NAME

       nbd_aio_opt_set_meta_context - select specific meta contexts, with implicit query list

SYNOPSIS

        #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 (
              struct nbd_handle *h,
              nbd_context_callback context_callback,
              nbd_completion_callback completion_callback
            );

DESCRIPTION

       Request that the server supply all recognized meta contexts registered through prior calls
       to nbd_add_meta_context(3), 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".  For more information see "Non-NULL
       parameters" in libnbd(3).

HANDLE STATE

       nbd_aio_opt_set_meta_context 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 1

SEE ALSO

       nbd_add_meta_context(3), nbd_aio_is_connecting(3),
       nbd_aio_opt_set_meta_context_queries(3), nbd_connect_uri(3), nbd_create(3), nbd_opt_go(3),
       nbd_opt_set_meta_context(3), nbd_set_export_name(3), nbd_set_opt_mode(3),
       nbd_set_request_meta_context(3), libnbd(3).

AUTHORS

       Eric Blake

       Richard W.M. Jones

COPYRIGHT

       Copyright Red Hat

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