Initial import

1 files changed, 3407 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..e049becaa
--- /dev/null
+++ b/drivers/md/dm-cache-target.c
@@ -0,0 +1,3407 @@
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+#include "dm-bio-prison.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/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
+ */
+
+/*----------------------------------------------------------------*/
+
+static size_t bitset_size_in_bytes(unsigned nr_entries)
+{
+	return sizeof(unsigned long) * dm_div_up(nr_entries, BITS_PER_LONG);
+}
+
+static unsigned long *alloc_bitset(unsigned nr_entries)
+{
+	size_t s = bitset_size_in_bytes(nr_entries);
+	return vzalloc(s);
+}
+
+static void clear_bitset(void *bitset, unsigned nr_entries)
+{
+	size_t s = bitset_size_in_bytes(nr_entries);
+	memset(bitset, 0, s);
+}
+
+static void free_bitset(unsigned long *bits)
+{
+	vfree(bits);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * 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;
+	void *bi_private;
+};
+
+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;
+	h->bi_private = bio->bi_private;
+
+	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;
+	bio->bi_private = h->bi_private;
+
+	/*
+	 * Must bump bi_remaining to allow bio to complete with
+	 * restored bi_end_io.
+	 */
+	atomic_inc(&bio->bi_remaining);
+}
+
+/*----------------------------------------------------------------*/
+
+#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)
+
+/*
+ * FIXME: the cache is read/write for the time being.
+ */
+enum cache_metadata_mode {
+	CM_WRITE,		/* metadata may be changed */
+	CM_READ_ONLY,		/* metadata may not be changed */
+};
+
+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;
+};
+
+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 copies_avoided;
+	atomic_t cache_cell_clash;
+	atomic_t commit_count;
+	atomic_t discard_count;
+};
+
+/*
+ * 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;
+};
+
+struct invalidation_request {
+	struct list_head list;
+	struct cblock_range *cblocks;
+
+	atomic_t complete;
+	int err;
+
+	wait_queue_head_t result_wait;
+};
+
+struct cache {
+	struct dm_target *ti;
+	struct dm_target_callbacks callbacks;
+
+	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;
+
+	/*
+	 * Fields for converting from sectors to blocks.
+	 */
+	uint32_t sectors_per_block;
+	int sectors_per_block_shift;
+
+	spinlock_t lock;
+	struct bio_list deferred_bios;
+	struct bio_list deferred_flush_bios;
+	struct bio_list deferred_writethrough_bios;
+	struct list_head quiesced_migrations;
+	struct list_head completed_migrations;
+	struct list_head need_commit_migrations;
+	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;
+
+	wait_queue_head_t quiescing_wait;
+	atomic_t quiescing;
+	atomic_t quiescing_ack;
+
+	/*
+	 * cache_size entries, dirty if set
+	 */
+	atomic_t nr_dirty;
+	unsigned long *dirty_bitset;
+
+	/*
+	 * 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 workqueue_struct *wq;
+	struct work_struct worker;
+
+	struct delayed_work waker;
+	unsigned long last_commit_jiffies;
+
+	struct dm_bio_prison *prison;
+	struct dm_deferred_set *all_io_ds;
+
+	mempool_t *migration_pool;
+
+	struct dm_cache_policy *policy;
+	unsigned policy_nr_args;
+
+	bool need_tick_bio:1;
+	bool sized:1;
+	bool invalidate:1;
+	bool commit_requested:1;
+	bool loaded_mappings:1;
+	bool loaded_discards:1;
+
+	/*
+	 * Cache features such as write-through.
+	 */
+	struct cache_features features;
+
+	struct cache_stats stats;
+
+	/*
+	 * Invalidation fields.
+	 */
+	spinlock_t invalidation_lock;
+	struct list_head invalidation_requests;
+};
+
+struct per_bio_data {
+	bool tick:1;
+	unsigned req_nr:2;
+	struct dm_deferred_entry *all_io_entry;
+	struct dm_hook_info hook_info;
+
+	/*
+	 * writethrough fields.  These MUST remain at the end of this
+	 * structure and the 'cache' member must be the first as it
+	 * is used to determine the offset of the writethrough fields.
+	 */
+	struct cache *cache;
+	dm_cblock_t cblock;
+	struct dm_bio_details bio_details;
+};
+
+struct dm_cache_migration {
+	struct list_head list;
+	struct cache *cache;
+
+	unsigned long start_jiffies;
+	dm_oblock_t old_oblock;
+	dm_oblock_t new_oblock;
+	dm_cblock_t cblock;
+
+	bool err:1;
+	bool discard:1;
+	bool writeback:1;
+	bool demote:1;
+	bool promote:1;
+	bool requeue_holder:1;
+	bool invalidate:1;
+
+	struct dm_bio_prison_cell *old_ocell;
+	struct dm_bio_prison_cell *new_ocell;
+};
+
+/*
+ * Processing a bio in the worker thread may require these memory
+ * allocations.  We prealloc to avoid deadlocks (the same worker thread
+ * frees them back to the mempool).
+ */
+struct prealloc {
+	struct dm_cache_migration *mg;
+	struct dm_bio_prison_cell *cell1;
+	struct dm_bio_prison_cell *cell2;
+};
+
+static void wake_worker(struct cache *cache)
+{
+	queue_work(cache->wq, &cache->worker);
+}
+
+/*----------------------------------------------------------------*/
+
+static struct dm_bio_prison_cell *alloc_prison_cell(struct cache *cache)
+{
+	/* FIXME: change to use a local slab. */
+	return dm_bio_prison_alloc_cell(cache->prison, GFP_NOWAIT);
+}
+
+static void free_prison_cell(struct cache *cache, struct dm_bio_prison_cell *cell)
+{
+	dm_bio_prison_free_cell(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_NOWAIT);
+	if (mg) {
+		mg->cache = cache;
+		atomic_inc(&mg->cache->nr_allocated_migrations);
+	}
+
+	return mg;
+}
+
+static void free_migration(struct dm_cache_migration *mg)
+{
+	if (atomic_dec_and_test(&mg->cache->nr_allocated_migrations))
+		wake_up(&mg->cache->migration_wait);
+
+	mempool_free(mg, mg->cache->migration_pool);
+}
+
+static int prealloc_data_structs(struct cache *cache, struct prealloc *p)
+{
+	if (!p->mg) {
+		p->mg = alloc_migration(cache);
+		if (!p->mg)
+			return -ENOMEM;
+	}
+
+	if (!p->cell1) {
+		p->cell1 = alloc_prison_cell(cache);
+		if (!p->cell1)
+			return -ENOMEM;
+	}
+
+	if (!p->cell2) {
+		p->cell2 = alloc_prison_cell(cache);
+		if (!p->cell2)
+			return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void prealloc_free_structs(struct cache *cache, struct prealloc *p)
+{
+	if (p->cell2)
+		free_prison_cell(cache, p->cell2);
+
+	if (p->cell1)
+		free_prison_cell(cache, p->cell1);
+
+	if (p->mg)
+		free_migration(p->mg);
+}
+
+static struct dm_cache_migration *prealloc_get_migration(struct prealloc *p)
+{
+	struct dm_cache_migration *mg = p->mg;
+
+	BUG_ON(!mg);
+	p->mg = NULL;
+
+	return mg;
+}
+
+/*
+ * You must have a cell within the prealloc struct to return.  If not this
+ * function will BUG() rather than returning NULL.
+ */
+static struct dm_bio_prison_cell *prealloc_get_cell(struct prealloc *p)
+{
+	struct dm_bio_prison_cell *r = NULL;
+
+	if (p->cell1) {
+		r = p->cell1;
+		p->cell1 = NULL;
+
+	} else if (p->cell2) {
+		r = p->cell2;
+		p->cell2 = NULL;
+	} else
+		BUG();
+
+	return r;
+}
+
+/*
+ * You can't have more than two cells in a prealloc struct.  BUG() will be
+ * called if you try and overfill.
