer abstraction
+ *
+ * For the asynchronous I/O, libusb implements the concept of a generic
+ * transfer entity for all types of I/O (control, bulk, interrupt,
+ * isochronous). The generic transfer object must be treated slightly
+ * differently depending on which type of I/O you are performing with it.
+ *
+ * This is represented by the public libusb_transfer structure type.
+ *
+ * \section asynctrf Asynchronous transfers
+ *
+ * We can view asynchronous I/O as a 5 step process:
+ * -# <b>Allocation</b>: allocate a libusb_transfer
+ * -# <b>Filling</b>: populate the libusb_transfer instance with information
+ *    about the transfer you wish to perform
+ * -# <b>Submission</b>: ask libusb to submit the transfer
+ * -# <b>Completion handling</b>: examine transfer results in the
+ *    libusb_transfer structure
+ * -# <b>Deallocation</b>: clean up resources
+ * 
+ *
+ * \subsection asyncalloc Allocation
+ *
+ * This step involves allocating memory for a USB transfer. This is the
+ * generic transfer object mentioned above. At this stage, the transfer
+ * is "blank" with no details about what type of I/O it will be used for.
+ *
+ * Allocation is done with the libusb_alloc_transfer() function. You must use
+ * this function rather than allocating your own transfers.
+ *
+ * \subsection asyncfill Filling
+ *
+ * This step is where you take a previously allocated transfer and fill it
+ * with information to determine the message type and direction, data buffer,
+ * callback function, etc.
+ *
+ * You can either fill the required fields yourself or you can use the
+ * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
+ * and libusb_fill_interrupt_transfer().
+ *
+ * \subsection asyncsubmit Submission
+ *
+ * When you have allocated a transfer and filled it, you can submit it using
+ * libusb_submit_transfer(). This function returns immediately but can be
+ * regarded as firing off the I/O request in the background.
+ *
+ * \subsection asynccomplete Completion handling
+ *
+ * After a transfer has been submitted, one of four things can happen to it:
+ *
+ * - The transfer completes (i.e. some data was transferred)
+ * - The transfer has a timeout and the timeout expires before all data is
+ * transferred
+ * - The transfer fails due to an error
+ * - The transfer is cancelled
+ *
+ * Each of these will cause the user-specified transfer callback function to
+ * be invoked. It is up to the callback function to determine which of the
+ * above actually happened and to act accordingly.
+ *
+ * The user-specified callback is passed a pointer to the libusb_transfer
+ * structure which was used to setup and submit the transfer. At completion
+ * time, libusb has populated this structure with results of the transfer:
+ * success or failure reason, number of bytes of data transferred, etc. See
+ * the libusb_transfer structure documentation for more information.
+ *
+ * \subsection Deallocation
+ *
+ * When a transfer has completed (i.e. the callback function has been invoked),
+ * you are advised to free the transfer (unless you wish to resubmit it, see
+ * below). Transfers are deallocated with libusb_free_transfer().
+ *
+ * It is undefined behaviour to free a transfer which has not completed.
+ *
+ * \section asyncresubmit Resubmission
+ *
+ * You may be wondering why allocation, filling, and submission are all
+ * separated above where they could reasonably be combined into a single
+ * operation.
+ *
+ * The reason for separation is to allow you to resubmit transfers without
+ * having to allocate new ones every time. This is especially useful for
+ * common situations dealing with interrupt endpoints - you allocate one
+ * transfer, fill and submit it, and when it returns with results you just
+ * resubmit it for the next interrupt.
+ *
+ * \section asynccancel Cancellation
+ *
+ * Another advantage of using the asynchronous interface is that you have
+ * the ability to cancel transfers which have not yet completed. This is
+ * done by calling the libusb_cancel_transfer() function.
+ *
+ * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
+ * cancellation actually completes, the transfer's callback function will
+ * be invoked, and the callback function should check the transfer status to
+ * determine that it was cancelled.
+ *
+ * Freeing the transfer after it has been cancelled but before cancellation
+ * has completed will result in undefined behaviour.
+ *
+ * When a transfer is cancelled, some of the data may have been transferred.
+ * libusb will communicate this to you in the transfer callback. Do not assume
+ * that no data was transferred.
+ *
+ * \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
+ *
+ * If your device does not have predictable transfer sizes (or it misbehaves),
+ * your application may submit a request for data on an IN endpoint which is
+ * smaller than the data that the device wishes to send. In some circumstances
+ * this will cause an overflow, which is a nasty condition to deal with. See
+ * the \ref packetoverflow page for discussion.
+ *
+ * \section asyncctrl Considerations for control transfers
+ *
+ * The <tt>libusb_transfer</tt> structure is generic and hence does not
+ * include specific fields for the control-specific setup packet structure.
+ *
+ * In order to perform a control transfer, you must place the 8-byte setup
+ * packet at the start of the data buffer. To simplify this, you could
+ * cast the buffer pointer to type struct libusb_control_setup, or you can
+ * use the helper function libusb_fill_control_setup().
+ *
+ * The wLength field placed in the setup packet must be the length you would
+ * expect to be sent in the setup packet: the length of the payload that
+ * follows (or the expected maximum number of bytes to receive). However,
+ * the length field of the libusb_transfer object must be the length of
+ * the data buffer - i.e. it should be wLength <em>plus</em> the size of
+ * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
+ *
+ * If you use the helper functions, this is simplified for you:
+ * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
+ * data you are sending/requesting.
+ * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
+ * request size as the wLength value (i.e. do not include the extra space you
+ * allocated for the control setup).
+ * -# If this is a host-to-device transfer, place the data to be transferred
+ * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
+ * -# Call libusb_fill_control_transfer() to associate the data buffer with
+ * the transfer (and to set the remaining details such as callback and timeout).
+ *   - Note that there is no parameter to set the length field of the transfer.
+ *     The length is automatically inferred from the wLength field of the setup
+ *     packet.
+ * -# Submit the transfer.
+ *
+ * The multi-byte control setup fields (wValue, wIndex and wLength) must
+ * be given in little-endian byte order (the endianness of the USB bus).
+ * Endianness conversion is transparently handled by
+ * libusb_fill_control_setup() which is documented to accept host-endian
+ * values.
+ *
+ * Further considerations are needed when handling transfer completion in
+ * your callback function:
+ * - As you might expect, the setup packet will still be sitting at the start
+ * of the data buffer.
+ * - If this was a device-to-host transfer, the received data will be sitting
+ * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
+ * - The actual_length field of the transfer structure is relative to the
+ * wLength of the setup packet, rather than the size of the data buffer. So,
+ * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
+ * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
+ * transferred in entirity.
+ *
+ * To simplify parsing of setup packets and obtaining the data from the
+ * correct offset, you may wish to use the libusb_control_transfer_get_data()
+ * and libusb_control_transfer_get_setup() functions within your transfer
+ * callback.
+ *
+ * Even though control endpoints do not halt, a completed control transfer
+ * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
+ * request was not supported.
+ *
+ * \section asyncintr Considerations for interrupt transfers
+ * 
+ * All interrupt transfers are performed using the polling interval presented
+ * by the bInterval value of the endpoint descriptor.
+ *
+ * \section asynciso Considerations for isochronous transfers
+ *
+ * Isochronous transfers are more complicated than transfers to
+ * non-isochronous endpoints.
+ *
+ * To perform I/O to an isochronous endpoint, allocate the transfer by calling
+ * libusb_alloc_transfer() with an appropriate number of isochronous packets.
+ *
+ * During filling, set \ref libusb_transfer::type "type" to
+ * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
+ * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
+ * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
+ * or equal to the number of packets you requested during allocation.
+ * libusb_alloc_transfer() does not set either of these fields for you, given
+ * that you might not even use the transfer on an isochronous endpoint.
+ *
+ * Next, populate the length field for the first num_iso_packets entries in
+ * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
+ * 5.6.3 of the USB2 specifications describe how the maximum isochronous
+ * packet length is determined by the wMaxPacketSize field in the endpoint
+ * descriptor.
+ * Two functions can help you here:
+ *
+ * - libusb_get_max_iso_packet_size() is an easy way to determine the max
+ *   packet size for an isochronous endpoint. Note that the maximum packet
+ *   size is actually the maximum number of bytes that can be transmitted in
+ *   a single microframe, therefore this function multiplies the maximum number
+ *   of bytes per transaction by the number of transaction opportunities per
+ *   microframe.
+ * - libusb_set_iso_packet_lengths() assigns the same length to all packets
+ *   within a transfer, which is usually what you want.
+ *
+ * For outgoing transfers, you'll obviously fill the buffer and populate the
+ * packet descriptors in hope that all the data gets transferred. For incoming
+ * transfers, you must ensure the buffer has sufficient capacity for
+ * the situation where all packets transfer the full amount of requested data.
+ *
+ * Completion handling requires some extra consideration. The
+ * \ref libusb_transfer::actual_length "actual_length" field of the transfer
+ * is meaningless and should not be examined; instead you must refer to the
+ * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
+ * each individual packet.
+ *
+ * The \ref libusb_transfer::status "status" field of the transfer is also a
+ * little misleading:
+ *  - If the packets were submitted and the isochronous data microframes
+ *    completed normally, status will have value
+ *    \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
+ *    "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
+ *    delays are not counted as transfer errors; the transfer.status field may
+ *    indicate COMPLETED even if some or all of the packets failed. Refer to
+ *    the \ref libusb_iso_packet_descriptor::status "status" field of each
+ *    individual packet to determine packet failures.
+ *  - The status field will have value
+ *    \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
+ *    "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
+ *  - Other transfer status codes occur with normal behaviour.
+ *
+ * The data for each packet will be found at an offset into the buffer that
+ * can be calculated as if each prior packet completed in full. The
+ * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
+ * functions may help you here.
+ *
+ * \section asyncmem Memory caveats
+ *
+ * In most circumstances, it is not safe to use stack memory for transfer
+ * buffers. This is because the function that fired off the asynchronous
+ * transfer may return before libusb has finished using the buffer, and when
+ * the function returns it's stack gets destroyed. This is true for both
+ * host-to-device and device-to-host transfers.
+ *
+ * The only case in which it is safe to use stack memory is where you can
+ * guarantee that the function owning the stack space for the buffer does not
+ * return until after the transfer's callback function has completed. In every
+ * other case, you need to use heap memory instead.
+ *
+ * \section asyncflags Fine control
+ *
+ * Through using this asynchronous interface, you may find yourself repeating
+ * a few simple operations many times. You can apply a bitwise OR of certain
+ * flags to a transfer to simplify certain things:
+ * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
+ *   "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
+ *   less than the requested amount of data being marked with status
+ *   \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
+ *   (they would normally be regarded as COMPLETED)
+ * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
+ *   "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
+ *   buffer when freeing the transfer.
+ * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
+ *   "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
+ *   transfer after the transfer callback returns.
+ *
+ * \section asyncevent Event handling
+ *
+ * In accordance of the aim of being a lightweight library, libusb does not
+ * create threads internally. This means that libusb code does not execute
+ * at any time other than when your application is calling a libusb function.
+ * However, an asynchronous model requires that libusb perform work at various
+ * points in time - namely processing the results of previously-submitted
+ * transfers and invoking the user-supplied callback function.
+ *
+ * This gives rise to the libusb_handle_events() function which your
+ * application must call into when libusb has work do to. This gives libusb
+ * the opportunity to reap pending transfers, invoke callbacks, etc.
+ *
+ * The first issue to discuss here is how your application can figure out
+ * when libusb has work to do. In fact, there are two naive options which
+ * do not actually require your application to know this:
+ * -# Periodically call libusb_handle_events() in non-blocking mode at fixed
+ *    short intervals from your main loop
+ * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
+ *    thread.
+ *
+ * The first option is plainly not very nice, and will cause unnecessary 
+ * CPU wakeups leading to increased power usage and decreased battery life.
+ * The second option is not very nice either, but may be the nicest option
+ * available to you if the "proper" approach can not be applied to your
+ * application (read on...).
+ * 
+ * The recommended option is to integrate libusb with your application main
+ * event loop. libusb exposes a set of file descriptors which allow you to do
+ * this. Your main loop is probably already calling poll() or select() or a
+ * variant on a set of file descriptors for other event sources (e.g. keyboard
+ * button presses, mouse movements, network sockets, etc). You then add
+ * libusb's file descriptors to your poll()/select() calls, and when activity
+ * is detected on such descriptors you know it is time to call
+ * libusb_handle_events().
+ *
+ * There is one final event handling complication. libusb supports
+ * asynchronous transfers which time out after a specified time period, and
+ * this requires that libusb is called into at or after the timeout so that
+ * the timeout can be handled. So, in addition to considering libusb's file
+ * descriptors in your main event loop, you must also consider that libusb
+ * sometimes needs to be called into at fixed points in time even when there
+ * is no file descriptor activity.
+ *
+ * For the details on retrieving the set of file descriptors and determining
+ * the next timeout, see the \ref poll "polling and timing" API documentation.
+ */
+
+/**
+ * @defgroup poll Polling and timing
+ *
+ * This page documents libusb's functions for polling events and timing.
+ * These functions are only necessary for users of the
+ * \ref asyncio "asynchronous API". If you are only using the simpler
+ * \ref syncio "synchronous API" then you do not need to ever call these
+ * functions.
+ *
+ * The justification for the functionality described here has already been
+ * discussed in the \ref asyncevent "event handling" section of the
+ * asynchronous API documentation. In summary, libusb does not create internal
+ * threads for event processing and hence relies on your application calling
+ * into libusb at certain points in time so that pending events can be handled.
+ * In order to know precisely when libusb needs to be called into, libusb
+ * offers you a set of pollable file descriptors and information about when
+ * the next timeout expires.
+ *
+ * If you are using the asynchronous I/O API, you must take one of the two
+ * following options, otherwise your I/O will not complete.
+ *
+ * \section pollsimple The simple option
+ *
+ * If your application revolves solely around libusb and does not need to
+ * handle other event sources, you can have a program structure as follows:
+\code
+// initialize libusb
+// find and open device
+// maybe fire off some initial async I/O
+
+while (user_has_not_requested_exit)
+	libusb_handle_events(ctx);
+
+// clean up and exit
+\endcode
+ *
+ * With such a simple main loop, you do not have to worry about managing
+ * sets of file descriptors or handling timeouts. libusb_handle_events() will
+ * handle those details internally.
+ *
+ * \section pollmain The more advanced option
+ *
+ * In more advanced applications, you will already have a main loop which
+ * is monitoring other event sources: network sockets, X11 events, mouse
+ * movements, etc. Through exposing a set of file descriptors, libusb is
+ * designed to cleanly integrate into such main loops.
+ *
+ * In addition to polling file descriptors for the other event sources, you
+ * take a set of file descriptors from libusb and monitor those too. When you
+ * detect activity on libusb's file descriptors, you call
+ * libusb_handle_events_timeout() in non-blocking mode.
+ *
+ * What's more, libusb may also need to handle events at specific moments in
+ * time. No file descriptor activity is generated at these times, so your
+ * own application needs to be continually aware of when the next one of these
+ * moments occurs (through calling libusb_get_next_timeout()), and then it
+ * needs to call libusb_handle_events_timeout() in non-blocking mode when
+ * these moments occur. This means that you need to adjust your
+ * poll()/select() timeout accordingly.
+ *
+ * libusb provides you with a set of file descriptors to poll and expects you
+ * to poll all of them, treating them as a single entity. The meaning of each
+ * file descriptor in the set is an internal implementation detail,
+ * platform-dependent and may vary from release to release. Don't try and
+ * interpret the meaning of the file descriptors, just do as libusb indicates,
+ * polling all of them at once.
+ *
+ * In pseudo-code, you want something that looks like:
+\code
+// initialise libusb
+
+libusb_get_pollfds(ctx)
+while (user has not requested application exit) {
+	libusb_get_next_timeout(ctx);
+	poll(on libusb file descriptors plus any other event sources of interest,
+		using a timeout no larger than the value libusb just suggested)
+	if (poll() indicated activity on libusb file descriptors)
+		libusb_handle_events_timeout(ctx, 0);
+	if (time has elapsed to or beyond the libusb timeout)
+		libusb_handle_events_timeout(ctx, 0);
+	// handle events from other sources here
+}
+
+// clean up and exit
+\endcode
+ *
+ * \subsection polltime Notes on time-based events
+ *
+ * The above complication with having to track time and call into libusb at
+ * specific moments is a bit of a headache. For maximum compatibility, you do
+ * need to write your main loop as above, but you may decide that you can
+ * restrict the supported platforms of your application and get away with
+ * a more simplistic scheme.
+ *
+ * These time-based event complications are \b not required on the following
+ * platforms:
+ *  - Darwin
+ *  - Linux, provided that the following version requirements are satisfied:
+ *   - Linux v2.6.27 or newer, compiled with timerfd support
+ *   - glibc v2.9 or newer
+ *   - libusb v1.0.5 or newer
+ *
+ * Under these configurations, libusb_get_next_timeout() will \em always return
+ * 0, so your main loop can be simplified to:
+\code
+// initialise libusb
+
+libusb_get_pollfds(ctx)
+while (user has not requested application exit) {
+	poll(on libusb file descriptors plus any other event sources of interest,
+		using any timeout that you like)
+	if (poll() indicated activity on libusb file descriptors)
+		libusb_handle_events_timeout(ctx, 0);
+	// handle events from other sources here
+}
+
+// clean up and exit
+\endcode
+ *
+ * Do remember that if you simplify your main loop to the above, you will
+ * lose compatibility with some platforms (including legacy Linux platforms,
+ * and <em>any future platforms supported by libusb which may have time-based
+ * event requirements</em>). The resultant problems will likely appear as
+ * strange bugs in your application.
+ *
+ * You can use the libusb_pollfds_handle_timeouts() function to do a runtime
+ * check to see if it is safe to ignore the time-based event complications.
+ * If your application has taken the shortcut of ignoring libusb's next timeout
+ * in your main loop, then you are advised to check the return value of
+ * libusb_pollfds_handle_timeouts() during application startup, and to abort
+ * if the platform does suffer from these timing complications.
+ *
+ * \subsection fdsetchange Changes in the file descriptor set
+ *
+ * The set of file descriptors that libusb uses as event sources may change
+ * during the life of your application. Rather than having to repeatedly
+ * call libusb_get_pollfds(), you can set up notification functions for when
+ * the file descriptor set changes using libusb_set_pollfd_notifiers().
+ *
+ * \subsection mtissues Multi-threaded considerations
+ *
+ * Unfortunately, the situation is complicated further when multiple threads
+ * come into play. If two threads are monitoring the same file descriptors,
+ * the fact that only one thread will be woken up when an event occurs causes
+ * some headaches.
+ *
+ * The events lock, event waiters lock, and libusb_handle_events_locked()
+ * entities are added to solve these problems. You do not need to be concerned
+ * with these entities otherwise.
+ *
+ * See the extra documentation: \ref mtasync
+ */
+
+/** \page mtasync Multi-threaded applications and asynchronous I/O
+ *
+ * libusb is a thread-safe library, but extra considerations must be applied
+ * to applications which interact with libusb from multiple threads.
+ *
+ * The underlying issue that must be addressed is that all libusb I/O
+ * revolves around monitoring file descriptors through the poll()/select()
+ * system calls. This is directly exposed at the
+ * \ref asyncio "asynchronous interface" but it is important to note that the
+ * \ref syncio "synchronous interface" is implemented on top of the
+ * asynchonrous interface, therefore the same considerations apply.
+ *
+ * The issue is that if two or more threads are concurrently calling poll()
+ * or select() on libusb's file descriptors then only one of those threads
+ * will be woken up when an event arrives. The others will be completely
+ * oblivious that anything has happened.
+ *
+ * Consider the following pseudo-code, which submits an asynchronous transfer
+ * then waits for its completion. This style is one way you could implement a
+ * synchronous interface on top of the asynchronous interface (and libusb
+ * does something similar, albeit more advanced due to the complications
+ * explained on this page).
+ *
+\code
+void cb(struct libusb_transfer *transfer)
+{
+	int *completed = transfer->user_data;
+	*completed = 1;
+}
+
+void myfunc() {
+	struct libusb_transfer *transfer;
+	unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE];
+	int completed = 0;
+
+	transfer = libusb_alloc_transfer(0);
+	libusb_fill_control_setup(buffer,
+		LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
+	libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
+	libusb_submit_transfer(transfer);
+
+	while (!completed) {
+		poll(libusb file descriptors, 120*1000);
+		if (poll indicates activity)
+			libusb_handle_events_timeout(ctx, 0);
+	}
+	printf("completed!");
+	// other code here
+}
+\endcode
+ *
+ * Here we are <em>serializing</em> completion of an asynchronous event
+ * against a condition - the condition being completion of a specific transfer.
+ * The poll() loop has a long timeout to minimize CPU usage during situations
+ * when nothing is happening (it could reasonably be unlimited).
+ *
+ * If this is the only thread that is polling libusb's file descriptors, there
+ * is no problem: there is no danger that another thread will swallow up the
+ * event that we are interested in. On the other hand, if there is another
+ * thread polling the same descriptors, there is a chance that it will receive
+ * the event that we were interested in. In this situation, <tt>myfunc()</tt>
+ * will only realise that the transfer has completed on the next iteration of
+ * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
+ * undesirable, and don't even think about using short timeouts to circumvent
+ * this issue!
+ * 
+ * The solution here is to ensure that no two threads are ever polling the
+ * file descriptors at the same time. A naive implementation of this would
+ * impact the capabilities of the library, so libusb offers the scheme
+ * documented below to ensure no loss of functionality.
+ *
+ * Before we go any further, it is worth mentioning that all libusb-wrapped
+ * event handling procedures fully adhere to the scheme documented below.
+ * This includes libusb_handle_events() and all the synchronous I/O functions - 
+ * libusb hides this headache from you. You do not need to worry about any
+ * of these issues if you stick to that level.
+ *
+ * The problem is when we consider the fact that libusb exposes file
+ * descriptors to allow for you to integrate asynchronous USB I/O into
+ * existing main loops, effectively allowing you to do some work behind
+ * libusb's back. If you do take libusb's file descriptors and pass them to
+ * poll()/select() yourself, you need to be aware of the associated issues.
+ *
+ * \section eventlock The events lock
+ *
+ * The first concept to be introduced is the events lock. The events lock
+ * is used to serialize threads that want to handle events, such that only
+ * one thread is handling events at any one time.
+ *
+ * You must take the events lock before polling libusb file descriptors,
+ * using libusb_lock_events(). You must release the lock as soon as you have
+ * aborted your poll()/select() loop, using libusb_unlock_events().
+ *
+ * \section threadwait Letting other threads do the work for you
+ *
+ * Although the events lock is a critical part of the solution, it is not
+ * enough on it's own. You might wonder if the following is sufficient...
+\code
+	libusb_lock_events(ctx);
+	while (!completed) {
+		poll(libusb file descriptors, 120*1000);
+		if (poll indicates activity)
+			libusb_handle_events_timeout(ctx, 0);
+	}
+	libusb_unlock_events(ctx);
+\endcode
+ * ...and the answer is that it is not. This is because the transfer in the
+ * code shown above may take a long time (say 30 seconds) to complete, and
+ * the lock is not released until the transfer is completed.
+ *
+ * Another thread with similar code that wants to do event handling may be
+ * working with a transfer that completes after a few milliseconds. Despite
+ * having such a quick completion time, the other thread cannot check that
+ * status of its transfer until the code above has finished (30 seconds later)
+ * due to contention on the lock.
+ *
+ * To solve this, libusb offers you a mechanism to determine when another
+ * thread is handling events. It also offers a mechanism to block your thread
+ * until the event handling thread has completed an event (and this mechanism
+ * does not involve polling of file descriptors).
+ *
+ * After determining that another thread is currently handling events, you
+ * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
+ * You then re-check that some other thread is still handling events, and if
+ * so, you call libusb_wait_for_event().
+ *
+ * libusb_wait_for_event() puts your application to sleep until an event
+ * occurs, or until a thread releases the events lock. When either of these
+ * things happen, your thread is woken up, and should re-check the condition
+ * it was waiting on. It should also re-check that another thread is handling
+ * events, and if not, it should start handling events itself.
+ *
+ * This looks like the following, as pseudo-code:
+\code
+retry:
+if (libusb_try_lock_events(ctx) == 0) {
+	// we obtained the event lock: do our own event handling
+	while (!completed) {
+		if (!libusb_event_handling_ok(ctx)) {
+			libusb_unlock_events(ctx);
+			goto retry;
+		}
+		poll(libusb file descriptors, 120*1000);
+		if (poll indicates activity)
+			libusb_handle_events_locked(ctx, 0);
+	}
+	libusb_unlock_events(ctx);
+} else {
+	// another thread is doing event handling. wait for it to signal us that
+	// an event has completed
+	libusb_lock_event_waiters(ctx);
+
+	while (!completed) {
+		// now that we have the event waiters lock, double check that another
+		// thread is still handling events for us. (it may have ceased handling
+		// events in the time it took us to reach this point)
+		if (!libusb_event_handler_active(ctx)) {
+			// whoever was handling events is no longer doing so, try again
+			libusb_unlock_event_waiters(ctx);
+			goto retry;
+		}
+	
+		libusb_wait_for_event(ctx);
+	}
+	libusb_unlock_event_waiters(ctx);
+}
+printf("completed!\n");
+\endcode
+ *
+ * A naive look at the above code may suggest that this can only support
+ * one event waiter (hence a total of 2 competing threads, the other doing
+ * event handling), because the event waiter seems to have taken the event
+ * waiters lock while waiting for an event. However, the system does support
+ * multiple event waiters, because libusb_wait_for_event() actually drops
+ * the lock while waiting, and reaquires it before continuing.
+ *
+ * We have now implemented code which can dynamically handle situations where
+ * nobody is handling events (so we should do it ourselves), and it can also
+ * handle situations where another thread is doing event handling (so we can
+ * piggyback onto them). It is also equipped to handle a combination of
+ * the two, for example, another thread is doing event handling, but for
+ * whatever reason it stops doing so before our condition is met, so we take
+ * over the event handling.
+ *
+ * Four functions were introduced in the above pseudo-code. Their importance
+ * should be apparent from the code shown above.
+ * -# libusb_try_lock_events() is a non-blocking function which attempts
+ *    to acquire the events lock but returns a failure code if it is contended.
+ * -# libusb_event_handling_ok() checks that libusb is still happy for your
+ *    thread to be performing event handling. Sometimes, libusb needs to
+ *    interrupt the event handler, and this is how you can check if you have
+ *    been interrupted. If this function returns 0, the correct behaviour is
+ *    for you to give up the event handling lock, and then to repeat the cycle.
+ *    The following libusb_try_lock_events() will fail, so you will become an
+ *    events waiter. For more information on this, read \ref fullstory below.
+ * -# libusb_handle_events_locked() is a variant of
+ *    libusb_handle_events_timeout() that you can call while holding the
+ *    events lock. libusb_handle_events_timeout() itself implements similar
+ *    logic to the above, so be sure not to call it when you are
+ *    "working behind libusb's back", as is the case here.
+ * -# libusb_event_handler_active() determines if someone is currently
+ *    holding the events lock
+ *
+ * You might be wondering why there is no function to wake up all threads
+ * blocked on libusb_wait_for_event(). This is because libusb can do this
+ * internally: it will wake up all such threads when someone calls
+ * libusb_unlock_events() or when a transfer completes (at the point after its
+ * callback has returned).
+ *
+ * \subsection fullstory The full story
+ *
+ * The above explanation should be enough to get you going, but if you're
+ * really thinking through the issues then you may be left with some more
+ * questions regarding libusb's internals. If you're curious, read on, and if
+ * not, skip to the next section to avoid confusing yourself!
+ *
+ * The immediate question that may spring to mind is: what if one thread
+ * modifies the set of file descriptors that need to be polled while another
+ * thread is doing event handling?
+ *
+ * There are 2 situations in which this may happen.
+ * -# libusb_open() will add another file descriptor to the poll set,
+ *    therefore it is desirable to interrupt the event handler so that it
+ *    restarts, picking up the new descriptor.
+ * -# libusb_close() will remove a file descriptor from the poll set. There
+ *    are all kinds of race conditions that could arise here, so it is
+ *    important that nobody is doing event handling at this time.
+ *
+ * libusb handles these issues internally, so application developers do not
+ * have to stop their event handlers while opening/closing devices. Here's how
+ * it works, focusing on the libusb_close() situation first:
+ *
+ * -# During initialization, libusb opens an internal pipe, and it adds the read
+ *    end of this pipe to the set of file descriptors to be polled.
+ * -# During libusb_close(), libusb writes some dummy data on this control pipe.
+ *    This immediately interrupts the event handler. libusb also records
+ *    internally that it is trying to interrupt event handlers for this
+ *    high-priority event.
+ * -# At this point, some of the functions described above start behaving
+ *    differently:
+ *   - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
+ *     OK for event handling to continue.
+ *   - libusb_try_lock_events() starts returning 1, indicating that another
+ *     thread holds the event handling lock, even if the lock is uncontended.
+ *   - libusb_event_handler_active() starts returning 1, indicating that
+ *     another thread is doing event handling, even if that is not true.
+ * -# The above changes in behaviour result in the event handler stopping and
+ *    giving up the events lock very quickly, giving the high-priority
+ *    libusb_close() operation a "free ride" to acquire the events lock. All
+ *    threads that are competing to do event handling become event waiters.
+ * -# With the events lock held inside libusb_close(), libusb can safely remove
+ *    a file descriptor from the poll set, in the safety of knowledge that
+ *    nobody is polling those descriptors or trying to access the poll set.
+ * -# After obtaining the events lock, the close operation completes very
+ *    quickly (usually a matter of milliseconds) and then immediately releases
+ *    the events lock.
+ * -# At the same time, the behaviour of libusb_event_handling_ok() and friends
+ *    reverts to the original, documented behaviour.
+ * -# The release of the events lock causes the threads that are waiting for
+ *    events to be woken up and to start competing to become event handlers
+ *    again. One of them will succeed; it will then re-obtain the list of poll
+ *    descriptors, and USB I/O will then continue as normal.
+ *
+ * libusb_open() is similar, and is actually a more simplistic case. Upon a
+ * call to libusb_open():
+ *
+ * -# The device is opened and a file descriptor is added to the poll set.
+ * -# libusb sends some dummy data on the control pipe, and records that it
+ *    is trying to modify the poll descriptor set.
+ * -# The event handler is interrupted, and the same behaviour change as for
+ *    libusb_close() takes effect, causing all event handling threads to become
+ *    event waiters.
+ * -# The libusb_open() implementation takes its free ride to the events lock.
+ * -# Happy that it has successfully paused the events handler, libusb_open()
+ *    releases the events lock.
+ * -# The event waiter threads are all woken up and compete to become event
+ *    handlers again. The one that succeeds will obtain the list of poll
+ *    descriptors again, which will include the addition of the new device.
+ *
+ * \subsection concl Closing remarks
+ *
+ * The above may seem a little complicated, but hopefully I have made it clear
+ * why such complications are necessary. Also, do not forget that this only
+ * applies to applications that take libusb's file descriptors and integrate
+ * them into their own polling loops.
+ *
+ * You may decide that it is OK for your multi-threaded application to ignore
+ * some of the rules and locks detailed above, because you don't think that
+ * two threads can ever be polling the descriptors at the same time. If that
+ * is the case, then that's good news for you because you don't have to worry.
+ * But be careful here; remember that the synchronous I/O functions do event
+ * handling internally. If you have one thread doing event handling in a loop
+ * (without implementing the rules and locking semantics documented above)
+ * and another trying to send a synchronous USB transfer, you will end up with
+ * two threads monitoring the same descriptors, and the above-described
+ * undesirable behaviour occuring. The solution is for your polling thread to
+ * play by the rules; the synchronous I/O functions do so, and this will result
+ * in them getting along in perfect harmony.
+ *
+ * If you do have a dedicated thread doing event handling, it is perfectly
+ * legal for it to take the event handling lock for long periods of time. Any
+ * synchronous I/O functions you call from other threads will transparently
+ * fall back to the "event waiters" mechanism detailed above. The only
+ * consideration that your event handling thread must apply is the one related
+ * to libusb_event_handling_ok(): you must call this before every poll(), and
+ * give up the events lock if instructed.
+ */
+
+int usbi_io_init(struct libusb_context *ctx)
+{
+	int r;
+
+	pthread_mutex_init(&ctx->flying_transfers_lock, NULL);
+	pthread_mutex_init(&ctx->pollfds_lock, NULL);
+	pthread_mutex_init(&ctx->pollfd_modify_lock, NULL);
+	pthread_mutex_init(&ctx->events_lock, NULL);
+	pthread_mutex_init(&ctx->event_waiters_lock, NULL);
+	pthread_cond_init(&ctx->event_waiters_cond, NULL);
+	list_init(&ctx->flying_transfers);
+	list_init(&ctx->pollfds);
+
+	/* FIXME should use an eventfd on kernels that support it */
+	r = pipe(ctx->ctrl_pipe);
+	if (r < 0)
+		return LIBUSB_ERROR_OTHER;
+
+	r = usbi_add_pollfd(ctx, ctx->ctrl_pipe[0], POLLIN);
+	if (r < 0)
+		return r;
+
+#ifdef USBI_TIMERFD_AVAILABLE
+	ctx->timerfd = timerfd_create(usbi_backend->get_timerfd_clockid(),
+		TFD_NONBLOCK);
+	if (ctx->timerfd >= 0) {
+		usbi_dbg("using timerfd for timeouts");
+		r = usbi_add_pollfd(ctx, ctx->timerfd, POLLIN);
+		if (r < 0) {
+			close(ctx->timerfd);
+			return r;
+		}
+	} else {
+		usbi_dbg("timerfd not available (code %d error %d)", ctx->timerfd, errno);
+		ctx->timerfd = -1;
+	}
+#endif
+
+	return 0;
+}
+
+void usbi_io_exit(struct libusb_context *ctx)
+{
+	usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
+	close(ctx->ctrl_pipe[0]);
+	close(ctx->ctrl_pipe[1]);
+#ifdef USBI_TIMERFD_AVAILABLE
+	if (usbi_using_timerfd(ctx)) {
+		usbi_remove_pollfd(ctx, ctx->timerfd);
+		close(ctx->timerfd);
+	}
+#endif
+}
+
+static int calculate_timeout(struct usbi_transfer *transfer)
+{
+	int r;
+	struct timespec current_time;
+	unsigned int timeout =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;
+
+	if (!timeout)
+		return 0;
+
+	r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &current_time);
+	if (r < 0) {
+		usbi_err(ITRANSFER_CTX(transfer),
+			"failed to read monotonic clock, errno=%d", errno);
+		return r;
+	}
+
+	current_time.tv_sec += timeout / 1000;
+	current_time.tv_nsec += (timeout % 1000) * 1000000;
+
+	if (current_time.tv_nsec > 1000000000) {
+		current_time.tv_nsec -= 1000000000;
+		current_time.tv_sec++;
+	}
+
+	TIMESPEC_TO_TIMEVAL(&transfer->timeout, &current_time);
+	return 0;
+}
+
+/* add a transfer to the (timeout-sorted) active transfers list.
+ * returns 1 if the transfer has a timeout and it is the timeout next to
+ * expire */
+static int add_to_flying_list(struct usbi_transfer *transfer)
+{
+	struct usbi_transfer *cur;
+	struct timeval *timeout = &transfer->timeout;
+	struct libusb_context *ctx = ITRANSFER_CTX(transfer);
+	int r = 0;
+	int first = 1;
+
+	pthread_mutex_lock(&ctx->flying_transfers_lock);
+
+	/* if we have no other flying transfers, start the list with this one */
+	if (list_empty(&ctx->flying_transfers)) {
+		list_add(&transfer->list, &ctx->flying_transfers);
+		if (timerisset(timeout))
+			r = 1;
+		goto out;
+	}
+
+	/* if we have infinite timeout, append to end of list */
+	if (!timerisset(timeout)) {
+		list_add_tail(&transfer->list, &ctx->flying_transfers);
+		goto out;
+	}
+
+	/* otherwise, find appropriate place in list */
+	list_for_each_entry(cur, &ctx->flying_transfers, list) {
+		/* find first timeout that occurs after the transfer in question */
+		struct timeval *cur_tv = &cur->timeout;
+
+		if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
+				(cur_tv->tv_sec == timeout->tv_sec &&
+					cur_tv->tv_usec > timeout->tv_usec)) {
+			list_add_tail(&transfer->list, &cur->list);
+			r = first;
+			goto out;
+		}
+		first = 0;
+	}
+
+	/* otherwise we need to be inserted at the end */
+	list_add_tail(&transfer->list, &ctx->flying_transfers);
+out:
+	pthread_mutex_unlock(&ctx->flying_transfers_lock);
+	return r;
+}
+
+/** \ingroup asyncio
+ * Allocate a libusb transfer with a specified number of isochronous packet
+ * descriptors. The returned transfer is pre-initialized for you. When the new
+ * transfer is no longer needed, it should be freed with
+ * libusb_free_transfer().
+ *
+ * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
+ * interrupt) should specify an iso_packets count of zero.
