text: /*
   * 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 "dm-io-tracker.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
   */
  
  /*----------------------------------------------------------------*/
  
  /*
   * 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 dm_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);
  		dm_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);
  
  	dm_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;
  
  	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);
  	}
  
  	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);
  	}
  }
  
  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 = dm_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;
  	}
  
  	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);
  	}
  }
  
  /*
   * 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;
  	}
  }
  
  /*----------------------------------------------------------------
   * 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);
  
  	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 bdev_nr_sectors(dev->bdev);
  }
  
  /*----------------------------------------------------------------*/
  
  /*
   * 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);
  	dm_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)
  {
  	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);
  
  	return policy_load_mapping(cache->policy, oblock, cblock, dirty, hint, hint_valid);
  }
  
  /*
   * 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]);
  		break;
  
  	case STATUSTYPE_IMA:
  		DMEMIT_TARGET_NAME_VERSION(ti->type);
  		if (get_cache_mode(cache) == CM_FAIL)
  			DMEMIT(",metadata_mode=fail");
  		else if (get_cache_mode(cache) == CM_READ_ONLY)
  			DMEMIT(",metadata_mode=ro");
  		else
  			DMEMIT(",metadata_mode=rw");
  
  		format_dev_t(buf, cache->metadata_dev->bdev->bd_dev);
  		DMEMIT(",cache_metadata_device=%s", buf);
  		format_dev_t(buf, cache->cache_dev->bdev->bd_dev);
  		DMEMIT(",cache_device=%s", buf);
  		format_dev_t(buf, cache->origin_dev->bdev->bd_dev);
  		DMEMIT(",cache_origin_device=%s", buf);
  		DMEMIT(",writethrough=%c", writethrough_mode(cache) ? 'y' : 'n');
  		DMEMIT(",writeback=%c", writeback_mode(cache) ? 'y' : 'n');
  		DMEMIT(",passthrough=%c", passthrough_mode(cache) ? 'y' : 'n');
  		DMEMIT(",metadata2=%c", cache->features.metadata_version == 2 ? 'y' : 'n');
  		DMEMIT(",no_discard_passdown=%c", cache->features.discard_passdown ? 'n' : 'y');
  		DMEMIT(";");
  		break;
  	}
  
  	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 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");
  