nbd_is_rotational - Man Page

is the NBD disk rotational (like a disk)?

Synopsis

 #include <libnbd.h>

 int nbd_is_rotational (struct nbd_handle *h);

Description

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.

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.

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 1.0.

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

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), “Flag calls” in libnbd(3), libnbd(3).

Authors

Eric Blake

Richard W.M. Jones

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

Referenced By

libnbd(3).

2020-10-05 libnbd-1.5.4