+ *
+ * For transfers intended for isochronous endpoints, specify an appropriate
+ * number of packet descriptors to be allocated as part of the transfer.
+ * The returned transfer is not specially initialized for isochronous I/O;
+ * you are still required to set the
+ * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
+ * \ref libusb_transfer::type "type" fields accordingly.
+ *
+ * It is safe to allocate a transfer with some isochronous packets and then
+ * use it on a non-isochronous endpoint. If you do this, ensure that at time
+ * of submission, num_iso_packets is 0 and that type is set appropriately.
+ *
+ * \param iso_packets number of isochronous packet descriptors to allocate
+ * \returns a newly allocated transfer, or NULL on error
+ */
+API_EXPORTED struct libusb_transfer *libusb_alloc_transfer(int iso_packets)
+{
+	size_t os_alloc_size = usbi_backend->transfer_priv_size
+		+ (usbi_backend->add_iso_packet_size * iso_packets);
+	int alloc_size = sizeof(struct usbi_transfer)
+		+ sizeof(struct libusb_transfer)
+		+ (sizeof(struct libusb_iso_packet_descriptor) * iso_packets)
+		+ os_alloc_size;
+	struct usbi_transfer *itransfer = malloc(alloc_size);
+	if (!itransfer)
+		return NULL;
+
+	memset(itransfer, 0, alloc_size);
+	itransfer->num_iso_packets = iso_packets;
+	pthread_mutex_init(&itransfer->lock, NULL);
+	return __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+}
+
+/** \ingroup asyncio
+ * Free a transfer structure. This should be called for all transfers
+ * allocated with libusb_alloc_transfer().
+ *
+ * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
+ * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
+ * non-NULL, this function will also free the transfer buffer using the
+ * standard system memory allocator (e.g. free()).
+ *
+ * It is legal to call this function with a NULL transfer. In this case,
+ * the function will simply return safely.
+ *
+ * It is not legal to free an active transfer (one which has been submitted
+ * and has not yet completed).
+ *
+ * \param transfer the transfer to free
+ */
+API_EXPORTED void libusb_free_transfer(struct libusb_transfer *transfer)
+{
+	struct usbi_transfer *itransfer;
+	if (!transfer)
+		return;
+
+	if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER && transfer->buffer)
+		free(transfer->buffer);
+
+	itransfer = __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
+	pthread_mutex_destroy(&itransfer->lock);
+	free(itransfer);
+}
+
+/** \ingroup asyncio
+ * Submit a transfer. This function will fire off the USB transfer and then
+ * return immediately.
+ *
+ * \param transfer the transfer to submit
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+API_EXPORTED int libusb_submit_transfer(struct libusb_transfer *transfer)
+{
+	struct libusb_context *ctx = TRANSFER_CTX(transfer);
+	struct usbi_transfer *itransfer =
+		__LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
+	int r;
+	int first;
+
+	pthread_mutex_lock(&itransfer->lock);
+	itransfer->transferred = 0;
+	itransfer->flags = 0;
+	r = calculate_timeout(itransfer);
+	if (r < 0) {
+		r = LIBUSB_ERROR_OTHER;
+		goto out;
+	}
+
+	first = add_to_flying_list(itransfer);
+	r = usbi_backend->submit_transfer(itransfer);
+	if (r) {
+		pthread_mutex_lock(&ctx->flying_transfers_lock);
+		list_del(&itransfer->list);
+		pthread_mutex_unlock(&ctx->flying_transfers_lock);
+	}
+#ifdef USBI_TIMERFD_AVAILABLE
+	else if (first && usbi_using_timerfd(ctx)) {
+		/* if this transfer has the lowest timeout of all active transfers,
+		 * rearm the timerfd with this transfer's timeout */
+		const struct itimerspec it = { {0, 0},
+			{ itransfer->timeout.tv_sec, itransfer->timeout.tv_usec * 1000 } };
+		usbi_dbg("arm timerfd for timeout in %dms (first in line)", transfer->timeout);
+		r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
+		if (r < 0)
+			r = LIBUSB_ERROR_OTHER;
+	}
+#endif
+
+out:
+	pthread_mutex_unlock(&itransfer->lock);
+	return r;
+}
+
+/** \ingroup asyncio
+ * Asynchronously cancel a previously submitted transfer.
+ * This function returns immediately, but this does not indicate cancellation
+ * is complete. Your callback function will be invoked at some later time
+ * with a transfer status of
+ * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
+ * "LIBUSB_TRANSFER_CANCELLED."
+ *
+ * \param transfer the transfer to cancel
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the transfer is already complete or
+ * cancelled.
+ * \returns a LIBUSB_ERROR code on failure
+ */
+API_EXPORTED int libusb_cancel_transfer(struct libusb_transfer *transfer)
+{
+	struct usbi_transfer *itransfer =
+		__LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
+	int r;
+
+	usbi_dbg("");
+	pthread_mutex_lock(&itransfer->lock);
+	r = usbi_backend->cancel_transfer(itransfer);
+	if (r < 0)
+		usbi_err(TRANSFER_CTX(transfer),
+			"cancel transfer failed error %d", r);
+	pthread_mutex_unlock(&itransfer->lock);
+	return r;
+}
+
+#ifdef USBI_TIMERFD_AVAILABLE
+static int disarm_timerfd(struct libusb_context *ctx)
+{
+	const struct itimerspec disarm_timer = { { 0, 0 }, { 0, 0 } };
+	int r;
+
+	usbi_dbg("");
+	r = timerfd_settime(ctx->timerfd, 0, &disarm_timer, NULL);
+	if (r < 0)
+		return LIBUSB_ERROR_OTHER;
+	else
+		return 0;
+}
+
+/* iterates through the flying transfers, and rearms the timerfd based on the
+ * next upcoming timeout.
+ * must be called with flying_list locked.
+ * returns 0 if there was no timeout to arm, 1 if the next timeout was armed,
+ * or a LIBUSB_ERROR code on failure.
+ */
+static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
+{
+	struct usbi_transfer *transfer;
+
+	list_for_each_entry(transfer, &ctx->flying_transfers, list) {
+		struct timeval *cur_tv = &transfer->timeout;
+
+		/* if we've reached transfers of infinite timeout, then we have no
+		 * arming to do */
+		if (!timerisset(cur_tv))
+			return 0;
+
+		/* act on first transfer that is not already cancelled */
+		if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
+			int r;
+			const struct itimerspec it = { {0, 0},
+				{ cur_tv->tv_sec, cur_tv->tv_usec * 1000 } };
+			usbi_dbg("next timeout originally %dms", __USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
+			r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
+			if (r < 0)
+				return LIBUSB_ERROR_OTHER;
+			return 1;
+		}
+	}
+
+	return 0;
+}
+#else
+static int disarm_timerfd(struct libusb_context *ctx)
+{
+	return 0;
+}
+static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
+{
+	return 0;
+}
+#endif
+
+/* Handle completion of a transfer (completion might be an error condition).
+ * This will invoke the user-supplied callback function, which may end up
+ * freeing the transfer. Therefore you cannot use the transfer structure
+ * after calling this function, and you should free all backend-specific
+ * data before calling it.
+ * Do not call this function with the usbi_transfer lock held. User-specified
+ * callback functions may attempt to directly resubmit the transfer, which
+ * will attempt to take the lock. */
+int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
+	enum libusb_transfer_status status)
+{
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct libusb_context *ctx = TRANSFER_CTX(transfer);
+	uint8_t flags;
+	int r;
+
+	/* FIXME: could be more intelligent with the timerfd here. we don't need
+	 * to disarm the timerfd if there was no timer running, and we only need
+	 * to rearm the timerfd if the transfer that expired was the one with
+	 * the shortest timeout. */
+
+	pthread_mutex_lock(&ctx->flying_transfers_lock);
+	list_del(&itransfer->list);
+	r = arm_timerfd_for_next_timeout(ctx);
+	pthread_mutex_unlock(&ctx->flying_transfers_lock);
+
+	if (r < 0) {
+		return r;
+	} else if (r == 0) {
+		r = disarm_timerfd(ctx);
+		if (r < 0)
+			return r;
+	}
+
+	if (status == LIBUSB_TRANSFER_COMPLETED
+			&& transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
+		int rqlen = transfer->length;
+		if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
+			rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
+		if (rqlen != itransfer->transferred) {
+			usbi_dbg("interpreting short transfer as error");
+			status = LIBUSB_TRANSFER_ERROR;
+		}
+	}
+
+	flags = transfer->flags;
+	transfer->status = status;
+	transfer->actual_length = itransfer->transferred;
+	if (transfer->callback)
+		transfer->callback(transfer);
+	/* transfer might have been freed by the above call, do not use from
+	 * this point. */
+	if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
+		libusb_free_transfer(transfer);
+	pthread_mutex_lock(&ctx->event_waiters_lock);
+	pthread_cond_broadcast(&ctx->event_waiters_cond);
+	pthread_mutex_unlock(&ctx->event_waiters_lock);
+	return 0;
+}
+
+/* Similar to usbi_handle_transfer_completion() but exclusively for transfers
+ * that were asynchronously cancelled. The same concerns w.r.t. freeing of
+ * transfers exist here.
+ * Do not call this function with the usbi_transfer lock held. User-specified
+ * callback functions may attempt to directly resubmit the transfer, which
+ * will attempt to take the lock. */
+int usbi_handle_transfer_cancellation(struct usbi_transfer *transfer)
+{
+	/* if the URB was cancelled due to timeout, report timeout to the user */
+	if (transfer->flags & USBI_TRANSFER_TIMED_OUT) {
+		usbi_dbg("detected timeout cancellation");
+		return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
+	}
+
+	/* otherwise its a normal async cancel */
+	return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
+}
+
+/** \ingroup poll
+ * Attempt to acquire the event handling lock. This lock is used to ensure that
+ * only one thread is monitoring libusb event sources at any one time.
+ *
+ * You only need to use this lock if you are developing an application
+ * which calls poll() or select() on libusb's file descriptors directly.
+ * If you stick to libusb's event handling loop functions (e.g.
+ * libusb_handle_events()) then you do not need to be concerned with this
+ * locking.
+ *
+ * While holding this lock, you are trusted to actually be handling events.
+ * If you are no longer handling events, you must call libusb_unlock_events()
+ * as soon as possible.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \returns 0 if the lock was obtained successfully
+ * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
+ * \see \ref mtasync
+ */
+API_EXPORTED int libusb_try_lock_events(libusb_context *ctx)
+{
+	int r;
+	USBI_GET_CONTEXT(ctx);
+
+	/* is someone else waiting to modify poll fds? if so, don't let this thread
+	 * start event handling */
+	pthread_mutex_lock(&ctx->pollfd_modify_lock);
+	r = ctx->pollfd_modify;
+	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+	if (r) {
+		usbi_dbg("someone else is modifying poll fds");
+		return 1;
+	}
+
+	r = pthread_mutex_trylock(&ctx->events_lock);
+	if (r)
+		return 1;
+
+	ctx->event_handler_active = 1;	
+	return 0;
+}
+
+/** \ingroup poll
+ * Acquire the event handling lock, blocking until successful acquisition if
+ * it is contended. This lock is used to ensure that only one thread is
+ * monitoring libusb event sources at any one time.
+ *
+ * You only need to use this lock if you are developing an application
+ * which calls poll() or select() on libusb's file descriptors directly.
+ * If you stick to libusb's event handling loop functions (e.g.
+ * libusb_handle_events()) then you do not need to be concerned with this
+ * locking.
+ *
+ * While holding this lock, you are trusted to actually be handling events.
+ * If you are no longer handling events, you must call libusb_unlock_events()
+ * as soon as possible.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \see \ref mtasync
+ */
+API_EXPORTED void libusb_lock_events(libusb_context *ctx)
+{
+	USBI_GET_CONTEXT(ctx);
+	pthread_mutex_lock(&ctx->events_lock);
+	ctx->event_handler_active = 1;
+}
+
+/** \ingroup poll
+ * Release the lock previously acquired with libusb_try_lock_events() or
+ * libusb_lock_events(). Releasing this lock will wake up any threads blocked
+ * on libusb_wait_for_event().
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \see \ref mtasync
+ */
+API_EXPORTED void libusb_unlock_events(libusb_context *ctx)
+{
+	USBI_GET_CONTEXT(ctx);
+	ctx->event_handler_active = 0;
+	pthread_mutex_unlock(&ctx->events_lock);
+
+	/* FIXME: perhaps we should be a bit more efficient by not broadcasting
+	 * the availability of the events lock when we are modifying pollfds
+	 * (check ctx->pollfd_modify)? */
+	pthread_mutex_lock(&ctx->event_waiters_lock);
+	pthread_cond_broadcast(&ctx->event_waiters_cond);
+	pthread_mutex_unlock(&ctx->event_waiters_lock);
+}
+
+/** \ingroup poll
+ * Determine if it is still OK for this thread to be doing event handling.
+ *
+ * Sometimes, libusb needs to temporarily pause all event handlers, and this
+ * is the function you should use before polling file descriptors to see if
+ * this is the case.
+ *
+ * If this function instructs your thread to give up the events lock, you
+ * should just continue the usual logic that is documented in \ref mtasync.
+ * On the next iteration, your thread will fail to obtain the events lock,
+ * and will hence become an event waiter.
+ *
+ * This function should be called while the events lock is held: you don't
+ * need to worry about the results of this function if your thread is not
+ * the current event handler.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \returns 1 if event handling can start or continue
+ * \returns 0 if this thread must give up the events lock
+ * \see \ref fullstory "Multi-threaded I/O: the full story"
+ */
+API_EXPORTED int libusb_event_handling_ok(libusb_context *ctx)
+{
+	int r;
+	USBI_GET_CONTEXT(ctx);
+
+	/* is someone else waiting to modify poll fds? if so, don't let this thread
+	 * continue event handling */
+	pthread_mutex_lock(&ctx->pollfd_modify_lock);
+	r = ctx->pollfd_modify;
+	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+	if (r) {
+		usbi_dbg("someone else is modifying poll fds");
+		return 0;
+	}
+
+	return 1;
+}
+
+
+/** \ingroup poll
+ * Determine if an active thread is handling events (i.e. if anyone is holding
+ * the event handling lock).
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \returns 1 if a thread is handling events
+ * \returns 0 if there are no threads currently handling events
+ * \see \ref mtasync
+ */
+API_EXPORTED int libusb_event_handler_active(libusb_context *ctx)
+{
+	int r;
+	USBI_GET_CONTEXT(ctx);
+
+	/* is someone else waiting to modify poll fds? if so, don't let this thread
+	 * start event handling -- indicate that event handling is happening */
+	pthread_mutex_lock(&ctx->pollfd_modify_lock);
+	r = ctx->pollfd_modify;
+	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
+	if (r) {
+		usbi_dbg("someone else is modifying poll fds");
+		return 1;
+	}
+
+	return ctx->event_handler_active;
+}
+
+/** \ingroup poll
+ * Acquire the event waiters lock. This lock is designed to be obtained under
+ * the situation where you want to be aware when events are completed, but
+ * some other thread is event handling so calling libusb_handle_events() is not
+ * allowed.
+ *
+ * You then obtain this lock, re-check that another thread is still handling
+ * events, then call libusb_wait_for_event().
+ *
+ * You only need to use this lock if you are developing an application
+ * which calls poll() or select() on libusb's file descriptors directly,
+ * <b>and</b> may potentially be handling events from 2 threads simultaenously.
+ * If you stick to libusb's event handling loop functions (e.g.
+ * libusb_handle_events()) then you do not need to be concerned with this
+ * locking.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \see \ref mtasync
+ */
+API_EXPORTED void libusb_lock_event_waiters(libusb_context *ctx)
+{
+	USBI_GET_CONTEXT(ctx);
+	pthread_mutex_lock(&ctx->event_waiters_lock);
+}
+
+/** \ingroup poll
+ * Release the event waiters lock.
+ * \param ctx the context to operate on, or NULL for the default context
+ * \see \ref mtasync
+ */
+API_EXPORTED void libusb_unlock_event_waiters(libusb_context *ctx)
+{
+	USBI_GET_CONTEXT(ctx);
+	pthread_mutex_unlock(&ctx->event_waiters_lock);
+}
+
+/** \ingroup poll
+ * Wait for another thread to signal completion of an event. Must be called
+ * with the event waiters lock held, see libusb_lock_event_waiters().
+ *
+ * This function will block until any of the following conditions are met:
+ * -# The timeout expires
+ * -# A transfer completes
+ * -# A thread releases the event handling lock through libusb_unlock_events()
+ *
+ * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
+ * the callback for the transfer has completed. Condition 3 is important
+ * because it means that the thread that was previously handling events is no
+ * longer doing so, so if any events are to complete, another thread needs to
+ * step up and start event handling.
+ *
+ * This function releases the event waiters lock before putting your thread
+ * to sleep, and reacquires the lock as it is being woken up.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param tv maximum timeout for this blocking function. A NULL value
+ * indicates unlimited timeout.
+ * \returns 0 after a transfer completes or another thread stops event handling
+ * \returns 1 if the timeout expired
+ * \see \ref mtasync
+ */
+API_EXPORTED int libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
+{
+	struct timespec timeout;
+	int r;
+
+	USBI_GET_CONTEXT(ctx);
+	if (tv == NULL) {
+		pthread_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
+		return 0;
+	}
+
+	r = usbi_backend->clock_gettime(USBI_CLOCK_REALTIME, &timeout);
+	if (r < 0) {
+		usbi_err(ctx, "failed to read realtime clock, error %d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	timeout.tv_sec += tv->tv_sec;
+	timeout.tv_nsec += tv->tv_usec * 1000;
+	if (timeout.tv_nsec > 1000000000) {
+		timeout.tv_nsec -= 1000000000;
+		timeout.tv_sec++;
+	}
+
+	r = pthread_cond_timedwait(&ctx->event_waiters_cond,
+		&ctx->event_waiters_lock, &timeout);
+	return (r == ETIMEDOUT);
+}
+
+static void handle_timeout(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	int r;
+
+	itransfer->flags |= USBI_TRANSFER_TIMED_OUT;
+	r = libusb_cancel_transfer(transfer);
+	if (r < 0)
+		usbi_warn(TRANSFER_CTX(transfer),
+			"async cancel failed %d errno=%d", r, errno);
+}
+
+#ifdef USBI_OS_HANDLES_TIMEOUT
+static int handle_timeouts_locked(struct libusb_context *ctx)
+{
+	return 0;
+}
+static int handle_timeouts(struct libusb_context *ctx)
+{
+	return 0;
+}
+#else
+static int handle_timeouts_locked(struct libusb_context *ctx)
+{
+	int r;
+	struct timespec systime_ts;
+	struct timeval systime;
+	struct usbi_transfer *transfer;
+
+	if (list_empty(&ctx->flying_transfers))
+		return 0;
+
+	/* get current time */
+	r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &systime_ts);
+	if (r < 0)
+		return r;
+
+	TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
+
+	/* iterate through flying transfers list, finding all transfers that
+	 * have expired timeouts */
+	list_for_each_entry(transfer, &ctx->flying_transfers, list) {
+		struct timeval *cur_tv = &transfer->timeout;
+
+		/* if we've reached transfers of infinite timeout, we're all done */
+		if (!timerisset(cur_tv))
+			return 0;
+
+		/* ignore timeouts we've already handled */
+		if (transfer->flags & USBI_TRANSFER_TIMED_OUT)
+			continue;
+
+		/* if transfer has non-expired timeout, nothing more to do */
+		if ((cur_tv->tv_sec > systime.tv_sec) ||
+				(cur_tv->tv_sec == systime.tv_sec &&
+					cur_tv->tv_usec > systime.tv_usec))
+			return 0;
+	
+		/* otherwise, we've got an expired timeout to handle */
+		handle_timeout(transfer);
+	}
+	return 0;
+}
+
+static int handle_timeouts(struct libusb_context *ctx)
+{
+	int r;
+	USBI_GET_CONTEXT(ctx);
+	pthread_mutex_lock(&ctx->flying_transfers_lock);
+	r = handle_timeouts_locked(ctx);
+	pthread_mutex_unlock(&ctx->flying_transfers_lock);
+	return r;
+}
+#endif
+
+#ifdef USBI_TIMERFD_AVAILABLE
+static int handle_timerfd_trigger(struct libusb_context *ctx)
+{
+	int r;
+
+	r = disarm_timerfd(ctx);
+	if (r < 0)
+		return r;
+
+	pthread_mutex_lock(&ctx->flying_transfers_lock);
+
+	/* process the timeout that just happened */
+	r = handle_timeouts_locked(ctx);
+	if (r < 0)
+		goto out;
+
+	/* arm for next timeout*/
+	r = arm_timerfd_for_next_timeout(ctx);
+
+out:
+	pthread_mutex_unlock(&ctx->flying_transfers_lock);
+	return r;
+}
+#endif
+
+/* do the actual event handling. assumes that no other thread is concurrently
+ * doing the same thing. */
+static int handle_events(struct libusb_context *ctx, struct timeval *tv)
+{
+	int r;
+	struct usbi_pollfd *ipollfd;
+	nfds_t nfds = 0;
+	struct pollfd *fds;
+	int i = -1;
+	int timeout_ms;
+
+	pthread_mutex_lock(&ctx->pollfds_lock);
+	list_for_each_entry(ipollfd, &ctx->pollfds, list)
+		nfds++;
+
+	/* TODO: malloc when number of fd's changes, not on every poll */
+	fds = malloc(sizeof(*fds) * nfds);
+	if (!fds)
+		return LIBUSB_ERROR_NO_MEM;
+
+	list_for_each_entry(ipollfd, &ctx->pollfds, list) {
+		struct libusb_pollfd *pollfd = &ipollfd->pollfd;
+		int fd = pollfd->fd;
+		i++;
+		fds[i].fd = fd;
+		fds[i].events = pollfd->events;
+		fds[i].revents = 0;
+	}
+	pthread_mutex_unlock(&ctx->pollfds_lock);
+
+	timeout_ms = (tv->tv_sec * 1000) + (tv->tv_usec / 1000);
+
+	/* round up to next millisecond */
+	if (tv->tv_usec % 1000)
+		timeout_ms++;
+
+	usbi_dbg("poll() %d fds with timeout in %dms", nfds, timeout_ms);
+	r = poll(fds, nfds, timeout_ms);
+	usbi_dbg("poll() returned %d", r);
+	if (r == 0) {
+		free(fds);
+		return handle_timeouts(ctx);
+	} else if (r == -1 && errno == EINTR) {
+		free(fds);
+		return LIBUSB_ERROR_INTERRUPTED;
+	} else if (r < 0) {
+		free(fds);
+		usbi_err(ctx, "poll failed %d err=%d\n", r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	/* fd[0] is always the ctrl pipe */
+	if (fds[0].revents) {
+		/* another thread wanted to interrupt event handling, and it succeeded!
+		 * handle any other events that cropped up at the same time, and
+		 * simply return */
+		usbi_dbg("caught a fish on the control pipe");
+
+		if (r == 1) {
+			r = 0;
+			goto handled;
+		} else {
+			/* prevent OS backend from trying to handle events on ctrl pipe */
+			fds[0].revents = 0;
+			r--;
+		}
+	}
+
+#ifdef USBI_TIMERFD_AVAILABLE
+	/* on timerfd configurations, fds[1] is the timerfd */
+	if (usbi_using_timerfd(ctx) && fds[1].revents) {
+		/* timerfd indicates that a timeout has expired */
+		int ret;
+		usbi_dbg("timerfd triggered");
+
+		ret = handle_timerfd_trigger(ctx);
+		if (ret < 0) {
+			/* return error code */
+			r = ret;
+			goto handled;
+		} else if (r == 1) {
+			/* no more active file descriptors, nothing more to do */
+			r = 0;
+			goto handled;
+		} else {
+			/* more events pending...
+			 * prevent OS backend from trying to handle events on timerfd */
+			fds[1].revents = 0;
+			r--;
+		}
+	}
+#endif
+
+	r = usbi_backend->handle_events(ctx, fds, nfds, r);
+	if (r)
+		usbi_err(ctx, "backend handle_events failed with error %d", r);
+
+handled:
+	free(fds);
+	return r;
+}
+
+/* returns the smallest of:
+ *  1. timeout of next URB
+ *  2. user-supplied timeout
+ * returns 1 if there is an already-expired timeout, otherwise returns 0
+ * and populates out
+ */
+static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
+	struct timeval *out)
+{
+	struct timeval timeout;
+	int r = libusb_get_next_timeout(ctx, &timeout);
+	if (r) {
+		/* timeout already expired? */
+		if (!timerisset(&timeout))
+			return 1;
+
+		/* choose the smallest of next URB timeout or user specified timeout */
+		if (timercmp(&timeout, tv, <))
+			*out = timeout;
+		else
+			*out = *tv;
+	} else {
+		*out = *tv;
+	}
+	return 0;
+}
+
+/** \ingroup poll
+ * Handle any pending events.
+ *
+ * libusb determines "pending events" by checking if any timeouts have expired
+ * and by checking the set of file descriptors for activity.
+ *
+ * If a zero timeval is passed, this function will handle any already-pending
+ * events and then immediately return in non-blocking style.
+ *
+ * If a non-zero timeval is passed and no events are currently pending, this
+ * function will block waiting for events to handle up until the specified
+ * timeout. If an event arrives or a signal is raised, this function will
+ * return early.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param tv the maximum time to block waiting for events, or zero for
+ * non-blocking mode
+ * \returns 0 on success, or a LIBUSB_ERROR code on failure
+ */
+API_EXPORTED int libusb_handle_events_timeout(libusb_context *ctx,
+	struct timeval *tv)
+{
+	int r;
+	struct timeval poll_timeout;
+
+	USBI_GET_CONTEXT(ctx);
+	r = get_next_timeout(ctx, tv, &poll_timeout);
+	if (r) {
+		/* timeout already expired */
+		return handle_timeouts(ctx);
+	}
+
+retry:
+	if (libusb_try_lock_events(ctx) == 0) {
+		/* we obtained the event lock: do our own event handling */
+		r = handle_events(ctx, &poll_timeout);
+		libusb_unlock_events(ctx);
+		return r;
+	}
+
+	/* another thread is doing event handling. wait for pthread events that
+	 * notify event completion. */
+	libusb_lock_event_waiters(ctx);
+
+	if (!libusb_event_handler_active(ctx)) {
+		/* we hit a race: whoever was event handling earlier finished in the
+		 * time it took us to reach this point. try the cycle again. */
+		libusb_unlock_event_waiters(ctx);
+		usbi_dbg("event handler was active but went away, retrying");
+		goto retry;
+	}
+
+	usbi_dbg("another thread is doing event handling");
+	r = libusb_wait_for_event(ctx, &poll_timeout);
+	libusb_unlock_event_waiters(ctx);
+
+	if (r < 0)
+		return r;
+	else if (r == 1)
+		return handle_timeouts(ctx);
+	else
+		return 0;
+}
+
+/** \ingroup poll
+ * Handle any pending events in blocking mode. There is currently a timeout
+ * hardcoded at 60 seconds but we plan to make it unlimited in future. For
+ * finer control over whether this function is blocking or non-blocking, or
+ * for control over the timeout, use libusb_handle_events_timeout() instead.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \returns 0 on success, or a LIBUSB_ERROR code on failure
+ */
+API_EXPORTED int libusb_handle_events(libusb_context *ctx)
+{
+	struct timeval tv;
+	tv.tv_sec = 60;
+	tv.tv_usec = 0;
+	return libusb_handle_events_timeout(ctx, &tv);
+}
+
+/** \ingroup poll
+ * Handle any pending events by polling file descriptors, without checking if
+ * any other threads are already doing so. Must be called with the event lock
+ * held, see libusb_lock_events().
+ *
+ * This function is designed to be called under the situation where you have
+ * taken the event lock and are calling poll()/select() directly on libusb's
+ * file descriptors (as opposed to using libusb_handle_events() or similar).
+ * You detect events on libusb's descriptors, so you then call this function
+ * with a zero timeout value (while still holding the event lock).
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param tv the maximum time to block waiting for events, or zero for
+ * non-blocking mode
+ * \returns 0 on success, or a LIBUSB_ERROR code on failure
+ * \see \ref mtasync
+ */
+API_EXPORTED int libusb_handle_events_locked(libusb_context *ctx,
+	struct timeval *tv)
+{
+	int r;
+	struct timeval poll_timeout;
+
+	USBI_GET_CONTEXT(ctx);
+	r = get_next_timeout(ctx, tv, &poll_timeout);
+	if (r) {
+		/* timeout already expired */
+		return handle_timeouts(ctx);
+	}
+
+	return handle_events(ctx, &poll_timeout);
+}
+
+/** \ingroup poll
+ * Determines whether your application must apply special timing considerations
+ * when monitoring libusb's file descriptors.
+ *
+ * This function is only useful for applications which retrieve and poll
+ * libusb's file descriptors in their own main loop (\ref pollmain).
+ *
+ * Ordinarily, libusb's event handler needs to be called into at specific
+ * moments in time (in addition to times when there is activity on the file
+ * descriptor set). The usual approach is to use libusb_get_next_timeout()
+ * to learn about when the next timeout occurs, and to adjust your
+ * poll()/select() timeout accordingly so that you can make a call into the
+ * library at that time.
+ *
+ * Some platforms supported by libusb do not come with this baggage - any
+ * events relevant to timing will be represented by activity on the file
+ * descriptor set, and libusb_get_next_timeout() will always return 0.
+ * This function allows you to detect whether you are running on such a
+ * platform.
+ *
+ * Since v1.0.5.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \returns 0 if you must call into libusb at times determined by
+ * libusb_get_next_timeout(), or 1 if all timeout events are handled internally
+ * or through regular activity on the file descriptors.
+ * \see \ref pollmain "Polling libusb file descriptors for event handling"
+ */
+API_EXPORTED int libusb_pollfds_handle_timeouts(libusb_context *ctx)
+{
+#if defined(USBI_OS_HANDLES_TIMEOUT)
+	return 1;
+#elif defined(USBI_TIMERFD_AVAILABLE)
+	USBI_GET_CONTEXT(ctx);
+	return usbi_using_timerfd(ctx);
+#else
+	return 0;
+#endif
+}
+
+/** \ingroup poll
+ * Determine the next internal timeout that libusb needs to handle. You only
+ * need to use this function if you are calling poll() or select() or similar
+ * on libusb's file descriptors yourself - you do not need to use it if you
+ * are calling libusb_handle_events() or a variant directly.
+ * 
+ * You should call this function in your main loop in order to determine how
+ * long to wait for select() or poll() to return results. libusb needs to be
+ * called into at this timeout, so you should use it as an upper bound on
+ * your select() or poll() call.
+ *
+ * When the timeout has expired, call into libusb_handle_events_timeout()
+ * (perhaps in non-blocking mode) so that libusb can handle the timeout.
+ *
+ * This function may return 1 (success) and an all-zero timeval. If this is
+ * the case, it indicates that libusb has a timeout that has already expired
+ * so you should call libusb_handle_events_timeout() or similar immediately.
+ * A return code of 0 indicates that there are no pending timeouts.
+ *
+ * On some platforms, this function will always returns 0 (no pending
+ * timeouts). See \ref polltime.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param tv output location for a relative time against the current
+ * clock in which libusb must be called into in order to process timeout events
+ * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
+ * or LIBUSB_ERROR_OTHER on failure
+ */
+API_EXPORTED int libusb_get_next_timeout(libusb_context *ctx,
+	struct timeval *tv)
+{
+#ifndef USBI_OS_HANDLES_TIMEOUT
+	struct usbi_transfer *transfer;
+	struct timespec cur_ts;
+	struct timeval cur_tv;
+	struct timeval *next_timeout;
+	int r;
+	int found = 0;
+
+	USBI_GET_CONTEXT(ctx);
+	if (usbi_using_timerfd(ctx))
+		return 0;
+
+	pthread_mutex_lock(&ctx->flying_transfers_lock);
+	if (list_empty(&ctx->flying_transfers)) {
+		pthread_mutex_unlock(&ctx->flying_transfers_lock);
+		usbi_dbg("no URBs, no timeout!");
+		return 0;
+	}
+
+	/* find next transfer which hasn't already been processed as timed out */
+	list_for_each_entry(transfer, &ctx->flying_transfers, list) {
+		if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
+			found = 1;
+			break;
+		}
+	}
+	pthread_mutex_unlock(&ctx->flying_transfers_lock);
+
+	if (!found) {
+		usbi_dbg("all URBs have already been processed for timeouts");
+		return 0;
+	}
+
+	next_timeout = &transfer->timeout;
+
+	/* no timeout for next transfer */
+	if (!timerisset(next_timeout)) {
+		usbi_dbg("no URBs with timeouts, no timeout!");
+		return 0;
+	}
+
+	r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &cur_ts);
+	if (r < 0) {
+		usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+	TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
+
+	if (timercmp(&cur_tv, next_timeout, >=)) {
+		usbi_dbg("first timeout already expired");
+		timerclear(tv);
+	} else {
+		timersub(next_timeout, &cur_tv, tv);
+		usbi_dbg("next timeout in %d.%06ds", tv->tv_sec, tv->tv_usec);
+	}
+
+	return 1;
+#else
+	return 0;
+#endif
+}
+
+/** \ingroup poll
+ * Register notification functions for file descriptor additions/removals.
+ * These functions will be invoked for every new or removed file descriptor
+ * that libusb uses as an event source.
+ *
+ * To remove notifiers, pass NULL values for the function pointers.
+ *
+ * Note that file descriptors may have been added even before you register
+ * these notifiers (e.g. at libusb_init() time).
+ *
+ * Additionally, note that the removal notifier may be called during
+ * libusb_exit() (e.g. when it is closing file descriptors that were opened
+ * and added to the poll set at libusb_init() time). If you don't want this,
+ * remove the notifiers immediately before calling libusb_exit().
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param added_cb pointer to function for addition notifications
+ * \param removed_cb pointer to function for removal notifications
+ * \param user_data User data to be passed back to callbacks (useful for
+ * passing context information)
+ */
+API_EXPORTED void libusb_set_pollfd_notifiers(libusb_context *ctx,
+	libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
+	void *user_data)
+{
+	USBI_GET_CONTEXT(ctx);
+	ctx->fd_added_cb = added_cb;
+	ctx->fd_removed_cb = removed_cb;
+	ctx->fd_cb_user_data = user_data;
+}
+
+/* Add a file descriptor to the list of file descriptors to be monitored.
+ * events should be specified as a bitmask of events passed to poll(), e.g.
+ * POLLIN and/or POLLOUT. */
+int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events)
+{
+	struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
+	if (!ipollfd)
+		return LIBUSB_ERROR_NO_MEM;
+
+	usbi_dbg("add fd %d events %d", fd, events);
+	ipollfd->pollfd.fd = fd;
+	ipollfd->pollfd.events = events;
+	pthread_mutex_lock(&ctx->pollfds_lock);
+	list_add_tail(&ipollfd->list, &ctx->pollfds);
+	pthread_mutex_unlock(&ctx->pollfds_lock);
+
+	if (ctx->fd_added_cb)
+		ctx->fd_added_cb(fd, events, ctx->fd_cb_user_data);
+	return 0;
+}
+
+/* Remove a file descriptor from the list of file descriptors to be polled. */
+void usbi_remove_pollfd(struct libusb_context *ctx, int fd)
+{
+	struct usbi_pollfd *ipollfd;
+	int found = 0;
+
+	usbi_dbg("remove fd %d", fd);
+	pthread_mutex_lock(&ctx->pollfds_lock);
+	list_for_each_entry(ipollfd, &ctx->pollfds, list)
+		if (ipollfd->pollfd.fd == fd) {
+			found = 1;
+			break;
+		}
+
+	if (!found) {
+		usbi_dbg("couldn't find fd %d to remove", fd);
+		pthread_mutex_unlock(&ctx->pollfds_lock);
+		return;
+	}
+
+	list_del(&ipollfd->list);
+	pthread_mutex_unlock(&ctx->pollfds_lock);
+	free(ipollfd);
+	if (ctx->fd_removed_cb)
+		ctx->fd_removed_cb(fd, ctx->fd_cb_user_data);
+}
+
+/** \ingroup poll
+ * Retrieve a list of file descriptors that should be polled by your main loop
+ * as libusb event sources.
+ *
+ * The returned list is NULL-terminated and should be freed with free() when
+ * done. The actual list contents must not be touched.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \returns a NULL-terminated list of libusb_pollfd structures, or NULL on
+ * error
+ */
+API_EXPORTED const struct libusb_pollfd **libusb_get_pollfds(
+	libusb_context *ctx)
+{
+	struct libusb_pollfd **ret = NULL;
+	struct usbi_pollfd *ipollfd;
+	size_t i = 0;
+	size_t cnt = 0;
+	USBI_GET_CONTEXT(ctx);
+
+	pthread_mutex_lock(&ctx->pollfds_lock);
+	list_for_each_entry(ipollfd, &ctx->pollfds, list)
+		cnt++;
+
+	ret = calloc(cnt + 1, sizeof(struct libusb_pollfd *));
+	if (!ret)
+		goto out;
+
+	list_for_each_entry(ipollfd, &ctx->pollfds, list)
+		ret[i++] = (struct libusb_pollfd *) ipollfd;
+	ret[cnt] = NULL;
+
+out:
+	pthread_mutex_unlock(&ctx->pollfds_lock);
+	return (const struct libusb_pollfd **) ret;
+}
+
+/* Backends call this from handle_events to report disconnection of a device.
