WSL2-Linux-Kernel/drivers/md/dm-thin.c

/*
 * Copyright (C) 2011 Red Hat UK.
 *
 * This file is released under the GPL.
 */

#include "dm-thin-metadata.h"

#include <linux/device-mapper.h>
#include <linux/dm-io.h>
#include <linux/dm-kcopyd.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>

#define	DM_MSG_PREFIX	"thin"

/*
 * Tunable constants
 */
#define ENDIO_HOOK_POOL_SIZE 10240
#define DEFERRED_SET_SIZE 64
#define MAPPING_POOL_SIZE 1024
#define PRISON_CELLS 1024

/*
 * 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)

/*
 * The metadata device is currently limited in size.  The limitation is
 * checked lower down in dm-space-map-metadata, but we also check it here
 * so we can fail early.
 *
 * We have one block of index, which can hold 255 index entries.  Each
 * index entry contains allocation info about 16k metadata blocks.
 */
#define METADATA_DEV_MAX_SECTORS (255 * (1 << 14) * (THIN_METADATA_BLOCK_SIZE / (1 << 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 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_mappings).  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.
 */

/*----------------------------------------------------------------*/

/*
 * Sometimes we can't deal with a bio straight away.  We put them in prison
 * where they can't cause any mischief.  Bios are put in a cell identified
 * by a key, multiple bios can be in the same cell.  When the cell is
 * subsequently unlocked the bios become available.
 */
struct bio_prison;

struct cell_key {
	int virtual;
	dm_thin_id dev;
	dm_block_t block;
};

struct cell {
	struct hlist_node list;
	struct bio_prison *prison;
	struct cell_key key;
	unsigned count;
	struct bio_list bios;
};

struct bio_prison {
	spinlock_t lock;
	mempool_t *cell_pool;

	unsigned nr_buckets;
	unsigned hash_mask;
	struct hlist_head *cells;
};

static uint32_t calc_nr_buckets(unsigned nr_cells)
{
	uint32_t n = 128;

	nr_cells /= 4;
	nr_cells = min(nr_cells, 8192u);

	while (n < nr_cells)
		n <<= 1;

	return n;
}

/*
 * @nr_cells should be the number of cells you want in use _concurrently_.
 * Don't confuse it with the number of distinct keys.
 */
static struct bio_prison *prison_create(unsigned nr_cells)
{
	unsigned i;
	uint32_t nr_buckets = calc_nr_buckets(nr_cells);
	size_t len = sizeof(struct bio_prison) +
		(sizeof(struct hlist_head) * nr_buckets);
	struct bio_prison *prison = kmalloc(len, GFP_KERNEL);

	if (!prison)
		return NULL;

	spin_lock_init(&prison->lock);
	prison->cell_pool = mempool_create_kmalloc_pool(nr_cells,
							sizeof(struct cell));
	if (!prison->cell_pool) {
		kfree(prison);
		return NULL;
	}

	prison->nr_buckets = nr_buckets;
	prison->hash_mask = nr_buckets - 1;
	prison->cells = (struct hlist_head *) (prison + 1);
	for (i = 0; i < nr_buckets; i++)
		INIT_HLIST_HEAD(prison->cells + i);

	return prison;
}

static void prison_destroy(struct bio_prison *prison)
{
	mempool_destroy(prison->cell_pool);
	kfree(prison);
}

static uint32_t hash_key(struct bio_prison *prison, struct cell_key *key)
{
	const unsigned long BIG_PRIME = 4294967291UL;
	uint64_t hash = key->block * BIG_PRIME;

	return (uint32_t) (hash & prison->hash_mask);
}

static int keys_equal(struct cell_key *lhs, struct cell_key *rhs)
{
	       return (lhs->virtual == rhs->virtual) &&
		       (lhs->dev == rhs->dev) &&
		       (lhs->block == rhs->block);
}

static struct cell *__search_bucket(struct hlist_head *bucket,
				    struct cell_key *key)
{
	struct cell *cell;
	struct hlist_node *tmp;

	hlist_for_each_entry(cell, tmp, bucket, list)
		if (keys_equal(&cell->key, key))
			return cell;

	return NULL;
}

/*
 * This may block if a new cell needs allocating.  You must ensure that
 * cells will be unlocked even if the calling thread is blocked.
 *
 * Returns the number of entries in the cell prior to the new addition
 * or < 0 on failure.
 */
static int bio_detain(struct bio_prison *prison, struct cell_key *key,
		      struct bio *inmate, struct cell **ref)
{
	int r;
	unsigned long flags;
	uint32_t hash = hash_key(prison, key);
	struct cell *uninitialized_var(cell), *cell2 = NULL;

	BUG_ON(hash > prison->nr_buckets);

	spin_lock_irqsave(&prison->lock, flags);
	cell = __search_bucket(prison->cells + hash, key);

	if (!cell) {
		/*
		 * Allocate a new cell
		 */
		spin_unlock_irqrestore(&prison->lock, flags);
		cell2 = mempool_alloc(prison->cell_pool, GFP_NOIO);
		spin_lock_irqsave(&prison->lock, flags);

		/*
		 * We've been unlocked, so we have to double check that
		 * nobody else has inserted this cell in the meantime.
		 */
		cell = __search_bucket(prison->cells + hash, key);

		if (!cell) {
			cell = cell2;
			cell2 = NULL;

			cell->prison = prison;
			memcpy(&cell->key, key, sizeof(cell->key));
			cell->count = 0;
			bio_list_init(&cell->bios);
			hlist_add_head(&cell->list, prison->cells + hash);
		}
	}

	r = cell->count++;
	bio_list_add(&cell->bios, inmate);
	spin_unlock_irqrestore(&prison->lock, flags);

	if (cell2)
		mempool_free(cell2, prison->cell_pool);

