=head1 NAME

nbd_aio_peek_command_completed - check if any command has completed

=head1 SYNOPSIS

 #include <libnbd.h>

 int64_t nbd_aio_peek_command_completed (
           struct nbd_handle *h
         );

=head1 DESCRIPTION

Return the unique positive
64 bit cookie of the first non-retired but
completed command, C<0> if there are in-flight commands but none of
them are awaiting retirement, or C<-1> on error including when there
are no in-flight commands. Any cookie returned by this function must
still be passed to L<nbd_aio_command_completed(3)> to actually retire
the command and learn whether the command was successful.

=head1 RETURN VALUE

This call returns a 64 bit signed 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 VERSION

This function first appeared in libnbd 1.0.

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_PEEK_COMMAND_COMPLETED 1

=head1 SEE ALSO

L<nbd_aio_command_completed(3)>,
L<nbd_create(3)>,
L<libnbd(3)>.

=head1 AUTHORS

Eric Blake

Richard W.M. Jones

=head1 COPYRIGHT

Copyright Red Hat
