blk_queue_ordered — does this queue support ordered writes
int blk_queue_ordered
(struct request_queue * q, unsigned ordered, prepare_flush_fn * prepare_flush_fn);
the request queue
one of QUEUE_ORDERED_*
rq setup helper for cache flush ordered writes
For journalled file systems, doing ordered writes on a commit block instead of explicitly doing wait_on_buffer (which is bad for performance) can be a big win. Block drivers supporting this feature should call this function and indicate so.