nbd_aio_connect_unix(3)

nbd_aio_connect_unix(3) — libnbd manual 💅

okay bestie, welcome to the libnbd page for nbd_aio_connect_unix(3). This is the one where you start an async connection to an NBD server over a Unix domain socket, and it is lowkey iconic. 🫶

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✨ NAME ✨

nbd_aio_connect_unix — connect to the NBD server over a Unix domain socket

🎀 SYNOPSIS 🎀

        #include <libnbd.h>

        int nbd_aio_connect_unix (
              struct nbd_handle *h, const char *unixsocket
            );

💖 DESCRIPTION 💖

This function begins connecting to the NBD server over the Unix domain socket "unixsocket". The parameters behave exactly as documented in nbd_connect_unix(3), no cap. ✨

🌸 RETURN VALUE 🌸

If the call is successful, the function returns 0. Slay. If not, see the errors below.

🔥 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).

🦋 NOTES 🦋

🦋 Asynchronous connect call 🦋

You can check if the connection attempt is still underway by calling nbd_aio_is_connecting(3). If nbd_set_opt_mode(3) is enabled, the connection is ready for manual option negotiation once nbd_aio_is_negotiating(3) returns true; otherwise, the connection attempt will include the NBD handshake, and is ready for use once nbd_aio_is_ready(3) returns true. ✨

🌈 HANDLE STATE 🌈

nbd_aio_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_AIO_CONNECT_UNIX 1

🍓 EXAMPLE 🍓

This example is also available as examples/aio-connect-read.c in the libnbd source code. It’s giving main character async energy. 💅

        /* This example shows how to use the AIO (asynchronous) low
         * level API to connect to a server and read the disk.
         *
         * Here are a few ways to try this example:
         *
         * nbdkit -U - linuxdisk . \
         *   --run './aio-connect-read $unixsocket'
         *
         * nbdkit -U - floppy . \
         *   --run './aio-connect-read $unixsocket'
         *
         * nbdkit -U - pattern size=1M \
         *   --run './aio-connect-read $unixsocket'
         */

        #include <stdio.h>
        #include <stdlib.h>
        #include <stdint.h>
        #include <inttypes.h>
        #include <errno.h>
        #include <assert.h>

        #include <libnbd.h>

        #define NR_SECTORS 32
        #define SECTOR_SIZE 512

        struct data {
          uint64_t offset;
          char sector[SECTOR_SIZE];
        };

        static int
        hexdump (void *user_data, int *error)
        {
          struct data *data = user_data;
          FILE *pp;

          if (*error) {
            errno = *error;
            perror ("failed to read");
            exit (EXIT_FAILURE);
          }

          printf ("sector at offset 0x%" PRIx64 ":\n",
                  data->offset);
          pp = popen ("hexdump -C", "w");
          if (pp == NULL) {
            perror ("popen: hexdump");
            exit (EXIT_FAILURE);
          }
          fwrite (data->sector, SECTOR_SIZE, 1, pp);
          pclose (pp);
          printf ("\n");

          /* Returning 1 from the callback automatically retires
           * the command.
           */
          return 1;
        }

        static struct data data[NR_SECTORS];

        int
        main (int argc, char *argv[])
        {
          struct nbd_handle *nbd;
          size_t i;

          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.
           * This only starts the connection.
           */
          if (nbd_aio_connect_unix (nbd, argv[1]) == -1) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }

          /* Wait for the connection to complete.  The use of
           * nbd_poll here is only as an example.  You could also
           * integrate this with poll(2), glib or another main
           * loop.  Read libnbd(3) and the source file lib/poll.c.
           */
          while (!nbd_aio_is_ready (nbd)) {
            if (nbd_poll (nbd, -1) == -1) {
              fprintf (stderr, "%s\n", nbd_get_error ());
              exit (EXIT_FAILURE);
            }
          }

          assert (nbd_get_size (nbd) >= NR_SECTORS * SECTOR_SIZE);

          /* Issue read commands for the first NR sectors. */
          for (i = 0; i < NR_SECTORS; ++i) {
            data[i].offset = i * SECTOR_SIZE;

            /* The callback (hexdump) is called when the command
             * completes.  The buffer must continue to exist while
             * the command is running.
             */
            if (nbd_aio_pread (nbd, data[i].sector, SECTOR_SIZE,
                               data[i].offset,
                               (nbd_completion_callback) {
                                 .callback = hexdump,
                                 .user_data = &data[i],
                               }, 0) == -1) {
              fprintf (stderr, "%s\n", nbd_get_error ());
              exit (EXIT_FAILURE);
            }
          }

          /* Run the main loop until all the commands have
           * completed and retired.  Again the use of nbd_poll
           * here is only as an example.
           */
          while (nbd_aio_in_flight (nbd) > 0) {
            if (nbd_poll (nbd, -1) == -1) {
              fprintf (stderr, "%s\n", nbd_get_error ());
              exit (EXIT_FAILURE);
            }
          }

          /* Close the libnbd handle. */
          nbd_close (nbd);

          exit (EXIT_SUCCESS);
        }

🌟 SEE ALSO 🌟

• nbd_aio_is_connecting(3)
• nbd_aio_is_negotiating(3)
• nbd_aio_is_ready(3)
• nbd_connect_unix(3)
• nbd_create(3)
• nbd_set_opt_mode(3)
• libnbd(3)

🫶 AUTHORS 🫶

• Eric Blake
• Richard W.M. Jones

💜 COPYRIGHT 💜

Copyright Red Hat

📜 LICENSE 📜

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 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

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okay that’s the whole page, bestie. This was nbd_aio_connect_unix(3) from libnbd-1.25.8, dated 2026-10-13 — go forth and async-connect responsibly. 🫶💖✨