dm-thin.c 69.1 KB
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/*
 * 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
 */
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#define ENDIO_HOOK_POOL_SIZE 1024
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#define DEFERRED_SET_SIZE 64
#define MAPPING_POOL_SIZE 1024
#define PRISON_CELLS 1024
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#define COMMIT_PERIOD HZ
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/*
 * 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 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
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 * (process_prepared_mapping).  This act of inserting breaks some
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 * 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;
};

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struct dm_bio_prison_cell {
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	struct hlist_node list;
	struct bio_prison *prison;
	struct cell_key key;
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	struct bio *holder;
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	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;
}

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static struct kmem_cache *_cell_cache;

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/*
 * @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);
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	prison->cell_pool = mempool_create_slab_pool(nr_cells, _cell_cache);
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	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);
}

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static struct dm_bio_prison_cell *__search_bucket(struct hlist_head *bucket,
						  struct cell_key *key)
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{
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	struct dm_bio_prison_cell *cell;
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	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.
 *
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 * Returns 1 if the cell was already held, 0 if @inmate is the new holder.
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 */
static int bio_detain(struct bio_prison *prison, struct cell_key *key,
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		      struct bio *inmate, struct dm_bio_prison_cell **ref)
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{
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	int r = 1;
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	unsigned long flags;
	uint32_t hash = hash_key(prison, key);
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	struct dm_bio_prison_cell *cell, *cell2;
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	BUG_ON(hash > prison->nr_buckets);

	spin_lock_irqsave(&prison->lock, flags);

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	cell = __search_bucket(prison->cells + hash, key);
	if (cell) {
		bio_list_add(&cell->bios, inmate);
		goto out;
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	}

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	/*
	 * Allocate a new cell
	 */
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	spin_unlock_irqrestore(&prison->lock, flags);
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	cell2 = mempool_alloc(prison->cell_pool, GFP_NOIO);
	spin_lock_irqsave(&prison->lock, flags);
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	/*
	 * 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) {
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		mempool_free(cell2, prison->cell_pool);
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		bio_list_add(&cell->bios, inmate);
		goto out;
	}

	/*
	 * Use new cell.
	 */
	cell = cell2;

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

	r = 0;

out:
	spin_unlock_irqrestore(&prison->lock, flags);
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	*ref = cell;

	return r;
}

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

	hlist_del(&cell->list);

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	if (inmates) {
		bio_list_add(inmates, cell->holder);
		bio_list_merge(inmates, &cell->bios);
	}
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	mempool_free(cell, prison->cell_pool);
}

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static void cell_release(struct dm_bio_prison_cell *cell, struct bio_list *bios)
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{
	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.
 */
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static void __cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
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{
	BUG_ON(cell->holder != bio);
	BUG_ON(!bio_list_empty(&cell->bios));
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	__cell_release(cell, NULL);
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}

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static void cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
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{
	unsigned long flags;
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	struct bio_prison *prison = cell->prison;
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	spin_lock_irqsave(&prison->lock, flags);
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	__cell_release_singleton(cell, bio);
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	spin_unlock_irqrestore(&prison->lock, flags);
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}

/*
 * Sometimes we don't want the holder, just the additional bios.
 */
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static void __cell_release_no_holder(struct dm_bio_prison_cell *cell,
				     struct bio_list *inmates)
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{
	struct bio_prison *prison = cell->prison;

	hlist_del(&cell->list);
	bio_list_merge(inmates, &cell->bios);

	mempool_free(cell, prison->cell_pool);
}

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static void cell_release_no_holder(struct dm_bio_prison_cell *cell,
				   struct bio_list *inmates)
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{
	unsigned long flags;
	struct bio_prison *prison = cell->prison;
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	spin_lock_irqsave(&prison->lock, flags);
	__cell_release_no_holder(cell, inmates);
	spin_unlock_irqrestore(&prison->lock, flags);
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}

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static void cell_error(struct dm_bio_prison_cell *cell)
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{
	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.
 */
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struct dm_thin_new_mapping;
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struct pool_features {
	unsigned zero_new_blocks:1;
	unsigned discard_enabled:1;
	unsigned discard_passdown:1;
};

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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;
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	uint32_t sectors_per_block;
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	int sectors_per_block_shift;
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	struct pool_features pf;
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	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;
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	struct delayed_work waker;
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	unsigned long last_commit_jiffies;
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	unsigned ref_count;
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	spinlock_t lock;
	struct bio_list deferred_bios;
	struct bio_list deferred_flush_bios;
	struct list_head prepared_mappings;
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	struct list_head prepared_discards;
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	struct bio_list retry_on_resume_list;

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	struct deferred_set shared_read_ds;
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	struct deferred_set all_io_ds;
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	struct dm_thin_new_mapping *next_mapping;
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	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;
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	struct pool_features pf;
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};

