Provided by: libnbd-dev_1.2.2-1ubuntu2_amd64 bug


       nbd_is_read_only - is the NBD export read-only?


        #include <libnbd.h>

        int nbd_is_read_only (struct nbd_handle *h);


       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.


       This call returns a boolean value.


       On error "-1" is returned.

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


       The handle must be connected and finished handshaking with the server, or shut down,
       otherwise this call will return an 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_IS_READ_ONLY 1


       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>

        main (int argc, char *argv[])
          struct nbd_handle *nbd;
          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);

          /* 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);

          /* 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);
          PRINT_FLAG (nbd_is_read_only);
          PRINT_FLAG (nbd_is_rotational);

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

          exit (EXIT_SUCCESS);


       "Flag calls" in libnbd(3), nbd_create(3), libnbd(3).


       Eric Blake

       Richard W.M. Jones


       Copyright (C) 2019 Red Hat Inc.


       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