Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3521 insertions, 0 deletions

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
new file mode 100644
index 000000000..f98ad4366
--- /dev/null
+++ b/drivers/md/dm-cache-target.c
@@ -0,0 +1,3521 @@
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+#include "dm-bio-prison-v2.h"
+#include "dm-bio-record.h"
+#include "dm-cache-metadata.h"
+
+#include <linux/dm-io.h>
+#include <linux/dm-kcopyd.h>
+#include <linux/jiffies.h>
+#include <linux/init.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/rwsem.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#define DM_MSG_PREFIX "cache"
+
+DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(cache_copy_throttle,
+	"A percentage of time allocated for copying to and/or from cache");
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Glossary:
+ *
+ * oblock: index of an origin block
+ * cblock: index of a cache block
+ * promotion: movement of a block from origin to cache
+ * demotion: movement of a block from cache to origin
+ * migration: movement of a block between the origin and cache device,
+ *	      either direction
+ */
+
+/*----------------------------------------------------------------*/
+
+struct io_tracker {
+	spinlock_t lock;
+
+	/*
+	 * Sectors of in-flight IO.
+	 */
+	sector_t in_flight;
+
+	/*
+	 * The time, in jiffies, when this device became idle (if it is
+	 * indeed idle).
+	 */
+	unsigned long idle_time;
+	unsigned long last_update_time;
+};
+
+static void iot_init(struct io_tracker *iot)
+{
+	spin_lock_init(&iot->lock);
+	iot->in_flight = 0ul;
+	iot->idle_time = 0ul;
+	iot->last_update_time = jiffies;
+}
+
+static bool __iot_idle_for(struct io_tracker *iot, unsigned long jifs)
+{
+	if (iot->in_flight)
+		return false;
+
+	return time_after(jiffies, iot->idle_time + jifs);
+}
+
+static bool iot_idle_for(struct io_tracker *iot, unsigned long jifs)
+{
+	bool r;
+
+	spin_lock_irq(&iot->lock);
+	r = __iot_idle_for(iot, jifs);
+	spin_unlock_irq(&iot->lock);
+
+	return r;
+}
+
+static void iot_io_begin(struct io_tracker *iot, sector_t len)
+{
+	spin_lock_irq(&iot->lock);
+	iot->in_flight += len;
+	spin_unlock_irq(&iot->lock);
+}
+
+static void __iot_io_end(struct io_tracker *iot, sector_t len)
+{
+	if (!len)
+		return;
+
+	iot->in_flight -= len;
+	if (!iot->in_flight)
+		iot->idle_time = jiffies;
+}
+
+static void iot_io_end(struct io_tracker *iot, sector_t len)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&iot->lock, flags);
+	__iot_io_end(iot, len);
+	spin_unlock_irqrestore(&iot->lock, flags);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Represents a chunk of future work.  'input' allows continuations to pass
+ * values between themselves, typically error values.
+ */
+struct continuation {
+	struct work_struct ws;
+	blk_status_t input;
+};
+
+static inline void init_continuation(struct continuation *k,
+				     void (*fn)(struct work_struct *))
+{
+	INIT_WORK(&k->ws, fn);
+	k->input = 0;
+}
+
+static inline void queue_continuation(struct workqueue_struct *wq,
+				      struct continuation *k)
+{
+	queue_work(wq, &k->ws);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The batcher collects together pieces of work that need a particular
+ * operation to occur before they can proceed (typically a commit).
+ */
+struct batcher {
+	/*
+	 * The operation that everyone is waiting for.
+	 */
+	blk_status_t (*commit_op)(void *context);
+	void *commit_context;
+
+	/*
+	 * This is how bios should be issued once the commit op is complete
+	 * (accounted_request).
+	 */
+	void (*issue_op)(struct bio *bio, void *context);
+	void *issue_context;
+
+	/*
+	 * Queued work gets put on here after commit.
+	 */
+	struct workqueue_struct *wq;
+
+	spinlock_t lock;
+	struct list_head work_items;
+	struct bio_list bios;
+	struct work_struct commit_work;
+
+	bool commit_scheduled;
+};
+
+static void __commit(struct work_struct *_ws)
+{
+	struct batcher *b = container_of(_ws, struct batcher, commit_work);
+	blk_status_t r;
+	struct list_head work_items;
+	struct work_struct *ws, *tmp;
+	struct continuation *k;
+	struct bio *bio;
+	struct bio_list bios;
+
+	INIT_LIST_HEAD(&work_items);
+	bio_list_init(&bios);
+
+	/*
+	 * We have to grab these before the commit_op to avoid a race
+	 * condition.
+	 */
+	spin_lock_irq(&b->lock);
+	list_splice_init(&b->work_items, &work_items);
+	bio_list_merge(&bios, &b->bios);
+	bio_list_init(&b->bios);
+	b->commit_scheduled = false;
+	spin_unlock_irq(&b->lock);
+
+	r = b->commit_op(b->commit_context);
+
+	list_for_each_entry_safe(ws, tmp, &work_items, entry) {
+		k = container_of(ws, struct continuation, ws);
+		k->input = r;
+		INIT_LIST_HEAD(&ws->entry); /* to avoid a WARN_ON */
+		queue_work(b->wq, ws);
+	}
+
+	while ((bio = bio_list_pop(&bios))) {
+		if (r) {
+			bio->bi_status = r;
+			bio_endio(bio);
+		} else
+			b->issue_op(bio, b->issue_context);
+	}
+}
+
+static void batcher_init(struct batcher *b,
+			 blk_status_t (*commit_op)(void *),
+			 void *commit_context,
+			 void (*issue_op)(struct bio *bio, void *),
+			 void *issue_context,
+			 struct workqueue_struct *wq)
+{
+	b->commit_op = commit_op;
+	b->commit_context = commit_context;
+	b->issue_op = issue_op;
+	b->issue_context = issue_context;
+	b->wq = wq;
+
+	spin_lock_init(&b->lock);
+	INIT_LIST_HEAD(&b->work_items);
+	bio_list_init(&b->bios);
+	INIT_WORK(&b->commit_work, __commit);
+	b->commit_scheduled = false;
+}
+
+static void async_commit(struct batcher *b)
+{
+	queue_work(b->wq, &b->commit_work);
+}
+
+static void continue_after_commit(struct batcher *b, struct continuation *k)
+{
+	bool commit_scheduled;
+
+	spin_lock_irq(&b->lock);
+	commit_scheduled = b->commit_scheduled;
+	list_add_tail(&k->ws.entry, &b->work_items);
+	spin_unlock_irq(&b->lock);
+
+	if (commit_scheduled)
+		async_commit(b);
+}
+
+/*
+ * Bios are errored if commit failed.
+ */
+static void issue_after_commit(struct batcher *b, struct bio *bio)
+{
+       bool commit_scheduled;
+
+       spin_lock_irq(&b->lock);
+       commit_scheduled = b->commit_scheduled;
+       bio_list_add(&b->bios, bio);
+       spin_unlock_irq(&b->lock);
+
+       if (commit_scheduled)
+	       async_commit(b);
+}
+
+/*
+ * Call this if some urgent work is waiting for the commit to complete.
+ */
+static void schedule_commit(struct batcher *b)
+{
+	bool immediate;
+
+	spin_lock_irq(&b->lock);
+	immediate = !list_empty(&b->work_items) || !bio_list_empty(&b->bios);
+	b->commit_scheduled = true;
+	spin_unlock_irq(&b->lock);
+
+	if (immediate)
+		async_commit(b);
+}
+
+/*
+ * There are a couple of places where we let a bio run, but want to do some
+ * work before calling its endio function.  We do this by temporarily
+ * changing the endio fn.
+ */
+struct dm_hook_info {
+	bio_end_io_t *bi_end_io;
+};
+
+static void dm_hook_bio(struct dm_hook_info *h, struct bio *bio,
+			bio_end_io_t *bi_end_io, void *bi_private)
+{
+	h->bi_end_io = bio->bi_end_io;
+
+	bio->bi_end_io = bi_end_io;
+	bio->bi_private = bi_private;
+}
+
+static void dm_unhook_bio(struct dm_hook_info *h, struct bio *bio)
+{
+	bio->bi_end_io = h->bi_end_io;
+}
+
+/*----------------------------------------------------------------*/
+
+#define MIGRATION_POOL_SIZE 128
+#define COMMIT_PERIOD HZ
+#define MIGRATION_COUNT_WINDOW 10
+
+/*
+ * The block size of the device holding cache data must be
+ * between 32KB and 1GB.
+ */
+#define DATA_DEV_BLOCK_SIZE_MIN_SECTORS (32 * 1024 >> SECTOR_SHIFT)
+#define DATA_DEV_BLOCK_SIZE_MAX_SECTORS (1024 * 1024 * 1024 >> SECTOR_SHIFT)
+
+enum cache_metadata_mode {
+	CM_WRITE,		/* metadata may be changed */
+	CM_READ_ONLY,		/* metadata may not be changed */
+	CM_FAIL
+};
+
+enum cache_io_mode {
+	/*
+	 * Data is written to cached blocks only.  These blocks are marked
+	 * dirty.  If you lose the cache device you will lose data.
+	 * Potential performance increase for both reads and writes.
+	 */
+	CM_IO_WRITEBACK,
+
+	/*
+	 * Data is written to both cache and origin.  Blocks are never
+	 * dirty.  Potential performance benfit for reads only.
+	 */
+	CM_IO_WRITETHROUGH,
+
+	/*
+	 * A degraded mode useful for various cache coherency situations
+	 * (eg, rolling back snapshots).  Reads and writes always go to the
+	 * origin.  If a write goes to a cached oblock, then the cache
+	 * block is invalidated.
+	 */
+	CM_IO_PASSTHROUGH
+};
+
+struct cache_features {
+	enum cache_metadata_mode mode;
+	enum cache_io_mode io_mode;
+	unsigned metadata_version;
+	bool discard_passdown:1;
+};
+
+struct cache_stats {
+	atomic_t read_hit;
+	atomic_t read_miss;
+	atomic_t write_hit;
+	atomic_t write_miss;
+	atomic_t demotion;
+	atomic_t promotion;
+	atomic_t writeback;
+	atomic_t copies_avoided;
+	atomic_t cache_cell_clash;
+	atomic_t commit_count;
+	atomic_t discard_count;
+};
+
+struct cache {
+	struct dm_target *ti;
+	spinlock_t lock;
+
+	/*
+	 * Fields for converting from sectors to blocks.
+	 */
+	int sectors_per_block_shift;
+	sector_t sectors_per_block;
+
+	struct dm_cache_metadata *cmd;
+
+	/*
+	 * Metadata is written to this device.
+	 */
+	struct dm_dev *metadata_dev;
+
+	/*
+	 * The slower of the two data devices.  Typically a spindle.
+	 */
+	struct dm_dev *origin_dev;
+
+	/*
+	 * The faster of the two data devices.  Typically an SSD.
+	 */
+	struct dm_dev *cache_dev;
+
+	/*
+	 * Size of the origin device in _complete_ blocks and native sectors.
+	 */
+	dm_oblock_t origin_blocks;
+	sector_t origin_sectors;
+
+	/*
+	 * Size of the cache device in blocks.
+	 */
+	dm_cblock_t cache_size;
+
+	/*
+	 * Invalidation fields.
+	 */
+	spinlock_t invalidation_lock;
+	struct list_head invalidation_requests;
+
+	sector_t migration_threshold;
+	wait_queue_head_t migration_wait;
+	atomic_t nr_allocated_migrations;
+
+	/*
+	 * The number of in flight migrations that are performing
+	 * background io. eg, promotion, writeback.
+	 */
+	atomic_t nr_io_migrations;
+
+	struct bio_list deferred_bios;
+
+	struct rw_semaphore quiesce_lock;
+
+	/*
+	 * origin_blocks entries, discarded if set.
+	 */
+	dm_dblock_t discard_nr_blocks;
+	unsigned long *discard_bitset;
+	uint32_t discard_block_size; /* a power of 2 times sectors per block */
+
+	/*
+	 * Rather than reconstructing the table line for the status we just
+	 * save it and regurgitate.
+	 */
+	unsigned nr_ctr_args;
+	const char **ctr_args;
+
+	struct dm_kcopyd_client *copier;
+	struct work_struct deferred_bio_worker;
+	struct work_struct migration_worker;
+	struct workqueue_struct *wq;
+	struct delayed_work waker;
+	struct dm_bio_prison_v2 *prison;
+
+	/*
+	 * cache_size entries, dirty if set
+	 */
+	unsigned long *dirty_bitset;
+	atomic_t nr_dirty;
+
+	unsigned policy_nr_args;
+	struct dm_cache_policy *policy;
+
+	/*
+	 * Cache features such as write-through.