+ */
+static void prealloc_put_cell(struct prealloc *p, struct dm_bio_prison_cell *cell)
+{
+	if (!p->cell2)
+		p->cell2 = cell;
+
+	else if (!p->cell1)
+		p->cell1 = cell;
+
+	else
+		BUG();
+}
+
+/*----------------------------------------------------------------*/
+
+static void build_key(dm_oblock_t begin, dm_oblock_t end, struct dm_cell_key *key)
+{
+	key->virtual = 0;
+	key->dev = 0;
+	key->block_begin = from_oblock(begin);
+	key->block_end = from_oblock(end);
+}
+
+/*
+ * The caller hands in a preallocated cell, and a free function for it.
+ * The cell will be freed if there's an error, or if it wasn't used because
+ * a cell with that key already exists.
+ */
+typedef void (*cell_free_fn)(void *context, struct dm_bio_prison_cell *cell);
+
+static int bio_detain_range(struct cache *cache, dm_oblock_t oblock_begin, dm_oblock_t oblock_end,
+			    struct bio *bio, struct dm_bio_prison_cell *cell_prealloc,
+			    cell_free_fn free_fn, void *free_context,
+			    struct dm_bio_prison_cell **cell_result)
+{
+	int r;
+	struct dm_cell_key key;
+
+	build_key(oblock_begin, oblock_end, &key);
+	r = dm_bio_detain(cache->prison, &key, bio, cell_prealloc, cell_result);
+	if (r)
+		free_fn(free_context, cell_prealloc);
+
+	return r;
+}
+
+static int bio_detain(struct cache *cache, dm_oblock_t oblock,
+		      struct bio *bio, struct dm_bio_prison_cell *cell_prealloc,
+		      cell_free_fn free_fn, void *free_context,
+		      struct dm_bio_prison_cell **cell_result)
+{
+	dm_oblock_t end = to_oblock(from_oblock(oblock) + 1ULL);
+	return bio_detain_range(cache, oblock, end, bio,
+				cell_prealloc, free_fn, free_context, cell_result);
+}
+
+static int get_cell(struct cache *cache,
+		    dm_oblock_t oblock,
+		    struct prealloc *structs,
+		    struct dm_bio_prison_cell **cell_result)
+{
+	int r;
+	struct dm_cell_key key;
+	struct dm_bio_prison_cell *cell_prealloc;
+
+	cell_prealloc = prealloc_get_cell(structs);
+
+	build_key(oblock, to_oblock(from_oblock(oblock) + 1ULL), &key);
+	r = dm_get_cell(cache->prison, &key, cell_prealloc, cell_result);
+	if (r)
+		prealloc_put_cell(structs, cell_prealloc);
+
+	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_oblock_t oblock, 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, oblock);
+	}
+}
+
+static void clear_dirty(struct cache *cache, dm_oblock_t oblock, dm_cblock_t cblock)
+{
+	if (test_and_clear_bit(from_cblock(cblock), cache->dirty_bitset)) {
+		policy_clear_dirty(cache->policy, oblock);
+		if (atomic_dec_return(&cache->nr_dirty) == 0)
+			dm_table_event(cache->ti->table);
+	}
+}
+
+/*----------------------------------------------------------------*/
+
+static bool block_size_is_power_of_two(struct cache *cache)
+{
+	return cache->sectors_per_block_shift >= 0;
+}
+
+/* gcc on ARM generates spurious references to __udivdi3 and __umoddi3 */
+#if defined(CONFIG_ARM) && __GNUC__ == 4 && __GNUC_MINOR__ <= 6
+__always_inline
+#endif
+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 dm_oblock_t dblock_to_oblock(struct cache *cache, dm_dblock_t dblock)
+{
+	return to_oblock(from_dblock(dblock) * oblocks_per_dblock(cache));
+}
+
+static void set_discard(struct cache *cache, dm_dblock_t b)
+{
+	unsigned long flags;
+
+	BUG_ON(from_dblock(b) >= from_dblock(cache->discard_nr_blocks));
+	atomic_inc(&cache->stats.discard_count);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	set_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static void clear_discard(struct cache *cache, dm_dblock_t b)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	clear_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static bool is_discarded(struct cache *cache, dm_dblock_t b)
+{
+	int r;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	r = test_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	return r;
+}
+
+static bool is_discarded_oblock(struct cache *cache, dm_oblock_t b)
+{
+	int r;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	r = test_bit(from_dblock(oblock_to_dblock(cache, b)),
+		     cache->discard_bitset);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+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;
+
+	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);
+}
+
+/*----------------------------------------------------------------
+ * Per bio data
+ *--------------------------------------------------------------*/
+
+/*
+ * If using writeback, leave out struct per_bio_data's writethrough fields.
+ */
+#define PB_DATA_SIZE_WB (offsetof(struct per_bio_data, cache))
+#define PB_DATA_SIZE_WT (sizeof(struct per_bio_data))
+
+static bool writethrough_mode(struct cache_features *f)
+{
+	return f->io_mode == CM_IO_WRITETHROUGH;
+}
+
+static bool writeback_mode(struct cache_features *f)
+{
+	return f->io_mode == CM_IO_WRITEBACK;
+}
+
+static bool passthrough_mode(struct cache_features *f)
+{
+	return f->io_mode == CM_IO_PASSTHROUGH;
+}
+
+static size_t get_per_bio_data_size(struct cache *cache)
+{
+	return writethrough_mode(&cache->features) ? PB_DATA_SIZE_WT : PB_DATA_SIZE_WB;
+}
+
+static struct per_bio_data *get_per_bio_data(struct bio *bio, size_t data_size)
+{
+	struct per_bio_data *pb = dm_per_bio_data(bio, data_size);
+	BUG_ON(!pb);
+	return pb;
+}
+
+static struct per_bio_data *init_per_bio_data(struct bio *bio, size_t data_size)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio, data_size);
+
+	pb->tick = false;
+	pb->req_nr = dm_bio_get_target_bio_nr(bio);
+	pb->all_io_entry = NULL;
+
+	return pb;
+}
+
+/*----------------------------------------------------------------
+ * Remapping
+ *--------------------------------------------------------------*/
+static void remap_to_origin(struct cache *cache, struct bio *bio)
+{
+	bio->bi_bdev = 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->bi_bdev = 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)
+{
+	unsigned long flags;
+	size_t pb_data_size = get_per_bio_data_size(cache);
+	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	if (cache->need_tick_bio &&
+	    !(bio->bi_rw & (REQ_FUA | REQ_FLUSH | REQ_DISCARD))) {
+		pb->tick = true;
+		cache->need_tick_bio = false;
+	}
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static void remap_to_origin_clear_discard(struct cache *cache, struct bio *bio,
+				  dm_oblock_t oblock)
+{
+	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_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, oblock, 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 int bio_triggers_commit(struct cache *cache, struct bio *bio)
+{
+	return bio->bi_rw & (REQ_FLUSH | REQ_FUA);
+}
+
+/*
+ * You must increment the deferred set whilst the prison cell is held.  To
+ * encourage this, we ask for 'cell' to be passed in.
+ */
+static void inc_ds(struct cache *cache, struct bio *bio,
+		   struct dm_bio_prison_cell *cell)
+{
+	size_t pb_data_size = get_per_bio_data_size(cache);
+	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
+
+	BUG_ON(!cell);
+	BUG_ON(pb->all_io_entry);
+
+	pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+}
+
+static void issue(struct cache *cache, struct bio *bio)
+{
+	unsigned long flags;
+
+	if (!bio_triggers_commit(cache, bio)) {
+		generic_make_request(bio);
+		return;
+	}
+
+	/*
+	 * Batch together any bios that trigger commits and then issue a
+	 * single commit for them in do_worker().
