text: /*
   * Copyright (C) 2011-2012 Red Hat UK.
   *
   * This file is released under the GPL.
   */
  
  #include "dm-thin-metadata.h"
  #include "dm-bio-prison.h"
  #include "dm.h"
  
  #include <linux/device-mapper.h>
  #include <linux/dm-io.h>
  #include <linux/dm-kcopyd.h>
  #include <linux/jiffies.h>
  #include <linux/log2.h>
  #include <linux/list.h>
  #include <linux/rculist.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/vmalloc.h>
  #include <linux/sort.h>
  #include <linux/rbtree.h>
  
  #define	DM_MSG_PREFIX	"thin"
  
  /*
   * Tunable constants
   */
  #define ENDIO_HOOK_POOL_SIZE 1024
  #define MAPPING_POOL_SIZE 1024
  #define COMMIT_PERIOD HZ
  #define NO_SPACE_TIMEOUT_SECS 60
  
  static unsigned no_space_timeout_secs = NO_SPACE_TIMEOUT_SECS;
  
  DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
  		"A percentage of time allocated for copy on write");
  
  /*
   * The block size of the device holding pool data must be
   * between 64KB and 1GB.
   */
  #define DATA_DEV_BLOCK_SIZE_MIN_SECTORS (64 * 1024 >> SECTOR_SHIFT)
  #define DATA_DEV_BLOCK_SIZE_MAX_SECTORS (1024 * 1024 * 1024 >> SECTOR_SHIFT)
  
  /*
   * Device id is restricted to 24 bits.
   */
  #define MAX_DEV_ID ((1 << 24) - 1)
  
  /*
   * How do we handle breaking sharing of data blocks?
   * =================================================
   *
   * We use a standard copy-on-write btree to store the mappings for the
   * devices (note I'm talking about copy-on-write of the metadata here, not
   * the data).  When you take an internal snapshot you clone the root node
   * of the origin btree.  After this there is no concept of an origin or a
   * snapshot.  They are just two device trees that happen to point to the
   * same data blocks.
   *
   * When we get a write in we decide if it's to a shared data block using
   * some timestamp magic.  If it is, we have to break sharing.
   *
   * Let's say we write to a shared block in what was the origin.  The
   * steps are:
   *
   * i) plug io further to this physical block. (see bio_prison code).
   *
   * ii) quiesce any read io to that shared data block.  Obviously
   * including all devices that share this block.  (see dm_deferred_set code)
   *
   * iii) copy the data block to a newly allocate block.  This step can be
   * missed out if the io covers the block. (schedule_copy).
   *
   * iv) insert the new mapping into the origin's btree
   * (process_prepared_mapping).  This act of inserting breaks some
   * sharing of btree nodes between the two devices.  Breaking sharing only
   * effects the btree of that specific device.  Btrees for the other
   * devices that share the block never change.  The btree for the origin
   * device as it was after the last commit is untouched, ie. we're using
   * persistent data structures in the functional programming sense.
   *
   * v) unplug io to this physical block, including the io that triggered
   * the breaking of sharing.
   *
   * Steps (ii) and (iii) occur in parallel.
   *
   * The metadata _doesn't_ need to be committed before the io continues.  We
   * get away with this because the io is always written to a _new_ block.
   * If there's a crash, then:
   *
   * - The origin mapping will point to the old origin block (the shared
   * one).  This will contain the data as it was before the io that triggered
   * the breaking of sharing came in.
   *
   * - The snap mapping still points to the old block.  As it would after
   * the commit.
   *
   * The downside of this scheme is the timestamp magic isn't perfect, and
   * will continue to think that data block in the snapshot device is shared
   * even after the write to the origin has broken sharing.  I suspect data
   * blocks will typically be shared by many different devices, so we're
   * breaking sharing n + 1 times, rather than n, where n is the number of
   * devices that reference this data block.  At the moment I think the
   * benefits far, far outweigh the disadvantages.
   */
  
  /*----------------------------------------------------------------*/
  
  /*
   * Key building.
   */
  enum lock_space {
  	VIRTUAL,
  	PHYSICAL
  };
  
  static void build_key(struct dm_thin_device *td, enum lock_space ls,
  		      dm_block_t b, dm_block_t e, struct dm_cell_key *key)
  {
  	key->virtual = (ls == VIRTUAL);
  	key->dev = dm_thin_dev_id(td);
  	key->block_begin = b;
  	key->block_end = e;
  }
  
  static void build_data_key(struct dm_thin_device *td, dm_block_t b,
  			   struct dm_cell_key *key)
  {
  	build_key(td, PHYSICAL, b, b + 1llu, key);
  }
  
  static void build_virtual_key(struct dm_thin_device *td, dm_block_t b,
  			      struct dm_cell_key *key)
  {
  	build_key(td, VIRTUAL, b, b + 1llu, key);
  }
  
  /*----------------------------------------------------------------*/
  
  #define THROTTLE_THRESHOLD (1 * HZ)
  
  struct throttle {
  	struct rw_semaphore lock;
  	unsigned long threshold;
  	bool throttle_applied;
  };
  
  static void throttle_init(struct throttle *t)
  {
  	init_rwsem(&t->lock);
  	t->throttle_applied = false;
  }
  
  static void throttle_work_start(struct throttle *t)
  {
  	t->threshold = jiffies + THROTTLE_THRESHOLD;
  }
  
  static void throttle_work_update(struct throttle *t)
  {
  	if (!t->throttle_applied && jiffies > t->threshold) {
  		down_write(&t->lock);
  		t->throttle_applied = true;
  	}
  }
  
  static void throttle_work_complete(struct throttle *t)
  {
  	if (t->throttle_applied) {
  		t->throttle_applied = false;
  		up_write(&t->lock);
  	}
  }
  
  static void throttle_lock(struct throttle *t)
  {
  	down_read(&t->lock);
  }
  
  static void throttle_unlock(struct throttle *t)
  {
  	up_read(&t->lock);
  }
  
  /*----------------------------------------------------------------*/
  
  /*
   * A pool device ties together a metadata device and a data device.  It
   * also provides the interface for creating and destroying internal
   * devices.
   */
  struct dm_thin_new_mapping;
  
  /*
   * The pool runs in 4 modes.  Ordered in degraded order for comparisons.
   */
  enum pool_mode {
  	PM_WRITE,		/* metadata may be changed */
  	PM_OUT_OF_DATA_SPACE,	/* metadata may be changed, though data may not be allocated */
  	PM_READ_ONLY,		/* metadata may not be changed */
  	PM_FAIL,		/* all I/O fails */
  };
  
  struct pool_features {
  	enum pool_mode mode;
  
  	bool zero_new_blocks:1;
  	bool discard_enabled:1;
  	bool discard_passdown:1;
  	bool error_if_no_space:1;
  };
  
  struct thin_c;
  typedef void (*process_bio_fn)(struct thin_c *tc, struct bio *bio);
  typedef void (*process_cell_fn)(struct thin_c *tc, struct dm_bio_prison_cell *cell);
  typedef void (*process_mapping_fn)(struct dm_thin_new_mapping *m);
  
  #define CELL_SORT_ARRAY_SIZE 8192
  
  struct pool {
  	struct list_head list;
  	struct dm_target *ti;	/* Only set if a pool target is bound */
  
  	struct mapped_device *pool_md;
  	struct block_device *md_dev;
  	struct dm_pool_metadata *pmd;
  
  	dm_block_t low_water_blocks;
  	uint32_t sectors_per_block;
  	int sectors_per_block_shift;
  
  	struct pool_features pf;
  	bool low_water_triggered:1;	/* A dm event has been sent */
  	bool suspended:1;
  	bool out_of_data_space:1;
  
  	struct dm_bio_prison *prison;
  	struct dm_kcopyd_client *copier;
  
  	struct workqueue_struct *wq;
  	struct throttle throttle;
  	struct work_struct worker;
  	struct delayed_work waker;
  	struct delayed_work no_space_timeout;
  
  	unsigned long last_commit_jiffies;
  	unsigned ref_count;
  
  	spinlock_t lock;
  	struct bio_list deferred_flush_bios;
  	struct list_head prepared_mappings;
  	struct list_head prepared_discards;
  	struct list_head prepared_discards_pt2;
  	struct list_head active_thins;
  
  	struct dm_deferred_set *shared_read_ds;
  	struct dm_deferred_set *all_io_ds;
  
  	struct dm_thin_new_mapping *next_mapping;
  	mempool_t *mapping_pool;
  
  	process_bio_fn process_bio;
  	process_bio_fn process_discard;
  
  	process_cell_fn process_cell;
  	process_cell_fn process_discard_cell;
  
  	process_mapping_fn process_prepared_mapping;
  	process_mapping_fn process_prepared_discard;
  	process_mapping_fn process_prepared_discard_pt2;
  
  	struct dm_bio_prison_cell **cell_sort_array;
  };
  
  static enum pool_mode get_pool_mode(struct pool *pool);
  static void metadata_operation_failed(struct pool *pool, const char *op, int r);
  
  /*
   * Target context for a pool.
   */
  struct pool_c {
  	struct dm_target *ti;
  	struct pool *pool;
  	struct dm_dev *data_dev;
  	struct dm_dev *metadata_dev;
  	struct dm_target_callbacks callbacks;
  
  	dm_block_t low_water_blocks;
  	struct pool_features requested_pf; /* Features requested during table load */
  	struct pool_features adjusted_pf;  /* Features used after adjusting for constituent devices */
  };
  
  /*
   * Target context for a thin.
   */
  struct thin_c {
  	struct list_head list;
  	struct dm_dev *pool_dev;
  	struct dm_dev *origin_dev;
  	sector_t origin_size;
  	dm_thin_id dev_id;
  
  	struct pool *pool;
  	struct dm_thin_device *td;
  	struct mapped_device *thin_md;
  
  	bool requeue_mode:1;
  	spinlock_t lock;
  	struct list_head deferred_cells;
  	struct bio_list deferred_bio_list;
  	struct bio_list retry_on_resume_list;
  	struct rb_root sort_bio_list; /* sorted list of deferred bios */
  
  	/*
  	 * Ensures the thin is not destroyed until the worker has finished
  	 * iterating the active_thins list.
  	 */
  	atomic_t refcount;
  	struct completion can_destroy;
  };
  
  /*----------------------------------------------------------------*/
  
  static bool block_size_is_power_of_two(struct pool *pool)
  {
  	return pool->sectors_per_block_shift >= 0;
  }
  
  static sector_t block_to_sectors(struct pool *pool, dm_block_t b)
  {
  	return block_size_is_power_of_two(pool) ?
  		(b << pool->sectors_per_block_shift) :
  		(b * pool->sectors_per_block);
  }
  
  /*----------------------------------------------------------------*/
  
  struct discard_op {
  	struct thin_c *tc;
  	struct blk_plug plug;
  	struct bio *parent_bio;
  	struct bio *bio;
  };
  
  static void begin_discard(struct discard_op *op, struct thin_c *tc, struct bio *parent)
  {
  	BUG_ON(!parent);
  
  	op->tc = tc;
  	blk_start_plug(&op->plug);
  	op->parent_bio = parent;
  	op->bio = NULL;
  }
  
  static int issue_discard(struct discard_op *op, dm_block_t data_b, dm_block_t data_e)
  {
  	struct thin_c *tc = op->tc;
  	sector_t s = block_to_sectors(tc->pool, data_b);
  	sector_t len = block_to_sectors(tc->pool, data_e - data_b);
  
  	return __blkdev_issue_discard(tc->pool_dev->bdev, s, len,
  				      GFP_NOWAIT, 0, &op->bio);
  }
  
  static void end_discard(struct discard_op *op, int r)
  {
  	if (op->bio) {
  		/*
  		 * Even if one of the calls to issue_discard failed, we
  		 * need to wait for the chain to complete.
  		 */
  		bio_chain(op->bio, op->parent_bio);
  		bio_set_op_attrs(op->bio, REQ_OP_DISCARD, 0);
  		submit_bio(op->bio);
  	}
  
  	blk_finish_plug(&op->plug);
  
  	/*
  	 * Even if r is set, there could be sub discards in flight that we
  	 * need to wait for.
  	 */
  	if (r && !op->parent_bio->bi_error)
  		op->parent_bio->bi_error = r;
  	bio_endio(op->parent_bio);
  }
  
  /*----------------------------------------------------------------*/
  
  /*
   * wake_worker() is used when new work is queued and when pool_resume is
   * ready to continue deferred IO processing.
   */
  static void wake_worker(struct pool *pool)
  {
  	queue_work(pool->wq, &pool->worker);
  }
  
  /*----------------------------------------------------------------*/
  
  static int bio_detain(struct pool *pool, struct dm_cell_key *key, struct bio *bio,
  		      struct dm_bio_prison_cell **cell_result)
  {
  	int r;
  	struct dm_bio_prison_cell *cell_prealloc;
  
  	/*
  	 * Allocate a cell from the prison's mempool.
  	 * This might block but it can't fail.
  	 */
  	cell_prealloc = dm_bio_prison_alloc_cell(pool->prison, GFP_NOIO);
  
  	r = dm_bio_detain(pool->prison, key, bio, cell_prealloc, cell_result);
  	if (r)
  		/*
  		 * We reused an old cell; we can get rid of
  		 * the new one.
  		 */
  		dm_bio_prison_free_cell(pool->prison, cell_prealloc);
  
  	return r;
  }
  
  static void cell_release(struct pool *pool,
  			 struct dm_bio_prison_cell *cell,
  			 struct bio_list *bios)
  {
  	dm_cell_release(pool->prison, cell, bios);
  	dm_bio_prison_free_cell(pool->prison, cell);
  }
  
  static void cell_visit_release(struct pool *pool,
  			       void (*fn)(void *, struct dm_bio_prison_cell *),
  			       void *context,
  			       struct dm_bio_prison_cell *cell)
  {
  	dm_cell_visit_release(pool->prison, fn, context, cell);
  	dm_bio_prison_free_cell(pool->prison, cell);
  }
  
  static void cell_release_no_holder(struct pool *pool,
  				   struct dm_bio_prison_cell *cell,
  				   struct bio_list *bios)
  {
  	dm_cell_release_no_holder(pool->prison, cell, bios);
  	dm_bio_prison_free_cell(pool->prison, cell);
  }
  
  static void cell_error_with_code(struct pool *pool,
  				 struct dm_bio_prison_cell *cell, int error_code)
  {
  	dm_cell_error(pool->prison, cell, error_code);
  	dm_bio_prison_free_cell(pool->prison, cell);
  }
  
  static int get_pool_io_error_code(struct pool *pool)
  {
  	return pool->out_of_data_space ? -ENOSPC : -EIO;
  }
  
  static void cell_error(struct pool *pool, struct dm_bio_prison_cell *cell)
  {
  	int error = get_pool_io_error_code(pool);
  
  	cell_error_with_code(pool, cell, error);
  }
  
  static void cell_success(struct pool *pool, struct dm_bio_prison_cell *cell)
  {
  	cell_error_with_code(pool, cell, 0);
  }
  
  static void cell_requeue(struct pool *pool, struct dm_bio_prison_cell *cell)
  {
  	cell_error_with_code(pool, cell, DM_ENDIO_REQUEUE);
  }
  
  /*----------------------------------------------------------------*/
  
  /*
   * A global list of pools that uses a struct mapped_device as a key.
   */
  static struct dm_thin_pool_table {
  	struct mutex mutex;
  	struct list_head pools;
  } dm_thin_pool_table;
  
  static void pool_table_init(void)
  {
  	mutex_init(&dm_thin_pool_table.mutex);
  	INIT_LIST_HEAD(&dm_thin_pool_table.pools);
  }
  
  static void __pool_table_insert(struct pool *pool)
  {
  	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
  	list_add(&pool->list, &dm_thin_pool_table.pools);
  }
  
  static void __pool_table_remove(struct pool *pool)
  {
  	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
  	list_del(&pool->list);
  }
  
  static struct pool *__pool_table_lookup(struct mapped_device *md)
  {
  	struct pool *pool = NULL, *tmp;
  
  	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
  
  	list_for_each_entry(tmp, &dm_thin_pool_table.pools, list) {
  		if (tmp->pool_md == md) {
  			pool = tmp;
  			break;
  		}
  	}
  
  	return pool;
  }
  
  static struct pool *__pool_table_lookup_metadata_dev(struct block_device *md_dev)
  {
  	struct pool *pool = NULL, *tmp;
  
  	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
  
  	list_for_each_entry(tmp, &dm_thin_pool_table.pools, list) {
  		if (tmp->md_dev == md_dev) {
  			pool = tmp;
  			break;
  		}
  	}
  
  	return pool;
  }
  
  /*----------------------------------------------------------------*/
  
  struct dm_thin_endio_hook {
  	struct thin_c *tc;
  	struct dm_deferred_entry *shared_read_entry;
  	struct dm_deferred_entry *all_io_entry;
  	struct dm_thin_new_mapping *overwrite_mapping;
  	struct rb_node rb_node;
  	struct dm_bio_prison_cell *cell;
  };
  
  static void __merge_bio_list(struct bio_list *bios, struct bio_list *master)
  {
  	bio_list_merge(bios, master);
  	bio_list_init(master);
  }
  
  static void error_bio_list(struct bio_list *bios, int error)
  {
  	struct bio *bio;
  
  	while ((bio = bio_list_pop(bios))) {
  		bio->bi_error = error;
  		bio_endio(bio);
  	}
  }
  
  static void error_thin_bio_list(struct thin_c *tc, struct bio_list *master, int error)
  {
  	struct bio_list bios;
  	unsigned long flags;
  
  	bio_list_init(&bios);
  
  	spin_lock_irqsave(&tc->lock, flags);
  	__merge_bio_list(&bios, master);
  	spin_unlock_irqrestore(&tc->lock, flags);
  
  	error_bio_list(&bios, error);
  }
  
  static void requeue_deferred_cells(struct thin_c *tc)
  {
  	struct pool *pool = tc->pool;
  	unsigned long flags;
  	struct list_head cells;
  	struct dm_bio_prison_cell *cell, *tmp;
  
