13  * indicates a simple flush request.  If there is data, REQ_PREFLUSH indicates
28  * The actual execution of flush is double buffered.  Whenever a request
31  * REQ_OP_FLUSH is issued and the pending_idx is toggled.  When the flush
37  * flush.
39  * C1. At any given time, only one flush shall be in progress.  This makes
42  * C2. Flush is deferred if any request is executing DATA of its sequence.
90 	 * If flush has been pending longer than the following timeout,
124 	return 1 << ffz(rq->flush.seq);  in blk_flush_cur_seq()
130 	 * After flush data completion, @rq->bio is %NULL but we need to  in blk_flush_restore_request()
138 	rq->end_io = rq->flush.saved_end_io;  in blk_flush_restore_request()
158  * blk_flush_complete_seq - complete flush sequence
160  * @fq: flush queue
164  * @rq just completed @seq part of its flush sequence, record the
178 	BUG_ON(rq->flush.seq & seq);  in blk_flush_complete_seq()
179 	rq->flush.seq |= seq;  in blk_flush_complete_seq()
190 		/* queue for flush */  in blk_flush_complete_seq()
193 		list_move_tail(&rq->flush.list, pending);  in blk_flush_complete_seq()
197 		list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);  in blk_flush_complete_seq()
204 		 * flush sequencing and may already have gone through the  in blk_flush_complete_seq()
205 		 * flush data request completion path.  Restore @rq for  in blk_flush_complete_seq()
208 		list_del_init(&rq->flush.list);  in blk_flush_complete_seq()
240 	 * Flush request has to be marked as IDLE when it is really ended  in flush_end_io()
260 	/* account completion of the flush request */  in flush_end_io()
264 	list_for_each_entry_safe(rq, n, running, flush.list) {  in flush_end_io()
281  * blk_kick_flush - consider issuing flush request
283  * @fq: flush queue
286  * Flush related states of @q have changed, consider issuing flush request.
298 		list_first_entry(pending, struct request, flush.list);  in blk_kick_flush()
312 	 * Issue flush and toggle pending_idx.  This makes pending_idx  in blk_kick_flush()
313 	 * different from running_idx, which means flush is in flight.  in blk_kick_flush()
322 	 * the tag's ownership for flush req.  in blk_kick_flush()
324 	 * In case of IO scheduler, flush rq need to borrow scheduler tag  in blk_kick_flush()
335 		 * this flush request as INFLIGHT for avoiding double  in blk_kick_flush()
416 	 * An empty flush handed down from a stacking driver may  in blk_insert_flush()
429 	 * If there's data but flush is not necessary, the request can be  in blk_insert_flush()
430 	 * processed directly without going through flush machinery.  Queue  in blk_insert_flush()
440 	 * @rq should go through flush machinery.  Mark it part of flush  in blk_insert_flush()
443 	memset(&rq->flush, 0, sizeof(rq->flush));  in blk_insert_flush()
444 	INIT_LIST_HEAD(&rq->flush.list);  in blk_insert_flush()
446 	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */  in blk_insert_flush()
456  * blkdev_issue_flush - queue a flush
457  * @bdev:	blockdev to issue flush for
460  *    Issue a flush for the block device in question.
502 	/* bio based request queue hasn't flush queue */  in blk_free_flush_queue()