	*ref = cell;

	return r;
}

/*
 * @inmates must have been initialised prior to this call
 */
static void __cell_release(struct cell *cell, struct bio_list *inmates)
{
	struct bio_prison *prison = cell->prison;

	hlist_del(&cell->list);

	if (inmates)
		bio_list_merge(inmates, &cell->bios);

	mempool_free(cell, prison->cell_pool);
}

static void cell_release(struct cell *cell, struct bio_list *bios)
{
	unsigned long flags;
	struct bio_prison *prison = cell->prison;

	spin_lock_irqsave(&prison->lock, flags);
	__cell_release(cell, bios);
	spin_unlock_irqrestore(&prison->lock, flags);
}

/*
 * There are a couple of places where we put a bio into a cell briefly
 * before taking it out again.  In these situations we know that no other
 * bio may be in the cell.  This function releases the cell, and also does
 * a sanity check.
 */
static void cell_release_singleton(struct cell *cell, struct bio *bio)
{
	struct bio_prison *prison = cell->prison;
	struct bio_list bios;
	struct bio *b;
	unsigned long flags;

	bio_list_init(&bios);

	spin_lock_irqsave(&prison->lock, flags);
	__cell_release(cell, &bios);
	spin_unlock_irqrestore(&prison->lock, flags);

	b = bio_list_pop(&bios);
	BUG_ON(b != bio);
	BUG_ON(!bio_list_empty(&bios));
}

static void cell_error(struct cell *cell)
{
	struct bio_prison *prison = cell->prison;
	struct bio_list bios;
	struct bio *bio;
	unsigned long flags;

	bio_list_init(&bios);

	spin_lock_irqsave(&prison->lock, flags);
	__cell_release(cell, &bios);
	spin_unlock_irqrestore(&prison->lock, flags);

	while ((bio = bio_list_pop(&bios)))
		bio_io_error(bio);
}

/*----------------------------------------------------------------*/

/*
 * We use the deferred set to keep track of pending reads to shared blocks.
 * We do this to ensure the new mapping caused by a write isn't performed
 * until these prior reads have completed.  Otherwise the insertion of the
 * new mapping could free the old block that the read bios are mapped to.
 */

struct deferred_set;
struct deferred_entry {
	struct deferred_set *ds;
	unsigned count;
	struct list_head work_items;
};

struct deferred_set {
	spinlock_t lock;
	unsigned current_entry;
	unsigned sweeper;
	struct deferred_entry entries[DEFERRED_SET_SIZE];
};

static void ds_init(struct deferred_set *ds)
{
	int i;

	spin_lock_init(&ds->lock);
	ds->current_entry = 0;
	ds->sweeper = 0;
	for (i = 0; i < DEFERRED_SET_SIZE; i++) {
		ds->entries[i].ds = ds;
		ds->entries[i].count = 0;
		INIT_LIST_HEAD(&ds->entries[i].work_items);
	}
}

static struct deferred_entry *ds_inc(struct deferred_set *ds)
{
	unsigned long flags;
	struct deferred_entry *entry;

	spin_lock_irqsave(&ds->lock, flags);
	entry = ds->entries + ds->current_entry;
	entry->count++;
	spin_unlock_irqrestore(&ds->lock, flags);

	return entry;
}

static unsigned ds_next(unsigned index)
{
	return (index + 1) % DEFERRED_SET_SIZE;
}

static void __sweep(struct deferred_set *ds, struct list_head *head)
{
	while ((ds->sweeper != ds->current_entry) &&
	       !ds->entries[ds->sweeper].count) {
		list_splice_init(&ds->entries[ds->sweeper].work_items, head);
		ds->sweeper = ds_next(ds->sweeper);
	}

	if ((ds->sweeper == ds->current_entry) && !ds->entries[ds->sweeper].count)
		list_splice_init(&ds->entries[ds->sweeper].work_items, head);
}

static void ds_dec(struct deferred_entry *entry, struct list_head *head)
{
	unsigned long flags;

	spin_lock_irqsave(&entry->ds->lock, flags);
	BUG_ON(!entry->count);
	--entry->count;
	__sweep(entry->ds, head);
	spin_unlock_irqrestore(&entry->ds->lock, flags);
}

/*
 * Returns 1 if deferred or 0 if no pending items to delay job.
 */
static int ds_add_work(struct deferred_set *ds, struct list_head *work)
{
	int r = 1;
	unsigned long flags;
	unsigned next_entry;

	spin_lock_irqsave(&ds->lock, flags);
	if ((ds->sweeper == ds->current_entry) &&
	    !ds->entries[ds->current_entry].count)
		r = 0;
	else {
		list_add(work, &ds->entries[ds->current_entry].work_items);
		next_entry = ds_next(ds->current_entry);
		if (!ds->entries[next_entry].count)
			ds->current_entry = next_entry;
	}
	spin_unlock_irqrestore(&ds->lock, flags);

	return r;
}

/*----------------------------------------------------------------*/

/*
 * Key building.
 */
static void build_data_key(struct dm_thin_device *td,
			   dm_block_t b, struct cell_key *key)
{
	key->virtual = 0;
	key->dev = dm_thin_dev_id(td);
	key->block = b;
}

static void build_virtual_key(struct dm_thin_device *td, dm_block_t b,
			      struct cell_key *key)
{
	key->virtual = 1;
	key->dev = dm_thin_dev_id(td);
	key->block = b;
}