/*
 * Target context for a thin.
 */
struct thin_c {
	struct dm_dev *pool_dev;
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	struct dm_dev *origin_dev;
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	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;
}

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

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struct dm_thin_endio_hook {
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	struct thin_c *tc;
	struct deferred_entry *shared_read_entry;
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	struct deferred_entry *all_io_entry;
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	struct dm_thin_new_mapping *overwrite_mapping;
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};

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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))) {
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		struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;

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		if (h->tc == tc)
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			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)
{
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	sector_t block_nr = bio->bi_sector;

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	if (tc->pool->sectors_per_block_shift < 0)
		(void) sector_div(block_nr, tc->pool->sectors_per_block);
	else
		block_nr >>= tc->pool->sectors_per_block_shift;
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	return block_nr;
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}

static void remap(struct thin_c *tc, struct bio *bio, dm_block_t block)
{
	struct pool *pool = tc->pool;
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	sector_t bi_sector = bio->bi_sector;
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	bio->bi_bdev = tc->pool_dev->bdev;
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	if (tc->pool->sectors_per_block_shift < 0)
		bio->bi_sector = (block * pool->sectors_per_block) +
				 sector_div(bi_sector, pool->sectors_per_block);
	else
		bio->bi_sector = (block << pool->sectors_per_block_shift) |
				(bi_sector & (pool->sectors_per_block - 1));
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}

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static void remap_to_origin(struct thin_c *tc, struct bio *bio)
{
	bio->bi_bdev = tc->origin_dev->bdev;
}

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

	/*
	 * 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);
}

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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);
}

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/*
 * 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.
 */
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struct dm_thin_new_mapping {
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	struct list_head list;

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	unsigned quiesced:1;
	unsigned prepared:1;
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	unsigned pass_discard:1;
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	struct thin_c *tc;
	dm_block_t virt_block;
	dm_block_t data_block;
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	struct dm_bio_prison_cell *cell, *cell2;
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	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;
};

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static void __maybe_add_mapping(struct dm_thin_new_mapping *m)
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{
	struct pool *pool = m->tc->pool;

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	if (m->quiesced && m->prepared) {
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		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;
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	struct dm_thin_new_mapping *m = context;
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	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;
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	struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;
	struct dm_thin_new_mapping *m = h->overwrite_mapping;
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	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);
}

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

/*
 * Workqueue.
 */

/*
 * Prepared mapping jobs.
 */

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

	bio_list_init(&bios);

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

	wake_worker(pool);
}

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static void process_prepared_mapping(struct dm_thin_new_mapping *m)
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{
	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) {
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		cell_defer_except(tc, m->cell);
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		bio_endio(bio, 0);
	} else
		cell_defer(tc, m->cell, m->data_block);

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

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static void process_prepared_discard(struct dm_thin_new_mapping *m)
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{
	int r;
	struct thin_c *tc = m->tc;

	r = dm_thin_remove_block(tc->td, m->virt_block);
	if (r)
		DMERR("dm_thin_remove_block() failed");

	/*
	 * Pass the discard down to the underlying device?
	 */
	if (m->pass_discard)
		remap_and_issue(tc, m->bio, m->data_block);
	else
		bio_endio(m->bio, 0);

	cell_defer_except(tc, m->cell);
	cell_defer_except(tc, m->cell2);
	mempool_free(m, tc->pool->mapping_pool);
}

static void process_prepared(struct pool *pool, struct list_head *head,
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			     void (*fn)(struct dm_thin_new_mapping *))
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{
	unsigned long flags;
	struct list_head maps;
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	struct dm_thin_new_mapping *m, *tmp;
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	INIT_LIST_HEAD(&maps);
	spin_lock_irqsave(&pool->lock, flags);
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	list_splice_init(head, &maps);
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	spin_unlock_irqrestore(&pool->lock, flags);

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

/*
 * Deferred bio jobs.
 */
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static int io_overlaps_block(struct pool *pool, struct bio *bio)
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{
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	return bio->bi_size == (pool->sectors_per_block << SECTOR_SHIFT);
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}

static int io_overwrites_block(struct pool *pool, struct bio *bio)
{
	return (bio_data_dir(bio) == WRITE) &&
		io_overlaps_block(pool, bio);
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}

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;
}

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static struct dm_thin_new_mapping *get_next_mapping(struct pool *pool)
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{
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	struct dm_thin_new_mapping *r = pool->next_mapping;
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	BUG_ON(!pool->next_mapping);

	pool->next_mapping = NULL;

	return r;
}

static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
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			  struct dm_dev *origin, dm_block_t data_origin,
			  dm_block_t data_dest,
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			  struct dm_bio_prison_cell *cell, struct bio *bio)
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{
	int r;
	struct pool *pool = tc->pool;
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	struct dm_thin_new_mapping *m = get_next_mapping(pool);
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	INIT_LIST_HEAD(&m->list);
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	m->quiesced = 0;
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	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;

