nbd_connect_unix3

Usage

 #include <libnbd.h>
 int nbd_connect_unix (
       struct nbd_handle *h, const char *unixsocket
     );

Overview

Connect (synchronously) over the named Unix domain socket ("unixsocket") to an NBD server running on the same machine.

This call returns when the connection has been made. By default, this proceeds all the way to transmission phase, but nbd_set_opt_mode(3) can be used for manual control over option negotiation performed before transmission phase.

Return value

If the call is successful the function returns 0.

Errors

On error -1 is returned.

Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

The following parameters must not be NULL: "h", "unixsocket". For more information see "Non-NULL parameters" in libnbd(3).

Handle state

nbd_connect_unix can be called when the handle is in the following state:

 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ✅ allowed              │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ❌ error                │
 │ Connected to the server             │ ❌ error                │
 │ Connection shut down                │ ❌ error                │
 │ Handle dead                         │ ❌ error                │
 └─────────────────────────────────────┴─────────────────────────┘

Version

This function first appeared in libnbd 1.0.

If you need to test if this function is available at compile time check if the following macro is defined:

 #define LIBNBD_HAVE_NBD_CONNECT_UNIX 1

Examples

This example is also available as examples/fetch-first-sector.c in the libnbd source code.

 /* This example shows how to connect to an NBD server
  * and fetch and print the first sector (usually the
  * boot sector or partition table or filesystem
  * superblock).
  *
  * You can test it with nbdkit like this:
  *
  * nbdkit -U - floppy . \
  *   --run './fetch-first-sector $unixsocket'
  *
  * The nbdkit floppy plugin creates an MBR disk so the
  * first sector is the partition table.
  */
 #include <stdio.h>
 #include <stdlib.h>
 #include <libnbd.h>
 int
 main (int argc, char *argv[])
 {
   struct nbd_handle *nbd;
   char buf[512];
   FILE *pp;
   if (argc != 2) {
     fprintf (stderr, "%s socket\n", argv[0]);
     exit (EXIT_FAILURE);
   }
   /* Create the libnbd handle. */
   nbd = nbd_create ();
   if (nbd == NULL) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
   /* Connect to the NBD server over a
    * Unix domain socket.
    */
   if (nbd_connect_unix (nbd, argv[1]) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
   /* Read the first sector synchronously. */
   if (nbd_pread (nbd, buf, sizeof buf, 0, 0) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
   /* Close the libnbd handle. */
   nbd_close (nbd);
   /* Print the first sector. */
   pp = popen ("hexdump -C", "w");
   if (pp == NULL) {
     perror ("popen: hexdump");
     exit (EXIT_FAILURE);
   }
   fwrite (buf, sizeof buf, 1, pp);
   pclose (pp);
   exit (EXIT_SUCCESS);
 }