dm thin: tidy discard support

[linux-2.6-block.git] / drivers / md / dm-thin.c

/*
 * Copyright (C) 2011-2012 Red Hat UK.
 *
 * This file is released under the GPL.
 */

#include "dm-thin-metadata.h"
#include "dm.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 1024
#define DEFERRED_SET_SIZE 64
#define MAPPING_POOL_SIZE 1024
#define PRISON_CELLS 1024
#define COMMIT_PERIOD HZ

/*
 * 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
 * (process_prepared_mapping).  This act of inserting breaks some
 * sharing of btree nodes between the two devices.  Breaking sharing only
 * effects the btree of that specific device.  Btrees for the other
 * devices that share the block never change.  The btree for the origin
 * device as it was after the last commit is untouched, ie. we're using
 * persistent data structures in the functional programming sense.
 *
 * v) unplug io to this physical block, including the io that triggered
 * the breaking of sharing.
 *
 * Steps (ii) and (iii) occur in parallel.
 *
 * The metadata _doesn't_ need to be committed before the io continues.  We
 * get away with this because the io is always written to a _new_ block.
 * If there's a crash, then:
 *
 * - The origin mapping will point to the old origin block (the shared
 * one).  This will contain the data as it was before the io that triggered
 * the breaking of sharing came in.
 *
 * - The snap mapping still points to the old block.  As it would after
 * the commit.
 *
 * The downside of this scheme is the timestamp magic isn't perfect, and
 * will continue to think that data block in the snapshot device is shared
 * even after the write to the origin has broken sharing.  I suspect data
 * blocks will typically be shared by many different devices, so we're
 * breaking sharing n + 1 times, rather than n, where n is the number of
 * devices that reference this data block.  At the moment I think the
 * benefits far, far outweigh the disadvantages.
 */

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

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

static struct kmem_cache *_cell_cache;

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

        BUG_ON(hash > prison->nr_buckets);

        spin_lock_irqsave(&prison->lock, flags);

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

        /*
         * 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) {
                mempool_free(cell2, prison->cell_pool);
                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);

        *ref = cell;

        return r;
}

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

        hlist_del(&cell->list);

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

        mempool_free(cell, prison->cell_pool);
}

static void cell_release(struct dm_bio_prison_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 dm_bio_prison_cell *cell, struct bio *bio)
{
        BUG_ON(cell->holder != bio);
        BUG_ON(!bio_list_empty(&cell->bios));

        __cell_release(cell, NULL);
}

static void cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
{
        unsigned long flags;
        struct bio_prison *prison = cell->prison;

        spin_lock_irqsave(&prison->lock, flags);
        __cell_release_singleton(cell, bio);
        spin_unlock_irqrestore(&prison->lock, flags);
}

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

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

        mempool_free(cell, prison->cell_pool);
}

static void cell_release_no_holder(struct dm_bio_prison_cell *cell,
                                   struct bio_list *inmates)
{
        unsigned long flags;
        struct bio_prison *prison = cell->prison;

        spin_lock_irqsave(&prison->lock, flags);
        __cell_release_no_holder(cell, inmates);
        spin_unlock_irqrestore(&prison->lock, flags);
}

static void cell_error(struct dm_bio_prison_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 dm_thin_new_mapping;

/*
 * The pool runs in 3 modes.  Ordered in degraded order for comparisons.
 */
enum pool_mode {
        PM_WRITE,               /* metadata may be changed */
        PM_READ_ONLY,           /* metadata may not be changed */
        PM_FAIL,                /* all I/O fails */
};

struct pool_features {
        enum pool_mode mode;

        bool zero_new_blocks:1;
        bool discard_enabled:1;
        bool discard_passdown:1;
};

struct thin_c;
typedef void (*process_bio_fn)(struct thin_c *tc, struct bio *bio);
typedef void (*process_mapping_fn)(struct dm_thin_new_mapping *m);

struct pool {
        struct list_head list;
        struct dm_target *ti;   /* Only set if a pool target is bound */

        struct mapped_device *pool_md;
        struct block_device *md_dev;
        struct dm_pool_metadata *pmd;

        dm_block_t low_water_blocks;
        uint32_t sectors_per_block;
        int sectors_per_block_shift;

        struct pool_features pf;
        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;
        struct delayed_work waker;

        unsigned long last_commit_jiffies;
        unsigned ref_count;

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

        struct bio_list retry_on_resume_list;

        struct deferred_set shared_read_ds;
        struct deferred_set all_io_ds;

        struct dm_thin_new_mapping *next_mapping;
        mempool_t *mapping_pool;
        mempool_t *endio_hook_pool;

        process_bio_fn process_bio;
        process_bio_fn process_discard;

        process_mapping_fn process_prepared_mapping;
        process_mapping_fn process_prepared_discard;
};

static enum pool_mode get_pool_mode(struct pool *pool);
static void set_pool_mode(struct pool *pool, enum pool_mode mode);

