nbd_get_size - Man Page

 #include <libnbd.h>

 int64_t nbd_get_size (
           struct nbd_handle *h
         );

Returns the size in bytes of the NBD export.

Note that this call fails with EOVERFLOW for an unlikely server that advertises a size which cannot fit in a 64-bit signed integer.

nbdinfo(1) --size option is a way to access this API from shell scripts.

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

This call returns a 64 bit signed integer ≥ 0.

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).

nbd_get_size 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 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_GET_SIZE 1

This example is also available as examples/get-size.c in the libnbd source code.

 /* This example shows how to connect to an NBD
  * server and read the size of the disk.
  *
  * You can test it with nbdkit like this:
  *
  * nbdkit -U - memory 1M \
  *   --run './get-size $unixsocket'
  */

 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <inttypes.h>

 #include <libnbd.h>

 int
 main (int argc, char *argv[])
 {
   struct nbd_handle *nbd;
   int64_t size;

   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 the size in bytes and print it. */
   size = nbd_get_size (nbd);
   if (size == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
   printf ("%s: size = %" PRIi64 " bytes\n",
           argv[1], size);

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

   exit (EXIT_SUCCESS);
 }

nbd_create(3), nbd_opt_info(3), "Size of the export" in libnbd(3), libnbd(3), nbdinfo(1).

Eric Blake

Richard W.M. Jones

Copyright Red Hat

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(3), libnbd-release-notes-1.18(1), NBD(3), nbd_get_block_size(3), nbd_opt_info(3).