+	 */
+	struct cache_features features;
+
+	struct cache_stats stats;
+
+	bool need_tick_bio:1;
+	bool sized:1;
+	bool invalidate:1;
+	bool commit_requested:1;
+	bool loaded_mappings:1;
+	bool loaded_discards:1;
+
+	struct rw_semaphore background_work_lock;
+
+	struct batcher committer;
+	struct work_struct commit_ws;
+
+	struct io_tracker tracker;
+
+	mempool_t migration_pool;
+
+	struct bio_set bs;
+};
+
+struct per_bio_data {
+	bool tick:1;
+	unsigned req_nr:2;
+	struct dm_bio_prison_cell_v2 *cell;
+	struct dm_hook_info hook_info;
+	sector_t len;
+};
+
+struct dm_cache_migration {
+	struct continuation k;
+	struct cache *cache;
+
+	struct policy_work *op;
+	struct bio *overwrite_bio;
+	struct dm_bio_prison_cell_v2 *cell;
+
+	dm_cblock_t invalidate_cblock;
+	dm_oblock_t invalidate_oblock;
+};
+
+/*----------------------------------------------------------------*/
+
+static bool writethrough_mode(struct cache *cache)
+{
+	return cache->features.io_mode == CM_IO_WRITETHROUGH;
+}
+
+static bool writeback_mode(struct cache *cache)
+{
+	return cache->features.io_mode == CM_IO_WRITEBACK;
+}
+
+static inline bool passthrough_mode(struct cache *cache)
+{
+	return unlikely(cache->features.io_mode == CM_IO_PASSTHROUGH);
+}
+
+/*----------------------------------------------------------------*/
+
+static void wake_deferred_bio_worker(struct cache *cache)
+{
+	queue_work(cache->wq, &cache->deferred_bio_worker);
+}
+
+static void wake_migration_worker(struct cache *cache)
+{
+	if (passthrough_mode(cache))
+		return;
+
+	queue_work(cache->wq, &cache->migration_worker);
+}
+
+/*----------------------------------------------------------------*/
+
+static struct dm_bio_prison_cell_v2 *alloc_prison_cell(struct cache *cache)
+{
+	return dm_bio_prison_alloc_cell_v2(cache->prison, GFP_NOIO);
+}
+
+static void free_prison_cell(struct cache *cache, struct dm_bio_prison_cell_v2 *cell)
+{
+	dm_bio_prison_free_cell_v2(cache->prison, cell);
+}
+
+static struct dm_cache_migration *alloc_migration(struct cache *cache)
+{
+	struct dm_cache_migration *mg;
+
+	mg = mempool_alloc(&cache->migration_pool, GFP_NOIO);
+
+	memset(mg, 0, sizeof(*mg));
+
+	mg->cache = cache;
+	atomic_inc(&cache->nr_allocated_migrations);
+
+	return mg;
+}
+
+static void free_migration(struct dm_cache_migration *mg)
+{
+	struct cache *cache = mg->cache;
+
+	if (atomic_dec_and_test(&cache->nr_allocated_migrations))
+		wake_up(&cache->migration_wait);
+
+	mempool_free(mg, &cache->migration_pool);
+}
+
+/*----------------------------------------------------------------*/
+
+static inline dm_oblock_t oblock_succ(dm_oblock_t b)
+{
+	return to_oblock(from_oblock(b) + 1ull);
+}
+
+static void build_key(dm_oblock_t begin, dm_oblock_t end, struct dm_cell_key_v2 *key)
+{
+	key->virtual = 0;
+	key->dev = 0;
+	key->block_begin = from_oblock(begin);
+	key->block_end = from_oblock(end);
+}
+
+/*
+ * We have two lock levels.  Level 0, which is used to prevent WRITEs, and
+ * level 1 which prevents *both* READs and WRITEs.
+ */
+#define WRITE_LOCK_LEVEL 0
+#define READ_WRITE_LOCK_LEVEL 1
+
+static unsigned lock_level(struct bio *bio)
+{
+	return bio_data_dir(bio) == WRITE ?
+		WRITE_LOCK_LEVEL :
+		READ_WRITE_LOCK_LEVEL;
+}
+
+/*----------------------------------------------------------------
+ * Per bio data
+ *--------------------------------------------------------------*/
+
+static struct per_bio_data *get_per_bio_data(struct bio *bio)
+{
+	struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
+	BUG_ON(!pb);
+	return pb;
+}
+
+static struct per_bio_data *init_per_bio_data(struct bio *bio)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	pb->tick = false;
+	pb->req_nr = dm_bio_get_target_bio_nr(bio);
+	pb->cell = NULL;
+	pb->len = 0;
+
+	return pb;
+}
+
+/*----------------------------------------------------------------*/
+
+static void defer_bio(struct cache *cache, struct bio *bio)
+{
+	spin_lock_irq(&cache->lock);
+	bio_list_add(&cache->deferred_bios, bio);
+	spin_unlock_irq(&cache->lock);
+
+	wake_deferred_bio_worker(cache);
+}
+
+static void defer_bios(struct cache *cache, struct bio_list *bios)
+{
+	spin_lock_irq(&cache->lock);
+	bio_list_merge(&cache->deferred_bios, bios);
+	bio_list_init(bios);
+	spin_unlock_irq(&cache->lock);
+
+	wake_deferred_bio_worker(cache);
+}
+
+/*----------------------------------------------------------------*/
+
+static bool bio_detain_shared(struct cache *cache, dm_oblock_t oblock, struct bio *bio)
+{
+	bool r;
+	struct per_bio_data *pb;
+	struct dm_cell_key_v2 key;
+	dm_oblock_t end = to_oblock(from_oblock(oblock) + 1ULL);
+	struct dm_bio_prison_cell_v2 *cell_prealloc, *cell;
+
+	cell_prealloc = alloc_prison_cell(cache); /* FIXME: allow wait if calling from worker */
+
+	build_key(oblock, end, &key);
+	r = dm_cell_get_v2(cache->prison, &key, lock_level(bio), bio, cell_prealloc, &cell);
+	if (!r) {
+		/*
+		 * Failed to get the lock.
+		 */
+		free_prison_cell(cache, cell_prealloc);
+		return r;
+	}
+
+	if (cell != cell_prealloc)
+		free_prison_cell(cache, cell_prealloc);
+
+	pb = get_per_bio_data(bio);
+	pb->cell = cell;
+
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+static bool is_dirty(struct cache *cache, dm_cblock_t b)
+{
+	return test_bit(from_cblock(b), cache->dirty_bitset);
+}
+
+static void set_dirty(struct cache *cache, dm_cblock_t cblock)
+{
+	if (!test_and_set_bit(from_cblock(cblock), cache->dirty_bitset)) {
+		atomic_inc(&cache->nr_dirty);
+		policy_set_dirty(cache->policy, cblock);
+	}
+}
+
+/*
+ * These two are called when setting after migrations to force the policy
+ * and dirty bitset to be in sync.
+ */
+static void force_set_dirty(struct cache *cache, dm_cblock_t cblock)
+{
+	if (!test_and_set_bit(from_cblock(cblock), cache->dirty_bitset))
+		atomic_inc(&cache->nr_dirty);
+	policy_set_dirty(cache->policy, cblock);
+}
+
+static void force_clear_dirty(struct cache *cache, dm_cblock_t cblock)
+{
+	if (test_and_clear_bit(from_cblock(cblock), cache->dirty_bitset)) {
+		if (atomic_dec_return(&cache->nr_dirty) == 0)
+			dm_table_event(cache->ti->table);
+	}
+
+	policy_clear_dirty(cache->policy, cblock);
+}
+
+/*----------------------------------------------------------------*/
+
+static bool block_size_is_power_of_two(struct cache *cache)
+{
+	return cache->sectors_per_block_shift >= 0;
+}
+
+static dm_block_t block_div(dm_block_t b, uint32_t n)
+{
+	do_div(b, n);
+
+	return b;
+}
+
+static dm_block_t oblocks_per_dblock(struct cache *cache)
+{
+	dm_block_t oblocks = cache->discard_block_size;
+
+	if (block_size_is_power_of_two(cache))
+		oblocks >>= cache->sectors_per_block_shift;
+	else
+		oblocks = block_div(oblocks, cache->sectors_per_block);
+
+	return oblocks;
+}
+
+static dm_dblock_t oblock_to_dblock(struct cache *cache, dm_oblock_t oblock)
+{
+	return to_dblock(block_div(from_oblock(oblock),
+				   oblocks_per_dblock(cache)));
+}
+
+static void set_discard(struct cache *cache, dm_dblock_t b)
+{
+	BUG_ON(from_dblock(b) >= from_dblock(cache->discard_nr_blocks));
+	atomic_inc(&cache->stats.discard_count);
+
+	spin_lock_irq(&cache->lock);
+	set_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irq(&cache->lock);
+}
+
+static void clear_discard(struct cache *cache, dm_dblock_t b)
+{
+	spin_lock_irq(&cache->lock);
+	clear_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irq(&cache->lock);
+}
+
+static bool is_discarded(struct cache *cache, dm_dblock_t b)
+{
+	int r;
+	spin_lock_irq(&cache->lock);
+	r = test_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irq(&cache->lock);
+
+	return r;
+}
+
+static bool is_discarded_oblock(struct cache *cache, dm_oblock_t b)
+{
+	int r;
+	spin_lock_irq(&cache->lock);
+	r = test_bit(from_dblock(oblock_to_dblock(cache, b)),
+		     cache->discard_bitset);
+	spin_unlock_irq(&cache->lock);
+
+	return r;
+}
+
+/*----------------------------------------------------------------
+ * Remapping
+ *--------------------------------------------------------------*/
+static void remap_to_origin(struct cache *cache, struct bio *bio)
+{
+	bio_set_dev(bio, cache->origin_dev->bdev);
+}
+
+static void remap_to_cache(struct cache *cache, struct bio *bio,
+			   dm_cblock_t cblock)
+{
+	sector_t bi_sector = bio->bi_iter.bi_sector;
+	sector_t block = from_cblock(cblock);
+
+	bio_set_dev(bio, cache->cache_dev->bdev);
+	if (!block_size_is_power_of_two(cache))
+		bio->bi_iter.bi_sector =
+			(block * cache->sectors_per_block) +
+			sector_div(bi_sector, cache->sectors_per_block);
+	else
+		bio->bi_iter.bi_sector =
+			(block << cache->sectors_per_block_shift) |
+			(bi_sector & (cache->sectors_per_block - 1));
+}
+
+static void check_if_tick_bio_needed(struct cache *cache, struct bio *bio)
+{
+	struct per_bio_data *pb;
+
+	spin_lock_irq(&cache->lock);
+	if (cache->need_tick_bio && !op_is_flush(bio->bi_opf) &&
+	    bio_op(bio) != REQ_OP_DISCARD) {
+		pb = get_per_bio_data(bio);
+		pb->tick = true;
+		cache->need_tick_bio = false;
+	}
+	spin_unlock_irq(&cache->lock);
+}
+
+static void __remap_to_origin_clear_discard(struct cache *cache, struct bio *bio,
+					    dm_oblock_t oblock, bool bio_has_pbd)
+{
+	if (bio_has_pbd)
+		check_if_tick_bio_needed(cache, bio);
+	remap_to_origin(cache, bio);
+	if (bio_data_dir(bio) == WRITE)
+		clear_discard(cache, oblock_to_dblock(cache, oblock));
+}
+
+static void remap_to_origin_clear_discard(struct cache *cache, struct bio *bio,
+					  dm_oblock_t oblock)
+{
+	// FIXME: check_if_tick_bio_needed() is called way too much through this interface
+	__remap_to_origin_clear_discard(cache, bio, oblock, true);
+}
+
+static void remap_to_cache_dirty(struct cache *cache, struct bio *bio,
+				 dm_oblock_t oblock, dm_cblock_t cblock)
+{
+	check_if_tick_bio_needed(cache, bio);
+	remap_to_cache(cache, bio, cblock);
+	if (bio_data_dir(bio) == WRITE) {
+		set_dirty(cache, cblock);
+		clear_discard(cache, oblock_to_dblock(cache, oblock));
+	}
+}
+
+static dm_oblock_t get_bio_block(struct cache *cache, struct bio *bio)
+{
+	sector_t block_nr = bio->bi_iter.bi_sector;
+
+	if (!block_size_is_power_of_two(cache))
+		(void) sector_div(block_nr, cache->sectors_per_block);
+	else
+		block_nr >>= cache->sectors_per_block_shift;
+
+	return to_oblock(block_nr);
+}
+
+static bool accountable_bio(struct cache *cache, struct bio *bio)
+{
+	return bio_op(bio) != REQ_OP_DISCARD;
+}
+
+static void accounted_begin(struct cache *cache, struct bio *bio)
+{
+	struct per_bio_data *pb;
+
+	if (accountable_bio(cache, bio)) {
+		pb = get_per_bio_data(bio);
+		pb->len = bio_sectors(bio);
+		iot_io_begin(&cache->tracker, pb->len);
+	}
+}
+
+static void accounted_complete(struct cache *cache, struct bio *bio)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	iot_io_end(&cache->tracker, pb->len);
+}
+
+static void accounted_request(struct cache *cache, struct bio *bio)
+{
+	accounted_begin(cache, bio);
+	submit_bio_noacct(bio);
+}
+
+static void issue_op(struct bio *bio, void *context)
+{
+	struct cache *cache = context;
+	accounted_request(cache, bio);
+}
+
+/*
+ * When running in writethrough mode we need to send writes to clean blocks
+ * to both the cache and origin devices.  Clone the bio and send them in parallel.
