nbd_set_request_meta_context - Man Page

control whether connect automatically requests meta contexts

Synopsis

 #include <libnbd.h>

 int nbd_set_request_meta_context (struct nbd_handle *h,
                                   bool request);

Description

This function controls whether the act of connecting to an export (all nbd_connect_* calls when nbd_set_opt_mode(3) is false, or nbd_opt_go(3) and nbd_opt_info(3) when option mode is enabled) will also try to issue NBD_OPT_SET_META_CONTEXT when the server supports structured replies and any contexts were registered by nbd_add_meta_context(3).  The default setting is true; however the extra step of negotiating meta contexts is not always desirable: performing both info and go on the same export works without needing to re-negotiate contexts on the second call; integration testing of other servers may benefit from manual invocation of nbd_opt_set_meta_context(3) at other times in the negotiation sequence; and even when using just nbd_opt_info(3), it can be faster to collect the server's results by relying on the callback function passed to nbd_opt_list_meta_context(3) than a series of post-process calls to nbd_can_meta_context(3).

Note that this control has no effect if the server does not negotiate structured replies, or if the client did not request any contexts via nbd_add_meta_context(3).  Setting this control to false may cause nbd_block_status(3) to fail.

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

The handle must be newly created, or negotiating, otherwise this call will return an error.

Version

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:

 #define LIBNBD_HAVE_NBD_SET_REQUEST_META_CONTEXT 1

See Also

nbd_add_meta_context(3), nbd_block_status(3), nbd_can_meta_context(3), nbd_create(3), nbd_get_request_meta_context(3), nbd_get_structured_replies_negotiated(3), nbd_opt_go(3), nbd_opt_info(3), nbd_opt_list_meta_context(3), nbd_opt_set_meta_context(3), nbd_set_opt_mode(3), libnbd(3).

Authors

Eric Blake

Richard W.M. Jones

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

Referenced By

libnbd(3), NBD(3), nbd_aio_opt_set_meta_context(3), nbd_aio_opt_set_meta_context_queries(3), nbd_can_meta_context(3), nbd_get_request_meta_context(3), nbd_opt_go(3), nbd_opt_info(3), nbd_opt_set_meta_context(3), nbd_opt_set_meta_context_queries(3).

2022-11-03 libnbd-1.15.7