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	if (!ds_add_work(&pool->shared_read_ds, &m->list))
		m->quiesced = 1;
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	/*
	 * 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)) {
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		struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;

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		h->overwrite_mapping = m;
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		m->bio = bio;
		save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
		remap_and_issue(tc, bio, data_dest);
	} else {
		struct dm_io_region from, to;

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		from.bdev = origin->bdev;
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		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);
		}
	}
}

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static void schedule_internal_copy(struct thin_c *tc, dm_block_t virt_block,
				   dm_block_t data_origin, dm_block_t data_dest,
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				   struct dm_bio_prison_cell *cell, struct bio *bio)
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{
	schedule_copy(tc, virt_block, tc->pool_dev,
		      data_origin, data_dest, cell, bio);
}

static void schedule_external_copy(struct thin_c *tc, dm_block_t virt_block,
				   dm_block_t data_dest,
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				   struct dm_bio_prison_cell *cell, struct bio *bio)
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{
	schedule_copy(tc, virt_block, tc->origin_dev,
		      virt_block, data_dest, cell, bio);
}

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static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
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			  dm_block_t data_block, struct dm_bio_prison_cell *cell,
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			  struct bio *bio)
{
	struct pool *pool = tc->pool;
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	struct dm_thin_new_mapping *m = get_next_mapping(pool);
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	INIT_LIST_HEAD(&m->list);
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	m->quiesced = 1;
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	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.
	 */
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	if (!pool->pf.zero_new_blocks)
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		process_prepared_mapping(m);

	else if (io_overwrites_block(pool, bio)) {
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		struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;

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		h->overwrite_mapping = m;
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		m->bio = bio;
		save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
		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)
{
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	struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;
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	struct thin_c *tc = h->tc;
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	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);
}

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static void no_space(struct dm_bio_prison_cell *cell)
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{
	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);
}

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static void process_discard(struct thin_c *tc, struct bio *bio)
{
	int r;
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	unsigned long flags;
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	struct pool *pool = tc->pool;
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	struct dm_bio_prison_cell *cell, *cell2;
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	struct cell_key key, key2;
	dm_block_t block = get_bio_block(tc, bio);
	struct dm_thin_lookup_result lookup_result;
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	struct dm_thin_new_mapping *m;
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	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:
		/*
		 * Check nobody is fiddling with this pool block.  This can
		 * happen if someone's in the process of breaking sharing
		 * on this block.
		 */
		build_data_key(tc->td, lookup_result.block, &key2);
		if (bio_detain(tc->pool->prison, &key2, bio, &cell2)) {
			cell_release_singleton(cell, bio);
			break;
		}

		if (io_overlaps_block(pool, bio)) {
			/*
			 * 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;
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			m->pass_discard = (!lookup_result.shared) && pool->pf.discard_passdown;
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			m->virt_block = block;
			m->data_block = lookup_result.block;
			m->cell = cell;
			m->cell2 = cell2;
			m->err = 0;
			m->bio = bio;

			if (!ds_add_work(&pool->all_io_ds, &m->list)) {
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				spin_lock_irqsave(&pool->lock, flags);
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				list_add(&m->list, &pool->prepared_discards);
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				spin_unlock_irqrestore(&pool->lock, flags);
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				wake_worker(pool);
			}
		} else {
			/*
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			 * The DM core makes sure that the discard doesn't span
			 * a block boundary.  So we submit the discard of a
			 * partial block appropriately.
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			 */
			cell_release_singleton(cell, bio);
			cell_release_singleton(cell2, bio);
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			if ((!lookup_result.shared) && pool->pf.discard_passdown)
				remap_and_issue(tc, bio, lookup_result.block);
			else
				bio_endio(bio, 0);
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		}
		break;

	case -ENODATA:
		/*
		 * It isn't provisioned, just forget it.
		 */
		cell_release_singleton(cell, bio);
		bio_endio(bio, 0);
		break;

	default:
		DMERR("discard: find block unexpectedly returned %d", r);
		cell_release_singleton(cell, bio);
		bio_io_error(bio);
		break;
	}
}