+ */
+static void remap_to_origin_and_cache(struct cache *cache, struct bio *bio,
+				      dm_oblock_t oblock, dm_cblock_t cblock)
+{
+	struct bio *origin_bio = bio_clone_fast(bio, GFP_NOIO, &cache->bs);
+
+	BUG_ON(!origin_bio);
+
+	bio_chain(origin_bio, bio);
+	/*
+	 * Passing false to __remap_to_origin_clear_discard() skips
+	 * all code that might use per_bio_data (since clone doesn't have it)
+	 */
+	__remap_to_origin_clear_discard(cache, origin_bio, oblock, false);
+	submit_bio(origin_bio);
+
+	remap_to_cache(cache, bio, cblock);
+}
+
+/*----------------------------------------------------------------
+ * Failure modes
+ *--------------------------------------------------------------*/
+static enum cache_metadata_mode get_cache_mode(struct cache *cache)
+{
+	return cache->features.mode;
+}
+
+static const char *cache_device_name(struct cache *cache)
+{
+	return dm_table_device_name(cache->ti->table);
+}
+
+static void notify_mode_switch(struct cache *cache, enum cache_metadata_mode mode)
+{
+	const char *descs[] = {
+		"write",
+		"read-only",
+		"fail"
+	};
+
+	dm_table_event(cache->ti->table);
+	DMINFO("%s: switching cache to %s mode",
+	       cache_device_name(cache), descs[(int)mode]);
+}
+
+static void set_cache_mode(struct cache *cache, enum cache_metadata_mode new_mode)
+{
+	bool needs_check;
+	enum cache_metadata_mode old_mode = get_cache_mode(cache);
+
+	if (dm_cache_metadata_needs_check(cache->cmd, &needs_check)) {
+		DMERR("%s: unable to read needs_check flag, setting failure mode.",
+		      cache_device_name(cache));
+		new_mode = CM_FAIL;
+	}
+
+	if (new_mode == CM_WRITE && needs_check) {
+		DMERR("%s: unable to switch cache to write mode until repaired.",
+		      cache_device_name(cache));
+		if (old_mode != new_mode)
+			new_mode = old_mode;
+		else
+			new_mode = CM_READ_ONLY;
+	}
+
+	/* Never move out of fail mode */
+	if (old_mode == CM_FAIL)
+		new_mode = CM_FAIL;
+
+	switch (new_mode) {
+	case CM_FAIL:
+	case CM_READ_ONLY:
+		dm_cache_metadata_set_read_only(cache->cmd);
+		break;
+
+	case CM_WRITE:
+		dm_cache_metadata_set_read_write(cache->cmd);
+		break;
+	}
+
+	cache->features.mode = new_mode;
+
+	if (new_mode != old_mode)
+		notify_mode_switch(cache, new_mode);
+}
+
+static void abort_transaction(struct cache *cache)
+{
+	const char *dev_name = cache_device_name(cache);
+
+	if (get_cache_mode(cache) >= CM_READ_ONLY)
+		return;
+
+	DMERR_LIMIT("%s: aborting current metadata transaction", dev_name);
+	if (dm_cache_metadata_abort(cache->cmd)) {
+		DMERR("%s: failed to abort metadata transaction", dev_name);
+		set_cache_mode(cache, CM_FAIL);
+	}
+
+	if (dm_cache_metadata_set_needs_check(cache->cmd)) {
+		DMERR("%s: failed to set 'needs_check' flag in metadata", dev_name);
+		set_cache_mode(cache, CM_FAIL);
+	}
+}
+
+static void metadata_operation_failed(struct cache *cache, const char *op, int r)
+{
+	DMERR_LIMIT("%s: metadata operation '%s' failed: error = %d",
+		    cache_device_name(cache), op, r);
+	abort_transaction(cache);
+	set_cache_mode(cache, CM_READ_ONLY);
+}
+
+/*----------------------------------------------------------------*/
+
+static void load_stats(struct cache *cache)
+{
+	struct dm_cache_statistics stats;
+
+	dm_cache_metadata_get_stats(cache->cmd, &stats);
+	atomic_set(&cache->stats.read_hit, stats.read_hits);
+	atomic_set(&cache->stats.read_miss, stats.read_misses);
+	atomic_set(&cache->stats.write_hit, stats.write_hits);
+	atomic_set(&cache->stats.write_miss, stats.write_misses);
+}
+
+static void save_stats(struct cache *cache)
+{
+	struct dm_cache_statistics stats;
+
+	if (get_cache_mode(cache) >= CM_READ_ONLY)
+		return;
+
+	stats.read_hits = atomic_read(&cache->stats.read_hit);
+	stats.read_misses = atomic_read(&cache->stats.read_miss);
+	stats.write_hits = atomic_read(&cache->stats.write_hit);
+	stats.write_misses = atomic_read(&cache->stats.write_miss);
+
+	dm_cache_metadata_set_stats(cache->cmd, &stats);
+}
+
+static void update_stats(struct cache_stats *stats, enum policy_operation op)
+{
+	switch (op) {
+	case POLICY_PROMOTE:
+		atomic_inc(&stats->promotion);
+		break;
+
+	case POLICY_DEMOTE:
+		atomic_inc(&stats->demotion);
+		break;
+
+	case POLICY_WRITEBACK:
+		atomic_inc(&stats->writeback);
+		break;
+	}
+}
+
+/*----------------------------------------------------------------
+ * Migration processing
+ *
+ * Migration covers moving data from the origin device to the cache, or
+ * vice versa.
+ *--------------------------------------------------------------*/
+
+static void inc_io_migrations(struct cache *cache)
+{
+	atomic_inc(&cache->nr_io_migrations);
+}
+
+static void dec_io_migrations(struct cache *cache)
+{
+	atomic_dec(&cache->nr_io_migrations);
+}
+
+static bool discard_or_flush(struct bio *bio)
+{
+	return bio_op(bio) == REQ_OP_DISCARD || op_is_flush(bio->bi_opf);
+}
+
+static void calc_discard_block_range(struct cache *cache, struct bio *bio,
+				     dm_dblock_t *b, dm_dblock_t *e)
+{
+	sector_t sb = bio->bi_iter.bi_sector;
+	sector_t se = bio_end_sector(bio);
+
+	*b = to_dblock(dm_sector_div_up(sb, cache->discard_block_size));
+
+	if (se - sb < cache->discard_block_size)
+		*e = *b;
+	else
+		*e = to_dblock(block_div(se, cache->discard_block_size));
+}
+
+/*----------------------------------------------------------------*/
+
+static void prevent_background_work(struct cache *cache)
+{
+	lockdep_off();
+	down_write(&cache->background_work_lock);
+	lockdep_on();
+}
+
+static void allow_background_work(struct cache *cache)
+{
+	lockdep_off();
+	up_write(&cache->background_work_lock);
+	lockdep_on();
+}
+
+static bool background_work_begin(struct cache *cache)
+{
+	bool r;
+
+	lockdep_off();
+	r = down_read_trylock(&cache->background_work_lock);
+	lockdep_on();
+
+	return r;
+}
+
+static void background_work_end(struct cache *cache)
+{
+	lockdep_off();
+	up_read(&cache->background_work_lock);
+	lockdep_on();
+}
+
+/*----------------------------------------------------------------*/
+
+static bool bio_writes_complete_block(struct cache *cache, struct bio *bio)
+{
+	return (bio_data_dir(bio) == WRITE) &&
+		(bio->bi_iter.bi_size == (cache->sectors_per_block << SECTOR_SHIFT));
+}
+
+static bool optimisable_bio(struct cache *cache, struct bio *bio, dm_oblock_t block)
+{
+	return writeback_mode(cache) &&
+		(is_discarded_oblock(cache, block) || bio_writes_complete_block(cache, bio));
+}
+
+static void quiesce(struct dm_cache_migration *mg,
+		    void (*continuation)(struct work_struct *))
+{
+	init_continuation(&mg->k, continuation);
+	dm_cell_quiesce_v2(mg->cache->prison, mg->cell, &mg->k.ws);
+}
+
+static struct dm_cache_migration *ws_to_mg(struct work_struct *ws)
+{
+	struct continuation *k = container_of(ws, struct continuation, ws);
+	return container_of(k, struct dm_cache_migration, k);
+}
+
+static void copy_complete(int read_err, unsigned long write_err, void *context)
+{
+	struct dm_cache_migration *mg = container_of(context, struct dm_cache_migration, k);
+
+	if (read_err || write_err)
+		mg->k.input = BLK_STS_IOERR;
+
+	queue_continuation(mg->cache->wq, &mg->k);
+}
+
+static void copy(struct dm_cache_migration *mg, bool promote)
+{
+	struct dm_io_region o_region, c_region;
+	struct cache *cache = mg->cache;
+
+	o_region.bdev = cache->origin_dev->bdev;
+	o_region.sector = from_oblock(mg->op->oblock) * cache->sectors_per_block;
+	o_region.count = cache->sectors_per_block;
+
+	c_region.bdev = cache->cache_dev->bdev;
+	c_region.sector = from_cblock(mg->op->cblock) * cache->sectors_per_block;
+	c_region.count = cache->sectors_per_block;
+
+	if (promote)
+		dm_kcopyd_copy(cache->copier, &o_region, 1, &c_region, 0, copy_complete, &mg->k);
+	else
+		dm_kcopyd_copy(cache->copier, &c_region, 1, &o_region, 0, copy_complete, &mg->k);
+}
+
+static void bio_drop_shared_lock(struct cache *cache, struct bio *bio)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	if (pb->cell && dm_cell_put_v2(cache->prison, pb->cell))
+		free_prison_cell(cache, pb->cell);
+	pb->cell = NULL;
+}
+
+static void overwrite_endio(struct bio *bio)
+{
+	struct dm_cache_migration *mg = bio->bi_private;
+	struct cache *cache = mg->cache;
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	dm_unhook_bio(&pb->hook_info, bio);
+
+	if (bio->bi_status)
+		mg->k.input = bio->bi_status;
+
+	queue_continuation(cache->wq, &mg->k);
+}
+
+static void overwrite(struct dm_cache_migration *mg,
+		      void (*continuation)(struct work_struct *))
+{
+	struct bio *bio = mg->overwrite_bio;
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	dm_hook_bio(&pb->hook_info, bio, overwrite_endio, mg);
+
+	/*
+	 * The overwrite bio is part of the copy operation, as such it does
+	 * not set/clear discard or dirty flags.
+	 */
+	if (mg->op->op == POLICY_PROMOTE)
+		remap_to_cache(mg->cache, bio, mg->op->cblock);
+	else
+		remap_to_origin(mg->cache, bio);
+
+	init_continuation(&mg->k, continuation);
+	accounted_request(mg->cache, bio);
+}
+
+/*
+ * Migration steps:
+ *
+ * 1) exclusive lock preventing WRITEs
+ * 2) quiesce
+ * 3) copy or issue overwrite bio
+ * 4) upgrade to exclusive lock preventing READs and WRITEs
+ * 5) quiesce
+ * 6) update metadata and commit
+ * 7) unlock
+ */
+static void mg_complete(struct dm_cache_migration *mg, bool success)
+{
+	struct bio_list bios;
+	struct cache *cache = mg->cache;
+	struct policy_work *op = mg->op;
+	dm_cblock_t cblock = op->cblock;
+
+	if (success)
+		update_stats(&cache->stats, op->op);
+
+	switch (op->op) {
+	case POLICY_PROMOTE:
+		clear_discard(cache, oblock_to_dblock(cache, op->oblock));
+		policy_complete_background_work(cache->policy, op, success);
+
+		if (mg->overwrite_bio) {
+			if (success)
+				force_set_dirty(cache, cblock);
+			else if (mg->k.input)
+				mg->overwrite_bio->bi_status = mg->k.input;
+			else
+				mg->overwrite_bio->bi_status = BLK_STS_IOERR;
+			bio_endio(mg->overwrite_bio);
+		} else {
+			if (success)
+				force_clear_dirty(cache, cblock);
+			dec_io_migrations(cache);
+		}
+		break;
+
+	case POLICY_DEMOTE:
+		/*
+		 * We clear dirty here to update the nr_dirty counter.
+		 */
+		if (success)
+			force_clear_dirty(cache, cblock);
+		policy_complete_background_work(cache->policy, op, success);
+		dec_io_migrations(cache);
+		break;
+
+	case POLICY_WRITEBACK:
+		if (success)
+			force_clear_dirty(cache, cblock);
+		policy_complete_background_work(cache->policy, op, success);
+		dec_io_migrations(cache);
+		break;
+	}
+
+	bio_list_init(&bios);
+	if (mg->cell) {
+		if (dm_cell_unlock_v2(cache->prison, mg->cell, &bios))
+			free_prison_cell(cache, mg->cell);
+	}
+
+	free_migration(mg);
+	defer_bios(cache, &bios);
+	wake_migration_worker(cache);
+
+	background_work_end(cache);
+}
+
+static void mg_success(struct work_struct *ws)
+{
+	struct dm_cache_migration *mg = ws_to_mg(ws);
+	mg_complete(mg, mg->k.input == 0);
+}
+
+static void mg_update_metadata(struct work_struct *ws)
+{
+	int r;
+	struct dm_cache_migration *mg = ws_to_mg(ws);
+	struct cache *cache = mg->cache;
+	struct policy_work *op = mg->op;
+
+	switch (op->op) {
+	case POLICY_PROMOTE:
+		r = dm_cache_insert_mapping(cache->cmd, op->cblock, op->oblock);
+		if (r) {
+			DMERR_LIMIT("%s: migration failed; couldn't insert mapping",
+				    cache_device_name(cache));
+			metadata_operation_failed(cache, "dm_cache_insert_mapping", r);
+
+			mg_complete(mg, false);
+			return;
+		}
+		mg_complete(mg, true);
+		break;
+
+	case POLICY_DEMOTE:
+		r = dm_cache_remove_mapping(cache->cmd, op->cblock);
+		if (r) {
+			DMERR_LIMIT("%s: migration failed; couldn't update on disk metadata",
+				    cache_device_name(cache));
+			metadata_operation_failed(cache, "dm_cache_remove_mapping", r);
+
+			mg_complete(mg, false);
+			return;
+		}
+
+		/*
+		 * It would be nice if we only had to commit when a REQ_FLUSH
+		 * comes through.  But there's one scenario that we have to
+		 * look out for:
+		 *
+		 * - vblock x in a cache block
+		 * - domotion occurs
+		 * - cache block gets reallocated and over written
+		 * - crash
+		 *
+		 * When we recover, because there was no commit the cache will
+		 * rollback to having the data for vblock x in the cache block.