+ * The transfers get cancelled appropriately.
+ */
+void usbi_handle_disconnect(struct libusb_device_handle *handle)
+{
+	struct usbi_transfer *cur;
+	struct usbi_transfer *to_cancel;
+
+	usbi_dbg("device %d.%d",
+		handle->dev->bus_number, handle->dev->device_address);
+
+	/* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
+	 * status code.
+	 * 
+	 * this is a bit tricky because:
+	 * 1. we can't do transfer completion while holding flying_transfers_lock
+	 * 2. the transfers list can change underneath us - if we were to build a
+	 *    list of transfers to complete (while holding look), the situation
+	 *    might be different by the time we come to free them
+	 *
+	 * so we resort to a loop-based approach as below
+	 * FIXME: is this still potentially racy?
+	 */
+
+	while (1) {
+		pthread_mutex_lock(&HANDLE_CTX(handle)->flying_transfers_lock);
+		to_cancel = NULL;
+		list_for_each_entry(cur, &HANDLE_CTX(handle)->flying_transfers, list)
+			if (__USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == handle) {
+				to_cancel = cur;
+				break;
+			}
+		pthread_mutex_unlock(&HANDLE_CTX(handle)->flying_transfers_lock);
+
+		if (!to_cancel)
+			break;
+
+		usbi_backend->clear_transfer_priv(to_cancel);
+		usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);
+	}
+
+}
+
diff --git a/libusb/libusb.h b/libusb/libusb.h
new file mode 100644
index 0000000..483d76a
--- /dev/null
+++ b/libusb/libusb.h
@@ -0,0 +1,1241 @@
+/*
+ * Public libusb header file
+ * Copyright (C) 2007-2008 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef __LIBUSB_H__
+#define __LIBUSB_H__
+
+#include <stdint.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <time.h>
+#include <limits.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** \def libusb_cpu_to_le16
+ * \ingroup misc
+ * Convert a 16-bit value from host-endian to little-endian format. On
+ * little endian systems, this function does nothing. On big endian systems,
+ * the bytes are swapped.
+ * \param x the host-endian value to convert
+ * \returns the value in little-endian byte order
+ */
+#define libusb_cpu_to_le16(x) ({ \
+	union { \
+		uint8_t  b8[2]; \
+		uint16_t b16; \
+	} _tmp; \
+	uint16_t _tmp2 = (uint16_t)(x); \
+	_tmp.b8[1] = _tmp2 >> 8; \
+	_tmp.b8[0] = _tmp2 & 0xff; \
+	_tmp.b16; \
+})
+
+/** \def libusb_le16_to_cpu
+ * \ingroup misc
+ * Convert a 16-bit value from little-endian to host-endian format. On
+ * little endian systems, this function does nothing. On big endian systems,
+ * the bytes are swapped.
+ * \param x the little-endian value to convert
+ * \returns the value in host-endian byte order
+ */
+#define libusb_le16_to_cpu libusb_cpu_to_le16
+
+/* standard USB stuff */
+
+/** \ingroup desc
+ * Device and/or Interface Class codes */
+enum libusb_class_code {
+	/** In the context of a \ref libusb_device_descriptor "device descriptor",
+	 * this bDeviceClass value indicates that each interface specifies its
+	 * own class information and all interfaces operate independently.
+	 */
+	LIBUSB_CLASS_PER_INTERFACE = 0,
+
+	/** Audio class */
+	LIBUSB_CLASS_AUDIO = 1,
+
+	/** Communications class */
+	LIBUSB_CLASS_COMM = 2,
+
+	/** Human Interface Device class */
+	LIBUSB_CLASS_HID = 3,
+
+	/** Printer dclass */
+	LIBUSB_CLASS_PRINTER = 7,
+
+	/** Picture transfer protocol class */
+	LIBUSB_CLASS_PTP = 6,
+
+	/** Mass storage class */
+	LIBUSB_CLASS_MASS_STORAGE = 8,
+
+	/** Hub class */
+	LIBUSB_CLASS_HUB = 9,
+
+	/** Data class */
+	LIBUSB_CLASS_DATA = 10,
+
+	/** Wireless class */
+	LIBUSB_CLASS_WIRELESS = 0xe0,
+
+	/** Application class */
+	LIBUSB_CLASS_APPLICATION = 0xfe,
+
+	/** Class is vendor-specific */
+	LIBUSB_CLASS_VENDOR_SPEC = 0xff
+};
+
+/** \ingroup desc
+ * Descriptor types as defined by the USB specification. */
+enum libusb_descriptor_type {
+	/** Device descriptor. See libusb_device_descriptor. */
+	LIBUSB_DT_DEVICE = 0x01,
+
+	/** Configuration descriptor. See libusb_config_descriptor. */
+	LIBUSB_DT_CONFIG = 0x02,
+
+	/** String descriptor */
+	LIBUSB_DT_STRING = 0x03,
+
+	/** Interface descriptor. See libusb_interface_descriptor. */
+	LIBUSB_DT_INTERFACE = 0x04,
+
+	/** Endpoint descriptor. See libusb_endpoint_descriptor. */
+	LIBUSB_DT_ENDPOINT = 0x05,
+
+	/** HID descriptor */
+	LIBUSB_DT_HID = 0x21,
+
+	/** HID report descriptor */
+	LIBUSB_DT_REPORT = 0x22,
+
+	/** Physical descriptor */
+	LIBUSB_DT_PHYSICAL = 0x23,
+
+	/** Hub descriptor */
+	LIBUSB_DT_HUB = 0x29
+};
+
+/* Descriptor sizes per descriptor type */
+#define LIBUSB_DT_DEVICE_SIZE			18
+#define LIBUSB_DT_CONFIG_SIZE			9
+#define LIBUSB_DT_INTERFACE_SIZE		9
+#define LIBUSB_DT_ENDPOINT_SIZE		7
+#define LIBUSB_DT_ENDPOINT_AUDIO_SIZE	9	/* Audio extension */
+#define LIBUSB_DT_HUB_NONVAR_SIZE		7
+
+#define LIBUSB_ENDPOINT_ADDRESS_MASK	0x0f    /* in bEndpointAddress */
+#define LIBUSB_ENDPOINT_DIR_MASK		0x80
+
+/** \ingroup desc
+ * Endpoint direction. Values for bit 7 of the
+ * \ref libusb_endpoint_descriptor::bEndpointAddress "endpoint address" scheme.
+ */
+enum libusb_endpoint_direction {
+	/** In: device-to-host */
+	LIBUSB_ENDPOINT_IN = 0x80,
+
+	/** Out: host-to-device */
+	LIBUSB_ENDPOINT_OUT = 0x00
+};
+
+#define LIBUSB_TRANSFER_TYPE_MASK			0x03    /* in bmAttributes */
+
+/** \ingroup desc
+ * Endpoint transfer type. Values for bits 0:1 of the
+ * \ref libusb_endpoint_descriptor::bmAttributes "endpoint attributes" field.
+ */
+enum libusb_transfer_type {
+	/** Control endpoint */
+	LIBUSB_TRANSFER_TYPE_CONTROL = 0,
+
+	/** Isochronous endpoint */
+	LIBUSB_TRANSFER_TYPE_ISOCHRONOUS = 1,
+
+	/** Bulk endpoint */
+	LIBUSB_TRANSFER_TYPE_BULK = 2,
+
+	/** Interrupt endpoint */
+	LIBUSB_TRANSFER_TYPE_INTERRUPT = 3
+};
+
+/** \ingroup misc
+ * Standard requests, as defined in table 9-3 of the USB2 specifications */
+enum libusb_standard_request {
+	/** Request status of the specific recipient */
+	LIBUSB_REQUEST_GET_STATUS = 0x00,
+
+	/** Clear or disable a specific feature */
+	LIBUSB_REQUEST_CLEAR_FEATURE = 0x01,
+
+	/* 0x02 is reserved */
+
+	/** Set or enable a specific feature */
+	LIBUSB_REQUEST_SET_FEATURE = 0x03,
+
+	/* 0x04 is reserved */
+
+	/** Set device address for all future accesses */
+	LIBUSB_REQUEST_SET_ADDRESS = 0x05,
+
+	/** Get the specified descriptor */
+	LIBUSB_REQUEST_GET_DESCRIPTOR = 0x06,
+
+	/** Used to update existing descriptors or add new descriptors */
+	LIBUSB_REQUEST_SET_DESCRIPTOR = 0x07,
+
+	/** Get the current device configuration value */
+	LIBUSB_REQUEST_GET_CONFIGURATION = 0x08,
+
+	/** Set device configuration */
+	LIBUSB_REQUEST_SET_CONFIGURATION = 0x09,
+
+	/** Return the selected alternate setting for the specified interface */
+	LIBUSB_REQUEST_GET_INTERFACE = 0x0A,
+
+	/** Select an alternate interface for the specified interface */
+	LIBUSB_REQUEST_SET_INTERFACE = 0x0B,
+
+	/** Set then report an endpoint's synchronization frame */
+	LIBUSB_REQUEST_SYNCH_FRAME = 0x0C
+};
+
+/** \ingroup misc
+ * Request type bits of the
+ * \ref libusb_control_setup::bmRequestType "bmRequestType" field in control
+ * transfers. */
+enum libusb_request_type {
+	/** Standard */
+	LIBUSB_REQUEST_TYPE_STANDARD = (0x00 << 5),
+
+	/** Class */
+	LIBUSB_REQUEST_TYPE_CLASS = (0x01 << 5),
+
+	/** Vendor */
+	LIBUSB_REQUEST_TYPE_VENDOR = (0x02 << 5),
+
+	/** Reserved */
+	LIBUSB_REQUEST_TYPE_RESERVED = (0x03 << 5)
+};
+
+/** \ingroup misc
+ * Recipient bits of the
+ * \ref libusb_control_setup::bmRequestType "bmRequestType" field in control
+ * transfers. Values 4 through 31 are reserved. */
+enum libusb_request_recipient {
+	/** Device */
+	LIBUSB_RECIPIENT_DEVICE = 0x00,
+
+	/** Interface */
+	LIBUSB_RECIPIENT_INTERFACE = 0x01,
+
+	/** Endpoint */
+	LIBUSB_RECIPIENT_ENDPOINT = 0x02,
+
+	/** Other */
+	LIBUSB_RECIPIENT_OTHER = 0x03
+};
+
+#define LIBUSB_ISO_SYNC_TYPE_MASK		0x0C
+
+/** \ingroup desc
+ * Synchronization type for isochronous endpoints. Values for bits 2:3 of the
+ * \ref libusb_endpoint_descriptor::bmAttributes "bmAttributes" field in
+ * libusb_endpoint_descriptor.
+ */
+enum libusb_iso_sync_type {
+	/** No synchronization */
+	LIBUSB_ISO_SYNC_TYPE_NONE = 0,
+
+	/** Asynchronous */
+	LIBUSB_ISO_SYNC_TYPE_ASYNC = 1,
+
+	/** Adaptive */
+	LIBUSB_ISO_SYNC_TYPE_ADAPTIVE = 2,
+
+	/** Synchronous */
+	LIBUSB_ISO_SYNC_TYPE_SYNC = 3
+};
+
+#define LIBUSB_ISO_USAGE_TYPE_MASK 0x30
+
+/** \ingroup desc
+ * Usage type for isochronous endpoints. Values for bits 4:5 of the
+ * \ref libusb_endpoint_descriptor::bmAttributes "bmAttributes" field in
+ * libusb_endpoint_descriptor.
+ */
+enum libusb_iso_usage_type {
+	/** Data endpoint */
+	LIBUSB_ISO_USAGE_TYPE_DATA = 0,
+
+	/** Feedback endpoint */
+	LIBUSB_ISO_USAGE_TYPE_FEEDBACK = 1,
+
+	/** Implicit feedback Data endpoint */
+	LIBUSB_ISO_USAGE_TYPE_IMPLICIT = 2
+};
+
+/** \ingroup desc
+ * A structure representing the standard USB device descriptor. This
+ * descriptor is documented in section 9.6.1 of the USB 2.0 specification.
+ * All multiple-byte fields are represented in host-endian format.
+ */
+struct libusb_device_descriptor {
+	/** Size of this descriptor (in bytes) */
+	uint8_t  bLength;
+
+	/** Descriptor type. Will have value
+	 * \ref libusb_descriptor_type::LIBUSB_DT_DEVICE LIBUSB_DT_DEVICE in this
+	 * context. */
+	uint8_t  bDescriptorType;
+
+	/** USB specification release number in binary-coded decimal. A value of
+	 * 0x0200 indicates USB 2.0, 0x0110 indicates USB 1.1, etc. */
+	uint16_t bcdUSB;
+
+	/** USB-IF class code for the device. See \ref libusb_class_code. */
+	uint8_t  bDeviceClass;
+
+	/** USB-IF subclass code for the device, qualified by the bDeviceClass
+	 * value */
+	uint8_t  bDeviceSubClass;
+
+	/** USB-IF protocol code for the device, qualified by the bDeviceClass and
+	 * bDeviceSubClass values */
+	uint8_t  bDeviceProtocol;
+
+	/** Maximum packet size for endpoint 0 */
+	uint8_t  bMaxPacketSize0;
+
+	/** USB-IF vendor ID */
+	uint16_t idVendor;
+
+	/** USB-IF product ID */
+	uint16_t idProduct;
+
+	/** Device release number in binary-coded decimal */
+	uint16_t bcdDevice;
+
+	/** Index of string descriptor describing manufacturer */
+	uint8_t  iManufacturer;
+
+	/** Index of string descriptor describing product */
+	uint8_t  iProduct;
+
+	/** Index of string descriptor containing device serial number */
+	uint8_t  iSerialNumber;
+
+	/** Number of possible configurations */
+	uint8_t  bNumConfigurations;
+};
+
+/** \ingroup desc
+ * A structure representing the standard USB endpoint descriptor. This
+ * descriptor is documented in section 9.6.3 of the USB 2.0 specification.
+ * All multiple-byte fields are represented in host-endian format.
+ */
+struct libusb_endpoint_descriptor {
+	/** Size of this descriptor (in bytes) */
+	uint8_t  bLength;
+
+	/** Descriptor type. Will have value
+	 * \ref libusb_descriptor_type::LIBUSB_DT_ENDPOINT LIBUSB_DT_ENDPOINT in
+	 * this context. */
+	uint8_t  bDescriptorType;
+
+	/** The address of the endpoint described by this descriptor. Bits 0:3 are
+	 * the endpoint number. Bits 4:6 are reserved. Bit 7 indicates direction,
+	 * see \ref libusb_endpoint_direction.
+	 */
+	uint8_t  bEndpointAddress;
+
+	/** Attributes which apply to the endpoint when it is configured using
+	 * the bConfigurationValue. Bits 0:1 determine the transfer type and
+	 * correspond to \ref libusb_transfer_type. Bits 2:3 are only used for
+	 * isochronous endpoints and correspond to \ref libusb_iso_sync_type.
+	 * Bits 4:5 are also only used for isochronous endpoints and correspond to
+	 * \ref libusb_iso_usage_type. Bits 6:7 are reserved.
+	 */
+	uint8_t  bmAttributes;
+
+	/** Maximum packet size this endpoint is capable of sending/receiving. */
+	uint16_t wMaxPacketSize;
+
+	/** Interval for polling endpoint for data transfers. */
+	uint8_t  bInterval;
+
+	/** For audio devices only: the rate at which synchronization feedback
+	 * is provided. */
+	uint8_t  bRefresh;
+
+	/** For audio devices only: the address if the synch endpoint */
+	uint8_t  bSynchAddress;
+
+	/** Extra descriptors. If libusb encounters unknown endpoint descriptors,
+	 * it will store them here, should you wish to parse them. */
+	const unsigned char *extra;
+
+	/** Length of the extra descriptors, in bytes. */
+	int extra_length;
+};
+
+/** \ingroup desc
+ * A structure representing the standard USB interface descriptor. This
+ * descriptor is documented in section 9.6.5 of the USB 2.0 specification.
+ * All multiple-byte fields are represented in host-endian format.
+ */
+struct libusb_interface_descriptor {
+	/** Size of this descriptor (in bytes) */
+	uint8_t  bLength;
+
+	/** Descriptor type. Will have value
+	 * \ref libusb_descriptor_type::LIBUSB_DT_INTERFACE LIBUSB_DT_INTERFACE
+	 * in this context. */
+	uint8_t  bDescriptorType;
+
+	/** Number of this interface */
+	uint8_t  bInterfaceNumber;
+
+	/** Value used to select this alternate setting for this interface */
+	uint8_t  bAlternateSetting;
+
+	/** Number of endpoints used by this interface (excluding the control
+	 * endpoint). */
+	uint8_t  bNumEndpoints;
+
+	/** USB-IF class code for this interface. See \ref libusb_class_code. */
+	uint8_t  bInterfaceClass;
+
+	/** USB-IF subclass code for this interface, qualified by the
+	 * bInterfaceClass value */
+	uint8_t  bInterfaceSubClass;
+
+	/** USB-IF protocol code for this interface, qualified by the
+	 * bInterfaceClass and bInterfaceSubClass values */
+	uint8_t  bInterfaceProtocol;
+
+	/** Index of string descriptor describing this interface */
+	uint8_t  iInterface;
+
+	/** Array of endpoint descriptors. This length of this array is determined
+	 * by the bNumEndpoints field. */
+	const struct libusb_endpoint_descriptor *endpoint;
+
+	/** Extra descriptors. If libusb encounters unknown interface descriptors,
+	 * it will store them here, should you wish to parse them. */
+	const unsigned char *extra;
+
+	/** Length of the extra descriptors, in bytes. */
+	int extra_length;
+};
+
+/** \ingroup desc
+ * A collection of alternate settings for a particular USB interface.
+ */
+struct libusb_interface {
+	/** Array of interface descriptors. The length of this array is determined
+	 * by the num_altsetting field. */
+	const struct libusb_interface_descriptor *altsetting;
+
+	/** The number of alternate settings that belong to this interface */
+	int num_altsetting;
+};
+
+/** \ingroup desc
+ * A structure representing the standard USB configuration descriptor. This
+ * descriptor is documented in section 9.6.3 of the USB 2.0 specification.
+ * All multiple-byte fields are represented in host-endian format.
+ */
+struct libusb_config_descriptor {
+	/** Size of this descriptor (in bytes) */
+	uint8_t  bLength;
+
+	/** Descriptor type. Will have value
+	 * \ref libusb_descriptor_type::LIBUSB_DT_CONFIG LIBUSB_DT_CONFIG
+	 * in this context. */
+	uint8_t  bDescriptorType;
+
+	/** Total length of data returned for this configuration */
+	uint16_t wTotalLength;
+
+	/** Number of interfaces supported by this configuration */
+	uint8_t  bNumInterfaces;
+
+	/** Identifier value for this configuration */
+	uint8_t  bConfigurationValue;
+
+	/** Index of string descriptor describing this configuration */
+	uint8_t  iConfiguration;
+
+	/** Configuration characteristics */
+	uint8_t  bmAttributes;
+
+	/** Maximum power consumption of the USB device from this bus in this
+	 * configuration when the device is fully opreation. Expressed in units
+	 * of 2 mA. */
+	uint8_t  MaxPower;
+
+	/** Array of interfaces supported by this configuration. The length of
+	 * this array is determined by the bNumInterfaces field. */
+	const struct libusb_interface *interface;
+
+	/** Extra descriptors. If libusb encounters unknown configuration
+	 * descriptors, it will store them here, should you wish to parse them. */
+	const unsigned char *extra;
+
+	/** Length of the extra descriptors, in bytes. */
+	int extra_length;
+};
+
+/** \ingroup asyncio
+ * Setup packet for control transfers. */
+struct libusb_control_setup {
+	/** Request type. Bits 0:4 determine recipient, see
+	 * \ref libusb_request_recipient. Bits 5:6 determine type, see
+	 * \ref libusb_request_type. Bit 7 determines data transfer direction, see
+	 * \ref libusb_endpoint_direction.
+	 */
+	uint8_t  bmRequestType;
+
+	/** Request. If the type bits of bmRequestType are equal to
+	 * \ref libusb_request_type::LIBUSB_REQUEST_TYPE_STANDARD
+	 * "LIBUSB_REQUEST_TYPE_STANDARD" then this field refers to
+	 * \ref libusb_standard_request. For other cases, use of this field is
+	 * application-specific. */
+	uint8_t  bRequest;
+
+	/** Value. Varies according to request */
+	uint16_t wValue;
+
+	/** Index. Varies according to request, typically used to pass an index
+	 * or offset */
+	uint16_t wIndex;
+
+	/** Number of bytes to transfer */
+	uint16_t wLength;
+};
+
+#define LIBUSB_CONTROL_SETUP_SIZE (sizeof(struct libusb_control_setup))
+
+/* libusb */
+
+struct libusb_context;
+struct libusb_device;
+struct libusb_device_handle;
+
+/** \ingroup lib
+ * Structure representing a libusb session. The concept of individual libusb
+ * sessions allows for your program to use two libraries (or dynamically
+ * load two modules) which both independently use libusb. This will prevent
+ * interference between the individual libusb users - for example
+ * libusb_set_debug() will not affect the other user of the library, and
+ * libusb_exit() will not destroy resources that the other user is still
+ * using.
+ *
+ * Sessions are created by libusb_init() and destroyed through libusb_exit().
+ * If your application is guaranteed to only ever include a single libusb
+ * user (i.e. you), you do not have to worry about contexts: pass NULL in
+ * every function call where a context is required. The default context
+ * will be used.
+ *
+ * For more information, see \ref contexts.
+ */
+typedef struct libusb_context libusb_context;
+
+/** \ingroup dev
+ * Structure representing a USB device detected on the system. This is an
+ * opaque type for which you are only ever provided with a pointer, usually
+ * originating from libusb_get_device_list().
+ *
+ * Certain operations can be performed on a device, but in order to do any
+ * I/O you will have to first obtain a device handle using libusb_open().
+ *
+ * Devices are reference counted with libusb_device_ref() and
+ * libusb_device_unref(), and are freed when the reference count reaches 0.
+ * New devices presented by libusb_get_device_list() have a reference count of
+ * 1, and libusb_free_device_list() can optionally decrease the reference count
+ * on all devices in the list. libusb_open() adds another reference which is
+ * later destroyed by libusb_close().
+ */
+typedef struct libusb_device libusb_device;
+
+
+/** \ingroup dev
+ * Structure representing a handle on a USB device. This is an opaque type for
+ * which you are only ever provided with a pointer, usually originating from
+ * libusb_open().
+ *
+ * A device handle is used to perform I/O and other operations. When finished
+ * with a device handle, you should call libusb_close().
+ */
+typedef struct libusb_device_handle libusb_device_handle;
+
+/** \ingroup misc
+ * Error codes. Most libusb functions return 0 on success or one of these
+ * codes on failure.
+ */
+enum libusb_error {
+	/** Success (no error) */
+	LIBUSB_SUCCESS = 0,
+
+	/** Input/output error */
+	LIBUSB_ERROR_IO = -1,
+
+	/** Invalid parameter */
+	LIBUSB_ERROR_INVALID_PARAM = -2,
+
+	/** Access denied (insufficient permissions) */
+	LIBUSB_ERROR_ACCESS = -3,
+
+	/** No such device (it may have been disconnected) */
+	LIBUSB_ERROR_NO_DEVICE = -4,
+
+	/** Entity not found */
+	LIBUSB_ERROR_NOT_FOUND = -5,
+
+	/** Resource busy */
+	LIBUSB_ERROR_BUSY = -6,
+
+	/** Operation timed out */
+	LIBUSB_ERROR_TIMEOUT = -7,
+
+	/** Overflow */
+	LIBUSB_ERROR_OVERFLOW = -8,
+
+	/** Pipe error */
+	LIBUSB_ERROR_PIPE = -9,
+
+	/** System call interrupted (perhaps due to signal) */
+	LIBUSB_ERROR_INTERRUPTED = -10,
+
+	/** Insufficient memory */
+	LIBUSB_ERROR_NO_MEM = -11,
+
+	/** Operation not supported or unimplemented on this platform */
+	LIBUSB_ERROR_NOT_SUPPORTED = -12,
+
+	/** Other error */
+	LIBUSB_ERROR_OTHER = -99
+};
+
+/** \ingroup asyncio
+ * Transfer status codes */
+enum libusb_transfer_status {
+	/** Transfer completed without error. Note that this does not indicate
+	 * that the entire amount of requested data was transferred. */
+	LIBUSB_TRANSFER_COMPLETED,
+
+	/** Transfer failed */
+	LIBUSB_TRANSFER_ERROR,
+
+	/** Transfer timed out */
+	LIBUSB_TRANSFER_TIMED_OUT,
+
+	/** Transfer was cancelled */
+	LIBUSB_TRANSFER_CANCELLED,
+
+	/** For bulk/interrupt endpoints: halt condition detected (endpoint
+	 * stalled). For control endpoints: control request not supported. */
+	LIBUSB_TRANSFER_STALL,
+
+	/** Device was disconnected */
+	LIBUSB_TRANSFER_NO_DEVICE,
+
+	/** Device sent more data than requested */
+	LIBUSB_TRANSFER_OVERFLOW
+};
+
+/** \ingroup asyncio
+ * libusb_transfer.flags values */
+enum libusb_transfer_flags {
+	/** Report short frames as errors */
+	LIBUSB_TRANSFER_SHORT_NOT_OK = 1<<0,
+
+	/** Automatically free() transfer buffer during libusb_free_transfer() */
+	LIBUSB_TRANSFER_FREE_BUFFER = 1<<1,
+
+	/** Automatically call libusb_free_transfer() after callback returns.
+	 * If this flag is set, it is illegal to call libusb_free_transfer()
+	 * from your transfer callback, as this will result in a double-free
+	 * when this flag is acted upon. */
+	LIBUSB_TRANSFER_FREE_TRANSFER = 1<<2
+};
+
+/** \ingroup asyncio
+ * Isochronous packet descriptor. */
+struct libusb_iso_packet_descriptor {
+	/** Length of data to request in this packet */
+	unsigned int length;
+
+	/** Amount of data that was actually transferred */
+	unsigned int actual_length;
+
+	/** Status code for this packet */
+	enum libusb_transfer_status status;
+};
+
+struct libusb_transfer;
+
+/** \ingroup asyncio
+ * Asynchronous transfer callback function type. When submitting asynchronous
+ * transfers, you pass a pointer to a callback function of this type via the
+ * \ref libusb_transfer::callback "callback" member of the libusb_transfer
+ * structure. libusb will call this function later, when the transfer has
+ * completed or failed. See \ref asyncio for more information.
+ * \param transfer The libusb_transfer struct the callback function is being
+ * notified about.
+ */
+typedef void (*libusb_transfer_cb_fn)(struct libusb_transfer *transfer);
+
+/** \ingroup asyncio
+ * The generic USB transfer structure. The user populates this structure and
+ * then submits it in order to request a transfer. After the transfer has
+ * completed, the library populates the transfer with the results and passes
+ * it back to the user.
+ */
+struct libusb_transfer {
+	/** Handle of the device that this transfer will be submitted to */
+	libusb_device_handle *dev_handle;
+
+	/** A bitwise OR combination of \ref libusb_transfer_flags. */
+	uint8_t flags;
+
+	/** Address of the endpoint where this transfer will be sent. */
+	unsigned char endpoint;
+
+	/** Type of the endpoint from \ref libusb_transfer_type */
+	unsigned char type;
+
+	/** Timeout for this transfer in millseconds. A value of 0 indicates no
+	 * timeout. */
+	unsigned int timeout;
+
+	/** The status of the transfer. Read-only, and only for use within
+	 * transfer callback function.
+	 *
+	 * If this is an isochronous transfer, this field may read COMPLETED even
+	 * if there were errors in the frames. Use the
+	 * \ref libusb_iso_packet_descriptor::status "status" field in each packet
+	 * to determine if errors occurred. */
+	enum libusb_transfer_status status;
+
+	/** Length of the data buffer */
+	int length;
+
+	/** Actual length of data that was transferred. Read-only, and only for
+	 * use within transfer callback function. Not valid for isochronous
+	 * endpoint transfers. */
+	int actual_length;
+
+	/** Callback function. This will be invoked when the transfer completes,
+	 * fails, or is cancelled. */
+	libusb_transfer_cb_fn callback;
+
+	/** User context data to pass to the callback function. */
+	void *user_data;
+
+	/** Data buffer */
+	unsigned char *buffer;
+
+	/** Number of isochronous packets. Only used for I/O with isochronous
+	 * endpoints. */
+	int num_iso_packets;
+
+	/** Isochronous packet descriptors, for isochronous transfers only. */
+	struct libusb_iso_packet_descriptor iso_packet_desc
+#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)
+	[] /* valid C99 code */
+#else
+	[0] /* non-standard, but usually working code */
+#endif
+	;
+};
+
+int libusb_init(libusb_context **ctx);
+void libusb_exit(libusb_context *ctx);
+void libusb_set_debug(libusb_context *ctx, int level);
+
+ssize_t libusb_get_device_list(libusb_context *ctx,
+	libusb_device ***list);
+void libusb_free_device_list(libusb_device **list, int unref_devices);
+libusb_device *libusb_ref_device(libusb_device *dev);
+void libusb_unref_device(libusb_device *dev);
+
+int libusb_get_configuration(libusb_device_handle *dev, int *config);
+int libusb_get_device_descriptor(libusb_device *dev,
+	struct libusb_device_descriptor *desc);
+int libusb_get_active_config_descriptor(libusb_device *dev,
+	struct libusb_config_descriptor **config);
+int libusb_get_config_descriptor(libusb_device *dev, uint8_t config_index,
+	struct libusb_config_descriptor **config);
+int libusb_get_config_descriptor_by_value(libusb_device *dev,
+	uint8_t bConfigurationValue, struct libusb_config_descriptor **config);
+void libusb_free_config_descriptor(struct libusb_config_descriptor *config);
+uint8_t libusb_get_bus_number(libusb_device *dev);
+uint8_t libusb_get_device_address(libusb_device *dev);
+int libusb_get_max_packet_size(libusb_device *dev, unsigned char endpoint);
+int libusb_get_max_iso_packet_size(libusb_device *dev, unsigned char endpoint);
+
+int libusb_open(libusb_device *dev, libusb_device_handle **handle);
+void libusb_close(libusb_device_handle *dev_handle);
+libusb_device *libusb_get_device(libusb_device_handle *dev_handle);
+
+int libusb_set_configuration(libusb_device_handle *dev, int configuration);
+int libusb_claim_interface(libusb_device_handle *dev, int iface);
+int libusb_release_interface(libusb_device_handle *dev, int iface);
+
+libusb_device_handle *libusb_open_device_with_vid_pid(libusb_context *ctx,
+	uint16_t vendor_id, uint16_t product_id);
+
+int libusb_set_interface_alt_setting(libusb_device_handle *dev,
+	int interface_number, int alternate_setting);
+int libusb_clear_halt(libusb_device_handle *dev, unsigned char endpoint);
+int libusb_reset_device(libusb_device_handle *dev);
+
+int libusb_kernel_driver_active(libusb_device_handle *dev, int interface);
+int libusb_detach_kernel_driver(libusb_device_handle *dev, int interface);
+int libusb_attach_kernel_driver(libusb_device_handle *dev, int interface);
+
+/* async I/O */
+
+/** \ingroup asyncio
+ * Get the data section of a control transfer. This convenience function is here
+ * to remind you that the data does not start until 8 bytes into the actual
+ * buffer, as the setup packet comes first.
+ *
+ * Calling this function only makes sense from a transfer callback function,
+ * or situations where you have already allocated a suitably sized buffer at
+ * transfer->buffer.
+ *
+ * \param transfer a transfer
+ * \returns pointer to the first byte of the data section
+ */
+static inline unsigned char *libusb_control_transfer_get_data(
+	struct libusb_transfer *transfer)
+{
+	return transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE;
+}
+
+/** \ingroup asyncio
+ * Get the control setup packet of a control transfer. This convenience
+ * function is here to remind you that the control setup occupies the first
+ * 8 bytes of the transfer data buffer.
+ *
+ * Calling this function only makes sense from a transfer callback function,
+ * or situations where you have already allocated a suitably sized buffer at
+ * transfer->buffer.
+ *
+ * \param transfer a transfer
+ * \returns a casted pointer to the start of the transfer data buffer
+ */
+static inline struct libusb_control_setup *libusb_control_transfer_get_setup(
+	struct libusb_transfer *transfer)
+{
+	return (struct libusb_control_setup *) transfer->buffer;
+}
+
+/** \ingroup asyncio
+ * Helper function to populate the setup packet (first 8 bytes of the data
+ * buffer) for a control transfer. The wIndex, wValue and wLength values should
+ * be given in host-endian byte order.
+ *
+ * \param buffer buffer to output the setup packet into
+ * \param bmRequestType see the
+ * \ref libusb_control_setup::bmRequestType "bmRequestType" field of
+ * \ref libusb_control_setup
+ * \param bRequest see the
+ * \ref libusb_control_setup::bRequest "bRequest" field of
+ * \ref libusb_control_setup
+ * \param wValue see the
+ * \ref libusb_control_setup::wValue "wValue" field of
+ * \ref libusb_control_setup
+ * \param wIndex see the
+ * \ref libusb_control_setup::wIndex "wIndex" field of
+ * \ref libusb_control_setup
+ * \param wLength see the
+ * \ref libusb_control_setup::wLength "wLength" field of
+ * \ref libusb_control_setup
+ */
+static inline void libusb_fill_control_setup(unsigned char *buffer,
+	uint8_t bmRequestType, uint8_t bRequest, uint16_t wValue, uint16_t wIndex,
+	uint16_t wLength)
+{
+	struct libusb_control_setup *setup = (struct libusb_control_setup *) buffer;
+	setup->bmRequestType = bmRequestType;
+	setup->bRequest = bRequest;
+	setup->wValue = libusb_cpu_to_le16(wValue);
+	setup->wIndex = libusb_cpu_to_le16(wIndex);
+	setup->wLength = libusb_cpu_to_le16(wLength);
+}
+
+struct libusb_transfer *libusb_alloc_transfer(int iso_packets);
+int libusb_submit_transfer(struct libusb_transfer *transfer);
+int libusb_cancel_transfer(struct libusb_transfer *transfer);
+void libusb_free_transfer(struct libusb_transfer *transfer);
+
+/** \ingroup asyncio
+ * Helper function to populate the required \ref libusb_transfer fields
+ * for a control transfer.
+ *
+ * If you pass a transfer buffer to this function, the first 8 bytes will
+ * be interpreted as a control setup packet, and the wLength field will be
+ * used to automatically populate the \ref libusb_transfer::length "length"
+ * field of the transfer. Therefore the recommended approach is:
+ * -# Allocate a suitably sized data buffer (including space for control setup)
+ * -# Call libusb_fill_control_setup()
+ * -# If this is a host-to-device transfer with a data stage, put the data
+ *    in place after the setup packet
+ * -# Call this function
+ * -# Call libusb_submit_transfer()
+ *
+ * It is also legal to pass a NULL buffer to this function, in which case this
+ * function will not attempt to populate the length field. Remember that you
+ * must then populate the buffer and length fields later.
+ *
+ * \param transfer the transfer to populate
+ * \param dev_handle handle of the device that will handle the transfer
+ * \param buffer data buffer. If provided, this function will interpret the
+ * first 8 bytes as a setup packet and infer the transfer length from that.
+ * \param callback callback function to be invoked on transfer completion
+ * \param user_data user data to pass to callback function
+ * \param timeout timeout for the transfer in milliseconds
+ */
+static inline void libusb_fill_control_transfer(
+	struct libusb_transfer *transfer, libusb_device_handle *dev_handle,
+	unsigned char *buffer, libusb_transfer_cb_fn callback, void *user_data,
+	unsigned int timeout)
+{
+	struct libusb_control_setup *setup = (struct libusb_control_setup *) buffer;
+	transfer->dev_handle = dev_handle;
+	transfer->endpoint = 0;
+	transfer->type = LIBUSB_TRANSFER_TYPE_CONTROL;
+	transfer->timeout = timeout;
+	transfer->buffer = buffer;
+	if (setup)
+		transfer->length = LIBUSB_CONTROL_SETUP_SIZE
+			+ libusb_le16_to_cpu(setup->wLength);
+	transfer->user_data = user_data;
+	transfer->callback = callback;
+}
+
+/** \ingroup asyncio
+ * Helper function to populate the required \ref libusb_transfer fields
+ * for a bulk transfer.