+	 */
+	spin_lock_irqsave(&cache->lock, flags);
+	cache->commit_requested = true;
+	bio_list_add(&cache->deferred_flush_bios, bio);
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static void inc_and_issue(struct cache *cache, struct bio *bio, struct dm_bio_prison_cell *cell)
+{
+	inc_ds(cache, bio, cell);
+	issue(cache, bio);
+}
+
+static void defer_writethrough_bio(struct cache *cache, struct bio *bio)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	bio_list_add(&cache->deferred_writethrough_bios, bio);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void writethrough_endio(struct bio *bio, int err)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio, PB_DATA_SIZE_WT);
+
+	dm_unhook_bio(&pb->hook_info, bio);
+
+	if (err) {
+		bio_endio(bio, err);
+		return;
+	}
+
+	dm_bio_restore(&pb->bio_details, bio);
+	remap_to_cache(pb->cache, bio, pb->cblock);
+
+	/*
+	 * We can't issue this bio directly, since we're in interrupt
+	 * context.  So it gets put on a bio list for processing by the
+	 * worker thread.
+	 */
+	defer_writethrough_bio(pb->cache, bio);
+}
+
+/*
+ * When running in writethrough mode we need to send writes to clean blocks
+ * to both the cache and origin devices.  In future we'd like to clone the
+ * bio and send them in parallel, but for now we're doing them in
+ * series as this is easier.
+ */
+static void remap_to_origin_then_cache(struct cache *cache, struct bio *bio,
+				       dm_oblock_t oblock, dm_cblock_t cblock)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio, PB_DATA_SIZE_WT);
+
+	pb->cache = cache;
+	pb->cblock = cblock;
+	dm_hook_bio(&pb->hook_info, bio, writethrough_endio, NULL);
+	dm_bio_record(&pb->bio_details, bio);
+
+	remap_to_origin_clear_discard(pb->cache, bio, oblock);
+}
+
+/*----------------------------------------------------------------
+ * 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 void __cell_defer(struct cache *cache, struct dm_bio_prison_cell *cell,
+			 bool holder)
+{
+	(holder ? dm_cell_release : dm_cell_release_no_holder)
+		(cache->prison, cell, &cache->deferred_bios);
+	free_prison_cell(cache, cell);
+}
+
+static void cell_defer(struct cache *cache, struct dm_bio_prison_cell *cell,
+		       bool holder)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	__cell_defer(cache, cell, holder);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void free_io_migration(struct dm_cache_migration *mg)
+{
+	dec_io_migrations(mg->cache);
+	free_migration(mg);
+}
+
+static void migration_failure(struct dm_cache_migration *mg)
+{
+	struct cache *cache = mg->cache;
+
+	if (mg->writeback) {
+		DMWARN_LIMIT("writeback failed; couldn't copy block");
+		set_dirty(cache, mg->old_oblock, mg->cblock);
+		cell_defer(cache, mg->old_ocell, false);
+
+	} else if (mg->demote) {
+		DMWARN_LIMIT("demotion failed; couldn't copy block");
+		policy_force_mapping(cache->policy, mg->new_oblock, mg->old_oblock);
+
+		cell_defer(cache, mg->old_ocell, mg->promote ? false : true);
+		if (mg->promote)
+			cell_defer(cache, mg->new_ocell, true);
+	} else {
+		DMWARN_LIMIT("promotion failed; couldn't copy block");
+		policy_remove_mapping(cache->policy, mg->new_oblock);
+		cell_defer(cache, mg->new_ocell, true);
+	}
+
+	free_io_migration(mg);
+}
+
+static void migration_success_pre_commit(struct dm_cache_migration *mg)
+{
+	unsigned long flags;
+	struct cache *cache = mg->cache;
+
+	if (mg->writeback) {
+		clear_dirty(cache, mg->old_oblock, mg->cblock);
+		cell_defer(cache, mg->old_ocell, false);
+		free_io_migration(mg);
+		return;
+
+	} else if (mg->demote) {
+		if (dm_cache_remove_mapping(cache->cmd, mg->cblock)) {
+			DMWARN_LIMIT("demotion failed; couldn't update on disk metadata");
+			policy_force_mapping(cache->policy, mg->new_oblock,
+					     mg->old_oblock);
+			if (mg->promote)
+				cell_defer(cache, mg->new_ocell, true);
+			free_io_migration(mg);
+			return;
+		}
+	} else {
+		if (dm_cache_insert_mapping(cache->cmd, mg->cblock, mg->new_oblock)) {
+			DMWARN_LIMIT("promotion failed; couldn't update on disk metadata");
+			policy_remove_mapping(cache->policy, mg->new_oblock);
+			free_io_migration(mg);
+			return;
+		}
+	}
+
+	spin_lock_irqsave(&cache->lock, flags);
+	list_add_tail(&mg->list, &cache->need_commit_migrations);
+	cache->commit_requested = true;
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static void migration_success_post_commit(struct dm_cache_migration *mg)
+{
+	unsigned long flags;
+	struct cache *cache = mg->cache;
+
+	if (mg->writeback) {
+		DMWARN("writeback unexpectedly triggered commit");
+		return;
+
+	} else if (mg->demote) {
+		cell_defer(cache, mg->old_ocell, mg->promote ? false : true);
+
+		if (mg->promote) {
+			mg->demote = false;
+
+			spin_lock_irqsave(&cache->lock, flags);
+			list_add_tail(&mg->list, &cache->quiesced_migrations);
+			spin_unlock_irqrestore(&cache->lock, flags);
+
+		} else {
+			if (mg->invalidate)
+				policy_remove_mapping(cache->policy, mg->old_oblock);
+			free_io_migration(mg);
+		}
+
+	} else {
+		if (mg->requeue_holder) {
+			clear_dirty(cache, mg->new_oblock, mg->cblock);
+			cell_defer(cache, mg->new_ocell, true);
+		} else {
+			/*
+			 * The block was promoted via an overwrite, so it's dirty.
+			 */
+			set_dirty(cache, mg->new_oblock, mg->cblock);
+			bio_endio(mg->new_ocell->holder, 0);
+			cell_defer(cache, mg->new_ocell, false);
+		}
+		free_io_migration(mg);
+	}
+}
+
+static void copy_complete(int read_err, unsigned long write_err, void *context)
+{
+	unsigned long flags;
+	struct dm_cache_migration *mg = (struct dm_cache_migration *) context;
+	struct cache *cache = mg->cache;
+
+	if (read_err || write_err)
+		mg->err = true;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	list_add_tail(&mg->list, &cache->completed_migrations);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void issue_copy(struct dm_cache_migration *mg)
+{
+	int r;
+	struct dm_io_region o_region, c_region;
+	struct cache *cache = mg->cache;
+	sector_t cblock = from_cblock(mg->cblock);
+
+	o_region.bdev = cache->origin_dev->bdev;
+	o_region.count = cache->sectors_per_block;
+
+	c_region.bdev = cache->cache_dev->bdev;
+	c_region.sector = cblock * cache->sectors_per_block;
+	c_region.count = cache->sectors_per_block;
+
+	if (mg->writeback || mg->demote) {
+		/* demote */
+		o_region.sector = from_oblock(mg->old_oblock) * cache->sectors_per_block;
+		r = dm_kcopyd_copy(cache->copier, &c_region, 1, &o_region, 0, copy_complete, mg);
+	} else {
+		/* promote */
+		o_region.sector = from_oblock(mg->new_oblock) * cache->sectors_per_block;
+		r = dm_kcopyd_copy(cache->copier, &o_region, 1, &c_region, 0, copy_complete, mg);
+	}
+
+	if (r < 0) {
+		DMERR_LIMIT("issuing migration failed");
+		migration_failure(mg);
+	}
+}
+
+static void overwrite_endio(struct bio *bio, int err)
+{
+	struct dm_cache_migration *mg = bio->bi_private;
+	struct cache *cache = mg->cache;
+	size_t pb_data_size = get_per_bio_data_size(cache);
+	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
+	unsigned long flags;
+
+	dm_unhook_bio(&pb->hook_info, bio);
+
+	if (err)
+		mg->err = true;
+
+	mg->requeue_holder = false;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	list_add_tail(&mg->list, &cache->completed_migrations);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void issue_overwrite(struct dm_cache_migration *mg, struct bio *bio)
+{
+	size_t pb_data_size = get_per_bio_data_size(mg->cache);
+	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
+
+	dm_hook_bio(&pb->hook_info, bio, overwrite_endio, mg);
+	remap_to_cache_dirty(mg->cache, bio, mg->new_oblock, mg->cblock);
+
+	/*
+	 * No need to inc_ds() here, since the cell will be held for the
+	 * duration of the io.