+		 * But the cache block has since been overwritten, so it'll end
+		 * up pointing to data that was never in 'x' during the history
+		 * of the device.
+		 *
+		 * To avoid this issue we require a commit as part of the
+		 * demotion operation.
+		 */
+		init_continuation(&mg->k, mg_success);
+		continue_after_commit(&cache->committer, &mg->k);
+		schedule_commit(&cache->committer);
+		break;
+
+	case POLICY_WRITEBACK:
+		mg_complete(mg, true);
+		break;
+	}
+}
+
+static void mg_update_metadata_after_copy(struct work_struct *ws)
+{
+	struct dm_cache_migration *mg = ws_to_mg(ws);
+
+	/*
+	 * Did the copy succeed?
+	 */
+	if (mg->k.input)
+		mg_complete(mg, false);
+	else
+		mg_update_metadata(ws);
+}
+
+static void mg_upgrade_lock(struct work_struct *ws)
+{
+	int r;
+	struct dm_cache_migration *mg = ws_to_mg(ws);
+
+	/*
+	 * Did the copy succeed?
+	 */
+	if (mg->k.input)
+		mg_complete(mg, false);
+
+	else {
+		/*
+		 * Now we want the lock to prevent both reads and writes.
+		 */
+		r = dm_cell_lock_promote_v2(mg->cache->prison, mg->cell,
+					    READ_WRITE_LOCK_LEVEL);
+		if (r < 0)
+			mg_complete(mg, false);
+
+		else if (r)
+			quiesce(mg, mg_update_metadata);
+
+		else
+			mg_update_metadata(ws);
+	}
+}
+
+static void mg_full_copy(struct work_struct *ws)
+{
+	struct dm_cache_migration *mg = ws_to_mg(ws);
+	struct cache *cache = mg->cache;
+	struct policy_work *op = mg->op;
+	bool is_policy_promote = (op->op == POLICY_PROMOTE);
+
+	if ((!is_policy_promote && !is_dirty(cache, op->cblock)) ||
+	    is_discarded_oblock(cache, op->oblock)) {
+		mg_upgrade_lock(ws);
+		return;
+	}
+
+	init_continuation(&mg->k, mg_upgrade_lock);
+	copy(mg, is_policy_promote);
+}
+
+static void mg_copy(struct work_struct *ws)
+{
+	struct dm_cache_migration *mg = ws_to_mg(ws);
+
+	if (mg->overwrite_bio) {
+		/*
+		 * No exclusive lock was held when we last checked if the bio
+		 * was optimisable.  So we have to check again in case things
+		 * have changed (eg, the block may no longer be discarded).
+		 */
+		if (!optimisable_bio(mg->cache, mg->overwrite_bio, mg->op->oblock)) {
+			/*
+			 * Fallback to a real full copy after doing some tidying up.
+			 */
+			bool rb = bio_detain_shared(mg->cache, mg->op->oblock, mg->overwrite_bio);
+			BUG_ON(rb); /* An exclussive lock must _not_ be held for this block */
+			mg->overwrite_bio = NULL;
+			inc_io_migrations(mg->cache);
+			mg_full_copy(ws);
+			return;
+		}
+
+		/*
+		 * It's safe to do this here, even though it's new data
+		 * because all IO has been locked out of the block.
+		 *
+		 * mg_lock_writes() already took READ_WRITE_LOCK_LEVEL
+		 * so _not_ using mg_upgrade_lock() as continutation.
+		 */
+		overwrite(mg, mg_update_metadata_after_copy);
+
+	} else
+		mg_full_copy(ws);
+}
+
+static int mg_lock_writes(struct dm_cache_migration *mg)
+{
+	int r;
+	struct dm_cell_key_v2 key;
+	struct cache *cache = mg->cache;
+	struct dm_bio_prison_cell_v2 *prealloc;
+
+	prealloc = alloc_prison_cell(cache);
+
+	/*
+	 * Prevent writes to the block, but allow reads to continue.
+	 * Unless we're using an overwrite bio, in which case we lock
+	 * everything.
+	 */
+	build_key(mg->op->oblock, oblock_succ(mg->op->oblock), &key);
+	r = dm_cell_lock_v2(cache->prison, &key,
+			    mg->overwrite_bio ?  READ_WRITE_LOCK_LEVEL : WRITE_LOCK_LEVEL,
+			    prealloc, &mg->cell);
+	if (r < 0) {
+		free_prison_cell(cache, prealloc);
+		mg_complete(mg, false);
+		return r;
+	}
+
+	if (mg->cell != prealloc)
+		free_prison_cell(cache, prealloc);
+
+	if (r == 0)
+		mg_copy(&mg->k.ws);
+	else
+		quiesce(mg, mg_copy);
+
+	return 0;
+}
+
+static int mg_start(struct cache *cache, struct policy_work *op, struct bio *bio)
+{
+	struct dm_cache_migration *mg;
+
+	if (!background_work_begin(cache)) {
+		policy_complete_background_work(cache->policy, op, false);
+		return -EPERM;
+	}
+
+	mg = alloc_migration(cache);
+
+	mg->op = op;
+	mg->overwrite_bio = bio;
+
+	if (!bio)
+		inc_io_migrations(cache);
+
+	return mg_lock_writes(mg);
+}
+
+/*----------------------------------------------------------------
+ * invalidation processing
+ *--------------------------------------------------------------*/
+
+static void invalidate_complete(struct dm_cache_migration *mg, bool success)
+{
+	struct bio_list bios;
+	struct cache *cache = mg->cache;
+
+	bio_list_init(&bios);
+	if (dm_cell_unlock_v2(cache->prison, mg->cell, &bios))
+		free_prison_cell(cache, mg->cell);
+
+	if (!success && mg->overwrite_bio)
+		bio_io_error(mg->overwrite_bio);
+
+	free_migration(mg);
+	defer_bios(cache, &bios);
+
+	background_work_end(cache);
+}
+
+static void invalidate_completed(struct work_struct *ws)
+{
+	struct dm_cache_migration *mg = ws_to_mg(ws);
+	invalidate_complete(mg, !mg->k.input);
+}
+
+static int invalidate_cblock(struct cache *cache, dm_cblock_t cblock)
+{
+	int r = policy_invalidate_mapping(cache->policy, cblock);
+	if (!r) {
+		r = dm_cache_remove_mapping(cache->cmd, cblock);
+		if (r) {
+			DMERR_LIMIT("%s: invalidation failed; couldn't update on disk metadata",
+				    cache_device_name(cache));
+			metadata_operation_failed(cache, "dm_cache_remove_mapping", r);
+		}
+
+	} else if (r == -ENODATA) {
+		/*
+		 * Harmless, already unmapped.
+		 */
+		r = 0;
+
+	} else
+		DMERR("%s: policy_invalidate_mapping failed", cache_device_name(cache));
+
+	return r;
+}
+
+static void invalidate_remove(struct work_struct *ws)
+{
+	int r;
+	struct dm_cache_migration *mg = ws_to_mg(ws);
+	struct cache *cache = mg->cache;
+
+	r = invalidate_cblock(cache, mg->invalidate_cblock);
+	if (r) {
+		invalidate_complete(mg, false);
+		return;
+	}
+
+	init_continuation(&mg->k, invalidate_completed);
+	continue_after_commit(&cache->committer, &mg->k);
+	remap_to_origin_clear_discard(cache, mg->overwrite_bio, mg->invalidate_oblock);
+	mg->overwrite_bio = NULL;
+	schedule_commit(&cache->committer);
+}
+
+static int invalidate_lock(struct dm_cache_migration *mg)
+{
+	int r;
+	struct dm_cell_key_v2 key;
+	struct cache *cache = mg->cache;
+	struct dm_bio_prison_cell_v2 *prealloc;
+
+	prealloc = alloc_prison_cell(cache);
+
+	build_key(mg->invalidate_oblock, oblock_succ(mg->invalidate_oblock), &key);
+	r = dm_cell_lock_v2(cache->prison, &key,
+			    READ_WRITE_LOCK_LEVEL, prealloc, &mg->cell);
+	if (r < 0) {
+		free_prison_cell(cache, prealloc);
+		invalidate_complete(mg, false);
+		return r;
+	}
+
+	if (mg->cell != prealloc)
+		free_prison_cell(cache, prealloc);
+
+	if (r)
+		quiesce(mg, invalidate_remove);
+
+	else {
+		/*
+		 * We can't call invalidate_remove() directly here because we
+		 * might still be in request context.
+		 */
+		init_continuation(&mg->k, invalidate_remove);
+		queue_work(cache->wq, &mg->k.ws);
+	}
+
+	return 0;
+}
+
+static int invalidate_start(struct cache *cache, dm_cblock_t cblock,
+			    dm_oblock_t oblock, struct bio *bio)
+{
+	struct dm_cache_migration *mg;
+
+	if (!background_work_begin(cache))
+		return -EPERM;
+
+	mg = alloc_migration(cache);
+
+	mg->overwrite_bio = bio;
+	mg->invalidate_cblock = cblock;
+	mg->invalidate_oblock = oblock;
+
+	return invalidate_lock(mg);
+}
+
+/*----------------------------------------------------------------
+ * bio processing
+ *--------------------------------------------------------------*/
+
+enum busy {
+	IDLE,
+	BUSY
+};
+
+static enum busy spare_migration_bandwidth(struct cache *cache)
+{
+	bool idle = iot_idle_for(&cache->tracker, HZ);
+	sector_t current_volume = (atomic_read(&cache->nr_io_migrations) + 1) *
+		cache->sectors_per_block;
+
+	if (idle && current_volume <= cache->migration_threshold)
+		return IDLE;
+	else
+		return BUSY;
+}
+
+static void inc_hit_counter(struct cache *cache, struct bio *bio)
+{
+	atomic_inc(bio_data_dir(bio) == READ ?
+		   &cache->stats.read_hit : &cache->stats.write_hit);
+}
+
+static void inc_miss_counter(struct cache *cache, struct bio *bio)
+{
+	atomic_inc(bio_data_dir(bio) == READ ?
+		   &cache->stats.read_miss : &cache->stats.write_miss);
+}
+
+/*----------------------------------------------------------------*/
+
+static int map_bio(struct cache *cache, struct bio *bio, dm_oblock_t block,
+		   bool *commit_needed)
+{
+	int r, data_dir;
+	bool rb, background_queued;
+	dm_cblock_t cblock;
+
+	*commit_needed = false;
+
+	rb = bio_detain_shared(cache, block, bio);
+	if (!rb) {
+		/*
+		 * An exclusive lock is held for this block, so we have to
+		 * wait.  We set the commit_needed flag so the current
+		 * transaction will be committed asap, allowing this lock
+		 * to be dropped.
+		 */
+		*commit_needed = true;
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	data_dir = bio_data_dir(bio);
+
+	if (optimisable_bio(cache, bio, block)) {
+		struct policy_work *op = NULL;
+
+		r = policy_lookup_with_work(cache->policy, block, &cblock, data_dir, true, &op);
+		if (unlikely(r && r != -ENOENT)) {
+			DMERR_LIMIT("%s: policy_lookup_with_work() failed with r = %d",
+				    cache_device_name(cache), r);
+			bio_io_error(bio);
+			return DM_MAPIO_SUBMITTED;
+		}
+
+		if (r == -ENOENT && op) {
+			bio_drop_shared_lock(cache, bio);
+			BUG_ON(op->op != POLICY_PROMOTE);
+			mg_start(cache, op, bio);
+			return DM_MAPIO_SUBMITTED;
+		}
+	} else {
+		r = policy_lookup(cache->policy, block, &cblock, data_dir, false, &background_queued);
+		if (unlikely(r && r != -ENOENT)) {
+			DMERR_LIMIT("%s: policy_lookup() failed with r = %d",
+				    cache_device_name(cache), r);
+			bio_io_error(bio);
+			return DM_MAPIO_SUBMITTED;
+		}
+
+		if (background_queued)
+			wake_migration_worker(cache);
+	}
+
+	if (r == -ENOENT) {
+		struct per_bio_data *pb = get_per_bio_data(bio);
+
+		/*
+		 * Miss.
+		 */
+		inc_miss_counter(cache, bio);
+		if (pb->req_nr == 0) {
+			accounted_begin(cache, bio);
+			remap_to_origin_clear_discard(cache, bio, block);
+		} else {
+			/*
+			 * This is a duplicate writethrough io that is no
+			 * longer needed because the block has been demoted.
+			 */
+			bio_endio(bio);
+			return DM_MAPIO_SUBMITTED;
+		}
+	} else {
+		/*
+		 * Hit.