+ *
+ * \param transfer the transfer to populate
+ * \param dev_handle handle of the device that will handle the transfer
+ * \param endpoint address of the endpoint where this transfer will be sent
+ * \param buffer data buffer
+ * \param length length of data buffer
+ * \param callback callback function to be invoked on transfer completion
+ * \param user_data user data to pass to callback function
+ * \param timeout timeout for the transfer in milliseconds
+ */
+static inline void libusb_fill_bulk_transfer(struct libusb_transfer *transfer,
+	libusb_device_handle *dev_handle, unsigned char endpoint,
+	unsigned char *buffer, int length, libusb_transfer_cb_fn callback,
+	void *user_data, unsigned int timeout)
+{
+	transfer->dev_handle = dev_handle;
+	transfer->endpoint = endpoint;
+	transfer->type = LIBUSB_TRANSFER_TYPE_BULK;
+	transfer->timeout = timeout;
+	transfer->buffer = buffer;
+	transfer->length = length;
+	transfer->user_data = user_data;
+	transfer->callback = callback;
+}
+
+/** \ingroup asyncio
+ * Helper function to populate the required \ref libusb_transfer fields
+ * for an interrupt transfer.
+ *
+ * \param transfer the transfer to populate
+ * \param dev_handle handle of the device that will handle the transfer
+ * \param endpoint address of the endpoint where this transfer will be sent
+ * \param buffer data buffer
+ * \param length length of data buffer
+ * \param callback callback function to be invoked on transfer completion
+ * \param user_data user data to pass to callback function
+ * \param timeout timeout for the transfer in milliseconds
+ */
+static inline void libusb_fill_interrupt_transfer(
+	struct libusb_transfer *transfer, libusb_device_handle *dev_handle,
+	unsigned char endpoint, unsigned char *buffer, int length,
+	libusb_transfer_cb_fn callback, void *user_data, unsigned int timeout)
+{
+	transfer->dev_handle = dev_handle;
+	transfer->endpoint = endpoint;
+	transfer->type = LIBUSB_TRANSFER_TYPE_INTERRUPT;
+	transfer->timeout = timeout;
+	transfer->buffer = buffer;
+	transfer->length = length;
+	transfer->user_data = user_data;
+	transfer->callback = callback;
+}
+
+/** \ingroup asyncio
+ * Helper function to populate the required \ref libusb_transfer fields
+ * for an isochronous transfer.
+ *
+ * \param transfer the transfer to populate
+ * \param dev_handle handle of the device that will handle the transfer
+ * \param endpoint address of the endpoint where this transfer will be sent
+ * \param buffer data buffer
+ * \param length length of data buffer
+ * \param num_iso_packets the number of isochronous packets
+ * \param callback callback function to be invoked on transfer completion
+ * \param user_data user data to pass to callback function
+ * \param timeout timeout for the transfer in milliseconds
+ */
+static inline void libusb_fill_iso_transfer(struct libusb_transfer *transfer,
+	libusb_device_handle *dev_handle, unsigned char endpoint,
+	unsigned char *buffer, int length, int num_iso_packets,
+	libusb_transfer_cb_fn callback, void *user_data, unsigned int timeout)
+{
+	transfer->dev_handle = dev_handle;
+	transfer->endpoint = endpoint;
+	transfer->type = LIBUSB_TRANSFER_TYPE_ISOCHRONOUS;
+	transfer->timeout = timeout;
+	transfer->buffer = buffer;
+	transfer->length = length;
+	transfer->num_iso_packets = num_iso_packets;
+	transfer->user_data = user_data;
+	transfer->callback = callback;
+}
+
+/** \ingroup asyncio
+ * Convenience function to set the length of all packets in an isochronous
+ * transfer, based on the num_iso_packets field in the transfer structure.
+ *
+ * \param transfer a transfer
+ * \param length the length to set in each isochronous packet descriptor
+ * \see libusb_get_max_packet_size()
+ */
+static inline void libusb_set_iso_packet_lengths(
+	struct libusb_transfer *transfer, unsigned int length)
+{
+	int i;
+	for (i = 0; i < transfer->num_iso_packets; i++)
+		transfer->iso_packet_desc[i].length = length;
+}
+
+/** \ingroup asyncio
+ * Convenience function to locate the position of an isochronous packet
+ * within the buffer of an isochronous transfer.
+ *
+ * This is a thorough function which loops through all preceding packets,
+ * accumulating their lengths to find the position of the specified packet.
+ * Typically you will assign equal lengths to each packet in the transfer,
+ * and hence the above method is sub-optimal. You may wish to use
+ * libusb_get_iso_packet_buffer_simple() instead.
+ *
+ * \param transfer a transfer
+ * \param packet the packet to return the address of
+ * \returns the base address of the packet buffer inside the transfer buffer,
+ * or NULL if the packet does not exist.
+ * \see libusb_get_iso_packet_buffer_simple()
+ */
+static inline unsigned char *libusb_get_iso_packet_buffer(
+	struct libusb_transfer *transfer, unsigned int packet)
+{
+	int i;
+	size_t offset = 0;
+	int _packet;
+
+	/* oops..slight bug in the API. packet is an unsigned int, but we use
+	 * signed integers almost everywhere else. range-check and convert to
+	 * signed to avoid compiler warnings. FIXME for libusb-2. */
+	if (packet > INT_MAX)
+		return NULL;
+	_packet = packet;
+
+	if (_packet >= transfer->num_iso_packets)
+		return NULL;
+
+	for (i = 0; i < _packet; i++)
+		offset += transfer->iso_packet_desc[i].length;
+
+	return transfer->buffer + offset;
+}
+
+/** \ingroup asyncio
+ * Convenience function to locate the position of an isochronous packet
+ * within the buffer of an isochronous transfer, for transfers where each
+ * packet is of identical size.
+ *
+ * This function relies on the assumption that every packet within the transfer
+ * is of identical size to the first packet. Calculating the location of
+ * the packet buffer is then just a simple calculation:
+ * <tt>buffer + (packet_size * packet)</tt>
+ *
+ * Do not use this function on transfers other than those that have identical
+ * packet lengths for each packet.
+ *
+ * \param transfer a transfer
+ * \param packet the packet to return the address of
+ * \returns the base address of the packet buffer inside the transfer buffer,
+ * or NULL if the packet does not exist.
+ * \see libusb_get_iso_packet_buffer()
+ */
+static inline unsigned char *libusb_get_iso_packet_buffer_simple(
+	struct libusb_transfer *transfer, unsigned int packet)
+{
+	int _packet;
+
+	/* oops..slight bug in the API. packet is an unsigned int, but we use
+	 * signed integers almost everywhere else. range-check and convert to
+	 * signed to avoid compiler warnings. FIXME for libusb-2. */
+	if (packet > INT_MAX)
+		return NULL;
+	_packet = packet;
+
+	if (_packet >= transfer->num_iso_packets)
+		return NULL;
+
+	return transfer->buffer + (transfer->iso_packet_desc[0].length * _packet);
+}
+
+/* sync I/O */
+
+int libusb_control_transfer(libusb_device_handle *dev_handle,
+	uint8_t request_type, uint8_t request, uint16_t value, uint16_t index,
+	unsigned char *data, uint16_t length, unsigned int timeout);
+
+int libusb_bulk_transfer(libusb_device_handle *dev_handle,
+	unsigned char endpoint, unsigned char *data, int length,
+	int *actual_length, unsigned int timeout);
+
+int libusb_interrupt_transfer(libusb_device_handle *dev_handle,
+	unsigned char endpoint, unsigned char *data, int length,
+	int *actual_length, unsigned int timeout);
+
+/** \ingroup desc
+ * Retrieve a descriptor from the default control pipe.
+ * This is a convenience function which formulates the appropriate control
+ * message to retrieve the descriptor.
+ *
+ * \param dev a device handle
+ * \param desc_type the descriptor type, see \ref libusb_descriptor_type
+ * \param desc_index the index of the descriptor to retrieve
+ * \param data output buffer for descriptor
+ * \param length size of data buffer
+ * \returns number of bytes returned in data, or LIBUSB_ERROR code on failure
+ */
+static inline int libusb_get_descriptor(libusb_device_handle *dev,
+	uint8_t desc_type, uint8_t desc_index, unsigned char *data, int length)
+{
+	return libusb_control_transfer(dev, LIBUSB_ENDPOINT_IN,
+		LIBUSB_REQUEST_GET_DESCRIPTOR, (desc_type << 8) | desc_index, 0, data,
+		length, 1000);
+}
+
+/** \ingroup desc
+ * Retrieve a descriptor from a device.
+ * This is a convenience function which formulates the appropriate control
+ * message to retrieve the descriptor. The string returned is Unicode, as
+ * detailed in the USB specifications.
+ *
+ * \param dev a device handle
+ * \param desc_index the index of the descriptor to retrieve
+ * \param langid the language ID for the string descriptor
+ * \param data output buffer for descriptor
+ * \param length size of data buffer
+ * \returns number of bytes returned in data, or LIBUSB_ERROR code on failure
+ * \see libusb_get_string_descriptor_ascii()
+ */
+static inline int libusb_get_string_descriptor(libusb_device_handle *dev,
+	uint8_t desc_index, uint16_t langid, unsigned char *data, int length)
+{
+	return libusb_control_transfer(dev, LIBUSB_ENDPOINT_IN,
+		LIBUSB_REQUEST_GET_DESCRIPTOR, (LIBUSB_DT_STRING << 8) | desc_index,
+		langid, data, length, 1000);
+}
+
+int libusb_get_string_descriptor_ascii(libusb_device_handle *dev,
+	uint8_t index, unsigned char *data, int length);
+
+/* polling and timeouts */
+
+int libusb_try_lock_events(libusb_context *ctx);
+void libusb_lock_events(libusb_context *ctx);
+void libusb_unlock_events(libusb_context *ctx);
+int libusb_event_handling_ok(libusb_context *ctx);
+int libusb_event_handler_active(libusb_context *ctx);
+void libusb_lock_event_waiters(libusb_context *ctx);
+void libusb_unlock_event_waiters(libusb_context *ctx);
+int libusb_wait_for_event(libusb_context *ctx, struct timeval *tv);
+
+int libusb_handle_events_timeout(libusb_context *ctx, struct timeval *tv);
+int libusb_handle_events(libusb_context *ctx);
+int libusb_handle_events_locked(libusb_context *ctx, struct timeval *tv);
+int libusb_pollfds_handle_timeouts(libusb_context *ctx);
+int libusb_get_next_timeout(libusb_context *ctx, struct timeval *tv);
+
+/** \ingroup poll
+ * File descriptor for polling
+ */
+struct libusb_pollfd {
+	/** Numeric file descriptor */
+	int fd;
+
+	/** Event flags to poll for from <poll.h>. POLLIN indicates that you
+	 * should monitor this file descriptor for becoming ready to read from,
+	 * and POLLOUT indicates that you should monitor this file descriptor for
+	 * nonblocking write readiness. */
+	short events;
+};
+
+/** \ingroup poll
+ * Callback function, invoked when a new file descriptor should be added
+ * to the set of file descriptors monitored for events.
+ * \param fd the new file descriptor
+ * \param events events to monitor for, see \ref libusb_pollfd for a
+ * description
+ * \param user_data User data pointer specified in
+ * libusb_set_pollfd_notifiers() call
+ * \see libusb_set_pollfd_notifiers()
+ */
+typedef void (*libusb_pollfd_added_cb)(int fd, short events, void *user_data);
+
+/** \ingroup poll
+ * Callback function, invoked when a file descriptor should be removed from
+ * the set of file descriptors being monitored for events. After returning
+ * from this callback, do not use that file descriptor again.
+ * \param fd the file descriptor to stop monitoring
+ * \param user_data User data pointer specified in
+ * libusb_set_pollfd_notifiers() call
+ * \see libusb_set_pollfd_notifiers()
+ */
+typedef void (*libusb_pollfd_removed_cb)(int fd, void *user_data);
+
+const struct libusb_pollfd **libusb_get_pollfds(libusb_context *ctx);
+void libusb_set_pollfd_notifiers(libusb_context *ctx,
+	libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
+	void *user_data);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/libusb/libusbi.h b/libusb/libusbi.h
new file mode 100644
index 0000000..10a4994
--- /dev/null
+++ b/libusb/libusbi.h
@@ -0,0 +1,810 @@
+/*
+ * Internal header for libusb
+ * Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef __LIBUSBI_H__
+#define __LIBUSBI_H__
+
+#include <config.h>
+
+#include <poll.h>
+#include <pthread.h>
+#include <stddef.h>
+#include <time.h>
+
+#include <libusb.h>
+
+#define DEVICE_DESC_LENGTH		18
+
+#define USB_MAXENDPOINTS	32
+#define USB_MAXINTERFACES	32
+#define USB_MAXCONFIG		8
+
+struct list_head {
+	struct list_head *prev, *next;
+};
+
+/* Get an entry from the list 
+ * 	ptr - the address of this list_head element in "type" 
+ * 	type - the data type that contains "member"
+ * 	member - the list_head element in "type" 
+ */
+#define list_entry(ptr, type, member) \
+	((type *)((char *)(ptr) - (unsigned long)(&((type *)0L)->member)))
+
+/* Get each entry from a list
+ *	pos - A structure pointer has a "member" element
+ *	head - list head
+ *	member - the list_head element in "pos"
+ */
+#define list_for_each_entry(pos, head, member)				\
+	for (pos = list_entry((head)->next, typeof(*pos), member);	\
+	     &pos->member != (head);					\
+	     pos = list_entry(pos->member.next, typeof(*pos), member))
+
+#define list_for_each_entry_safe(pos, n, head, member)			\
+        for (pos = list_entry((head)->next, typeof(*pos), member),	\
+		n = list_entry(pos->member.next, typeof(*pos), member);	\
+	     &pos->member != (head);					\
+	     pos = n, n = list_entry(n->member.next, typeof(*n), member))
+
+#define list_empty(entry) ((entry)->next == (entry))
+
+static inline void list_init(struct list_head *entry)
+{
+	entry->prev = entry->next = entry;
+}
+
+static inline void list_add(struct list_head *entry, struct list_head *head)
+{
+	entry->next = head->next;
+	entry->prev = head;
+
+	head->next->prev = entry;
+	head->next = entry;
+}
+
+static inline void list_add_tail(struct list_head *entry,
+	struct list_head *head)
+{
+	entry->next = head;
+	entry->prev = head->prev;
+
+	head->prev->next = entry;
+	head->prev = entry;
+}
+
+static inline void list_del(struct list_head *entry)
+{
+	entry->next->prev = entry->prev;
+	entry->prev->next = entry->next;
+}
+
+#define container_of(ptr, type, member) ({                      \
+        const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
+        (type *)( (char *)__mptr - offsetof(type,member) );})
+
+#define MIN(a, b)	((a) < (b) ? (a) : (b))
+#define MAX(a, b)	((a) > (b) ? (a) : (b))
+
+#define TIMESPEC_IS_SET(ts) ((ts)->tv_sec != 0 || (ts)->tv_nsec != 0)
+
+enum usbi_log_level {
+	LOG_LEVEL_DEBUG,
+	LOG_LEVEL_INFO,
+	LOG_LEVEL_WARNING,
+	LOG_LEVEL_ERROR,
+};
+
+void usbi_log(struct libusb_context *ctx, enum usbi_log_level,
+	const char *function, const char *format, ...);
+
+#ifdef ENABLE_LOGGING
+#define _usbi_log(ctx, level, fmt...) usbi_log(ctx, level, __FUNCTION__, fmt)
+#else
+#define _usbi_log(ctx, level, fmt...)
+#endif
+
+#ifdef ENABLE_DEBUG_LOGGING
+#define usbi_dbg(fmt...) _usbi_log(NULL, LOG_LEVEL_DEBUG, fmt)
+#else
+#define usbi_dbg(fmt...)
+#endif
+
+#define usbi_info(ctx, fmt...) _usbi_log(ctx, LOG_LEVEL_INFO, fmt)
+#define usbi_warn(ctx, fmt...) _usbi_log(ctx, LOG_LEVEL_WARNING, fmt)
+#define usbi_err(ctx, fmt...) _usbi_log(ctx, LOG_LEVEL_ERROR, fmt)
+
+#define USBI_GET_CONTEXT(ctx) if (!(ctx)) (ctx) = usbi_default_context
+#define DEVICE_CTX(dev) ((dev)->ctx)
+#define HANDLE_CTX(handle) (DEVICE_CTX((handle)->dev))
+#define TRANSFER_CTX(transfer) (HANDLE_CTX((transfer)->dev_handle))
+#define ITRANSFER_CTX(transfer) \
+	(TRANSFER_CTX(__USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)))
+
+extern struct libusb_context *usbi_default_context;
+
+struct libusb_context {
+	int debug;
+	int debug_fixed;
+
+	/* internal control pipe, used for interrupting event handling when
+	 * something needs to modify poll fds. */
+	int ctrl_pipe[2];
+
+	struct list_head usb_devs;
+	pthread_mutex_t usb_devs_lock;
+
+	/* A list of open handles. Backends are free to traverse this if required.
+	 */
+	struct list_head open_devs;
+	pthread_mutex_t open_devs_lock;
+
+	/* this is a list of in-flight transfer handles, sorted by timeout 
+	 * expiration. URBs to timeout the soonest are placed at the beginning of
+	 * the list, URBs that will time out later are placed after, and urbs with
+	 * infinite timeout are always placed at the very end. */
+	struct list_head flying_transfers;
+	pthread_mutex_t flying_transfers_lock;
+
+	/* list of poll fds */
+	struct list_head pollfds;
+	pthread_mutex_t pollfds_lock;
+
+	/* a counter that is set when we want to interrupt event handling, in order
+	 * to modify the poll fd set. and a lock to protect it. */
+	unsigned int pollfd_modify;
+	pthread_mutex_t pollfd_modify_lock;
+
+	/* user callbacks for pollfd changes */
+	libusb_pollfd_added_cb fd_added_cb;
+	libusb_pollfd_removed_cb fd_removed_cb;
+	void *fd_cb_user_data;
+
+	/* ensures that only one thread is handling events at any one time */
+	pthread_mutex_t events_lock;
+
+	/* used to see if there is an active thread doing event handling */
+	int event_handler_active;
+
+	/* used to wait for event completion in threads other than the one that is
+	 * event handling */
+	pthread_mutex_t event_waiters_lock;
+	pthread_cond_t event_waiters_cond;
+
+#ifdef USBI_TIMERFD_AVAILABLE
+	/* used for timeout handling, if supported by OS.
+	 * this timerfd is maintained to trigger on the next pending timeout */
+	int timerfd;
+#endif
+};
+
+#ifdef USBI_TIMERFD_AVAILABLE
+#define usbi_using_timerfd(ctx) ((ctx)->timerfd >= 0)
+#else
+#define usbi_using_timerfd(ctx) (0)
+#endif
+
+struct libusb_device {
+	/* lock protects refcnt, everything else is finalized at initialization
+	 * time */
+	pthread_mutex_t lock;
+	int refcnt;
+
+	struct libusb_context *ctx;
+
+	uint8_t bus_number;
+	uint8_t device_address;
+	uint8_t num_configurations;
+
+	struct list_head list;
+	unsigned long session_data;
+	unsigned char os_priv[0];
+};
+
+struct libusb_device_handle {
+	/* lock protects claimed_interfaces */
+	pthread_mutex_t lock;
+	unsigned long claimed_interfaces;
+
+	struct list_head list;
+	struct libusb_device *dev;
+	unsigned char os_priv[0];
+};
+
+#define USBI_TRANSFER_TIMED_OUT	 			(1<<0)
+
+enum {
+  USBI_CLOCK_MONOTONIC,
+  USBI_CLOCK_REALTIME
+};
+
+/* in-memory transfer layout:
+ *
+ * 1. struct usbi_transfer
+ * 2. struct libusb_transfer (which includes iso packets) [variable size]
+ * 3. os private data [variable size]
+ *
+ * from a libusb_transfer, you can get the usbi_transfer by rewinding the
+ * appropriate number of bytes.
+ * the usbi_transfer includes the number of allocated packets, so you can
+ * determine the size of the transfer and hence the start and length of the
+ * OS-private data.
+ */
+
+struct usbi_transfer {
+	int num_iso_packets;
+	struct list_head list;
+	struct timeval timeout;
+	int transferred;
+	uint8_t flags;
+
+	/* this lock is held during libusb_submit_transfer() and
+	 * libusb_cancel_transfer() (allowing the OS backend to prevent duplicate
+	 * cancellation, submission-during-cancellation, etc). the OS backend
+	 * should also take this lock in the handle_events path, to prevent the user
+	 * cancelling the transfer from another thread while you are processing
+	 * its completion (presumably there would be races within your OS backend
+	 * if this were possible). */
+	pthread_mutex_t lock;
+};
+
+#define __USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer) \
+	((struct libusb_transfer *)(((void *)(transfer)) \
+		+ sizeof(struct usbi_transfer)))
+#define __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer) \
+	((struct usbi_transfer *)(((void *)(transfer)) \
+		- sizeof(struct usbi_transfer)))
+
+static inline void *usbi_transfer_get_os_priv(struct usbi_transfer *transfer)
+{
+	return ((void *)transfer) + sizeof(struct usbi_transfer)
+		+ sizeof(struct libusb_transfer)
+		+ (transfer->num_iso_packets
+			* sizeof(struct libusb_iso_packet_descriptor));
+}
+
+/* bus structures */
+
+/* All standard descriptors have these 2 fields in common */
+struct usb_descriptor_header {
+	uint8_t  bLength;
+	uint8_t  bDescriptorType;
+};
+
+/* shared data and functions */
+
+int usbi_io_init(struct libusb_context *ctx);
+void usbi_io_exit(struct libusb_context *ctx);
+
+struct libusb_device *usbi_alloc_device(struct libusb_context *ctx,
+	unsigned long session_id);
+struct libusb_device *usbi_get_device_by_session_id(struct libusb_context *ctx,
+	unsigned long session_id);
+int usbi_sanitize_device(struct libusb_device *dev);
+void usbi_handle_disconnect(struct libusb_device_handle *handle);
+
+int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
+	enum libusb_transfer_status status);
+int usbi_handle_transfer_cancellation(struct usbi_transfer *transfer);
+
+int usbi_parse_descriptor(unsigned char *source, char *descriptor, void *dest,
+	int host_endian);
+int usbi_get_config_index_by_value(struct libusb_device *dev,
+	uint8_t bConfigurationValue, int *idx);
+
+/* polling */
+
+struct usbi_pollfd {
+	/* must come first */
+	struct libusb_pollfd pollfd;
+
+	struct list_head list;
+};
+
+int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events);
+void usbi_remove_pollfd(struct libusb_context *ctx, int fd);
+
+/* device discovery */
+
+/* we traverse usbfs without knowing how many devices we are going to find.
+ * so we create this discovered_devs model which is similar to a linked-list
+ * which grows when required. it can be freed once discovery has completed,
+ * eliminating the need for a list node in the libusb_device structure
+ * itself. */
+struct discovered_devs {
+	size_t len;
+	size_t capacity;
+	struct libusb_device *devices[0];
+};
+
+struct discovered_devs *discovered_devs_append(
+	struct discovered_devs *discdevs, struct libusb_device *dev);
+
+/* OS abstraction */
+
+/* This is the interface that OS backends need to implement.
+ * All fields are mandatory, except ones explicitly noted as optional. */
+struct usbi_os_backend {
+	/* A human-readable name for your backend, e.g. "Linux usbfs" */
+	const char *name;
+
+	/* Perform initialization of your backend. You might use this function
+	 * to determine specific capabilities of the system, allocate required
+	 * data structures for later, etc.
+	 *
+	 * This function is called when a libusb user initializes the library
+	 * prior to use.
+	 *
+	 * Return 0 on success, or a LIBUSB_ERROR code on failure.
+	 */
+	int (*init)(struct libusb_context *ctx);
+
+	/* Deinitialization. Optional. This function should destroy anything
+	 * that was set up by init.
+	 *
+	 * This function is called when the user deinitializes the library.
+	 */
+	void (*exit)(void);
+
+	/* Enumerate all the USB devices on the system, returning them in a list
+	 * of discovered devices.
+	 *
+	 * Your implementation should enumerate all devices on the system,
+	 * regardless of whether they have been seen before or not.
+	 *
+	 * When you have found a device, compute a session ID for it. The session
+	 * ID should uniquely represent that particular device for that particular
+	 * connection session since boot (i.e. if you disconnect and reconnect a
+	 * device immediately after, it should be assigned a different session ID).
+	 * If your OS cannot provide a unique session ID as described above,
+	 * presenting a session ID of (bus_number << 8 | device_address) should
+	 * be sufficient. Bus numbers and device addresses wrap and get reused,
+	 * but that is an unlikely case.
+	 *
+	 * After computing a session ID for a device, call
+	 * usbi_get_device_by_session_id(). This function checks if libusb already
+	 * knows about the device, and if so, it provides you with a libusb_device
+	 * structure for it.
+	 *
+	 * If usbi_get_device_by_session_id() returns NULL, it is time to allocate
+	 * a new device structure for the device. Call usbi_alloc_device() to
+	 * obtain a new libusb_device structure with reference count 1. Populate
+	 * the bus_number and device_address attributes of the new device, and
+	 * perform any other internal backend initialization you need to do. At
+	 * this point, you should be ready to provide device descriptors and so
+	 * on through the get_*_descriptor functions. Finally, call
+	 * usbi_sanitize_device() to perform some final sanity checks on the
+	 * device. Assuming all of the above succeeded, we can now continue.
+	 * If any of the above failed, remember to unreference the device that
+	 * was returned by usbi_alloc_device().
+	 *
+	 * At this stage we have a populated libusb_device structure (either one
+	 * that was found earlier, or one that we have just allocated and
+	 * populated). This can now be added to the discovered devices list
+	 * using discovered_devs_append(). Note that discovered_devs_append()
+	 * may reallocate the list, returning a new location for it, and also
+	 * note that reallocation can fail. Your backend should handle these
+	 * error conditions appropriately.
+	 *
+	 * This function should not generate any bus I/O and should not block.
+	 * If I/O is required (e.g. reading the active configuration value), it is
+	 * OK to ignore these suggestions :)
+	 *
+	 * This function is executed when the user wishes to retrieve a list
+	 * of USB devices connected to the system.
+	 *
+	 * Return 0 on success, or a LIBUSB_ERROR code on failure.
+	 */
+	int (*get_device_list)(struct libusb_context *ctx,
+		struct discovered_devs **discdevs);
+
+	/* Open a device for I/O and other USB operations. The device handle
+	 * is preallocated for you, you can retrieve the device in question
+	 * through handle->dev.
+	 *
+	 * Your backend should allocate any internal resources required for I/O
+	 * and other operations so that those operations can happen (hopefully)
+	 * without hiccup. This is also a good place to inform libusb that it
+	 * should monitor certain file descriptors related to this device -
+	 * see the usbi_add_pollfd() function.
+	 *
+	 * This function should not generate any bus I/O and should not block.
+	 *
+	 * This function is called when the user attempts to obtain a device
+	 * handle for a device.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_ACCESS if the user has insufficient permissions
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since
+	 *   discovery
+	 * - another LIBUSB_ERROR code on other failure
+	 *
+	 * Do not worry about freeing the handle on failed open, the upper layers
+	 * do this for you.
+	 */
+	int (*open)(struct libusb_device_handle *handle);
+
+	/* Close a device such that the handle cannot be used again. Your backend
+	 * should destroy any resources that were allocated in the open path.
+	 * This may also be a good place to call usbi_remove_pollfd() to inform
+	 * libusb of any file descriptors associated with this device that should
+	 * no longer be monitored.
+	 *
+	 * This function is called when the user closes a device handle.
+	 */
+	void (*close)(struct libusb_device_handle *handle);
+
+	/* Retrieve the device descriptor from a device.
+	 *
+	 * The descriptor should be retrieved from memory, NOT via bus I/O to the
+	 * device. This means that you may have to cache it in a private structure
+	 * during get_device_list enumeration. Alternatively, you may be able
+	 * to retrieve it from a kernel interface (some Linux setups can do this)
+	 * still without generating bus I/O.
+	 *
+	 * This function is expected to write DEVICE_DESC_LENGTH (18) bytes into
+	 * buffer, which is guaranteed to be big enough.
+	 *
+	 * This function is called when sanity-checking a device before adding
+	 * it to the list of discovered devices, and also when the user requests
+	 * to read the device descriptor.
+	 *
+	 * This function is expected to return the descriptor in bus-endian format
+	 * (LE). If it returns the multi-byte values in host-endian format,
+	 * set the host_endian output parameter to "1".
+	 *
+	 * Return 0 on success or a LIBUSB_ERROR code on failure.
+	 */
+	int (*get_device_descriptor)(struct libusb_device *device,
+		unsigned char *buffer, int *host_endian);
+
+	/* Get the ACTIVE configuration descriptor for a device.
+	 *
+	 * The descriptor should be retrieved from memory, NOT via bus I/O to the
+	 * device. This means that you may have to cache it in a private structure
+	 * during get_device_list enumeration. You may also have to keep track
+	 * of which configuration is active when the user changes it.
+	 *
+	 * This function is expected to write len bytes of data into buffer, which
+	 * is guaranteed to be big enough. If you can only do a partial write,
+	 * return an error code.
+	 *
+	 * This function is expected to return the descriptor in bus-endian format
+	 * (LE). If it returns the multi-byte values in host-endian format,
+	 * set the host_endian output parameter to "1".
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the device is in unconfigured state
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*get_active_config_descriptor)(struct libusb_device *device,
+		unsigned char *buffer, size_t len, int *host_endian);
+
+	/* Get a specific configuration descriptor for a device.
+	 *
+	 * The descriptor should be retrieved from memory, NOT via bus I/O to the
+	 * device. This means that you may have to cache it in a private structure
+	 * during get_device_list enumeration.
+	 *
+	 * The requested descriptor is expressed as a zero-based index (i.e. 0
+	 * indicates that we are requesting the first descriptor). The index does
+	 * not (necessarily) equal the bConfigurationValue of the configuration
+	 * being requested.
+	 *
+	 * This function is expected to write len bytes of data into buffer, which
+	 * is guaranteed to be big enough. If you can only do a partial write,
+	 * return an error code.
+	 *
+	 * This function is expected to return the descriptor in bus-endian format
+	 * (LE). If it returns the multi-byte values in host-endian format,
+	 * set the host_endian output parameter to "1".
+	 *
+	 * Return 0 on success or a LIBUSB_ERROR code on failure.
+	 */
+	int (*get_config_descriptor)(struct libusb_device *device,
+		uint8_t config_index, unsigned char *buffer, size_t len,
+		int *host_endian);
+
+	/* Get the bConfigurationValue for the active configuration for a device.
+	 * Optional. This should only be implemented if you can retrieve it from
+	 * cache (don't generate I/O).
+	 *
+	 * If you cannot retrieve this from cache, either do not implement this
+	 * function, or return LIBUSB_ERROR_NOT_SUPPORTED. This will cause
+	 * libusb to retrieve the information through a standard control transfer.
+	 *
+	 * This function must be non-blocking.
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - LIBUSB_ERROR_NOT_SUPPORTED if the value cannot be retrieved without
+	 *   blocking
+	 * - another LIBUSB_ERROR code on other failure.
+	 */
+	int (*get_configuration)(struct libusb_device_handle *handle, int *config);
+
+	/* Set the active configuration for a device.
+	 *
+	 * A configuration value of -1 should put the device in unconfigured state.
+	 *
+	 * This function can block.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
+	 * - LIBUSB_ERROR_BUSY if interfaces are currently claimed (and hence
+	 *   configuration cannot be changed)
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure.
+	 */
+	int (*set_configuration)(struct libusb_device_handle *handle, int config);
+
+	/* Claim an interface. When claimed, the application can then perform
+	 * I/O to an interface's endpoints.
+	 *
+	 * This function should not generate any bus I/O and should not block.
+	 * Interface claiming is a logical operation that simply ensures that
+	 * no other drivers/applications are using the interface, and after
+	 * claiming, no other drivers/applicatiosn can use the interface because
+	 * we now "own" it.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the interface does not exist
+	 * - LIBUSB_ERROR_BUSY if the interface is in use by another driver/app
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*claim_interface)(struct libusb_device_handle *handle, int iface);
+
+	/* Release a previously claimed interface.
+	 *
+	 * This function should also generate a SET_INTERFACE control request,
+	 * resetting the alternate setting of that interface to 0. It's OK for
+	 * this function to block as a result.
+	 *
+	 * You will only ever be asked to release an interface which was
+	 * successfully claimed earlier.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*release_interface)(struct libusb_device_handle *handle, int iface);
+
+	/* Set the alternate setting for an interface.
+	 *
+	 * You will only ever be asked to set the alternate setting for an
+	 * interface which was successfully claimed earlier.
+	 *
+	 * It's OK for this function to block.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the alternate setting does not exist
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*set_interface_altsetting)(struct libusb_device_handle *handle,
+		int iface, int altsetting);
+
+	/* Clear a halt/stall condition on an endpoint.
+	 *
+	 * It's OK for this function to block.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*clear_halt)(struct libusb_device_handle *handle,
+		unsigned char endpoint);
+
+	/* Perform a USB port reset to reinitialize a device.
+	 *
+	 * If possible, the handle should still be usable after the reset
+	 * completes, assuming that the device descriptors did not change during
+	 * reset and all previous interface state can be restored.
+	 *
+	 * If something changes, or you cannot easily locate/verify the resetted
+	 * device, return LIBUSB_ERROR_NOT_FOUND. This prompts the application
+	 * to close the old handle and re-enumerate the device.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if re-enumeration is required, or if the device
+	 *   has been disconnected since it was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*reset_device)(struct libusb_device_handle *handle);
+
+	/* Determine if a kernel driver is active on an interface. Optional.
+	 *
+	 * The presence of a kernel driver on an interface indicates that any
+	 * calls to claim_interface would fail with the LIBUSB_ERROR_BUSY code.
+	 *
+	 * Return:
+	 * - 0 if no driver is active
+	 * - 1 if a driver is active
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*kernel_driver_active)(struct libusb_device_handle *handle,
+		int interface);
+	
+	/* Detach a kernel driver from an interface. Optional.
+	 *
+	 * After detaching a kernel driver, the interface should be available
+	 * for claim.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
+	 * - LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*detach_kernel_driver)(struct libusb_device_handle *handle,
+		int interface);
+
+	/* Attach a kernel driver to an interface. Optional.
+	 *
+	 * Reattach a kernel driver to the device.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
+	 * - LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - LIBUSB_ERROR_BUSY if a program or driver has claimed the interface,
+	 *   preventing reattachment
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*attach_kernel_driver)(struct libusb_device_handle *handle,
+		int interface);
+
+	/* Destroy a device. Optional.
+	 *
+	 * This function is called when the last reference to a device is
+	 * destroyed. It should free any resources allocated in the get_device_list
+	 * path.
+	 */
+	void (*destroy_device)(struct libusb_device *dev);
+
+	/* Submit a transfer. Your implementation should take the transfer,
+	 * morph it into whatever form your platform requires, and submit it
+	 * asynchronously.
+	 *
+	 * This function must not block.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*submit_transfer)(struct usbi_transfer *itransfer);
+
+	/* Cancel a previously submitted transfer.
+	 *
+	 * This function must not block. The transfer cancellation must complete
+	 * later, resulting in a call to usbi_handle_transfer_cancellation()
+	 * from the context of handle_events.
+	 */
+	int (*cancel_transfer)(struct usbi_transfer *itransfer);
+
+	/* Clear a transfer as if it has completed or cancelled, but do not
+	 * report any completion/cancellation to the library. You should free
+	 * all private data from the transfer as if you were just about to report
+	 * completion or cancellation.
+	 *
+	 * This function might seem a bit out of place. It is used when libusb
+	 * detects a disconnected device - it calls this function for all pending
+	 * transfers before reporting completion (with the disconnect code) to
+	 * the user. Maybe we can improve upon this internal interface in future.
+	 */
+	void (*clear_transfer_priv)(struct usbi_transfer *itransfer);
+
+	/* Handle any pending events. This involves monitoring any active
+	 * transfers and processing their completion or cancellation.
+	 *
+	 * The function is passed an array of pollfd structures (size nfds)
+	 * as a result of the poll() system call. The num_ready parameter
+	 * indicates the number of file descriptors that have reported events
+	 * (i.e. the poll() return value). This should be enough information
+	 * for you to determine which actions need to be taken on the currently
+	 * active transfers.
+	 *
+	 * For any cancelled transfers, call usbi_handle_transfer_cancellation().
+	 * For completed transfers, call usbi_handle_transfer_completion().
+	 * For control/bulk/interrupt transfers, populate the "transferred"
+	 * element of the appropriate usbi_transfer structure before calling the
+	 * above functions. For isochronous transfers, populate the status and
+	 * transferred fields of the iso packet descriptors of the transfer.
+	 *
+	 * This function should also be able to detect disconnection of the
+	 * device, reporting that situation with usbi_handle_disconnect().
+	 *
+	 * When processing an event related to a transfer, you probably want to
+	 * take usbi_transfer.lock to prevent races. See the documentation for
+	 * the usbi_transfer structure.
+	 *
+	 * Return 0 on success, or a LIBUSB_ERROR code on failure.
