/*

   * Functions to sequence PREFLUSH 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_{PREFLUSH|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_PREFLUSH makes sense, which
   * indicates a simple flush request.  If there is data, REQ_PREFLUSH 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, PREFLUSH 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_PREFLUSH 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_PREFLUSH
   * 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

   * fq->flush_queue[fq->flush_pending_idx].  Once certain criteria are met, a

   * REQ_OP_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 PREFLUSH/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 PREFLUSH) requests.

   *
   * For devices which support FUA, it isn't clear whether C2 (and thus C3)
   * is beneficial.
   *

   * Note that a sequenced PREFLUSH/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 RQF_FLUSH_SEQ in

   * req_bio_endio().
   *

   * The above peculiarity requires that each PREFLUSH/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 <linux/blk-mq.h>

  
  #include "blk.h"

  #include "blk-mq.h"

  #include "blk-mq-tag.h"

  #include "blk-mq-sched.h"

  /* PREFLUSH/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,
  			   struct blk_flush_queue *fq);

  static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)

  {

  	unsigned int policy = 0;

  	if (blk_rq_sectors(rq))
  		policy |= REQ_FSEQ_DATA;

  	if (fflags & (1UL << QUEUE_FLAG_WC)) {

  		if (rq->cmd_flags & REQ_PREFLUSH)

  			policy |= REQ_FSEQ_PREFLUSH;

  		if (!(fflags & (1UL << QUEUE_FLAG_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->rq_flags &= ~RQF_FLUSH_SEQ;

  	rq->end_io = rq->flush.saved_end_io;

  }

  static bool blk_flush_queue_rq(struct request *rq, bool add_front)

  {

  	if (rq->q->mq_ops) {

  		blk_mq_add_to_requeue_list(rq, add_front, true);

  		return false;
  	} else {

  		if (add_front)
  			list_add(&rq->queuelist, &rq->q->queue_head);
  		else
  			list_add_tail(&rq->queuelist, &rq->q->queue_head);

  		return true;
  	}

  }

  /**
   * blk_flush_complete_seq - complete flush sequence

   * @rq: PREFLUSH/FUA request being sequenced

   * @fq: flush queue

   * @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 or fq->mq_flush_lock)

   *
   * RETURNS:
   * %true if requests were added to the dispatch queue, %false otherwise.
   */

  static bool blk_flush_complete_seq(struct request *rq,
  				   struct blk_flush_queue *fq,

  				   unsigned int seq, blk_status_t error)

  {

  	struct request_queue *q = rq->q;

  	struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];

  	bool queued = false, kicked;

  
  	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))

  			fq->flush_pending_since = jiffies;

  		list_move_tail(&rq->flush.list, pending);
  		break;
  
  	case REQ_FSEQ_DATA:

  		list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);

  		queued = blk_flush_queue_rq(rq, 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);

  		if (q->mq_ops)

  			blk_mq_end_request(rq, error);

  		else
  			__blk_end_request_all(rq, error);

  		break;
  
  	default:
  		BUG();
  	}

  	kicked = blk_kick_flush(q, fq);

  	return kicked | queued;

  }

  static void flush_end_io(struct request *flush_rq, blk_status_t error)

  {

  	struct request_queue *q = flush_rq->q;

  	struct list_head *running;

  	bool queued = false;
  	struct request *rq, *n;

  	unsigned long flags = 0;

  	struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);

  	if (q->mq_ops) {

  		struct blk_mq_hw_ctx *hctx;
  
  		/* release the tag's ownership to the req cloned from */

  		spin_lock_irqsave(&fq->mq_flush_lock, flags);

  		hctx = blk_mq_map_queue(q, flush_rq->mq_ctx->cpu);

  		blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);

  		flush_rq->tag = -1;

  	}

  	running = &fq->flush_queue[fq->flush_running_idx];
  	BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);

  
  	/* account completion of the flush request */

  	fq->flush_running_idx ^= 1;

  
  	if (!q->mq_ops)
  		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, fq, 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 || fq->flush_queue_delayed) {

  		WARN_ON(q->mq_ops);
  		blk_run_queue_async(q);

  	}

  	fq->flush_queue_delayed = 0;

  	if (q->mq_ops)

  		spin_unlock_irqrestore(&fq->mq_flush_lock, flags);

  }

  /**
   * blk_kick_flush - consider issuing flush request
   * @q: request_queue being kicked

   * @fq: flush queue

   *
   * 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 or fq->mq_flush_lock)

   *
   * RETURNS:
   * %true if flush was issued, %false otherwise.
   */

  static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)

  {

  	struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];

  	struct request *first_rq =
  		list_first_entry(pending, struct request, flush.list);

  	struct request *flush_rq = fq->flush_rq;

  
  	/* C1 described at the top of this file */

  	if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))

  		return false;

  	/* C2 and C3
  	 *
  	 * For blk-mq + scheduling, we can risk having all driver tags
  	 * assigned to empty flushes, and we deadlock if we are expecting
  	 * other requests to make progress. Don't defer for that case.
  	 */

  	if (!list_empty(&fq->flush_data_in_flight) &&

  	    !(q->mq_ops && q->elevator) &&

  	    time_before(jiffies,

  			fq->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.
  	 */

  	fq->flush_pending_idx ^= 1;

  	blk_rq_init(q, flush_rq);

  
  	/*
  	 * Borrow tag from the first request since they can't

  	 * be in flight at the same time. And acquire the tag's
  	 * ownership for flush req.