+		 */
+		inc_hit_counter(cache, bio);
+
+		/*
+		 * Passthrough always maps to the origin, invalidating any
+		 * cache blocks that are written to.
+		 */
+		if (passthrough_mode(cache)) {
+			if (bio_data_dir(bio) == WRITE) {
+				bio_drop_shared_lock(cache, bio);
+				atomic_inc(&cache->stats.demotion);
+				invalidate_start(cache, cblock, block, bio);
+			} else
+				remap_to_origin_clear_discard(cache, bio, block);
+		} else {
+			if (bio_data_dir(bio) == WRITE && writethrough_mode(cache) &&
+			    !is_dirty(cache, cblock)) {
+				remap_to_origin_and_cache(cache, bio, block, cblock);
+				accounted_begin(cache, bio);
+			} else
+				remap_to_cache_dirty(cache, bio, block, cblock);
+		}
+	}
+
+	/*
+	 * dm core turns FUA requests into a separate payload and FLUSH req.
+	 */
+	if (bio->bi_opf & REQ_FUA) {
+		/*
+		 * issue_after_commit will call accounted_begin a second time.  So
+		 * we call accounted_complete() to avoid double accounting.
+		 */
+		accounted_complete(cache, bio);
+		issue_after_commit(&cache->committer, bio);
+		*commit_needed = true;
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	return DM_MAPIO_REMAPPED;
+}
+
+static bool process_bio(struct cache *cache, struct bio *bio)
+{
+	bool commit_needed;
+
+	if (map_bio(cache, bio, get_bio_block(cache, bio), &commit_needed) == DM_MAPIO_REMAPPED)
+		submit_bio_noacct(bio);
+
+	return commit_needed;
+}
+
+/*
+ * A non-zero return indicates read_only or fail_io mode.
+ */
+static int commit(struct cache *cache, bool clean_shutdown)
+{
+	int r;
+
+	if (get_cache_mode(cache) >= CM_READ_ONLY)
+		return -EINVAL;
+
+	atomic_inc(&cache->stats.commit_count);
+	r = dm_cache_commit(cache->cmd, clean_shutdown);
+	if (r)
+		metadata_operation_failed(cache, "dm_cache_commit", r);
+
+	return r;
+}
+
+/*
+ * Used by the batcher.
+ */
+static blk_status_t commit_op(void *context)
+{
+	struct cache *cache = context;
+
+	if (dm_cache_changed_this_transaction(cache->cmd))
+		return errno_to_blk_status(commit(cache, false));
+
+	return 0;
+}
+
+/*----------------------------------------------------------------*/
+
+static bool process_flush_bio(struct cache *cache, struct bio *bio)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	if (!pb->req_nr)
+		remap_to_origin(cache, bio);
+	else
+		remap_to_cache(cache, bio, 0);
+
+	issue_after_commit(&cache->committer, bio);
+	return true;
+}
+
+static bool process_discard_bio(struct cache *cache, struct bio *bio)
+{
+	dm_dblock_t b, e;
+
+	// FIXME: do we need to lock the region?  Or can we just assume the
+	// user wont be so foolish as to issue discard concurrently with
+	// other IO?
+	calc_discard_block_range(cache, bio, &b, &e);
+	while (b != e) {
+		set_discard(cache, b);
+		b = to_dblock(from_dblock(b) + 1);
+	}
+
+	if (cache->features.discard_passdown) {
+		remap_to_origin(cache, bio);
+		submit_bio_noacct(bio);
+	} else
+		bio_endio(bio);
+
+	return false;
+}
+
+static void process_deferred_bios(struct work_struct *ws)
+{
+	struct cache *cache = container_of(ws, struct cache, deferred_bio_worker);
+
+	bool commit_needed = false;
+	struct bio_list bios;
+	struct bio *bio;
+
+	bio_list_init(&bios);
+
+	spin_lock_irq(&cache->lock);
+	bio_list_merge(&bios, &cache->deferred_bios);
+	bio_list_init(&cache->deferred_bios);
+	spin_unlock_irq(&cache->lock);
+
+	while ((bio = bio_list_pop(&bios))) {
+		if (bio->bi_opf & REQ_PREFLUSH)
+			commit_needed = process_flush_bio(cache, bio) || commit_needed;
+
+		else if (bio_op(bio) == REQ_OP_DISCARD)
+			commit_needed = process_discard_bio(cache, bio) || commit_needed;
+
+		else
+			commit_needed = process_bio(cache, bio) || commit_needed;
+		cond_resched();
+	}
+
+	if (commit_needed)
+		schedule_commit(&cache->committer);
+}
+
+/*----------------------------------------------------------------
+ * Main worker loop
+ *--------------------------------------------------------------*/
+
+static void requeue_deferred_bios(struct cache *cache)
+{
+	struct bio *bio;
+	struct bio_list bios;
+
+	bio_list_init(&bios);
+	bio_list_merge(&bios, &cache->deferred_bios);
+	bio_list_init(&cache->deferred_bios);
+
+	while ((bio = bio_list_pop(&bios))) {
+		bio->bi_status = BLK_STS_DM_REQUEUE;
+		bio_endio(bio);
+		cond_resched();
+	}
+}
+
+/*
+ * We want to commit periodically so that not too much
+ * unwritten metadata builds up.
+ */
+static void do_waker(struct work_struct *ws)
+{
+	struct cache *cache = container_of(to_delayed_work(ws), struct cache, waker);
+
+	policy_tick(cache->policy, true);
+	wake_migration_worker(cache);
+	schedule_commit(&cache->committer);
+	queue_delayed_work(cache->wq, &cache->waker, COMMIT_PERIOD);
+}
+
+static void check_migrations(struct work_struct *ws)
+{
+	int r;
+	struct policy_work *op;
+	struct cache *cache = container_of(ws, struct cache, migration_worker);
+	enum busy b;
+
+	for (;;) {
+		b = spare_migration_bandwidth(cache);
+
+		r = policy_get_background_work(cache->policy, b == IDLE, &op);
+		if (r == -ENODATA)
+			break;
+
+		if (r) {
+			DMERR_LIMIT("%s: policy_background_work failed",
+				    cache_device_name(cache));
+			break;
+		}
+
+		r = mg_start(cache, op, NULL);
+		if (r)
+			break;
+
+		cond_resched();
+	}
+}
+
+/*----------------------------------------------------------------
+ * Target methods
+ *--------------------------------------------------------------*/
+
+/*
+ * This function gets called on the error paths of the constructor, so we
+ * have to cope with a partially initialised struct.
+ */
+static void destroy(struct cache *cache)
+{
+	unsigned i;
+
+	mempool_exit(&cache->migration_pool);
+
+	if (cache->prison)
+		dm_bio_prison_destroy_v2(cache->prison);
+
+	cancel_delayed_work_sync(&cache->waker);
+	if (cache->wq)
+		destroy_workqueue(cache->wq);
+
+	if (cache->dirty_bitset)
+		free_bitset(cache->dirty_bitset);
+
+	if (cache->discard_bitset)
+		free_bitset(cache->discard_bitset);
+
+	if (cache->copier)
+		dm_kcopyd_client_destroy(cache->copier);
+
+	if (cache->cmd)
+		dm_cache_metadata_close(cache->cmd);
+
+	if (cache->metadata_dev)
+		dm_put_device(cache->ti, cache->metadata_dev);
+
+	if (cache->origin_dev)
+		dm_put_device(cache->ti, cache->origin_dev);
+
+	if (cache->cache_dev)
+		dm_put_device(cache->ti, cache->cache_dev);
+
+	if (cache->policy)
+		dm_cache_policy_destroy(cache->policy);
+
+	for (i = 0; i < cache->nr_ctr_args ; i++)
+		kfree(cache->ctr_args[i]);
+	kfree(cache->ctr_args);
+
+	bioset_exit(&cache->bs);
+
+	kfree(cache);
+}
+
+static void cache_dtr(struct dm_target *ti)
+{
+	struct cache *cache = ti->private;
+
+	destroy(cache);
+}
+
+static sector_t get_dev_size(struct dm_dev *dev)
+{
+	return i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Construct a cache device mapping.
+ *
+ * cache <metadata dev> <cache dev> <origin dev> <block size>
+ *       <#feature args> [<feature arg>]*
+ *       <policy> <#policy args> [<policy arg>]*
+ *
+ * metadata dev    : fast device holding the persistent metadata
+ * cache dev	   : fast device holding cached data blocks
+ * origin dev	   : slow device holding original data blocks
+ * block size	   : cache unit size in sectors
+ *
+ * #feature args   : number of feature arguments passed
+ * feature args    : writethrough.  (The default is writeback.)
+ *
+ * policy	   : the replacement policy to use
+ * #policy args    : an even number of policy arguments corresponding
+ *		     to key/value pairs passed to the policy
+ * policy args	   : key/value pairs passed to the policy
+ *		     E.g. 'sequential_threshold 1024'
+ *		     See cache-policies.txt for details.
+ *
+ * Optional feature arguments are:
+ *   writethrough  : write through caching that prohibits cache block
+ *		     content from being different from origin block content.
+ *		     Without this argument, the default behaviour is to write
+ *		     back cache block contents later for performance reasons,
+ *		     so they may differ from the corresponding origin blocks.
+ */
+struct cache_args {
+	struct dm_target *ti;
+
+	struct dm_dev *metadata_dev;
+
+	struct dm_dev *cache_dev;
+	sector_t cache_sectors;
+
+	struct dm_dev *origin_dev;
+	sector_t origin_sectors;
+
+	uint32_t block_size;
+
+	const char *policy_name;
+	int policy_argc;
+	const char **policy_argv;
+
+	struct cache_features features;
+};
+
+static void destroy_cache_args(struct cache_args *ca)
+{
+	if (ca->metadata_dev)
+		dm_put_device(ca->ti, ca->metadata_dev);
+
+	if (ca->cache_dev)
+		dm_put_device(ca->ti, ca->cache_dev);
+
+	if (ca->origin_dev)
+		dm_put_device(ca->ti, ca->origin_dev);
+
+	kfree(ca);
+}
+
+static bool at_least_one_arg(struct dm_arg_set *as, char **error)
+{
+	if (!as->argc) {
+		*error = "Insufficient args";
+		return false;
+	}
+
+	return true;
+}
+
+static int parse_metadata_dev(struct cache_args *ca, struct dm_arg_set *as,
+			      char **error)
+{
+	int r;
+	sector_t metadata_dev_size;
+	char b[BDEVNAME_SIZE];
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	r = dm_get_device(ca->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
+			  &ca->metadata_dev);
+	if (r) {
+		*error = "Error opening metadata device";
+		return r;
+	}
+
+	metadata_dev_size = get_dev_size(ca->metadata_dev);
+	if (metadata_dev_size > DM_CACHE_METADATA_MAX_SECTORS_WARNING)
+		DMWARN("Metadata device %s is larger than %u sectors: excess space will not be used.",
+		       bdevname(ca->metadata_dev->bdev, b), THIN_METADATA_MAX_SECTORS);
+
+	return 0;
+}
+
+static int parse_cache_dev(struct cache_args *ca, struct dm_arg_set *as,
+			   char **error)
+{
+	int r;
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	r = dm_get_device(ca->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
+			  &ca->cache_dev);
+	if (r) {
+		*error = "Error opening cache device";
+		return r;
+	}
+	ca->cache_sectors = get_dev_size(ca->cache_dev);
+
+	return 0;
+}
+
+static int parse_origin_dev(struct cache_args *ca, struct dm_arg_set *as,
+			    char **error)
+{
+	int r;
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	r = dm_get_device(ca->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
+			  &ca->origin_dev);
+	if (r) {
+		*error = "Error opening origin device";
+		return r;
+	}
+
+	ca->origin_sectors = get_dev_size(ca->origin_dev);
+	if (ca->ti->len > ca->origin_sectors) {
+		*error = "Device size larger than cached device";
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int parse_block_size(struct cache_args *ca, struct dm_arg_set *as,
+			    char **error)
+{
+	unsigned long block_size;
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	if (kstrtoul(dm_shift_arg(as), 10, &block_size) || !block_size ||
+	    block_size < DATA_DEV_BLOCK_SIZE_MIN_SECTORS ||
+	    block_size > DATA_DEV_BLOCK_SIZE_MAX_SECTORS ||
+	    block_size & (DATA_DEV_BLOCK_SIZE_MIN_SECTORS - 1)) {
+		*error = "Invalid data block size";
+		return -EINVAL;
+	}
+
+	if (block_size > ca->cache_sectors) {
+		*error = "Data block size is larger than the cache device";
+		return -EINVAL;
+	}
+
+	ca->block_size = block_size;
+
+	return 0;
+}
+
+static void init_features(struct cache_features *cf)
+{
+	cf->mode = CM_WRITE;
+	cf->io_mode = CM_IO_WRITEBACK;
+	cf->metadata_version = 1;
+	cf->discard_passdown = true;
+}
+
+static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
+			  char **error)
+{
+	static const struct dm_arg _args[] = {
+		{0, 3, "Invalid number of cache feature arguments"},
+	};
+
+	int r, mode_ctr = 0;
+	unsigned argc;
+	const char *arg;
+	struct cache_features *cf = &ca->features;
+
+	init_features(cf);
+
+	r = dm_read_arg_group(_args, as, &argc, error);
+	if (r)
+		return -EINVAL;
+
+	while (argc--) {
+		arg = dm_shift_arg(as);
+
+		if (!strcasecmp(arg, "writeback")) {
+			cf->io_mode = CM_IO_WRITEBACK;
+			mode_ctr++;
+		}
+
+		else if (!strcasecmp(arg, "writethrough")) {
+			cf->io_mode = CM_IO_WRITETHROUGH;
+			mode_ctr++;
+		}
+
+		else if (!strcasecmp(arg, "passthrough")) {
+			cf->io_mode = CM_IO_PASSTHROUGH;
+			mode_ctr++;
+		}
+
+		else if (!strcasecmp(arg, "metadata2"))
+			cf->metadata_version = 2;
+
+		else if (!strcasecmp(arg, "no_discard_passdown"))
+			cf->discard_passdown = false;
+
+		else {
+			*error = "Unrecognised cache feature requested";
+			return -EINVAL;
+		}
+	}
+
+	if (mode_ctr > 1) {
+		*error = "Duplicate cache io_mode features requested";
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int parse_policy(struct cache_args *ca, struct dm_arg_set *as,
+			char **error)
+{
+	static const struct dm_arg _args[] = {
+		{0, 1024, "Invalid number of policy arguments"},
+	};
+
+	int r;
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	ca->policy_name = dm_shift_arg(as);
+
+	r = dm_read_arg_group(_args, as, &ca->policy_argc, error);
+	if (r)
+		return -EINVAL;
+
+	ca->policy_argv = (const char **)as->argv;
+	dm_consume_args(as, ca->policy_argc);
+
+	return 0;
+}
+
+static int parse_cache_args(struct cache_args *ca, int argc, char **argv,
+			    char **error)
+{
+	int r;
+	struct dm_arg_set as;
+
+	as.argc = argc;
+	as.argv = argv;
+
+	r = parse_metadata_dev(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_cache_dev(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_origin_dev(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_block_size(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_features(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_policy(ca, &as, error);
+	if (r)
+		return r;
+
+	return 0;
+}
+
+/*----------------------------------------------------------------*/
+
+static struct kmem_cache *migration_cache;
+
+#define NOT_CORE_OPTION 1
+
+static int process_config_option(struct cache *cache, const char *key, const char *value)
+{
+	unsigned long tmp;
+
+	if (!strcasecmp(key, "migration_threshold")) {
+		if (kstrtoul(value, 10, &tmp))
+			return -EINVAL;
+
+		cache->migration_threshold = tmp;
+		return 0;
+	}
+
+	return NOT_CORE_OPTION;
+}
+
+static int set_config_value(struct cache *cache, const char *key, const char *value)
+{
+	int r = process_config_option(cache, key, value);
+
+	if (r == NOT_CORE_OPTION)
+		r = policy_set_config_value(cache->policy, key, value);
+
+	if (r)
+		DMWARN("bad config value for %s: %s", key, value);
+
+	return r;
+}
+
+static int set_config_values(struct cache *cache, int argc, const char **argv)
+{
+	int r = 0;
+
+	if (argc & 1) {
+		DMWARN("Odd number of policy arguments given but they should be <key> <value> pairs.");
+		return -EINVAL;
+	}
+
+	while (argc) {
+		r = set_config_value(cache, argv[0], argv[1]);
+		if (r)
+			break;
+
+		argc -= 2;
+		argv += 2;
+	}
+
+	return r;
+}
+
+static int create_cache_policy(struct cache *cache, struct cache_args *ca,
+			       char **error)
+{
+	struct dm_cache_policy *p = dm_cache_policy_create(ca->policy_name,
+							   cache->cache_size,
+							   cache->origin_sectors,
+							   cache->sectors_per_block);
+	if (IS_ERR(p)) {
+		*error = "Error creating cache's policy";
+		return PTR_ERR(p);
+	}
+	cache->policy = p;
+	BUG_ON(!cache->policy);
+
+	return 0;
+}
+
+/*
+ * We want the discard block size to be at least the size of the cache
+ * block size and have no more than 2^14 discard blocks across the origin.
