nbd_shutdown(3)

💅 nbd_shutdown(3) — libnbd edition, bestie

okay so this is a page from the LIBNBD manual set, and today's main character is nbd_shutdown(3) — the "bye bestie 👋" function. Let's get into it.

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✨ NAME ✨

nbd_shutdown — disconnect from the NBD server 🫶

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🌸 SYNOPSIS 🌸

#include <libnbd.h>

int nbd_shutdown (
      struct nbd_handle *h, uint32_t flags
    );

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🦋 DESCRIPTION 🦋

So what this does is it issues the disconnect command to the NBD server. It's the polite way to tell the server "we're leaving 💅", which is cute and all — but ngl, from the client's point of view it has literally zero advantage over just abruptly closing the connection (that's nbd_close(3) if you were wondering, go look at it).

This function works whether or not the handle is ready for transmission of commands — lowkey flexible like that. If you need more fine-grained control though, go check out nbd_aio_opt_abort(3) and nbd_aio_disconnect(3).

The flags argument is a bitmask, and it can include zero or more of these shutdown flags:

• "LIBNBD_SHUTDOWN_ABANDON_PENDING" = 0x10000 — if there are any pending requests that haven't been sent to the server yet (peep nbd_aio_in_flight(3)), this abandons them without sending them, instead of the usual practice of issuing those commands first before telling the server you intend to disconnect. so it's giving "leave without saying bye to the group chat" energy 🙈

For convenience, the constant "LIBNBD_SHUTDOWN_MASK" is available to describe all the shutdown flags recognized by this build of libnbd. bestie, a future version of the library may add new flags — so keep that in mind, iykyk 👑

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💖 RETURN VALUE 💖

If the call is successful the function returns 0. slay ✨

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

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👑 HANDLE STATE 👑

nbd_shutdown 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 — ❌ error
• Handle dead — ❌ error

so basically: mid-handshake or fully connected = go off, everything else = not it 🙅‍♀️

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🌈 VERSION 🌈

This function first appeared in libnbd 1.0. iconic behavior tbh.

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

#define LIBNBD_HAVE_NBD_SHUTDOWN 1

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🎀 EXAMPLE 🎀

This example is also available as examples/reads-and-writes.c in the libnbd source code. fr fr, go read it there too.

/* This example shows how to do synchronous reads
 * and writes randomly over the first megabyte of an
 * NBD server.  Note this will destroy any existing
 * content on the NBD server.
 *
 * To test it with nbdkit and a RAM disk:
 *
 * nbdkit -U - memory 1M \
 *     --run './simple-reads-and-writes $unixsocket'
 */

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

#include <libnbd.h>

int
main (int argc, char *argv[])
{
  struct nbd_handle *nbd;
  char buf[512];
  size_t i;
  int64_t exportsize;
  uint64_t offset;

  srand (time (NULL));

  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);
  }

  /* Get the size of the disk and check
   * it's large enough.
   */
  exportsize = nbd_get_size (nbd);
  if (exportsize == -1) {
    fprintf (stderr, "%s\n", nbd_get_error ());
    exit (EXIT_FAILURE);
  }
  assert (exportsize >= sizeof buf);

  /* Check that the server is writable. */
  if (nbd_is_read_only (nbd) == 1) {
    fprintf (stderr, "%s: "
             "error: this NBD export is read-only\n",
             argv[0]);
    exit (EXIT_FAILURE);
  }

  for (i = 0; i < sizeof buf; ++i)
    buf[i] = rand ();

  /* 1000 writes. */
  for (i = 0; i < 1000; ++i) {
    offset = rand () % (exportsize - sizeof buf);

    if (nbd_pwrite (nbd, buf, sizeof buf,
                    offset, 0) == -1) {
      fprintf (stderr, "%s\n", nbd_get_error ());
      exit (EXIT_FAILURE);
    }
  }

  /* 1000 reads and writes. */
  for (i = 0; i < 1000; ++i) {
    offset = rand () % (exportsize - sizeof buf);
    if (nbd_pread (nbd, buf, sizeof buf,
                   offset, 0) == -1) {
      fprintf (stderr, "%s\n", nbd_get_error ());
      exit (EXIT_FAILURE);
    }

    offset = rand () % (exportsize - sizeof buf);
    if (nbd_pwrite (nbd, buf, sizeof buf,
                    offset, 0) == -1) {
      fprintf (stderr, "%s\n", nbd_get_error ());
      exit (EXIT_FAILURE);
    }
  }

  /* Sends a graceful shutdown to the server. */
  if (nbd_shutdown (nbd, 0) == -1) {
    fprintf (stderr, "%s\n", nbd_get_error ());
    exit (EXIT_FAILURE);
  }

  nbd_close (nbd);

  exit (EXIT_SUCCESS);
}

⚠️ heads up bestie: the comment in there literally says this will destroy any existing content on the NBD server. that's not a drill, that's the whole vibe. 🙈

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🔥 SEE ALSO 🔥

nbd_aio_disconnect(3), nbd_aio_in_flight(3), nbd_aio_opt_abort(3), nbd_close(3), nbd_create(3), libnbd(3).

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💜 AUTHORS 💜

Eric Blake

Richard W.M. Jones

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🍓 COPYRIGHT 🍓

Copyright Red Hat

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🧚 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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and that's the page, bestie 🫶 this lil shutie came from libnbd-1.25.8, dated 2026-10-13 — and yes, it's still nbd_shutdown(3) at the end. mwah 💋