fuse_lowlevel: Add max_pages support (#384)

Starting with kernel version 4.20 fuse supports a new property
'max_pages' which is the maximum number of pages that can be used per
request. This can be set via an argument during initialization.
This new property allows writes to be larger than 128k.

This patch sets the property if the matching capability is set
(FUSE_MAX_PAGES). It will also set max_write to 1MiB. Filesystems have
the possibility to decrease this size by setting max_write to a smaller
size. The max_pages and bufsize fields are adjusted accordingly.

Cc: Constantine Shulyupin <const@MakeLinux.com>
Signed-off-by: Markus Pargmann <scosu@quobyte.com>

2 files changed, 27 insertions, 9 deletions

diff --git a/lib/fuse_i.h b/lib/fuse_i.h
index cf35551..d38b630 100644
--- a/lib/fuse_i.h
+++ b/lib/fuse_i.h
@@ -131,3 +131,9 @@ struct fuse *fuse_new_31(struct fuse_args *args, const struct fuse_operations *o
 int fuse_loop_mt_32(struct fuse *f, struct fuse_loop_config *config);
 int fuse_session_loop_mt_32(struct fuse_session *se, struct fuse_loop_config *config);
 
+#define FUSE_MAX_MAX_PAGES 256
+#define FUSE_DEFAULT_MAX_PAGES_PER_REQ 32
+
+/* room needed in buffer to accommodate header */
+#define FUSE_BUFFER_HEADER_SIZE 0x1000
+
diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
index c96e211..3684b8b 100644
--- a/lib/fuse_lowlevel.c
+++ b/lib/fuse_lowlevel.c
@@ -1909,6 +1909,14 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 			se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV;
 		if (arg->flags & FUSE_NO_OPENDIR_SUPPORT)
 			se->conn.capable |= FUSE_CAP_NO_OPENDIR_SUPPORT;
+		if (!(arg->flags & FUSE_MAX_PAGES)) {
+			size_t max_bufsize =
+				FUSE_DEFAULT_MAX_PAGES_PER_REQ * getpagesize()
+				+ FUSE_BUFFER_HEADER_SIZE;
+			if (bufsize > max_bufsize) {
+				bufsize = max_bufsize;
+			}
+		}
 	} else {
 		se->conn.max_readahead = 0;
 	}
@@ -1955,10 +1963,10 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 			bufsize);
 		bufsize = FUSE_MIN_READ_BUFFER;
 	}
+	se->bufsize = bufsize;
 
-	bufsize -= 4096;
-	if (bufsize < se->conn.max_write)
-		se->conn.max_write = bufsize;
+	if (se->conn.max_write > bufsize - FUSE_BUFFER_HEADER_SIZE)
+		se->conn.max_write = bufsize - FUSE_BUFFER_HEADER_SIZE;
 
 	se->got_init = 1;
 	if (se->op.init)
@@ -1985,6 +1993,14 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 		return;
 	}
 
+	if (se->conn.max_write < bufsize - FUSE_BUFFER_HEADER_SIZE) {
+		se->bufsize = se->conn.max_write + FUSE_BUFFER_HEADER_SIZE;
+	}
+	if (arg->flags & FUSE_MAX_PAGES) {
+		outarg.flags |= FUSE_MAX_PAGES;
+		outarg.max_pages = (se->conn.max_write - 1) / getpagesize() + 1;
+	}
+
 	/* Always enable big writes, this is superseded
 	   by the max_write option */
 	outarg.flags |= FUSE_BIG_WRITES;
@@ -2807,11 +2823,6 @@ restart:
 	return res;
 }
 
-#define KERNEL_BUF_PAGES 32
-
-/* room needed in buffer to accommodate header */
-#define HEADER_SIZE 0x1000
-
 struct fuse_session *fuse_session_new(struct fuse_args *args,
 				      const struct fuse_lowlevel_ops *op,
 				      size_t op_size, void *userdata)
@@ -2872,7 +2883,8 @@ struct fuse_session *fuse_session_new(struct fuse_args *args,
 	if (se->debug)
 		fprintf(stderr, "FUSE library version: %s\n", PACKAGE_VERSION);
 
-	se->bufsize = KERNEL_BUF_PAGES * getpagesize() + HEADER_SIZE;
+	se->bufsize = FUSE_MAX_MAX_PAGES * getpagesize() +
+		FUSE_BUFFER_HEADER_SIZE;
 
 	list_init_req(&se->list);
 	list_init_req(&se->interrupts);