+ */
+#define MAX_DISCARD_BLOCKS (1 << 14)
+
+static bool too_many_discard_blocks(sector_t discard_block_size,
+				    sector_t origin_size)
+{
+	(void) sector_div(origin_size, discard_block_size);
+
+	return origin_size > MAX_DISCARD_BLOCKS;
+}
+
+static sector_t calculate_discard_block_size(sector_t cache_block_size,
+					     sector_t origin_size)
+{
+	sector_t discard_block_size = cache_block_size;
+
+	if (origin_size)
+		while (too_many_discard_blocks(discard_block_size, origin_size))
+			discard_block_size *= 2;
+
+	return discard_block_size;
+}
+
+static void set_cache_size(struct cache *cache, dm_cblock_t size)
+{
+	dm_block_t nr_blocks = from_cblock(size);
+
+	if (nr_blocks > (1 << 20) && cache->cache_size != size)
+		DMWARN_LIMIT("You have created a cache device with a lot of individual cache blocks (%llu)\n"
+			     "All these mappings can consume a lot of kernel memory, and take some time to read/write.\n"
+			     "Please consider increasing the cache block size to reduce the overall cache block count.",
+			     (unsigned long long) nr_blocks);
+
+	cache->cache_size = size;
+}
+
+#define DEFAULT_MIGRATION_THRESHOLD 2048
+
+static int cache_create(struct cache_args *ca, struct cache **result)
+{
+	int r = 0;
+	char **error = &ca->ti->error;
+	struct cache *cache;
+	struct dm_target *ti = ca->ti;
+	dm_block_t origin_blocks;
+	struct dm_cache_metadata *cmd;
+	bool may_format = ca->features.mode == CM_WRITE;
+
+	cache = kzalloc(sizeof(*cache), GFP_KERNEL);
+	if (!cache)
+		return -ENOMEM;
+
+	cache->ti = ca->ti;
+	ti->private = cache;
+	ti->num_flush_bios = 2;
+	ti->flush_supported = true;
+
+	ti->num_discard_bios = 1;
+	ti->discards_supported = true;
+
+	ti->per_io_data_size = sizeof(struct per_bio_data);
+
+	cache->features = ca->features;
+	if (writethrough_mode(cache)) {
+		/* Create bioset for writethrough bios issued to origin */
+		r = bioset_init(&cache->bs, BIO_POOL_SIZE, 0, 0);
+		if (r)
+			goto bad;
+	}
+
+	cache->metadata_dev = ca->metadata_dev;
+	cache->origin_dev = ca->origin_dev;
+	cache->cache_dev = ca->cache_dev;
+
+	ca->metadata_dev = ca->origin_dev = ca->cache_dev = NULL;
+
+	origin_blocks = cache->origin_sectors = ca->origin_sectors;
+	origin_blocks = block_div(origin_blocks, ca->block_size);
+	cache->origin_blocks = to_oblock(origin_blocks);
+
+	cache->sectors_per_block = ca->block_size;
+	if (dm_set_target_max_io_len(ti, cache->sectors_per_block)) {
+		r = -EINVAL;
+		goto bad;
+	}
+
+	if (ca->block_size & (ca->block_size - 1)) {
+		dm_block_t cache_size = ca->cache_sectors;
+
+		cache->sectors_per_block_shift = -1;
+		cache_size = block_div(cache_size, ca->block_size);
+		set_cache_size(cache, to_cblock(cache_size));
+	} else {
+		cache->sectors_per_block_shift = __ffs(ca->block_size);
+		set_cache_size(cache, to_cblock(ca->cache_sectors >> cache->sectors_per_block_shift));
+	}
+
+	r = create_cache_policy(cache, ca, error);
+	if (r)
+		goto bad;
+
+	cache->policy_nr_args = ca->policy_argc;
+	cache->migration_threshold = DEFAULT_MIGRATION_THRESHOLD;
+
+	r = set_config_values(cache, ca->policy_argc, ca->policy_argv);
+	if (r) {
+		*error = "Error setting cache policy's config values";
+		goto bad;
+	}
+
+	cmd = dm_cache_metadata_open(cache->metadata_dev->bdev,
+				     ca->block_size, may_format,
+				     dm_cache_policy_get_hint_size(cache->policy),
+				     ca->features.metadata_version);
+	if (IS_ERR(cmd)) {
+		*error = "Error creating metadata object";
+		r = PTR_ERR(cmd);
+		goto bad;
+	}
+	cache->cmd = cmd;
+	set_cache_mode(cache, CM_WRITE);
+	if (get_cache_mode(cache) != CM_WRITE) {
+		*error = "Unable to get write access to metadata, please check/repair metadata.";
+		r = -EINVAL;
+		goto bad;
+	}
+
+	if (passthrough_mode(cache)) {
+		bool all_clean;
+
+		r = dm_cache_metadata_all_clean(cache->cmd, &all_clean);
+		if (r) {
+			*error = "dm_cache_metadata_all_clean() failed";
+			goto bad;
+		}
+
+		if (!all_clean) {
+			*error = "Cannot enter passthrough mode unless all blocks are clean";
+			r = -EINVAL;
+			goto bad;
+		}
+
+		policy_allow_migrations(cache->policy, false);
+	}
+
+	spin_lock_init(&cache->lock);
+	bio_list_init(&cache->deferred_bios);
+	atomic_set(&cache->nr_allocated_migrations, 0);
+	atomic_set(&cache->nr_io_migrations, 0);
+	init_waitqueue_head(&cache->migration_wait);
+
+	r = -ENOMEM;
+	atomic_set(&cache->nr_dirty, 0);
+	cache->dirty_bitset = alloc_bitset(from_cblock(cache->cache_size));
+	if (!cache->dirty_bitset) {
+		*error = "could not allocate dirty bitset";
+		goto bad;
+	}
+	clear_bitset(cache->dirty_bitset, from_cblock(cache->cache_size));
+
+	cache->discard_block_size =
+		calculate_discard_block_size(cache->sectors_per_block,
+					     cache->origin_sectors);
+	cache->discard_nr_blocks = to_dblock(dm_sector_div_up(cache->origin_sectors,
+							      cache->discard_block_size));
+	cache->discard_bitset = alloc_bitset(from_dblock(cache->discard_nr_blocks));
+	if (!cache->discard_bitset) {
+		*error = "could not allocate discard bitset";
+		goto bad;
+	}
+	clear_bitset(cache->discard_bitset, from_dblock(cache->discard_nr_blocks));
+
+	cache->copier = dm_kcopyd_client_create(&dm_kcopyd_throttle);
+	if (IS_ERR(cache->copier)) {
+		*error = "could not create kcopyd client";
+		r = PTR_ERR(cache->copier);
+		goto bad;
+	}
+
+	cache->wq = alloc_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM, 0);
+	if (!cache->wq) {
+		*error = "could not create workqueue for metadata object";
+		goto bad;
+	}
+	INIT_WORK(&cache->deferred_bio_worker, process_deferred_bios);
+	INIT_WORK(&cache->migration_worker, check_migrations);
+	INIT_DELAYED_WORK(&cache->waker, do_waker);
+
+	cache->prison = dm_bio_prison_create_v2(cache->wq);
+	if (!cache->prison) {
+		*error = "could not create bio prison";
+		goto bad;
+	}
+
+	r = mempool_init_slab_pool(&cache->migration_pool, MIGRATION_POOL_SIZE,
+				   migration_cache);
+	if (r) {
+		*error = "Error creating cache's migration mempool";
+		goto bad;
+	}
+
+	cache->need_tick_bio = true;
+	cache->sized = false;
+	cache->invalidate = false;
+	cache->commit_requested = false;
+	cache->loaded_mappings = false;
+	cache->loaded_discards = false;
+
+	load_stats(cache);
+
+	atomic_set(&cache->stats.demotion, 0);
+	atomic_set(&cache->stats.promotion, 0);
+	atomic_set(&cache->stats.copies_avoided, 0);
+	atomic_set(&cache->stats.cache_cell_clash, 0);
+	atomic_set(&cache->stats.commit_count, 0);
+	atomic_set(&cache->stats.discard_count, 0);
+
+	spin_lock_init(&cache->invalidation_lock);
+	INIT_LIST_HEAD(&cache->invalidation_requests);
+
+	batcher_init(&cache->committer, commit_op, cache,
+		     issue_op, cache, cache->wq);
+	iot_init(&cache->tracker);
+
+	init_rwsem(&cache->background_work_lock);
+	prevent_background_work(cache);
+
+	*result = cache;
+	return 0;
+bad:
+	destroy(cache);
+	return r;
+}
+
+static int copy_ctr_args(struct cache *cache, int argc, const char **argv)
+{
+	unsigned i;
+	const char **copy;
+
+	copy = kcalloc(argc, sizeof(*copy), GFP_KERNEL);
+	if (!copy)
+		return -ENOMEM;
+	for (i = 0; i < argc; i++) {
+		copy[i] = kstrdup(argv[i], GFP_KERNEL);
+		if (!copy[i]) {
+			while (i--)
+				kfree(copy[i]);
+			kfree(copy);
+			return -ENOMEM;
+		}
+	}
+
+	cache->nr_ctr_args = argc;
+	cache->ctr_args = copy;
+
+	return 0;
+}
+
+static int cache_ctr(struct dm_target *ti, unsigned argc, char **argv)
+{
+	int r = -EINVAL;
+	struct cache_args *ca;
+	struct cache *cache = NULL;
+
+	ca = kzalloc(sizeof(*ca), GFP_KERNEL);
+	if (!ca) {
+		ti->error = "Error allocating memory for cache";
+		return -ENOMEM;
+	}
+	ca->ti = ti;
+
+	r = parse_cache_args(ca, argc, argv, &ti->error);
+	if (r)
+		goto out;
+
+	r = cache_create(ca, &cache);
+	if (r)
+		goto out;
+
+	r = copy_ctr_args(cache, argc - 3, (const char **)argv + 3);
+	if (r) {
+		destroy(cache);
+		goto out;
+	}
+
+	ti->private = cache;
+out:
+	destroy_cache_args(ca);
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+static int cache_map(struct dm_target *ti, struct bio *bio)
+{
+	struct cache *cache = ti->private;
+
+	int r;
+	bool commit_needed;
+	dm_oblock_t block = get_bio_block(cache, bio);
+
+	init_per_bio_data(bio);
+	if (unlikely(from_oblock(block) >= from_oblock(cache->origin_blocks))) {
+		/*
+		 * This can only occur if the io goes to a partial block at
+		 * the end of the origin device.  We don't cache these.
