=head1 NAME

nbd_aio_opt_set_meta_context_queries - select specific meta contexts,
with explicit query list

=head1 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_queries (
       struct nbd_handle *h, char **queries,
       nbd_context_callback context_callback,
       nbd_completion_callback completion_callback
     );

=head1 DESCRIPTION

Request that the server supply all recognized meta contexts
passed in through C<queries>, in conjunction with the export
previously specified by the most recent L<nbd_set_export_name(3)>
or L<nbd_connect_uri(3)>.  This can only be used
if L<nbd_set_opt_mode(3)> enabled option mode.  Normally, this
function is redundant, as L<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 L<nbd_set_request_meta_context(3)> to
bypass the automatic context request normally performed by
L<nbd_opt_go(3)>.

To determine when the request completes, wait for
L<nbd_aio_is_connecting(3)> to return false.  Or supply the optional
C<completion_callback> which will be invoked as described in
L<libnbd(3)/Completion callbacks>, 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.

=head1 RETURN VALUE

This call returns an integer E<ge> C<0>.

=head1 ERRORS

On error C<-1> is returned.

Refer to L<libnbd(3)/ERROR HANDLING>
for how to get further details of the error.

The following parameters must not be NULL: C<h>, C<queries>.
For more information see L<libnbd(3)/Non-NULL parameters>.

=head1 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                │
 └─────────────────────────────────────┴─────────────────────────┘

=head1 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

=head1 SEE ALSO

L<nbd_aio_is_connecting(3)>,
L<nbd_aio_opt_set_meta_context(3)>,
L<nbd_connect_uri(3)>,
L<nbd_create(3)>,
L<nbd_opt_go(3)>,
L<nbd_opt_set_meta_context_queries(3)>,
L<nbd_set_export_name(3)>,
L<nbd_set_opt_mode(3)>,
L<nbd_set_request_meta_context(3)>,
L<libnbd(3)>.

=head1 AUTHORS

Eric Blake

Richard W.M. Jones

=head1 COPYRIGHT

Copyright Red Hat