  	 */
  	if (q->mq_ops) {

  		struct blk_mq_hw_ctx *hctx;

  		flush_rq->mq_ctx = first_rq->mq_ctx;
  		flush_rq->tag = first_rq->tag;

  		fq->orig_rq = first_rq;

  		hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);

  		blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);

  	}

  	flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;

  	flush_rq->rq_flags |= RQF_FLUSH_SEQ;

  	flush_rq->rq_disk = first_rq->rq_disk;
  	flush_rq->end_io = flush_end_io;

  	return blk_flush_queue_rq(flush_rq, false);

  }

  static void flush_data_end_io(struct request *rq, blk_status_t error)

  {

  	struct request_queue *q = rq->q;

  	struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);

  	lockdep_assert_held(q->queue_lock);

  	/*

  	 * Updating q->in_flight[] here for making this tag usable
  	 * early. Because in blk_queue_start_tag(),
  	 * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
  	 * reserve tags for sync I/O.
  	 *
  	 * More importantly this way can avoid the following I/O
  	 * deadlock:
  	 *
  	 * - suppose there are 40 fua requests comming to flush queue
  	 *   and queue depth is 31
  	 * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
  	 *   tag for async I/O any more
  	 * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
  	 *   and flush_data_end_io() is called
  	 * - the other rqs still can't go ahead if not updating
  	 *   q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
  	 *   are held in flush data queue and make no progress of
  	 *   handling post flush rq
  	 * - only after the post flush rq is handled, all these rqs
  	 *   can be completed
  	 */
  
  	elv_completed_request(q, rq);
  
  	/* for avoiding double accounting */

  	rq->rq_flags &= ~RQF_STARTED;

  
  	/*

  	 * After populating an empty queue, kick it to avoid stall.  Read
  	 * the comment in flush_end_io().
  	 */

  	if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))

  		blk_run_queue_async(q);

  }

  static void mq_flush_data_end_io(struct request *rq, blk_status_t error)

  {
  	struct request_queue *q = rq->q;
  	struct blk_mq_hw_ctx *hctx;

  	struct blk_mq_ctx *ctx = rq->mq_ctx;

  	unsigned long flags;

  	struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);

  	hctx = blk_mq_map_queue(q, ctx->cpu);

  
  	/*
  	 * After populating an empty queue, kick it to avoid stall.  Read
  	 * the comment in flush_end_io().
  	 */

  	spin_lock_irqsave(&fq->mq_flush_lock, flags);

  	blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);

  	spin_unlock_irqrestore(&fq->mq_flush_lock, flags);

  
  	blk_mq_run_hw_queue(hctx, true);

  }

  /**

   * blk_insert_flush - insert a new PREFLUSH/FUA request

   * @rq: request to insert
   *

   * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.

   * or __blk_mq_run_hw_queue() to dispatch request.

   * @rq is being submitted.  Analyze what needs to be done and put it on the
   * right queue.

   */
  void blk_insert_flush(struct request *rq)

  {

  	struct request_queue *q = rq->q;

  	unsigned long fflags = q->queue_flags;	/* may change, cache */

  	unsigned int policy = blk_flush_policy(fflags, rq);

  	struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);

  	if (!q->mq_ops)
  		lockdep_assert_held(q->queue_lock);

  	/*
  	 * @policy now records what operations need to be done.  Adjust

  	 * REQ_PREFLUSH and FUA for the driver.

  	 */

  	rq->cmd_flags &= ~REQ_PREFLUSH;

  	if (!(fflags & (1UL << QUEUE_FLAG_FUA)))

  		rq->cmd_flags &= ~REQ_FUA;
  
  	/*

  	 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
  	 * of those flags, we have to set REQ_SYNC to avoid skewing
  	 * the request accounting.
  	 */
  	rq->cmd_flags |= REQ_SYNC;
  
  	/*

  	 * 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) {

  		if (q->mq_ops)

  			blk_mq_end_request(rq, 0);

  		else

  			__blk_end_request(rq, 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))) {

  		if (q->mq_ops)

  			blk_mq_sched_insert_request(rq, false, true, false, false);

  		else

  			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->rq_flags |= RQF_FLUSH_SEQ;

  	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */

  	if (q->mq_ops) {
  		rq->end_io = mq_flush_data_end_io;

  		spin_lock_irq(&fq->mq_flush_lock);

  		blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);

  		spin_unlock_irq(&fq->mq_flush_lock);

  		return;
  	}

  	rq->end_io = flush_data_end_io;

  	blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);

  }

  /**

   * 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.

   */

  int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,

  		sector_t *error_sector)

  {

  	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_set_dev(bio, bdev);

  	bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;

  	ret = submit_bio_wait(bio);

  
  	/*
  	 * 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_iter.bi_sector;

  	bio_put(bio);
  	return ret;
  }

  EXPORT_SYMBOL(blkdev_issue_flush);

  struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
  		int node, int cmd_size)

  {

  	struct blk_flush_queue *fq;
  	int rq_sz = sizeof(struct request);

  	fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);

  	if (!fq)
  		goto fail;

  	if (q->mq_ops)

  		spin_lock_init(&fq->mq_flush_lock);

  	rq_sz = round_up(rq_sz + cmd_size, cache_line_size());

  	fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);

  	if (!fq->flush_rq)
  		goto fail_rq;
  
  	INIT_LIST_HEAD(&fq->flush_queue[0]);
  	INIT_LIST_HEAD(&fq->flush_queue[1]);
  	INIT_LIST_HEAD(&fq->flush_data_in_flight);
  
  	return fq;
  
   fail_rq:
  	kfree(fq);
   fail:
  	return NULL;

  }

  void blk_free_flush_queue(struct blk_flush_queue *fq)

  {

  	/* bio based request queue hasn't flush queue */
  	if (!fq)
  		return;

  	kfree(fq->flush_rq);
  	kfree(fq);
  }