nbd_get_export_description(3)

okay bestie, welcome to the libnbd manual page for nbd_get_export_description(3) — yes, it’s giving “the server might have sent a lil description, let’s go get it” 💅. It’s C library stuff, but we’re gonna make it make sense.

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✨ NAME ✨

nbd_get_export_description — return the export description, if the server has one 💖

🛠 SYNOPSIS 🛠

include this, bestie:

        #include <libnbd.h>

        char * nbd_get_export_description (
                 struct nbd_handle *h
               );

🫶 DESCRIPTION 🫶

The NBD protocol is like, “servers may optionally report an export description,” no cap. This function reports any description that the server returned.

Some servers are unlikely to report a description unless the client specifically hinted about wanting it, via nbd_set_full_info(3). For qemu-nbd(8), a description is set with -D.

🎁 RETURN VALUE 🎁

This call returns a string. The caller must free the returned string to avoid a memory leak. yes, free it bestie — don’t ghost your malloc 😭.

😭 ERRORS 😭

On error NULL 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. For more information see "Non-NULL parameters" in libnbd(3).

🦋 HANDLE STATE 🦋

nbd_get_export_description can be called when the handle is in the following states:

• Handle created, before connecting — ❌ error
• Connecting — ❌ error
• Connecting & handshaking (opt_mode) — ✅ allowed
• Connected to the server — ✅ allowed
• Connection shut down — ✅ allowed
• Handle dead — ❌ error

🌸 VERSION 🌸

This function first appeared in libnbd 1.4.

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

#define LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION 1

🧚 EXAMPLE 🧚

This example is also available as examples/server-flags.c in the libnbd source code.

        /* This example shows how to connect to an NBD
         * server and print the export flags.
         *
         * You can test it with nbdkit like this:
         *
         * nbdkit -U - memory 1M \
         *   --run './server-flags $unixsocket'
         */

        #include <stdio.h>
        #include <stdlib.h>
        #include <stdbool.h>

        #include <libnbd.h>

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

          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);
          }

          /* Request full information. */
        #if LIBNBD_HAVE_NBD_SET_FULL_INFO /* Added in 1.4 */
          if (nbd_set_full_info (nbd, true) == -1) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }
        #endif

          /* 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);
          }

          /* See if the server provided extra details,
           * using functions added in 1.4
           */
        #if LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION
          str = nbd_get_canonical_export_name (nbd);
          if (str)
            printf ("canonical_name = %s\n", str);
          free (str);
          str = nbd_get_export_description (nbd);
          if (str)
            printf ("description = %s\n", str);
          free (str);
        #endif

          /* Read and print the flags. */
        #define PRINT_FLAG(flag_fn)                     \
          flag = flag_fn (nbd);                         \
          if (flag == -1) {                             \
            fprintf (stderr, "%s\n", nbd_get_error ()); \
            exit (EXIT_FAILURE);                        \
          }                                             \
          printf (#flag_fn " = %s\n",                   \
                  flag ? "true" : "false");

          PRINT_FLAG (nbd_can_cache);
          PRINT_FLAG (nbd_can_df);
          PRINT_FLAG (nbd_can_flush);
          PRINT_FLAG (nbd_can_fua);
          PRINT_FLAG (nbd_can_multi_conn);
          PRINT_FLAG (nbd_can_trim);
          PRINT_FLAG (nbd_can_zero);
        #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO
          /* Added in 1.2 */
          PRINT_FLAG (nbd_can_fast_zero);
        #endif
        #if LIBNBD_HAVE_NBD_CAN_BLOCK_STATUS_PAYLOAD
          /* Added in 1.18 */
          PRINT_FLAG (nbd_can_block_status_payload);
        #endif
          PRINT_FLAG (nbd_is_read_only);
          PRINT_FLAG (nbd_is_rotational);

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

          exit (EXIT_SUCCESS);
        }

slay, that’s the whole example 🫶

👀 SEE ALSO 👀

• nbd_create(3)
• nbd_opt_info(3)
• nbd_set_full_info(3)
• libnbd(3)

💜 AUTHORS 💜

shoutout to the authors:

• Eric Blake
• Richard W.M. Jones

🎀 COPYRIGHT 🎀

Copyright Red Hat

⚖️ LICENSE ⚖️

okay legal bestie, here’s the license text exactly as it needs to be:

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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and that’s the whole page, bestie 💖 libnbd-1.25.8 · 2026-10-13 · nbd_get_export_description(3) — periodt.