noble (3) nbd_opt_set_meta_context_queries.3.gz

Provided by: libnbd-dev_1.20.0-1_amd64 bug

NAME
       nbd_opt_set_meta_context_queries - select specific meta contexts, using explicit 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;

        int nbd_opt_set_meta_context_queries (
              struct nbd_handle *h, char **queries,
              nbd_context_callback context_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).

       The NBD protocol allows a client to decide how many queries to ask the server.  This function takes an
       explicit list of queries; to instead reuse an implicit list, see nbd_opt_set_meta_context(3).  Since this
       function is primarily designed for testing servers, libnbd does not prevent the use of this function on
       an empty list or when nbd_set_request_structured_replies(3) has disabled structured replies, in order to
       see how a server behaves.

       The "context" function is called once per server reply, with any "user_data" passed to this function, and
       with "name" supplied by the server.  Additionally, each server name will remain visible through
       nbd_can_meta_context(3) until the next attempt at nbd_set_export_name(3) or nbd_opt_set_meta_context(3),
       as well as nbd_opt_go(3) or nbd_opt_info(3) that trigger an automatic meta context request.  Remember
       that it is not safe to call any "nbd_*" APIs from within the context of the callback function.  At
       present, the return value of the callback is ignored, although a return of -1 should be avoided.

       For convenience, when this function succeeds, it returns the number of replies returned by the server.

       Not all servers understand this request, and even when it is understood, the server might intentionally
       send an empty list because it does not support the requested context, or may encounter a failure after
       delivering partial results.  Thus, this function may succeed even when no contexts are reported, or may
       fail but have a non-empty list.


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_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_OPT_SET_META_CONTEXT_QUERIES 1


SEE ALSO
       nbd_aio_opt_set_meta_context_queries(3), nbd_can_meta_context(3), nbd_connect_uri(3), nbd_create(3),
       nbd_opt_go(3), nbd_opt_info(3), nbd_opt_list_meta_context_queries(3), nbd_opt_set_meta_context(3),
       nbd_set_export_name(3), nbd_set_opt_mode(3), nbd_set_request_meta_context(3),
       nbd_set_request_structured_replies(3), libnbd(3).


AUTHORS
       Eric Blake

       Richard W.M. Jones


       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