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,
118 	return 1 << ffz(rq->flush.seq);  in blk_flush_cur_seq()
124 	 * After flush data completion, @rq->bio is %NULL but we need to  in blk_flush_restore_request()
132 	rq->end_io = rq->flush.saved_end_io;  in blk_flush_restore_request()
152  * blk_flush_complete_seq - complete flush sequence
154  * @fq: flush queue
158  * @rq just completed @seq part of its flush sequence, record the
172 	BUG_ON(rq->flush.seq & seq);  in blk_flush_complete_seq()
173 	rq->flush.seq |= seq;  in blk_flush_complete_seq()
184 		/* queue for flush */  in blk_flush_complete_seq()
187 		list_move_tail(&rq->flush.list, pending);  in blk_flush_complete_seq()
191 		list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);  in blk_flush_complete_seq()
198 		 * flush sequencing and may already have gone through the  in blk_flush_complete_seq()
199 		 * flush data request completion path.  Restore @rq for  in blk_flush_complete_seq()
203 		list_del_init(&rq->flush.list);  in blk_flush_complete_seq()
235 	 * Flush request has to be marked as IDLE when it is really ended  in flush_end_io()
253 	/* account completion of the flush request */  in flush_end_io()
257 	list_for_each_entry_safe(rq, n, running, flush.list) {  in flush_end_io()
268  * blk_kick_flush - consider issuing flush request
270  * @fq: flush queue
273  * Flush related states of @q have changed, consider issuing flush request.
285 		list_first_entry(pending, struct request, flush.list);  in blk_kick_flush()
299 	 * Issue flush and toggle pending_idx.  This makes pending_idx  in blk_kick_flush()
300 	 * different from running_idx, which means flush is in flight.  in blk_kick_flush()
309 	 * the tag's ownership for flush req.  in blk_kick_flush()
311 	 * In case of IO scheduler, flush rq need to borrow scheduler tag  in blk_kick_flush()
322 		 * this flush request as INFLIGHT for avoiding double  in blk_kick_flush()
394 	 * An empty flush handed down from a stacking driver may  in blk_insert_flush()
407 	 * If there's data but flush is not necessary, the request can be  in blk_insert_flush()
408 	 * processed directly without going through flush machinery.  Queue  in blk_insert_flush()
418 	 * @rq should go through flush machinery.  Mark it part of flush  in blk_insert_flush()
421 	memset(&rq->flush, 0, sizeof(rq->flush));  in blk_insert_flush()
422 	INIT_LIST_HEAD(&rq->flush.list);  in blk_insert_flush()
424 	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */  in blk_insert_flush()
434  * blkdev_issue_flush - queue a flush
435  * @bdev:	blockdev to issue flush for
439  *    Issue a flush for the block device in question.
490 	/* bio based request queue hasn't flush queue */  in blk_free_flush_queue()