+	 */
+	int (*handle_events)(struct libusb_context *ctx,
+		struct pollfd *fds, nfds_t nfds, int num_ready);
+
+	/* Get time from specified clock. At least two clocks must be implemented
+	   by the backend: USBI_CLOCK_REALTIME, and USBI_CLOCK_MONOTONIC.
+
+	   Description of clocks:
+	     USBI_CLOCK_REALTIME : clock returns time since system epoch.
+	     USBI_CLOCK_MONOTONIC: clock returns time since unspecified start
+	                             time (usually boot).
+	 */
+	int (*clock_gettime)(int clkid, struct timespec *tp);
+
+#ifdef USBI_TIMERFD_AVAILABLE
+	/* clock ID of the clock that should be used for timerfd */
+	clockid_t (*get_timerfd_clockid)(void);
+#endif
+
+	/* Number of bytes to reserve for per-device private backend data.
+	 * This private data area is accessible through the "os_priv" field of
+	 * struct libusb_device. */
+	size_t device_priv_size;
+
+	/* Number of bytes to reserve for per-handle private backend data.
+	 * This private data area is accessible through the "os_priv" field of
+	 * struct libusb_device. */
+	size_t device_handle_priv_size;
+
+	/* Number of bytes to reserve for per-transfer private backend data.
+	 * This private data area is accessible by calling
+	 * usbi_transfer_get_os_priv() on the appropriate usbi_transfer instance.
+	 */
+	size_t transfer_priv_size;
+
+	/* Mumber of additional bytes for os_priv for each iso packet.
+	 * Can your backend use this? */
+	/* FIXME: linux can't use this any more. if other OS's cannot either,
+	 * then remove this */
+	size_t add_iso_packet_size;
+};
+
+extern const struct usbi_os_backend * const usbi_backend;
+
+extern const struct usbi_os_backend linux_usbfs_backend;
+extern const struct usbi_os_backend darwin_backend;
+
+#endif
+
diff --git a/libusb/os/darwin_usb.c b/libusb/os/darwin_usb.c
new file mode 100644
index 0000000..0e69e77
--- /dev/null
+++ b/libusb/os/darwin_usb.c
@@ -0,0 +1,1513 @@
+/*
+ * darwin backend for libusb 1.0
+ * Copyright (C) 2008-2010 Nathan Hjelm <hjelmn@users.sourceforge.net>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <mach/clock.h>
+#include <mach/clock_types.h>
+#include <mach/mach_host.h>
+
+#include <mach/mach_port.h>
+#include <IOKit/IOCFBundle.h>
+#include <IOKit/usb/IOUSBLib.h>
+#include <IOKit/IOCFPlugIn.h>
+
+#include "darwin_usb.h"
+
+static mach_port_t  libusb_darwin_mp = 0; /* master port */
+static CFRunLoopRef libusb_darwin_acfl = NULL; /* async cf loop */
+static int initCount = 0;
+
+/* async event thread */
+static pthread_t libusb_darwin_at;
+
+static int darwin_get_config_descriptor(struct libusb_device *dev, uint8_t config_index, unsigned char *buffer, size_t len, int *host_endian);
+static int darwin_claim_interface(struct libusb_device_handle *dev_handle, int iface);
+static int darwin_release_interface(struct libusb_device_handle *dev_handle, int iface);
+static int darwin_reset_device(struct libusb_device_handle *dev_handle);
+static void darwin_async_io_callback (void *refcon, IOReturn result, void *arg0);
+
+static const char *darwin_error_str (int result) {
+  switch (result) {
+  case kIOReturnSuccess:
+    return "no error";
+  case kIOReturnNotOpen:
+    return "device not opened for exclusive access";
+  case kIOReturnNoDevice:
+    return "no connection to an IOService";
+  case kIOUSBNoAsyncPortErr:
+    return "no async port has been opened for interface";
+  case kIOReturnExclusiveAccess:
+    return "another process has device opened for exclusive access";
+  case kIOUSBPipeStalled:
+    return "pipe is stalled";
+  case kIOReturnError:
+    return "could not establish a connection to the Darwin kernel";
+  case kIOUSBTransactionTimeout:
+    return "transaction timed out";
+  case kIOReturnBadArgument:
+    return "invalid argument";
+  case kIOReturnAborted:
+    return "transaction aborted";
+  case kIOReturnNotResponding:
+    return "device not responding";
+  case kIOReturnOverrun:
+    return "data overrun";
+  case kIOReturnCannotWire:
+    return "physical memory can not be wired down";
+  default:
+    return "unknown error";
+  }
+}
+
+static int darwin_to_libusb (int result) {
+  switch (result) {
+  case kIOReturnSuccess:
+    return LIBUSB_SUCCESS;
+  case kIOReturnNotOpen:
+  case kIOReturnNoDevice:
+    return LIBUSB_ERROR_NO_DEVICE;
+  case kIOReturnExclusiveAccess:
+    return LIBUSB_ERROR_ACCESS;
+  case kIOUSBPipeStalled:
+    return LIBUSB_ERROR_PIPE;
+  case kIOReturnBadArgument:
+    return LIBUSB_ERROR_INVALID_PARAM;
+  case kIOUSBTransactionTimeout:
+    return LIBUSB_ERROR_TIMEOUT;
+  case kIOReturnNotResponding:
+  case kIOReturnAborted:
+  case kIOReturnError:
+  case kIOUSBNoAsyncPortErr:
+  default:
+    return LIBUSB_ERROR_OTHER;
+  }
+}
+
+
+static int ep_to_pipeRef(struct libusb_device_handle *dev_handle, uint8_t ep, uint8_t *pipep, uint8_t *ifcp) {
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)dev_handle->os_priv;
+
+  /* current interface */
+  struct __darwin_interface *cInterface;
+
+  int8_t i, iface;
+
+  usbi_info (HANDLE_CTX(dev_handle), "converting ep address 0x%02x to pipeRef and interface", ep);
+
+  for (iface = 0 ; iface < USB_MAXINTERFACES ; iface++) {
+    cInterface = &priv->interfaces[iface];
+
+    if (dev_handle->claimed_interfaces & (1 << iface)) {
+      for (i = 0 ; i < cInterface->num_endpoints ; i++) {
+	if (cInterface->endpoint_addrs[i] == ep) {
+	  *pipep = i + 1;
+	  *ifcp = iface;
+	  usbi_info (HANDLE_CTX(dev_handle), "pipe %d on interface %d matches", *pipep, *ifcp);
+	  return 0;
+	}
+      }
+    }
+  }
+
+  /* No pipe found with the correct endpoint address */
+  usbi_warn (HANDLE_CTX(dev_handle), "no pipeRef found with endpoint address 0x%02x.", ep);
+  
+  return -1;
+}
+
+static int usb_setup_device_iterator (io_iterator_t *deviceIterator) {
+  return IOServiceGetMatchingServices(libusb_darwin_mp, IOServiceMatching(kIOUSBDeviceClassName), deviceIterator);
+}
+
+static usb_device_t **usb_get_next_device (io_iterator_t deviceIterator, UInt32 *locationp) {
+  io_cf_plugin_ref_t *plugInInterface = NULL;
+  usb_device_t **device;
+  io_service_t usbDevice;
+  long result;
+  SInt32 score;
+
+  if (!IOIteratorIsValid (deviceIterator))
+    return NULL;
+
+
+  while ((usbDevice = IOIteratorNext(deviceIterator))) {
+    result = IOCreatePlugInInterfaceForService(usbDevice, kIOUSBDeviceUserClientTypeID,
+					       kIOCFPlugInInterfaceID, &plugInInterface,
+					       &score);
+    if (kIOReturnSuccess == result && plugInInterface)
+      break;
+
+    usbi_dbg ("libusb/darwin.c usb_get_next_device: could not set up plugin for service: %s\n", darwin_error_str (result));
+  }
+
+  if (!usbDevice)
+    return NULL;
+
+  (void)IOObjectRelease(usbDevice);
+  (void)(*plugInInterface)->QueryInterface(plugInInterface, CFUUIDGetUUIDBytes(DeviceInterfaceID),
+					   (LPVOID)&device);
+
+  (*plugInInterface)->Stop(plugInInterface);
+  IODestroyPlugInInterface (plugInInterface);
+  
+  (*(device))->GetLocationID(device, locationp);
+
+  return device;
+}
+
+static kern_return_t darwin_get_device (uint32_t dev_location, usb_device_t ***darwin_device) {
+  kern_return_t kresult;
+  UInt32        location;
+  io_iterator_t deviceIterator;
+
+  kresult = usb_setup_device_iterator (&deviceIterator);
+  if (kresult)
+    return kresult;
+
+  /* This port of libusb uses locations to keep track of devices. */
+  while ((*darwin_device = usb_get_next_device (deviceIterator, &location)) != NULL) {
+    if (location == dev_location)
+      break;
+
+    (**darwin_device)->Release(*darwin_device);
+  }
+
+  IOObjectRelease (deviceIterator);
+
+  if (!(*darwin_device))
+    return kIOReturnNoDevice;
+
+  return kIOReturnSuccess;
+}
+
+
+
+static void darwin_devices_detached (void *ptr, io_iterator_t rem_devices) {  
+  struct libusb_context *ctx = (struct libusb_context *)ptr;
+  struct libusb_device_handle *handle;
+  struct darwin_device_priv *dpriv;
+  struct darwin_device_handle_priv *priv;
+
+  io_service_t device;
+  long location;
+  CFTypeRef locationCF;
+  UInt32 message;
+
+  usbi_info (ctx, "a device has been detached");
+
+  while ((device = IOIteratorNext (rem_devices)) != 0) {
+    /* get the location from the i/o registry */
+    locationCF = IORegistryEntryCreateCFProperty (device, CFSTR(kUSBDevicePropertyLocationID), kCFAllocatorDefault, 0);
+
+    CFNumberGetValue(locationCF, kCFNumberLongType, &location);
+    CFRelease (locationCF);
+    IOObjectRelease (device);
+
+    pthread_mutex_lock(&ctx->open_devs_lock);
+    list_for_each_entry(handle, &ctx->open_devs, list) {
+      dpriv = (struct darwin_device_priv *)handle->dev->os_priv;
+
+      /* the device may have been opened several times. write to each handle's event descriptor */
+      if (dpriv->location == location  && handle->os_priv) {
+	priv  = (struct darwin_device_handle_priv *)handle->os_priv;
+
+	message = MESSAGE_DEVICE_GONE;
+	write (priv->fds[1], &message, sizeof (message));
+      }
+    }
+
+    pthread_mutex_unlock(&ctx->open_devs_lock);
+  }
+}
+
+static void darwin_clear_iterator (io_iterator_t iter) {
+  io_service_t device;
+
+  while ((device = IOIteratorNext (iter)) != 0)
+    IOObjectRelease (device);
+}
+
+static void *event_thread_main (void *arg0) {
+  IOReturn kresult;
+  struct libusb_context *ctx = (struct libusb_context *)arg0;
+
+  /* hotplug (device removal) source */
+  CFRunLoopSourceRef     libusb_notification_cfsource;
+  io_notification_port_t libusb_notification_port;
+  io_iterator_t          libusb_rem_device_iterator;
+
+  usbi_info (ctx, "creating hotplug event source");
+
+  CFRetain (CFRunLoopGetCurrent ());
+
+  /* add the notification port to the run loop */
+  libusb_notification_port     = IONotificationPortCreate (libusb_darwin_mp);
+  libusb_notification_cfsource = IONotificationPortGetRunLoopSource (libusb_notification_port);
+  CFRunLoopAddSource(CFRunLoopGetCurrent (), libusb_notification_cfsource, kCFRunLoopDefaultMode);
+
+  /* create notifications for removed devices */
+  kresult = IOServiceAddMatchingNotification (libusb_notification_port, kIOTerminatedNotification,
+					      IOServiceMatching(kIOUSBDeviceClassName),
+					      (IOServiceMatchingCallback)darwin_devices_detached,
+					      (void *)ctx, &libusb_rem_device_iterator);
+ 
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (ctx, "could not add hotplug event source: %s", darwin_error_str (kresult));
+
+    pthread_exit ((void *)kresult);
+  }
+
+  /* arm notifiers */
+  darwin_clear_iterator (libusb_rem_device_iterator);
+
+  /* let the main thread know about the async runloop */
+  libusb_darwin_acfl = CFRunLoopGetCurrent ();
+
+  usbi_info (ctx, "libopenusb/darwin.c event_thread_main: thread ready to receive events");
+
+  /* run the runloop */
+  CFRunLoopRun();
+
+  usbi_info (ctx, "libopenusb/darwin.c event_thread_main: thread exiting");
+
+  /* delete notification port */
+  CFRunLoopSourceInvalidate (libusb_notification_cfsource);
+  IONotificationPortDestroy (libusb_notification_port);
+
+  CFRelease (CFRunLoopGetCurrent ());
+
+  libusb_darwin_acfl = NULL;
+
+  pthread_exit (0);
+}
+
+static int darwin_init(struct libusb_context *ctx) {
+  IOReturn kresult;
+
+  if (!(initCount++)) {
+    /* Create the master port for talking to IOKit */
+    if (!libusb_darwin_mp) {
+      kresult = IOMasterPort (MACH_PORT_NULL, &libusb_darwin_mp);
+
+      if (kresult != kIOReturnSuccess || !libusb_darwin_mp)
+	return darwin_to_libusb (kresult);
+    }
+
+    pthread_create (&libusb_darwin_at, NULL, event_thread_main, (void *)ctx);
+
+    while (!libusb_darwin_acfl)
+      usleep (10);
+  }
+
+  return 0;
+}
+
+static void darwin_exit (void) {
+  if (!(--initCount)) {
+    void *ret;
+
+    /* stop the async runloop */
+    CFRunLoopStop (libusb_darwin_acfl);
+    pthread_join (libusb_darwin_at, &ret);
+
+    if (libusb_darwin_mp)
+      mach_port_deallocate(mach_task_self(), libusb_darwin_mp);
+
+    libusb_darwin_mp = 0;
+  }
+}
+
+static int darwin_get_device_descriptor(struct libusb_device *dev, unsigned char *buffer, int *host_endian) {
+  struct darwin_device_priv *priv = (struct darwin_device_priv *)dev->os_priv;
+
+  /* return cached copy */
+  memmove (buffer, &(priv->dev_descriptor), DEVICE_DESC_LENGTH);
+
+  *host_endian = 0;
+
+  return 0;
+}
+
+static int get_configuration_index (struct libusb_device *dev, int config_value) {
+  struct darwin_device_priv *priv = (struct darwin_device_priv *)dev->os_priv;
+  UInt8 i, numConfig;
+  IOUSBConfigurationDescriptorPtr desc;
+  IOReturn kresult;
+
+  /* is there a simpler way to determine the index? */
+  kresult = (*(priv->device))->GetNumberOfConfigurations (priv->device, &numConfig);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  for (i = 0 ; i < numConfig ; i++) {
+    (*(priv->device))->GetConfigurationDescriptorPtr (priv->device, i, &desc);
+
+    if (libusb_le16_to_cpu (desc->bConfigurationValue) == config_value)
+      return i;
+  }
+
+  /* configuration not found */
+  return LIBUSB_ERROR_OTHER;
+}
+
+static int darwin_get_active_config_descriptor(struct libusb_device *dev, unsigned char *buffer, size_t len, int *host_endian) {
+  struct darwin_device_priv *priv = (struct darwin_device_priv *)dev->os_priv;
+  UInt8 config_value;
+  int config_index;
+  IOReturn kresult;
+
+  kresult = (*(priv->device))->GetConfiguration (priv->device, &config_value);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  config_index = get_configuration_index (dev, config_value);
+  if (config_index < 0)
+    return config_index;
+
+  return darwin_get_config_descriptor (dev, config_index, buffer, len, host_endian);
+}
+
+static int darwin_get_config_descriptor(struct libusb_device *dev, uint8_t config_index, unsigned char *buffer, size_t len, int *host_endian) {
+  struct darwin_device_priv *priv = (struct darwin_device_priv *)dev->os_priv;
+  IOUSBConfigurationDescriptorPtr desc;
+  IOReturn kresult;
+  usb_device_t **device = NULL;
+
+  if (!priv)
+    return LIBUSB_ERROR_OTHER;
+
+  if (!priv->device) {
+    kresult = darwin_get_device (priv->location, &device);
+    if (kresult || !device) {
+      usbi_err (DEVICE_CTX (dev), "could not find device: %s", darwin_error_str (kresult));
+
+      return darwin_to_libusb (kresult);
+    }
+
+    /* don't have to open the device to get a config descriptor */
+  } else
+    device = priv->device;
+
+  kresult = (*device)->GetConfigurationDescriptorPtr (device, config_index, &desc);
+  if (kresult == kIOReturnSuccess) {
+    /* copy descriptor */
+    if (libusb_le16_to_cpu(desc->wTotalLength) < len)
+      len = libusb_le16_to_cpu(desc->wTotalLength);
+
+    memmove (buffer, desc, len);
+
+    /* GetConfigurationDescriptorPtr returns the descriptor in USB bus order */
+    *host_endian = 0;
+  }
+
+  if (!priv->device)
+    (*device)->Release (device);
+
+  return darwin_to_libusb (kresult);
+}
+
+static int process_new_device (struct libusb_context *ctx, usb_device_t **device, UInt32 locationID, struct discovered_devs **_discdevs) {
+  struct darwin_device_priv *priv;
+  struct libusb_device *dev; 
+  struct discovered_devs *discdevs;
+  UInt16                address, idVendor, idProduct;
+  UInt8                 bDeviceClass, bDeviceSubClass;
+  IOUSBDevRequest      req;
+  int ret = 0, need_unref = 0;
+
+  do {
+    dev = usbi_get_device_by_session_id(ctx, locationID);
+    if (!dev) {
+      usbi_info (ctx, "allocating new device for location 0x%08x", locationID);
+      dev = usbi_alloc_device(ctx, locationID);
+      need_unref = 1;
+    } else
+      usbi_info (ctx, "using existing device for location 0x%08x", locationID);
+
+    if (!dev) {
+      ret = LIBUSB_ERROR_NO_MEM;
+      break;
+    }
+
+    priv = (struct darwin_device_priv *)dev->os_priv;
+
+    /* Set up request for device descriptor */
+    req.bmRequestType = USBmakebmRequestType(kUSBIn, kUSBStandard, kUSBDevice);
+    req.bRequest      = kUSBRqGetDescriptor;
+    req.wValue        = kUSBDeviceDesc << 8;
+    req.wIndex        = 0;
+    req.wLength       = sizeof(IOUSBDeviceDescriptor);
+    req.pData         = &(priv->dev_descriptor);
+    
+    (*(device))->GetDeviceAddress (device, (USBDeviceAddress *)&address);
+    (*(device))->GetDeviceProduct (device, &idProduct);
+    (*(device))->GetDeviceVendor (device, &idVendor);
+    (*(device))->GetDeviceClass (device, &bDeviceClass);
+    (*(device))->GetDeviceSubClass (device, &bDeviceSubClass);
+
+    /**** retrieve device descriptors ****/
+    /* device must be open for DeviceRequest */
+    (*device)->USBDeviceOpen(device);
+
+    ret = (*(device))->DeviceRequest (device, &req);
+    if (ret != kIOReturnSuccess) {
+      int try_unsuspend = 1;
+#if DeviceVersion >= 320
+      UInt32 info;
+
+      /* device may be suspended. unsuspend it and try again */
+      /* IOUSBFamily 320+ provides a way to detect device suspension but earlier versions do not */
+      (void)(*device)->GetUSBDeviceInformation (device, &info);
+
+      try_unsuspend = info & (1 << kUSBInformationDeviceIsSuspendedBit);
+#endif
+
+      if (try_unsuspend) {
+	/* resume the device */
+	(void)(*device)->USBDeviceSuspend (device, 0);
+
+	ret = (*(device))->DeviceRequest (device, &req);
+
+	/* resuspend the device */
+	(void)(*device)->USBDeviceSuspend (device, 1);
+      }
+    }
+
+    (*device)->USBDeviceClose (device);
+
+    if (ret != kIOReturnSuccess) {
+      usbi_warn (ctx, "could not retrieve device descriptor: %s. skipping device", darwin_error_str (ret));
+      ret = -1;
+      break;
+    }
+
+    /**** end: retrieve device descriptors ****/
+    
+    /* catch buggy hubs (which appear to be virtual). Apple's own USB prober has problems with these devices. */
+    if (libusb_le16_to_cpu (priv->dev_descriptor.idProduct) != idProduct) {
+      /* not a valid device */
+      usbi_warn (ctx, "idProduct from iokit (%04x) does not match idProduct in descriptor (%04x). skipping device",
+		 idProduct, libusb_le16_to_cpu (priv->dev_descriptor.idProduct));
+      ret = -1;
+      break;
+    }
+
+    dev->bus_number     = locationID >> 24;
+    dev->device_address = address;
+
+    /* save our location, we'll need this later */
+    priv->location = locationID;
+    snprintf(priv->sys_path, 20, "%03i-%04x-%04x-%02x-%02x", address, idVendor, idProduct, bDeviceClass, bDeviceSubClass);
+
+    ret = usbi_sanitize_device (dev);
+    if (ret < 0)
+      break;
+
+    /* append the device to the list of discovered devices */
+    discdevs = discovered_devs_append(*_discdevs, dev);
+    if (!discdevs) {
+      ret = LIBUSB_ERROR_NO_MEM;
+      break;
+    }
+    
+    *_discdevs = discdevs;
+  
+    usbi_info (ctx, "found device with address %d at %s", dev->device_address, priv->sys_path);
+  } while (0);
+
+  if (need_unref)
+    libusb_unref_device(dev);
+
+  return ret;
+}
+
+static int darwin_get_device_list(struct libusb_context *ctx, struct discovered_devs **_discdevs) {
+  io_iterator_t        deviceIterator;
+  usb_device_t         **device;
+  kern_return_t        kresult;
+  UInt32               location;
+
+  if (!libusb_darwin_mp)
+    return LIBUSB_ERROR_INVALID_PARAM;
+  
+  kresult = usb_setup_device_iterator (&deviceIterator);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  while ((device = usb_get_next_device (deviceIterator, &location)) != NULL) {
+    (void) process_new_device (ctx, device, location, _discdevs);
+
+    (*(device))->Release(device);
+  }
+
+  IOObjectRelease(deviceIterator);
+
+  return 0;
+}
+
+static int darwin_open (struct libusb_device_handle *dev_handle) {
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)dev_handle->os_priv;
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)dev_handle->dev->os_priv;
+  usb_device_t  **darwin_device;
+  IOReturn kresult;
+
+  if (0 == dpriv->open_count) {
+    kresult = darwin_get_device (dpriv->location, &darwin_device);
+    if (kresult) {
+      usbi_err (HANDLE_CTX (dev_handle), "could not find device: %s", darwin_error_str (kresult));
+      return darwin_to_libusb (kresult);
+    }
+
+    dpriv->device = darwin_device;
+
+    /* try to open the device */
+    kresult = (*(dpriv->device))->USBDeviceOpenSeize (dpriv->device);
+
+    if (kresult != kIOReturnSuccess) {
+      usbi_err (HANDLE_CTX (dev_handle), "USBDeviceOpen: %s", darwin_error_str(kresult));
+
+      switch (kresult) {
+      case kIOReturnExclusiveAccess:
+	/* it is possible to perform some actions on a device that is not open so do not return an error */
+	priv->is_open = 0;
+
+	break;
+      default:
+	(*(dpriv->device))->Release (dpriv->device);
+	dpriv->device = NULL;
+	return darwin_to_libusb (kresult);
+      }
+    } else {
+      priv->is_open = 1;
+
+      /* create async event source */
+      kresult = (*(dpriv->device))->CreateDeviceAsyncEventSource (dpriv->device, &priv->cfSource);
+
+      CFRetain (libusb_darwin_acfl);
+
+      /* add the cfSource to the aync run loop */
+      CFRunLoopAddSource(libusb_darwin_acfl, priv->cfSource, kCFRunLoopCommonModes);
+    }
+  }
+
+  /* device opened successfully */
+  dpriv->open_count++;
+
+  /* create a file descriptor for notifications */
+  pipe (priv->fds);
+
+  /* set the pipe to be non-blocking */
+  fcntl (priv->fds[1], F_SETFD, O_NONBLOCK);
+
+  usbi_add_pollfd(HANDLE_CTX(dev_handle), priv->fds[0], POLLIN);
+
+  usbi_info (HANDLE_CTX (dev_handle), "device open for access");
+
+  return 0;
+}
+
+static void darwin_close (struct libusb_device_handle *dev_handle) {
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)dev_handle->os_priv;
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)dev_handle->dev->os_priv;
+  IOReturn kresult;
+  int i;
+
+  if (dpriv->open_count == 0) {
+    /* something is probably very wrong if this is the case */
+    usbi_err (HANDLE_CTX (dev_handle), "Close called on a device that was not open!\n");
+    return;
+  }
+
+  dpriv->open_count--;
+
+  /* make sure all interfaces are released */
+  for (i = 0 ; i < USB_MAXINTERFACES ; i++)
+    if (dev_handle->claimed_interfaces & (1 << i))
+      libusb_release_interface (dev_handle, i);
+
+  if (0 == dpriv->open_count) {
+    if (priv->is_open) {
+      /* delete the device's async event source */
+      if (priv->cfSource) {
+	CFRunLoopRemoveSource (libusb_darwin_acfl, priv->cfSource, kCFRunLoopDefaultMode);
+	CFRelease (priv->cfSource);
+      }
+
+      /* close the device */
+      kresult = (*(dpriv->device))->USBDeviceClose(dpriv->device);
+      if (kresult) {
+	/* Log the fact that we had a problem closing the file, however failing a
+	 * close isn't really an error, so return success anyway */
+	usbi_err (HANDLE_CTX (dev_handle), "USBDeviceClose: %s", darwin_error_str(kresult));
+      }
+    }
+  
+    kresult = (*(dpriv->device))->Release(dpriv->device);
+    if (kresult) {
+      /* Log the fact that we had a problem closing the file, however failing a
+       * close isn't really an error, so return success anyway */
+      usbi_err (HANDLE_CTX (dev_handle), "Release: %s", darwin_error_str(kresult));
+    }
+
+    dpriv->device = NULL;
+  }
+
+  /* file descriptors are maintained per-instance */
+  usbi_remove_pollfd (HANDLE_CTX (dev_handle), priv->fds[0]);
+  close (priv->fds[1]);
+  close (priv->fds[0]);
+
+  priv->fds[0] = priv->fds[1] = -1;
+}
+
+static int darwin_get_configuration(struct libusb_device_handle *dev_handle, int *config) {
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)dev_handle->dev->os_priv;
+  UInt8 configNum;
+  IOReturn kresult;
+
+  kresult = (*(dpriv->device))->GetConfiguration (dpriv->device, &configNum);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  *config = (int) configNum;
+
+  return 0;
+}
+
+static int darwin_set_configuration(struct libusb_device_handle *dev_handle, int config) {
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)dev_handle->dev->os_priv;
+  IOReturn kresult;
+  int i;
+
+  /* Setting configuration will invalidate the interface, so we need
+     to reclaim it. First, dispose of existing interfaces, if any. */
+  for (i = 0 ; i < USB_MAXINTERFACES ; i++)
+    if (dev_handle->claimed_interfaces & (1 << i))
+      darwin_release_interface (dev_handle, i);
+
+  kresult = (*(dpriv->device))->SetConfiguration (dpriv->device, config);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  /* Reclaim any interfaces. */
+  for (i = 0 ; i < USB_MAXINTERFACES ; i++)
+    if (dev_handle->claimed_interfaces & (1 << i))
+      darwin_claim_interface (dev_handle, i);
+
+  return 0;
+}
+
+static int darwin_get_interface (usb_device_t **darwin_device, uint8_t ifc, io_service_t *usbInterfacep) {
+  IOUSBFindInterfaceRequest request;
+  uint8_t                   current_interface;
+  kern_return_t             kresult;
+  io_iterator_t             interface_iterator;
+
+  *usbInterfacep = IO_OBJECT_NULL;
+  
+  /* Setup the Interface Request */
+  request.bInterfaceClass    = kIOUSBFindInterfaceDontCare;
+  request.bInterfaceSubClass = kIOUSBFindInterfaceDontCare;
+  request.bInterfaceProtocol = kIOUSBFindInterfaceDontCare;
+  request.bAlternateSetting  = kIOUSBFindInterfaceDontCare;
+
+  kresult = (*(darwin_device))->CreateInterfaceIterator(darwin_device, &request, &interface_iterator);
+  if (kresult)
+    return kresult;
+
+  for ( current_interface = 0 ; current_interface <= ifc ; current_interface++ )
+    *usbInterfacep = IOIteratorNext(interface_iterator);
+  
+  /* done with the interface iterator */
+  IOObjectRelease(interface_iterator);
+  
+  return 0;
+}
+
+static int get_endpoints (struct libusb_device_handle *dev_handle, int iface) {
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)dev_handle->os_priv;
+
+  /* current interface */
+  struct __darwin_interface *cInterface = &priv->interfaces[iface];
+
+  kern_return_t kresult;
+
+  u_int8_t numep, direction, number;
+  u_int8_t dont_care1, dont_care3;
+  u_int16_t dont_care2;
+  int i;
+
+  usbi_info (HANDLE_CTX (dev_handle), "building table of endpoints.");
+  
+  /* retrieve the total number of endpoints on this interface */
+  kresult = (*(cInterface->interface))->GetNumEndpoints(cInterface->interface, &numep);
+  if (kresult) {
+    usbi_err (HANDLE_CTX (dev_handle), "can't get number of endpoints for interface: %s", darwin_error_str(kresult));
+    return darwin_to_libusb (kresult);
+  }
+
+  /* iterate through pipe references */
+  for (i = 1 ; i <= numep ; i++) {
+    kresult = (*(cInterface->interface))->GetPipeProperties(cInterface->interface, i, &direction, &number, &dont_care1,
+							    &dont_care2, &dont_care3);
+
+    if (kresult != kIOReturnSuccess) {
+      usbi_err (HANDLE_CTX (dev_handle), "error getting pipe information for pipe %d: %s", i, darwin_error_str(kresult));
+
+      return darwin_to_libusb (kresult);
+    }
+
+    usbi_info (HANDLE_CTX (dev_handle), "interface: %i pipe %i: dir: %i number: %i", iface, i, direction, number);
+
+    cInterface->endpoint_addrs[i - 1] = ((direction << 7 & LIBUSB_ENDPOINT_DIR_MASK) | (number & LIBUSB_ENDPOINT_ADDRESS_MASK));
+  }
+
+  cInterface->num_endpoints = numep;
+  
+  return 0;
+}
+
+static int darwin_claim_interface(struct libusb_device_handle *dev_handle, int iface) {
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)dev_handle->dev->os_priv;
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)dev_handle->os_priv;
+  io_service_t          usbInterface = IO_OBJECT_NULL;
+  IOReturn kresult;
+  IOCFPlugInInterface **plugInInterface = NULL;
+  SInt32                score;
+  uint8_t               new_config;
+
+  /* current interface */
+  struct __darwin_interface *cInterface = &priv->interfaces[iface];
+
+  kresult = darwin_get_interface (dpriv->device, iface, &usbInterface);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  /* make sure we have an interface */
+  if (!usbInterface) {
+    u_int8_t nConfig;     /* Index of configuration to use */
+    IOUSBConfigurationDescriptorPtr configDesc; /* to describe which configuration to select */
+    /* Only a composite class device with no vendor-specific driver will
+       be configured. Otherwise, we need to do it ourselves, or there
+       will be no interfaces for the device. */
+
+    usbi_info (HANDLE_CTX (dev_handle), "no interface found; selecting configuration" );
+
+    kresult = (*(dpriv->device))->GetNumberOfConfigurations (dpriv->device, &nConfig);
+    if (kresult != kIOReturnSuccess) {
+      usbi_err (HANDLE_CTX (dev_handle), "GetNumberOfConfigurations: %s", darwin_error_str(kresult));
+      return darwin_to_libusb(kresult);
+    }
+    
+    if (nConfig < 1) {
+      usbi_err (HANDLE_CTX (dev_handle), "GetNumberOfConfigurations: no configurations");
+      return LIBUSB_ERROR_OTHER;
+    }
+
+    usbi_info (HANDLE_CTX (dev_handle), "device has %d configuration%s. using the first",
+	      (int)nConfig, (nConfig > 1 ? "s" : "") );
+
+    /* Always use the first configuration */
+    kresult = (*(dpriv->device))->GetConfigurationDescriptorPtr (dpriv->device, 0, &configDesc);
+    if (kresult != kIOReturnSuccess) {
+      usbi_err (HANDLE_CTX (dev_handle), "GetConfigurationDescriptorPtr: %s",
+		darwin_error_str(kresult));
+
+      new_config = 1;
+    } else
+      new_config = configDesc->bConfigurationValue;
+
+    usbi_info (HANDLE_CTX (dev_handle), "new configuration value is %d", new_config);
+
+    /* set the configuration */
+    kresult = darwin_set_configuration (dev_handle, new_config);
+    if (kresult != LIBUSB_SUCCESS) {
+      usbi_err (HANDLE_CTX (dev_handle), "could not set configuration");
+      return kresult;
+    }
+
+    kresult = darwin_get_interface (dpriv->device, iface, &usbInterface);
+    if (kresult) {
+      usbi_err (HANDLE_CTX (dev_handle), "darwin_get_interface: %s", darwin_error_str(kresult));
+      return darwin_to_libusb (kresult);
+    }
+  }
+
+  if (!usbInterface) {
+    usbi_err (HANDLE_CTX (dev_handle), "interface not found");
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+  
+  /* get an interface to the device's interface */
+  kresult = IOCreatePlugInInterfaceForService (usbInterface, kIOUSBInterfaceUserClientTypeID,
+					       kIOCFPlugInInterfaceID, &plugInInterface, &score);
+  if (kresult) {
+    usbi_err (HANDLE_CTX (dev_handle), "IOCreatePlugInInterfaceForService: %s", darwin_error_str(kresult));
+    return darwin_to_libusb (kresult);
+  }
+
+  if (!plugInInterface) {
+    usbi_err (HANDLE_CTX (dev_handle), "plugin interface not found");
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  /* ignore release error */
+  (void)IOObjectRelease (usbInterface);
+  
+  /* Do the actual claim */
+  kresult = (*plugInInterface)->QueryInterface(plugInInterface,
+					       CFUUIDGetUUIDBytes(kIOUSBInterfaceInterfaceID),
+					       (LPVOID)&cInterface->interface);
+  if (kresult || !cInterface->interface) {
+    usbi_err (HANDLE_CTX (dev_handle), "QueryInterface: %s", darwin_error_str(kresult));
+    return darwin_to_libusb (kresult);
+  }
+  
+  /* We no longer need the intermediate plug-in */
+  (*plugInInterface)->Release(plugInInterface);
+