/*----------------------------------------------------------------*/

/*
 * A pool device ties together a metadata device and a data device.  It
 * also provides the interface for creating and destroying internal
 * devices.
 */
struct new_mapping;
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;

	uint32_t sectors_per_block;
	unsigned block_shift;
	dm_block_t offset_mask;
	dm_block_t low_water_blocks;

	unsigned zero_new_blocks:1;
	unsigned low_water_triggered:1;	/* A dm event has been sent */
	unsigned no_free_space:1;	/* A -ENOSPC warning has been issued */

	struct bio_prison *prison;
	struct dm_kcopyd_client *copier;

	struct workqueue_struct *wq;
	struct work_struct worker;

	unsigned ref_count;

	spinlock_t lock;
	struct bio_list deferred_bios;
	struct bio_list deferred_flush_bios;
	struct list_head prepared_mappings;

	struct bio_list retry_on_resume_list;

	struct deferred_set ds;	/* FIXME: move to thin_c */

	struct new_mapping *next_mapping;
	mempool_t *mapping_pool;
	mempool_t *endio_hook_pool;
};

/*
 * 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;
	unsigned zero_new_blocks:1;
};

/*
 * Target context for a thin.
 */
struct thin_c {
	struct dm_dev *pool_dev;
	dm_thin_id dev_id;

	struct pool *pool;
	struct dm_thin_device *td;
};

/*----------------------------------------------------------------*/

/*
 * 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;
}

/*----------------------------------------------------------------*/

static void __requeue_bio_list(struct thin_c *tc, struct bio_list *master)
{
	struct bio *bio;
	struct bio_list bios;

	bio_list_init(&bios);
	bio_list_merge(&bios, master);
	bio_list_init(master);

	while ((bio = bio_list_pop(&bios))) {
		if (dm_get_mapinfo(bio)->ptr == tc)
			bio_endio(bio, DM_ENDIO_REQUEUE);
		else
			bio_list_add(master, bio);
	}
}

static void requeue_io(struct thin_c *tc)
{
	struct pool *pool = tc->pool;
	unsigned long flags;

	spin_lock_irqsave(&pool->lock, flags);
	__requeue_bio_list(tc, &pool->deferred_bios);
	__requeue_bio_list(tc, &pool->retry_on_resume_list);
	spin_unlock_irqrestore(&pool->lock, flags);
}

/*
 * 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)
{
	return bio->bi_sector >> tc->pool->block_shift;
}

static void remap(struct thin_c *tc, struct bio *bio, dm_block_t block)
{
	struct pool *pool = tc->pool;

	bio->bi_bdev = tc->pool_dev->bdev;
	bio->bi_sector = (block << pool->block_shift) +
		(bio->bi_sector & pool->offset_mask);
}

static void remap_and_issue(struct thin_c *tc, struct bio *bio,
			    dm_block_t block)
{
	struct pool *pool = tc->pool;
	unsigned long flags;

	remap(tc, bio, block);

	/*
	 * Batch together any FUA/FLUSH bios we find and then issue
	 * a single commit for them in process_deferred_bios().
	 */
	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
		spin_lock_irqsave(&pool->lock, flags);
		bio_list_add(&pool->deferred_flush_bios, bio);
		spin_unlock_irqrestore(&pool->lock, flags);
	} else
		generic_make_request(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);
}

/*----------------------------------------------------------------*/

/*
 * Bio endio functions.
 */
struct endio_hook {
	struct thin_c *tc;
	bio_end_io_t *saved_bi_end_io;
	struct deferred_entry *entry;
};

struct new_mapping {
	struct list_head list;

	int prepared;

	struct thin_c *tc;
	dm_block_t virt_block;
	dm_block_t data_block;
	struct cell *cell;
	int err;

	/*
	 * 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 __maybe_add_mapping(struct new_mapping *m)
{
	struct pool *pool = m->tc->pool;

	if (list_empty(&m->list) && m->prepared) {
		list_add(&m->list, &pool->prepared_mappings);
		wake_worker(pool);
	}
}

static void copy_complete(int read_err, unsigned long write_err, void *context)
{
	unsigned long flags;
	struct new_mapping *m = context;
	struct pool *pool = m->tc->pool;

	m->err = read_err || write_err ? -EIO : 0;

	spin_lock_irqsave(&pool->lock, flags);
	m->prepared = 1;
	__maybe_add_mapping(m);
	spin_unlock_irqrestore(&pool->lock, flags);
}

static void overwrite_endio(struct bio *bio, int err)
{
	unsigned long flags;
	struct new_mapping *m = dm_get_mapinfo(bio)->ptr;
	struct pool *pool = m->tc->pool;

	m->err = err;

	spin_lock_irqsave(&pool->lock, flags);
	m->prepared = 1;
	__maybe_add_mapping(m);
	spin_unlock_irqrestore(&pool->lock, flags);
}

static void shared_read_endio(struct bio *bio, int err)
{
	struct list_head mappings;
	struct new_mapping *m, *tmp;
	struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
	unsigned long flags;
	struct pool *pool = h->tc->pool;

	bio->bi_end_io = h->saved_bi_end_io;
	bio_endio(bio, err);

