/* * Functions to sequence FLUSH and FUA writes. * * Copyright (C) 2011		Max Planck Institute for Gravitational Physics * Copyright (C) 2011		Tejun Heo <tj@kernel.org> * * This file is released under the GPLv2. * * REQ_{FLUSH|FUA} requests are decomposed to sequences consisted of three * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request * properties and hardware capability. * * If a request doesn't have data, only REQ_FLUSH makes sense, which * indicates a simple flush request.  If there is data, REQ_FLUSH indicates * that the device cache should be flushed before the data is executed, and * REQ_FUA means that the data must be on non-volatile media on request * completion. * * If the device doesn't have writeback cache, FLUSH and FUA don't make any * difference.  The requests are either completed immediately if there's no * data or executed as normal requests otherwise. * * If the device has writeback cache and supports FUA, REQ_FLUSH is * translated to PREFLUSH but REQ_FUA is passed down directly with DATA. * * If the device has writeback cache and doesn't support FUA, REQ_FLUSH is * translated to PREFLUSH and REQ_FUA to POSTFLUSH. * * The actual execution of flush is double buffered.  Whenever a request * needs to execute PRE or POSTFLUSH, it queues at * q->flush_queue[q->flush_pending_idx].  Once certain criteria are met, a * flush is issued and the pending_idx is toggled.  When the flush * completes, all the requests which were pending are proceeded to the next * step.  This allows arbitrary merging of different types of FLUSH/FUA * requests. * * Currently, the following conditions are used to determine when to issue * flush. * * C1. At any given time, only one flush shall be in progress.  This makes *     double buffering sufficient. * * C2. Flush is deferred if any request is executing DATA of its sequence. *     This avoids issuing separate POSTFLUSHes for requests which shared *     PREFLUSH. * * C3. The second condition is ignored if there is a request which has *     waited longer than FLUSH_PENDING_TIMEOUT.  This is to avoid *     starvation in the unlikely case where there are continuous stream of *     FUA (without FLUSH) requests. * * For devices which support FUA, it isn't clear whether C2 (and thus C3) * is beneficial. * * Note that a sequenced FLUSH/FUA request with DATA is completed twice. * Once while executing DATA and again after the whole sequence is * complete.  The first completion updates the contained bio but doesn't * finish it so that the bio submitter is notified only after the whole * sequence is complete.  This is implemented by testing REQ_FLUSH_SEQ in * req_bio_endio(). * * The above peculiarity requires that each FLUSH/FUA request has only one * bio attached to it, which is guaranteed as they aren't allowed to be * merged in the usual way. */ #include <linux/kernel.h>#include <linux/module.h>#include <linux/bio.h>#include <linux/blkdev.h>#include <linux/gfp.h> #include "blk.h" /* FLUSH/FUA sequences */enum {	REQ_FSEQ_PREFLUSH	= (1 << 0), /* pre-flushing in progress */	REQ_FSEQ_DATA		= (1 << 1), /* data write in progress */	REQ_FSEQ_POSTFLUSH	= (1 << 2), /* post-flushing in progress */	REQ_FSEQ_DONE		= (1 << 3), 	REQ_FSEQ_ACTIONS	= REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |				  REQ_FSEQ_POSTFLUSH, 	/*	 * If flush has been pending longer than the following timeout,	 * it's issued even if flush_data requests are still in flight.	 */	FLUSH_PENDING_TIMEOUT	= 5 * HZ,}; static bool blk_kick_flush(struct request_queue *q); static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq){	unsigned int policy = 0; 	if (blk_rq_sectors(rq))		policy |= REQ_FSEQ_DATA; 	if (fflags & REQ_FLUSH) {		if (rq->cmd_flags & REQ_FLUSH)			policy |= REQ_FSEQ_PREFLUSH;		if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))			policy |= REQ_FSEQ_POSTFLUSH;	}	return policy;} static unsigned int blk_flush_cur_seq(struct request *rq){	return 1 << ffz(rq->flush.seq);} static void blk_flush_restore_request(struct request *rq){	/*	 * After flush data completion, @rq->bio is %NULL but we need to	 * complete the bio again.  @rq->biotail is guaranteed to equal the	 * original @rq->bio.  Restore it.	 */	rq->bio = rq->biotail; 	/* make @rq a normal request */	rq->cmd_flags &= ~REQ_FLUSH_SEQ;	rq->end_io = rq->flush.saved_end_io;} /** * blk_flush_complete_seq - complete flush sequence * @rq: FLUSH/FUA request being sequenced * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero) * @error: whether an error occurred * * @rq just completed @seq part of its flush sequence, record the * completion and trigger the next step. * * CONTEXT: * spin_lock_irq(q->queue_lock) * * RETURNS: * %true if requests were added to the dispatch queue, %false otherwise. */static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,				   int error){	struct request_queue *q = rq->q;	struct list_head *pending = &q->flush_queue[q->flush_pending_idx];	bool queued = false; 	BUG_ON(rq->flush.seq & seq);	rq->flush.seq |= seq; 	if (likely(!error))		seq = blk_flush_cur_seq(rq);	else		seq = REQ_FSEQ_DONE; 	switch (seq) {	case REQ_FSEQ_PREFLUSH:	case REQ_FSEQ_POSTFLUSH:		/* queue for flush */		if (list_empty(pending))			q->flush_pending_since = jiffies;		list_move_tail(&rq->flush.list, pending);		break; 	case REQ_FSEQ_DATA:		list_move_tail(&rq->flush.list, &q->flush_data_in_flight);		list_add(&rq->queuelist, &q->queue_head);		queued = true;		break; 	case REQ_FSEQ_DONE:		/*		 * @rq was previously adjusted by blk_flush_issue() for		 * flush sequencing and may already have gone through the		 * flush data request completion path.  Restore @rq for		 * normal completion and end it.		 */		BUG_ON(!list_empty(&rq->queuelist));		list_del_init(&rq->flush.list);		blk_flush_restore_request(rq);		__blk_end_request_all(rq, error);		break; 	default:		BUG();	} 	return blk_kick_flush(q) | queued;} static void flush_end_io(struct request *flush_rq, int error){	struct request_queue *q = flush_rq->q;	struct list_head *running = &q->flush_queue[q->flush_running_idx];	bool queued = false;	struct request *rq, *n; 	BUG_ON(q->flush_pending_idx == q->flush_running_idx); 	/* account completion of the flush request */	q->flush_running_idx ^= 1;	elv_completed_request(q, flush_rq); 	/* and push the waiting requests to the next stage */	list_for_each_entry_safe(rq, n, running, flush.list) {		unsigned int seq = blk_flush_cur_seq(rq); 		BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);		queued |= blk_flush_complete_seq(rq, seq, error);	} 	/*	 * Kick the queue to avoid stall for two cases:	 * 1. Moving a request silently to empty queue_head may stall the	 * queue.	 * 2. When flush request is running in non-queueable queue, the	 * queue is hold. Restart the queue after flush request is finished	 * to avoid stall.	 * This function is called from request completion path and calling	 * directly into request_fn may confuse the driver.  Always use	 * kblockd.	 */	if (queued || q->flush_queue_delayed)		blk_run_queue_async(q);	q->flush_queue_delayed = 0;} /** * blk_kick_flush - consider issuing flush request * @q: request_queue being kicked * * Flush related states of @q have changed, consider issuing flush request. * Please read the comment at the top of this file for more info. * * CONTEXT: * spin_lock_irq(q->queue_lock) * * RETURNS: * %true if flush was issued, %false otherwise. */static bool blk_kick_flush(struct request_queue *q){	struct list_head *pending = &q->flush_queue[q->flush_pending_idx];	struct request *first_rq =		list_first_entry(pending, struct request, flush.list); 	/* C1 described at the top of this file */	if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending))		return false; 	/* C2 and C3 */	if (!list_empty(&q->flush_data_in_flight) &&	    time_before(jiffies,			q->flush_pending_since + FLUSH_PENDING_TIMEOUT))		return false; 	/*	 * Issue flush and toggle pending_idx.  This makes pending_idx	 * different from running_idx, which means flush is in flight.	 */	blk_rq_init(q, &q->flush_rq);	q->flush_rq.cmd_type = REQ_TYPE_FS;	q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;	q->flush_rq.rq_disk = first_rq->rq_disk;	q->flush_rq.end_io = flush_end_io; 	q->flush_pending_idx ^= 1;	list_add_tail(&q->flush_rq.queuelist, &q->queue_head);	return true;} static void flush_data_end_io(struct request *rq, int error){	struct request_queue *q = rq->q; 	/*	 * After populating an empty queue, kick it to avoid stall.  Read	 * the comment in flush_end_io().	 */	if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))		blk_run_queue_async(q);} /** * blk_insert_flush - insert a new FLUSH/FUA request * @rq: request to insert * * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions. * @rq is being submitted.  