nbd_shutdown(3) LIBNBD nbd_shutdown(3)

nbd_shutdown - disconnect from the NBD server

#include <libnbd.h>
int nbd_shutdown (
      struct nbd_handle *h, uint32_t flags
    );

Issue the disconnect command to the NBD server. This is a nice way to tell the server we are going away, but from the client's point of view has no advantage over abruptly closing the connection (see nbd_close(3)).

This function works whether or not the handle is ready for transmission of commands. If more fine-grained control is needed, see nbd_aio_opt_abort(3) and nbd_aio_disconnect(3).

The "flags" argument is a bitmask, including zero or more of the following shutdown flags:

"LIBNBD_SHUTDOWN_ABANDON_PENDING" = 0x10000
If there are any pending requests which have not yet been sent to the server (see nbd_aio_in_flight(3)), abandon them without sending them to the server, rather than the usual practice of issuing those commands before informing the server of the intent to disconnect.

For convenience, the constant "LIBNBD_SHUTDOWN_MASK" is available to describe all shutdown flags recognized by this build of libnbd. A future version of the library may add new flags.

If the call is successful the function returns 0.

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).

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                │
└─────────────────────────────────────┴─────────────────────────┘

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_SHUTDOWN 1

This example is also available as examples/reads-and-writes.c in the libnbd source code.

/* 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 <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);
}

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

Eric Blake

Richard W.M. Jones

Copyright Red Hat

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

2024-05-31 libnbd-1.20.0