nbd_opt_structured_reply - request the server to enable structured replies


 #include <libnbd.h>

 int nbd_opt_structured_reply (
       struct nbd_handle *h


Request that the server use structured replies, by sending NBD_OPT_STRUCTURED_REPLY. This can only be used if nbd_set_opt_mode(3) enabled option mode; furthermore, libnbd defaults to automatically requesting this unless you use nbd_set_request_structured_replies(3) prior to connecting. This function is mainly useful for integration testing of corner cases in server handling.

This function returns true if the server replies with success, false if the server replies with an error, and fails only if the server does not reply (such as for a loss of connection). Note that some servers fail a second request as redundant; libnbd assumes that once one request has succeeded, then structured replies are supported (as visible by nbd_get_structured_replies_negotiated(3)) regardless if later calls to this function return false. Similarly, a server may fail this request if extended headers are already negotiated, since extended headers take priority.


This call returns a boolean value.


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_opt_structured_reply 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                │


This function first appeared in libnbd 1.16.

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



nbd_aio_opt_structured_reply(3), nbd_create(3), nbd_get_structured_replies_negotiated(3), nbd_opt_go(3), nbd_set_opt_mode(3), nbd_set_request_structured_replies(3), libnbd(3).


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