=head1 NAME

nbd_get_size - return the export size

=head1 SYNOPSIS

 #include <libnbd.h>

 int64_t nbd_get_size (
           struct nbd_handle *h
         );

=head1 DESCRIPTION

Returns the size in bytes of the NBD export.

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

L<nbdinfo(1)> I<--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.

=head1 RETURN VALUE

This call returns a 64 bit signed integer E<ge> C<0>.

=head1 ERRORS

On error C<-1> is returned.

Refer to L<libnbd(3)/ERROR HANDLING>
for how to get further details of the error.

The following parameters must not be NULL: C<h>.
For more information see L<libnbd(3)/Non-NULL parameters>.

=head1 HANDLE STATE

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

=head1 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_GET_SIZE 1

=head1 EXAMPLE

This example is also available as F<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);
 }

=head1 SEE ALSO

L<nbd_create(3)>,
L<nbd_opt_info(3)>,
L<libnbd(3)/Size of the export>,
L<libnbd(3)>,
L<nbdinfo(1)>.

=head1 AUTHORS

Eric Blake

Richard W.M. Jones

=head1 COPYRIGHT

Copyright Red Hat