	INIT_LIST_HEAD(&mappings);
	ds_dec(h->entry, &mappings);

	spin_lock_irqsave(&pool->lock, flags);
	list_for_each_entry_safe(m, tmp, &mappings, list) {
		list_del(&m->list);
		INIT_LIST_HEAD(&m->list);
		__maybe_add_mapping(m);
	}
	spin_unlock_irqrestore(&pool->lock, flags);

	mempool_free(h, pool->endio_hook_pool);
}

/*----------------------------------------------------------------*/

/*
 * Workqueue.
 */

/*
 * Prepared mapping jobs.
 */

/*
 * This sends the bios in the cell back to the deferred_bios list.
 */
static void cell_defer(struct thin_c *tc, struct cell *cell,
		       dm_block_t data_block)
{
	struct pool *pool = tc->pool;
	unsigned long flags;

	spin_lock_irqsave(&pool->lock, flags);
	cell_release(cell, &pool->deferred_bios);
	spin_unlock_irqrestore(&tc->pool->lock, flags);

	wake_worker(pool);
}

/*
 * Same as cell_defer above, except it omits one particular detainee,
 * a write bio that covers the block and has already been processed.
 */
static void cell_defer_except(struct thin_c *tc, struct cell *cell,
			      struct bio *exception)
{
	struct bio_list bios;
	struct bio *bio;
	struct pool *pool = tc->pool;
	unsigned long flags;

	bio_list_init(&bios);
	cell_release(cell, &bios);

	spin_lock_irqsave(&pool->lock, flags);
	while ((bio = bio_list_pop(&bios)))
		if (bio != exception)
			bio_list_add(&pool->deferred_bios, bio);
	spin_unlock_irqrestore(&pool->lock, flags);

	wake_worker(pool);
}

static void process_prepared_mapping(struct new_mapping *m)
{
	struct thin_c *tc = m->tc;
	struct bio *bio;
	int r;

	bio = m->bio;
	if (bio)
		bio->bi_end_io = m->saved_bi_end_io;

	if (m->err) {
		cell_error(m->cell);
		return;
	}

	/*
	 * 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_block, m->data_block);
	if (r) {
		DMERR("dm_thin_insert_block() failed");
		cell_error(m->cell);
		return;
	}

	/*
	 * 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) {
		cell_defer_except(tc, m->cell, bio);
		bio_endio(bio, 0);
	} else
		cell_defer(tc, m->cell, m->data_block);

	list_del(&m->list);
	mempool_free(m, tc->pool->mapping_pool);
}

static void process_prepared_mappings(struct pool *pool)
{
	unsigned long flags;
	struct list_head maps;
	struct new_mapping *m, *tmp;

	INIT_LIST_HEAD(&maps);
	spin_lock_irqsave(&pool->lock, flags);
	list_splice_init(&pool->prepared_mappings, &maps);
	spin_unlock_irqrestore(&pool->lock, flags);

	list_for_each_entry_safe(m, tmp, &maps, list)
		process_prepared_mapping(m);
}

/*
 * Deferred bio jobs.
 */
static int io_overwrites_block(struct pool *pool, struct bio *bio)
{
	return ((bio_data_dir(bio) == WRITE) &&
		!(bio->bi_sector & pool->offset_mask)) &&
		(bio->bi_size == (pool->sectors_per_block << SECTOR_SHIFT));
}

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 new_mapping *get_next_mapping(struct pool *pool)
{
	struct new_mapping *r = pool->next_mapping;

	BUG_ON(!pool->next_mapping);

	pool->next_mapping = NULL;

	return r;
}

static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
			  dm_block_t data_origin, dm_block_t data_dest,
			  struct cell *cell, struct bio *bio)
{
	int r;
	struct pool *pool = tc->pool;
	struct new_mapping *m = get_next_mapping(pool);

	INIT_LIST_HEAD(&m->list);
	m->prepared = 0;
	m->tc = tc;
	m->virt_block = virt_block;
	m->data_block = data_dest;
	m->cell = cell;
	m->err = 0;
	m->bio = NULL;

	ds_add_work(&pool->ds, &m->list);

	/*
	 * 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)) {
		m->bio = bio;
		save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
		dm_get_mapinfo(bio)->ptr = m;
		remap_and_issue(tc, bio, data_dest);
	} else {
		struct dm_io_region from, to;

		from.bdev = tc->pool_dev->bdev;
		from.sector = data_origin * pool->sectors_per_block;
		from.count = pool->sectors_per_block;

		to.bdev = tc->pool_dev->bdev;
		to.sector = data_dest * pool->sectors_per_block;
		to.count = pool->sectors_per_block;

		r = dm_kcopyd_copy(pool->copier, &from, 1, &to,
				   0, copy_complete, m);
		if (r < 0) {
			mempool_free(m, pool->mapping_pool);
			DMERR("dm_kcopyd_copy() failed");
			cell_error(cell);
		}
	}
}

static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
			  dm_block_t data_block, struct cell *cell,
			  struct bio *bio)
{
	struct pool *pool = tc->pool;
	struct new_mapping *m = get_next_mapping(pool);

	INIT_LIST_HEAD(&m->list);
	m->prepared = 0;
	m->tc = tc;
	m->virt_block = virt_block;
	m->data_block = data_block;
	m->cell = cell;
	m->err = 0;
	m->bio = NULL;

	/*
	 * 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->zero_new_blocks)
		process_prepared_mapping(m);

	else if (io_overwrites_block(pool, bio)) {
		m->bio = bio;
		save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
		dm_get_mapinfo(bio)->ptr = m;
		remap_and_issue(tc, bio, data_block);