Analyze what needs to be done and put it on the * right queue. * * CONTEXT: * spin_lock_irq(q->queue_lock) */void blk_insert_flush(struct request *rq){	struct request_queue *q = rq->q;	unsigned int fflags = q->flush_flags;	/* may change, cache */	unsigned int policy = blk_flush_policy(fflags, rq); 	/*	 * @policy now records what operations need to be done.  Adjust	 * REQ_FLUSH and FUA for the driver.	 */	rq->cmd_flags &= ~REQ_FLUSH;	if (!(fflags & REQ_FUA))		rq->cmd_flags &= ~REQ_FUA; 	/*	 * An empty flush handed down from a stacking driver may	 * translate into nothing if the underlying device does not	 * advertise a write-back cache.  In this case, simply	 * complete the request.	 */	if (!policy) {		__blk_end_bidi_request(rq, 0, 0, 0);		return;	} 	BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */ 	/*	 * If there's data but flush is not necessary, the request can be	 * processed directly without going through flush machinery.  Queue	 * for normal execution.	 */	if ((policy & REQ_FSEQ_DATA) &&	    !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {		list_add_tail(&rq->queuelist, &q->queue_head);		return;	} 	/*	 * @rq should go through flush machinery.  Mark it part of flush	 * sequence and submit for further processing.	 */	memset(&rq->flush, 0, sizeof(rq->flush));	INIT_LIST_HEAD(&rq->flush.list);	rq->cmd_flags |= REQ_FLUSH_SEQ;	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */	rq->end_io = flush_data_end_io; 	blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);} /** * blk_abort_flushes - @q is being aborted, abort flush requests * @q: request_queue being aborted * * To be called from elv_abort_queue().  @q is being aborted.  Prepare all * FLUSH/FUA requests for abortion. * * CONTEXT: * spin_lock_irq(q->queue_lock) */void blk_abort_flushes(struct request_queue *q){	struct request *rq, *n;	int i; 	/*	 * Requests in flight for data are already owned by the dispatch	 * queue or the device driver.  Just restore for normal completion.	 */	list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) {		list_del_init(&rq->flush.list);		blk_flush_restore_request(rq);	} 	/*	 * We need to give away requests on flush queues.  Restore for	 * normal completion and put them on the dispatch queue.	 */	for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) {		list_for_each_entry_safe(rq, n, &q->flush_queue[i],					 flush.list) {			list_del_init(&rq->flush.list);			blk_flush_restore_request(rq);			list_add_tail(&rq->queuelist, &q->queue_head);		}	}} static void bio_end_flush(struct bio *bio, int err){	if (err)		clear_bit(BIO_UPTODATE, &bio->bi_flags);	if (bio->bi_private)		complete(bio->bi_private);	bio_put(bio);} /** * blkdev_issue_flush - queue a flush * @bdev:	blockdev to issue flush for * @gfp_mask:	memory allocation flags (for bio_alloc) * @error_sector:	error sector * * Description: *    Issue a flush for the block device in question. Caller can supply *    room for storing the error offset in case of a flush error, if they *    wish to. If WAIT flag is not passed then caller may check only what *    request was pushed in some internal queue for later handling. */int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,		sector_t *error_sector){	DECLARE_COMPLETION_ONSTACK(wait);	struct request_queue *q;	struct bio *bio;	int ret = 0; 	if (bdev->bd_disk == NULL)		return -ENXIO; 	q = bdev_get_queue(bdev);	if (!q)		return -ENXIO; 	/*	 * some block devices may not have their queue correctly set up here	 * (e.g. loop device without a backing file) and so issuing a flush	 * here will panic. Ensure there is a request function before issuing	 * the flush.	 */	if (!q->make_request_fn)		return -ENXIO; 	bio = bio_alloc(gfp_mask, 0);	bio->bi_end_io = bio_end_flush;	bio->bi_bdev = bdev;	bio->bi_private = &wait; 	bio_get(bio);	submit_bio(WRITE_FLUSH, bio);	wait_for_completion(&wait); 	/*	 * The driver must store the error location in ->bi_sector, if	 * it supports it. For non-stacked drivers, this should be	 * copied from blk_rq_pos(rq).	 */	if (error_sector)               *error_sector = bio->bi_sector; 	if (!bio_flagged(bio, BIO_UPTODATE))		ret = -EIO; 	bio_put(bio);	return ret;}EXPORT_SYMBOL(blkdev_issue_flush);