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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,
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			  struct dm_bio_prison_cell *cell)
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{
	int r;
	dm_block_t data_block;

	r = alloc_data_block(tc, &data_block);
	switch (r) {
	case 0:
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		schedule_internal_copy(tc, block, lookup_result->block,
				       data_block, cell, bio);
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		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)
{
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	struct dm_bio_prison_cell *cell;
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	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 {
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		struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;
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		h->shared_read_entry = ds_inc(&pool->shared_read_ds);
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		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,
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			    struct dm_bio_prison_cell *cell)
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{
	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:
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		if (tc->origin_dev)
			schedule_external_copy(tc, block, data_block, cell, bio);
		else
			schedule_zero(tc, block, data_block, cell, bio);
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		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);
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	struct dm_bio_prison_cell *cell;
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	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:
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		if (bio_data_dir(bio) == READ && tc->origin_dev) {
			cell_release_singleton(cell, bio);
			remap_to_origin_and_issue(tc, bio);
		} else
			provision_block(tc, bio, block, cell);
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		break;

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

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static int need_commit_due_to_time(struct pool *pool)
{
	return jiffies < pool->last_commit_jiffies ||
	       jiffies > pool->last_commit_jiffies + COMMIT_PERIOD;
}

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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))) {
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		struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;
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		struct thin_c *tc = h->tc;

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		/*
		 * 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;
		}
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		if (bio->bi_rw & REQ_DISCARD)
			process_discard(tc, bio);
		else
			process_bio(tc, bio);
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	}

	/*
	 * 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);

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	if (bio_list_empty(&bios) && !need_commit_due_to_time(pool))
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		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;
	}
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	pool->last_commit_jiffies = jiffies;
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	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);

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	process_prepared(pool, &pool->prepared_mappings, process_prepared_mapping);
	process_prepared(pool, &pool->prepared_discards, process_prepared_discard);
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	process_deferred_bios(pool);
}

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/*
 * 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);
}

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

/*
 * 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);
}

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static struct dm_thin_endio_hook *thin_hook_bio(struct thin_c *tc, struct bio *bio)
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{
	struct pool *pool = tc->pool;
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	struct dm_thin_endio_hook *h = mempool_alloc(pool->endio_hook_pool, GFP_NOIO);
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	h->tc = tc;
	h->shared_read_entry = NULL;
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	h->all_io_entry = bio->bi_rw & REQ_DISCARD ? NULL : ds_inc(&pool->all_io_ds);
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	h->overwrite_mapping = NULL;

	return h;
}

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/*
 * 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;

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	map_context->ptr = thin_hook_bio(tc, bio);
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	if (bio->bi_rw & (REQ_DISCARD | REQ_FLUSH | REQ_FUA)) {
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		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;
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	pool->pf = pt->pf;
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	/*
	 * If discard_passdown was enabled verify that the data device
	 * supports discards.  Disable discard_passdown if not; otherwise
	 * -EOPNOTSUPP will be returned.
	 */
	if (pt->pf.discard_passdown) {
		struct request_queue *q = bdev_get_queue(pt->data_dev->bdev);
		if (!q || !blk_queue_discard(q)) {
			char buf[BDEVNAME_SIZE];
			DMWARN("Discard unsupported by data device (%s): Disabling discard passdown.",
			       bdevname(pt->data_dev->bdev, buf));
			pool->pf.discard_passdown = 0;
		}
	}

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	return 0;
}

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

/*----------------------------------------------------------------
 * Pool creation
 *--------------------------------------------------------------*/
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/* Initialize pool features. */
static void pool_features_init(struct pool_features *pf)
{
	pf->zero_new_blocks = 1;
	pf->discard_enabled = 1;
	pf->discard_passdown = 1;
}

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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);
}

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static struct kmem_cache *_new_mapping_cache;
static struct kmem_cache *_endio_hook_cache;

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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;
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	if (block_size & (block_size - 1))
		pool->sectors_per_block_shift = -1;
	else
		pool->sectors_per_block_shift = __ffs(block_size);
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	pool->low_water_blocks = 0;
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	pool_features_init(&pool->pf);
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	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);
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	INIT_DELAYED_WORK(&pool->waker, do_waker);
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	spin_lock_init(&pool->lock);
	bio_list_init(&pool->deferred_bios);
	bio_list_init(&pool->deferred_flush_bios);
	INIT_LIST_HEAD(&pool->prepared_mappings);
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	INIT_LIST_HEAD(&pool->prepared_discards);
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	pool->low_water_triggered = 0;
	pool->no_free_space = 0;
	bio_list_init(&pool->retry_on_resume_list);
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	ds_init(&pool->shared_read_ds);
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	ds_init(&pool->all_io_ds);
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	pool->next_mapping = NULL;
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	pool->mapping_pool = mempool_create_slab_pool(MAPPING_POOL_SIZE,
						      _new_mapping_cache);
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	if (!pool->mapping_pool) {
		*error = "Error creating pool's mapping mempool";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_mapping_pool;
	}

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	pool->endio_hook_pool = mempool_create_slab_pool(ENDIO_HOOK_POOL_SIZE,
							 _endio_hook_cache);
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	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;
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	pool->last_commit_jiffies = jiffies;
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	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,
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