+  /* claim the interface */
+  kresult = (*(cInterface->interface))->USBInterfaceOpen(cInterface->interface);
+  if (kresult) {
+    usbi_err (HANDLE_CTX (dev_handle), "USBInterfaceOpen: %s", darwin_error_str(kresult));
+    return darwin_to_libusb (kresult);
+  }
+
+  /* update list of endpoints */
+  kresult = get_endpoints (dev_handle, iface);
+  if (kresult) {
+    /* this should not happen */
+    darwin_release_interface (dev_handle, iface);
+    usbi_err (HANDLE_CTX (dev_handle), "could not build endpoint table");
+    return kresult;
+  }
+
+  cInterface->cfSource = NULL;
+
+  /* create async event source */
+  kresult = (*(cInterface->interface))->CreateInterfaceAsyncEventSource (cInterface->interface, &cInterface->cfSource);
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (HANDLE_CTX (dev_handle), "could not create async event source");
+
+    /* can't continue without an async event source */
+    (void)darwin_release_interface (dev_handle, iface);
+
+    return darwin_to_libusb (kresult);
+  }
+
+  /* add the cfSource to the async thread's run loop */
+  CFRunLoopAddSource(libusb_darwin_acfl, cInterface->cfSource, kCFRunLoopDefaultMode);
+
+  usbi_info (HANDLE_CTX (dev_handle), "interface opened");
+
+  return 0;
+}
+
+static int darwin_release_interface(struct libusb_device_handle *dev_handle, int iface) {
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)dev_handle->os_priv;
+  IOReturn kresult;
+
+  /* current interface */
+  struct __darwin_interface *cInterface = &priv->interfaces[iface];
+
+  /* Check to see if an interface is open */
+  if (!cInterface->interface)
+    return LIBUSB_SUCCESS;
+
+  /* clean up endpoint data */
+  cInterface->num_endpoints = 0;
+  
+  /* delete the interface's async event source */
+  if (cInterface->cfSource) {
+    CFRunLoopRemoveSource (libusb_darwin_acfl, cInterface->cfSource, kCFRunLoopDefaultMode);
+    CFRelease (cInterface->cfSource);
+  }
+
+  kresult = (*(cInterface->interface))->USBInterfaceClose(cInterface->interface);
+  if (kresult)
+    usbi_err (HANDLE_CTX (dev_handle), "USBInterfaceClose: %s", darwin_error_str(kresult));
+
+  kresult = (*(cInterface->interface))->Release(cInterface->interface);
+  if (kresult != kIOReturnSuccess)
+    usbi_err (HANDLE_CTX (dev_handle), "Release: %s", darwin_error_str(kresult));
+
+  cInterface->interface = IO_OBJECT_NULL;
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_set_interface_altsetting(struct libusb_device_handle *dev_handle, int iface, int altsetting) {
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)dev_handle->os_priv;
+  IOReturn kresult;
+
+  /* current interface */
+  struct __darwin_interface *cInterface = &priv->interfaces[iface];
+
+  if (!cInterface->interface)
+    return LIBUSB_ERROR_NO_DEVICE;
+
+  kresult = (*(cInterface->interface))->SetAlternateInterface (cInterface->interface, altsetting);
+  if (kresult != kIOReturnSuccess)
+    darwin_reset_device (dev_handle);
+
+  /* update list of endpoints */
+  kresult = get_endpoints (dev_handle, iface);
+  if (kresult) {
+    /* this should not happen */
+    darwin_release_interface (dev_handle, iface);
+    usbi_err (HANDLE_CTX (dev_handle), "could not build endpoint table");
+    return kresult;
+  }
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_clear_halt(struct libusb_device_handle *dev_handle, unsigned char endpoint) {
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)dev_handle->os_priv;
+
+  /* current interface */
+  struct __darwin_interface *cInterface;
+  uint8_t pipeRef, iface;
+  IOReturn kresult;
+
+  /* determine the interface/endpoint to use */
+  if (ep_to_pipeRef (dev_handle, endpoint, &pipeRef, &iface) != 0) {
+    usbi_err (HANDLE_CTX (dev_handle), "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  cInterface = &priv->interfaces[iface];
+
+#if (InterfaceVersion < 190)
+  kresult = (*(cInterface->interface))->ClearPipeStall(cInterface->interface, pipeRef);
+#else
+  /* newer versions of darwin support clearing additional bits on the device's endpoint */
+  kresult = (*(cInterface->interface))->ClearPipeStallBothEnds(cInterface->interface, pipeRef);
+#endif
+  if (kresult)
+    usbi_err (HANDLE_CTX (dev_handle), "ClearPipeStall: %s", darwin_error_str (kresult));
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_reset_device(struct libusb_device_handle *dev_handle) {
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)dev_handle->dev->os_priv;
+  IOReturn kresult;
+
+  kresult = (*(dpriv->device))->ResetDevice (dpriv->device);
+  if (kresult)
+    usbi_err (HANDLE_CTX (dev_handle), "ResetDevice: %s", darwin_error_str (kresult));
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_kernel_driver_active(struct libusb_device_handle *dev_handle, int interface) {
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)dev_handle->dev->os_priv;
+  io_service_t usbInterface;
+  CFTypeRef driver;
+  IOReturn kresult;
+
+  kresult = darwin_get_interface (dpriv->device, interface, &usbInterface);
+  if (kresult) {
+    usbi_err (HANDLE_CTX (dev_handle), "darwin_get_interface: %s", darwin_error_str(kresult));
+
+    return darwin_to_libusb (kresult);
+  }
+  
+  driver = IORegistryEntryCreateCFProperty (usbInterface, kIOBundleIdentifierKey, kCFAllocatorDefault, 0);
+  IOObjectRelease (usbInterface);
+
+  if (driver) {
+    CFRelease (driver);
+
+    return 1;
+  }
+
+  /* no driver */
+  return 0;
+}
+
+/* attaching/detaching kernel drivers is not currently supported (maybe in the future?) */
+static int darwin_attach_kernel_driver (struct libusb_device_handle *dev_handle, int interface) {
+  return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int darwin_detach_kernel_driver (struct libusb_device_handle *dev_handle, int interface) {
+  return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static void darwin_destroy_device(struct libusb_device *dev) {
+}
+
+static int submit_bulk_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)transfer->dev_handle->os_priv;
+
+  IOReturn               ret;
+  uint8_t                is_read; /* 0 = we're reading, 1 = we're writing */
+  uint8_t                transferType;
+  /* None of the values below are used in libusb for bulk transfers */
+  uint8_t                direction, number, interval, pipeRef, iface;
+  uint16_t               maxPacketSize;
+
+  struct __darwin_interface *cInterface;
+
+  /* are we reading or writing? */
+  is_read = transfer->endpoint & LIBUSB_ENDPOINT_IN;
+  
+  if (ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, &iface) != 0) {
+    usbi_err (TRANSFER_CTX (transfer), "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  cInterface = &priv->interfaces[iface];
+
+  (*(cInterface->interface))->GetPipeProperties (cInterface->interface, pipeRef, &direction, &number,
+						 &transferType, &maxPacketSize, &interval);
+  
+  /* submit the request */
+  /* timeouts are unavailable on interrupt endpoints */
+  if (transferType == kUSBInterrupt) {
+    if (is_read)
+      ret = (*(cInterface->interface))->ReadPipeAsync(cInterface->interface, pipeRef, transfer->buffer,
+						      transfer->length, darwin_async_io_callback, itransfer);
+    else
+      ret = (*(cInterface->interface))->WritePipeAsync(cInterface->interface, pipeRef, transfer->buffer,
+						       transfer->length, darwin_async_io_callback, itransfer);
+  } else {
+    if (is_read)
+      ret = (*(cInterface->interface))->ReadPipeAsyncTO(cInterface->interface, pipeRef, transfer->buffer,
+							transfer->length, transfer->timeout, transfer->timeout,
+							darwin_async_io_callback, (void *)itransfer);
+    else
+      ret = (*(cInterface->interface))->WritePipeAsyncTO(cInterface->interface, pipeRef, transfer->buffer,
+							 transfer->length, transfer->timeout, transfer->timeout,
+							 darwin_async_io_callback, (void *)itransfer);
+  }
+
+  if (ret)
+    usbi_err (TRANSFER_CTX (transfer), "bulk transfer failed (dir = %s): %s (code = 0x%08x)", is_read ? "In" : "Out",
+	       darwin_error_str(ret), ret);
+
+  return darwin_to_libusb (ret);
+}
+
+static int submit_iso_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)transfer->dev_handle->os_priv;
+
+  IOReturn                kresult;
+  uint8_t                 is_read; /* 0 = we're writing, 1 = we're reading */
+  uint8_t                 pipeRef, iface;
+  UInt64                  frame;
+  AbsoluteTime            atTime;
+  int                     i;
+
+  struct __darwin_interface *cInterface;
+
+  /* are we reading or writing? */
+  is_read = transfer->endpoint & LIBUSB_ENDPOINT_IN;
+  
+  /* construct an array of IOUSBIsocFrames */
+  tpriv->isoc_framelist = (IOUSBIsocFrame*) calloc (transfer->num_iso_packets, sizeof(IOUSBIsocFrame));
+  if (!tpriv->isoc_framelist)
+    return LIBUSB_ERROR_NO_MEM;
+
+  /* copy the frame list from the libusb descriptor (the structures differ only is member order) */
+  for (i = 0 ; i < transfer->num_iso_packets ; i++)
+    tpriv->isoc_framelist[i].frReqCount = transfer->iso_packet_desc[i].length;
+
+  /* determine the interface/endpoint to use */
+  if (ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, &iface) != 0) {
+    usbi_err (TRANSFER_CTX (transfer), "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  cInterface = &priv->interfaces[iface];
+
+  /* Last but not least we need the bus frame number */
+  kresult = (*(cInterface->interface))->GetBusFrameNumber(cInterface->interface, &frame, &atTime);
+  if (kresult) {
+    usbi_err (TRANSFER_CTX (transfer), "failed to get bus frame number: %d", kresult);
+    free(tpriv->isoc_framelist);
+    tpriv->isoc_framelist = NULL;
+
+    return darwin_to_libusb (kresult);
+  }
+
+  /* schedule for a frame a little in the future */
+  frame += 2;
+	
+  /* submit the request */
+  if (is_read)
+    kresult = (*(cInterface->interface))->ReadIsochPipeAsync(cInterface->interface, pipeRef, transfer->buffer, frame,
+							     transfer->num_iso_packets, tpriv->isoc_framelist, darwin_async_io_callback,
+							     itransfer);
+  else
+    kresult = (*(cInterface->interface))->WriteIsochPipeAsync(cInterface->interface, pipeRef, transfer->buffer, frame,
+							      transfer->num_iso_packets, tpriv->isoc_framelist, darwin_async_io_callback,
+							      itransfer);
+
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (TRANSFER_CTX (transfer), "isochronous transfer failed (dir: %s): %s", is_read ? "In" : "Out",
+	       darwin_error_str(kresult));
+    free (tpriv->isoc_framelist);
+    tpriv->isoc_framelist = NULL;
+  }
+
+  return darwin_to_libusb (kresult);
+}
+
+static int submit_control_transfer(struct usbi_transfer *itransfer) {  
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct libusb_control_setup *setup = (struct libusb_control_setup *) transfer->buffer;
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)transfer->dev_handle->dev->os_priv;
+  struct darwin_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+
+  IOReturn               kresult;
+
+  bzero(&tpriv->req, sizeof(tpriv->req));
+
+  /* IOUSBDeviceInterface expects the request in cpu endianess */
+  tpriv->req.bmRequestType     = setup->bmRequestType;
+  tpriv->req.bRequest          = setup->bRequest;
+  /* these values should be in bus order from libusb_fill_control_setup */
+  tpriv->req.wValue            = OSSwapLittleToHostInt16 (setup->wValue);
+  tpriv->req.wIndex            = OSSwapLittleToHostInt16 (setup->wIndex);
+  tpriv->req.wLength           = OSSwapLittleToHostInt16 (setup->wLength);
+  /* data is stored after the libusb control block */
+  tpriv->req.pData             = transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE;
+  tpriv->req.completionTimeout = transfer->timeout;
+  tpriv->req.noDataTimeout     = transfer->timeout;
+
+  /* all transfers in libusb-1.0 are async */
+  kresult = (*(dpriv->device))->DeviceRequestAsyncTO(dpriv->device, &(tpriv->req), darwin_async_io_callback, itransfer);
+
+  if (kresult != kIOReturnSuccess)
+    usbi_err (TRANSFER_CTX (transfer), "control request failed: %s", darwin_error_str(kresult));
+  
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_submit_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+  switch (transfer->type) {
+  case LIBUSB_TRANSFER_TYPE_CONTROL:
+    return submit_control_transfer(itransfer);
+  case LIBUSB_TRANSFER_TYPE_BULK:
+  case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+    return submit_bulk_transfer(itransfer);
+  case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+    return submit_iso_transfer(itransfer);
+  default:
+    usbi_err (TRANSFER_CTX(transfer), "unknown endpoint type %d", transfer->type);
+    return LIBUSB_ERROR_INVALID_PARAM;
+  }
+}
+
+static int cancel_control_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_device_priv *dpriv = (struct darwin_device_priv *)transfer->dev_handle->dev->os_priv;
+  IOReturn kresult;
+
+  usbi_info (ITRANSFER_CTX (itransfer), "WARNING: aborting all transactions control pipe");
+
+  kresult = (*(dpriv->device))->USBDeviceAbortPipeZero (dpriv->device);
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_abort_transfers (struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)transfer->dev_handle->os_priv;
+  struct __darwin_interface *cInterface;
+  uint8_t pipeRef, iface;
+  IOReturn kresult;
+
+  if (ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, &iface) != 0) {
+    usbi_err (TRANSFER_CTX (transfer), "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  cInterface = &priv->interfaces[iface];
+
+  usbi_info (ITRANSFER_CTX (itransfer), "WARNING: aborting all transactions on interface %d pipe %d", iface, pipeRef);
+
+  /* abort transactions */
+  (*(cInterface->interface))->AbortPipe (cInterface->interface, pipeRef);
+  
+  usbi_info (ITRANSFER_CTX (itransfer), "calling clear pipe stall to clear the data toggle bit");
+
+  /* clear the data toggle bit */
+#if (InterfaceVersion < 190)
+  kresult = (*(cInterface->interface))->ClearPipeStall(cInterface->interface, pipeRef);
+#else
+  /* newer versions of darwin support clearing additional bits on the device's endpoint */
+  kresult = (*(cInterface->interface))->ClearPipeStallBothEnds(cInterface->interface, pipeRef);
+#endif
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_cancel_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+  switch (transfer->type) {
+  case LIBUSB_TRANSFER_TYPE_CONTROL:
+    return cancel_control_transfer(itransfer);
+  case LIBUSB_TRANSFER_TYPE_BULK:
+  case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+  case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+    return darwin_abort_transfers (itransfer);
+  default:
+    usbi_err (TRANSFER_CTX(transfer), "unknown endpoint type %d", transfer->type);
+    return LIBUSB_ERROR_INVALID_PARAM;
+  }
+}
+
+static void darwin_clear_transfer_priv (struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+
+  if (transfer->type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS && tpriv->isoc_framelist) {
+    free (tpriv->isoc_framelist);
+    tpriv->isoc_framelist = NULL;
+  }
+}
+
+static void darwin_async_io_callback (void *refcon, IOReturn result, void *arg0) {
+  struct usbi_transfer *itransfer = (struct usbi_transfer *)refcon;
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_device_handle_priv *priv = (struct darwin_device_handle_priv *)transfer->dev_handle->os_priv;
+  UInt32 message;
+
+  usbi_info (ITRANSFER_CTX (itransfer), "an async io operation has completed");
+
+  /* send a completion message to the device's file descriptor */
+  message = MESSAGE_ASYNC_IO_COMPLETE;
+  write (priv->fds[1], &message, sizeof (message));
+  write (priv->fds[1], &itransfer, sizeof (itransfer));
+  write (priv->fds[1], &result, sizeof (IOReturn));
+  write (priv->fds[1], &arg0, sizeof (UInt32));
+}
+
+static int darwin_transfer_status (struct usbi_transfer *itransfer, kern_return_t result) {
+  switch (result) {
+  case kIOReturnSuccess:
+    return LIBUSB_TRANSFER_COMPLETED;
+  case kIOReturnAborted:
+    return LIBUSB_TRANSFER_CANCELLED;
+  case kIOUSBPipeStalled:
+    usbi_warn (ITRANSFER_CTX (itransfer), "transfer error: pipe is stalled");
+    return LIBUSB_TRANSFER_STALL;
+  case kIOReturnOverrun:
+    usbi_err (ITRANSFER_CTX (itransfer), "transfer error: data overrun", darwin_error_str (result));
+    return LIBUSB_TRANSFER_OVERFLOW;
+  case kIOUSBTransactionTimeout:
+    usbi_err (ITRANSFER_CTX (itransfer), "transfer error: timed out");
+    return LIBUSB_TRANSFER_TIMED_OUT;
+  default:
+    usbi_err (ITRANSFER_CTX (itransfer), "transfer error: %s (value = 0x%08x)", darwin_error_str (result), result);
+    return LIBUSB_TRANSFER_ERROR;
+  }
+}
+
+static void darwin_handle_callback (struct usbi_transfer *itransfer, kern_return_t result, UInt32 io_size) {
+  struct libusb_transfer *transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+  int isIsoc      = LIBUSB_TRANSFER_TYPE_ISOCHRONOUS == transfer->type;
+  int isBulk      = LIBUSB_TRANSFER_TYPE_BULK == transfer->type;
+  int isControl   = LIBUSB_TRANSFER_TYPE_CONTROL == transfer->type;
+  int isInterrupt = LIBUSB_TRANSFER_TYPE_INTERRUPT == transfer->type;
+  int i;
+
+  if (!isIsoc && !isBulk && !isControl && !isInterrupt) {
+    usbi_err (TRANSFER_CTX(transfer), "unknown endpoint type %d", transfer->type);
+    return;
+  }
+
+  usbi_info (ITRANSFER_CTX (itransfer), "handling %s completion with kernel status %d",
+	     isControl ? "control" : isBulk ? "bulk" : isIsoc ? "isoc" : "interrupt", result);
+
+  if (kIOReturnSuccess == result) {
+    if (isIsoc && tpriv->isoc_framelist) {
+      /* copy isochronous results back */
+
+      for (i = 0; i < transfer->num_iso_packets ; i++) {
+	struct libusb_iso_packet_descriptor *lib_desc = transfer->iso_packet_desc;
+	lib_desc->status = darwin_to_libusb (tpriv->isoc_framelist[i].frStatus);
+	lib_desc->actual_length = tpriv->isoc_framelist[i].frActCount;
+      }
+    } else if (!isIsoc)
+      itransfer->transferred += io_size;
+  }
+
+  /* it is ok to handle cancelled transfers without calling usbi_handle_transfer_cancellation (we catch timeout transfers) */
+  usbi_handle_transfer_completion (itransfer, darwin_transfer_status (itransfer, result));
+}
+
+static int op_handle_events(struct libusb_context *ctx, struct pollfd *fds, nfds_t nfds, int num_ready) {
+  struct usbi_transfer *itransfer;
+  UInt32 io_size;
+  IOReturn kresult;
+  int i = 0, ret;
+  UInt32 message;
+
+  pthread_mutex_lock(&ctx->open_devs_lock);
+  for (i = 0; i < nfds && num_ready > 0; i++) {
+    struct pollfd *pollfd = &fds[i];
+    struct libusb_device_handle *handle;
+    struct darwin_device_handle_priv *hpriv = NULL;
+
+    usbi_info (ctx, "checking fd %i with revents = %x", fds[i], pollfd->revents);
+
+    if (!pollfd->revents)
+      continue;
+
+    num_ready--;
+    list_for_each_entry(handle, &ctx->open_devs, list) {
+      hpriv =  (struct darwin_device_handle_priv *)handle->os_priv;
+      if (hpriv->fds[0] == pollfd->fd)
+	break;
+    }
+
+    if (!(pollfd->revents & POLLERR)) {
+      ret = read (hpriv->fds[0], &message, sizeof (message));
+      if (ret < sizeof (message))
+	continue;
+    } else
+      /* could not poll the device-- response is to delete the device (this seems a little heavy-handed) */
+      message = MESSAGE_DEVICE_GONE;
+
+    switch (message) {
+    case MESSAGE_DEVICE_GONE:
+      /* remove the device's async port from the runloop */
+      if (hpriv->cfSource) {
+	if (libusb_darwin_acfl)
+	  CFRunLoopRemoveSource (libusb_darwin_acfl, hpriv->cfSource, kCFRunLoopDefaultMode);
+	CFRelease (hpriv->cfSource);
+	hpriv->cfSource = NULL;
+      }
+
+      usbi_remove_pollfd(HANDLE_CTX(handle), hpriv->fds[0]);
+      usbi_handle_disconnect(handle);
+      
+      /* done with this device */
+      continue;
+    case MESSAGE_ASYNC_IO_COMPLETE:
+      read (hpriv->fds[0], &itransfer, sizeof (itransfer));
+      read (hpriv->fds[0], &kresult, sizeof (IOReturn));
+      read (hpriv->fds[0], &io_size, sizeof (UInt32));
+
+      darwin_handle_callback (itransfer, kresult, io_size);
+      break;
+    default:
+      usbi_err (ctx, "unknown message received from device pipe");
+    }
+  }
+
+  pthread_mutex_unlock(&ctx->open_devs_lock);
+
+  return 0;
+}
+
+static int darwin_clock_gettime(int clk_id, struct timespec *tp) {
+  mach_timespec_t sys_time;
+  clock_serv_t clock_ref;
+
+  switch (clk_id) {
+  case USBI_CLOCK_REALTIME:
+    /* CLOCK_REALTIME represents time since the epoch */
+    host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &clock_ref);
+    break;
+  case USBI_CLOCK_MONOTONIC:
+    /* use system boot time as reference for the monotonic clock */
+    host_get_clock_service(mach_host_self(), SYSTEM_CLOCK, &clock_ref);
+    break;
+  default:
+    return LIBUSB_ERROR_INVALID_PARAM;
+  }
+
+  clock_get_time (clock_ref, &sys_time);
+
+  tp->tv_sec  = sys_time.tv_sec;
+  tp->tv_nsec = sys_time.tv_nsec;
+
+  return 0;
+}
+
+const struct usbi_os_backend darwin_backend = {
+	.name = "Darwin",
+	.init = darwin_init,
+	.exit = darwin_exit,
+	.get_device_list = darwin_get_device_list,
+	.get_device_descriptor = darwin_get_device_descriptor,
+	.get_active_config_descriptor = darwin_get_active_config_descriptor,
+	.get_config_descriptor = darwin_get_config_descriptor,
+
+	.open = darwin_open,
+	.close = darwin_close,
+	.get_configuration = darwin_get_configuration,
+	.set_configuration = darwin_set_configuration,
+	.claim_interface = darwin_claim_interface,
+	.release_interface = darwin_release_interface,
+
+	.set_interface_altsetting = darwin_set_interface_altsetting,
+	.clear_halt = darwin_clear_halt,
+	.reset_device = darwin_reset_device,
+
+	.kernel_driver_active = darwin_kernel_driver_active,
+	.detach_kernel_driver = darwin_detach_kernel_driver,
+	.attach_kernel_driver = darwin_attach_kernel_driver,
+
+	.destroy_device = darwin_destroy_device,
+
+	.submit_transfer = darwin_submit_transfer,
+	.cancel_transfer = darwin_cancel_transfer,
+	.clear_transfer_priv = darwin_clear_transfer_priv,
+
+	.handle_events = op_handle_events,
+
+	.clock_gettime = darwin_clock_gettime,
+
+	.device_priv_size = sizeof(struct darwin_device_priv),
+	.device_handle_priv_size = sizeof(struct darwin_device_handle_priv),
+	.transfer_priv_size = sizeof(struct darwin_transfer_priv),
+	.add_iso_packet_size = 0,
+};
+
diff --git a/libusb/os/darwin_usb.h b/libusb/os/darwin_usb.h
new file mode 100644
index 0000000..a7b31eb
--- /dev/null
+++ b/libusb/os/darwin_usb.h
@@ -0,0 +1,161 @@
+/*
+ * darwin backend for libusb 1.0
+ * Copyright (C) 2008-2009 Nathan Hjelm <hjelmn@users.sourceforge.net>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#if !defined(LIBUSB_DARWIN_H)
+#define LIBUSB_DARWIN_H
+
+#include "libusbi.h"
+
+#include <IOKit/IOCFBundle.h>
+#include <IOKit/usb/IOUSBLib.h>
+#include <IOKit/IOCFPlugIn.h>
+
+/* IOUSBInterfaceInferface */
+#if defined (kIOUSBInterfaceInterfaceID300)
+
+#define usb_interface_t IOUSBInterfaceInterface300
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID300
+#define InterfaceVersion 300
+
+#elif defined (kIOUSBInterfaceInterfaceID245)
+
+#define usb_interface_t IOUSBInterfaceInterface245
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID245
+#define InterfaceVersion 245
+
+#elif defined (kIOUSBInterfaceInterfaceID220)
+
+#define usb_interface_t IOUSBInterfaceInterface220
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID220
+#define InterfaceVersion 220
+
+#elif defined (kIOUSBInterfaceInterfaceID197)
+
+#define usb_interface_t IOUSBInterfaceInterface197
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID197
+#define InterfaceVersion 197
+
+#elif defined (kIOUSBInterfaceInterfaceID190)
+
+#define usb_interface_t IOUSBInterfaceInterface190
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID190
+#define InterfaceVersion 190
+
+#elif defined (kIOUSBInterfaceInterfaceID182)
+
+#define usb_interface_t IOUSBInterfaceInterface182
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID182
+#define InterfaceVersion 182
+
+#else
+
+#error "IOUSBFamily is too old. Please upgrade your OS"
+
+#endif
+
+/* IOUSBDeviceInterface */
+#if defined (kIOUSBDeviceInterfaceID320)
+
+#define usb_device_t    IOUSBDeviceInterface320
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID320
+#define DeviceVersion 320
+
+#elif defined (kIOUSBDeviceInterfaceID300)
+
+#define usb_device_t    IOUSBDeviceInterface300
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID300
+#define DeviceVersion 300
+
+#elif defined (kIOUSBDeviceInterfaceID245)
+
+#define usb_device_t    IOUSBDeviceInterface245
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID245
+#define DeviceVersion 245
+
+#elif defined (kIOUSBDeviceInterfaceID197)
+
+#define usb_device_t    IOUSBDeviceInterface197
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID197
+#define DeviceVersion 197
+
+#elif defined (kIOUSBDeviceInterfaceID187)
+
+#define usb_device_t    IOUSBDeviceInterface187
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID187
+#define DeviceVersion 187
+
+#elif defined (kIOUSBDeviceInterfaceID182)
+
+#define usb_device_t    IOUSBDeviceInterface182
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID182
+#define DeviceVersion 182
+
+#else
+
+#error "IOUSBFamily is too old. Please upgrade your OS"
+
+#endif
+
+typedef IOCFPlugInInterface *io_cf_plugin_ref_t;
+typedef IONotificationPortRef io_notification_port_t;
+
+/* private structures */
+struct darwin_device_priv {
+  IOUSBDeviceDescriptor dev_descriptor;
+  UInt32                location;
+  char                  sys_path[21];
+  usb_device_t        **device;
+  int                  open_count;
+};
+
+struct darwin_device_handle_priv {
+  int                  is_open;
+  CFRunLoopSourceRef   cfSource;
+  int                  fds[2];
+
+  struct __darwin_interface {
+    usb_interface_t    **interface;
+    uint8_t              num_endpoints;
+    CFRunLoopSourceRef   cfSource;
+    uint8_t            endpoint_addrs[USB_MAXENDPOINTS];
+  } interfaces[USB_MAXINTERFACES];
+};
+
+struct darwin_transfer_priv {
+  /* Isoc */
+  IOUSBIsocFrame *isoc_framelist;
+
+  /* Control */
+#if !defined (LIBUSB_NO_TIMEOUT_DEVICE)
+  IOUSBDevRequestTO req;
+#else
+  IOUSBDevRequest req;
+#endif
+
+  /* Bulk */
+};
+
+enum {
+  MESSAGE_DEVICE_GONE,
+  MESSAGE_ASYNC_IO_COMPLETE
+};
+
+
+
+#endif
diff --git a/libusb/os/linux_usbfs.c b/libusb/os/linux_usbfs.c
new file mode 100644
index 0000000..65f29ae
--- /dev/null
+++ b/libusb/os/linux_usbfs.c
@@ -0,0 +1,2205 @@
+/*
+ * Linux usbfs backend for libusb
+ * Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/utsname.h>
+#include <unistd.h>
+
+#include "libusb.h"
+#include "libusbi.h"
+#include "linux_usbfs.h"
+
+/* sysfs vs usbfs:
+ * opening a usbfs node causes the device to be resumed, so we attempt to
+ * avoid this during enumeration.
+ *
+ * sysfs allows us to read the kernel's in-memory copies of device descriptors
+ * and so forth, avoiding the need to open the device:
+ *  - The binary "descriptors" file was added in 2.6.23.
+ *  - The "busnum" file was added in 2.6.22
+ *  - The "devnum" file has been present since pre-2.6.18
+ *  - the "bConfigurationValue" file has been present since pre-2.6.18
+ *
+ * If we have bConfigurationValue, busnum, and devnum, then we can determine
+ * the active configuration without having to open the usbfs node in RDWR mode.
+ * We assume this is the case if we see the busnum file (indicates 2.6.22+).
+ * The busnum file is important as that is the only way we can relate sysfs
+ * devices to usbfs nodes.
+ *
+ * If we also have descriptors, we can obtain the device descriptor and active 
+ * configuration without touching usbfs at all.
+ *
+ * The descriptors file originally only contained the active configuration
+ * descriptor alongside the device descriptor, but all configurations are
+ * included as of Linux 2.6.26.
+ */
+
+/* endianness for multi-byte fields:
+ *
+ * Descriptors exposed by usbfs have the multi-byte fields in the device
+ * descriptor as host endian. Multi-byte fields in the other descriptors are
+ * bus-endian. The kernel documentation says otherwise, but it is wrong.
+ */
+
+static const char *usbfs_path = NULL;
+
+/* Linux 2.6.32 adds support for a bulk continuation URB flag. this basically
+ * allows us to mark URBs as being part of a specific logical transfer when
+ * we submit them to the kernel. then, on any error error except a
+ * cancellation, all URBs within that transfer will be cancelled with the
+ * endpoint is disabled, meaning that no more data can creep in during the
+ * time it takes to cancel the remaining URBs.
+ *
+ * The BULK_CONTINUATION flag must be set on all URBs within a bulk transfer
+ * (in either direction) except the first.
+ * For IN transfers, we must also set SHORT_NOT_OK on all the URBs.
+ * For OUT transfers, SHORT_NOT_OK must not be set. The effective behaviour
+ * (where an OUT transfer does not complete, the rest of the URBs in the
+ * transfer get cancelled) is already in effect, and setting this flag is
+ * disallowed (a kernel with USB debugging enabled will reject such URBs).
+ */
+static int supports_flag_bulk_continuation = -1;
+
+/* clock ID for monotonic clock, as not all clock sources are available on all
+ * systems. appropriate choice made at initialization time. */
+static clockid_t monotonic_clkid = -1;
+
+/* do we have a busnum to relate devices? this also implies that we can read
+ * the active configuration through bConfigurationValue */
+static int sysfs_can_relate_devices = -1;
+
+/* do we have a descriptors file? */
+static int sysfs_has_descriptors = -1;
+
+struct linux_device_priv {
+	char *sysfs_dir;
+	unsigned char *dev_descriptor;
+	unsigned char *config_descriptor;
+};
+
+struct linux_device_handle_priv {
+	int fd;
+};
+
+enum reap_action {
+	NORMAL = 0,
+	/* submission failed after the first URB, so await cancellation/completion
+	 * of all the others */
+	SUBMIT_FAILED,
+
+	/* cancelled by user or timeout */
+	CANCELLED,
+
+	/* completed multi-URB transfer in non-final URB */
+	COMPLETED_EARLY,
+};
+
+struct linux_transfer_priv {
+	union {
+		struct usbfs_urb *urbs;
+		struct usbfs_urb **iso_urbs;
+	};
+
+	enum reap_action reap_action;
+	int num_urbs;
+	unsigned int num_retired;
+
+	/* next iso packet in user-supplied transfer to be populated */
+	int iso_packet_offset;
+};
+
+static void __get_usbfs_path(struct libusb_device *dev, char *path)
+{
+	snprintf(path, PATH_MAX, "%s/%03d/%03d", usbfs_path, dev->bus_number,
+		dev->device_address);
+}
+
+static struct linux_device_priv *__device_priv(struct libusb_device *dev)
+{
+	return (struct linux_device_priv *) dev->os_priv;
+}
+
+static struct linux_device_handle_priv *__device_handle_priv(
+	struct libusb_device_handle *handle)
+{
+	return (struct linux_device_handle_priv *) handle->os_priv;
+}
+
+static int check_usb_vfs(const char *dirname)
+{
+	DIR *dir;
+	struct dirent *entry;
+	int found = 0;
+
+	dir = opendir(dirname);
+	if (!dir)
+		return 0;
+
+	while ((entry = readdir(dir)) != NULL) {
+		if (entry->d_name[0] == '.')
