NAME

       nbd_is_read_only - is the NBD export read-only?

SYNOPSIS

        #include <libnbd.h>

        int nbd_is_read_only (
              struct nbd_handle *h
            );

DESCRIPTION

       Returns true if the NBD export is read-only; writes and write-like operations will fail.

       This call does not block, because it returns data that is saved in the handle from the NBD
       protocol handshake.

RETURN VALUE

       This call returns a boolean value.

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_is_read_only 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                │ ✅ allowed              │
        │ 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_IS_READ_ONLY 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
        #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_create(3), nbd_opt_info(3), "Flag calls" in libnbd(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