+	 */
+	generic_make_request(bio);
+}
+
+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 void avoid_copy(struct dm_cache_migration *mg)
+{
+	atomic_inc(&mg->cache->stats.copies_avoided);
+	migration_success_pre_commit(mg);
+}
+
+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 issue_discard(struct dm_cache_migration *mg)
+{
+	dm_dblock_t b, e;
+	struct bio *bio = mg->new_ocell->holder;
+
+	calc_discard_block_range(mg->cache, bio, &b, &e);
+	while (b != e) {
+		set_discard(mg->cache, b);
+		b = to_dblock(from_dblock(b) + 1);
+	}
+
+	bio_endio(bio, 0);
+	cell_defer(mg->cache, mg->new_ocell, false);
+	free_migration(mg);
+}
+
+static void issue_copy_or_discard(struct dm_cache_migration *mg)
+{
+	bool avoid;
+	struct cache *cache = mg->cache;
+
+	if (mg->discard) {
+		issue_discard(mg);
+		return;
+	}
+
+	if (mg->writeback || mg->demote)
+		avoid = !is_dirty(cache, mg->cblock) ||
+			is_discarded_oblock(cache, mg->old_oblock);
+	else {
+		struct bio *bio = mg->new_ocell->holder;
+
+		avoid = is_discarded_oblock(cache, mg->new_oblock);
+
+		if (writeback_mode(&cache->features) &&
+		    !avoid && bio_writes_complete_block(cache, bio)) {
+			issue_overwrite(mg, bio);
+			return;
+		}
+	}
+
+	avoid ? avoid_copy(mg) : issue_copy(mg);
+}
+
+static void complete_migration(struct dm_cache_migration *mg)
+{
+	if (mg->err)
+		migration_failure(mg);
+	else
+		migration_success_pre_commit(mg);
+}
+
+static void process_migrations(struct cache *cache, struct list_head *head,
+			       void (*fn)(struct dm_cache_migration *))
+{
+	unsigned long flags;
+	struct list_head list;
+	struct dm_cache_migration *mg, *tmp;
+
+	INIT_LIST_HEAD(&list);
+	spin_lock_irqsave(&cache->lock, flags);
+	list_splice_init(head, &list);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	list_for_each_entry_safe(mg, tmp, &list, list)
+		fn(mg);
+}
+
+static void __queue_quiesced_migration(struct dm_cache_migration *mg)
+{
+	list_add_tail(&mg->list, &mg->cache->quiesced_migrations);
+}
+
+static void queue_quiesced_migration(struct dm_cache_migration *mg)
+{
+	unsigned long flags;
+	struct cache *cache = mg->cache;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	__queue_quiesced_migration(mg);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void queue_quiesced_migrations(struct cache *cache, struct list_head *work)
+{
+	unsigned long flags;
+	struct dm_cache_migration *mg, *tmp;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	list_for_each_entry_safe(mg, tmp, work, list)
+		__queue_quiesced_migration(mg);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void check_for_quiesced_migrations(struct cache *cache,
+					  struct per_bio_data *pb)
+{
+	struct list_head work;
+
+	if (!pb->all_io_entry)
+		return;
+
+	INIT_LIST_HEAD(&work);
+	dm_deferred_entry_dec(pb->all_io_entry, &work);
+
+	if (!list_empty(&work))
+		queue_quiesced_migrations(cache, &work);
+}
+
+static void quiesce_migration(struct dm_cache_migration *mg)
+{
+	if (!dm_deferred_set_add_work(mg->cache->all_io_ds, &mg->list))
+		queue_quiesced_migration(mg);
+}
+
+static void promote(struct cache *cache, struct prealloc *structs,
+		    dm_oblock_t oblock, dm_cblock_t cblock,
+		    struct dm_bio_prison_cell *cell)
+{
+	struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+	mg->err = false;
+	mg->discard = false;
+	mg->writeback = false;
+	mg->demote = false;
+	mg->promote = true;
+	mg->requeue_holder = true;
+	mg->invalidate = false;
+	mg->cache = cache;
+	mg->new_oblock = oblock;
+	mg->cblock = cblock;
+	mg->old_ocell = NULL;
+	mg->new_ocell = cell;
+	mg->start_jiffies = jiffies;
+
+	inc_io_migrations(cache);
+	quiesce_migration(mg);
+}
+
+static void writeback(struct cache *cache, struct prealloc *structs,
+		      dm_oblock_t oblock, dm_cblock_t cblock,
+		      struct dm_bio_prison_cell *cell)
+{
+	struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+	mg->err = false;
+	mg->discard = false;
+	mg->writeback = true;
+	mg->demote = false;
+	mg->promote = false;
+	mg->requeue_holder = true;
+	mg->invalidate = false;
+	mg->cache = cache;
+	mg->old_oblock = oblock;
+	mg->cblock = cblock;
+	mg->old_ocell = cell;
+	mg->new_ocell = NULL;
+	mg->start_jiffies = jiffies;
+
+	inc_io_migrations(cache);
+	quiesce_migration(mg);
+}
+
+static void demote_then_promote(struct cache *cache, struct prealloc *structs,
+				dm_oblock_t old_oblock, dm_oblock_t new_oblock,
+				dm_cblock_t cblock,
+				struct dm_bio_prison_cell *old_ocell,
+				struct dm_bio_prison_cell *new_ocell)
+{
+	struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+	mg->err = false;
+	mg->discard = false;
+	mg->writeback = false;
+	mg->demote = true;
+	mg->promote = true;
+	mg->requeue_holder = true;
+	mg->invalidate = false;
+	mg->cache = cache;
+	mg->old_oblock = old_oblock;
+	mg->new_oblock = new_oblock;
+	mg->cblock = cblock;
+	mg->old_ocell = old_ocell;
+	mg->new_ocell = new_ocell;
+	mg->start_jiffies = jiffies;
+
+	inc_io_migrations(cache);
+	quiesce_migration(mg);
+}
+
+/*
+ * Invalidate a cache entry.  No writeback occurs; any changes in the cache
+ * block are thrown away.