+			continue;
+
+		/* We assume if we find any files that it must be the right place */
+		found = 1;
+		break;
+	}
+
+	closedir(dir);
+	return found;
+}
+
+static const char *find_usbfs_path(void)
+{
+	const char *path = "/dev/bus/usb";
+	const char *ret = NULL;
+
+	if (check_usb_vfs(path)) {
+		ret = path;
+	} else {
+		path = "/proc/bus/usb";
+		if (check_usb_vfs(path))
+			ret = path;
+	}
+
+	usbi_dbg("found usbfs at %s", ret);
+	return ret;
+}
+
+/* the monotonic clock is not usable on all systems (e.g. embedded ones often
+ * seem to lack it). fall back to REALTIME if we have to. */
+static clockid_t find_monotonic_clock(void)
+{
+	struct timespec ts;
+	int r;
+
+	/* Linux 2.6.28 adds CLOCK_MONOTONIC_RAW but we don't use it
+	 * because it's not available through timerfd */
+	r = clock_gettime(CLOCK_MONOTONIC, &ts);
+	if (r == 0) {
+		return CLOCK_MONOTONIC;
+	} else {
+		usbi_dbg("monotonic clock doesn't work, errno %d", errno);
+		return CLOCK_REALTIME;
+	}
+}
+
+/* bulk continuation URB flag available from Linux 2.6.32 */
+static int check_flag_bulk_continuation(void)
+{
+	struct utsname uts;
+	int sublevel;
+
+	if (uname(&uts) < 0)
+		return -1;
+	if (strlen(uts.release) < 4)
+		return 0;
+	if (strncmp(uts.release, "2.6.", 4) != 0)
+		return 0;
+
+	sublevel = atoi(uts.release + 4);
+	return sublevel >= 32;
+}
+
+static int op_init(struct libusb_context *ctx)
+{
+	struct stat statbuf;
+	int r;
+
+	usbfs_path = find_usbfs_path();
+	if (!usbfs_path) {
+		usbi_err(ctx, "could not find usbfs");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	if (monotonic_clkid == -1)
+		monotonic_clkid = find_monotonic_clock();
+
+	if (supports_flag_bulk_continuation == -1) {
+		supports_flag_bulk_continuation = check_flag_bulk_continuation();
+		if (supports_flag_bulk_continuation == -1) {
+			usbi_err(ctx, "error checking for bulk continuation support");
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+
+	if (supports_flag_bulk_continuation)
+		usbi_dbg("bulk continuation flag supported");
+
+	r = stat(SYSFS_DEVICE_PATH, &statbuf);
+	if (r == 0 && S_ISDIR(statbuf.st_mode)) {
+		usbi_dbg("found usb devices in sysfs");
+	} else {
+		usbi_dbg("sysfs usb info not available");
+		sysfs_has_descriptors = 0;
+		sysfs_can_relate_devices = 0;
+	}
+
+	return 0;
+}
+
+static int usbfs_get_device_descriptor(struct libusb_device *dev,
+	unsigned char *buffer)
+{
+	struct linux_device_priv *priv = __device_priv(dev);
+
+	/* return cached copy */
+	memcpy(buffer, priv->dev_descriptor, DEVICE_DESC_LENGTH);
+	return 0;
+}
+
+static int __open_sysfs_attr(struct libusb_device *dev, const char *attr)
+{
+	struct linux_device_priv *priv = __device_priv(dev);
+	char filename[PATH_MAX];
+	int fd;
+
+	snprintf(filename, PATH_MAX, "%s/%s/%s",
+		SYSFS_DEVICE_PATH, priv->sysfs_dir, attr);
+	fd = open(filename, O_RDONLY);
+	if (fd < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"open %s failed ret=%d errno=%d", filename, fd, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return fd;
+}
+
+static int sysfs_get_device_descriptor(struct libusb_device *dev,
+	unsigned char *buffer)
+{
+	int fd;
+	ssize_t r;
+
+	/* sysfs provides access to an in-memory copy of the device descriptor,
+	 * so we use that rather than keeping our own copy */
+
+	fd = __open_sysfs_attr(dev, "descriptors");
+	if (fd < 0)
+		return fd;
+
+	r = read(fd, buffer, DEVICE_DESC_LENGTH);;
+	close(fd);
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev), "read failed, ret=%d errno=%d", fd, errno);
+		return LIBUSB_ERROR_IO;
+	} else if (r < DEVICE_DESC_LENGTH) {
+		usbi_err(DEVICE_CTX(dev), "short read %d/%d", r, DEVICE_DESC_LENGTH);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return 0;
+}
+
+static int op_get_device_descriptor(struct libusb_device *dev,
+	unsigned char *buffer, int *host_endian)
+{
+	if (sysfs_has_descriptors) {
+		return sysfs_get_device_descriptor(dev, buffer);
+	} else {
+		*host_endian = 1;
+		return usbfs_get_device_descriptor(dev, buffer);
+	}
+}
+
+static int usbfs_get_active_config_descriptor(struct libusb_device *dev,
+	unsigned char *buffer, size_t len)
+{
+	struct linux_device_priv *priv = __device_priv(dev);
+	if (!priv->config_descriptor)
+		return LIBUSB_ERROR_NOT_FOUND; /* device is unconfigured */
+
+	/* retrieve cached copy */
+	memcpy(buffer, priv->config_descriptor, len);
+	return 0;
+}
+
+/* read the bConfigurationValue for a device */
+static int sysfs_get_active_config(struct libusb_device *dev, int *config)
+{
+	char *endptr;
+	char tmp[4] = {0, 0, 0, 0};
+	long num;
+	int fd;
+	size_t r;
+
+	fd = __open_sysfs_attr(dev, "bConfigurationValue");
+	if (fd < 0)
+		return fd;
+
+	r = read(fd, tmp, sizeof(tmp));
+	close(fd);
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev), 
+			"read bConfigurationValue failed ret=%d errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	} else if (r == 0) {
+		usbi_err(DEVICE_CTX(dev), "device unconfigured");
+		*config = -1;
+		return 0;
+	}
+
+	if (tmp[sizeof(tmp) - 1] != 0) {
+		usbi_err(DEVICE_CTX(dev), "not null-terminated?");
+		return LIBUSB_ERROR_IO;
+	} else if (tmp[0] == 0) {
+		usbi_err(DEVICE_CTX(dev), "no configuration value?");
+		return LIBUSB_ERROR_IO;
+	}
+
+	num = strtol(tmp, &endptr, 10);
+	if (endptr == tmp) {
+		usbi_err(DEVICE_CTX(dev), "error converting '%s' to integer", tmp);
+		return LIBUSB_ERROR_IO;
+	}
+
+	*config = (int) num;
+	return 0;
+}
+
+/* takes a usbfs/descriptors fd seeked to the start of a configuration, and
+ * seeks to the next one. */
+static int seek_to_next_config(struct libusb_context *ctx, int fd,
+	int host_endian)
+{
+	struct libusb_config_descriptor config;
+	unsigned char tmp[6];
+	off_t off;
+	int r;
+
+	/* read first 6 bytes of descriptor */
+	r = read(fd, tmp, sizeof(tmp));
+	if (r < 0) {
+		usbi_err(ctx, "read failed ret=%d errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	} else if (r < sizeof(tmp)) {
+		usbi_err(ctx, "short descriptor read %d/%d", r, sizeof(tmp));
+		return LIBUSB_ERROR_IO;
+	}
+
+	/* seek forward to end of config */
+	usbi_parse_descriptor(tmp, "bbwbb", &config, host_endian);
+	off = lseek(fd, config.wTotalLength - sizeof(tmp), SEEK_CUR);
+	if (off < 0) {
+		usbi_err(ctx, "seek failed ret=%d errno=%d", off, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return 0;
+}
+
+static int sysfs_get_active_config_descriptor(struct libusb_device *dev,
+	unsigned char *buffer, size_t len)
+{
+	int fd;
+	ssize_t r;
+	off_t off;
+	int to_copy;
+	int config;
+	unsigned char tmp[6];
+
+	r = sysfs_get_active_config(dev, &config);
+	if (r < 0)
+		return r;
+	if (config == -1)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	usbi_dbg("active configuration %d", config);
+
+	/* sysfs provides access to an in-memory copy of the device descriptor,
+	 * so we use that rather than keeping our own copy */
+
+	fd = __open_sysfs_attr(dev, "descriptors");
+	if (fd < 0)
+		return fd;
+
+	/* device might have been unconfigured since we read bConfigurationValue,
+	 * so first check that there is any config descriptor data at all... */
+	off = lseek(fd, 0, SEEK_END);
+	if (off < 1) {
+		usbi_err(DEVICE_CTX(dev), "end seek failed, ret=%d errno=%d",
+			off, errno);
+		close(fd);
+		return LIBUSB_ERROR_IO;
+	} else if (off == DEVICE_DESC_LENGTH) {
+		close(fd);
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	off = lseek(fd, DEVICE_DESC_LENGTH, SEEK_SET);
+	if (off < 0) {
+		usbi_err(DEVICE_CTX(dev), "seek failed, ret=%d errno=%d", off, errno);
+		close(fd);
+		return LIBUSB_ERROR_IO;
+	}
+
+	/* unbounded loop: we expect the descriptor to be present under all
+	 * circumstances */
+	while (1) {
+		r = read(fd, tmp, sizeof(tmp));
+		if (r < 0) {
+			usbi_err(DEVICE_CTX(dev), "read failed, ret=%d errno=%d",
+				fd, errno);
+			return LIBUSB_ERROR_IO;
+		} else if (r < sizeof(tmp)) {
+			usbi_err(DEVICE_CTX(dev), "short read %d/%d", r, sizeof(tmp));
+			return LIBUSB_ERROR_IO;
+		}
+
+		/* check bConfigurationValue */
+		if (tmp[5] == config)
+			break;
+
+		/* try the next descriptor */
+		off = lseek(fd, 0 - sizeof(tmp), SEEK_CUR);
+		if (off < 0)
+			return LIBUSB_ERROR_IO;
+
+		r = seek_to_next_config(DEVICE_CTX(dev), fd, 1);
+		if (r < 0)
+			return r;
+	}
+
+	to_copy = (len < sizeof(tmp)) ? len : sizeof(tmp);
+	memcpy(buffer, tmp, to_copy);
+	if (len > sizeof(tmp)) {
+		r = read(fd, buffer + sizeof(tmp), len - sizeof(tmp));
+		if (r < 0) {
+			usbi_err(DEVICE_CTX(dev), "read failed, ret=%d errno=%d",
+				fd, errno);
+			r = LIBUSB_ERROR_IO;
+		} else if (r == 0) {
+			usbi_dbg("device is unconfigured");
+			r = LIBUSB_ERROR_NOT_FOUND;
+		} else if (r < len - sizeof(tmp)) {
+			usbi_err(DEVICE_CTX(dev), "short read %d/%d", r, len);
+			r = LIBUSB_ERROR_IO;
+		}
+	} else {
+		r = 0;
+	}
+
+	close(fd);
+	return r;
+}
+
+static int op_get_active_config_descriptor(struct libusb_device *dev,
+	unsigned char *buffer, size_t len, int *host_endian)
+{
+	if (sysfs_has_descriptors) {
+		return sysfs_get_active_config_descriptor(dev, buffer, len);
+	} else {
+		return usbfs_get_active_config_descriptor(dev, buffer, len);
+	}
+}
+
+/* takes a usbfs fd, attempts to find the requested config and copy a certain
+ * amount of it into an output buffer. */
+static int get_config_descriptor(struct libusb_context *ctx, int fd,
+	uint8_t config_index, unsigned char *buffer, size_t len)
+{
+	off_t off;
+	ssize_t r;
+
+	off = lseek(fd, DEVICE_DESC_LENGTH, SEEK_SET);
+	if (off < 0) {
+		usbi_err(ctx, "seek failed ret=%d errno=%d", off, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	/* might need to skip some configuration descriptors to reach the
+	 * requested configuration */
+	while (config_index > 0) {
+		r = seek_to_next_config(ctx, fd, 0);
+		if (r < 0)
+			return r;
+		config_index--;
+	}
+
+	/* read the rest of the descriptor */
+	r = read(fd, buffer, len);
+	if (r < 0) {
+		usbi_err(ctx, "read failed ret=%d errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	} else if (r < len) {
+		usbi_err(ctx, "short output read %d/%d", r, len);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return 0;
+}
+
+static int op_get_config_descriptor(struct libusb_device *dev,
+	uint8_t config_index, unsigned char *buffer, size_t len, int *host_endian)
+{
+	char filename[PATH_MAX];
+	int fd;
+	int r;
+
+	/* always read from usbfs: sysfs only has the active descriptor
+	 * this will involve waking the device up, but oh well! */
+
+	/* FIXME: the above is no longer true, new kernels have all descriptors
+	 * in the descriptors file. but its kinda hard to detect if the kernel
+	 * is sufficiently new. */
+
+	__get_usbfs_path(dev, filename);
+	fd = open(filename, O_RDONLY);
+	if (fd < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"open '%s' failed, ret=%d errno=%d", filename, fd, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	r = get_config_descriptor(DEVICE_CTX(dev), fd, config_index, buffer, len);
+	close(fd);
+	return r;
+}
+
+/* cache the active config descriptor in memory. a value of -1 means that
+ * we aren't sure which one is active, so just assume the first one. 
+ * only for usbfs. */
+static int cache_active_config(struct libusb_device *dev, int fd,
+	int active_config)
+{
+	struct linux_device_priv *priv = __device_priv(dev);
+	struct libusb_config_descriptor config;
+	unsigned char tmp[8];
+	unsigned char *buf;
+	int idx;
+	int r;
+
+	if (active_config == -1) {
+		idx = 0;
+	} else {
+		r = usbi_get_config_index_by_value(dev, active_config, &idx);
+		if (r < 0)
+			return r;
+		if (idx == -1)
+			return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	r = get_config_descriptor(DEVICE_CTX(dev), fd, idx, tmp, sizeof(tmp));
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev), "first read error %d", r);
+		return r;
+	}
+
+	usbi_parse_descriptor(tmp, "bbw", &config, 0);
+	buf = malloc(config.wTotalLength);
+	if (!buf)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = get_config_descriptor(DEVICE_CTX(dev), fd, idx, buf,
+		config.wTotalLength);
+	if (r < 0) {
+		free(buf);
+		return r;
+	}
+
+	if (priv->config_descriptor)
+		free(priv->config_descriptor);
+	priv->config_descriptor = buf;
+	return 0;
+}
+
+/* send a control message to retrieve active configuration */
+static int usbfs_get_active_config(struct libusb_device *dev, int fd)
+{
+	unsigned char active_config = 0;
+	int r;
+
+	struct usbfs_ctrltransfer ctrl = {
+		.bmRequestType = LIBUSB_ENDPOINT_IN,
+		.bRequest = LIBUSB_REQUEST_GET_CONFIGURATION,
+		.wValue = 0,
+		.wIndex = 0,
+		.wLength = 1,
+		.timeout = 1000,
+		.data = &active_config
+	};
+
+	r = ioctl(fd, IOCTL_USBFS_CONTROL, &ctrl);
+	if (r < 0) {
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		/* we hit this error path frequently with buggy devices :( */
+		usbi_warn(DEVICE_CTX(dev),
+			"get_configuration failed ret=%d errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return active_config;
+}
+
+static int initialize_device(struct libusb_device *dev, uint8_t busnum,
+	uint8_t devaddr, const char *sysfs_dir)
+{
+	struct linux_device_priv *priv = __device_priv(dev);
+	unsigned char *dev_buf;
+	char path[PATH_MAX];
+	int fd;
+	int active_config = 0;
+	int device_configured = 1;
+	ssize_t r;
+
+	dev->bus_number = busnum;
+	dev->device_address = devaddr;
+
+	if (sysfs_dir) {
+		priv->sysfs_dir = malloc(strlen(sysfs_dir) + 1);
+		if (!priv->sysfs_dir)
+			return LIBUSB_ERROR_NO_MEM;
+		strcpy(priv->sysfs_dir, sysfs_dir);
+	}
+
+	if (sysfs_has_descriptors)
+		return 0;
+
+	/* cache device descriptor in memory so that we can retrieve it later
+	 * without waking the device up (op_get_device_descriptor) */
+
+	priv->dev_descriptor = NULL;
+	priv->config_descriptor = NULL;
+
+	if (sysfs_can_relate_devices) {
+		int tmp = sysfs_get_active_config(dev, &active_config);
+		if (tmp < 0)
+			return tmp;
+		if (active_config == -1)
+			device_configured = 0;
+	}
+
+	__get_usbfs_path(dev, path);
+	fd = open(path, O_RDWR);
+	if (fd < 0 && errno == EACCES) {
+		fd = open(path, O_RDONLY);
+		/* if we only have read-only access to the device, we cannot
+		 * send a control message to determine the active config. just
+		 * assume the first one is active. */
+		active_config = -1;
+	}
+
+	if (fd < 0) {
+		usbi_err(DEVICE_CTX(dev), "open failed, ret=%d errno=%d", fd, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	if (!sysfs_can_relate_devices) {
+		if (active_config == -1) {
+			/* if we only have read-only access to the device, we cannot
+			 * send a control message to determine the active config. just
+			 * assume the first one is active. */
+			usbi_warn(DEVICE_CTX(dev), "access to %s is read-only; cannot "
+				"determine active configuration descriptor", path);
+		} else {
+			active_config = usbfs_get_active_config(dev, fd);
+			if (active_config == LIBUSB_ERROR_IO) {
+				/* buggy devices sometimes fail to report their active config.
+				 * assume unconfigured and continue the probing */
+				usbi_warn(DEVICE_CTX(dev), "couldn't query active "
+					"configuration, assumung unconfigured");
+				device_configured = 0;
+			} else if (active_config < 0) {
+				close(fd);
+				return active_config;
+			} else if (active_config == 0) {
+				/* some buggy devices have a configuration 0, but we're
+				 * reaching into the corner of a corner case here, so let's
+				 * not support buggy devices in these circumstances.
+				 * stick to the specs: a configuration value of 0 means
+				 * unconfigured. */
+				usbi_dbg("active cfg 0? assuming unconfigured device");
+				device_configured = 0;
+			}
+		}
+	}
+
+	dev_buf = malloc(DEVICE_DESC_LENGTH);
+	if (!dev_buf) {
+		close(fd);
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	r = read(fd, dev_buf, DEVICE_DESC_LENGTH);
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"read descriptor failed ret=%d errno=%d", fd, errno);
+		free(dev_buf);
+		close(fd);
+		return LIBUSB_ERROR_IO;
+	} else if (r < DEVICE_DESC_LENGTH) {
+		usbi_err(DEVICE_CTX(dev), "short descriptor read (%d)", r);
+		free(dev_buf);
+		close(fd);
+		return LIBUSB_ERROR_IO;
+	}
+
+	/* bit of a hack: set num_configurations now because cache_active_config()
+	 * calls usbi_get_config_index_by_value() which uses it */
+	dev->num_configurations = dev_buf[DEVICE_DESC_LENGTH - 1];
+
+	if (device_configured) {
+		r = cache_active_config(dev, fd, active_config);
+		if (r < 0) {
+			close(fd);
+			free(dev_buf);
+			return r;
+		}
+	}
+
+	close(fd);
+	priv->dev_descriptor = dev_buf;
+	return 0;
+}
+
+static int enumerate_device(struct libusb_context *ctx,
+	struct discovered_devs **_discdevs, uint8_t busnum, uint8_t devaddr,
+	const char *sysfs_dir)
+{
+	struct discovered_devs *discdevs;
+	unsigned long session_id;
+	int need_unref = 0;
+	struct libusb_device *dev;
+	int r = 0;
+
+	/* FIXME: session ID is not guaranteed unique as addresses can wrap and
+	 * will be reused. instead we should add a simple sysfs attribute with
+	 * a session ID. */
+	session_id = busnum << 8 | devaddr;
+	usbi_dbg("busnum %d devaddr %d session_id %ld", busnum, devaddr,
+		session_id);
+
+	dev = usbi_get_device_by_session_id(ctx, session_id);
+	if (dev) {
+		usbi_dbg("using existing device for %d/%d (session %ld)",
+			busnum, devaddr, session_id);
+	} else {
+		usbi_dbg("allocating new device for %d/%d (session %ld)",
+			busnum, devaddr, session_id);
+		dev = usbi_alloc_device(ctx, session_id);
+		if (!dev)
+			return LIBUSB_ERROR_NO_MEM;
+		need_unref = 1;
+		r = initialize_device(dev, busnum, devaddr, sysfs_dir);
+		if (r < 0)
+			goto out;
+		r = usbi_sanitize_device(dev);
+		if (r < 0)
+			goto out;
+	}
+
+	discdevs = discovered_devs_append(*_discdevs, dev);
+	if (!discdevs)
+		r = LIBUSB_ERROR_NO_MEM;
+	else
+		*_discdevs = discdevs;
+
+out:
+	if (need_unref)
+		libusb_unref_device(dev);
+	return r;
+}
+
+/* open a bus directory and adds all discovered devices to discdevs. on
+ * failure (non-zero return) the pre-existing discdevs should be destroyed
+ * (and devices freed). on success, the new discdevs pointer should be used
+ * as it may have been moved. */
+static int usbfs_scan_busdir(struct libusb_context *ctx,
+	struct discovered_devs **_discdevs, uint8_t busnum)
+{
+	DIR *dir;
+	char dirpath[PATH_MAX];
+	struct dirent *entry;
+	struct discovered_devs *discdevs = *_discdevs;
+	int r = 0;
+
+	snprintf(dirpath, PATH_MAX, "%s/%03d", usbfs_path, busnum);
+	usbi_dbg("%s", dirpath);
+	dir = opendir(dirpath);
+	if (!dir) {
+		usbi_err(ctx, "opendir '%s' failed, errno=%d", dirpath, errno);
+		/* FIXME: should handle valid race conditions like hub unplugged
+		 * during directory iteration - this is not an error */
+		return LIBUSB_ERROR_IO;
+	}
+
+	while ((entry = readdir(dir))) {
+		int devaddr;
+
+		if (entry->d_name[0] == '.')
+			continue;
+
+		devaddr = atoi(entry->d_name);
+		if (devaddr == 0) {
+			usbi_dbg("unknown dir entry %s", entry->d_name);
+			continue;
+		}
+
+		r = enumerate_device(ctx, &discdevs, busnum, (uint8_t) devaddr, NULL);
+		if (r < 0)
+			goto out;
+	}
+
+	*_discdevs = discdevs;
+out:
+	closedir(dir);
+	return r;
+}
+
+static int usbfs_get_device_list(struct libusb_context *ctx,
+	struct discovered_devs **_discdevs)
+{
+	struct dirent *entry;
+	DIR *buses = opendir(usbfs_path);
+	struct discovered_devs *discdevs = *_discdevs;
+	int r = 0;
+
+	if (!buses) {
+		usbi_err(ctx, "opendir buses failed errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	while ((entry = readdir(buses))) {
+		struct discovered_devs *discdevs_new = discdevs;
+		int busnum;
+
+		if (entry->d_name[0] == '.')
+			continue;
+
+		busnum = atoi(entry->d_name);
+		if (busnum == 0) {
+			usbi_dbg("unknown dir entry %s", entry->d_name);
+			continue;
+		}
+
+		r = usbfs_scan_busdir(ctx, &discdevs_new, busnum);
+		if (r < 0)
+			goto out;
+		discdevs = discdevs_new;
+	}
+
+out:
+	closedir(buses);
+	*_discdevs = discdevs;
+	return r;
+
+}
+
+static int sysfs_scan_device(struct libusb_context *ctx,
+	struct discovered_devs **_discdevs, const char *devname,
+	int *usbfs_fallback)
+{
+	int r;
+	FILE *fd;
+	char filename[PATH_MAX];
+	int busnum;
+	int devaddr;
+
+	usbi_dbg("scan %s", devname);
+
+	/* determine descriptors presence ahead of time, we need to know this
+	 * when we reach initialize_device */
+	if (sysfs_has_descriptors == -1) {
+		struct stat statbuf;
+
+		snprintf(filename, PATH_MAX, "%s/%s/descriptors", SYSFS_DEVICE_PATH,
+			devname);
+		r = stat(filename, &statbuf);
+		if (r == 0 && S_ISREG(statbuf.st_mode)) {
+			usbi_dbg("sysfs descriptors available");
+			sysfs_has_descriptors = 1;
+		} else {
+			usbi_dbg("sysfs descriptors not available");
+			sysfs_has_descriptors = 0;
+		}
+	}
+
+	snprintf(filename, PATH_MAX, "%s/%s/busnum", SYSFS_DEVICE_PATH, devname);
+	fd = fopen(filename, "r");
+	if (!fd) {
+		if (errno == ENOENT) {
+			usbi_dbg("busnum not found, cannot relate sysfs to usbfs, "
+				"falling back on pure usbfs");
+			sysfs_can_relate_devices = 0;
+			*usbfs_fallback = 1;
+			return LIBUSB_ERROR_OTHER;
+		}
+		usbi_err(ctx, "open busnum failed, errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	sysfs_can_relate_devices = 1;
+
+	r = fscanf(fd, "%d", &busnum);
+	fclose(fd);
+	if (r != 1) {
+		usbi_err(ctx, "fscanf busnum returned %d, errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	snprintf(filename, PATH_MAX, "%s/%s/devnum", SYSFS_DEVICE_PATH, devname);
+	fd = fopen(filename, "r");
+	if (!fd) {
+		usbi_err(ctx, "open devnum failed, errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	r = fscanf(fd, "%d", &devaddr);
+	fclose(fd);
+	if (r != 1) {
+		usbi_err(ctx, "fscanf devnum returned %d, errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	usbi_dbg("bus=%d dev=%d", busnum, devaddr);
+	if (busnum > 255 || devaddr > 255)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	return enumerate_device(ctx, _discdevs, busnum & 0xff, devaddr & 0xff,
+		devname);
+}
+
+static int sysfs_get_device_list(struct libusb_context *ctx,
+	struct discovered_devs **_discdevs, int *usbfs_fallback)
+{
+	struct discovered_devs *discdevs = *_discdevs;
+	DIR *devices = opendir(SYSFS_DEVICE_PATH);
+	struct dirent *entry;
+	int r = 0;
+
+	if (!devices) {
+		usbi_err(ctx, "opendir devices failed errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	while ((entry = readdir(devices))) {
+		struct discovered_devs *discdevs_new = discdevs;
+
+		if ((!isdigit(entry->d_name[0]) && strncmp(entry->d_name, "usb", 3))
+				|| strchr(entry->d_name, ':'))
+			continue;
+
+		r = sysfs_scan_device(ctx, &discdevs_new, entry->d_name,
+			usbfs_fallback);
+		if (r < 0)
+			goto out;
+		discdevs = discdevs_new;
+	}	
+
+out:
+	closedir(devices);
+	*_discdevs = discdevs;
+	return r;
+}
+
+static int op_get_device_list(struct libusb_context *ctx,
+	struct discovered_devs **_discdevs)
+{
+	/* we can retrieve device list and descriptors from sysfs or usbfs.
+	 * sysfs is preferable, because if we use usbfs we end up resuming
+	 * any autosuspended USB devices. however, sysfs is not available
+	 * everywhere, so we need a usbfs fallback too.
+	 *
+	 * as described in the "sysfs vs usbfs" comment, sometimes we have
+	 * sysfs but not enough information to relate sysfs devices to usbfs
+	 * nodes. the usbfs_fallback variable is used to indicate that we should
+	 * fall back on usbfs.
+	 */
+	if (sysfs_can_relate_devices != 0) {
+		int usbfs_fallback = 0;
+		int r = sysfs_get_device_list(ctx, _discdevs, &usbfs_fallback);
+		if (!usbfs_fallback)
+			return r;
+	}
+
+	return usbfs_get_device_list(ctx, _discdevs);
+}
+
+static int op_open(struct libusb_device_handle *handle)
+{
+	struct linux_device_handle_priv *hpriv = __device_handle_priv(handle);
+	char filename[PATH_MAX];
+
+	__get_usbfs_path(handle->dev, filename);
+	hpriv->fd = open(filename, O_RDWR);
+	if (hpriv->fd < 0) {
+		if (errno == EACCES) {
+			fprintf(stderr, "libusb couldn't open USB device %s: "
+				"Permission denied.\n"
+				"libusb requires write access to USB device nodes.\n",
+				filename);
+			return LIBUSB_ERROR_ACCESS;
+		} else if (errno == ENOENT) {
+			return LIBUSB_ERROR_NO_DEVICE;
+		} else {
+			usbi_err(HANDLE_CTX(handle),
+				"open failed, code %d errno %d", hpriv->fd, errno);
+			return LIBUSB_ERROR_IO;
+		}
+	}
+
+	return usbi_add_pollfd(HANDLE_CTX(handle), hpriv->fd, POLLOUT);
+}
+
+static void op_close(struct libusb_device_handle *dev_handle)
+{
+	int fd = __device_handle_priv(dev_handle)->fd;
+	usbi_remove_pollfd(HANDLE_CTX(dev_handle), fd);
+	close(fd);
+}
+
+static int op_get_configuration(struct libusb_device_handle *handle,
+	int *config)
+{
+	int r;
+	if (sysfs_can_relate_devices != 1)
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+
+	r = sysfs_get_active_config(handle->dev, config);
+	if (*config == -1)
+		*config = 0;
+
+	return 0;
+}
+
+static int op_set_configuration(struct libusb_device_handle *handle, int config)
+{
+	struct linux_device_priv *priv = __device_priv(handle->dev);
+	int fd = __device_handle_priv(handle)->fd;
+	int r = ioctl(fd, IOCTL_USBFS_SETCONFIG, &config);
+	if (r) {
+		if (errno == EINVAL)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == EBUSY)
+			return LIBUSB_ERROR_BUSY;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "failed, error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	if (!sysfs_has_descriptors) {
+		/* update our cached active config descriptor */
+		if (config == -1) {
+			if (priv->config_descriptor) {
+				free(priv->config_descriptor);
+				priv->config_descriptor = NULL;
+			}
+		} else {
+			r = cache_active_config(handle->dev, fd, config);
+			if (r < 0)
+				usbi_warn(HANDLE_CTX(handle),
+					"failed to update cached config descriptor, error %d", r);
+		}
+	}
+
+	return 0;
+}
+
+static int op_claim_interface(struct libusb_device_handle *handle, int iface)
+{
+	int fd = __device_handle_priv(handle)->fd;
+	int r = ioctl(fd, IOCTL_USBFS_CLAIMINTF, &iface);
+	if (r) {
+		if (errno == ENOENT)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == EBUSY)
+			return LIBUSB_ERROR_BUSY;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"claim interface failed, error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+	return 0;
+}
+
+static int op_release_interface(struct libusb_device_handle *handle, int iface)
+{
+	int fd = __device_handle_priv(handle)->fd;
+	int r = ioctl(fd, IOCTL_USBFS_RELEASEINTF, &iface);
+	if (r) {
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"release interface failed, error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+	return 0;
+}
+
+static int op_set_interface(struct libusb_device_handle *handle, int iface,
+	int altsetting)
+{
+	int fd = __device_handle_priv(handle)->fd;
+	struct usbfs_setinterface setintf;
+	int r;
+
+	setintf.interface = iface;
+	setintf.altsetting = altsetting;
+	r = ioctl(fd, IOCTL_USBFS_SETINTF, &setintf);
+	if (r) {
+		if (errno == EINVAL)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"setintf failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_clear_halt(struct libusb_device_handle *handle,
+	unsigned char endpoint)
+{
+	int fd = __device_handle_priv(handle)->fd;
+	unsigned int _endpoint = endpoint;
+	int r = ioctl(fd, IOCTL_USBFS_CLEAR_HALT, &_endpoint);
+	if (r) {
+		if (errno == ENOENT)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"clear_halt failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_reset_device(struct libusb_device_handle *handle)
+{
+	int fd = __device_handle_priv(handle)->fd;
+	int r = ioctl(fd, IOCTL_USBFS_RESET, NULL);
+	if (r) {
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NOT_FOUND;
+
+		usbi_err(HANDLE_CTX(handle),
+			"reset failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_kernel_driver_active(struct libusb_device_handle *handle,
+	int interface)
+{
+	int fd = __device_handle_priv(handle)->fd;
+	struct usbfs_getdriver getdrv;
+	int r;
+
+	getdrv.interface = interface;
+	r = ioctl(fd, IOCTL_USBFS_GETDRIVER, &getdrv);
+	if (r) {
+		if (errno == ENODATA)
+			return 0;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"get driver failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 1;
+}
+
+static int op_detach_kernel_driver(struct libusb_device_handle *handle,
+	int interface)
+{
+	int fd = __device_handle_priv(handle)->fd;
+	struct usbfs_ioctl command;
+	int r;
+
+	command.ifno = interface;
+	command.ioctl_code = IOCTL_USBFS_DISCONNECT;
+	command.data = NULL;
+
+	r = ioctl(fd, IOCTL_USBFS_IOCTL, &command);
+	if (r) {
+		if (errno == ENODATA)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == EINVAL)
+			return LIBUSB_ERROR_INVALID_PARAM;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"detach failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_attach_kernel_driver(struct libusb_device_handle *handle,
+	int interface)
+{
+	int fd = __device_handle_priv(handle)->fd;
+	struct usbfs_ioctl command;
+	int r;
+
+	command.ifno = interface;
+	command.ioctl_code = IOCTL_USBFS_CONNECT;
+	command.data = NULL;
+
+	r = ioctl(fd, IOCTL_USBFS_IOCTL, &command);
+	if (r < 0) {
+		if (errno == ENODATA)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == EINVAL)
+			return LIBUSB_ERROR_INVALID_PARAM;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+		else if (errno == EBUSY)
+			return LIBUSB_ERROR_BUSY;
+
+		usbi_err(HANDLE_CTX(handle),
+			"attach failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	} else if (r == 0) {
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	return 0;
+}
+
+static void op_destroy_device(struct libusb_device *dev)
+{
+	struct linux_device_priv *priv = __device_priv(dev);
+	if (!sysfs_has_descriptors) {
+		if (priv->dev_descriptor)
+			free(priv->dev_descriptor);
+		if (priv->config_descriptor)
+			free(priv->config_descriptor);
+	}
+	if (priv->sysfs_dir)
+		free(priv->sysfs_dir);
+}
+
+static void free_iso_urbs(struct linux_transfer_priv *tpriv)
+{
+	int i;
+	for (i = 0; i < tpriv->num_urbs; i++) {
+		struct usbfs_urb *urb = tpriv->iso_urbs[i];
+		if (!urb)
+			break;
+		free(urb);
+	}
+
+	free(tpriv->iso_urbs);
+	tpriv->iso_urbs = NULL;
+}
+
+static int submit_bulk_transfer(struct usbi_transfer *itransfer,
+	unsigned char urb_type)
+{
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		__device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb *urbs;
+	int is_out = (transfer->endpoint & LIBUSB_ENDPOINT_DIR_MASK)
+		== LIBUSB_ENDPOINT_OUT;
+	int r;
+	int i;
+	size_t alloc_size;
+
+	if (tpriv->urbs)
+		return LIBUSB_ERROR_BUSY;
+
+	/* usbfs places a 16kb limit on bulk URBs. we divide up larger requests
+	 * into smaller units to meet such restriction, then fire off all the
+	 * units at once. it would be simpler if we just fired one unit at a time,
+	 * but there is a big performance gain through doing it this way. */
+	int num_urbs = transfer->length / MAX_BULK_BUFFER_LENGTH;
+	int last_urb_partial = 0;
+
+	if (transfer->length == 0) {
+		num_urbs = 1;
+	} else if ((transfer->length % MAX_BULK_BUFFER_LENGTH) > 0) {
+		last_urb_partial = 1;
+		num_urbs++;
+	}
+	usbi_dbg("need %d urbs for new transfer with length %d", num_urbs,
+		transfer->length);
+	alloc_size = num_urbs * sizeof(struct usbfs_urb);
+	urbs = malloc(alloc_size);
+	if (!urbs)
+		return LIBUSB_ERROR_NO_MEM;
+	memset(urbs, 0, alloc_size);
+	tpriv->urbs = urbs;
+	tpriv->num_urbs = num_urbs;
+	tpriv->num_retired = 0;
+	tpriv->reap_action = NORMAL;
+
+	for (i = 0; i < num_urbs; i++) {
+		struct usbfs_urb *urb = &urbs[i];
+		urb->usercontext = itransfer;
+		urb->type = urb_type;
+		urb->endpoint = transfer->endpoint;
+		urb->buffer = transfer->buffer + (i * MAX_BULK_BUFFER_LENGTH);
+		if (supports_flag_bulk_continuation && !is_out)
+			urb->flags = USBFS_URB_SHORT_NOT_OK;
+		if (i == num_urbs - 1 && last_urb_partial)
+			urb->buffer_length = transfer->length % MAX_BULK_BUFFER_LENGTH;
+		else if (transfer->length == 0)
+			urb->buffer_length = 0;
+		else
+			urb->buffer_length = MAX_BULK_BUFFER_LENGTH;
+
+		if (i > 0 && supports_flag_bulk_continuation)
+			urb->flags |= USBFS_URB_BULK_CONTINUATION;
+
+		r = ioctl(dpriv->fd, IOCTL_USBFS_SUBMITURB, urb);
+		if (r < 0) {
+			int j;
+
+			if (errno == ENODEV) {
+				r = LIBUSB_ERROR_NO_DEVICE;
+			} else {
+				usbi_err(TRANSFER_CTX(transfer),
+					"submiturb failed error %d errno=%d", r, errno);
+				r = LIBUSB_ERROR_IO;
+			}
+	
+			/* if the first URB submission fails, we can simply free up and
+			 * return failure immediately. */
+			if (i == 0) {
+				usbi_dbg("first URB failed, easy peasy");
+				free(urbs);
+				tpriv->urbs = NULL;
+				return r;
+			}
+
+			/* if it's not the first URB that failed, the situation is a bit
+			 * tricky. we must discard all previous URBs. there are
+			 * complications:
+			 *  - discarding is asynchronous - discarded urbs will be reaped
+			 *    later. the user must not have freed the transfer when the
+			 *    discarded URBs are reaped, otherwise libusb will be using
+			 *    freed memory.
+			 *  - the earlier URBs may have completed successfully and we do
+			 *    not want to throw away any data.
+			 * so, in this case we discard all the previous URBs BUT we report
+			 * that the transfer was submitted successfully. then later when
+			 * the final discard completes we can report error to the user.
+			 */
+			tpriv->reap_action = SUBMIT_FAILED;
+
+			/* The URBs we haven't submitted yet we count as already
+			 * retired. */
+			tpriv->num_retired += num_urbs - i;
+			for (j = 0; j < i; j++) {
+				int tmp = ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, &urbs[j]);
+				if (tmp && errno != EINVAL)
+					usbi_warn(TRANSFER_CTX(transfer),
+						"unrecognised discard errno %d", errno);
+			}
+
+			usbi_dbg("reporting successful submission but waiting for %d "
+				"discards before reporting error", i);
+			return 0;
+		}
+	}
+
+	return 0;
+}
+
+static int submit_iso_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		__device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb **urbs;
+	size_t alloc_size;
+	int num_packets = transfer->num_iso_packets;
+	int i;
+	int this_urb_len = 0;
+	int num_urbs = 1;
+	int packet_offset = 0;
+	unsigned int packet_len;
+	unsigned char *urb_buffer = transfer->buffer;
+
+	if (tpriv->iso_urbs)
+		return LIBUSB_ERROR_BUSY;
+
+	/* usbfs places a 32kb limit on iso URBs. we divide up larger requests
+	 * into smaller units to meet such restriction, then fire off all the
+	 * units at once. it would be simpler if we just fired one unit at a time,
+	 * but there is a big performance gain through doing it this way. */
+
+	/* calculate how many URBs we need */
+	for (i = 0; i < num_packets; i++) {
+		int space_remaining = MAX_ISO_BUFFER_LENGTH - this_urb_len;
+		packet_len = transfer->iso_packet_desc[i].length;
+
+		if (packet_len > space_remaining) {
+			num_urbs++;
+			this_urb_len = packet_len;
+		} else {
+			this_urb_len += packet_len;
+		}
+	}
+	usbi_dbg("need %d 32k URBs for transfer", num_urbs);
+
+	alloc_size = num_urbs * sizeof(*urbs);
+	urbs = malloc(alloc_size);
+	if (!urbs)
+		return LIBUSB_ERROR_NO_MEM;
+	memset(urbs, 0, alloc_size);
+
+	tpriv->iso_urbs = urbs;
+	tpriv->num_urbs = num_urbs;
+	tpriv->num_retired = 0;
+	tpriv->reap_action = NORMAL;
+	tpriv->iso_packet_offset = 0;
+
+	/* allocate + initialize each URB with the correct number of packets */
+	for (i = 0; i < num_urbs; i++) {
+		struct usbfs_urb *urb;
+		int space_remaining_in_urb = MAX_ISO_BUFFER_LENGTH;
+		int urb_packet_offset = 0;
+		unsigned char *urb_buffer_orig = urb_buffer;
+		int j;
+		int k;
+
+		/* swallow up all the packets we can fit into this URB */
+		while (packet_offset < transfer->num_iso_packets) {
+			packet_len = transfer->iso_packet_desc[packet_offset].length;
+			if (packet_len <= space_remaining_in_urb) {
+				/* throw it in */
+				urb_packet_offset++;
+				packet_offset++;
+				space_remaining_in_urb -= packet_len;
+				urb_buffer += packet_len;
+			} else {
+				/* it can't fit, save it for the next URB */
+				break;
+			}
+		}
+
+		alloc_size = sizeof(*urb)
+			+ (urb_packet_offset * sizeof(struct usbfs_iso_packet_desc));
+		urb = malloc(alloc_size);
+		if (!urb) {
+			free_iso_urbs(tpriv);
+			return LIBUSB_ERROR_NO_MEM;
+		}
+		memset(urb, 0, alloc_size);
+		urbs[i] = urb;
+
+		/* populate packet lengths */
+		for (j = 0, k = packet_offset - urb_packet_offset;
+				k < packet_offset; k++, j++) {
+			packet_len = transfer->iso_packet_desc[k].length;
+			urb->iso_frame_desc[j].length = packet_len;
+		}
+
+		urb->usercontext = itransfer;
+		urb->type = USBFS_URB_TYPE_ISO;
+		/* FIXME: interface for non-ASAP data? */
+		urb->flags = USBFS_URB_ISO_ASAP;
+		urb->endpoint = transfer->endpoint;
+		urb->number_of_packets = urb_packet_offset;
+		urb->buffer = urb_buffer_orig;
+	}
+
+	/* submit URBs */
+	for (i = 0; i < num_urbs; i++) {
+		int r = ioctl(dpriv->fd, IOCTL_USBFS_SUBMITURB, urbs[i]);
+		if (r < 0) {
+			int j;
+
+			if (errno == ENODEV) {
+				r = LIBUSB_ERROR_NO_DEVICE;
+			} else {
+				usbi_err(TRANSFER_CTX(transfer),
+					"submiturb failed error %d errno=%d", r, errno);
+				r = LIBUSB_ERROR_IO;
+			}
+
+			/* if the first URB submission fails, we can simply free up and
+			 * return failure immediately. */
+			if (i == 0) {
+				usbi_dbg("first URB failed, easy peasy");
+				free_iso_urbs(tpriv);
+				return r;
+			}
+
+			/* if it's not the first URB that failed, the situation is a bit
+			 * tricky. we must discard all previous URBs. there are
+			 * complications:
+			 *  - discarding is asynchronous - discarded urbs will be reaped
+			 *    later. the user must not have freed the transfer when the
+			 *    discarded URBs are reaped, otherwise libusb will be using
+			 *    freed memory.