  	INIT_LIST_HEAD(&cells);
  
  	spin_lock_irqsave(&tc->lock, flags);
  	list_splice_init(&tc->deferred_cells, &cells);
  	spin_unlock_irqrestore(&tc->lock, flags);
  
  	list_for_each_entry_safe(cell, tmp, &cells, user_list)
  		cell_requeue(pool, cell);
  }
  
  static void requeue_io(struct thin_c *tc)
  {
  	struct bio_list bios;
  	unsigned long flags;
  
  	bio_list_init(&bios);
  
  	spin_lock_irqsave(&tc->lock, flags);
  	__merge_bio_list(&bios, &tc->deferred_bio_list);
  	__merge_bio_list(&bios, &tc->retry_on_resume_list);
  	spin_unlock_irqrestore(&tc->lock, flags);
  
  	error_bio_list(&bios, DM_ENDIO_REQUEUE);
  	requeue_deferred_cells(tc);
  }
  
  static void error_retry_list_with_code(struct pool *pool, int error)
  {
  	struct thin_c *tc;
  
  	rcu_read_lock();
  	list_for_each_entry_rcu(tc, &pool->active_thins, list)
  		error_thin_bio_list(tc, &tc->retry_on_resume_list, error);
  	rcu_read_unlock();
  }
  
  static void error_retry_list(struct pool *pool)
  {
  	int error = get_pool_io_error_code(pool);
  
  	error_retry_list_with_code(pool, error);
  }
  
  /*
   * This section of code contains the logic for processing a thin device's IO.
   * Much of the code depends on pool object resources (lists, workqueues, etc)
   * but most is exclusively called from the thin target rather than the thin-pool
   * target.
   */
  
  static dm_block_t get_bio_block(struct thin_c *tc, struct bio *bio)
  {
  	struct pool *pool = tc->pool;
  	sector_t block_nr = bio->bi_iter.bi_sector;
  
  	if (block_size_is_power_of_two(pool))
  		block_nr >>= pool->sectors_per_block_shift;
  	else
  		(void) sector_div(block_nr, pool->sectors_per_block);
  
  	return block_nr;
  }
  
  /*
   * Returns the _complete_ blocks that this bio covers.
   */
  static void get_bio_block_range(struct thin_c *tc, struct bio *bio,
  				dm_block_t *begin, dm_block_t *end)
  {
  	struct pool *pool = tc->pool;
  	sector_t b = bio->bi_iter.bi_sector;
  	sector_t e = b + (bio->bi_iter.bi_size >> SECTOR_SHIFT);
  
  	b += pool->sectors_per_block - 1ull; /* so we round up */
  
  	if (block_size_is_power_of_two(pool)) {
  		b >>= pool->sectors_per_block_shift;
  		e >>= pool->sectors_per_block_shift;
  	} else {
  		(void) sector_div(b, pool->sectors_per_block);
  		(void) sector_div(e, pool->sectors_per_block);
  	}
  
  	if (e < b)
  		/* Can happen if the bio is within a single block. */
  		e = b;
  
  	*begin = b;
  	*end = e;
  }
  
  static void remap(struct thin_c *tc, struct bio *bio, dm_block_t block)
  {
  	struct pool *pool = tc->pool;
  	sector_t bi_sector = bio->bi_iter.bi_sector;
  
  	bio->bi_bdev = tc->pool_dev->bdev;
  	if (block_size_is_power_of_two(pool))
  		bio->bi_iter.bi_sector =
  			(block << pool->sectors_per_block_shift) |
  			(bi_sector & (pool->sectors_per_block - 1));
  	else
  		bio->bi_iter.bi_sector = (block * pool->sectors_per_block) +
  				 sector_div(bi_sector, pool->sectors_per_block);
  }
  
  static void remap_to_origin(struct thin_c *tc, struct bio *bio)
  {
  	bio->bi_bdev = tc->origin_dev->bdev;
  }
  
  static int bio_triggers_commit(struct thin_c *tc, struct bio *bio)
  {
  	return (bio->bi_opf & (REQ_PREFLUSH | REQ_FUA)) &&
  		dm_thin_changed_this_transaction(tc->td);
  }
  
  static void inc_all_io_entry(struct pool *pool, struct bio *bio)
  {
  	struct dm_thin_endio_hook *h;
  
  	if (bio_op(bio) == REQ_OP_DISCARD)
  		return;
  
  	h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  	h->all_io_entry = dm_deferred_entry_inc(pool->all_io_ds);
  }
  
  static void issue(struct thin_c *tc, struct bio *bio)
  {
  	struct pool *pool = tc->pool;
  	unsigned long flags;
  
  	if (!bio_triggers_commit(tc, bio)) {
  		generic_make_request(bio);
  		return;
  	}
  
  	/*
  	 * Complete bio with an error if earlier I/O caused changes to
  	 * the metadata that can't be committed e.g, due to I/O errors
  	 * on the metadata device.
  	 */
  	if (dm_thin_aborted_changes(tc->td)) {
  		bio_io_error(bio);
  		return;
  	}
  
  	/*
  	 * Batch together any bios that trigger commits and then issue a
  	 * single commit for them in process_deferred_bios().
  	 */
  	spin_lock_irqsave(&pool->lock, flags);
  	bio_list_add(&pool->deferred_flush_bios, bio);
  	spin_unlock_irqrestore(&pool->lock, flags);
  }
  
  static void remap_to_origin_and_issue(struct thin_c *tc, struct bio *bio)
  {
  	remap_to_origin(tc, bio);
  	issue(tc, bio);
  }
  
  static void remap_and_issue(struct thin_c *tc, struct bio *bio,
  			    dm_block_t block)
  {
  	remap(tc, bio, block);
  	issue(tc, bio);
  }
  
  /*----------------------------------------------------------------*/
  
  /*
   * Bio endio functions.
   */
  struct dm_thin_new_mapping {
  	struct list_head list;
  
  	bool pass_discard:1;
  	bool maybe_shared:1;
  
  	/*
  	 * Track quiescing, copying and zeroing preparation actions.  When this
  	 * counter hits zero the block is prepared and can be inserted into the
  	 * btree.
  	 */
  	atomic_t prepare_actions;
  
  	int err;
  	struct thin_c *tc;
  	dm_block_t virt_begin, virt_end;
  	dm_block_t data_block;
  	struct dm_bio_prison_cell *cell;
  
  	/*
  	 * If the bio covers the whole area of a block then we can avoid
  	 * zeroing or copying.  Instead this bio is hooked.  The bio will
  	 * still be in the cell, so care has to be taken to avoid issuing
  	 * the bio twice.
  	 */
  	struct bio *bio;
  	bio_end_io_t *saved_bi_end_io;
  };
  
  static void __complete_mapping_preparation(struct dm_thin_new_mapping *m)
  {
  	struct pool *pool = m->tc->pool;
  
  	if (atomic_dec_and_test(&m->prepare_actions)) {
  		list_add_tail(&m->list, &pool->prepared_mappings);
  		wake_worker(pool);
  	}
  }
  
  static void complete_mapping_preparation(struct dm_thin_new_mapping *m)
  {
  	unsigned long flags;
  	struct pool *pool = m->tc->pool;
  
  	spin_lock_irqsave(&pool->lock, flags);
  	__complete_mapping_preparation(m);
  	spin_unlock_irqrestore(&pool->lock, flags);
  }
  
  static void copy_complete(int read_err, unsigned long write_err, void *context)
  {
  	struct dm_thin_new_mapping *m = context;
  
  	m->err = read_err || write_err ? -EIO : 0;
  	complete_mapping_preparation(m);
  }
  
  static void overwrite_endio(struct bio *bio)
  {
  	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  	struct dm_thin_new_mapping *m = h->overwrite_mapping;
  
  	bio->bi_end_io = m->saved_bi_end_io;
  
  	m->err = bio->bi_error;
  	complete_mapping_preparation(m);
  }
  
  /*----------------------------------------------------------------*/
  
  /*
   * Workqueue.
   */
  
  /*
   * Prepared mapping jobs.
   */
  
  /*
   * This sends the bios in the cell, except the original holder, back
   * to the deferred_bios list.
   */
  static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *cell)
  {
  	struct pool *pool = tc->pool;
  	unsigned long flags;
  
  	spin_lock_irqsave(&tc->lock, flags);
  	cell_release_no_holder(pool, cell, &tc->deferred_bio_list);
  	spin_unlock_irqrestore(&tc->lock, flags);
  
  	wake_worker(pool);
  }
  
  static void thin_defer_bio(struct thin_c *tc, struct bio *bio);
  
  struct remap_info {
  	struct thin_c *tc;
  	struct bio_list defer_bios;
  	struct bio_list issue_bios;
  };
  
  static void __inc_remap_and_issue_cell(void *context,
  				       struct dm_bio_prison_cell *cell)
  {
  	struct remap_info *info = context;
  	struct bio *bio;
  
  	while ((bio = bio_list_pop(&cell->bios))) {
  		if (bio->bi_opf & (REQ_PREFLUSH | REQ_FUA) ||
  		    bio_op(bio) == REQ_OP_DISCARD)
  			bio_list_add(&info->defer_bios, bio);
  		else {
  			inc_all_io_entry(info->tc->pool, bio);
  
  			/*
  			 * We can't issue the bios with the bio prison lock
  			 * held, so we add them to a list to issue on
  			 * return from this function.
  			 */
  			bio_list_add(&info->issue_bios, bio);
  		}
  	}
  }
  
  static void inc_remap_and_issue_cell(struct thin_c *tc,
  				     struct dm_bio_prison_cell *cell,
  				     dm_block_t block)
  {
  	struct bio *bio;
  	struct remap_info info;
  
  	info.tc = tc;
  	bio_list_init(&info.defer_bios);
  	bio_list_init(&info.issue_bios);
  
  	/*
  	 * We have to be careful to inc any bios we're about to issue
  	 * before the cell is released, and avoid a race with new bios
  	 * being added to the cell.
  	 */
  	cell_visit_release(tc->pool, __inc_remap_and_issue_cell,
  			   &info, cell);
  
  	while ((bio = bio_list_pop(&info.defer_bios)))
  		thin_defer_bio(tc, bio);
  
  	while ((bio = bio_list_pop(&info.issue_bios)))
  		remap_and_issue(info.tc, bio, block);
  }
  
  static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
  {
  	cell_error(m->tc->pool, m->cell);
  	list_del(&m->list);
  	mempool_free(m, m->tc->pool->mapping_pool);
  }
  
  static void process_prepared_mapping(struct dm_thin_new_mapping *m)
  {
  	struct thin_c *tc = m->tc;
  	struct pool *pool = tc->pool;
  	struct bio *bio = m->bio;
  	int r;
  
  	if (m->err) {
  		cell_error(pool, m->cell);
  		goto out;
  	}
  
  	/*
  	 * Commit the prepared block into the mapping btree.
  	 * Any I/O for this block arriving after this point will get
  	 * remapped to it directly.
  	 */
  	r = dm_thin_insert_block(tc->td, m->virt_begin, m->data_block);
  	if (r) {
  		metadata_operation_failed(pool, "dm_thin_insert_block", r);
  		cell_error(pool, m->cell);
  		goto out;
  	}
  
  	/*
  	 * Release any bios held while the block was being provisioned.
  	 * If we are processing a write bio that completely covers the block,
  	 * we already processed it so can ignore it now when processing
  	 * the bios in the cell.
  	 */
  	if (bio) {
  		inc_remap_and_issue_cell(tc, m->cell, m->data_block);
  		bio_endio(bio);
  	} else {
  		inc_all_io_entry(tc->pool, m->cell->holder);
  		remap_and_issue(tc, m->cell->holder, m->data_block);
  		inc_remap_and_issue_cell(tc, m->cell, m->data_block);
  	}
  
  out:
  	list_del(&m->list);
  	mempool_free(m, pool->mapping_pool);
  }
  
  /*----------------------------------------------------------------*/
  
  static void free_discard_mapping(struct dm_thin_new_mapping *m)
  {
  	struct thin_c *tc = m->tc;
  	if (m->cell)
  		cell_defer_no_holder(tc, m->cell);
  	mempool_free(m, tc->pool->mapping_pool);
  }
  
  static void process_prepared_discard_fail(struct dm_thin_new_mapping *m)
  {
  	bio_io_error(m->bio);
  	free_discard_mapping(m);
  }
  
  static void process_prepared_discard_success(struct dm_thin_new_mapping *m)
  {
  	bio_endio(m->bio);
  	free_discard_mapping(m);
  }
  
  static void process_prepared_discard_no_passdown(struct dm_thin_new_mapping *m)
  {
  	int r;
  	struct thin_c *tc = m->tc;
  
  	r = dm_thin_remove_range(tc->td, m->cell->key.block_begin, m->cell->key.block_end);
  	if (r) {
  		metadata_operation_failed(tc->pool, "dm_thin_remove_range", r);
  		bio_io_error(m->bio);
  	} else
  		bio_endio(m->bio);
  
  	cell_defer_no_holder(tc, m->cell);
  	mempool_free(m, tc->pool->mapping_pool);
  }
  
  /*----------------------------------------------------------------*/
  
  static void passdown_double_checking_shared_status(struct dm_thin_new_mapping *m,
  						   struct bio *discard_parent)
  {
  	/*
  	 * We've already unmapped this range of blocks, but before we
  	 * passdown we have to check that these blocks are now unused.
  	 */
  	int r = 0;
  	bool used = true;
  	struct thin_c *tc = m->tc;
  	struct pool *pool = tc->pool;
  	dm_block_t b = m->data_block, e, end = m->data_block + m->virt_end - m->virt_begin;
  	struct discard_op op;
  
  	begin_discard(&op, tc, discard_parent);
  	while (b != end) {
  		/* find start of unmapped run */
  		for (; b < end; b++) {
  			r = dm_pool_block_is_used(pool->pmd, b, &used);
  			if (r)
  				goto out;
  
  			if (!used)
  				break;
  		}
  
  		if (b == end)
  			break;
  
  		/* find end of run */
  		for (e = b + 1; e != end; e++) {
  			r = dm_pool_block_is_used(pool->pmd, e, &used);
  			if (r)
  				goto out;
  
  			if (used)
  				break;
  		}
  
  		r = issue_discard(&op, b, e);
  		if (r)
  			goto out;
  
  		b = e;
  	}
  out:
  	end_discard(&op, r);
  }
  
  static void queue_passdown_pt2(struct dm_thin_new_mapping *m)
  {
  	unsigned long flags;
  	struct pool *pool = m->tc->pool;
  
  	spin_lock_irqsave(&pool->lock, flags);
  	list_add_tail(&m->list, &pool->prepared_discards_pt2);
  	spin_unlock_irqrestore(&pool->lock, flags);
  	wake_worker(pool);
  }
  
  static void passdown_endio(struct bio *bio)
  {
  	/*
  	 * It doesn't matter if the passdown discard failed, we still want
  	 * to unmap (we ignore err).
  	 */
  	queue_passdown_pt2(bio->bi_private);
  }
  
  static void process_prepared_discard_passdown_pt1(struct dm_thin_new_mapping *m)
  {
  	int r;
  	struct thin_c *tc = m->tc;
  	struct pool *pool = tc->pool;
  	struct bio *discard_parent;
  	dm_block_t data_end = m->data_block + (m->virt_end - m->virt_begin);
  
  	/*
  	 * Only this thread allocates blocks, so we can be sure that the
  	 * newly unmapped blocks will not be allocated before the end of
  	 * the function.
  	 */
  	r = dm_thin_remove_range(tc->td, m->virt_begin, m->virt_end);
  	if (r) {
  		metadata_operation_failed(pool, "dm_thin_remove_range", r);
  		bio_io_error(m->bio);
  		cell_defer_no_holder(tc, m->cell);
  		mempool_free(m, pool->mapping_pool);
  		return;
  	}
  
  	discard_parent = bio_alloc(GFP_NOIO, 1);
  	if (!discard_parent) {
  		DMWARN("%s: unable to allocate top level discard bio for passdown. Skipping passdown.",
  		       dm_device_name(tc->pool->pool_md));
  		queue_passdown_pt2(m);
  
  	} else {
  		discard_parent->bi_end_io = passdown_endio;
  		discard_parent->bi_private = m;
  
  		if (m->maybe_shared)
  			passdown_double_checking_shared_status(m, discard_parent);
  		else {
  			struct discard_op op;
  
  			begin_discard(&op, tc, discard_parent);
  			r = issue_discard(&op, m->data_block, data_end);
  			end_discard(&op, r);
  		}
  	}
  
  	/*
  	 * Increment the unmapped blocks.  This prevents a race between the
  	 * passdown io and reallocation of freed blocks.
  	 */
  	r = dm_pool_inc_data_range(pool->pmd, m->data_block, data_end);
  	if (r) {
  		metadata_operation_failed(pool, "dm_pool_inc_data_range", r);
  		bio_io_error(m->bio);
  		cell_defer_no_holder(tc, m->cell);
  		mempool_free(m, pool->mapping_pool);
  		return;
  	}
  }
  
  static void process_prepared_discard_passdown_pt2(struct dm_thin_new_mapping *m)
  {
  	int r;
  	struct thin_c *tc = m->tc;
  	struct pool *pool = tc->pool;
  
