nbd_shutdown(3)                     LIBNBD                     nbd_shutdown(3)


NAME
       nbd_shutdown - disconnect from the NBD server

SYNOPSIS
        #include <libnbd.h>

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

DESCRIPTION
       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.

RETURN VALUE
       If the call is successful the function returns 0.

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).

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                |
        <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>

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_SHUTDOWN 1

EXAMPLE
       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);
        }

SEE ALSO
       nbd_aio_disconnect(3), nbd_aio_in_flight(3), nbd_aio_opt_abort(3),
       nbd_close(3), nbd_create(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

libnbd-1.20.0                     2024-05-31                   nbd_shutdown(3)