nbd_get_size - return the export size
#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 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).
This call does not block, because it returns data that is saved in the handle from the NBD protocol handshake.
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 1This 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