=head1 NAME

nbd_aio_opt_set_meta_context - select specific meta contexts, with
implicit 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 (
       struct nbd_handle *h,
       nbd_context_callback context_callback,
       nbd_completion_callback completion_callback
     );

=head1 DESCRIPTION

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

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

=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 1

=head1 SEE ALSO

L<nbd_add_meta_context(3)>,
L<nbd_aio_is_connecting(3)>,
L<nbd_aio_opt_set_meta_context_queries(3)>,
L<nbd_connect_uri(3)>,
L<nbd_create(3)>,
L<nbd_opt_go(3)>,
L<nbd_opt_set_meta_context(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
