diff --git a/src/kernel/linux/v4.14/block/blk-flush.c b/src/kernel/linux/v4.14/block/blk-flush.c
new file mode 100644
index 0000000..6603352
--- /dev/null
+++ b/src/kernel/linux/v4.14/block/blk-flush.c
@@ -0,0 +1,584 @@
+/*
+ * 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_sched_restart(hctx);
+}
+
+/**
+ * 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);
+}