+		 * Just remap to the origin and carry on.
+		 */
+		remap_to_origin(cache, bio);
+		accounted_begin(cache, bio);
+		return DM_MAPIO_REMAPPED;
+	}
+
+	if (discard_or_flush(bio)) {
+		defer_bio(cache, bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	r = map_bio(cache, bio, block, &commit_needed);
+	if (commit_needed)
+		schedule_commit(&cache->committer);
+
+	return r;
+}
+
+static int cache_end_io(struct dm_target *ti, struct bio *bio, blk_status_t *error)
+{
+	struct cache *cache = ti->private;
+	unsigned long flags;
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	if (pb->tick) {
+		policy_tick(cache->policy, false);
+
+		spin_lock_irqsave(&cache->lock, flags);
+		cache->need_tick_bio = true;
+		spin_unlock_irqrestore(&cache->lock, flags);
+	}
+
+	bio_drop_shared_lock(cache, bio);
+	accounted_complete(cache, bio);
+
+	return DM_ENDIO_DONE;
+}
+
+static int write_dirty_bitset(struct cache *cache)
+{
+	int r;
+
+	if (get_cache_mode(cache) >= CM_READ_ONLY)
+		return -EINVAL;
+
+	r = dm_cache_set_dirty_bits(cache->cmd, from_cblock(cache->cache_size), cache->dirty_bitset);
+	if (r)
+		metadata_operation_failed(cache, "dm_cache_set_dirty_bits", r);
+
+	return r;
+}
+
+static int write_discard_bitset(struct cache *cache)
+{
+	unsigned i, r;
+
+	if (get_cache_mode(cache) >= CM_READ_ONLY)
+		return -EINVAL;
+
+	r = dm_cache_discard_bitset_resize(cache->cmd, cache->discard_block_size,
+					   cache->discard_nr_blocks);
+	if (r) {
+		DMERR("%s: could not resize on-disk discard bitset", cache_device_name(cache));
+		metadata_operation_failed(cache, "dm_cache_discard_bitset_resize", r);
+		return r;
+	}
+
+	for (i = 0; i < from_dblock(cache->discard_nr_blocks); i++) {
+		r = dm_cache_set_discard(cache->cmd, to_dblock(i),
+					 is_discarded(cache, to_dblock(i)));
+		if (r) {
+			metadata_operation_failed(cache, "dm_cache_set_discard", r);
+			return r;
+		}
+	}
+
+	return 0;
+}
+
+static int write_hints(struct cache *cache)
+{
+	int r;
+
+	if (get_cache_mode(cache) >= CM_READ_ONLY)
+		return -EINVAL;
+
+	r = dm_cache_write_hints(cache->cmd, cache->policy);
+	if (r) {
+		metadata_operation_failed(cache, "dm_cache_write_hints", r);
+		return r;
+	}
+
+	return 0;
+}
+
+/*
+ * returns true on success
+ */
+static bool sync_metadata(struct cache *cache)
+{
+	int r1, r2, r3, r4;
+
+	r1 = write_dirty_bitset(cache);
+	if (r1)
+		DMERR("%s: could not write dirty bitset", cache_device_name(cache));
+
+	r2 = write_discard_bitset(cache);
+	if (r2)
+		DMERR("%s: could not write discard bitset", cache_device_name(cache));
+
+	save_stats(cache);
+
+	r3 = write_hints(cache);
+	if (r3)
+		DMERR("%s: could not write hints", cache_device_name(cache));
+
+	/*
+	 * If writing the above metadata failed, we still commit, but don't
+	 * set the clean shutdown flag.  This will effectively force every
+	 * dirty bit to be set on reload.
+	 */
+	r4 = commit(cache, !r1 && !r2 && !r3);
+	if (r4)
+		DMERR("%s: could not write cache metadata", cache_device_name(cache));
+
+	return !r1 && !r2 && !r3 && !r4;
+}
+
+static void cache_postsuspend(struct dm_target *ti)
+{
+	struct cache *cache = ti->private;
+
+	prevent_background_work(cache);
+	BUG_ON(atomic_read(&cache->nr_io_migrations));
+
+	cancel_delayed_work_sync(&cache->waker);
+	drain_workqueue(cache->wq);
+	WARN_ON(cache->tracker.in_flight);
+
+	/*
+	 * If it's a flush suspend there won't be any deferred bios, so this
+	 * call is harmless.
+	 */
+	requeue_deferred_bios(cache);
+
+	if (get_cache_mode(cache) == CM_WRITE)
+		(void) sync_metadata(cache);
+}
+
+static int load_mapping(void *context, dm_oblock_t oblock, dm_cblock_t cblock,
+			bool dirty, uint32_t hint, bool hint_valid)
+{
+	int r;
+	struct cache *cache = context;
+
+	if (dirty) {
+		set_bit(from_cblock(cblock), cache->dirty_bitset);
+		atomic_inc(&cache->nr_dirty);
+	} else
+		clear_bit(from_cblock(cblock), cache->dirty_bitset);
+
+	r = policy_load_mapping(cache->policy, oblock, cblock, dirty, hint, hint_valid);
+	if (r)
+		return r;
+
+	return 0;
+}
+
+/*
+ * The discard block size in the on disk metadata is not
+ * neccessarily the same as we're currently using.  So we have to
+ * be careful to only set the discarded attribute if we know it
+ * covers a complete block of the new size.
+ */
+struct discard_load_info {
+	struct cache *cache;
+
+	/*
+	 * These blocks are sized using the on disk dblock size, rather
+	 * than the current one.
+	 */
+	dm_block_t block_size;
+	dm_block_t discard_begin, discard_end;
+};
+
+static void discard_load_info_init(struct cache *cache,
+				   struct discard_load_info *li)
+{
+	li->cache = cache;
+	li->discard_begin = li->discard_end = 0;
+}
+
+static void set_discard_range(struct discard_load_info *li)
+{
+	sector_t b, e;
+
+	if (li->discard_begin == li->discard_end)
+		return;
+
+	/*
+	 * Convert to sectors.
+	 */
+	b = li->discard_begin * li->block_size;
+	e = li->discard_end * li->block_size;
+
+	/*
+	 * Then convert back to the current dblock size.
+	 */
+	b = dm_sector_div_up(b, li->cache->discard_block_size);
+	sector_div(e, li->cache->discard_block_size);
+
+	/*
+	 * The origin may have shrunk, so we need to check we're still in
+	 * bounds.
+	 */
+	if (e > from_dblock(li->cache->discard_nr_blocks))
+		e = from_dblock(li->cache->discard_nr_blocks);
+
+	for (; b < e; b++)
+		set_discard(li->cache, to_dblock(b));
+}
+
+static int load_discard(void *context, sector_t discard_block_size,
+			dm_dblock_t dblock, bool discard)
+{
+	struct discard_load_info *li = context;
+
+	li->block_size = discard_block_size;
+
+	if (discard) {
+		if (from_dblock(dblock) == li->discard_end)
+			/*
+			 * We're already in a discard range, just extend it.
+			 */
+			li->discard_end = li->discard_end + 1ULL;
+
+		else {
+			/*
+			 * Emit the old range and start a new one.
+			 */
+			set_discard_range(li);
+			li->discard_begin = from_dblock(dblock);
+			li->discard_end = li->discard_begin + 1ULL;
+		}
+	} else {
+		set_discard_range(li);
+		li->discard_begin = li->discard_end = 0;
+	}
+
+	return 0;
+}
+
+static dm_cblock_t get_cache_dev_size(struct cache *cache)
+{
+	sector_t size = get_dev_size(cache->cache_dev);
+	(void) sector_div(size, cache->sectors_per_block);
+	return to_cblock(size);
+}
+
+static bool can_resize(struct cache *cache, dm_cblock_t new_size)
+{
+	if (from_cblock(new_size) > from_cblock(cache->cache_size)) {
+		if (cache->sized) {
+			DMERR("%s: unable to extend cache due to missing cache table reload",
+			      cache_device_name(cache));
+			return false;
+		}
+	}
+
+	/*
+	 * We can't drop a dirty block when shrinking the cache.
+	 */
+	while (from_cblock(new_size) < from_cblock(cache->cache_size)) {
+		new_size = to_cblock(from_cblock(new_size) + 1);
+		if (is_dirty(cache, new_size)) {
+			DMERR("%s: unable to shrink cache; cache block %llu is dirty",
+			      cache_device_name(cache),
+			      (unsigned long long) from_cblock(new_size));
+			return false;
+		}
+	}
+
+	return true;
+}
+
+static int resize_cache_dev(struct cache *cache, dm_cblock_t new_size)
+{
+	int r;
+
+	r = dm_cache_resize(cache->cmd, new_size);
+	if (r) {
+		DMERR("%s: could not resize cache metadata", cache_device_name(cache));
+		metadata_operation_failed(cache, "dm_cache_resize", r);
+		return r;
+	}
+
+	set_cache_size(cache, new_size);
+
+	return 0;
+}
+
+static int cache_preresume(struct dm_target *ti)
+{
+	int r = 0;
+	struct cache *cache = ti->private;
+	dm_cblock_t csize = get_cache_dev_size(cache);
+
+	/*
+	 * Check to see if the cache has resized.
+	 */
+	if (!cache->sized) {
+		r = resize_cache_dev(cache, csize);
+		if (r)
+			return r;
+
+		cache->sized = true;
+
+	} else if (csize != cache->cache_size) {
+		if (!can_resize(cache, csize))
+			return -EINVAL;
+
+		r = resize_cache_dev(cache, csize);
+		if (r)
+			return r;
+	}
+
+	if (!cache->loaded_mappings) {
+		r = dm_cache_load_mappings(cache->cmd, cache->policy,
+					   load_mapping, cache);
+		if (r) {
+			DMERR("%s: could not load cache mappings", cache_device_name(cache));
+			metadata_operation_failed(cache, "dm_cache_load_mappings", r);
+			return r;
+		}
+
+		cache->loaded_mappings = true;
+	}
+
+	if (!cache->loaded_discards) {
+		struct discard_load_info li;
+
+		/*
+		 * The discard bitset could have been resized, or the
+		 * discard block size changed.  To be safe we start by
+		 * setting every dblock to not discarded.