/*
 * Target context for a pool.
 */
struct pool_c {
        struct dm_target *ti;
        struct pool *pool;
        struct dm_dev *data_dev;
        struct dm_dev *metadata_dev;
        struct dm_target_callbacks callbacks;

        dm_block_t low_water_blocks;
        struct pool_features pf;
};

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

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

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

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

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

        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;

        return block_nr;
}

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

        bio->bi_bdev = tc->pool_dev->bdev;
        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));
}

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

static int bio_triggers_commit(struct thin_c *tc, struct bio *bio)
{
        return (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) &&
                dm_thin_changed_this_transaction(tc->td);
}

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

        if (!bio_triggers_commit(tc, bio)) {
                generic_make_request(bio);
                return;
        }

        /*
         * Complete bio with an error if earlier I/O caused changes to
         * the metadata that can't be committed e.g, due to I/O errors
         * on the metadata device.
         */
        if (dm_thin_aborted_changes(tc->td)) {
                bio_io_error(bio);
                return;
        }

        /*
         * Batch together any bios that trigger commits and then issue a
         * single commit for them in process_deferred_bios().
         */
        spin_lock_irqsave(&pool->lock, flags);
        bio_list_add(&pool->deferred_flush_bios, bio);
        spin_unlock_irqrestore(&pool->lock, flags);
}

static void remap_to_origin_and_issue(struct thin_c *tc, struct bio *bio)
{
        remap_to_origin(tc, bio);
        issue(tc, bio);
}

static void remap_and_issue(struct thin_c *tc, struct bio *bio,
                            dm_block_t block)
{
        remap(tc, bio, block);
        issue(tc, bio);
}

/*
 * 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 dm_thin_new_mapping {
        struct list_head list;

        unsigned quiesced:1;
        unsigned prepared:1;
        unsigned pass_discard:1;

        struct thin_c *tc;
        dm_block_t virt_block;
        dm_block_t data_block;
        struct dm_bio_prison_cell *cell, *cell2;
        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 dm_thin_new_mapping *m)
{
        struct pool *pool = m->tc->pool;

        if (m->quiesced && 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 dm_thin_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 dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;
        struct dm_thin_new_mapping *m = h->overwrite_mapping;
        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.
 */
static void cell_defer(struct thin_c *tc, struct dm_bio_prison_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 dm_bio_prison_cell *cell)
{
        struct bio_list bios;
        struct pool *pool = tc->pool;
        unsigned long flags;

        bio_list_init(&bios);

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

        wake_worker(pool);
}

static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
{
        if (m->bio)
                m->bio->bi_end_io = m->saved_bi_end_io;
        cell_error(m->cell);
        list_del(&m->list);
        mempool_free(m, m->tc->pool->mapping_pool);
}
static void process_prepared_mapping(struct dm_thin_new_mapping *m)
{
        struct thin_c *tc = m->tc;
        struct 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);
                goto out;
        }

        /*
         * Commit the prepared block into the mapping btree.
         * Any I/O for this block arriving after this point will get
         * remapped to it directly.
         */
        r = dm_thin_insert_block(tc->td, m->virt_block, m->data_block);
        if (r) {
                DMERR("dm_thin_insert_block() failed");
                cell_error(m->cell);
                goto out;
        }

        /*
         * Release any bios held while the block was being provisioned.
         * If we are processing a write bio that completely covers the block,
         * we already processed it so can ignore it now when processing
         * the bios in the cell.
         */
        if (bio) {
                cell_defer_except(tc, m->cell);
                bio_endio(bio, 0);
        } else
                cell_defer(tc, m->cell, m->data_block);

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

static void process_prepared_discard_fail(struct dm_thin_new_mapping *m)
{
        struct thin_c *tc = m->tc;

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

static void process_prepared_discard_passdown(struct dm_thin_new_mapping *m)
{
        struct thin_c *tc = m->tc;

        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_discard(struct dm_thin_new_mapping *m)
{
        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");

        process_prepared_discard_passdown(m);
}

static void process_prepared(struct pool *pool, struct list_head *head,
                             process_mapping_fn *fn)
{
        unsigned long flags;
        struct list_head maps;
        struct dm_thin_new_mapping *m, *tmp;

