nbd_opt_info - Man Page

request the server for information about an export

Synopsis

 #include <libnbd.h>

 int nbd_opt_info (
       struct nbd_handle *h
     );

Request that the server supply information about the export name previously specified by the most recent nbd_set_export_name(3) or nbd_connect_uri(3). This can only be used if nbd_set_opt_mode(3) enabled option mode.

If successful, functions like nbd_is_read_only(3) and nbd_get_size(3) will report details about that export. If nbd_set_request_meta_context(3) is set (the default) and structured replies or extended headers were negotiated, it is also valid to use nbd_can_meta_context(3) after this call. However, it may be more efficient to clear that setting and manually utilize nbd_opt_list_meta_context(3) with its callback approach, for learning which contexts an export supports. In general, if nbd_opt_go(3) is called next, that call will likely succeed with the details remaining the same, although this is not guaranteed by all servers.

Not all servers understand this request, and even when it is understood, the server might fail the request even when a corresponding nbd_opt_go(3) would succeed.

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.

The following parameters must not be NULL: h. For more information see "Non-NULL parameters" in libnbd(3).

Handle State

nbd_opt_info can be called when the handle is in the following state:

 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ❌ error                │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ✅ allowed              │
 │ Connected to the server             │ ❌ error                │
 │ Connection shut down                │ ❌ error                │
 │ Handle dead                         │ ❌ 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_OPT_INFO 1

Authors

Eric Blake

Richard W.M. Jones

Copyright

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