  	/*
  	 * The passdown has completed, so now we can decrement all those
  	 * unmapped blocks.
  	 */
  	r = dm_pool_dec_data_range(pool->pmd, m->data_block,
  				   m->data_block + (m->virt_end - m->virt_begin));
  	if (r) {
  		metadata_operation_failed(pool, "dm_pool_dec_data_range", r);
  		bio_io_error(m->bio);
  	} else
  		bio_endio(m->bio);
  
  	cell_defer_no_holder(tc, m->cell);
  	mempool_free(m, pool->mapping_pool);
  }
  
  static void process_prepared(struct pool *pool, struct list_head *head,
  			     process_mapping_fn *fn)
  {
  	unsigned long flags;
  	struct list_head maps;
  	struct dm_thin_new_mapping *m, *tmp;
  
  	INIT_LIST_HEAD(&maps);
  	spin_lock_irqsave(&pool->lock, flags);
  	list_splice_init(head, &maps);
  	spin_unlock_irqrestore(&pool->lock, flags);
  
  	list_for_each_entry_safe(m, tmp, &maps, list)
  		(*fn)(m);
  }
  
  /*
   * Deferred bio jobs.
   */
  static int io_overlaps_block(struct pool *pool, struct bio *bio)
  {
  	return bio->bi_iter.bi_size ==
  		(pool->sectors_per_block << SECTOR_SHIFT);
  }
  
  static int io_overwrites_block(struct pool *pool, struct bio *bio)
  {
  	return (bio_data_dir(bio) == WRITE) &&
  		io_overlaps_block(pool, bio);
  }
  
  static void save_and_set_endio(struct bio *bio, bio_end_io_t **save,
  			       bio_end_io_t *fn)
  {
  	*save = bio->bi_end_io;
  	bio->bi_end_io = fn;
  }
  
  static int ensure_next_mapping(struct pool *pool)
  {
  	if (pool->next_mapping)
  		return 0;
  
  	pool->next_mapping = mempool_alloc(pool->mapping_pool, GFP_ATOMIC);
  
  	return pool->next_mapping ? 0 : -ENOMEM;
  }
  
  static struct dm_thin_new_mapping *get_next_mapping(struct pool *pool)
  {
  	struct dm_thin_new_mapping *m = pool->next_mapping;
  
  	BUG_ON(!pool->next_mapping);
  
  	memset(m, 0, sizeof(struct dm_thin_new_mapping));
  	INIT_LIST_HEAD(&m->list);
  	m->bio = NULL;
  
  	pool->next_mapping = NULL;
  
  	return m;
  }
  
  static void ll_zero(struct thin_c *tc, struct dm_thin_new_mapping *m,
  		    sector_t begin, sector_t end)
  {
  	int r;
  	struct dm_io_region to;
  
  	to.bdev = tc->pool_dev->bdev;
  	to.sector = begin;
  	to.count = end - begin;
  
  	r = dm_kcopyd_zero(tc->pool->copier, 1, &to, 0, copy_complete, m);
  	if (r < 0) {
  		DMERR_LIMIT("dm_kcopyd_zero() failed");
  		copy_complete(1, 1, m);
  	}
  }
  
  static void remap_and_issue_overwrite(struct thin_c *tc, struct bio *bio,
  				      dm_block_t data_begin,
  				      struct dm_thin_new_mapping *m)
  {
  	struct pool *pool = tc->pool;
  	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  
  	h->overwrite_mapping = m;
  	m->bio = bio;
  	save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
  	inc_all_io_entry(pool, bio);
  	remap_and_issue(tc, bio, data_begin);
  }
  
  /*
   * A partial copy also needs to zero the uncopied region.
   */
  static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
  			  struct dm_dev *origin, dm_block_t data_origin,
  			  dm_block_t data_dest,
  			  struct dm_bio_prison_cell *cell, struct bio *bio,
  			  sector_t len)
  {
  	int r;
  	struct pool *pool = tc->pool;
  	struct dm_thin_new_mapping *m = get_next_mapping(pool);
  
  	m->tc = tc;
  	m->virt_begin = virt_block;
  	m->virt_end = virt_block + 1u;
  	m->data_block = data_dest;
  	m->cell = cell;
  
  	/*
  	 * quiesce action + copy action + an extra reference held for the
  	 * duration of this function (we may need to inc later for a
  	 * partial zero).
  	 */
  	atomic_set(&m->prepare_actions, 3);
  
  	if (!dm_deferred_set_add_work(pool->shared_read_ds, &m->list))
  		complete_mapping_preparation(m); /* already quiesced */
  
  	/*
  	 * IO to pool_dev remaps to the pool target's data_dev.
  	 *
  	 * If the whole block of data is being overwritten, we can issue the
  	 * bio immediately. Otherwise we use kcopyd to clone the data first.
  	 */
  	if (io_overwrites_block(pool, bio))
  		remap_and_issue_overwrite(tc, bio, data_dest, m);
  	else {
  		struct dm_io_region from, to;
  
  		from.bdev = origin->bdev;
  		from.sector = data_origin * pool->sectors_per_block;
  		from.count = len;
  
  		to.bdev = tc->pool_dev->bdev;
  		to.sector = data_dest * pool->sectors_per_block;
  		to.count = len;
  
  		r = dm_kcopyd_copy(pool->copier, &from, 1, &to,
  				   0, copy_complete, m);
  		if (r < 0) {
  			DMERR_LIMIT("dm_kcopyd_copy() failed");
  			copy_complete(1, 1, m);
  
  			/*
  			 * We allow the zero to be issued, to simplify the
  			 * error path.  Otherwise we'd need to start
  			 * worrying about decrementing the prepare_actions
  			 * counter.
  			 */
  		}
  
  		/*
  		 * Do we need to zero a tail region?
  		 */
  		if (len < pool->sectors_per_block && pool->pf.zero_new_blocks) {
  			atomic_inc(&m->prepare_actions);
  			ll_zero(tc, m,
  				data_dest * pool->sectors_per_block + len,
  				(data_dest + 1) * pool->sectors_per_block);
  		}
  	}
  
  	complete_mapping_preparation(m); /* drop our ref */
  }
  
  static void schedule_internal_copy(struct thin_c *tc, dm_block_t virt_block,
  				   dm_block_t data_origin, dm_block_t data_dest,
  				   struct dm_bio_prison_cell *cell, struct bio *bio)
  {
  	schedule_copy(tc, virt_block, tc->pool_dev,
  		      data_origin, data_dest, cell, bio,
  		      tc->pool->sectors_per_block);
  }
  
  static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
  			  dm_block_t data_block, struct dm_bio_prison_cell *cell,
  			  struct bio *bio)
  {
  	struct pool *pool = tc->pool;
  	struct dm_thin_new_mapping *m = get_next_mapping(pool);
  
  	atomic_set(&m->prepare_actions, 1); /* no need to quiesce */
  	m->tc = tc;
  	m->virt_begin = virt_block;
  	m->virt_end = virt_block + 1u;
  	m->data_block = data_block;
  	m->cell = cell;
  
  	/*
  	 * If the whole block of data is being overwritten or we are not
  	 * zeroing pre-existing data, we can issue the bio immediately.
  	 * Otherwise we use kcopyd to zero the data first.
  	 */
  	if (pool->pf.zero_new_blocks) {
  		if (io_overwrites_block(pool, bio))
  			remap_and_issue_overwrite(tc, bio, data_block, m);
  		else
  			ll_zero(tc, m, data_block * pool->sectors_per_block,
  				(data_block + 1) * pool->sectors_per_block);
  	} else
  		process_prepared_mapping(m);
  }
  
  static void schedule_external_copy(struct thin_c *tc, dm_block_t virt_block,
  				   dm_block_t data_dest,
  				   struct dm_bio_prison_cell *cell, struct bio *bio)
  {
  	struct pool *pool = tc->pool;
  	sector_t virt_block_begin = virt_block * pool->sectors_per_block;
  	sector_t virt_block_end = (virt_block + 1) * pool->sectors_per_block;
  
  	if (virt_block_end <= tc->origin_size)
  		schedule_copy(tc, virt_block, tc->origin_dev,
  			      virt_block, data_dest, cell, bio,
  			      pool->sectors_per_block);
  
  	else if (virt_block_begin < tc->origin_size)
  		schedule_copy(tc, virt_block, tc->origin_dev,
  			      virt_block, data_dest, cell, bio,
  			      tc->origin_size - virt_block_begin);
  
  	else
  		schedule_zero(tc, virt_block, data_dest, cell, bio);
  }
  
  static void set_pool_mode(struct pool *pool, enum pool_mode new_mode);
  
  static void check_for_space(struct pool *pool)
  {
  	int r;
  	dm_block_t nr_free;
  
  	if (get_pool_mode(pool) != PM_OUT_OF_DATA_SPACE)
  		return;
  
  	r = dm_pool_get_free_block_count(pool->pmd, &nr_free);
  	if (r)
  		return;
  
  	if (nr_free)
  		set_pool_mode(pool, PM_WRITE);
  }
  
  /*
   * A non-zero return indicates read_only or fail_io mode.
   * Many callers don't care about the return value.
   */
  static int commit(struct pool *pool)
  {
  	int r;
  
  	if (get_pool_mode(pool) >= PM_READ_ONLY)
  		return -EINVAL;
  
  	r = dm_pool_commit_metadata(pool->pmd);
  	if (r)
  		metadata_operation_failed(pool, "dm_pool_commit_metadata", r);
  	else
  		check_for_space(pool);
  
  	return r;
  }
  
  static void check_low_water_mark(struct pool *pool, dm_block_t free_blocks)
  {
  	unsigned long flags;
  
  	if (free_blocks <= pool->low_water_blocks && !pool->low_water_triggered) {
  		DMWARN("%s: reached low water mark for data device: sending event.",
  		       dm_device_name(pool->pool_md));
  		spin_lock_irqsave(&pool->lock, flags);
  		pool->low_water_triggered = true;
  		spin_unlock_irqrestore(&pool->lock, flags);
  		dm_table_event(pool->ti->table);
  	}
  }
  
  static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
  {
  	int r;
  	dm_block_t free_blocks;
  	struct pool *pool = tc->pool;
  
  	if (WARN_ON(get_pool_mode(pool) != PM_WRITE))
  		return -EINVAL;
  
  	r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
  	if (r) {
  		metadata_operation_failed(pool, "dm_pool_get_free_block_count", r);
  		return r;
  	}
  
  	check_low_water_mark(pool, free_blocks);
  
  	if (!free_blocks) {
  		/*
  		 * Try to commit to see if that will free up some
  		 * more space.
  		 */
  		r = commit(pool);
  		if (r)
  			return r;
  
  		r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
  		if (r) {
  			metadata_operation_failed(pool, "dm_pool_get_free_block_count", r);
  			return r;
  		}
  
  		if (!free_blocks) {
  			set_pool_mode(pool, PM_OUT_OF_DATA_SPACE);
  			return -ENOSPC;
  		}
  	}
  
  	r = dm_pool_alloc_data_block(pool->pmd, result);
  	if (r) {
  		metadata_operation_failed(pool, "dm_pool_alloc_data_block", r);
  		return r;
  	}
  
  	return 0;
  }
  
  /*
   * If we have run out of space, queue bios until the device is
   * resumed, presumably after having been reloaded with more space.
   */
  static void retry_on_resume(struct bio *bio)
  {
  	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  	struct thin_c *tc = h->tc;
  	unsigned long flags;
  
  	spin_lock_irqsave(&tc->lock, flags);
  	bio_list_add(&tc->retry_on_resume_list, bio);
  	spin_unlock_irqrestore(&tc->lock, flags);
  }
  
  static int should_error_unserviceable_bio(struct pool *pool)
  {
  	enum pool_mode m = get_pool_mode(pool);
  
  	switch (m) {
  	case PM_WRITE:
  		/* Shouldn't get here */
  		DMERR_LIMIT("bio unserviceable, yet pool is in PM_WRITE mode");
  		return -EIO;
  
  	case PM_OUT_OF_DATA_SPACE:
  		return pool->pf.error_if_no_space ? -ENOSPC : 0;
  
  	case PM_READ_ONLY:
  	case PM_FAIL:
  		return -EIO;
  	default:
  		/* Shouldn't get here */
  		DMERR_LIMIT("bio unserviceable, yet pool has an unknown mode");
  		return -EIO;
  	}
  }
  
  static void handle_unserviceable_bio(struct pool *pool, struct bio *bio)
  {
  	int error = should_error_unserviceable_bio(pool);
  
  	if (error) {
  		bio->bi_error = error;
  		bio_endio(bio);
  	} else
  		retry_on_resume(bio);
  }
  
  static void retry_bios_on_resume(struct pool *pool, struct dm_bio_prison_cell *cell)
  {
  	struct bio *bio;
  	struct bio_list bios;
  	int error;
  
  	error = should_error_unserviceable_bio(pool);
  	if (error) {
  		cell_error_with_code(pool, cell, error);
  		return;
  	}
  
  	bio_list_init(&bios);
  	cell_release(pool, cell, &bios);
  
  	while ((bio = bio_list_pop(&bios)))
  		retry_on_resume(bio);
  }
  
  static void process_discard_cell_no_passdown(struct thin_c *tc,
  					     struct dm_bio_prison_cell *virt_cell)
  {
  	struct pool *pool = tc->pool;
  	struct dm_thin_new_mapping *m = get_next_mapping(pool);
  
  	/*
  	 * We don't need to lock the data blocks, since there's no
  	 * passdown.  We only lock data blocks for allocation and breaking sharing.
  	 */
  	m->tc = tc;
  	m->virt_begin = virt_cell->key.block_begin;
  	m->virt_end = virt_cell->key.block_end;
  	m->cell = virt_cell;
  	m->bio = virt_cell->holder;
  
  	if (!dm_deferred_set_add_work(pool->all_io_ds, &m->list))
  		pool->process_prepared_discard(m);
  }
  
  static void break_up_discard_bio(struct thin_c *tc, dm_block_t begin, dm_block_t end,
  				 struct bio *bio)
  {
  	struct pool *pool = tc->pool;
  
  	int r;
  	bool maybe_shared;
  	struct dm_cell_key data_key;
  	struct dm_bio_prison_cell *data_cell;
  	struct dm_thin_new_mapping *m;
  	dm_block_t virt_begin, virt_end, data_begin;
  
  	while (begin != end) {
  		r = ensure_next_mapping(pool);
  		if (r)
  			/* we did our best */
  			return;
  
  		r = dm_thin_find_mapped_range(tc->td, begin, end, &virt_begin, &virt_end,
  					      &data_begin, &maybe_shared);
  		if (r)
  			/*
  			 * Silently fail, letting any mappings we've
  			 * created complete.
  			 */
  			break;
  
  		build_key(tc->td, PHYSICAL, data_begin, data_begin + (virt_end - virt_begin), &data_key);
  		if (bio_detain(tc->pool, &data_key, NULL, &data_cell)) {
  			/* contention, we'll give up with this range */
  			begin = virt_end;
  			continue;
  		}
  
  		/*
  		 * IO may still be going to the destination block.  We must
  		 * quiesce before we can do the removal.
  		 */
  		m = get_next_mapping(pool);
  		m->tc = tc;
  		m->maybe_shared = maybe_shared;
  		m->virt_begin = virt_begin;
  		m->virt_end = virt_end;
  		m->data_block = data_begin;
  		m->cell = data_cell;
  		m->bio = bio;
  
  		/*
  		 * The parent bio must not complete before sub discard bios are
  		 * chained to it (see end_discard's bio_chain)!
  		 *
  		 * This per-mapping bi_remaining increment is paired with
  		 * the implicit decrement that occurs via bio_endio() in
  		 * end_discard().
  		 */
  		bio_inc_remaining(bio);
  		if (!dm_deferred_set_add_work(pool->all_io_ds, &m->list))
  			pool->process_prepared_discard(m);
  
  		begin = virt_end;
  	}
  }
  
  static void process_discard_cell_passdown(struct thin_c *tc, struct dm_bio_prison_cell *virt_cell)
  {
  	struct bio *bio = virt_cell->holder;
  	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  
  	/*
  	 * The virt_cell will only get freed once the origin bio completes.
  	 * This means it will remain locked while all the individual
  	 * passdown bios are in flight.
  	 */
  	h->cell = virt_cell;
  	break_up_discard_bio(tc, virt_cell->key.block_begin, virt_cell->key.block_end, bio);
  
