that requests are restarted in the order they were queue. This may happen
if the driver needs to use blk_queue_invalidate_tags().
-Tagging also defines a new request flag, REQ_QUEUED. This is set whenever
-a request is currently tagged. You should not use this flag directly,
-blk_rq_tagged(rq) is the portable way to do so.
-
3.3 I/O Submission
The routine submit_bio() is used to submit a single io. Higher level i/o