nbd_opt_list_meta_context_queries(3)                                    LIBNBD


NAME
       nbd_opt_list_meta_context_queries - list available 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_list_meta_context_queries (
              struct nbd_handle *h, char **queries,
              nbd_context_callback context_callback
            );

DESCRIPTION
       Request that the server list available meta contexts associated with
       the export previously specified by the most recent
       nbd_set_export_name(3) or nbd_connect_uri(3), and with an explicit list
       of queries provided as a parameter (see nbd_opt_list_meta_context(3) if
       you want to reuse an implicit query list instead).  This can only be
       used if nbd_set_opt_mode(3) enabled option mode.

       The NBD protocol allows a client to decide how many queries to ask the
       server.  For this function, the list is explicit in the "queries"
       parameter.  When the list is empty, a server will typically reply with
       all contexts that it supports; when the list is non-empty, the server
       will reply only with supported contexts that match the client's
       request.  Note that a reply by the server might be encoded to represent
       several feasible contexts within one string, rather than multiple
       strings per actual context name that would actually succeed during
       nbd_opt_go(3); so it is still necessary to use nbd_can_meta_context(3)
       after connecting to see which contexts are actually supported.

       The "context" function is called once per server reply, with any
       "user_data" passed to this function, and with "name" supplied by the
       server.  Remember that it is not safe to call nbd_add_meta_context(3)
       from within the context of the callback function; rather, your code
       must copy any "name" needed for later use after this function
       completes.  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.
       Likewise, the NBD protocol does not specify an upper bound for the
       number of replies that might be advertised, so client code should be
       aware that a server may send a lengthy 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_list_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_LIST_META_CONTEXT_QUERIES 1

SEE ALSO
       nbd_add_meta_context(3), nbd_aio_opt_list_meta_context_queries(3),
       nbd_can_meta_context(3), nbd_connect_uri(3), nbd_create(3),
       nbd_opt_go(3), nbd_opt_list_meta_context(3), nbd_set_export_name(3),
       nbd_set_opt_mode(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

libnbd-1.20.0                     2024-05-31
                                          nbd_opt_list_meta_context_queries(3)