  	/*
  	 * We complete the bio now, knowing that the bi_remaining field
  	 * will prevent completion until the sub range discards have
  	 * completed.
  	 */
  	bio_endio(bio);
  }
  
  static void process_discard_bio(struct thin_c *tc, struct bio *bio)
  {
  	dm_block_t begin, end;
  	struct dm_cell_key virt_key;
  	struct dm_bio_prison_cell *virt_cell;
  
  	get_bio_block_range(tc, bio, &begin, &end);
  	if (begin == end) {
  		/*
  		 * The discard covers less than a block.
  		 */
  		bio_endio(bio);
  		return;
  	}
  
  	build_key(tc->td, VIRTUAL, begin, end, &virt_key);
  	if (bio_detain(tc->pool, &virt_key, bio, &virt_cell))
  		/*
  		 * Potential starvation issue: We're relying on the
  		 * fs/application being well behaved, and not trying to
  		 * send IO to a region at the same time as discarding it.
  		 * If they do this persistently then it's possible this
  		 * cell will never be granted.
  		 */
  		return;
  
  	tc->pool->process_discard_cell(tc, virt_cell);
  }
  
  static void break_sharing(struct thin_c *tc, struct bio *bio, dm_block_t block,
  			  struct dm_cell_key *key,
  			  struct dm_thin_lookup_result *lookup_result,
  			  struct dm_bio_prison_cell *cell)
  {
  	int r;
  	dm_block_t data_block;
  	struct pool *pool = tc->pool;
  
  	r = alloc_data_block(tc, &data_block);
  	switch (r) {
  	case 0:
  		schedule_internal_copy(tc, block, lookup_result->block,
  				       data_block, cell, bio);
  		break;
  
  	case -ENOSPC:
  		retry_bios_on_resume(pool, cell);
  		break;
  
  	default:
  		DMERR_LIMIT("%s: alloc_data_block() failed: error = %d",
  			    __func__, r);
  		cell_error(pool, cell);
  		break;
  	}
  }
  
  static void __remap_and_issue_shared_cell(void *context,
  					  struct dm_bio_prison_cell *cell)
  {
  	struct remap_info *info = context;
  	struct bio *bio;
  
  	while ((bio = bio_list_pop(&cell->bios))) {
  		if ((bio_data_dir(bio) == WRITE) ||
  		    (bio->bi_opf & (REQ_PREFLUSH | REQ_FUA) ||
  		     bio_op(bio) == REQ_OP_DISCARD))
  			bio_list_add(&info->defer_bios, bio);
  		else {
  			struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));;
  
  			h->shared_read_entry = dm_deferred_entry_inc(info->tc->pool->shared_read_ds);
  			inc_all_io_entry(info->tc->pool, bio);
  			bio_list_add(&info->issue_bios, bio);
  		}
  	}
  }
  
  static void remap_and_issue_shared_cell(struct thin_c *tc,
  					struct dm_bio_prison_cell *cell,
  					dm_block_t block)
  {
  	struct bio *bio;
  	struct remap_info info;
  
  	info.tc = tc;
  	bio_list_init(&info.defer_bios);
  	bio_list_init(&info.issue_bios);
  
  	cell_visit_release(tc->pool, __remap_and_issue_shared_cell,
  			   &info, cell);
  
  	while ((bio = bio_list_pop(&info.defer_bios)))
  		thin_defer_bio(tc, bio);
  
  	while ((bio = bio_list_pop(&info.issue_bios)))
  		remap_and_issue(tc, bio, block);
  }
  
  static void process_shared_bio(struct thin_c *tc, struct bio *bio,
  			       dm_block_t block,
  			       struct dm_thin_lookup_result *lookup_result,
  			       struct dm_bio_prison_cell *virt_cell)
  {
  	struct dm_bio_prison_cell *data_cell;
  	struct pool *pool = tc->pool;
  	struct dm_cell_key key;
  
  	/*
  	 * If cell is already occupied, then sharing is already in the process
  	 * of being broken so we have nothing further to do here.
  	 */
  	build_data_key(tc->td, lookup_result->block, &key);
  	if (bio_detain(pool, &key, bio, &data_cell)) {
  		cell_defer_no_holder(tc, virt_cell);
  		return;
  	}
  
  	if (bio_data_dir(bio) == WRITE && bio->bi_iter.bi_size) {
  		break_sharing(tc, bio, block, &key, lookup_result, data_cell);
  		cell_defer_no_holder(tc, virt_cell);
  	} else {
  		struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  
  		h->shared_read_entry = dm_deferred_entry_inc(pool->shared_read_ds);
  		inc_all_io_entry(pool, bio);
  		remap_and_issue(tc, bio, lookup_result->block);
  
  		remap_and_issue_shared_cell(tc, data_cell, lookup_result->block);
  		remap_and_issue_shared_cell(tc, virt_cell, lookup_result->block);
  	}
  }
  
  static void provision_block(struct thin_c *tc, struct bio *bio, dm_block_t block,
  			    struct dm_bio_prison_cell *cell)
  {
  	int r;
  	dm_block_t data_block;
  	struct pool *pool = tc->pool;
  
  	/*
  	 * Remap empty bios (flushes) immediately, without provisioning.
  	 */
  	if (!bio->bi_iter.bi_size) {
  		inc_all_io_entry(pool, bio);
  		cell_defer_no_holder(tc, cell);
  
  		remap_and_issue(tc, bio, 0);
  		return;
  	}
  
  	/*
  	 * Fill read bios with zeroes and complete them immediately.
  	 */
  	if (bio_data_dir(bio) == READ) {
  		zero_fill_bio(bio);
  		cell_defer_no_holder(tc, cell);
  		bio_endio(bio);
  		return;
  	}
  
  	r = alloc_data_block(tc, &data_block);
  	switch (r) {
  	case 0:
  		if (tc->origin_dev)
  			schedule_external_copy(tc, block, data_block, cell, bio);
  		else
  			schedule_zero(tc, block, data_block, cell, bio);
  		break;
  
  	case -ENOSPC:
  		retry_bios_on_resume(pool, cell);
  		break;
  
  	default:
  		DMERR_LIMIT("%s: alloc_data_block() failed: error = %d",
  			    __func__, r);
  		cell_error(pool, cell);
  		break;
  	}
  }
  
  static void process_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
  {
  	int r;
  	struct pool *pool = tc->pool;
  	struct bio *bio = cell->holder;
  	dm_block_t block = get_bio_block(tc, bio);
  	struct dm_thin_lookup_result lookup_result;
  
  	if (tc->requeue_mode) {
  		cell_requeue(pool, cell);
  		return;
  	}
  
  	r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
  	switch (r) {
  	case 0:
  		if (lookup_result.shared)
  			process_shared_bio(tc, bio, block, &lookup_result, cell);
  		else {
  			inc_all_io_entry(pool, bio);
  			remap_and_issue(tc, bio, lookup_result.block);
  			inc_remap_and_issue_cell(tc, cell, lookup_result.block);
  		}
  		break;
  
  	case -ENODATA:
  		if (bio_data_dir(bio) == READ && tc->origin_dev) {
  			inc_all_io_entry(pool, bio);
  			cell_defer_no_holder(tc, cell);
  
  			if (bio_end_sector(bio) <= tc->origin_size)
  				remap_to_origin_and_issue(tc, bio);
  
  			else if (bio->bi_iter.bi_sector < tc->origin_size) {
  				zero_fill_bio(bio);
  				bio->bi_iter.bi_size = (tc->origin_size - bio->bi_iter.bi_sector) << SECTOR_SHIFT;
  				remap_to_origin_and_issue(tc, bio);
  
  			} else {
  				zero_fill_bio(bio);
  				bio_endio(bio);
  			}
  		} else
  			provision_block(tc, bio, block, cell);
  		break;
  
  	default:
  		DMERR_LIMIT("%s: dm_thin_find_block() failed: error = %d",
  			    __func__, r);
  		cell_defer_no_holder(tc, cell);
  		bio_io_error(bio);
  		break;
  	}
  }
  
  static void process_bio(struct thin_c *tc, struct bio *bio)
  {
  	struct pool *pool = tc->pool;
  	dm_block_t block = get_bio_block(tc, bio);
  	struct dm_bio_prison_cell *cell;
  	struct dm_cell_key key;
  
  	/*
  	 * If cell is already occupied, then the block is already
  	 * being provisioned so we have nothing further to do here.
  	 */
  	build_virtual_key(tc->td, block, &key);
  	if (bio_detain(pool, &key, bio, &cell))
  		return;
  
  	process_cell(tc, cell);
  }
  
  static void __process_bio_read_only(struct thin_c *tc, struct bio *bio,
  				    struct dm_bio_prison_cell *cell)
  {
  	int r;
  	int rw = bio_data_dir(bio);
  	dm_block_t block = get_bio_block(tc, bio);
  	struct dm_thin_lookup_result lookup_result;
  
  	r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
  	switch (r) {
  	case 0:
  		if (lookup_result.shared && (rw == WRITE) && bio->bi_iter.bi_size) {
  			handle_unserviceable_bio(tc->pool, bio);
  			if (cell)
  				cell_defer_no_holder(tc, cell);
  		} else {
  			inc_all_io_entry(tc->pool, bio);
  			remap_and_issue(tc, bio, lookup_result.block);
  			if (cell)
  				inc_remap_and_issue_cell(tc, cell, lookup_result.block);
  		}
  		break;
  
  	case -ENODATA:
  		if (cell)
  			cell_defer_no_holder(tc, cell);
  		if (rw != READ) {
  			handle_unserviceable_bio(tc->pool, bio);
  			break;
  		}
  
  		if (tc->origin_dev) {
  			inc_all_io_entry(tc->pool, bio);
  			remap_to_origin_and_issue(tc, bio);
  			break;
  		}
  
  		zero_fill_bio(bio);
  		bio_endio(bio);
  		break;
  
  	default:
  		DMERR_LIMIT("%s: dm_thin_find_block() failed: error = %d",
  			    __func__, r);
  		if (cell)
  			cell_defer_no_holder(tc, cell);
  		bio_io_error(bio);
  		break;
  	}
  }
  
  static void process_bio_read_only(struct thin_c *tc, struct bio *bio)
  {
  	__process_bio_read_only(tc, bio, NULL);
  }
  
  static void process_cell_read_only(struct thin_c *tc, struct dm_bio_prison_cell *cell)
  {
  	__process_bio_read_only(tc, cell->holder, cell);
  }
  
  static void process_bio_success(struct thin_c *tc, struct bio *bio)
  {
  	bio_endio(bio);
  }
  
  static void process_bio_fail(struct thin_c *tc, struct bio *bio)
  {
  	bio_io_error(bio);
  }
  
  static void process_cell_success(struct thin_c *tc, struct dm_bio_prison_cell *cell)
  {
  	cell_success(tc->pool, cell);
  }
  
  static void process_cell_fail(struct thin_c *tc, struct dm_bio_prison_cell *cell)
  {
  	cell_error(tc->pool, cell);
  }
  
  /*
   * FIXME: should we also commit due to size of transaction, measured in
   * metadata blocks?
   */
  static int need_commit_due_to_time(struct pool *pool)
  {
  	return !time_in_range(jiffies, pool->last_commit_jiffies,
  			      pool->last_commit_jiffies + COMMIT_PERIOD);
  }
  
  #define thin_pbd(node) rb_entry((node), struct dm_thin_endio_hook, rb_node)
  #define thin_bio(pbd) dm_bio_from_per_bio_data((pbd), sizeof(struct dm_thin_endio_hook))
  
  static void __thin_bio_rb_add(struct thin_c *tc, struct bio *bio)
  {
  	struct rb_node **rbp, *parent;
  	struct dm_thin_endio_hook *pbd;
  	sector_t bi_sector = bio->bi_iter.bi_sector;
  
  	rbp = &tc->sort_bio_list.rb_node;
  	parent = NULL;
  	while (*rbp) {
  		parent = *rbp;
  		pbd = thin_pbd(parent);
  
  		if (bi_sector < thin_bio(pbd)->bi_iter.bi_sector)
  			rbp = &(*rbp)->rb_left;
  		else
  			rbp = &(*rbp)->rb_right;
  	}
  
  	pbd = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  	rb_link_node(&pbd->rb_node, parent, rbp);
  	rb_insert_color(&pbd->rb_node, &tc->sort_bio_list);
  }
  
  static void __extract_sorted_bios(struct thin_c *tc)
  {
  	struct rb_node *node;
  	struct dm_thin_endio_hook *pbd;
  	struct bio *bio;
  
  	for (node = rb_first(&tc->sort_bio_list); node; node = rb_next(node)) {
  		pbd = thin_pbd(node);
  		bio = thin_bio(pbd);
  
  		bio_list_add(&tc->deferred_bio_list, bio);
  		rb_erase(&pbd->rb_node, &tc->sort_bio_list);
  	}
  
  	WARN_ON(!RB_EMPTY_ROOT(&tc->sort_bio_list));
  }
  
  static void __sort_thin_deferred_bios(struct thin_c *tc)
  {
  	struct bio *bio;
  	struct bio_list bios;
  
  	bio_list_init(&bios);
  	bio_list_merge(&bios, &tc->deferred_bio_list);
  	bio_list_init(&tc->deferred_bio_list);
  
  	/* Sort deferred_bio_list using rb-tree */
  	while ((bio = bio_list_pop(&bios)))
  		__thin_bio_rb_add(tc, bio);
  
  	/*
  	 * Transfer the sorted bios in sort_bio_list back to
  	 * deferred_bio_list to allow lockless submission of
  	 * all bios.
  	 */
  	__extract_sorted_bios(tc);
  }
  
  static void process_thin_deferred_bios(struct thin_c *tc)
  {
  	struct pool *pool = tc->pool;
  	unsigned long flags;
  	struct bio *bio;
  	struct bio_list bios;
  	struct blk_plug plug;
  	unsigned count = 0;
  
  	if (tc->requeue_mode) {
  		error_thin_bio_list(tc, &tc->deferred_bio_list, DM_ENDIO_REQUEUE);
  		return;
  	}
  
  	bio_list_init(&bios);
  
  	spin_lock_irqsave(&tc->lock, flags);
  
  	if (bio_list_empty(&tc->deferred_bio_list)) {
  		spin_unlock_irqrestore(&tc->lock, flags);
  		return;
  	}
  
  	__sort_thin_deferred_bios(tc);
  
  	bio_list_merge(&bios, &tc->deferred_bio_list);
  	bio_list_init(&tc->deferred_bio_list);
  
  	spin_unlock_irqrestore(&tc->lock, flags);
  
  	blk_start_plug(&plug);
  	while ((bio = bio_list_pop(&bios))) {
  		/*
  		 * If we've got no free new_mapping structs, and processing
  		 * this bio might require one, we pause until there are some
  		 * prepared mappings to process.
  		 */
  		if (ensure_next_mapping(pool)) {
  			spin_lock_irqsave(&tc->lock, flags);
  			bio_list_add(&tc->deferred_bio_list, bio);
  			bio_list_merge(&tc->deferred_bio_list, &bios);
  			spin_unlock_irqrestore(&tc->lock, flags);
  			break;
  		}
  
  		if (bio_op(bio) == REQ_OP_DISCARD)
  			pool->process_discard(tc, bio);
  		else
  			pool->process_bio(tc, bio);
  
  		if ((count++ & 127) == 0) {
  			throttle_work_update(&pool->throttle);
  			dm_pool_issue_prefetches(pool->pmd);
  		}
  	}
  	blk_finish_plug(&plug);
  }
  
  static int cmp_cells(const void *lhs, const void *rhs)
  {
  	struct dm_bio_prison_cell *lhs_cell = *((struct dm_bio_prison_cell **) lhs);
  	struct dm_bio_prison_cell *rhs_cell = *((struct dm_bio_prison_cell **) rhs);
  
  	BUG_ON(!lhs_cell->holder);
  	BUG_ON(!rhs_cell->holder);
  
  	if (lhs_cell->holder->bi_iter.bi_sector < rhs_cell->holder->bi_iter.bi_sector)
  		return -1;
  
  	if (lhs_cell->holder->bi_iter.bi_sector > rhs_cell->holder->bi_iter.bi_sector)
  		return 1;
  
  	return 0;
  }
  
  static unsigned sort_cells(struct pool *pool, struct list_head *cells)
  {
  	unsigned count = 0;
  	struct dm_bio_prison_cell *cell, *tmp;
  
  	list_for_each_entry_safe(cell, tmp, cells, user_list) {
  		if (count >= CELL_SORT_ARRAY_SIZE)
  			break;
  
  		pool->cell_sort_array[count++] = cell;
  		list_del(&cell->user_list);
  	}
  
  	sort(pool->cell_sort_array, count, sizeof(cell), cmp_cells, NULL);
  
  	return count;
  }
  
  static void process_thin_deferred_cells(struct thin_c *tc)
  {
  	struct pool *pool = tc->pool;
  	unsigned long flags;
  	struct list_head cells;
  	struct dm_bio_prison_cell *cell;
  	unsigned i, j, count;
  
  	INIT_LIST_HEAD(&cells);
  
  	spin_lock_irqsave(&tc->lock, flags);
  	list_splice_init(&tc->deferred_cells, &cells);
  	spin_unlock_irqrestore(&tc->lock, flags);
  
  	if (list_empty(&cells))
  		return;
  
  	do {
  		count = sort_cells(tc->pool, &cells);
  
  		for (i = 0; i < count; i++) {
  			cell = pool->cell_sort_array[i];
  			BUG_ON(!cell->holder);
  
  			/*
  			 * If we've got no free new_mapping structs, and processing
  			 * this bio might require one, we pause until there are some
  			 * prepared mappings to process.
  			 */
  			if (ensure_next_mapping(pool)) {
  				for (j = i; j < count; j++)
  					list_add(&pool->cell_sort_array[j]->user_list, &cells);
  
  				spin_lock_irqsave(&tc->lock, flags);
  				list_splice(&cells, &tc->deferred_cells);
  				spin_unlock_irqrestore(&tc->lock, flags);
  				return;
  			}
  
  			if (bio_op(cell->holder) == REQ_OP_DISCARD)
  				pool->process_discard_cell(tc, cell);
  			else
  				pool->process_cell(tc, cell);
  		}
  	} while (!list_empty(&cells));
  }
  
  static void thin_get(struct thin_c *tc);
  static void thin_put(struct thin_c *tc);
  
  /*
   * We can't hold rcu_read_lock() around code that can block.  So we
   * find a thin with the rcu lock held; bump a refcount; then drop
   * the lock.
   */
  static struct thin_c *get_first_thin(struct pool *pool)
  {
  	struct thin_c *tc = NULL;
  
  	rcu_read_lock();
  	if (!list_empty(&pool->active_thins)) {
  		tc = list_entry_rcu(pool->active_thins.next, struct thin_c, list);
  		thin_get(tc);
  	}
  	rcu_read_unlock();
  
  	return tc;
  }
  
  static struct thin_c *get_next_thin(struct pool *pool, struct thin_c *tc)
  {
  	struct thin_c *old_tc = tc;
  
  	rcu_read_lock();
  	list_for_each_entry_continue_rcu(tc, &pool->active_thins, list) {
  		thin_get(tc);
  		thin_put(old_tc);
  		rcu_read_unlock();
  		return tc;
  	}
  	thin_put(old_tc);
  	rcu_read_unlock();
  
  	return NULL;
  }
  
  static void process_deferred_bios(struct pool *pool)
  {
  	unsigned long flags;
  	struct bio *bio;
  	struct bio_list bios;
  	struct thin_c *tc;
  
  	tc = get_first_thin(pool);
  	while (tc) {
  		process_thin_deferred_cells(tc);
  		process_thin_deferred_bios(tc);
  		tc = get_next_thin(pool, tc);
  	}
  