+		 */
+		clear_bitset(cache->discard_bitset, from_dblock(cache->discard_nr_blocks));
+
+		discard_load_info_init(cache, &li);
+		r = dm_cache_load_discards(cache->cmd, load_discard, &li);
+		if (r) {
+			DMERR("%s: could not load origin discards", cache_device_name(cache));
+			metadata_operation_failed(cache, "dm_cache_load_discards", r);
+			return r;
+		}
+		set_discard_range(&li);
+
+		cache->loaded_discards = true;
+	}
+
+	return r;
+}
+
+static void cache_resume(struct dm_target *ti)
+{
+	struct cache *cache = ti->private;
+
+	cache->need_tick_bio = true;
+	allow_background_work(cache);
+	do_waker(&cache->waker.work);
+}
+
+static void emit_flags(struct cache *cache, char *result,
+		       unsigned maxlen, ssize_t *sz_ptr)
+{
+	ssize_t sz = *sz_ptr;
+	struct cache_features *cf = &cache->features;
+	unsigned count = (cf->metadata_version == 2) + !cf->discard_passdown + 1;
+
+	DMEMIT("%u ", count);
+
+	if (cf->metadata_version == 2)
+		DMEMIT("metadata2 ");
+
+	if (writethrough_mode(cache))
+		DMEMIT("writethrough ");
+
+	else if (passthrough_mode(cache))
+		DMEMIT("passthrough ");
+
+	else if (writeback_mode(cache))
+		DMEMIT("writeback ");
+
+	else {
+		DMEMIT("unknown ");
+		DMERR("%s: internal error: unknown io mode: %d",
+		      cache_device_name(cache), (int) cf->io_mode);
+	}
+
+	if (!cf->discard_passdown)
+		DMEMIT("no_discard_passdown ");
+
+	*sz_ptr = sz;
+}
+
+/*
+ * Status format:
+ *
+ * <metadata block size> <#used metadata blocks>/<#total metadata blocks>
+ * <cache block size> <#used cache blocks>/<#total cache blocks>
+ * <#read hits> <#read misses> <#write hits> <#write misses>
+ * <#demotions> <#promotions> <#dirty>
+ * <#features> <features>*
+ * <#core args> <core args>
+ * <policy name> <#policy args> <policy args>* <cache metadata mode> <needs_check>
+ */
+static void cache_status(struct dm_target *ti, status_type_t type,
+			 unsigned status_flags, char *result, unsigned maxlen)
+{
+	int r = 0;
+	unsigned i;
+	ssize_t sz = 0;
+	dm_block_t nr_free_blocks_metadata = 0;
+	dm_block_t nr_blocks_metadata = 0;
+	char buf[BDEVNAME_SIZE];
+	struct cache *cache = ti->private;
+	dm_cblock_t residency;
+	bool needs_check;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		if (get_cache_mode(cache) == CM_FAIL) {
+			DMEMIT("Fail");
+			break;
+		}
+
+		/* Commit to ensure statistics aren't out-of-date */
+		if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti))
+			(void) commit(cache, false);
+
+		r = dm_cache_get_free_metadata_block_count(cache->cmd, &nr_free_blocks_metadata);
+		if (r) {
+			DMERR("%s: dm_cache_get_free_metadata_block_count returned %d",
+			      cache_device_name(cache), r);
+			goto err;
+		}
+
+		r = dm_cache_get_metadata_dev_size(cache->cmd, &nr_blocks_metadata);
+		if (r) {
+			DMERR("%s: dm_cache_get_metadata_dev_size returned %d",
+			      cache_device_name(cache), r);
+			goto err;
+		}
+
+		residency = policy_residency(cache->policy);
+
+		DMEMIT("%u %llu/%llu %llu %llu/%llu %u %u %u %u %u %u %lu ",
+		       (unsigned)DM_CACHE_METADATA_BLOCK_SIZE,
+		       (unsigned long long)(nr_blocks_metadata - nr_free_blocks_metadata),
+		       (unsigned long long)nr_blocks_metadata,
+		       (unsigned long long)cache->sectors_per_block,
+		       (unsigned long long) from_cblock(residency),
+		       (unsigned long long) from_cblock(cache->cache_size),
+		       (unsigned) atomic_read(&cache->stats.read_hit),
+		       (unsigned) atomic_read(&cache->stats.read_miss),
+		       (unsigned) atomic_read(&cache->stats.write_hit),
+		       (unsigned) atomic_read(&cache->stats.write_miss),
+		       (unsigned) atomic_read(&cache->stats.demotion),
+		       (unsigned) atomic_read(&cache->stats.promotion),
+		       (unsigned long) atomic_read(&cache->nr_dirty));
+
+		emit_flags(cache, result, maxlen, &sz);
+
+		DMEMIT("2 migration_threshold %llu ", (unsigned long long) cache->migration_threshold);
+
+		DMEMIT("%s ", dm_cache_policy_get_name(cache->policy));
+		if (sz < maxlen) {
+			r = policy_emit_config_values(cache->policy, result, maxlen, &sz);
+			if (r)
+				DMERR("%s: policy_emit_config_values returned %d",
+				      cache_device_name(cache), r);
+		}
+
+		if (get_cache_mode(cache) == CM_READ_ONLY)
+			DMEMIT("ro ");
+		else
+			DMEMIT("rw ");
+
+		r = dm_cache_metadata_needs_check(cache->cmd, &needs_check);
+
+		if (r || needs_check)
+			DMEMIT("needs_check ");
+		else
+			DMEMIT("- ");
+
+		break;
+
+	case STATUSTYPE_TABLE:
+		format_dev_t(buf, cache->metadata_dev->bdev->bd_dev);
+		DMEMIT("%s ", buf);
+		format_dev_t(buf, cache->cache_dev->bdev->bd_dev);
+		DMEMIT("%s ", buf);
+		format_dev_t(buf, cache->origin_dev->bdev->bd_dev);
+		DMEMIT("%s", buf);
+
+		for (i = 0; i < cache->nr_ctr_args - 1; i++)
+			DMEMIT(" %s", cache->ctr_args[i]);
+		if (cache->nr_ctr_args)
+			DMEMIT(" %s", cache->ctr_args[cache->nr_ctr_args - 1]);
+	}
+
+	return;
+
+err:
+	DMEMIT("Error");
+}
+
+/*
+ * Defines a range of cblocks, begin to (end - 1) are in the range.  end is
+ * the one-past-the-end value.
+ */
+struct cblock_range {
+	dm_cblock_t begin;
+	dm_cblock_t end;
+};
+
+/*
+ * A cache block range can take two forms:
+ *
+ * i) A single cblock, eg. '3456'
+ * ii) A begin and end cblock with a dash between, eg. 123-234
+ */
+static int parse_cblock_range(struct cache *cache, const char *str,
+			      struct cblock_range *result)
+{
+	char dummy;
+	uint64_t b, e;
+	int r;
+
+	/*
+	 * Try and parse form (ii) first.
+	 */
+	r = sscanf(str, "%llu-%llu%c", &b, &e, &dummy);
+	if (r < 0)
+		return r;
+
+	if (r == 2) {
+		result->begin = to_cblock(b);
+		result->end = to_cblock(e);
+		return 0;
+	}
+
+	/*
+	 * That didn't work, try form (i).
+	 */
+	r = sscanf(str, "%llu%c", &b, &dummy);
+	if (r < 0)
+		return r;
+
+	if (r == 1) {
+		result->begin = to_cblock(b);
+		result->end = to_cblock(from_cblock(result->begin) + 1u);
+		return 0;
+	}
+
+	DMERR("%s: invalid cblock range '%s'", cache_device_name(cache), str);
+	return -EINVAL;
+}
+
+static int validate_cblock_range(struct cache *cache, struct cblock_range *range)
+{
+	uint64_t b = from_cblock(range->begin);
+	uint64_t e = from_cblock(range->end);
+	uint64_t n = from_cblock(cache->cache_size);
+
+	if (b >= n) {
+		DMERR("%s: begin cblock out of range: %llu >= %llu",
+		      cache_device_name(cache), b, n);
+		return -EINVAL;
+	}
+
+	if (e > n) {
+		DMERR("%s: end cblock out of range: %llu > %llu",
+		      cache_device_name(cache), e, n);
+		return -EINVAL;
+	}
+
+	if (b >= e) {
+		DMERR("%s: invalid cblock range: %llu >= %llu",
+		      cache_device_name(cache), b, e);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static inline dm_cblock_t cblock_succ(dm_cblock_t b)
+{
+	return to_cblock(from_cblock(b) + 1);
+}
+
+static int request_invalidation(struct cache *cache, struct cblock_range *range)
+{
+	int r = 0;
+
+	/*
+	 * We don't need to do any locking here because we know we're in
+	 * passthrough mode.  There's is potential for a race between an
+	 * invalidation triggered by an io and an invalidation message.  This
+	 * is harmless, we must not worry if the policy call fails.
+	 */
+	while (range->begin != range->end) {
+		r = invalidate_cblock(cache, range->begin);
+		if (r)
+			return r;
+
+		range->begin = cblock_succ(range->begin);
+	}
+
+	cache->commit_requested = true;
+	return r;
+}
+
+static int process_invalidate_cblocks_message(struct cache *cache, unsigned count,
+					      const char **cblock_ranges)
+{
+	int r = 0;
+	unsigned i;
+	struct cblock_range range;
+
+	if (!passthrough_mode(cache)) {
+		DMERR("%s: cache has to be in passthrough mode for invalidation",
+		      cache_device_name(cache));
+		return -EPERM;
+	}
+
+	for (i = 0; i < count; i++) {
+		r = parse_cblock_range(cache, cblock_ranges[i], &range);
+		if (r)
+			break;
+
+		r = validate_cblock_range(cache, &range);
+		if (r)
+			break;
+
+		/*
+		 * Pass begin and end origin blocks to the worker and wake it.
+		 */
+		r = request_invalidation(cache, &range);
+		if (r)
+			break;
+	}
+
+	return r;
+}
+
+/*
+ * Supports
+ *	"<key> <value>"
+ * and
+ *     "invalidate_cblocks [(<begin>)|(<begin>-<end>)]*
+ *
+ * The key migration_threshold is supported by the cache target core.
+ */
+static int cache_message(struct dm_target *ti, unsigned argc, char **argv,
+			 char *result, unsigned maxlen)
+{
+	struct cache *cache = ti->private;
+
+	if (!argc)
+		return -EINVAL;
+
+	if (get_cache_mode(cache) >= CM_READ_ONLY) {
+		DMERR("%s: unable to service cache target messages in READ_ONLY or FAIL mode",
+		      cache_device_name(cache));
+		return -EOPNOTSUPP;
+	}
+
+	if (!strcasecmp(argv[0], "invalidate_cblocks"))
+		return process_invalidate_cblocks_message(cache, argc - 1, (const char **) argv + 1);
+
+	if (argc != 2)
+		return -EINVAL;
+
+	return set_config_value(cache, argv[0], argv[1]);
+}
+
+static int cache_iterate_devices(struct dm_target *ti,
+				 iterate_devices_callout_fn fn, void *data)
+{
+	int r = 0;
+	struct cache *cache = ti->private;
+
+	r = fn(ti, cache->cache_dev, 0, get_dev_size(cache->cache_dev), data);
+	if (!r)
+		r = fn(ti, cache->origin_dev, 0, ti->len, data);
+
+	return r;
+}
+
+static bool origin_dev_supports_discard(struct block_device *origin_bdev)
+{
+	struct request_queue *q = bdev_get_queue(origin_bdev);
+
+	return q && blk_queue_discard(q);
+}
+
+/*
+ * If discard_passdown was enabled verify that the origin device
+ * supports discards.  Disable discard_passdown if not.
+ */
+static void disable_passdown_if_not_supported(struct cache *cache)
+{
+	struct block_device *origin_bdev = cache->origin_dev->bdev;
+	struct queue_limits *origin_limits = &bdev_get_queue(origin_bdev)->limits;
+	const char *reason = NULL;
+	char buf[BDEVNAME_SIZE];
+
+	if (!cache->features.discard_passdown)
+		return;
+
+	if (!origin_dev_supports_discard(origin_bdev))
+		reason = "discard unsupported";
+
+	else if (origin_limits->max_discard_sectors < cache->sectors_per_block)
+		reason = "max discard sectors smaller than a block";
+
+	if (reason) {
+		DMWARN("Origin device (%s) %s: Disabling discard passdown.",
+		       bdevname(origin_bdev, buf), reason);
+		cache->features.discard_passdown = false;
+	}
+}
+
+static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
+{
+	struct block_device *origin_bdev = cache->origin_dev->bdev;
+	struct queue_limits *origin_limits = &bdev_get_queue(origin_bdev)->limits;
+
+	if (!cache->features.discard_passdown) {
+		/* No passdown is done so setting own virtual limits */
+		limits->max_discard_sectors = min_t(sector_t, cache->discard_block_size * 1024,
+						    cache->origin_sectors);
+		limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
+		return;
+	}
+
+	/*
+	 * cache_iterate_devices() is stacking both origin and fast device limits
+	 * but discards aren't passed to fast device, so inherit origin's limits.
+	 */
+	limits->max_discard_sectors = origin_limits->max_discard_sectors;
+	limits->max_hw_discard_sectors = origin_limits->max_hw_discard_sectors;
+	limits->discard_granularity = origin_limits->discard_granularity;
+	limits->discard_alignment = origin_limits->discard_alignment;
+	limits->discard_misaligned = origin_limits->discard_misaligned;
+}
+
+static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+	struct cache *cache = ti->private;
+	uint64_t io_opt_sectors = limits->io_opt >> SECTOR_SHIFT;
+
+	/*
+	 * If the system-determined stacked limits are compatible with the
+	 * cache's blocksize (io_opt is a factor) do not override them.
+	 */
+	if (io_opt_sectors < cache->sectors_per_block ||
+	    do_div(io_opt_sectors, cache->sectors_per_block)) {
+		blk_limits_io_min(limits, cache->sectors_per_block << SECTOR_SHIFT);
+		blk_limits_io_opt(limits, cache->sectors_per_block << SECTOR_SHIFT);
+	}
+
+	disable_passdown_if_not_supported(cache);
+	set_discard_limits(cache, limits);
+}
+
+/*----------------------------------------------------------------*/
+
+static struct target_type cache_target = {
+	.name = "cache",
+	.version = {2, 2, 0},
+	.module = THIS_MODULE,
+	.ctr = cache_ctr,
+	.dtr = cache_dtr,
+	.map = cache_map,
+	.end_io = cache_end_io,
+	.postsuspend = cache_postsuspend,
+	.preresume = cache_preresume,
+	.resume = cache_resume,
+	.status = cache_status,
+	.message = cache_message,
+	.iterate_devices = cache_iterate_devices,
+	.io_hints = cache_io_hints,
+};
+
+static int __init dm_cache_init(void)
+{
+	int r;
+
+	migration_cache = KMEM_CACHE(dm_cache_migration, 0);
+	if (!migration_cache)
+		return -ENOMEM;
+
+	r = dm_register_target(&cache_target);
+	if (r) {
+		DMERR("cache target registration failed: %d", r);
+		kmem_cache_destroy(migration_cache);
+		return r;
+	}
+
+	return 0;
+}
+
+static void __exit dm_cache_exit(void)
+{
+	dm_unregister_target(&cache_target);
+	kmem_cache_destroy(migration_cache);
+}
+
+module_init(dm_cache_init);
+module_exit(dm_cache_exit);
+
+MODULE_DESCRIPTION(DM_NAME " cache target");
+MODULE_AUTHOR("Joe Thornber <ejt@redhat.com>");
+MODULE_LICENSE("GPL");