+ */
+static void invalidate(struct cache *cache, struct prealloc *structs,
+		       dm_oblock_t oblock, dm_cblock_t cblock,
+		       struct dm_bio_prison_cell *cell)
+{
+	struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+	mg->err = false;
+	mg->discard = false;
+	mg->writeback = false;
+	mg->demote = true;
+	mg->promote = false;
+	mg->requeue_holder = true;
+	mg->invalidate = true;
+	mg->cache = cache;
+	mg->old_oblock = oblock;
+	mg->cblock = cblock;
+	mg->old_ocell = cell;
+	mg->new_ocell = NULL;
+	mg->start_jiffies = jiffies;
+
+	inc_io_migrations(cache);
+	quiesce_migration(mg);
+}
+
+static void discard(struct cache *cache, struct prealloc *structs,
+		    struct dm_bio_prison_cell *cell)
+{
+	struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+	mg->err = false;
+	mg->discard = true;
+	mg->writeback = false;
+	mg->demote = false;
+	mg->promote = false;
+	mg->requeue_holder = false;
+	mg->invalidate = false;
+	mg->cache = cache;
+	mg->old_ocell = NULL;
+	mg->new_ocell = cell;
+	mg->start_jiffies = jiffies;
+
+	quiesce_migration(mg);
+}
+
+/*----------------------------------------------------------------
+ * bio processing
+ *--------------------------------------------------------------*/
+static void defer_bio(struct cache *cache, struct bio *bio)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	bio_list_add(&cache->deferred_bios, bio);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void process_flush_bio(struct cache *cache, struct bio *bio)
+{
+	size_t pb_data_size = get_per_bio_data_size(cache);
+	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
+
+	BUG_ON(bio->bi_iter.bi_size);
+	if (!pb->req_nr)
+		remap_to_origin(cache, bio);
+	else
+		remap_to_cache(cache, bio, 0);
+
+	/*
+	 * REQ_FLUSH is not directed at any particular block so we don't
+	 * need to inc_ds().  REQ_FUA's are split into a write + REQ_FLUSH
+	 * by dm-core.
+	 */
+	issue(cache, bio);
+}
+
+static void process_discard_bio(struct cache *cache, struct prealloc *structs,
+				struct bio *bio)
+{
+	int r;
+	dm_dblock_t b, e;
+	struct dm_bio_prison_cell *cell_prealloc, *new_ocell;
+
+	calc_discard_block_range(cache, bio, &b, &e);
+	if (b == e) {
+		bio_endio(bio, 0);
+		return;
+	}
+
+	cell_prealloc = prealloc_get_cell(structs);
+	r = bio_detain_range(cache, dblock_to_oblock(cache, b), dblock_to_oblock(cache, e), bio, cell_prealloc,
+			     (cell_free_fn) prealloc_put_cell,
+			     structs, &new_ocell);
+	if (r > 0)
+		return;
+
+	discard(cache, structs, new_ocell);
+}
+
+static bool spare_migration_bandwidth(struct cache *cache)
+{
+	sector_t current_volume = (atomic_read(&cache->nr_io_migrations) + 1) *
+		cache->sectors_per_block;
+	return current_volume < cache->migration_threshold;
+}
+
+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);
+}
+
+/*----------------------------------------------------------------*/
+
+struct old_oblock_lock {
+	struct policy_locker locker;
+	struct cache *cache;
+	struct prealloc *structs;
+	struct dm_bio_prison_cell *cell;
+};
+
+static int null_locker(struct policy_locker *locker, dm_oblock_t b)
+{
+	/* This should never be called */
+	BUG();
+	return 0;
+}
+
+static int cell_locker(struct policy_locker *locker, dm_oblock_t b)
+{
+	struct old_oblock_lock *l = container_of(locker, struct old_oblock_lock, locker);
+	struct dm_bio_prison_cell *cell_prealloc = prealloc_get_cell(l->structs);
+
+	return bio_detain(l->cache, b, NULL, cell_prealloc,
+			  (cell_free_fn) prealloc_put_cell,
+			  l->structs, &l->cell);
+}
+
+static void process_bio(struct cache *cache, struct prealloc *structs,
+			struct bio *bio)
+{
+	int r;
+	bool release_cell = true;
+	dm_oblock_t block = get_bio_block(cache, bio);
+	struct dm_bio_prison_cell *cell_prealloc, *new_ocell;
+	struct policy_result lookup_result;
+	bool passthrough = passthrough_mode(&cache->features);
+	bool discarded_block, can_migrate;
+	struct old_oblock_lock ool;
+
+	/*
+	 * Check to see if that block is currently migrating.
+	 */
+	cell_prealloc = prealloc_get_cell(structs);
+	r = bio_detain(cache, block, bio, cell_prealloc,
+		       (cell_free_fn) prealloc_put_cell,
+		       structs, &new_ocell);
+	if (r > 0)
+		return;
+
+	discarded_block = is_discarded_oblock(cache, block);
+	can_migrate = !passthrough && (discarded_block || spare_migration_bandwidth(cache));
+
+	ool.locker.fn = cell_locker;
+	ool.cache = cache;
+	ool.structs = structs;
+	ool.cell = NULL;
+	r = policy_map(cache->policy, block, true, can_migrate, discarded_block,
+		       bio, &ool.locker, &lookup_result);
+
+	if (r == -EWOULDBLOCK)
+		/* migration has been denied */
+		lookup_result.op = POLICY_MISS;
+
+	switch (lookup_result.op) {
+	case POLICY_HIT:
+		if (passthrough) {
+			inc_miss_counter(cache, bio);
+
+			/*
+			 * Passthrough always maps to the origin,
+			 * invalidating any cache blocks that are written
+			 * to.
+			 */
+
+			if (bio_data_dir(bio) == WRITE) {
+				atomic_inc(&cache->stats.demotion);
+				invalidate(cache, structs, block, lookup_result.cblock, new_ocell);
+				release_cell = false;
+
+			} else {
+				/* FIXME: factor out issue_origin() */
+				remap_to_origin_clear_discard(cache, bio, block);
+				inc_and_issue(cache, bio, new_ocell);
+			}
+		} else {
+			inc_hit_counter(cache, bio);
+
+			if (bio_data_dir(bio) == WRITE &&
+			    writethrough_mode(&cache->features) &&
+			    !is_dirty(cache, lookup_result.cblock)) {
+				remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
+				inc_and_issue(cache, bio, new_ocell);
+
+			} else  {
+				remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
+				inc_and_issue(cache, bio, new_ocell);
+			}
+		}
+
+		break;
+
+	case POLICY_MISS:
+		inc_miss_counter(cache, bio);
+		remap_to_origin_clear_discard(cache, bio, block);
+		inc_and_issue(cache, bio, new_ocell);
+		break;
+
+	case POLICY_NEW:
+		atomic_inc(&cache->stats.promotion);
+		promote(cache, structs, block, lookup_result.cblock, new_ocell);
+		release_cell = false;
+		break;
+
+	case POLICY_REPLACE:
+		atomic_inc(&cache->stats.demotion);
+		atomic_inc(&cache->stats.promotion);
+		demote_then_promote(cache, structs, lookup_result.old_oblock,
+				    block, lookup_result.cblock,
+				    ool.cell, new_ocell);
+		release_cell = false;
+		break;
+
+	default:
+		DMERR_LIMIT("%s: erroring bio, unknown policy op: %u", __func__,
+			    (unsigned) lookup_result.op);
+		bio_io_error(bio);
+	}
+
+	if (release_cell)
+		cell_defer(cache, new_ocell, false);
+}
+
+static int need_commit_due_to_time(struct cache *cache)
+{
+	return !time_in_range(jiffies, cache->last_commit_jiffies,
+			      cache->last_commit_jiffies + COMMIT_PERIOD);
+}
+
+static int commit_if_needed(struct cache *cache)
+{
+	int r = 0;
+
+	if ((cache->commit_requested || need_commit_due_to_time(cache)) &&
+	    dm_cache_changed_this_transaction(cache->cmd)) {
+		atomic_inc(&cache->stats.commit_count);
+		cache->commit_requested = false;
+		r = dm_cache_commit(cache->cmd, false);
+		cache->last_commit_jiffies = jiffies;
+	}
+
+	return r;
+}
+
+static void process_deferred_bios(struct cache *cache)
+{
+	unsigned long flags;
+	struct bio_list bios;
+	struct bio *bio;
+	struct prealloc structs;
+
+	memset(&structs, 0, sizeof(structs));
+	bio_list_init(&bios);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	bio_list_merge(&bios, &cache->deferred_bios);
+	bio_list_init(&cache->deferred_bios);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	while (!bio_list_empty(&bios)) {
+		/*
+		 * If we've got no free migration structs, and processing
+		 * this bio might require one, we pause until there are some
+		 * prepared mappings to process.