	} else {
		int r;
		struct dm_io_region to;

		to.bdev = tc->pool_dev->bdev;
		to.sector = data_block * pool->sectors_per_block;
		to.count = pool->sectors_per_block;

		r = dm_kcopyd_zero(pool->copier, 1, &to, 0, copy_complete, m);
		if (r < 0) {
			mempool_free(m, pool->mapping_pool);
			DMERR("dm_kcopyd_zero() failed");
			cell_error(cell);
		}
	}
}

static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
{
	int r;
	dm_block_t free_blocks;
	unsigned long flags;
	struct pool *pool = tc->pool;

	r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
	if (r)
		return r;

	if (free_blocks <= pool->low_water_blocks && !pool->low_water_triggered) {
		DMWARN("%s: reached low water mark, sending event.",
		       dm_device_name(pool->pool_md));
		spin_lock_irqsave(&pool->lock, flags);
		pool->low_water_triggered = 1;
		spin_unlock_irqrestore(&pool->lock, flags);
		dm_table_event(pool->ti->table);
	}

	if (!free_blocks) {
		if (pool->no_free_space)
			return -ENOSPC;
		else {
			/*
			 * Try to commit to see if that will free up some
			 * more space.
			 */
			r = dm_pool_commit_metadata(pool->pmd);
			if (r) {
				DMERR("%s: dm_pool_commit_metadata() failed, error = %d",
				      __func__, r);
				return r;
			}

			r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
			if (r)
				return r;

			/*
			 * If we still have no space we set a flag to avoid
			 * doing all this checking and return -ENOSPC.
			 */
			if (!free_blocks) {
				DMWARN("%s: no free space available.",
				       dm_device_name(pool->pool_md));
				spin_lock_irqsave(&pool->lock, flags);
				pool->no_free_space = 1;
				spin_unlock_irqrestore(&pool->lock, flags);
				return -ENOSPC;
			}
		}
	}

	r = dm_pool_alloc_data_block(pool->pmd, result);
	if (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 thin_c *tc = dm_get_mapinfo(bio)->ptr;
	struct pool *pool = tc->pool;
	unsigned long flags;

	spin_lock_irqsave(&pool->lock, flags);
	bio_list_add(&pool->retry_on_resume_list, bio);
	spin_unlock_irqrestore(&pool->lock, flags);
}

static void no_space(struct cell *cell)
{
	struct bio *bio;
	struct bio_list bios;

	bio_list_init(&bios);
	cell_release(cell, &bios);

	while ((bio = bio_list_pop(&bios)))
		retry_on_resume(bio);
}

static void break_sharing(struct thin_c *tc, struct bio *bio, dm_block_t block,
			  struct cell_key *key,
			  struct dm_thin_lookup_result *lookup_result,
			  struct cell *cell)
{
	int r;
	dm_block_t data_block;

	r = alloc_data_block(tc, &data_block);
	switch (r) {
	case 0:
		schedule_copy(tc, block, lookup_result->block,
			      data_block, cell, bio);
		break;

	case -ENOSPC:
		no_space(cell);
		break;

	default:
		DMERR("%s: alloc_data_block() failed, error = %d", __func__, r);
		cell_error(cell);
		break;
	}
}

static void process_shared_bio(struct thin_c *tc, struct bio *bio,
			       dm_block_t block,
			       struct dm_thin_lookup_result *lookup_result)
{
	struct cell *cell;
	struct pool *pool = tc->pool;
	struct 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->prison, &key, bio, &cell))
		return;

	if (bio_data_dir(bio) == WRITE)
		break_sharing(tc, bio, block, &key, lookup_result, cell);
	else {
		struct endio_hook *h;
		h = mempool_alloc(pool->endio_hook_pool, GFP_NOIO);

		h->tc = tc;
		h->entry = ds_inc(&pool->ds);
		save_and_set_endio(bio, &h->saved_bi_end_io, shared_read_endio);
		dm_get_mapinfo(bio)->ptr = h;

		cell_release_singleton(cell, bio);
		remap_and_issue(tc, bio, lookup_result->block);
	}
}

static void provision_block(struct thin_c *tc, struct bio *bio, dm_block_t block,
			    struct cell *cell)
{
	int r;
	dm_block_t data_block;

	/*
	 * Remap empty bios (flushes) immediately, without provisioning.
	 */
	if (!bio->bi_size) {
		cell_release_singleton(cell, bio);
		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_release_singleton(cell, bio);
		bio_endio(bio, 0);
		return;
	}

	r = alloc_data_block(tc, &data_block);
	switch (r) {
	case 0:
		schedule_zero(tc, block, data_block, cell, bio);
		break;

	case -ENOSPC:
		no_space(cell);
		break;

	default:
		DMERR("%s: alloc_data_block() failed, error = %d", __func__, r);
		cell_error(cell);
		break;
	}
}

static void process_bio(struct thin_c *tc, struct bio *bio)
{
	int r;
	dm_block_t block = get_bio_block(tc, bio);
	struct cell *cell;
	struct cell_key key;
	struct dm_thin_lookup_result lookup_result;

