1 files changed, 2428 insertions, 0 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
new file mode 100644
index 00000000000..c3087575fef
--- /dev/null
+++ b/drivers/md/dm-thin.c
@@ -0,0 +1,2428 @@
+/*
+ * 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");