+		 */
+		if (prealloc_data_structs(cache, &structs)) {
+			spin_lock_irqsave(&cache->lock, flags);
+			bio_list_merge(&cache->deferred_bios, &bios);
+			spin_unlock_irqrestore(&cache->lock, flags);
+			break;
+		}
+
+		bio = bio_list_pop(&bios);
+
+		if (bio->bi_rw & REQ_FLUSH)
+			process_flush_bio(cache, bio);
+		else if (bio->bi_rw & REQ_DISCARD)
+			process_discard_bio(cache, &structs, bio);
+		else
+			process_bio(cache, &structs, bio);
+	}
+
+	prealloc_free_structs(cache, &structs);
+}
+
+static void process_deferred_flush_bios(struct cache *cache, bool submit_bios)
+{
+	unsigned long flags;
+	struct bio_list bios;
+	struct bio *bio;
+
+	bio_list_init(&bios);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	bio_list_merge(&bios, &cache->deferred_flush_bios);
+	bio_list_init(&cache->deferred_flush_bios);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	/*
+	 * These bios have already been through inc_ds()
+	 */
+	while ((bio = bio_list_pop(&bios)))
+		submit_bios ? generic_make_request(bio) : bio_io_error(bio);
+}
+
+static void process_deferred_writethrough_bios(struct cache *cache)
+{
+	unsigned long flags;
+	struct bio_list bios;
+	struct bio *bio;
+
+	bio_list_init(&bios);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	bio_list_merge(&bios, &cache->deferred_writethrough_bios);
+	bio_list_init(&cache->deferred_writethrough_bios);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	/*
+	 * These bios have already been through inc_ds()
+	 */
+	while ((bio = bio_list_pop(&bios)))
+		generic_make_request(bio);
+}
+
+static void writeback_some_dirty_blocks(struct cache *cache)
+{
+	int r = 0;
+	dm_oblock_t oblock;
+	dm_cblock_t cblock;
+	struct prealloc structs;
+	struct dm_bio_prison_cell *old_ocell;
+
+	memset(&structs, 0, sizeof(structs));
+
+	while (spare_migration_bandwidth(cache)) {
+		if (prealloc_data_structs(cache, &structs))
+			break;
+
+		r = policy_writeback_work(cache->policy, &oblock, &cblock);
+		if (r)
+			break;
+
+		r = get_cell(cache, oblock, &structs, &old_ocell);
+		if (r) {
+			policy_set_dirty(cache->policy, oblock);
+			break;
+		}
+
+		writeback(cache, &structs, oblock, cblock, old_ocell);
+	}
+
+	prealloc_free_structs(cache, &structs);
+}
+
+/*----------------------------------------------------------------
+ * Invalidations.
+ * Dropping something from the cache *without* writing back.
+ *--------------------------------------------------------------*/
+
+static void process_invalidation_request(struct cache *cache, struct invalidation_request *req)
+{
+	int r = 0;
+	uint64_t begin = from_cblock(req->cblocks->begin);
+	uint64_t end = from_cblock(req->cblocks->end);
+
+	while (begin != end) {
+		r = policy_remove_cblock(cache->policy, to_cblock(begin));
+		if (!r) {
+			r = dm_cache_remove_mapping(cache->cmd, to_cblock(begin));
+			if (r)
+				break;
+
+		} else if (r == -ENODATA) {
+			/* harmless, already unmapped */
+			r = 0;
+
+		} else {
+			DMERR("policy_remove_cblock failed");
+			break;
+		}
+
+		begin++;
+        }
+
+	cache->commit_requested = true;
+
+	req->err = r;
+	atomic_set(&req->complete, 1);
+
+	wake_up(&req->result_wait);
+}
+
+static void process_invalidation_requests(struct cache *cache)
+{
+	struct list_head list;
+	struct invalidation_request *req, *tmp;
+
+	INIT_LIST_HEAD(&list);
+	spin_lock(&cache->invalidation_lock);
+	list_splice_init(&cache->invalidation_requests, &list);
+	spin_unlock(&cache->invalidation_lock);
+
+	list_for_each_entry_safe (req, tmp, &list, list)
+		process_invalidation_request(cache, req);
+}
+
+/*----------------------------------------------------------------
+ * Main worker loop
+ *--------------------------------------------------------------*/
+static bool is_quiescing(struct cache *cache)
+{
+	return atomic_read(&cache->quiescing);
+}
+
+static void ack_quiescing(struct cache *cache)
+{
+	if (is_quiescing(cache)) {
+		atomic_inc(&cache->quiescing_ack);
+		wake_up(&cache->quiescing_wait);
+	}
+}
+
+static void wait_for_quiescing_ack(struct cache *cache)
+{
+	wait_event(cache->quiescing_wait, atomic_read(&cache->quiescing_ack));
+}
+
+static void start_quiescing(struct cache *cache)
+{
+	atomic_inc(&cache->quiescing);
+	wait_for_quiescing_ack(cache);
+}
+
+static void stop_quiescing(struct cache *cache)
+{
+	atomic_set(&cache->quiescing, 0);
+	atomic_set(&cache->quiescing_ack, 0);
+}
+
+static void wait_for_migrations(struct cache *cache)
+{
+	wait_event(cache->migration_wait, !atomic_read(&cache->nr_allocated_migrations));
+}
+
+static void stop_worker(struct cache *cache)
+{
+	cancel_delayed_work(&cache->waker);
+	flush_workqueue(cache->wq);
+}
+
+static void requeue_deferred_io(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_endio(bio, DM_ENDIO_REQUEUE);
+}
+
+static int more_work(struct cache *cache)
+{
+	if (is_quiescing(cache))
+		return !list_empty(&cache->quiesced_migrations) ||
+			!list_empty(&cache->completed_migrations) ||
+			!list_empty(&cache->need_commit_migrations);
+	else
+		return !bio_list_empty(&cache->deferred_bios) ||
+			!bio_list_empty(&cache->deferred_flush_bios) ||
+			!bio_list_empty(&cache->deferred_writethrough_bios) ||
+			!list_empty(&cache->quiesced_migrations) ||
+			!list_empty(&cache->completed_migrations) ||
+			!list_empty(&cache->need_commit_migrations) ||
+			cache->invalidate;
+}
+
+static void do_worker(struct work_struct *ws)
+{
+	struct cache *cache = container_of(ws, struct cache, worker);
+
+	do {
+		if (!is_quiescing(cache)) {
+			writeback_some_dirty_blocks(cache);
+			process_deferred_writethrough_bios(cache);
+			process_deferred_bios(cache);
+			process_invalidation_requests(cache);
+		}
+
+		process_migrations(cache, &cache->quiesced_migrations, issue_copy_or_discard);
+		process_migrations(cache, &cache->completed_migrations, complete_migration);
+
+		if (commit_if_needed(cache)) {
+			process_deferred_flush_bios(cache, false);
+			process_migrations(cache, &cache->need_commit_migrations, migration_failure);
+
+			/*
+			 * FIXME: rollback metadata or just go into a
+			 * failure mode and error everything
+			 */
+		} else {
+			process_deferred_flush_bios(cache, true);
+			process_migrations(cache, &cache->need_commit_migrations,
+					   migration_success_post_commit);
+		}
+
+		ack_quiescing(cache);
+
+	} while (more_work(cache));
+}
+
+/*
+ * 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);
+	wake_worker(cache);