	/*
	 * 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(tc->pool->prison, &key, bio, &cell))
		return;

	r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
	switch (r) {
	case 0:
		/*
		 * We can release this cell now.  This thread is the only
		 * one that puts bios into a cell, and we know there were
		 * no preceding bios.
		 */
		/*
		 * TODO: this will probably have to change when discard goes
		 * back in.
		 */
		cell_release_singleton(cell, bio);

		if (lookup_result.shared)
			process_shared_bio(tc, bio, block, &lookup_result);
		else
			remap_and_issue(tc, bio, lookup_result.block);
		break;

	case -ENODATA:
		provision_block(tc, bio, block, cell);
		break;

	default:
		DMERR("dm_thin_find_block() failed, error = %d", r);
		bio_io_error(bio);
		break;
	}
}

static void process_deferred_bios(struct pool *pool)
{
	unsigned long flags;
	struct bio *bio;
	struct bio_list bios;
	int r;

	bio_list_init(&bios);

	spin_lock_irqsave(&pool->lock, flags);
	bio_list_merge(&bios, &pool->deferred_bios);
	bio_list_init(&pool->deferred_bios);
	spin_unlock_irqrestore(&pool->lock, flags);

	while ((bio = bio_list_pop(&bios))) {
		struct thin_c *tc = dm_get_mapinfo(bio)->ptr;
		/*
		 * 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(&pool->lock, flags);
			bio_list_merge(&pool->deferred_bios, &bios);
			spin_unlock_irqrestore(&pool->lock, flags);

			break;
		}
		process_bio(tc, bio);
	}

	/*
	 * 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))
		return;

	r = dm_pool_commit_metadata(pool->pmd);
	if (r) {
		DMERR("%s: dm_pool_commit_metadata() failed, error = %d",
		      __func__, r);
		while ((bio = bio_list_pop(&bios)))
			bio_io_error(bio);
		return;
	}

	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);

	process_prepared_mappings(pool);
	process_deferred_bios(pool);
}

/*----------------------------------------------------------------*/

/*
 * 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(&pool->lock, flags);
	bio_list_add(&pool->deferred_bios, bio);
	spin_unlock_irqrestore(&pool->lock, flags);

	wake_worker(pool);
}

/*
 * Non-blocking function called from the thin target's map function.
 */
static int thin_bio_map(struct dm_target *ti, struct bio *bio,
			union map_info *map_context)
{
	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;

	/*
	 * Save the thin context for easy access from the deferred bio later.
	 */
	map_context->ptr = tc;

	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
		thin_defer_bio(tc, bio);
		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_bio(tc, bio);
			r = DM_MAPIO_SUBMITTED;
		} else {
			remap(tc, bio, result.block);
			r = DM_MAPIO_REMAPPED;
		}
		break;

	case -ENODATA:
		/*
		 * In future, the failed dm_thin_find_block above could
		 * provide the hint to load the metadata into cache.
		 */
	case -EWOULDBLOCK:
		thin_defer_bio(tc, bio);
		r = DM_MAPIO_SUBMITTED;
		break;
	}

	return r;
}

static int pool_is_congested(struct dm_target_callbacks *cb, int bdi_bits)
{
	int r;
	unsigned long flags;
	struct pool_c *pt = container_of(cb, struct pool_c, callbacks);

	spin_lock_irqsave(&pt->pool->lock, flags);
	r = !bio_list_empty(&pt->pool->retry_on_resume_list);
	spin_unlock_irqrestore(&pt->pool->lock, flags);

	if (!r) {
		struct request_queue *q = bdev_get_queue(pt->data_dev->bdev);
		r = bdi_congested(&q->backing_dev_info, bdi_bits);
	}

	return r;
}

static void __requeue_bios(struct pool *pool)
{
	bio_list_merge(&pool->deferred_bios, &pool->retry_on_resume_list);
	bio_list_init(&pool->retry_on_resume_list);
}

/*----------------------------------------------------------------
 * Binding of control targets to a pool object
 *--------------------------------------------------------------*/
static int bind_control_target(struct pool *pool, struct dm_target *ti)
{
	struct pool_c *pt = ti->private;

	pool->ti = ti;
	pool->low_water_blocks = pt->low_water_blocks;
	pool->zero_new_blocks = pt->zero_new_blocks;

	return 0;
}

static void unbind_control_target(struct pool *pool, struct dm_target *ti)
{
	if (pool->ti == ti)
		pool->ti = NULL;
}

/*----------------------------------------------------------------
 * Pool creation
 *--------------------------------------------------------------*/
static void __pool_destroy(struct pool *pool)
{
	__pool_table_remove(pool);

	if (dm_pool_metadata_close(pool->pmd) < 0)
		DMWARN("%s: dm_pool_metadata_close() failed.", __func__);

	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);
	mempool_destroy(pool->endio_hook_pool);
	kfree(pool);
}

static struct pool *pool_create(struct mapped_device *pool_md,
				struct block_device *metadata_dev,
				unsigned long block_size, char **error)
{
	int r;
	void *err_p;
	struct pool *pool;
	struct dm_pool_metadata *pmd;

	pmd = dm_pool_metadata_open(metadata_dev, block_size);
	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;
	pool->block_shift = ffs(block_size) - 1;
	pool->offset_mask = block_size - 1;
	pool->low_water_blocks = 0;
	pool->zero_new_blocks = 1;
	pool->prison = prison_create(PRISON_CELLS);
	if (!pool->prison) {
		*error = "Error creating pool's bio prison";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_prison;
	}

	pool->copier = dm_kcopyd_client_create();
	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;
	}

