1 files changed, 88 insertions, 0 deletions
diff --git a/toys/other/nbd_server.c b/toys/other/nbd_server.c
new file mode 100644
index 00000000..98c1937c
--- /dev/null
+++ b/toys/other/nbd_server.c
@@ -0,0 +1,88 @@
+/* nbd-server.c - network block device server
+ *
+ * Copyright 2022 Rob Landley <rob@landley.net>
+ *
+ * Not in SUSv4.
+ *
+ * See https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md
+
+// Work around dash in name trying to put - in function name.
+USE_NBD_SERVER(NEWTOY(nbd_server, "<1>1r", 0))
+USE_NBD_SERVER(OLDTOY(nbd-server, nbd_server, TOYFLAG_USR|TOYFLAG_BIN))
+
+config NBD_SERVER
+  bool "nbd-server"
+  default y
+  help
+    usage: nbd-server [-r] FILE
+
+    Serve a Network Block Device from FILE on stdin/out (ala inetd).
+
+    -r	Read only export
+*/
+
+// TODO: -r, block size, exit signal?
+
+#define FOR_nbd_server
+#include "toys.h"
+
+static int copy_loop(int from, int to, unsigned len)
+{
+  int try, rc = 0;
+
+  errno = 0;
+  while (len) {
+    xreadall(from, toybuf, try = len>4096 ? 4096 : len);
+    if (!rc && try != writeall(to, toybuf, try)) rc = errno;
+    len -= try;
+  }
+
+  return rc;
+}
+
+void nbd_server_main(void)
+{
+  unsigned long long *ll = (void *)toybuf, offset, handle;
+  unsigned short *ss = (void *)toybuf;
+  unsigned *uu = (void *)toybuf, type, length;
+  int fd = xopen(*toys.optargs, O_RDWR*!FLAG(r));
+
+  type = 1;
+  setsockopt(0, IPPROTO_TCP, TCP_NODELAY, &type, sizeof(int));
+
+  // Send original recipe negotiation, with device length and flags
+  memcpy(toybuf, "NBDMAGIC\x00\x00\x42\x02\x81\x86\x12\x53", 16);
+  ll[2] = SWAP_BE64(fdlength(fd));
+  uu[6] = SWAP_BE32(5+2*FLAG(r)); // has flags, can flush, maybe read only
+  xwrite(1, toybuf, 152);
+
+  // Simple loop, handles one request at a time with "simple" reply.
+  for (;;) {
+    // Fetch request into toybuf
+    xreadall(0, toybuf, 28);
+    if (SWAP_BE32(*uu) != 0x25609513) break;
+    type = SWAP_BE16(ss[3]);
+    handle = SWAP_BE64(ll[1]);
+    offset = SWAP_BE64(ll[2]);
+    length = SWAP_BE32(uu[6]);
+
+    // type 0 = read, 1 = write, 2 = disconnect, 3 = flush
+    if (type==2 || type>3) break;  // disconnect
+    if (type==3) { // flush
+      if (fdatasync(fd)) uu[1] = SWAP_BE32(errno);
+    } else {
+      xlseek(fd, offset, SEEK_SET);
+      if (type==1) { // write
+        uu[1] = copy_loop(0, fd, length);
+        ll[1] = SWAP_BE64(handle);
+      } else uu[1] = 0; // read never reports errors because send header first
+    }
+
+    // Simple reply in toybuf (handle stays put)
+    *uu = SWAP_BE32(0x67446698);
+    xwrite(1, toybuf, 16);
+
+    // Append read payload
+    if (!type) if (copy_loop(fd, 1, length)) break;
+  }
+}