NAME

       nbd_get_export_description - return the export description, if the server has one

SYNOPSIS

        #include <libnbd.h>

        char * nbd_get_export_description (struct nbd_handle *h);

DESCRIPTION

       The NBD protocol permits a server to report an optional export description.  This function
       reports any description returned by the server.

       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.

ERRORS

       On error "NULL" is returned.

       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

HANDLE STATE

       The handle must be negotiating, or connected with the server, or shut down, otherwise this
       call will return an 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 <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
          PRINT_FLAG (nbd_is_read_only);
          PRINT_FLAG (nbd_is_rotational);

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

          exit (EXIT_SUCCESS);
        }

SEE ALSO

       nbd_create(3), nbd_opt_info(3), nbd_set_full_info(3), libnbd(3).

AUTHORS

       Eric Blake

       Richard W.M. Jones

COPYRIGHT

       Copyright (C) 2019-2021 Red Hat Inc.

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