	INIT_WORK(&pool->worker, do_worker);
	spin_lock_init(&pool->lock);
	bio_list_init(&pool->deferred_bios);
	bio_list_init(&pool->deferred_flush_bios);
	INIT_LIST_HEAD(&pool->prepared_mappings);
	pool->low_water_triggered = 0;
	pool->no_free_space = 0;
	bio_list_init(&pool->retry_on_resume_list);
	ds_init(&pool->ds);

	pool->next_mapping = NULL;
	pool->mapping_pool =
		mempool_create_kmalloc_pool(MAPPING_POOL_SIZE, sizeof(struct new_mapping));
	if (!pool->mapping_pool) {
		*error = "Error creating pool's mapping mempool";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_mapping_pool;
	}

	pool->endio_hook_pool =
		mempool_create_kmalloc_pool(ENDIO_HOOK_POOL_SIZE, sizeof(struct endio_hook));
	if (!pool->endio_hook_pool) {
		*error = "Error creating pool's endio_hook mempool";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_endio_hook_pool;
	}
	pool->ref_count = 1;
	pool->pool_md = pool_md;
	pool->md_dev = metadata_dev;
	__pool_table_insert(pool);

	return pool;

bad_endio_hook_pool:
	mempool_destroy(pool->mapping_pool);
bad_mapping_pool:
	destroy_workqueue(pool->wq);
bad_wq:
	dm_kcopyd_client_destroy(pool->copier);
bad_kcopyd_client:
	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, char **error)
{
	struct pool *pool = __pool_table_lookup_metadata_dev(metadata_dev);

	if (pool) {
		if (pool->pool_md != pool_md)
			return ERR_PTR(-EBUSY);
		__pool_inc(pool);

	} else {
		pool = __pool_table_lookup(pool_md);
		if (pool) {
			if (pool->md_dev != metadata_dev)
				return ERR_PTR(-EINVAL);
			__pool_inc(pool);

		} else
			pool = pool_create(pool_md, metadata_dev, block_size, error);
	}

	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);
}

struct pool_features {
	unsigned zero_new_blocks:1;
};

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, 1, "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 = 0;
			continue;
		}

		ti->error = "Unrecognised pool feature requested";
		r = -EINVAL;
	}

	return r;
}

/*
 * 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.
 */
static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
	int r;
	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;
	sector_t metadata_dev_size;

	/*
	 * 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;

	r = dm_get_device(ti, argv[0], FMODE_READ | FMODE_WRITE, &metadata_dev);
	if (r) {
		ti->error = "Error opening metadata block device";
		goto out_unlock;
	}

	metadata_dev_size = i_size_read(metadata_dev->bdev->bd_inode) >> SECTOR_SHIFT;
	if (metadata_dev_size > METADATA_DEV_MAX_SECTORS) {
		ti->error = "Metadata device is too large";
		r = -EINVAL;
		goto out_metadata;
	}

	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 ||
	    !is_power_of_2(block_size)) {
		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;
	}

	/*
	 * Set default pool features.
	 */
	memset(&pf, 0, sizeof(pf));
	pf.zero_new_blocks = 1;

	dm_consume_args(&as, 4);
	r = parse_pool_features(&as, &pf, ti);
	if (r)
		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, &ti->error);
	if (IS_ERR(pool)) {
		r = PTR_ERR(pool);
		goto out_free_pt;
	}

	pt->pool = pool;
	pt->ti = ti;
	pt->metadata_dev = metadata_dev;
	pt->data_dev = data_dev;
	pt->low_water_blocks = low_water_blocks;
	pt->zero_new_blocks = pf.zero_new_blocks;
	ti->num_flush_requests = 1;
	ti->num_discard_requests = 0;
	ti->private = pt;

	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_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,
		    union map_info *map_context)
{
	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;
}

/*
 * 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;
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;
	dm_block_t data_size, sb_data_size;

	/*
	 * Take control of the pool object.
	 */
	r = bind_control_target(pool, ti);
	if (r)
		return r;

	data_size = ti->len >> pool->block_shift;
	r = dm_pool_get_data_dev_size(pool->pmd, &sb_data_size);
	if (r) {
		DMERR("failed to retrieve data device size");
		return r;
	}

	if (data_size < sb_data_size) {
		DMERR("pool target too small, is %llu blocks (expected %llu)",
		      data_size, sb_data_size);
		return -EINVAL;

	} else if (data_size > sb_data_size) {
		r = dm_pool_resize_data_dev(pool->pmd, data_size);
		if (r) {
			DMERR("failed to resize data device");
			return r;
		}

		r = dm_pool_commit_metadata(pool->pmd);
		if (r) {
			DMERR("%s: dm_pool_commit_metadata() failed, error = %d",
			      __func__, r);
			return r;
		}
	}

	return 0;
}

static void pool_resume(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->low_water_triggered = 0;
	pool->no_free_space = 0;
	__requeue_bios(pool);
	spin_unlock_irqrestore(&pool->lock, flags);

	wake_worker(pool);
}

static void pool_postsuspend(struct dm_target *ti)
{
	int r;
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;

	flush_workqueue(pool->wq);

	r = dm_pool_commit_metadata(pool->pmd);
	if (r < 0) {
		DMERR("%s: dm_pool_commit_metadata() failed, error = %d",
		      __func__, r);
		/* FIXME: invalidate device? error the next FUA or FLUSH bio ?*/
	}
}

