Many parts of the block layer are already byte granularity. The block driver interface, however, was still missing an interface that allows making use of this. This patch introduces a new BlockDriver interface, which is based on coroutines, vectored, has flags and uses a byte granularity. This is now the preferred interface for new drivers. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com>