nbd_get_canonical_export_name(3)

nbd_get_canonical_export_name(3)

okay bestie, welcome to the LIBNBD manual 💅 this page is literally all about nbd_get_canonical_export_name(3) — the function that asks the server for its canonical export name, if the server even has one. no cap.

🌸 NAME 🌸

nbd_get_canonical_export_name — return the canonical export name, if the server has one. that’s the whole vibe, but keep reading because the details eat ✨

✨ SYNOPSIS ✨

#include <libnbd.h>

char * nbd_get_canonical_export_name (
         struct nbd_handle *h
       );

🦋 DESCRIPTION 🦋

The NBD protocol permits a server to report an optional canonical export name, which may differ from the client’s request (as set by nbd_set_export_name(3) or nbd_connect_uri(3)). this function accesses any name returned by the server; it may be the same as the client request, but is more likely to differ when the client requested a connection to the default export name (an empty string "").

Some servers are unlikely to report a canonical name unless the client specifically hinted about wanting it, via nbd_set_full_info(3). so yeah, sometimes you gotta ask nicely first 🫶

💖 RETURN VALUE 💖

This call returns a string. The caller must free the returned string to avoid a memory leak. literally free it, bestie 😭 don’t leave your strings homeless.

😭 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 👑

vibe check: nbd_get_canonical_export_name can be called when the handle is in the following states, bestie:

• 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_CANONICAL_EXPORT_NAME 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);
}

🌈 SEE ALSO 🌈

nbd_connect_uri(3), nbd_create(3), nbd_get_export_name(3), nbd_opt_info(3), nbd_set_export_name(3), nbd_set_full_info(3), libnbd(3).

💜 AUTHORS 💜

• Eric Blake
• Richard W.M. Jones

⭐ COPYRIGHT ⭐

Copyright Red Hat

🧚 LICENSE 🧚

legal bestie moment — here’s the exact license text, no changes:

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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that’s the whole page, bestie — from libnbd-1.25.8, dated 2026-10-13. stay hydrated and may your strings always be freed 🫶💖