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;
}

/*
 * Messages supported:
 *   create_thin	<dev_id>
 *   create_snap	<dev_id> <origin_id>
 *   delete		<dev_id>
 *   trim		<dev_id> <new_size_in_sectors>
 *   set_transaction_id <current_trans_id> <new_trans_id>
 */
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 (!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
		DMWARN("Unrecognised thin pool target message received: %s", argv[0]);

	if (!r) {
		r = dm_pool_commit_metadata(pool->pmd);
		if (r)
			DMERR("%s message: dm_pool_commit_metadata() failed, error = %d",
			      argv[0], r);
	}

	return r;
}

/*
 * Status line is:
 *    <transaction id> <used metadata sectors>/<total metadata sectors>
 *    <used data sectors>/<total data sectors> <held metadata root>
 */
static int pool_status(struct dm_target *ti, status_type_t type,
		       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:
		r = dm_pool_get_metadata_transaction_id(pool->pmd,
							&transaction_id);
		if (r)
			return r;

		r = dm_pool_get_free_metadata_block_count(pool->pmd,
							  &nr_free_blocks_metadata);
		if (r)
			return r;

		r = dm_pool_get_metadata_dev_size(pool->pmd, &nr_blocks_metadata);
		if (r)
			return r;

		r = dm_pool_get_free_block_count(pool->pmd,
						 &nr_free_blocks_data);
		if (r)
			return r;

		r = dm_pool_get_data_dev_size(pool->pmd, &nr_blocks_data);
		if (r)
			return r;

		r = dm_pool_get_held_metadata_root(pool->pmd, &held_root);
		if (r)
			return r;

		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("-");

		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);

		DMEMIT("%u ", !pool->zero_new_blocks);

		if (!pool->zero_new_blocks)
			DMEMIT("skip_block_zeroing ");
		break;
	}

	return 0;
}

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 int pool_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
		      struct bio_vec *biovec, int max_size)
{
	struct pool_c *pt = ti->private;
	struct request_queue *q = bdev_get_queue(pt->data_dev->bdev);

	if (!q->merge_bvec_fn)
		return max_size;

	bvm->bi_bdev = pt->data_dev->bdev;

	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
}

static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
{
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;

	blk_limits_io_min(limits, 0);
	blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
}

static struct target_type pool_target = {
	.name = "thin-pool",
	.features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
		    DM_TARGET_IMMUTABLE,
	.version = {1, 0, 0},
	.module = THIS_MODULE,
	.ctr = pool_ctr,
	.dtr = pool_dtr,
	.map = pool_map,
	.postsuspend = pool_postsuspend,
	.preresume = pool_preresume,
	.resume = pool_resume,
	.message = pool_message,
	.status = pool_status,
	.merge = pool_merge,
	.iterate_devices = pool_iterate_devices,
	.io_hints = pool_io_hints,
};

/*----------------------------------------------------------------
 * Thin target methods
 *--------------------------------------------------------------*/
static void thin_dtr(struct dm_target *ti)
{
	struct thin_c *tc = ti->private;

	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);
	kfree(tc);

	mutex_unlock(&dm_thin_pool_table.mutex);
}

/*
 * Thin target parameters:
 *
 * <pool_dev> <dev_id>
 *
 * pool_dev: the path to the pool (eg, /dev/mapper/my_pool)
 * dev_id: the internal device identifier
 */
static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
	int r;
	struct thin_c *tc;
	struct dm_dev *pool_dev;
	struct mapped_device *pool_md;

	mutex_lock(&dm_thin_pool_table.mutex);

	if (argc != 2) {
		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;
	}

	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);

	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_thin_open;
	}

	ti->split_io = tc->pool->sectors_per_block;
	ti->num_flush_requests = 1;
	ti->num_discard_requests = 0;
	ti->discards_supported = 0;

	dm_put(pool_md);

	mutex_unlock(&dm_thin_pool_table.mutex);

	return 0;

bad_thin_open:
	__pool_dec(tc->pool);
bad_pool_lookup:
	dm_put(pool_md);
bad_common:
	dm_put_device(ti, tc->pool_dev);
bad_pool_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,
		    union map_info *map_context)
{
	bio->bi_sector -= ti->begin;

	return thin_bio_map(ti, bio, map_context);
}

static void thin_postsuspend(struct dm_target *ti)
{
	if (dm_noflush_suspending(ti))
		requeue_io((struct thin_c *)ti->private);
}

/*
 * <nr mapped sectors> <highest mapped sector>
 */
static int thin_status(struct dm_target *ti, status_type_t type,
		       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 (!tc->td)
		DMEMIT("-");
	else {
		switch (type) {
		case STATUSTYPE_INFO:
			r = dm_thin_get_mapped_count(tc->td, &mapped);
			if (r)
				return r;

			r = dm_thin_get_highest_mapped_block(tc->td, &highest);
			if (r < 0)
				return r;

			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);
			break;
		}
	}

	return 0;
}

static int thin_iterate_devices(struct dm_target *ti,
				iterate_devices_callout_fn fn, void *data)
{
	dm_block_t blocks;
	struct thin_c *tc = ti->private;

	/*
	 * 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 (!tc->pool->ti)
		return 0;	/* nothing is bound */

	blocks = tc->pool->ti->len >> tc->pool->block_shift;
	if (blocks)
		return fn(ti, tc->pool_dev, 0, tc->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;

	blk_limits_io_min(limits, 0);
	blk_limits_io_opt(limits, tc->pool->sectors_per_block << SECTOR_SHIFT);
}

static struct target_type thin_target = {
	.name = "thin",
	.version = {1, 0, 0},
	.module	= THIS_MODULE,
	.ctr = thin_ctr,
	.dtr = thin_dtr,
	.map = thin_map,
	.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)
		dm_unregister_target(&thin_target);

	return r;
}

static void dm_thin_exit(void)
{
	dm_unregister_target(&thin_target);
	dm_unregister_target(&pool_target);
}

module_init(dm_thin_init);
module_exit(dm_thin_exit);

MODULE_DESCRIPTION(DM_NAME "device-mapper thin provisioning target");
MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");