+	queue_delayed_work(cache->wq, &cache->waker, COMMIT_PERIOD);
+}
+
+/*----------------------------------------------------------------*/
+
+static int is_congested(struct dm_dev *dev, int bdi_bits)
+{
+	struct request_queue *q = bdev_get_queue(dev->bdev);
+	return bdi_congested(&q->backing_dev_info, bdi_bits);
+}
+
+static int cache_is_congested(struct dm_target_callbacks *cb, int bdi_bits)
+{
+	struct cache *cache = container_of(cb, struct cache, callbacks);
+
+	return is_congested(cache->origin_dev, bdi_bits) ||
+		is_congested(cache->cache_dev, bdi_bits);
+}
+
+/*----------------------------------------------------------------
+ * 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;
+
+	if (cache->migration_pool)
+		mempool_destroy(cache->migration_pool);
+
+	if (cache->all_io_ds)
+		dm_deferred_set_destroy(cache->all_io_ds);
+
+	if (cache->prison)
+		dm_bio_prison_destroy(cache->prison);
+
+	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);
+
+	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;
+}
+
+static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
+			  char **error)
+{
+	static struct dm_arg _args[] = {
+		{0, 1, "Invalid number of cache feature arguments"},
+	};
+
+	int r;
+	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;
+
+		else if (!strcasecmp(arg, "writethrough"))
+			cf->io_mode = CM_IO_WRITETHROUGH;
+
+		else if (!strcasecmp(arg, "passthrough"))
+			cf->io_mode = CM_IO_PASSTHROUGH;
+
+		else {
+			*error = "Unrecognised cache feature requested";
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static int parse_policy(struct cache_args *ca, struct dm_arg_set *as,
+			char **error)
+{
+	static 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;
+
+	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->discard_zeroes_data_unsupported = true;
+	ti->split_discard_bios = false;
+
+	cache->features = ca->features;
+	ti->per_bio_data_size = get_per_bio_data_size(cache);
+
+	cache->callbacks.congested_fn = cache_is_congested;
+	dm_table_add_target_callbacks(ti->table, &cache->callbacks);
+
+	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;
+
+	/* FIXME: factor out this whole section */
+	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));
+	if (IS_ERR(cmd)) {
+		*error = "Error creating metadata object";
+		r = PTR_ERR(cmd);
+		goto bad;
+	}
+	cache->cmd = cmd;
+
+	if (passthrough_mode(&cache->features)) {
+		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;
+		}
+	}
+
+	spin_lock_init(&cache->lock);
+	bio_list_init(&cache->deferred_bios);
+	bio_list_init(&cache->deferred_flush_bios);
+	bio_list_init(&cache->deferred_writethrough_bios);
+	INIT_LIST_HEAD(&cache->quiesced_migrations);
+	INIT_LIST_HEAD(&cache->completed_migrations);
+	INIT_LIST_HEAD(&cache->need_commit_migrations);
+	atomic_set(&cache->nr_allocated_migrations, 0);
+	atomic_set(&cache->nr_io_migrations, 0);
+	init_waitqueue_head(&cache->migration_wait);
+
+	init_waitqueue_head(&cache->quiescing_wait);
+	atomic_set(&cache->quiescing, 0);
+	atomic_set(&cache->quiescing_ack, 0);
+
+	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_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
+	if (!cache->wq) {
+		*error = "could not create workqueue for metadata object";
+		goto bad;
+	}
+	INIT_WORK(&cache->worker, do_worker);
+	INIT_DELAYED_WORK(&cache->waker, do_waker);
+	cache->last_commit_jiffies = jiffies;
+
+	cache->prison = dm_bio_prison_create();
+	if (!cache->prison) {
+		*error = "could not create bio prison";
+		goto bad;
+	}
+
+	cache->all_io_ds = dm_deferred_set_create();
+	if (!cache->all_io_ds) {
+		*error = "could not create all_io deferred set";
+		goto bad;
+	}
+
+	cache->migration_pool = mempool_create_slab_pool(MIGRATION_POOL_SIZE,
+							 migration_cache);
+	if (!cache->migration_pool) {
+		*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);
+
+	*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 cache *cache, struct bio *bio, struct dm_bio_prison_cell **cell)
+{
+	int r;
+	dm_oblock_t block = get_bio_block(cache, bio);
+	size_t pb_data_size = get_per_bio_data_size(cache);
+	bool can_migrate = false;
+	bool discarded_block;
+	struct policy_result lookup_result;
+	struct per_bio_data *pb = init_per_bio_data(bio, pb_data_size);
+	struct old_oblock_lock ool;
+
+	ool.locker.fn = null_locker;
+
+	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);
+		return DM_MAPIO_REMAPPED;
+	}
+
+	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA | REQ_DISCARD)) {
+		defer_bio(cache, bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	/*
+	 * Check to see if that block is currently migrating.
+	 */
+	*cell = alloc_prison_cell(cache);
+	if (!*cell) {
+		defer_bio(cache, bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	r = bio_detain(cache, block, bio, *cell,
+		       (cell_free_fn) free_prison_cell,
+		       cache, cell);
+	if (r) {
+		if (r < 0)
+			defer_bio(cache, bio);
+
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	discarded_block = is_discarded_oblock(cache, block);
+
+	r = policy_map(cache->policy, block, false, can_migrate, discarded_block,
+		       bio, &ool.locker, &lookup_result);
+	if (r == -EWOULDBLOCK) {
+		cell_defer(cache, *cell, true);
+		return DM_MAPIO_SUBMITTED;
+
+	} else if (r) {
+		DMERR_LIMIT("Unexpected return from cache replacement policy: %d", r);
+		cell_defer(cache, *cell, false);
+		bio_io_error(bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	r = DM_MAPIO_REMAPPED;
+	switch (lookup_result.op) {
+	case POLICY_HIT:
+		if (passthrough_mode(&cache->features)) {
+			if (bio_data_dir(bio) == WRITE) {
+				/*
+				 * We need to invalidate this block, so
+				 * defer for the worker thread.
+				 */
+				cell_defer(cache, *cell, true);
+				r = DM_MAPIO_SUBMITTED;
+
+			} else {
+				inc_miss_counter(cache, bio);
+				remap_to_origin_clear_discard(cache, bio, block);
+			}
+
+		} else {
+			inc_hit_counter(cache, bio);
+			if (bio_data_dir(bio) == WRITE && writethrough_mode(&cache->features) &&
+			    !is_dirty(cache, lookup_result.cblock))
+				remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
+			else
+				remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
+		}
+		break;
+
+	case POLICY_MISS:
+		inc_miss_counter(cache, bio);
+		if (pb->req_nr != 0) {
+			/*
+			 * This is a duplicate writethrough io that is no
+			 * longer needed because the block has been demoted.
