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NAME

nbd_aio_opt_set_meta_context_queries - select specific meta contexts, with explicit query list

#include <libnbd.h>
typedef struct {
int (*callback) (void *user_data, const char *name);
void *user_data;
void (*free) (void *user_data);
} nbd_context_callback;
typedef struct {
int (*callback) (void *user_data, int *error);
void *user_data;
void (*free) (void *user_data);
} nbd_completion_callback;
int nbd_aio_opt_set_meta_context_queries (
struct nbd_handle *h, char **queries,
nbd_context_callback context_callback,
nbd_completion_callback completion_callback
);

DESCRIPTION

Request that the server supply all recognized meta contexts passed in through "queries", in conjunction with the export 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. Normally, this function is redundant, as nbd_opt_go(3) automatically does the same task if structured replies or extended headers have already been negotiated. But manual control over meta context requests can be useful for fine-grained testing of how a server handles unusual negotiation sequences. Often, use of this function is coupled with nbd_set_request_meta_context(3) to bypass the automatic context request normally performed by nbd_opt_go(3).

To determine when the request completes, wait for nbd_aio_is_connecting(3) to return false. Or supply the optional "completion_callback" which will be invoked as described in "Completion callbacks" in libnbd(3), except that it is automatically retired regardless of return value. Note that detecting whether the server returns an error (as is done by the return value of the synchronous counterpart) is only possible with a completion callback.

RETURN VALUE

This call returns an integer ≥ 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", "queries". For more information see "Non-NULL parameters" in libnbd(3).

HANDLE STATE

nbd_aio_opt_set_meta_context_queries 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 1.16.

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

#define LIBNBD_HAVE_NBD_AIO_OPT_SET_META_CONTEXT_QUERIES 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

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