  	/*
  	 * If there are any deferred flush bios, we must commit
  	 * the metadata before issuing them.
  	 */
  	bio_list_init(&bios);
  	spin_lock_irqsave(&pool->lock, flags);
  	bio_list_merge(&bios, &pool->deferred_flush_bios);
  	bio_list_init(&pool->deferred_flush_bios);
  	spin_unlock_irqrestore(&pool->lock, flags);
  
  	if (bio_list_empty(&bios) &&
  	    !(dm_pool_changed_this_transaction(pool->pmd) && need_commit_due_to_time(pool)))
  		return;
  
  	if (commit(pool)) {
  		while ((bio = bio_list_pop(&bios)))
  			bio_io_error(bio);
  		return;
  	}
  	pool->last_commit_jiffies = jiffies;
  
  	while ((bio = bio_list_pop(&bios)))
  		generic_make_request(bio);
  }
  
  static void do_worker(struct work_struct *ws)
  {
  	struct pool *pool = container_of(ws, struct pool, worker);
  
  	throttle_work_start(&pool->throttle);
  	dm_pool_issue_prefetches(pool->pmd);
  	throttle_work_update(&pool->throttle);
  	process_prepared(pool, &pool->prepared_mappings, &pool->process_prepared_mapping);
  	throttle_work_update(&pool->throttle);
  	process_prepared(pool, &pool->prepared_discards, &pool->process_prepared_discard);
  	throttle_work_update(&pool->throttle);
  	process_prepared(pool, &pool->prepared_discards_pt2, &pool->process_prepared_discard_pt2);
  	throttle_work_update(&pool->throttle);
  	process_deferred_bios(pool);
  	throttle_work_complete(&pool->throttle);
  }
  
  /*
   * We want to commit periodically so that not too much
   * unwritten data builds up.
   */
  static void do_waker(struct work_struct *ws)
  {
  	struct pool *pool = container_of(to_delayed_work(ws), struct pool, waker);
  	wake_worker(pool);
  	queue_delayed_work(pool->wq, &pool->waker, COMMIT_PERIOD);
  }
  
  static void notify_of_pool_mode_change_to_oods(struct pool *pool);
  
  /*
   * We're holding onto IO to allow userland time to react.  After the
   * timeout either the pool will have been resized (and thus back in
   * PM_WRITE mode), or we degrade to PM_OUT_OF_DATA_SPACE w/ error_if_no_space.
   */
  static void do_no_space_timeout(struct work_struct *ws)
  {
  	struct pool *pool = container_of(to_delayed_work(ws), struct pool,
  					 no_space_timeout);
  
  	if (get_pool_mode(pool) == PM_OUT_OF_DATA_SPACE && !pool->pf.error_if_no_space) {
  		pool->pf.error_if_no_space = true;
  		notify_of_pool_mode_change_to_oods(pool);
  		error_retry_list_with_code(pool, -ENOSPC);
  	}
  }
  
  /*----------------------------------------------------------------*/
  
  struct pool_work {
  	struct work_struct worker;
  	struct completion complete;
  };
  
  static struct pool_work *to_pool_work(struct work_struct *ws)
  {
  	return container_of(ws, struct pool_work, worker);
  }
  
  static void pool_work_complete(struct pool_work *pw)
  {
  	complete(&pw->complete);
  }
  
  static void pool_work_wait(struct pool_work *pw, struct pool *pool,
  			   void (*fn)(struct work_struct *))
  {
  	INIT_WORK_ONSTACK(&pw->worker, fn);
  	init_completion(&pw->complete);
  	queue_work(pool->wq, &pw->worker);
  	wait_for_completion(&pw->complete);
  }
  
  /*----------------------------------------------------------------*/
  
  struct noflush_work {
  	struct pool_work pw;
  	struct thin_c *tc;
  };
  
  static struct noflush_work *to_noflush(struct work_struct *ws)
  {
  	return container_of(to_pool_work(ws), struct noflush_work, pw);
  }
  
  static void do_noflush_start(struct work_struct *ws)
  {
  	struct noflush_work *w = to_noflush(ws);
  	w->tc->requeue_mode = true;
  	requeue_io(w->tc);
  	pool_work_complete(&w->pw);
  }
  
  static void do_noflush_stop(struct work_struct *ws)
  {
  	struct noflush_work *w = to_noflush(ws);
  	w->tc->requeue_mode = false;
  	pool_work_complete(&w->pw);
  }
  
  static void noflush_work(struct thin_c *tc, void (*fn)(struct work_struct *))
  {
  	struct noflush_work w;
  
  	w.tc = tc;
  	pool_work_wait(&w.pw, tc->pool, fn);
  }
  
  /*----------------------------------------------------------------*/
  
  static enum pool_mode get_pool_mode(struct pool *pool)
  {
  	return pool->pf.mode;
  }
  
  static void notify_of_pool_mode_change(struct pool *pool, const char *new_mode)
  {
  	dm_table_event(pool->ti->table);
  	DMINFO("%s: switching pool to %s mode",
  	       dm_device_name(pool->pool_md), new_mode);
  }
  
  static void notify_of_pool_mode_change_to_oods(struct pool *pool)
  {
  	if (!pool->pf.error_if_no_space)
  		notify_of_pool_mode_change(pool, "out-of-data-space (queue IO)");
  	else
  		notify_of_pool_mode_change(pool, "out-of-data-space (error IO)");
  }
  
  static bool passdown_enabled(struct pool_c *pt)
  {
  	return pt->adjusted_pf.discard_passdown;
  }
  
  static void set_discard_callbacks(struct pool *pool)
  {
  	struct pool_c *pt = pool->ti->private;
  
  	if (passdown_enabled(pt)) {
  		pool->process_discard_cell = process_discard_cell_passdown;
  		pool->process_prepared_discard = process_prepared_discard_passdown_pt1;
  		pool->process_prepared_discard_pt2 = process_prepared_discard_passdown_pt2;
  	} else {
  		pool->process_discard_cell = process_discard_cell_no_passdown;
  		pool->process_prepared_discard = process_prepared_discard_no_passdown;
  	}
  }
  
  static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
  {
  	struct pool_c *pt = pool->ti->private;
  	bool needs_check = dm_pool_metadata_needs_check(pool->pmd);
  	enum pool_mode old_mode = get_pool_mode(pool);
  	unsigned long no_space_timeout = ACCESS_ONCE(no_space_timeout_secs) * HZ;
  
  	/*
  	 * Never allow the pool to transition to PM_WRITE mode if user
  	 * intervention is required to verify metadata and data consistency.
  	 */
  	if (new_mode == PM_WRITE && needs_check) {
  		DMERR("%s: unable to switch pool to write mode until repaired.",
  		      dm_device_name(pool->pool_md));
  		if (old_mode != new_mode)
  			new_mode = old_mode;
  		else
  			new_mode = PM_READ_ONLY;
  	}
  	/*
  	 * If we were in PM_FAIL mode, rollback of metadata failed.  We're
  	 * not going to recover without a thin_repair.	So we never let the
  	 * pool move out of the old mode.
  	 */
  	if (old_mode == PM_FAIL)
  		new_mode = old_mode;
  
  	switch (new_mode) {
  	case PM_FAIL:
  		if (old_mode != new_mode)
  			notify_of_pool_mode_change(pool, "failure");
  		dm_pool_metadata_read_only(pool->pmd);
  		pool->process_bio = process_bio_fail;
  		pool->process_discard = process_bio_fail;
  		pool->process_cell = process_cell_fail;
  		pool->process_discard_cell = process_cell_fail;
  		pool->process_prepared_mapping = process_prepared_mapping_fail;
  		pool->process_prepared_discard = process_prepared_discard_fail;
  
  		error_retry_list(pool);
  		break;
  
  	case PM_READ_ONLY:
  		if (old_mode != new_mode)
  			notify_of_pool_mode_change(pool, "read-only");
  		dm_pool_metadata_read_only(pool->pmd);
  		pool->process_bio = process_bio_read_only;
  		pool->process_discard = process_bio_success;
  		pool->process_cell = process_cell_read_only;
  		pool->process_discard_cell = process_cell_success;
  		pool->process_prepared_mapping = process_prepared_mapping_fail;
  		pool->process_prepared_discard = process_prepared_discard_success;
  
  		error_retry_list(pool);
  		break;
  
  	case PM_OUT_OF_DATA_SPACE:
  		/*
  		 * Ideally we'd never hit this state; the low water mark
  		 * would trigger userland to extend the pool before we
  		 * completely run out of data space.  However, many small
  		 * IOs to unprovisioned space can consume data space at an
  		 * alarming rate.  Adjust your low water mark if you're
  		 * frequently seeing this mode.
  		 */
  		if (old_mode != new_mode)
  			notify_of_pool_mode_change_to_oods(pool);
  		pool->out_of_data_space = true;
  		pool->process_bio = process_bio_read_only;
  		pool->process_discard = process_discard_bio;
  		pool->process_cell = process_cell_read_only;
  		pool->process_prepared_mapping = process_prepared_mapping;
  		set_discard_callbacks(pool);
  
  		if (!pool->pf.error_if_no_space && no_space_timeout)
  			queue_delayed_work(pool->wq, &pool->no_space_timeout, no_space_timeout);
  		break;
  
  	case PM_WRITE:
  		if (old_mode != new_mode)
  			notify_of_pool_mode_change(pool, "write");
  		pool->out_of_data_space = false;
  		pool->pf.error_if_no_space = pt->requested_pf.error_if_no_space;
  		dm_pool_metadata_read_write(pool->pmd);
  		pool->process_bio = process_bio;
  		pool->process_discard = process_discard_bio;
  		pool->process_cell = process_cell;
  		pool->process_prepared_mapping = process_prepared_mapping;
  		set_discard_callbacks(pool);
  		break;
  	}
  
  	pool->pf.mode = new_mode;
  	/*
  	 * The pool mode may have changed, sync it so bind_control_target()
  	 * doesn't cause an unexpected mode transition on resume.
  	 */
  	pt->adjusted_pf.mode = new_mode;
  }
  
  static void abort_transaction(struct pool *pool)
  {
  	const char *dev_name = dm_device_name(pool->pool_md);
  
  	DMERR_LIMIT("%s: aborting current metadata transaction", dev_name);
  	if (dm_pool_abort_metadata(pool->pmd)) {
  		DMERR("%s: failed to abort metadata transaction", dev_name);
  		set_pool_mode(pool, PM_FAIL);
  	}
  
  	if (dm_pool_metadata_set_needs_check(pool->pmd)) {
  		DMERR("%s: failed to set 'needs_check' flag in metadata", dev_name);
  		set_pool_mode(pool, PM_FAIL);
  	}
  }
  
  static void metadata_operation_failed(struct pool *pool, const char *op, int r)
  {
  	DMERR_LIMIT("%s: metadata operation '%s' failed: error = %d",
  		    dm_device_name(pool->pool_md), op, r);
  
  	abort_transaction(pool);
  	set_pool_mode(pool, PM_READ_ONLY);
  }
  
  /*----------------------------------------------------------------*/
  
  /*
   * Mapping functions.
   */
  
  /*
   * Called only while mapping a thin bio to hand it over to the workqueue.
   */
  static void thin_defer_bio(struct thin_c *tc, struct bio *bio)
  {
  	unsigned long flags;
  	struct pool *pool = tc->pool;
  
  	spin_lock_irqsave(&tc->lock, flags);
  	bio_list_add(&tc->deferred_bio_list, bio);
  	spin_unlock_irqrestore(&tc->lock, flags);
  
  	wake_worker(pool);
  }
  
  static void thin_defer_bio_with_throttle(struct thin_c *tc, struct bio *bio)
  {
  	struct pool *pool = tc->pool;
  
  	throttle_lock(&pool->throttle);
  	thin_defer_bio(tc, bio);
  	throttle_unlock(&pool->throttle);
  }
  
  static void thin_defer_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
  {
  	unsigned long flags;
  	struct pool *pool = tc->pool;
  
  	throttle_lock(&pool->throttle);
  	spin_lock_irqsave(&tc->lock, flags);
  	list_add_tail(&cell->user_list, &tc->deferred_cells);
  	spin_unlock_irqrestore(&tc->lock, flags);
  	throttle_unlock(&pool->throttle);
  
  	wake_worker(pool);
  }
  
  static void thin_hook_bio(struct thin_c *tc, struct bio *bio)
  {
  	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  
  	h->tc = tc;
  	h->shared_read_entry = NULL;
  	h->all_io_entry = NULL;
  	h->overwrite_mapping = NULL;
  	h->cell = NULL;
  }
  
  /*
   * Non-blocking function called from the thin target's map function.
   */
  static int thin_bio_map(struct dm_target *ti, struct bio *bio)
  {
  	int r;
  	struct thin_c *tc = ti->private;
  	dm_block_t block = get_bio_block(tc, bio);
  	struct dm_thin_device *td = tc->td;
  	struct dm_thin_lookup_result result;
  	struct dm_bio_prison_cell *virt_cell, *data_cell;
  	struct dm_cell_key key;
  
  	thin_hook_bio(tc, bio);
  
  	if (tc->requeue_mode) {
  		bio->bi_error = DM_ENDIO_REQUEUE;
  		bio_endio(bio);
  		return DM_MAPIO_SUBMITTED;
  	}
  
  	if (get_pool_mode(tc->pool) == PM_FAIL) {
  		bio_io_error(bio);
  		return DM_MAPIO_SUBMITTED;
  	}
  
  	if (bio->bi_opf & (REQ_PREFLUSH | REQ_FUA) ||
  	    bio_op(bio) == REQ_OP_DISCARD) {
  		thin_defer_bio_with_throttle(tc, bio);
  		return DM_MAPIO_SUBMITTED;
  	}
  
  	/*
  	 * We must hold the virtual cell before doing the lookup, otherwise
  	 * there's a race with discard.
  	 */
  	build_virtual_key(tc->td, block, &key);
  	if (bio_detain(tc->pool, &key, bio, &virt_cell))
  		return DM_MAPIO_SUBMITTED;
  
  	r = dm_thin_find_block(td, block, 0, &result);
  
  	/*
  	 * Note that we defer readahead too.
  	 */
  	switch (r) {
  	case 0:
  		if (unlikely(result.shared)) {
  			/*
  			 * We have a race condition here between the
  			 * result.shared value returned by the lookup and
  			 * snapshot creation, which may cause new
  			 * sharing.
  			 *
  			 * To avoid this always quiesce the origin before
  			 * taking the snap.  You want to do this anyway to
  			 * ensure a consistent application view
  			 * (i.e. lockfs).
  			 *
  			 * More distant ancestors are irrelevant. The
  			 * shared flag will be set in their case.
  			 */
  			thin_defer_cell(tc, virt_cell);
  			return DM_MAPIO_SUBMITTED;
  		}
  
  		build_data_key(tc->td, result.block, &key);
  		if (bio_detain(tc->pool, &key, bio, &data_cell)) {
  			cell_defer_no_holder(tc, virt_cell);
  			return DM_MAPIO_SUBMITTED;
  		}
  
  		inc_all_io_entry(tc->pool, bio);
  		cell_defer_no_holder(tc, data_cell);
  		cell_defer_no_holder(tc, virt_cell);
  
  		remap(tc, bio, result.block);
  		return DM_MAPIO_REMAPPED;
  
  	case -ENODATA:
  	case -EWOULDBLOCK:
  		thin_defer_cell(tc, virt_cell);
  		return DM_MAPIO_SUBMITTED;
  
  	default:
  		/*
  		 * Must always call bio_io_error on failure.
  		 * dm_thin_find_block can fail with -EINVAL if the
  		 * pool is switched to fail-io mode.
  		 */
  		bio_io_error(bio);
  		cell_defer_no_holder(tc, virt_cell);
  		return DM_MAPIO_SUBMITTED;
  	}
  }
  
  static int pool_is_congested(struct dm_target_callbacks *cb, int bdi_bits)
  {
  	struct pool_c *pt = container_of(cb, struct pool_c, callbacks);
  	struct request_queue *q;
  
  	if (get_pool_mode(pt->pool) == PM_OUT_OF_DATA_SPACE)
  		return 1;
  
  	q = bdev_get_queue(pt->data_dev->bdev);
  	return bdi_congested(&q->backing_dev_info, bdi_bits);
  }
  
  static void requeue_bios(struct pool *pool)
  {
  	unsigned long flags;
  	struct thin_c *tc;
  
  	rcu_read_lock();
  	list_for_each_entry_rcu(tc, &pool->active_thins, list) {
  		spin_lock_irqsave(&tc->lock, flags);
  		bio_list_merge(&tc->deferred_bio_list, &tc->retry_on_resume_list);
  		bio_list_init(&tc->retry_on_resume_list);
  		spin_unlock_irqrestore(&tc->lock, flags);
  	}
  	rcu_read_unlock();
  }
  
  /*----------------------------------------------------------------
   * Binding of control targets to a pool object
   *--------------------------------------------------------------*/
  static bool data_dev_supports_discard(struct pool_c *pt)
  {
  	struct request_queue *q = bdev_get_queue(pt->data_dev->bdev);
  
  	return q && blk_queue_discard(q);
  }
  
  static bool is_factor(sector_t block_size, uint32_t n)
  {
  	return !sector_div(block_size, n);
  }
  
