=head1 NAME

nbd_set_request_block_size - control whether NBD_OPT_GO requests block
size

=head1 SYNOPSIS

 #include <libnbd.h>

 int nbd_set_request_block_size (
       struct nbd_handle *h, bool request
     );

=head1 DESCRIPTION

By default, when connecting to an export,
libnbd requests that the
server report any block size restrictions.  The NBD protocol states
that a server may supply block sizes regardless of whether the client
requests them, and libnbd will report those block sizes (see
L<nbd_get_block_size(3)>); conversely, if a client does not request
block sizes, the server may reject the connection instead of dealing
with a client sending unaligned requests.  This function makes it
possible to test server behavior by emulating older clients.

Note that even when block size is requested, the server is not
obligated to provide any.  Furthermore, if block sizes are provided
(whether or not the client requested them), libnbd enforces alignment
to those sizes unless L<nbd_set_strict_mode(3)> is used to bypass
client-side safety checks.

=head1 RETURN VALUE

If the call is successful the function returns 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_set_request_block_size
can be called when the handle is in the following states:

 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ✅ allowed              │
 │ 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 1.12.

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

 #define LIBNBD_HAVE_NBD_SET_REQUEST_BLOCK_SIZE 1

=head1 SEE ALSO

L<nbd_create(3)>,
L<nbd_get_block_size(3)>,
L<nbd_get_request_block_size(3)>,
L<nbd_set_full_info(3)>,
L<nbd_set_strict_mode(3)>,
L<libnbd(3)>.

=head1 AUTHORS

Eric Blake

Richard W.M. Jones

=head1 COPYRIGHT

Copyright Red Hat
