NAME¶

nbd_set_full_info - control whether NBD_OPT_GO requests extra details

SYNOPSIS¶

 #include <libnbd.h>
 int nbd_set_full_info (struct nbd_handle *h, bool request);

DESCRIPTION¶

By default, when connecting to an export, libnbd only requests the details it needs to service data operations. The NBD protocol says that a server can supply optional information, such as a canonical name of the export (see nbd_get_canonical_export_name(3)) or a description of the export (see nbd_get_export_description(3)), but that a hint from the client makes it more likely for this extra information to be provided. This function controls whether libnbd will provide that hint.

Note that even when full info is requested, the server is not obligated to reply with all information that libnbd requested. Similarly, libnbd will ignore any optional server information that libnbd has not yet been taught to recognize.

RETURN VALUE¶

If the call is successful the function returns 0.

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 newly created, or negotiating, otherwise this call will return an error.

VERSION¶

This function first appeared in libnbd 1.4.

If you need to test if this function is available at compile time check if the following macro is defined:

 #define LIBNBD_HAVE_NBD_SET_FULL_INFO 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_get_canonical_export_name(3), nbd_get_export_description(3), nbd_get_full_info(3), libnbd(3).

AUTHORS¶

Eric Blake

Richard W.M. Jones

COPYRIGHT¶

Copyright (C) 2019-2020 Red Hat Inc.

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