  /*
   * If discard_passdown was enabled verify that the data device
   * supports discards.  Disable discard_passdown if not.
   */
  static void disable_passdown_if_not_supported(struct pool_c *pt)
  {
  	struct pool *pool = pt->pool;
  	struct block_device *data_bdev = pt->data_dev->bdev;
  	struct queue_limits *data_limits = &bdev_get_queue(data_bdev)->limits;
  	const char *reason = NULL;
  	char buf[BDEVNAME_SIZE];
  
  	if (!pt->adjusted_pf.discard_passdown)
  		return;
  
  	if (!data_dev_supports_discard(pt))
  		reason = "discard unsupported";
  
  	else if (data_limits->max_discard_sectors < pool->sectors_per_block)
  		reason = "max discard sectors smaller than a block";
  
  	if (reason) {
  		DMWARN("Data device (%s) %s: Disabling discard passdown.", bdevname(data_bdev, buf), reason);
  		pt->adjusted_pf.discard_passdown = false;
  	}
  }
  
  static int bind_control_target(struct pool *pool, struct dm_target *ti)
  {
  	struct pool_c *pt = ti->private;
  
  	/*
  	 * We want to make sure that a pool in PM_FAIL mode is never upgraded.
  	 */
  	enum pool_mode old_mode = get_pool_mode(pool);
  	enum pool_mode new_mode = pt->adjusted_pf.mode;
  
  	/*
  	 * Don't change the pool's mode until set_pool_mode() below.
  	 * Otherwise the pool's process_* function pointers may
  	 * not match the desired pool mode.
  	 */
  	pt->adjusted_pf.mode = old_mode;
  
  	pool->ti = ti;
  	pool->pf = pt->adjusted_pf;
  	pool->low_water_blocks = pt->low_water_blocks;
  
  	set_pool_mode(pool, new_mode);
  
  	return 0;
  }
  
  static void unbind_control_target(struct pool *pool, struct dm_target *ti)
  {
  	if (pool->ti == ti)
  		pool->ti = NULL;
  }
  
  /*----------------------------------------------------------------
   * Pool creation
   *--------------------------------------------------------------*/
  /* Initialize pool features. */
  static void pool_features_init(struct pool_features *pf)
  {
  	pf->mode = PM_WRITE;
  	pf->zero_new_blocks = true;
  	pf->discard_enabled = true;
  	pf->discard_passdown = true;
  	pf->error_if_no_space = false;
  }
  
  static void __pool_destroy(struct pool *pool)
  {
  	__pool_table_remove(pool);
  
  	vfree(pool->cell_sort_array);
  	if (dm_pool_metadata_close(pool->pmd) < 0)
  		DMWARN("%s: dm_pool_metadata_close() failed.", __func__);
  
  	dm_bio_prison_destroy(pool->prison);
  	dm_kcopyd_client_destroy(pool->copier);
  
  	if (pool->wq)
  		destroy_workqueue(pool->wq);
  
  	if (pool->next_mapping)
  		mempool_free(pool->next_mapping, pool->mapping_pool);
  	mempool_destroy(pool->mapping_pool);
  	dm_deferred_set_destroy(pool->shared_read_ds);
  	dm_deferred_set_destroy(pool->all_io_ds);
  	kfree(pool);
  }
  
  static struct kmem_cache *_new_mapping_cache;
  
  static struct pool *pool_create(struct mapped_device *pool_md,
  				struct block_device *metadata_dev,
  				unsigned long block_size,
  				int read_only, char **error)
  {
  	int r;
  	void *err_p;
  	struct pool *pool;
  	struct dm_pool_metadata *pmd;
  	bool format_device = read_only ? false : true;
  
  	pmd = dm_pool_metadata_open(metadata_dev, block_size, format_device);
  	if (IS_ERR(pmd)) {
  		*error = "Error creating metadata object";
  		return (struct pool *)pmd;
  	}
  
  	pool = kmalloc(sizeof(*pool), GFP_KERNEL);
  	if (!pool) {
  		*error = "Error allocating memory for pool";
  		err_p = ERR_PTR(-ENOMEM);
  		goto bad_pool;
  	}
  
  	pool->pmd = pmd;
  	pool->sectors_per_block = block_size;
  	if (block_size & (block_size - 1))
  		pool->sectors_per_block_shift = -1;
  	else
  		pool->sectors_per_block_shift = __ffs(block_size);
  	pool->low_water_blocks = 0;
  	pool_features_init(&pool->pf);
  	pool->prison = dm_bio_prison_create();
  	if (!pool->prison) {
  		*error = "Error creating pool's bio prison";
  		err_p = ERR_PTR(-ENOMEM);
  		goto bad_prison;
  	}
  
  	pool->copier = dm_kcopyd_client_create(&dm_kcopyd_throttle);
  	if (IS_ERR(pool->copier)) {
  		r = PTR_ERR(pool->copier);
  		*error = "Error creating pool's kcopyd client";
  		err_p = ERR_PTR(r);
  		goto bad_kcopyd_client;
  	}
  
  	/*
  	 * Create singlethreaded workqueue that will service all devices
  	 * that use this metadata.
  	 */
  	pool->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
  	if (!pool->wq) {
  		*error = "Error creating pool's workqueue";
  		err_p = ERR_PTR(-ENOMEM);
  		goto bad_wq;
  	}
  
  	throttle_init(&pool->throttle);
  	INIT_WORK(&pool->worker, do_worker);
  	INIT_DELAYED_WORK(&pool->waker, do_waker);
  	INIT_DELAYED_WORK(&pool->no_space_timeout, do_no_space_timeout);
  	spin_lock_init(&pool->lock);
  	bio_list_init(&pool->deferred_flush_bios);
  	INIT_LIST_HEAD(&pool->prepared_mappings);
  	INIT_LIST_HEAD(&pool->prepared_discards);
  	INIT_LIST_HEAD(&pool->prepared_discards_pt2);
  	INIT_LIST_HEAD(&pool->active_thins);
  	pool->low_water_triggered = false;
  	pool->suspended = true;
  	pool->out_of_data_space = false;
  
  	pool->shared_read_ds = dm_deferred_set_create();
  	if (!pool->shared_read_ds) {
  		*error = "Error creating pool's shared read deferred set";
  		err_p = ERR_PTR(-ENOMEM);
  		goto bad_shared_read_ds;
  	}
  
  	pool->all_io_ds = dm_deferred_set_create();
  	if (!pool->all_io_ds) {
  		*error = "Error creating pool's all io deferred set";
  		err_p = ERR_PTR(-ENOMEM);
  		goto bad_all_io_ds;
  	}
  
  	pool->next_mapping = NULL;
  	pool->mapping_pool = mempool_create_slab_pool(MAPPING_POOL_SIZE,
  						      _new_mapping_cache);
  	if (!pool->mapping_pool) {
  		*error = "Error creating pool's mapping mempool";
  		err_p = ERR_PTR(-ENOMEM);
  		goto bad_mapping_pool;
  	}
  
  	pool->cell_sort_array = vmalloc(sizeof(*pool->cell_sort_array) * CELL_SORT_ARRAY_SIZE);
  	if (!pool->cell_sort_array) {
  		*error = "Error allocating cell sort array";
  		err_p = ERR_PTR(-ENOMEM);
  		goto bad_sort_array;
  	}
  
  	pool->ref_count = 1;
  	pool->last_commit_jiffies = jiffies;
  	pool->pool_md = pool_md;
  	pool->md_dev = metadata_dev;
  	__pool_table_insert(pool);
  
  	return pool;
  
  bad_sort_array:
  	mempool_destroy(pool->mapping_pool);
  bad_mapping_pool:
  	dm_deferred_set_destroy(pool->all_io_ds);
  bad_all_io_ds:
  	dm_deferred_set_destroy(pool->shared_read_ds);
  bad_shared_read_ds:
  	destroy_workqueue(pool->wq);
  bad_wq:
  	dm_kcopyd_client_destroy(pool->copier);
  bad_kcopyd_client:
  	dm_bio_prison_destroy(pool->prison);
  bad_prison:
  	kfree(pool);
  bad_pool:
  	if (dm_pool_metadata_close(pmd))
  		DMWARN("%s: dm_pool_metadata_close() failed.", __func__);
  
  	return err_p;
  }
  
  static void __pool_inc(struct pool *pool)
  {
  	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
  	pool->ref_count++;
  }
  
  static void __pool_dec(struct pool *pool)
  {
  	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
  	BUG_ON(!pool->ref_count);
  	if (!--pool->ref_count)
  		__pool_destroy(pool);
  }
  
  static struct pool *__pool_find(struct mapped_device *pool_md,
  				struct block_device *metadata_dev,
  				unsigned long block_size, int read_only,
  				char **error, int *created)
  {
  	struct pool *pool = __pool_table_lookup_metadata_dev(metadata_dev);
  
  	if (pool) {
  		if (pool->pool_md != pool_md) {
  			*error = "metadata device already in use by a pool";
  			return ERR_PTR(-EBUSY);
  		}
  		__pool_inc(pool);
  
  	} else {
  		pool = __pool_table_lookup(pool_md);
  		if (pool) {
  			if (pool->md_dev != metadata_dev) {
  				*error = "different pool cannot replace a pool";
  				return ERR_PTR(-EINVAL);
  			}
  			__pool_inc(pool);
  
  		} else {
  			pool = pool_create(pool_md, metadata_dev, block_size, read_only, error);
  			*created = 1;
  		}
  	}
  
  	return pool;
  }
  
  /*----------------------------------------------------------------
   * Pool target methods
   *--------------------------------------------------------------*/
  static void pool_dtr(struct dm_target *ti)
  {
  	struct pool_c *pt = ti->private;
  
  	mutex_lock(&dm_thin_pool_table.mutex);
  
  	unbind_control_target(pt->pool, ti);
  	__pool_dec(pt->pool);
  	dm_put_device(ti, pt->metadata_dev);
  	dm_put_device(ti, pt->data_dev);
  	kfree(pt);
  
  	mutex_unlock(&dm_thin_pool_table.mutex);
  }
  
  static int parse_pool_features(struct dm_arg_set *as, struct pool_features *pf,
  			       struct dm_target *ti)
  {
  	int r;
  	unsigned argc;
  	const char *arg_name;
  
  	static struct dm_arg _args[] = {
  		{0, 4, "Invalid number of pool feature arguments"},
  	};
  
  	/*
  	 * No feature arguments supplied.
  	 */
  	if (!as->argc)
  		return 0;
  
  	r = dm_read_arg_group(_args, as, &argc, &ti->error);
  	if (r)
  		return -EINVAL;
  
  	while (argc && !r) {
  		arg_name = dm_shift_arg(as);
  		argc--;
  
  		if (!strcasecmp(arg_name, "skip_block_zeroing"))
  			pf->zero_new_blocks = false;
  
  		else if (!strcasecmp(arg_name, "ignore_discard"))
  			pf->discard_enabled = false;
  
  		else if (!strcasecmp(arg_name, "no_discard_passdown"))
  			pf->discard_passdown = false;
  
  		else if (!strcasecmp(arg_name, "read_only"))
  			pf->mode = PM_READ_ONLY;
  
  		else if (!strcasecmp(arg_name, "error_if_no_space"))
  			pf->error_if_no_space = true;
  
  		else {
  			ti->error = "Unrecognised pool feature requested";
  			r = -EINVAL;
  			break;
  		}
  	}
  
  	return r;
  }
  
  static void metadata_low_callback(void *context)
  {
  	struct pool *pool = context;
  
  	DMWARN("%s: reached low water mark for metadata device: sending event.",
  	       dm_device_name(pool->pool_md));
  
  	dm_table_event(pool->ti->table);
  }
  
  static sector_t get_dev_size(struct block_device *bdev)
  {
  	return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
  }
  
  static void warn_if_metadata_device_too_big(struct block_device *bdev)
  {
  	sector_t metadata_dev_size = get_dev_size(bdev);
  	char buffer[BDEVNAME_SIZE];
  
  	if (metadata_dev_size > THIN_METADATA_MAX_SECTORS_WARNING)
  		DMWARN("Metadata device %s is larger than %u sectors: excess space will not be used.",
  		       bdevname(bdev, buffer), THIN_METADATA_MAX_SECTORS);
  }
  
  static sector_t get_metadata_dev_size(struct block_device *bdev)
  {
  	sector_t metadata_dev_size = get_dev_size(bdev);
  
  	if (metadata_dev_size > THIN_METADATA_MAX_SECTORS)
  		metadata_dev_size = THIN_METADATA_MAX_SECTORS;
  
  	return metadata_dev_size;
  }
  
  static dm_block_t get_metadata_dev_size_in_blocks(struct block_device *bdev)
  {
  	sector_t metadata_dev_size = get_metadata_dev_size(bdev);
  
  	sector_div(metadata_dev_size, THIN_METADATA_BLOCK_SIZE);
  
  	return metadata_dev_size;
  }
  
  /*
   * When a metadata threshold is crossed a dm event is triggered, and
   * userland should respond by growing the metadata device.  We could let
   * userland set the threshold, like we do with the data threshold, but I'm
   * not sure they know enough to do this well.
   */
  static dm_block_t calc_metadata_threshold(struct pool_c *pt)
  {
  	/*
  	 * 4M is ample for all ops with the possible exception of thin
  	 * device deletion which is harmless if it fails (just retry the
  	 * delete after you've grown the device).
  	 */
  	dm_block_t quarter = get_metadata_dev_size_in_blocks(pt->metadata_dev->bdev) / 4;
  	return min((dm_block_t)1024ULL /* 4M */, quarter);
  }
  
  /*
   * thin-pool <metadata dev> <data dev>
   *	     <data block size (sectors)>
   *	     <low water mark (blocks)>
   *	     [<#feature args> [<arg>]*]
   *
   * Optional feature arguments are:
   *	     skip_block_zeroing: skips the zeroing of newly-provisioned blocks.
   *	     ignore_discard: disable discard
   *	     no_discard_passdown: don't pass discards down to the data device
   *	     read_only: Don't allow any changes to be made to the pool metadata.
   *	     error_if_no_space: error IOs, instead of queueing, if no space.
   */
  static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
  {
  	int r, pool_created = 0;
  	struct pool_c *pt;
  	struct pool *pool;
  	struct pool_features pf;
  	struct dm_arg_set as;
  	struct dm_dev *data_dev;
  	unsigned long block_size;
  	dm_block_t low_water_blocks;
  	struct dm_dev *metadata_dev;
  	fmode_t metadata_mode;
  
  	/*
  	 * FIXME Remove validation from scope of lock.
  	 */
  	mutex_lock(&dm_thin_pool_table.mutex);
  
  	if (argc < 4) {
  		ti->error = "Invalid argument count";
  		r = -EINVAL;
  		goto out_unlock;
  	}
  
  	as.argc = argc;
  	as.argv = argv;
  
  	/*
  	 * Set default pool features.
  	 */
  	pool_features_init(&pf);
  
  	dm_consume_args(&as, 4);
  	r = parse_pool_features(&as, &pf, ti);
  	if (r)
  		goto out_unlock;
  
  	metadata_mode = FMODE_READ | ((pf.mode == PM_READ_ONLY) ? 0 : FMODE_WRITE);
  	r = dm_get_device(ti, argv[0], metadata_mode, &metadata_dev);
  	if (r) {
  		ti->error = "Error opening metadata block device";
  		goto out_unlock;
  	}
  	warn_if_metadata_device_too_big(metadata_dev->bdev);
  
  	r = dm_get_device(ti, argv[1], FMODE_READ | FMODE_WRITE, &data_dev);
  	if (r) {
  		ti->error = "Error getting data device";
  		goto out_metadata;
  	}
  
  	if (kstrtoul(argv[2], 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)) {
  		ti->error = "Invalid block size";
  		r = -EINVAL;
  		goto out;
  	}
  
  	if (kstrtoull(argv[3], 10, (unsigned long long *)&low_water_blocks)) {
  		ti->error = "Invalid low water mark";
  		r = -EINVAL;
  		goto out;
  	}
  
  	pt = kzalloc(sizeof(*pt), GFP_KERNEL);
  	if (!pt) {
  		r = -ENOMEM;
  		goto out;
  	}
  
  	pool = __pool_find(dm_table_get_md(ti->table), metadata_dev->bdev,
  			   block_size, pf.mode == PM_READ_ONLY, &ti->error, &pool_created);
  	if (IS_ERR(pool)) {
  		r = PTR_ERR(pool);
  		goto out_free_pt;
  	}
  
  	/*
  	 * 'pool_created' reflects whether this is the first table load.
  	 * Top level discard support is not allowed to be changed after
  	 * initial load.  This would require a pool reload to trigger thin
  	 * device changes.
  	 */
  	if (!pool_created && pf.discard_enabled != pool->pf.discard_enabled) {
  		ti->error = "Discard support cannot be disabled once enabled";
  		r = -EINVAL;
  		goto out_flags_changed;
  	}
  
  	pt->pool = pool;
  	pt->ti = ti;
  	pt->metadata_dev = metadata_dev;
  	pt->data_dev = data_dev;
  	pt->low_water_blocks = low_water_blocks;
  	pt->adjusted_pf = pt->requested_pf = pf;
  	ti->num_flush_bios = 1;
  
  	/*
  	 * Only need to enable discards if the pool should pass
  	 * them down to the data device.  The thin device's discard
  	 * processing will cause mappings to be removed from the btree.
  	 */
  	ti->discard_zeroes_data_unsupported = true;
  	if (pf.discard_enabled && pf.discard_passdown) {
  		ti->num_discard_bios = 1;
  