+			 *  - the earlier URBs may have completed successfully and we do
+			 *    not want to throw away any data.
+			 * so, in this case we discard all the previous URBs BUT we report
+			 * that the transfer was submitted successfully. then later when
+			 * the final discard completes we can report error to the user.
+			 */
+			tpriv->reap_action = SUBMIT_FAILED;
+
+			/* The URBs we haven't submitted yet we count as already
+			 * retired. */
+			tpriv->num_retired = num_urbs - i;
+			for (j = 0; j < i; j++) {
+				int tmp = ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, urbs[j]);
+				if (tmp && errno != EINVAL)
+					usbi_warn(TRANSFER_CTX(transfer),
+						"unrecognised discard errno %d", errno);
+			}
+
+			usbi_dbg("reporting successful submission but waiting for %d "
+				"discards before reporting error", i);
+			return 0;
+		}
+	}
+
+	return 0;
+}
+
+static int submit_control_transfer(struct usbi_transfer *itransfer)
+{
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		__device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb *urb;
+	int r;
+
+	if (tpriv->urbs)
+		return LIBUSB_ERROR_BUSY;
+
+	if (transfer->length - LIBUSB_CONTROL_SETUP_SIZE > MAX_CTRL_BUFFER_LENGTH)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	urb = malloc(sizeof(struct usbfs_urb));
+	if (!urb)
+		return LIBUSB_ERROR_NO_MEM;
+	memset(urb, 0, sizeof(struct usbfs_urb));
+	tpriv->urbs = urb;
+	tpriv->reap_action = NORMAL;
+
+	urb->usercontext = itransfer;
+	urb->type = USBFS_URB_TYPE_CONTROL;
+	urb->endpoint = transfer->endpoint;
+	urb->buffer = transfer->buffer;
+	urb->buffer_length = transfer->length;
+
+	r = ioctl(dpriv->fd, IOCTL_USBFS_SUBMITURB, urb);
+	if (r < 0) {
+		free(urb);
+		tpriv->urbs = NULL;
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(TRANSFER_CTX(transfer),
+			"submiturb failed error %d errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+	return 0;
+}
+
+static int op_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		return submit_control_transfer(itransfer);
+	case LIBUSB_TRANSFER_TYPE_BULK:
+		return submit_bulk_transfer(itransfer, USBFS_URB_TYPE_BULK);
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		return submit_bulk_transfer(itransfer, USBFS_URB_TYPE_INTERRUPT);
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		return submit_iso_transfer(itransfer);
+	default:
+		usbi_err(TRANSFER_CTX(transfer),
+			"unknown endpoint type %d", transfer->type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+}
+
+static int cancel_control_transfer(struct usbi_transfer *itransfer)
+{
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		__device_handle_priv(transfer->dev_handle);
+	int r;
+
+	if (!tpriv->urbs)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	tpriv->reap_action = CANCELLED;
+	r = ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, tpriv->urbs);
+	if(r) {
+		if (errno == EINVAL) {
+			usbi_dbg("URB not found --> assuming ready to be reaped");
+			return 0;
+		} else {
+			usbi_err(TRANSFER_CTX(transfer),
+				"unrecognised DISCARD code %d", errno);
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+
+	return 0;
+}
+
+static int cancel_bulk_transfer(struct usbi_transfer *itransfer)
+{
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		__device_handle_priv(transfer->dev_handle);
+	int i;
+
+	if (!tpriv->urbs)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	tpriv->reap_action = CANCELLED;
+	for (i = 0; i < tpriv->num_urbs; i++) {
+		int tmp = ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, &tpriv->urbs[i]);
+		if (tmp && errno != EINVAL)
+			usbi_warn(TRANSFER_CTX(transfer),
+				"unrecognised discard errno %d", errno);
+	}
+	return 0;
+}
+
+static int cancel_iso_transfer(struct usbi_transfer *itransfer)
+{
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		__device_handle_priv(transfer->dev_handle);
+	int i;
+
+	if (!tpriv->iso_urbs)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	tpriv->reap_action = CANCELLED;
+	for (i = 0; i < tpriv->num_urbs; i++) {
+		int tmp = ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, tpriv->iso_urbs[i]);
+		if (tmp && errno != EINVAL)
+			usbi_warn(TRANSFER_CTX(transfer),
+				"unrecognised discard errno %d", errno);
+	}
+	return 0;
+}
+
+static int op_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		return cancel_control_transfer(itransfer);
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		return cancel_bulk_transfer(itransfer);
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		return cancel_iso_transfer(itransfer);
+	default:
+		usbi_err(TRANSFER_CTX(transfer),
+			"unknown endpoint type %d", transfer->type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+}
+
+static void op_clear_transfer_priv(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		free(tpriv->urbs);
+		tpriv->urbs = NULL;
+		break;
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		free_iso_urbs(tpriv);
+		break;
+	default:
+		usbi_err(TRANSFER_CTX(transfer),
+			"unknown endpoint type %d", transfer->type);
+	}
+}
+
+static int handle_bulk_completion(struct usbi_transfer *itransfer,
+	struct usbfs_urb *urb)
+{
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	int num_urbs = tpriv->num_urbs;
+	int urb_idx = urb - tpriv->urbs;
+	enum libusb_transfer_status status = LIBUSB_TRANSFER_COMPLETED;
+	int r = 0;
+
+	pthread_mutex_lock(&itransfer->lock);
+	usbi_dbg("handling completion status %d of bulk urb %d/%d", urb->status,
+		urb_idx + 1, num_urbs);
+
+	tpriv->num_retired++;
+
+	if (tpriv->reap_action != NORMAL) {
+		/* cancelled, submit_fail, or completed early */
+		usbi_dbg("abnormal reap: urb status %d", urb->status);
+
+		/* even though we're in the process of cancelling, it's possible that
+		 * we may receive some data in these URBs that we don't want to lose.
+		 * examples:
+		 * 1. while the kernel is cancelling all the packets that make up an
+		 *    URB, a few of them might complete. so we get back a successful
+		 *    cancellation *and* some data.
+		 * 2. we receive a short URB which marks the early completion condition,
+		 *    so we start cancelling the remaining URBs. however, we're too
+		 *    slow and another URB completes (or at least completes partially).
+		 *
+		 * When this happens, our objectives are not to lose any "surplus" data,
+		 * and also to stick it at the end of the previously-received data
+		 * (closing any holes), so that libusb reports the total amount of
+		 * transferred data and presents it in a contiguous chunk.
+		 */
+		if (urb->actual_length > 0) {
+			struct libusb_transfer *transfer =
+				__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+			unsigned char *target = transfer->buffer + itransfer->transferred;
+			usbi_dbg("received %d bytes of surplus data", urb->actual_length);
+			if (urb->buffer != target) {
+				usbi_dbg("moving surplus data from offset %d to offset %d",
+					(unsigned char *) urb->buffer - transfer->buffer,
+					target - transfer->buffer);
+				memmove(target, urb->buffer, urb->actual_length);
+			}
+			itransfer->transferred += urb->actual_length;
+		}
+
+		if (tpriv->num_retired == num_urbs) {
+			usbi_dbg("abnormal reap: last URB handled, reporting");
+			if (tpriv->reap_action == CANCELLED) {
+				free(tpriv->urbs);
+				tpriv->urbs = NULL;
+				pthread_mutex_unlock(&itransfer->lock);
+				r = usbi_handle_transfer_cancellation(itransfer);
+				goto out_unlock;
+			}
+			if (tpriv->reap_action != COMPLETED_EARLY)
+				status = LIBUSB_TRANSFER_ERROR;
+			goto completed;
+		}
+		goto out_unlock;
+	}
+
+	if (urb->status == 0 || urb->status == -EREMOTEIO ||
+			(urb->status == -EOVERFLOW && urb->actual_length > 0))
+		itransfer->transferred += urb->actual_length;
+
+
+	switch (urb->status) {
+	case 0:
+		break;
+	case -EREMOTEIO: /* short transfer */
+		break;
+	case -EPIPE:
+		usbi_dbg("detected endpoint stall");
+		status = LIBUSB_TRANSFER_STALL;
+		goto completed;
+	case -EOVERFLOW:
+		/* overflow can only ever occur in the last urb */
+		usbi_dbg("overflow, actual_length=%d", urb->actual_length);
+		status = LIBUSB_TRANSFER_OVERFLOW;
+		goto completed;
+	case -ETIME:
+	case -EPROTO:
+	case -EILSEQ:
+		usbi_dbg("low level error %d", urb->status);
+		status = LIBUSB_TRANSFER_ERROR;
+		goto completed;
+	default:
+		usbi_warn(ITRANSFER_CTX(itransfer),
+			"unrecognised urb status %d", urb->status);
+		status = LIBUSB_TRANSFER_ERROR;
+		goto completed;
+	}
+
+	/* if we're the last urb or we got less data than requested then we're
+	 * done */
+	if (urb_idx == num_urbs - 1) {
+		usbi_dbg("last URB in transfer --> complete!");
+	} else if (urb->actual_length < urb->buffer_length) {
+		struct libusb_transfer *transfer =
+			__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+		struct linux_device_handle_priv *dpriv =
+			__device_handle_priv(transfer->dev_handle);
+		int i;
+
+		usbi_dbg("short transfer %d/%d --> complete!", urb->actual_length,
+			urb->buffer_length);
+
+		/* we have to cancel the remaining urbs and wait for their completion
+		 * before reporting results */
+		tpriv->reap_action = COMPLETED_EARLY;
+		for (i = urb_idx + 1; i < tpriv->num_urbs; i++) {
+			/* remaining URBs with continuation flag are automatically
+			 * cancelled by the kernel */
+			if (tpriv->urbs[i].flags & USBFS_URB_BULK_CONTINUATION)
+				continue;
+			int tmp = ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, &tpriv->urbs[i]);
+			if (tmp && errno != EINVAL)
+				usbi_warn(TRANSFER_CTX(transfer),
+					"unrecognised discard errno %d", errno);
+		}
+		goto out_unlock;
+	} else {
+		goto out_unlock;
+	}
+
+completed:
+	free(tpriv->urbs);
+	tpriv->urbs = NULL;
+	pthread_mutex_unlock(&itransfer->lock);
+	return usbi_handle_transfer_completion(itransfer, status);
+out_unlock:
+	pthread_mutex_unlock(&itransfer->lock);
+	return r;
+}
+
+static int handle_iso_completion(struct usbi_transfer *itransfer,
+	struct usbfs_urb *urb)
+{
+	struct libusb_transfer *transfer =
+		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	int num_urbs = tpriv->num_urbs;
+	int urb_idx = 0;
+	int i;
+
+	pthread_mutex_lock(&itransfer->lock);
+	for (i = 0; i < num_urbs; i++) {
+		if (urb == tpriv->iso_urbs[i]) {
+			urb_idx = i + 1;
+			break;
+		}
+	}
+	if (urb_idx == 0) {
+		usbi_err(TRANSFER_CTX(transfer), "could not locate urb!");
+		pthread_mutex_unlock(&itransfer->lock);
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg("handling completion status %d of iso urb %d/%d", urb->status,
+		urb_idx, num_urbs);
+
+	if (urb->status == 0) {
+		/* copy isochronous results back in */
+
+		for (i = 0; i < urb->number_of_packets; i++) {
+			struct usbfs_iso_packet_desc *urb_desc = &urb->iso_frame_desc[i];
+			struct libusb_iso_packet_descriptor *lib_desc =
+				&transfer->iso_packet_desc[tpriv->iso_packet_offset++];
+			lib_desc->status = urb_desc->status;
+			lib_desc->actual_length = urb_desc->actual_length;
+		}
+	}
+
+	tpriv->num_retired++;
+
+	if (tpriv->reap_action != NORMAL) { /* cancelled or submit_fail */
+		usbi_dbg("CANCEL: urb status %d", urb->status);
+
+		if (tpriv->num_retired == num_urbs) {
+			usbi_dbg("CANCEL: last URB handled, reporting");
+			free_iso_urbs(tpriv);
+			if (tpriv->reap_action == CANCELLED) {
+				pthread_mutex_unlock(&itransfer->lock);
+				return usbi_handle_transfer_cancellation(itransfer);
+			} else {
+				pthread_mutex_unlock(&itransfer->lock);
+				return usbi_handle_transfer_completion(itransfer,
+					LIBUSB_TRANSFER_ERROR);
+			}
+		}
+		goto out;
+	}
+
+	switch (urb->status) {
+	case 0:
+		break;
+	case -ETIME:
+	case -EPROTO:
+	case -EILSEQ:
+		usbi_dbg("low-level USB error %d", urb->status);
+		break;
+	default:
+		usbi_warn(TRANSFER_CTX(transfer),
+			"unrecognised urb status %d", urb->status);
+		break;
+	}
+
+	/* if we're the last urb or we got less data than requested then we're
+	 * done */
+	if (urb_idx == num_urbs) {
+		usbi_dbg("last URB in transfer --> complete!");
+		free_iso_urbs(tpriv);
+		pthread_mutex_unlock(&itransfer->lock);
+		return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_COMPLETED);
+	}
+
+out:
+	pthread_mutex_unlock(&itransfer->lock);
+	return 0;
+}
+
+static int handle_control_completion(struct usbi_transfer *itransfer,
+	struct usbfs_urb *urb)
+{
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	int status;
+
+	pthread_mutex_lock(&itransfer->lock);
+	usbi_dbg("handling completion status %d", urb->status);
+
+	if (urb->status == 0)
+		itransfer->transferred += urb->actual_length;
+
+	if (tpriv->reap_action == CANCELLED) {
+		if (urb->status != 0 && urb->status != -ENOENT)
+			usbi_warn(ITRANSFER_CTX(itransfer),
+				"cancel: unrecognised urb status %d", urb->status);
+		free(tpriv->urbs);
+		tpriv->urbs = NULL;
+		pthread_mutex_unlock(&itransfer->lock);
+		return usbi_handle_transfer_cancellation(itransfer);
+	}
+
+	switch (urb->status) {
+	case 0:
+		itransfer->transferred = urb->actual_length;
+		status = LIBUSB_TRANSFER_COMPLETED;
+		break;
+	case -EPIPE:
+		usbi_dbg("unsupported control request");
+		status = LIBUSB_TRANSFER_STALL;
+		break;
+	case -ETIME:
+	case -EPROTO:
+	case -EILSEQ:
+		usbi_dbg("low-level bus error occurred");
+		status = LIBUSB_TRANSFER_ERROR;
+		break;
+	default:
+		usbi_warn(ITRANSFER_CTX(itransfer),
+			"unrecognised urb status %d", urb->status);
+		status = LIBUSB_TRANSFER_ERROR;
+		break;
+	}
+
+	free(tpriv->urbs);
+	tpriv->urbs = NULL;
+	pthread_mutex_unlock(&itransfer->lock);
+	return usbi_handle_transfer_completion(itransfer, status);
+}
+
+static int reap_for_handle(struct libusb_device_handle *handle)
+{
+	struct linux_device_handle_priv *hpriv = __device_handle_priv(handle);
+	int r;
+	struct usbfs_urb *urb;
+	struct usbi_transfer *itransfer;
+	struct libusb_transfer *transfer;
+
+	r = ioctl(hpriv->fd, IOCTL_USBFS_REAPURBNDELAY, &urb);
+	if (r == -1 && errno == EAGAIN)
+		return 1;
+	if (r < 0) {
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "reap failed error %d errno=%d",
+			r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	itransfer = urb->usercontext;
+	transfer = __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	usbi_dbg("urb type=%d status=%d transferred=%d", urb->type, urb->status,
+		urb->actual_length);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		return handle_iso_completion(itransfer, urb);
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		return handle_bulk_completion(itransfer, urb);
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		return handle_control_completion(itransfer, urb);
+	default:
+		usbi_err(HANDLE_CTX(handle), "unrecognised endpoint type %x",
+			transfer->type);
+		return LIBUSB_ERROR_OTHER;
+	}
+}
+
+static int op_handle_events(struct libusb_context *ctx,
+	struct pollfd *fds, nfds_t nfds, int num_ready)
+{
+	int r;
+	int i = 0;
+
+	pthread_mutex_lock(&ctx->open_devs_lock);
+	for (i = 0; i < nfds && num_ready > 0; i++) {
+		struct pollfd *pollfd = &fds[i];
+		struct libusb_device_handle *handle;
+		struct linux_device_handle_priv *hpriv = NULL;
+
+		if (!pollfd->revents)
+			continue;
+
+		num_ready--;
+		list_for_each_entry(handle, &ctx->open_devs, list) {
+			hpriv =  __device_handle_priv(handle);
+			if (hpriv->fd == pollfd->fd)
+				break;
+		}
+
+		if (pollfd->revents & POLLERR) {
+			usbi_remove_pollfd(HANDLE_CTX(handle), hpriv->fd);
+			usbi_handle_disconnect(handle);
+			continue;
+		}
+
+		r = reap_for_handle(handle);
+		if (r == 1 || r == LIBUSB_ERROR_NO_DEVICE)
+			continue;
+		else if (r < 0)
+			goto out;
+	}
+
+	r = 0;
+out:
+	pthread_mutex_unlock(&ctx->open_devs_lock);
+	return r;
+}
+
+static int op_clock_gettime(int clk_id, struct timespec *tp)
+{
+	switch (clk_id) {
+	case USBI_CLOCK_MONOTONIC:
+		return clock_gettime(monotonic_clkid, tp);
+	case USBI_CLOCK_REALTIME:
+		return clock_gettime(CLOCK_REALTIME, tp);
+	default:
+		return LIBUSB_ERROR_INVALID_PARAM;
+  }
+}
+
+#ifdef USBI_TIMERFD_AVAILABLE
+static clockid_t op_get_timerfd_clockid(void)
+{
+	return monotonic_clkid;
+
+}
+#endif
+
+const struct usbi_os_backend linux_usbfs_backend = {
+	.name = "Linux usbfs",
+	.init = op_init,
+	.exit = NULL,
+	.get_device_list = op_get_device_list,
+	.get_device_descriptor = op_get_device_descriptor,
+	.get_active_config_descriptor = op_get_active_config_descriptor,
+	.get_config_descriptor = op_get_config_descriptor,
+
+	.open = op_open,
+	.close = op_close,
+	.get_configuration = op_get_configuration,
+	.set_configuration = op_set_configuration,
+	.claim_interface = op_claim_interface,
+	.release_interface = op_release_interface,
+
+	.set_interface_altsetting = op_set_interface,
+	.clear_halt = op_clear_halt,
+	.reset_device = op_reset_device,
+
+	.kernel_driver_active = op_kernel_driver_active,
+	.detach_kernel_driver = op_detach_kernel_driver,
+	.attach_kernel_driver = op_attach_kernel_driver,
+
+	.destroy_device = op_destroy_device,
+
+	.submit_transfer = op_submit_transfer,
+	.cancel_transfer = op_cancel_transfer,
+	.clear_transfer_priv = op_clear_transfer_priv,
+
+	.handle_events = op_handle_events,
+
+	.clock_gettime = op_clock_gettime,
+
+#ifdef USBI_TIMERFD_AVAILABLE
+	.get_timerfd_clockid = op_get_timerfd_clockid,
+#endif
+
+	.device_priv_size = sizeof(struct linux_device_priv),
+	.device_handle_priv_size = sizeof(struct linux_device_handle_priv),
+	.transfer_priv_size = sizeof(struct linux_transfer_priv),
+	.add_iso_packet_size = 0,
+};
+
diff --git a/libusb/os/linux_usbfs.h b/libusb/os/linux_usbfs.h
new file mode 100644
index 0000000..bd02edc
--- /dev/null
+++ b/libusb/os/linux_usbfs.h
@@ -0,0 +1,138 @@
+/*
+ * usbfs header structures
+ * Copyright (C) 2007 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef __LIBUSB_USBFS_H__
+#define __LIBUSB_USBFS_H__
+
+#define SYSFS_DEVICE_PATH "/sys/bus/usb/devices"
+
+struct usbfs_ctrltransfer {
+	/* keep in sync with usbdevice_fs.h:usbdevfs_ctrltransfer */
+	uint8_t  bmRequestType;
+	uint8_t  bRequest;
+	uint16_t wValue;
+	uint16_t wIndex;
+	uint16_t wLength;
+
+	uint32_t timeout;	/* in milliseconds */
+
+	/* pointer to data */
+	void *data;
+};
+
+struct usbfs_bulktransfer {
+	/* keep in sync with usbdevice_fs.h:usbdevfs_bulktransfer */
+	unsigned int ep;
+	unsigned int len;
+	unsigned int timeout;	/* in milliseconds */
+
+	/* pointer to data */
+	void *data;
+};
+
+struct usbfs_setinterface {
+	/* keep in sync with usbdevice_fs.h:usbdevfs_setinterface */
+	unsigned int interface;
+	unsigned int altsetting;
+};
+
+#define USBFS_MAXDRIVERNAME 255
+
+struct usbfs_getdriver {
+	unsigned int interface;
+	char driver[USBFS_MAXDRIVERNAME + 1];
+};
+
+#define USBFS_URB_SHORT_NOT_OK		0x01
+#define USBFS_URB_ISO_ASAP			0x02
+#define USBFS_URB_BULK_CONTINUATION	0x04
+#define USBFS_URB_QUEUE_BULK		0x10
+
+enum usbfs_urb_type {
+	USBFS_URB_TYPE_ISO = 0,
+	USBFS_URB_TYPE_INTERRUPT = 1,
+	USBFS_URB_TYPE_CONTROL = 2,
+	USBFS_URB_TYPE_BULK = 3,
+};
+
+struct usbfs_iso_packet_desc {
+	unsigned int length;
+	unsigned int actual_length;
+	unsigned int status;
+};
+
+#define MAX_ISO_BUFFER_LENGTH		32768
+#define MAX_BULK_BUFFER_LENGTH		16384
+#define MAX_CTRL_BUFFER_LENGTH		4096
+
+struct usbfs_urb {
+	unsigned char type;
+	unsigned char endpoint;
+	int status;
+	unsigned int flags;
+	void *buffer;
+	int buffer_length;
+	int actual_length;
+	int start_frame;
+	int number_of_packets;
+	int error_count;
+	unsigned int signr;
+	void *usercontext;
+	struct usbfs_iso_packet_desc iso_frame_desc[0];
+};
+
+struct usbfs_connectinfo {
+	unsigned int devnum;
+	unsigned char slow;
+};
+
+struct usbfs_ioctl {
+	int ifno;	/* interface 0..N ; negative numbers reserved */
+	int ioctl_code;	/* MUST encode size + direction of data so the
+			 * macros in <asm/ioctl.h> give correct values */
+	void *data;	/* param buffer (in, or out) */
+};
+
+struct usbfs_hub_portinfo {
+	unsigned char numports;
+	unsigned char port[127];	/* port to device num mapping */
+};
+
+#define IOCTL_USBFS_CONTROL	_IOWR('U', 0, struct usbfs_ctrltransfer)
+#define IOCTL_USBFS_BULK		_IOWR('U', 2, struct usbfs_bulktransfer)
+#define IOCTL_USBFS_RESETEP	_IOR('U', 3, unsigned int)
+#define IOCTL_USBFS_SETINTF	_IOR('U', 4, struct usbfs_setinterface)
+#define IOCTL_USBFS_SETCONFIG	_IOR('U', 5, unsigned int)
+#define IOCTL_USBFS_GETDRIVER	_IOW('U', 8, struct usbfs_getdriver)
+#define IOCTL_USBFS_SUBMITURB	_IOR('U', 10, struct usbfs_urb)
+#define IOCTL_USBFS_DISCARDURB	_IO('U', 11)
+#define IOCTL_USBFS_REAPURB	_IOW('U', 12, void *)
+#define IOCTL_USBFS_REAPURBNDELAY	_IOW('U', 13, void *)
+#define IOCTL_USBFS_CLAIMINTF	_IOR('U', 15, unsigned int)
+#define IOCTL_USBFS_RELEASEINTF	_IOR('U', 16, unsigned int)
+#define IOCTL_USBFS_CONNECTINFO	_IOW('U', 17, struct usbfs_connectinfo)
+#define IOCTL_USBFS_IOCTL         _IOWR('U', 18, struct usbfs_ioctl)
+#define IOCTL_USBFS_HUB_PORTINFO	_IOR('U', 19, struct usbfs_hub_portinfo)
+#define IOCTL_USBFS_RESET		_IO('U', 20)
+#define IOCTL_USBFS_CLEAR_HALT	_IOR('U', 21, unsigned int)
+#define IOCTL_USBFS_DISCONNECT	_IO('U', 22)
+#define IOCTL_USBFS_CONNECT	_IO('U', 23)
+
+#endif
diff --git a/libusb/sync.c b/libusb/sync.c
new file mode 100644
index 0000000..bd4d970
--- /dev/null
+++ b/libusb/sync.c
@@ -0,0 +1,311 @@
+/*
+ * Synchronous I/O functions for libusb
+ * Copyright (C) 2007-2008 Daniel Drake <dsd@gentoo.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+#include <errno.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "libusbi.h"
+
+/**
+ * @defgroup syncio Synchronous device I/O
+ *
+ * This page documents libusb's synchronous (blocking) API for USB device I/O.
+ * This interface is easy to use but has some limitations. More advanced users
+ * may wish to consider using the \ref asyncio "asynchronous I/O API" instead.
+ */
+
+static void ctrl_transfer_cb(struct libusb_transfer *transfer)
+{
+	int *completed = transfer->user_data;
+	*completed = 1;
+	usbi_dbg("actual_length=%d", transfer->actual_length);
+	/* caller interprets result and frees transfer */
+}
+
+/** \ingroup syncio
+ * Perform a USB control transfer.
+ *
+ * The direction of the transfer is inferred from the bmRequestType field of
+ * the setup packet.
+ *
+ * The wValue, wIndex and wLength fields values should be given in host-endian
+ * byte order.
+ *
+ * \param dev_handle a handle for the device to communicate with
+ * \param bmRequestType the request type field for the setup packet
+ * \param bRequest the request field for the setup packet
+ * \param wValue the value field for the setup packet
+ * \param wIndex the index field for the setup packet
+ * \param data a suitably-sized data buffer for either input or output
+ * (depending on direction bits within bmRequestType)
+ * \param wLength the length field for the setup packet. The data buffer should
+ * be at least this size.
+ * \param timeout timeout (in millseconds) that this function should wait
+ * before giving up due to no response being received. For an unlimited
+ * timeout, use value 0.
+ * \returns on success, the number of bytes actually transferred
+ * \returns LIBUSB_ERROR_TIMEOUT if the transfer timed out
+ * \returns LIBUSB_ERROR_PIPE if the control request was not supported by the
+ * device
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failures
+ */
+API_EXPORTED int libusb_control_transfer(libusb_device_handle *dev_handle,
+	uint8_t bmRequestType, uint8_t bRequest, uint16_t wValue, uint16_t wIndex,
+	unsigned char *data, uint16_t wLength, unsigned int timeout)
+{
+	struct libusb_transfer *transfer = libusb_alloc_transfer(0);
+	unsigned char *buffer;
+	int completed = 0;
+	int r;
+
+	if (!transfer)
+		return LIBUSB_ERROR_NO_MEM;
+	
+	buffer = malloc(LIBUSB_CONTROL_SETUP_SIZE + wLength);
+	if (!buffer) {
+		libusb_free_transfer(transfer);
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	libusb_fill_control_setup(buffer, bmRequestType, bRequest, wValue, wIndex,
+		wLength);
+	if ((bmRequestType & LIBUSB_ENDPOINT_DIR_MASK) == LIBUSB_ENDPOINT_OUT)
+		memcpy(buffer + LIBUSB_CONTROL_SETUP_SIZE, data, wLength);
+
+	libusb_fill_control_transfer(transfer, dev_handle, buffer,
+		ctrl_transfer_cb, &completed, timeout);
+	transfer->flags = LIBUSB_TRANSFER_FREE_BUFFER;
+	r = libusb_submit_transfer(transfer);
+	if (r < 0) {
+		libusb_free_transfer(transfer);
+		return r;
+	}
+
+	while (!completed) {
+		r = libusb_handle_events(HANDLE_CTX(dev_handle));
+		if (r < 0) {
+			if (r == LIBUSB_ERROR_INTERRUPTED)
+				continue;
+			libusb_cancel_transfer(transfer);
+			while (!completed)
+				if (libusb_handle_events(HANDLE_CTX(dev_handle)) < 0)
+					break;
+			libusb_free_transfer(transfer);
+			return r;
+		}
+	}
+
+	if ((bmRequestType & LIBUSB_ENDPOINT_DIR_MASK) == LIBUSB_ENDPOINT_IN)
+		memcpy(data, libusb_control_transfer_get_data(transfer),
+			transfer->actual_length);
+
+	switch (transfer->status) {
+	case LIBUSB_TRANSFER_COMPLETED:
+		r = transfer->actual_length;
+		break;
+	case LIBUSB_TRANSFER_TIMED_OUT:
+		r = LIBUSB_ERROR_TIMEOUT;
+		break;
+	case LIBUSB_TRANSFER_STALL:
+		r = LIBUSB_ERROR_PIPE;
+		break;
+	case LIBUSB_TRANSFER_NO_DEVICE:
+		r = LIBUSB_ERROR_NO_DEVICE;
+		break;
+	default:
+		usbi_warn(HANDLE_CTX(dev_handle),
+			"unrecognised status code %d", transfer->status);
+		r = LIBUSB_ERROR_OTHER;
+	}
+
+	libusb_free_transfer(transfer);
+	return r;
+}
+
+static void bulk_transfer_cb(struct libusb_transfer *transfer)
+{
+	int *completed = transfer->user_data;
+	*completed = 1;
+	usbi_dbg("actual_length=%d", transfer->actual_length);
+	/* caller interprets results and frees transfer */
+}
+
+static int do_sync_bulk_transfer(struct libusb_device_handle *dev_handle,
+	unsigned char endpoint, unsigned char *buffer, int length,
+	int *transferred, unsigned int timeout, unsigned char type)
+{
+	struct libusb_transfer *transfer = libusb_alloc_transfer(0);
+	int completed = 0;
+	int r;
+
+	if (!transfer)
+		return LIBUSB_ERROR_NO_MEM;
+
+	libusb_fill_bulk_transfer(transfer, dev_handle, endpoint, buffer, length,
+		bulk_transfer_cb, &completed, timeout);
+	transfer->type = type;
+
+	r = libusb_submit_transfer(transfer);
+	if (r < 0) {
+		libusb_free_transfer(transfer);
+		return r;
+	}
+
+	while (!completed) {
+		r = libusb_handle_events(HANDLE_CTX(dev_handle));
+		if (r < 0) {
+			if (r == LIBUSB_ERROR_INTERRUPTED)
+				continue;
+			libusb_cancel_transfer(transfer);
+			while (!completed)
+				if (libusb_handle_events(HANDLE_CTX(dev_handle)) < 0)
+					break;
+			libusb_free_transfer(transfer);
+			return r;
+		}
+	}
+
+	*transferred = transfer->actual_length;
+	switch (transfer->status) {
+	case LIBUSB_TRANSFER_COMPLETED:
+		r = 0;
+		break;
+	case LIBUSB_TRANSFER_TIMED_OUT:
+		r = LIBUSB_ERROR_TIMEOUT;
+		break;
+	case LIBUSB_TRANSFER_STALL:
+		r = LIBUSB_ERROR_PIPE;
+		break;
+	case LIBUSB_TRANSFER_OVERFLOW:
+		r = LIBUSB_ERROR_OVERFLOW;
+		break;
+	case LIBUSB_TRANSFER_NO_DEVICE:
+		r = LIBUSB_ERROR_NO_DEVICE;
+		break;
+	default:
+		usbi_warn(HANDLE_CTX(dev_handle),
+			"unrecognised status code %d", transfer->status);
+		r = LIBUSB_ERROR_OTHER;
+	}
+
+	libusb_free_transfer(transfer);
+	return r;
+}
+
+/** \ingroup syncio
+ * Perform a USB bulk transfer. The direction of the transfer is inferred from
+ * the direction bits of the endpoint address.
+ *
+ * For bulk reads, the <tt>length</tt> field indicates the maximum length of
+ * data you are expecting to receive. If less data arrives than expected,
+ * this function will return that data, so be sure to check the
+ * <tt>transferred</tt> output parameter.
+ *
+ * You should also check the <tt>transferred</tt> parameter for bulk writes.
+ * Not all of the data may have been written.
+ *
+ * Also check <tt>transferred</tt> when dealing with a timeout error code.
+ * libusb may have to split your transfer into a number of chunks to satisfy
+ * underlying O/S requirements, meaning that the timeout may expire after
+ * the first few chunks have completed. libusb is careful not to lose any data
+ * that may have been transferred; do not assume that timeout conditions
+ * indicate a complete lack of I/O.
+ *
+ * \param dev_handle a handle for the device to communicate with
+ * \param endpoint the address of a valid endpoint to communicate with
+ * \param data a suitably-sized data buffer for either input or output
+ * (depending on endpoint)
+ * \param length for bulk writes, the number of bytes from data to be sent. for
+ * bulk reads, the maximum number of bytes to receive into the data buffer.
+ * \param transferred output location for the number of bytes actually
+ * transferred.
+ * \param timeout timeout (in millseconds) that this function should wait
+ * before giving up due to no response being received. For an unlimited
+ * timeout, use value 0.
+ *
+ * \returns 0 on success (and populates <tt>transferred</tt>)
+ * \returns LIBUSB_ERROR_TIMEOUT if the transfer timed out (and populates
+ * <tt>transferred</tt>)
+ * \returns LIBUSB_ERROR_PIPE if the endpoint halted
+ * \returns LIBUSB_ERROR_OVERFLOW if the device offered more data, see
+ * \ref packetoverflow
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failures
+ */
+API_EXPORTED int libusb_bulk_transfer(struct libusb_device_handle *dev_handle,
+	unsigned char endpoint, unsigned char *data, int length, int *transferred,
+	unsigned int timeout)
+{
+	return do_sync_bulk_transfer(dev_handle, endpoint, data, length,
+		transferred, timeout, LIBUSB_TRANSFER_TYPE_BULK);
+}
+
+/** \ingroup syncio
+ * Perform a USB interrupt transfer. The direction of the transfer is inferred
+ * from the direction bits of the endpoint address.
+ *
+ * For interrupt reads, the <tt>length</tt> field indicates the maximum length
+ * of data you are expecting to receive. If less data arrives than expected,
+ * this function will return that data, so be sure to check the
+ * <tt>transferred</tt> output parameter.
+ *
+ * You should also check the <tt>transferred</tt> parameter for interrupt
+ * writes. Not all of the data may have been written.
+ *
+ * Also check <tt>transferred</tt> when dealing with a timeout error code.
+ * libusb may have to split your transfer into a number of chunks to satisfy
+ * underlying O/S requirements, meaning that the timeout may expire after
+ * the first few chunks have completed. libusb is careful not to lose any data
+ * that may have been transferred; do not assume that timeout conditions
+ * indicate a complete lack of I/O.
+ *
+ * The default endpoint bInterval value is used as the polling interval.
+ *
+ * \param dev_handle a handle for the device to communicate with
+ * \param endpoint the address of a valid endpoint to communicate with
+ * \param data a suitably-sized data buffer for either input or output
+ * (depending on endpoint)
+ * \param length for bulk writes, the number of bytes from data to be sent. for
+ * bulk reads, the maximum number of bytes to receive into the data buffer.
+ * \param transferred output location for the number of bytes actually
+ * transferred.
+ * \param timeout timeout (in millseconds) that this function should wait
+ * before giving up due to no response being received. For an unlimited
+ * timeout, use value 0.
+ *
+ * \returns 0 on success (and populates <tt>transferred</tt>)
+ * \returns LIBUSB_ERROR_TIMEOUT if the transfer timed out
+ * \returns LIBUSB_ERROR_PIPE if the endpoint halted
+ * \returns LIBUSB_ERROR_OVERFLOW if the device offered more data, see
+ * \ref packetoverflow
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other error
+ */
+API_EXPORTED int libusb_interrupt_transfer(
+	struct libusb_device_handle *dev_handle, unsigned char endpoint,
+	unsigned char *data, int length, int *transferred, unsigned int timeout)
+{
+	return do_sync_bulk_transfer(dev_handle, endpoint, data, length,
+		transferred, timeout, LIBUSB_TRANSFER_TYPE_INTERRUPT);
+}
+