=head1 NAME

nbd_get_extended_headers_negotiated - see if extended headers are in
use

=head1 SYNOPSIS

 #include <libnbd.h>

 int nbd_get_extended_headers_negotiated (
       struct nbd_handle *h
     );

=head1 DESCRIPTION

After connecting you may call this
to find out if the connection is
using extended headers.  Note that this setting is sticky; this
can return true even after a second L<nbd_opt_extended_headers(3)>
returns false because the server detected a duplicate request.

When extended headers are not in use, commands are limited to a
32-bit length, even when the libnbd API uses a 64-bit parameter
to express the length.  But even when extended headers are
supported, the server may enforce other limits, visible through
L<nbd_get_block_size(3)>.

Note that when extended headers are negotiated, you should
prefer the use of L<nbd_block_status_64(3)> instead of
L<nbd_block_status(3)> if any of the meta contexts you requested
via L<nbd_add_meta_context(3)> might return 64-bit status
values; however, all of the well-known meta contexts covered
by current C<LIBNBD_CONTEXT_*> constants only return 32-bit
status.

=head1 RETURN VALUE

This call returns a boolean value.

=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_get_extended_headers_negotiated
can be called when the handle is in the following states:

 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ❌ error                │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ✅ allowed              │
 │ Connected to the server             │ ✅ allowed              │
 │ Connection shut down                │ ✅ allowed              │
 │ Handle dead                         │ ❌ error                │
 └─────────────────────────────────────┴─────────────────────────┘

=head1 VERSION

This function first appeared in libnbd 1.18.

If you need to test if this function is available at compile time
check if the following macro is defined:

 #define LIBNBD_HAVE_NBD_GET_EXTENDED_HEADERS_NEGOTIATED 1

=head1 SEE ALSO

L<nbd_add_meta_context(3)>,
L<nbd_block_status(3)>,
L<nbd_block_status_64(3)>,
L<nbd_cache(3)>,
L<nbd_create(3)>,
L<nbd_get_block_size(3)>,
L<nbd_get_protocol(3)>,
L<nbd_get_request_extended_headers(3)>,
L<nbd_get_structured_replies_negotiated(3)>,
L<nbd_opt_extended_headers(3)>,
L<nbd_set_request_extended_headers(3)>,
L<nbd_trim(3)>,
L<nbd_zero(3)>,
L<libnbd(3)>.

=head1 AUTHORS

Eric Blake

Richard W.M. Jones

=head1 COPYRIGHT

Copyright Red Hat