  		/*
  		 * Setting 'discards_supported' circumvents the normal
  		 * stacking of discard limits (this keeps the pool and
  		 * thin devices' discard limits consistent).
  		 */
  		ti->discards_supported = true;
  	}
  	ti->private = pt;
  
  	r = dm_pool_register_metadata_threshold(pt->pool->pmd,
  						calc_metadata_threshold(pt),
  						metadata_low_callback,
  						pool);
  	if (r)
  		goto out_flags_changed;
  
  	pt->callbacks.congested_fn = pool_is_congested;
  	dm_table_add_target_callbacks(ti->table, &pt->callbacks);
  
  	mutex_unlock(&dm_thin_pool_table.mutex);
  
  	return 0;
  
  out_flags_changed:
  	__pool_dec(pool);
  out_free_pt:
  	kfree(pt);
  out:
  	dm_put_device(ti, data_dev);
  out_metadata:
  	dm_put_device(ti, metadata_dev);
  out_unlock:
  	mutex_unlock(&dm_thin_pool_table.mutex);
  
  	return r;
  }
  
  static int pool_map(struct dm_target *ti, struct bio *bio)
  {
  	int r;
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  	unsigned long flags;
  
  	/*
  	 * As this is a singleton target, ti->begin is always zero.
  	 */
  	spin_lock_irqsave(&pool->lock, flags);
  	bio->bi_bdev = pt->data_dev->bdev;
  	r = DM_MAPIO_REMAPPED;
  	spin_unlock_irqrestore(&pool->lock, flags);
  
  	return r;
  }
  
  static int maybe_resize_data_dev(struct dm_target *ti, bool *need_commit)
  {
  	int r;
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  	sector_t data_size = ti->len;
  	dm_block_t sb_data_size;
  
  	*need_commit = false;
  
  	(void) sector_div(data_size, pool->sectors_per_block);
  
  	r = dm_pool_get_data_dev_size(pool->pmd, &sb_data_size);
  	if (r) {
  		DMERR("%s: failed to retrieve data device size",
  		      dm_device_name(pool->pool_md));
  		return r;
  	}
  
  	if (data_size < sb_data_size) {
  		DMERR("%s: pool target (%llu blocks) too small: expected %llu",
  		      dm_device_name(pool->pool_md),
  		      (unsigned long long)data_size, sb_data_size);
  		return -EINVAL;
  
  	} else if (data_size > sb_data_size) {
  		if (dm_pool_metadata_needs_check(pool->pmd)) {
  			DMERR("%s: unable to grow the data device until repaired.",
  			      dm_device_name(pool->pool_md));
  			return 0;
  		}
  
  		if (sb_data_size)
  			DMINFO("%s: growing the data device from %llu to %llu blocks",
  			       dm_device_name(pool->pool_md),
  			       sb_data_size, (unsigned long long)data_size);
  		r = dm_pool_resize_data_dev(pool->pmd, data_size);
  		if (r) {
  			metadata_operation_failed(pool, "dm_pool_resize_data_dev", r);
  			return r;
  		}
  
  		*need_commit = true;
  	}
  
  	return 0;
  }
  
  static int maybe_resize_metadata_dev(struct dm_target *ti, bool *need_commit)
  {
  	int r;
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  	dm_block_t metadata_dev_size, sb_metadata_dev_size;
  
  	*need_commit = false;
  
  	metadata_dev_size = get_metadata_dev_size_in_blocks(pool->md_dev);
  
  	r = dm_pool_get_metadata_dev_size(pool->pmd, &sb_metadata_dev_size);
  	if (r) {
  		DMERR("%s: failed to retrieve metadata device size",
  		      dm_device_name(pool->pool_md));
  		return r;
  	}
  
  	if (metadata_dev_size < sb_metadata_dev_size) {
  		DMERR("%s: metadata device (%llu blocks) too small: expected %llu",
  		      dm_device_name(pool->pool_md),
  		      metadata_dev_size, sb_metadata_dev_size);
  		return -EINVAL;
  
  	} else if (metadata_dev_size > sb_metadata_dev_size) {
  		if (dm_pool_metadata_needs_check(pool->pmd)) {
  			DMERR("%s: unable to grow the metadata device until repaired.",
  			      dm_device_name(pool->pool_md));
  			return 0;
  		}
  
  		warn_if_metadata_device_too_big(pool->md_dev);
  		DMINFO("%s: growing the metadata device from %llu to %llu blocks",
  		       dm_device_name(pool->pool_md),
  		       sb_metadata_dev_size, metadata_dev_size);
  		r = dm_pool_resize_metadata_dev(pool->pmd, metadata_dev_size);
  		if (r) {
  			metadata_operation_failed(pool, "dm_pool_resize_metadata_dev", r);
  			return r;
  		}
  
  		*need_commit = true;
  	}
  
  	return 0;
  }
  
  /*
   * Retrieves the number of blocks of the data device from
   * the superblock and compares it to the actual device size,
   * thus resizing the data device in case it has grown.
   *
   * This both copes with opening preallocated data devices in the ctr
   * being followed by a resume
   * -and-
   * calling the resume method individually after userspace has
   * grown the data device in reaction to a table event.
   */
  static int pool_preresume(struct dm_target *ti)
  {
  	int r;
  	bool need_commit1, need_commit2;
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  
  	/*
  	 * Take control of the pool object.
  	 */
  	r = bind_control_target(pool, ti);
  	if (r)
  		return r;
  
  	r = maybe_resize_data_dev(ti, &need_commit1);
  	if (r)
  		return r;
  
  	r = maybe_resize_metadata_dev(ti, &need_commit2);
  	if (r)
  		return r;
  
  	if (need_commit1 || need_commit2)
  		(void) commit(pool);
  
  	return 0;
  }
  
  static void pool_suspend_active_thins(struct pool *pool)
  {
  	struct thin_c *tc;
  
  	/* Suspend all active thin devices */
  	tc = get_first_thin(pool);
  	while (tc) {
  		dm_internal_suspend_noflush(tc->thin_md);
  		tc = get_next_thin(pool, tc);
  	}
  }
  
  static void pool_resume_active_thins(struct pool *pool)
  {
  	struct thin_c *tc;
  
  	/* Resume all active thin devices */
  	tc = get_first_thin(pool);
  	while (tc) {
  		dm_internal_resume(tc->thin_md);
  		tc = get_next_thin(pool, tc);
  	}
  }
  
  static void pool_resume(struct dm_target *ti)
  {
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  	unsigned long flags;
  
  	/*
  	 * Must requeue active_thins' bios and then resume
  	 * active_thins _before_ clearing 'suspend' flag.
  	 */
  	requeue_bios(pool);
  	pool_resume_active_thins(pool);
  
  	spin_lock_irqsave(&pool->lock, flags);
  	pool->low_water_triggered = false;
  	pool->suspended = false;
  	spin_unlock_irqrestore(&pool->lock, flags);
  
  	do_waker(&pool->waker.work);
  }
  
  static void pool_presuspend(struct dm_target *ti)
  {
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  	unsigned long flags;
  
  	spin_lock_irqsave(&pool->lock, flags);
  	pool->suspended = true;
  	spin_unlock_irqrestore(&pool->lock, flags);
  
  	pool_suspend_active_thins(pool);
  }
  
  static void pool_presuspend_undo(struct dm_target *ti)
  {
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  	unsigned long flags;
  
  	pool_resume_active_thins(pool);
  
  	spin_lock_irqsave(&pool->lock, flags);
  	pool->suspended = false;
  	spin_unlock_irqrestore(&pool->lock, flags);
  }
  
  static void pool_postsuspend(struct dm_target *ti)
  {
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  
  	cancel_delayed_work_sync(&pool->waker);
  	cancel_delayed_work_sync(&pool->no_space_timeout);
  	flush_workqueue(pool->wq);
  	(void) commit(pool);
  }
  
  static int check_arg_count(unsigned argc, unsigned args_required)
  {
  	if (argc != args_required) {
  		DMWARN("Message received with %u arguments instead of %u.",
  		       argc, args_required);
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int read_dev_id(char *arg, dm_thin_id *dev_id, int warning)
  {
  	if (!kstrtoull(arg, 10, (unsigned long long *)dev_id) &&
  	    *dev_id <= MAX_DEV_ID)
  		return 0;
  
  	if (warning)
  		DMWARN("Message received with invalid device id: %s", arg);
  
  	return -EINVAL;
  }
  
  static int process_create_thin_mesg(unsigned argc, char **argv, struct pool *pool)
  {
  	dm_thin_id dev_id;
  	int r;
  
  	r = check_arg_count(argc, 2);
  	if (r)
  		return r;
  
  	r = read_dev_id(argv[1], &dev_id, 1);
  	if (r)
  		return r;
  
  	r = dm_pool_create_thin(pool->pmd, dev_id);
  	if (r) {
  		DMWARN("Creation of new thinly-provisioned device with id %s failed.",
  		       argv[1]);
  		return r;
  	}
  
  	return 0;
  }
  
  static int process_create_snap_mesg(unsigned argc, char **argv, struct pool *pool)
  {
  	dm_thin_id dev_id;
  	dm_thin_id origin_dev_id;
  	int r;
  
  	r = check_arg_count(argc, 3);
  	if (r)
  		return r;
  
  	r = read_dev_id(argv[1], &dev_id, 1);
  	if (r)
  		return r;
  
  	r = read_dev_id(argv[2], &origin_dev_id, 1);
  	if (r)
  		return r;
  
  	r = dm_pool_create_snap(pool->pmd, dev_id, origin_dev_id);
  	if (r) {
  		DMWARN("Creation of new snapshot %s of device %s failed.",
  		       argv[1], argv[2]);
  		return r;
  	}
  
  	return 0;
  }
  
  static int process_delete_mesg(unsigned argc, char **argv, struct pool *pool)
  {
  	dm_thin_id dev_id;
  	int r;
  
  	r = check_arg_count(argc, 2);
  	if (r)
  		return r;
  
  	r = read_dev_id(argv[1], &dev_id, 1);
  	if (r)
  		return r;
  
  	r = dm_pool_delete_thin_device(pool->pmd, dev_id);
  	if (r)
  		DMWARN("Deletion of thin device %s failed.", argv[1]);
  
  	return r;
  }
  
  static int process_set_transaction_id_mesg(unsigned argc, char **argv, struct pool *pool)
  {
  	dm_thin_id old_id, new_id;
  	int r;
  
  	r = check_arg_count(argc, 3);
  	if (r)
  		return r;
  
  	if (kstrtoull(argv[1], 10, (unsigned long long *)&old_id)) {
  		DMWARN("set_transaction_id message: Unrecognised id %s.", argv[1]);
  		return -EINVAL;
  	}
  
  	if (kstrtoull(argv[2], 10, (unsigned long long *)&new_id)) {
  		DMWARN("set_transaction_id message: Unrecognised new id %s.", argv[2]);
  		return -EINVAL;
  	}
  
  	r = dm_pool_set_metadata_transaction_id(pool->pmd, old_id, new_id);
  	if (r) {
  		DMWARN("Failed to change transaction id from %s to %s.",
  		       argv[1], argv[2]);
  		return r;
  	}
  
  	return 0;
  }
  
  static int process_reserve_metadata_snap_mesg(unsigned argc, char **argv, struct pool *pool)
  {
  	int r;
  
  	r = check_arg_count(argc, 1);
  	if (r)
  		return r;
  
  	(void) commit(pool);
  
  	r = dm_pool_reserve_metadata_snap(pool->pmd);
  	if (r)
  		DMWARN("reserve_metadata_snap message failed.");
  
  	return r;
  }
  
  static int process_release_metadata_snap_mesg(unsigned argc, char **argv, struct pool *pool)
  {
  	int r;
  
  	r = check_arg_count(argc, 1);
  	if (r)
  		return r;
  
  	r = dm_pool_release_metadata_snap(pool->pmd);
  	if (r)
  		DMWARN("release_metadata_snap message failed.");
  
  	return r;
  }
  
  /*
   * Messages supported:
   *   create_thin	<dev_id>
   *   create_snap	<dev_id> <origin_id>
   *   delete		<dev_id>
   *   set_transaction_id <current_trans_id> <new_trans_id>
   *   reserve_metadata_snap
   *   release_metadata_snap
   */
  static int pool_message(struct dm_target *ti, unsigned argc, char **argv)
  {
  	int r = -EINVAL;
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  
  	if (get_pool_mode(pool) >= PM_READ_ONLY) {
  		DMERR("%s: unable to service pool target messages in READ_ONLY or FAIL mode",
  		      dm_device_name(pool->pool_md));
  		return -EOPNOTSUPP;
  	}
  
  	if (!strcasecmp(argv[0], "create_thin"))
  		r = process_create_thin_mesg(argc, argv, pool);
  
  	else if (!strcasecmp(argv[0], "create_snap"))
  		r = process_create_snap_mesg(argc, argv, pool);
  
  	else if (!strcasecmp(argv[0], "delete"))
  		r = process_delete_mesg(argc, argv, pool);
  
  	else if (!strcasecmp(argv[0], "set_transaction_id"))
  		r = process_set_transaction_id_mesg(argc, argv, pool);
  
  	else if (!strcasecmp(argv[0], "reserve_metadata_snap"))
  		r = process_reserve_metadata_snap_mesg(argc, argv, pool);
  
  	else if (!strcasecmp(argv[0], "release_metadata_snap"))
  		r = process_release_metadata_snap_mesg(argc, argv, pool);
  
  	else
  		DMWARN("Unrecognised thin pool target message received: %s", argv[0]);
  
  	if (!r)
  		(void) commit(pool);
  
  	return r;
  }
  
  static void emit_flags(struct pool_features *pf, char *result,
  		       unsigned sz, unsigned maxlen)
  {
  	unsigned count = !pf->zero_new_blocks + !pf->discard_enabled +
  		!pf->discard_passdown + (pf->mode == PM_READ_ONLY) +
  		pf->error_if_no_space;
  	DMEMIT("%u ", count);
  
  	if (!pf->zero_new_blocks)
  		DMEMIT("skip_block_zeroing ");
  
  	if (!pf->discard_enabled)
  		DMEMIT("ignore_discard ");
  
  	if (!pf->discard_passdown)
  		DMEMIT("no_discard_passdown ");
  
  	if (pf->mode == PM_READ_ONLY)
  		DMEMIT("read_only ");
  
  	if (pf->error_if_no_space)
  		DMEMIT("error_if_no_space ");
  }
  
  /*
   * Status line is:
   *    <transaction id> <used metadata sectors>/<total metadata sectors>
   *    <used data sectors>/<total data sectors> <held metadata root>
   *    <pool mode> <discard config> <no space config> <needs_check>
   */
  static void pool_status(struct dm_target *ti, status_type_t type,
  			unsigned status_flags, char *result, unsigned maxlen)
  {
  	int r;
  	unsigned sz = 0;
  	uint64_t transaction_id;
  	dm_block_t nr_free_blocks_data;
  	dm_block_t nr_free_blocks_metadata;
  	dm_block_t nr_blocks_data;
  	dm_block_t nr_blocks_metadata;
  	dm_block_t held_root;
  	char buf[BDEVNAME_SIZE];
  	char buf2[BDEVNAME_SIZE];
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  
  	switch (type) {
  	case STATUSTYPE_INFO:
  		if (get_pool_mode(pool) == PM_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(pool);
  
  		r = dm_pool_get_metadata_transaction_id(pool->pmd, &transaction_id);
  		if (r) {
  			DMERR("%s: dm_pool_get_metadata_transaction_id returned %d",
  			      dm_device_name(pool->pool_md), r);
  			goto err;
  		}
  
  		r = dm_pool_get_free_metadata_block_count(pool->pmd, &nr_free_blocks_metadata);
  		if (r) {
  			DMERR("%s: dm_pool_get_free_metadata_block_count returned %d",
  			      dm_device_name(pool->pool_md), r);
  			goto err;
  		}
  
  		r = dm_pool_get_metadata_dev_size(pool->pmd, &nr_blocks_metadata);
  		if (r) {
  			DMERR("%s: dm_pool_get_metadata_dev_size returned %d",
  			      dm_device_name(pool->pool_md), r);
  			goto err;
  		}
  
  		r = dm_pool_get_free_block_count(pool->pmd, &nr_free_blocks_data);
  		if (r) {
  			DMERR("%s: dm_pool_get_free_block_count returned %d",
  			      dm_device_name(pool->pool_md), r);
  			goto err;
  		}
  
  		r = dm_pool_get_data_dev_size(pool->pmd, &nr_blocks_data);
  		if (r) {
  			DMERR("%s: dm_pool_get_data_dev_size returned %d",
  			      dm_device_name(pool->pool_md), r);
  			goto err;
  		}
  
  		r = dm_pool_get_metadata_snap(pool->pmd, &held_root);
  		if (r) {
  			DMERR("%s: dm_pool_get_metadata_snap returned %d",
  			      dm_device_name(pool->pool_md), r);
  			goto err;
  		}
  