+			 */
+			bio_endio(bio, 0);
+			cell_defer(cache, *cell, false);
+			r = DM_MAPIO_SUBMITTED;
+
+		} else
+			remap_to_origin_clear_discard(cache, bio, block);
+
+		break;
+
+	default:
+		DMERR_LIMIT("%s: erroring bio: unknown policy op: %u", __func__,
+			    (unsigned) lookup_result.op);
+		cell_defer(cache, *cell, false);
+		bio_io_error(bio);
+		r = DM_MAPIO_SUBMITTED;
+	}
+
+	return r;
+}
+
+static int cache_map(struct dm_target *ti, struct bio *bio)
+{
+	int r;
+	struct dm_bio_prison_cell *cell = NULL;
+	struct cache *cache = ti->private;
+
+	r = __cache_map(cache, bio, &cell);
+	if (r == DM_MAPIO_REMAPPED && cell) {
+		inc_ds(cache, bio, cell);
+		cell_defer(cache, cell, false);
+	}
+
+	return r;
+}
+
+static int cache_end_io(struct dm_target *ti, struct bio *bio, int error)
+{
+	struct cache *cache = ti->private;
+	unsigned long flags;
+	size_t pb_data_size = get_per_bio_data_size(cache);
+	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
+
+	if (pb->tick) {
+		policy_tick(cache->policy);
+
+		spin_lock_irqsave(&cache->lock, flags);
+		cache->need_tick_bio = true;
+		spin_unlock_irqrestore(&cache->lock, flags);
+	}
+
+	check_for_quiesced_migrations(cache, pb);
+
+	return 0;
+}
+
+static int write_dirty_bitset(struct cache *cache)
+{
+	unsigned i, r;
+
+	for (i = 0; i < from_cblock(cache->cache_size); i++) {
+		r = dm_cache_set_dirty(cache->cmd, to_cblock(i),
+				       is_dirty(cache, to_cblock(i)));
+		if (r)
+			return r;
+	}
+
+	return 0;
+}
+
+static int write_discard_bitset(struct cache *cache)
+{
+	unsigned i, r;
+
+	r = dm_cache_discard_bitset_resize(cache->cmd, cache->discard_block_size,
+					   cache->discard_nr_blocks);
+	if (r) {
+		DMERR("could not resize on-disk discard bitset");
+		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)
+			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("could not write dirty bitset");
+
+	r2 = write_discard_bitset(cache);
+	if (r2)
+		DMERR("could not write discard bitset");
+
+	save_stats(cache);
+
+	r3 = dm_cache_write_hints(cache->cmd, cache->policy);
+	if (r3)
+		DMERR("could not write hints");
+
+	/*
+	 * 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 = dm_cache_commit(cache->cmd, !r1 && !r2 && !r3);
+	if (r4)
+		DMERR("could not write cache metadata.  Data loss may occur.");
+
+	return !r1 && !r2 && !r3 && !r4;
+}
+
+static void cache_postsuspend(struct dm_target *ti)
+{
+	struct cache *cache = ti->private;
+
+	start_quiescing(cache);
+	wait_for_migrations(cache);
+	stop_worker(cache);
+	requeue_deferred_io(cache);
+	stop_quiescing(cache);
+
+	(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;
+
+	r = policy_load_mapping(cache->policy, oblock, cblock, hint, hint_valid);
+	if (r)
+		return r;
+
+	if (dirty)
+		set_dirty(cache, oblock, cblock);
+	else
+		clear_dirty(cache, oblock, cblock);
+
+	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))
+		return true;
+
+	/*
+	 * 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("unable to shrink cache; cache block %llu is dirty",
+			      (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("could not resize cache metadata");
+		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("could not load cache mappings");
+			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("could not load origin discards");
+			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;
+	do_waker(&cache->waker.work);
+}
+
+/*
+ * 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>*
+ */
+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;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		/* Commit to ensure statistics aren't out-of-date */
+		if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti)) {
+			r = dm_cache_commit(cache->cmd, false);
+			if (r)
+				DMERR("could not commit metadata for accurate status");
+		}
+
+		r = dm_cache_get_free_metadata_block_count(cache->cmd,
+							   &nr_free_blocks_metadata);
+		if (r) {
+			DMERR("could not get metadata free block count");
+			goto err;
+		}
+
+		r = dm_cache_get_metadata_dev_size(cache->cmd, &nr_blocks_metadata);
+		if (r) {
+			DMERR("could not get metadata device size");
+			goto err;
+		}
+
+		residency = policy_residency(cache->policy);
+
+		DMEMIT("%u %llu/%llu %u %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,
+		       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));
+
+		if (writethrough_mode(&cache->features))
+			DMEMIT("1 writethrough ");
+
+		else if (passthrough_mode(&cache->features))
+			DMEMIT("1 passthrough ");
+
+		else if (writeback_mode(&cache->features))
+			DMEMIT("1 writeback ");
+
+		else {
+			DMERR("internal error: unknown io mode: %d", (int) cache->features.io_mode);
+			goto err;
+		}
+
+		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 + sz, maxlen - sz);
+			if (r)
+				DMERR("policy_emit_config_values returned %d", r);
+		}
+
+		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");
+}
+
+/*
+ * A cache block range can take two forms:
+ *
+ * i) A single cblock, eg. '3456'
+ * ii) A begin and end cblock with dots 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("invalid cblock range '%s'", 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("begin cblock out of range: %llu >= %llu", b, n);
+		return -EINVAL;
+	}
+
+	if (e > n) {
+		DMERR("end cblock out of range: %llu > %llu", e, n);
+		return -EINVAL;
+	}
+
+	if (b >= e) {
+		DMERR("invalid cblock range: %llu >= %llu", b, e);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int request_invalidation(struct cache *cache, struct cblock_range *range)
+{
+	struct invalidation_request req;
+
+	INIT_LIST_HEAD(&req.list);
+	req.cblocks = range;
+	atomic_set(&req.complete, 0);
+	req.err = 0;
+	init_waitqueue_head(&req.result_wait);
+
+	spin_lock(&cache->invalidation_lock);
+	list_add(&req.list, &cache->invalidation_requests);
+	spin_unlock(&cache->invalidation_lock);
+	wake_worker(cache);
+
+	wait_event(req.result_wait, atomic_read(&req.complete));
+	return req.err;
+}
+
+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->features)) {
+		DMERR("cache has to be in passthrough mode for invalidation");
+		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)
+{
+	struct cache *cache = ti->private;
+
+	if (!argc)
+		return -EINVAL;
+
+	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;
+}
+
+/*
+ * We assume I/O is going to the origin (which is the volume
+ * more likely to have restrictions e.g. by being striped).
+ * (Looking up the exact location of the data would be expensive
+ * and could always be out of date by the time the bio is submitted.)
+ */
+static int cache_bvec_merge(struct dm_target *ti,
+			    struct bvec_merge_data *bvm,
+			    struct bio_vec *biovec, int max_size)
+{
+	struct cache *cache = ti->private;
+	struct request_queue *q = bdev_get_queue(cache->origin_dev->bdev);
+
+	if (!q->merge_bvec_fn)
+		return max_size;
+
+	bvm->bi_bdev = cache->origin_dev->bdev;
+	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
+}
+
+static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
+{
+	/*
+	 * FIXME: these limits may be incompatible with the cache device
+	 */
+	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;
+}
+
+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);
+	}
+	set_discard_limits(cache, limits);
+}
+
+/*----------------------------------------------------------------*/
+
+static struct target_type cache_target = {
+	.name = "cache",
+	.version = {1, 6, 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,
+	.merge = cache_bvec_merge,
+	.io_hints = cache_io_hints,
+};
+
+static int __init dm_cache_init(void)
+{
+	int r;
+
+	r = dm_register_target(&cache_target);
+	if (r) {
+		DMERR("cache target registration failed: %d", r);
+		return r;
+	}
+
+	migration_cache = KMEM_CACHE(dm_cache_migration, 0);
+	if (!migration_cache) {
+		dm_unregister_target(&cache_target);
+		return -ENOMEM;
+	}
+
+	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");