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.
88 	 * If flush has been pending longer than the following timeout,
105 	return 1 << ffz(rq->flush.seq);  in blk_flush_cur_seq()
111 	 * After flush data completion, @rq->bio is %NULL but we need to  in blk_flush_restore_request()
121 	rq->end_io = rq->flush.saved_end_io;  in blk_flush_restore_request()
136  * blk_flush_complete_seq - complete flush sequence
138  * @fq: flush queue
142  * @rq just completed @seq part of its flush sequence, record the
156 	BUG_ON(rq->flush.seq & seq);  in blk_flush_complete_seq()
157 	rq->flush.seq |= seq;  in blk_flush_complete_seq()
168 		/* queue for flush */  in blk_flush_complete_seq()
185 		 * flush sequencing and may already have gone through the  in blk_flush_complete_seq()
186 		 * flush data request completion path.  Restore @rq for  in blk_flush_complete_seq()
221 	 * Flush request has to be marked as IDLE when it is really ended  in flush_end_io()
241 	/* account completion of the flush request */  in flush_end_io()
263  * blk_kick_flush - consider issuing flush request
265  * @fq: flush queue
268  * Flush related states of @q have changed, consider issuing flush request.
294 	 * Issue flush and toggle pending_idx.  This makes pending_idx  in blk_kick_flush()
295 	 * different from running_idx, which means flush is in flight.  in blk_kick_flush()
304 	 * the tag's ownership for flush req.  in blk_kick_flush()
306 	 * In case of IO scheduler, flush rq need to borrow scheduler tag  in blk_kick_flush()
371 	rq->flush.seq = 0;  in blk_rq_init_flush()
373 	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */  in blk_rq_init_flush()
378  * Insert a PREFLUSH/FUA request into the flush state machine.
379  * Returns true if the request has been consumed by the flush state machine,
389 	/* FLUSH/FUA request must never be merged */  in blk_insert_flush()
423 		 * An empty flush handed down from a stacking driver may  in blk_insert_flush()
432 		 * If there's data, but no flush is necessary, the request can  in blk_insert_flush()
433 		 * be processed directly without going through flush machinery.  in blk_insert_flush()
439 		 * Initialize the flush fields and completion handler to trigger  in blk_insert_flush()
440 		 * the post flush, and then just pass the command on.  in blk_insert_flush()
443 		rq->flush.seq |= REQ_FSEQ_PREFLUSH;  in blk_insert_flush()
450 		 * Mark the request as part of a flush sequence and submit it  in blk_insert_flush()
451 		 * for further processing to the flush state machine.  in blk_insert_flush()
462  * blkdev_issue_flush - queue a flush
463  * @bdev:	blockdev to issue flush for
466  *    Issue a flush for the block device in question.
507 	/* bio based request queue hasn't flush queue */  in blk_free_flush_queue()