  		DMEMIT("%llu %llu/%llu %llu/%llu ",
  		       (unsigned long long)transaction_id,
  		       (unsigned long long)(nr_blocks_metadata - nr_free_blocks_metadata),
  		       (unsigned long long)nr_blocks_metadata,
  		       (unsigned long long)(nr_blocks_data - nr_free_blocks_data),
  		       (unsigned long long)nr_blocks_data);
  
  		if (held_root)
  			DMEMIT("%llu ", held_root);
  		else
  			DMEMIT("- ");
  
  		if (pool->pf.mode == PM_OUT_OF_DATA_SPACE)
  			DMEMIT("out_of_data_space ");
  		else if (pool->pf.mode == PM_READ_ONLY)
  			DMEMIT("ro ");
  		else
  			DMEMIT("rw ");
  
  		if (!pool->pf.discard_enabled)
  			DMEMIT("ignore_discard ");
  		else if (pool->pf.discard_passdown)
  			DMEMIT("discard_passdown ");
  		else
  			DMEMIT("no_discard_passdown ");
  
  		if (pool->pf.error_if_no_space)
  			DMEMIT("error_if_no_space ");
  		else
  			DMEMIT("queue_if_no_space ");
  
  		if (dm_pool_metadata_needs_check(pool->pmd))
  			DMEMIT("needs_check ");
  		else
  			DMEMIT("- ");
  
  		break;
  
  	case STATUSTYPE_TABLE:
  		DMEMIT("%s %s %lu %llu ",
  		       format_dev_t(buf, pt->metadata_dev->bdev->bd_dev),
  		       format_dev_t(buf2, pt->data_dev->bdev->bd_dev),
  		       (unsigned long)pool->sectors_per_block,
  		       (unsigned long long)pt->low_water_blocks);
  		emit_flags(&pt->requested_pf, result, sz, maxlen);
  		break;
  	}
  	return;
  
  err:
  	DMEMIT("Error");
  }
  
  static int pool_iterate_devices(struct dm_target *ti,
  				iterate_devices_callout_fn fn, void *data)
  {
  	struct pool_c *pt = ti->private;
  
  	return fn(ti, pt->data_dev, 0, ti->len, data);
  }
  
  static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
  {
  	struct pool_c *pt = ti->private;
  	struct pool *pool = pt->pool;
  	sector_t io_opt_sectors = limits->io_opt >> SECTOR_SHIFT;
  
  	/*
  	 * If max_sectors is smaller than pool->sectors_per_block adjust it
  	 * to the highest possible power-of-2 factor of pool->sectors_per_block.
  	 * This is especially beneficial when the pool's data device is a RAID
  	 * device that has a full stripe width that matches pool->sectors_per_block
  	 * -- because even though partial RAID stripe-sized IOs will be issued to a
  	 *    single RAID stripe; when aggregated they will end on a full RAID stripe
  	 *    boundary.. which avoids additional partial RAID stripe writes cascading
  	 */
  	if (limits->max_sectors < pool->sectors_per_block) {
  		while (!is_factor(pool->sectors_per_block, limits->max_sectors)) {
  			if ((limits->max_sectors & (limits->max_sectors - 1)) == 0)
  				limits->max_sectors--;
  			limits->max_sectors = rounddown_pow_of_two(limits->max_sectors);
  		}
  	}
  
  	/*
  	 * If the system-determined stacked limits are compatible with the
  	 * pool's blocksize (io_opt is a factor) do not override them.
  	 */
  	if (io_opt_sectors < pool->sectors_per_block ||
  	    !is_factor(io_opt_sectors, pool->sectors_per_block)) {
  		if (is_factor(pool->sectors_per_block, limits->max_sectors))
  			blk_limits_io_min(limits, limits->max_sectors << SECTOR_SHIFT);
  		else
  			blk_limits_io_min(limits, pool->sectors_per_block << SECTOR_SHIFT);
  		blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
  	}
  
  	/*
  	 * pt->adjusted_pf is a staging area for the actual features to use.
  	 * They get transferred to the live pool in bind_control_target()
  	 * called from pool_preresume().
  	 */
  	if (!pt->adjusted_pf.discard_enabled) {
  		/*
  		 * Must explicitly disallow stacking discard limits otherwise the
  		 * block layer will stack them if pool's data device has support.
  		 * QUEUE_FLAG_DISCARD wouldn't be set but there is no way for the
  		 * user to see that, so make sure to set all discard limits to 0.
  		 */
  		limits->discard_granularity = 0;
  		return;
  	}
  
  	disable_passdown_if_not_supported(pt);
  
  	/*
  	 * The pool uses the same discard limits as the underlying data
  	 * device.  DM core has already set this up.
  	 */
  }
  
  static struct target_type pool_target = {
  	.name = "thin-pool",
  	.features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
  		    DM_TARGET_IMMUTABLE,
  	.version = {1, 19, 0},
  	.module = THIS_MODULE,
  	.ctr = pool_ctr,
  	.dtr = pool_dtr,
  	.map = pool_map,
  	.presuspend = pool_presuspend,
  	.presuspend_undo = pool_presuspend_undo,
  	.postsuspend = pool_postsuspend,
  	.preresume = pool_preresume,
  	.resume = pool_resume,
  	.message = pool_message,
  	.status = pool_status,
  	.iterate_devices = pool_iterate_devices,
  	.io_hints = pool_io_hints,
  };
  
  /*----------------------------------------------------------------
   * Thin target methods
   *--------------------------------------------------------------*/
  static void thin_get(struct thin_c *tc)
  {
  	atomic_inc(&tc->refcount);
  }
  
  static void thin_put(struct thin_c *tc)
  {
  	if (atomic_dec_and_test(&tc->refcount))
  		complete(&tc->can_destroy);
  }
  
  static void thin_dtr(struct dm_target *ti)
  {
  	struct thin_c *tc = ti->private;
  	unsigned long flags;
  
  	spin_lock_irqsave(&tc->pool->lock, flags);
  	list_del_rcu(&tc->list);
  	spin_unlock_irqrestore(&tc->pool->lock, flags);
  	synchronize_rcu();
  
  	thin_put(tc);
  	wait_for_completion(&tc->can_destroy);
  
  	mutex_lock(&dm_thin_pool_table.mutex);
  
  	__pool_dec(tc->pool);
  	dm_pool_close_thin_device(tc->td);
  	dm_put_device(ti, tc->pool_dev);
  	if (tc->origin_dev)
  		dm_put_device(ti, tc->origin_dev);
  	kfree(tc);
  
  	mutex_unlock(&dm_thin_pool_table.mutex);
  }
  
  /*
   * Thin target parameters:
   *
   * <pool_dev> <dev_id> [origin_dev]
   *
   * pool_dev: the path to the pool (eg, /dev/mapper/my_pool)
   * dev_id: the internal device identifier
   * origin_dev: a device external to the pool that should act as the origin
   *
   * If the pool device has discards disabled, they get disabled for the thin
   * device as well.
   */
  static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
  {
  	int r;
  	struct thin_c *tc;
  	struct dm_dev *pool_dev, *origin_dev;
  	struct mapped_device *pool_md;
  	unsigned long flags;
  
  	mutex_lock(&dm_thin_pool_table.mutex);
  
  	if (argc != 2 && argc != 3) {
  		ti->error = "Invalid argument count";
  		r = -EINVAL;
  		goto out_unlock;
  	}
  
  	tc = ti->private = kzalloc(sizeof(*tc), GFP_KERNEL);
  	if (!tc) {
  		ti->error = "Out of memory";
  		r = -ENOMEM;
  		goto out_unlock;
  	}
  	tc->thin_md = dm_table_get_md(ti->table);
  	spin_lock_init(&tc->lock);
  	INIT_LIST_HEAD(&tc->deferred_cells);
  	bio_list_init(&tc->deferred_bio_list);
  	bio_list_init(&tc->retry_on_resume_list);
  	tc->sort_bio_list = RB_ROOT;
  
  	if (argc == 3) {
  		r = dm_get_device(ti, argv[2], FMODE_READ, &origin_dev);
  		if (r) {
  			ti->error = "Error opening origin device";
  			goto bad_origin_dev;
  		}
  		tc->origin_dev = origin_dev;
  	}
  
  	r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &pool_dev);
  	if (r) {
  		ti->error = "Error opening pool device";
  		goto bad_pool_dev;
  	}
  	tc->pool_dev = pool_dev;
  
  	if (read_dev_id(argv[1], (unsigned long long *)&tc->dev_id, 0)) {
  		ti->error = "Invalid device id";
  		r = -EINVAL;
  		goto bad_common;
  	}
  
  	pool_md = dm_get_md(tc->pool_dev->bdev->bd_dev);
  	if (!pool_md) {
  		ti->error = "Couldn't get pool mapped device";
  		r = -EINVAL;
  		goto bad_common;
  	}
  
  	tc->pool = __pool_table_lookup(pool_md);
  	if (!tc->pool) {
  		ti->error = "Couldn't find pool object";
  		r = -EINVAL;
  		goto bad_pool_lookup;
  	}
  	__pool_inc(tc->pool);
  
  	if (get_pool_mode(tc->pool) == PM_FAIL) {
  		ti->error = "Couldn't open thin device, Pool is in fail mode";
  		r = -EINVAL;
  		goto bad_pool;
  	}
  
  	r = dm_pool_open_thin_device(tc->pool->pmd, tc->dev_id, &tc->td);
  	if (r) {
  		ti->error = "Couldn't open thin internal device";
  		goto bad_pool;
  	}
  
  	r = dm_set_target_max_io_len(ti, tc->pool->sectors_per_block);
  	if (r)
  		goto bad;
  
  	ti->num_flush_bios = 1;
  	ti->flush_supported = true;
  	ti->per_io_data_size = sizeof(struct dm_thin_endio_hook);
  
  	/* In case the pool supports discards, pass them on. */
  	ti->discard_zeroes_data_unsupported = true;
  	if (tc->pool->pf.discard_enabled) {
  		ti->discards_supported = true;
  		ti->num_discard_bios = 1;
  		ti->split_discard_bios = false;
  	}
  
  	mutex_unlock(&dm_thin_pool_table.mutex);
  
  	spin_lock_irqsave(&tc->pool->lock, flags);
  	if (tc->pool->suspended) {
  		spin_unlock_irqrestore(&tc->pool->lock, flags);
  		mutex_lock(&dm_thin_pool_table.mutex); /* reacquire for __pool_dec */
  		ti->error = "Unable to activate thin device while pool is suspended";
  		r = -EINVAL;
  		goto bad;
  	}
  	atomic_set(&tc->refcount, 1);
  	init_completion(&tc->can_destroy);
  	list_add_tail_rcu(&tc->list, &tc->pool->active_thins);
  	spin_unlock_irqrestore(&tc->pool->lock, flags);
  	/*
  	 * This synchronize_rcu() call is needed here otherwise we risk a
  	 * wake_worker() call finding no bios to process (because the newly
  	 * added tc isn't yet visible).  So this reduces latency since we
  	 * aren't then dependent on the periodic commit to wake_worker().
  	 */
  	synchronize_rcu();
  
  	dm_put(pool_md);
  
  	return 0;
  
  bad:
  	dm_pool_close_thin_device(tc->td);
  bad_pool:
  	__pool_dec(tc->pool);
  bad_pool_lookup:
  	dm_put(pool_md);
  bad_common:
  	dm_put_device(ti, tc->pool_dev);
  bad_pool_dev:
  	if (tc->origin_dev)
  		dm_put_device(ti, tc->origin_dev);
  bad_origin_dev:
  	kfree(tc);
  out_unlock:
  	mutex_unlock(&dm_thin_pool_table.mutex);
  
  	return r;
  }
  
  static int thin_map(struct dm_target *ti, struct bio *bio)
  {
  	bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);
  
  	return thin_bio_map(ti, bio);
  }
  
  static int thin_endio(struct dm_target *ti, struct bio *bio, int err)
  {
  	unsigned long flags;
  	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
  	struct list_head work;
  	struct dm_thin_new_mapping *m, *tmp;
  	struct pool *pool = h->tc->pool;
  
  	if (h->shared_read_entry) {
  		INIT_LIST_HEAD(&work);
  		dm_deferred_entry_dec(h->shared_read_entry, &work);
  
  		spin_lock_irqsave(&pool->lock, flags);
  		list_for_each_entry_safe(m, tmp, &work, list) {
  			list_del(&m->list);
  			__complete_mapping_preparation(m);
  		}
  		spin_unlock_irqrestore(&pool->lock, flags);
  	}
  
  	if (h->all_io_entry) {
  		INIT_LIST_HEAD(&work);
  		dm_deferred_entry_dec(h->all_io_entry, &work);
  		if (!list_empty(&work)) {
  			spin_lock_irqsave(&pool->lock, flags);
  			list_for_each_entry_safe(m, tmp, &work, list)
  				list_add_tail(&m->list, &pool->prepared_discards);
  			spin_unlock_irqrestore(&pool->lock, flags);
  			wake_worker(pool);
  		}
  	}
  
  	if (h->cell)
  		cell_defer_no_holder(h->tc, h->cell);
  
  	return 0;
  }
  
  static void thin_presuspend(struct dm_target *ti)
  {
  	struct thin_c *tc = ti->private;
  
  	if (dm_noflush_suspending(ti))
  		noflush_work(tc, do_noflush_start);
  }
  
  static void thin_postsuspend(struct dm_target *ti)
  {
  	struct thin_c *tc = ti->private;
  
  	/*
  	 * The dm_noflush_suspending flag has been cleared by now, so
  	 * unfortunately we must always run this.
  	 */
  	noflush_work(tc, do_noflush_stop);
  }
  
  static int thin_preresume(struct dm_target *ti)
  {
  	struct thin_c *tc = ti->private;
  
  	if (tc->origin_dev)
  		tc->origin_size = get_dev_size(tc->origin_dev->bdev);
  
  	return 0;
  }
  
  /*
   * <nr mapped sectors> <highest mapped sector>
   */
  static void thin_status(struct dm_target *ti, status_type_t type,
  			unsigned status_flags, char *result, unsigned maxlen)
  {
  	int r;
  	ssize_t sz = 0;
  	dm_block_t mapped, highest;
  	char buf[BDEVNAME_SIZE];
  	struct thin_c *tc = ti->private;
  
  	if (get_pool_mode(tc->pool) == PM_FAIL) {
  		DMEMIT("Fail");
  		return;
  	}
  
  	if (!tc->td)
  		DMEMIT("-");
  	else {
  		switch (type) {
  		case STATUSTYPE_INFO:
  			r = dm_thin_get_mapped_count(tc->td, &mapped);
  			if (r) {
  				DMERR("dm_thin_get_mapped_count returned %d", r);
  				goto err;
  			}
  
  			r = dm_thin_get_highest_mapped_block(tc->td, &highest);
  			if (r < 0) {
  				DMERR("dm_thin_get_highest_mapped_block returned %d", r);
  				goto err;
  			}
  
  			DMEMIT("%llu ", mapped * tc->pool->sectors_per_block);
  			if (r)
  				DMEMIT("%llu", ((highest + 1) *
  						tc->pool->sectors_per_block) - 1);
  			else
  				DMEMIT("-");
  			break;
  
  		case STATUSTYPE_TABLE:
  			DMEMIT("%s %lu",
  			       format_dev_t(buf, tc->pool_dev->bdev->bd_dev),
  			       (unsigned long) tc->dev_id);
  			if (tc->origin_dev)
  				DMEMIT(" %s", format_dev_t(buf, tc->origin_dev->bdev->bd_dev));
  			break;
  		}
  	}
  
  	return;
  
  err:
  	DMEMIT("Error");
  }
  
  static int thin_iterate_devices(struct dm_target *ti,
  				iterate_devices_callout_fn fn, void *data)
  {
  	sector_t blocks;
  	struct thin_c *tc = ti->private;
  	struct pool *pool = tc->pool;
  
  	/*
  	 * We can't call dm_pool_get_data_dev_size() since that blocks.  So
  	 * we follow a more convoluted path through to the pool's target.
  	 */
  	if (!pool->ti)
  		return 0;	/* nothing is bound */
  
  	blocks = pool->ti->len;
  	(void) sector_div(blocks, pool->sectors_per_block);
  	if (blocks)
  		return fn(ti, tc->pool_dev, 0, pool->sectors_per_block * blocks, data);
  
  	return 0;
  }
  
  static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
  {
  	struct thin_c *tc = ti->private;
  	struct pool *pool = tc->pool;
  
  	if (!pool->pf.discard_enabled)
  		return;
  
  	limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
  	limits->max_discard_sectors = 2048 * 1024 * 16; /* 16G */
  }
  
  static struct target_type thin_target = {
  	.name = "thin",
  	.version = {1, 19, 0},
  	.module	= THIS_MODULE,
  	.ctr = thin_ctr,
  	.dtr = thin_dtr,
  	.map = thin_map,
  	.end_io = thin_endio,
  	.preresume = thin_preresume,
  	.presuspend = thin_presuspend,
  	.postsuspend = thin_postsuspend,
  	.status = thin_status,
  	.iterate_devices = thin_iterate_devices,
  	.io_hints = thin_io_hints,
  };
  
  /*----------------------------------------------------------------*/
  
  static int __init dm_thin_init(void)
  {
  	int r;
  
  	pool_table_init();
  
  	r = dm_register_target(&thin_target);
  	if (r)
  		return r;
  
  	r = dm_register_target(&pool_target);
  	if (r)
  		goto bad_pool_target;
  
  	r = -ENOMEM;
  
  	_new_mapping_cache = KMEM_CACHE(dm_thin_new_mapping, 0);
  	if (!_new_mapping_cache)
  		goto bad_new_mapping_cache;
  
  	return 0;
  
  bad_new_mapping_cache:
  	dm_unregister_target(&pool_target);
  bad_pool_target:
  	dm_unregister_target(&thin_target);
  
  	return r;
  }
  
  static void dm_thin_exit(void)
  {
  	dm_unregister_target(&thin_target);
  	dm_unregister_target(&pool_target);
  
  	kmem_cache_destroy(_new_mapping_cache);
  }
  
  module_init(dm_thin_init);
  module_exit(dm_thin_exit);
  
  module_param_named(no_space_timeout, no_space_timeout_secs, uint, S_IRUGO | S_IWUSR);
  MODULE_PARM_DESC(no_space_timeout, "Out of data space queue IO timeout in seconds");
  
  MODULE_DESCRIPTION(DM_NAME " thin provisioning target");
  MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
  MODULE_LICENSE("GPL");
  