nbd_is_rotational - is the NBD disk rotational (like a disk)?

       Eric Blake

       Richard W.M. Jones

       Copyright Red Hat

       Returns true if the disk exposed over NBD is rotational (like a traditional floppy or hard disk).
       Returns false if the disk has no penalty for random access (like an SSD or RAM disk).

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

       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).

       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 <stdbool.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);
        }

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

       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-1.22.2                                      2025-06-16                               nbd_is_rotational(3)

       nbd_is_rotational - is the NBD disk rotational (like a disk)?

       This call returns a boolean value.

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

        #include <libnbd.h>

        int nbd_is_rotational (
              struct nbd_handle *h
            );

       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_ROTATIONAL 1