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

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

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

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

static void save_and_set_endio(struct bio *bio, bio_end_io_t **save,
                               bio_end_io_t *fn)
{
        *save = bio->bi_end_io;
        bio->bi_end_io = fn;
}

static int ensure_next_mapping(struct pool *pool)
{
        if (pool->next_mapping)
                return 0;

        pool->next_mapping = mempool_alloc(pool->mapping_pool, GFP_ATOMIC);

        return pool->next_mapping ? 0 : -ENOMEM;
}

static struct dm_thin_new_mapping *get_next_mapping(struct pool *pool)
{
        struct dm_thin_new_mapping *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,
                          struct dm_dev *origin, dm_block_t data_origin,
                          dm_block_t data_dest,
                          struct dm_bio_prison_cell *cell, struct bio *bio)
{
        int r;
        struct pool *pool = tc->pool;
        struct dm_thin_new_mapping *m = get_next_mapping(pool);

        INIT_LIST_HEAD(&m->list);
        m->quiesced = 0;
        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;

        if (!ds_add_work(&pool->shared_read_ds, &m->list))
                m->quiesced = 1;

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

                h->overwrite_mapping = m;
                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;

                from.bdev = origin->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_internal_copy(struct thin_c *tc, dm_block_t virt_block,
                                   dm_block_t data_origin, dm_block_t data_dest,
                                   struct dm_bio_prison_cell *cell, struct bio *bio)
{
        schedule_copy(tc, virt_block, tc->pool_dev,
                      data_origin, data_dest, cell, bio);
}

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

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

        INIT_LIST_HEAD(&m->list);
        m->quiesced = 1;
        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->pf.zero_new_blocks)
                process_prepared_mapping(m);

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

                h->overwrite_mapping = m;
                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 commit(struct pool *pool)
{
        int r;

        r = dm_pool_commit_metadata(pool->pmd);
        if (r)
                DMERR("commit failed, error = %d", r);

        return r;
}

/*
 * A non-zero return indicates read_only or fail_io mode.
 * Many callers don't care about the return value.
 */
static int commit_or_fallback(struct pool *pool)
{
        int r;

        if (get_pool_mode(pool) != PM_WRITE)
                return -EINVAL;

        r = commit(pool);
        if (r)
                set_pool_mode(pool, PM_READ_ONLY);

        return r;
}

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.
                         */
                        (void) commit_or_fallback(pool);

                        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 dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;
        struct thin_c *tc = h->tc;
        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 dm_bio_prison_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 process_discard(struct thin_c *tc, struct bio *bio)
{
        int r;
        unsigned long flags;
        struct pool *pool = tc->pool;
        struct dm_bio_prison_cell *cell, *cell2;
        struct cell_key key, key2;
        dm_block_t block = get_bio_block(tc, bio);
        struct dm_thin_lookup_result lookup_result;
        struct dm_thin_new_mapping *m;

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

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 dm_bio_prison_cell *cell)
{
        int r;
        dm_block_t data_block;

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

        case -ENOSPC:
                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 dm_bio_prison_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 && bio->bi_size)
                break_sharing(tc, bio, block, &key, lookup_result, cell);
        else {
                struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;

                h->shared_read_entry = ds_inc(&pool->shared_read_ds);

                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 dm_bio_prison_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:
                if (tc->origin_dev)
                        schedule_external_copy(tc, block, data_block, cell, bio);
                else
                        schedule_zero(tc, block, data_block, cell, bio);
                break;

        case -ENOSPC:
                no_space(cell);
                break;

        default:
                DMERR("%s: alloc_data_block() failed, error = %d", __func__, r);
                set_pool_mode(tc->pool, PM_READ_ONLY);
                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 dm_bio_prison_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:
                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);
                break;

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

static void process_bio_read_only(struct thin_c *tc, struct bio *bio)
{
        int r;
        int rw = bio_data_dir(bio);
        dm_block_t block = get_bio_block(tc, bio);
        struct dm_thin_lookup_result lookup_result;

        r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
        switch (r) {
        case 0:
                if (lookup_result.shared && (rw == WRITE) && bio->bi_size)
                        bio_io_error(bio);
                else
                        remap_and_issue(tc, bio, lookup_result.block);
                break;

        case -ENODATA:
                if (rw != READ) {
                        bio_io_error(bio);
                        break;
                }

                if (tc->origin_dev) {
                        remap_to_origin_and_issue(tc, bio);
                        break;
                }

                zero_fill_bio(bio);
                bio_endio(bio, 0);
                break;

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

static void process_bio_fail(struct thin_c *tc, struct bio *bio)
{
        bio_io_error(bio);
}

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

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

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

                /*
                 * 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;
                }

                if (bio->bi_rw & REQ_DISCARD)
                        pool->process_discard(tc, bio);
                else
                        pool->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) && !need_commit_due_to_time(pool))
                return;

        if (commit_or_fallback(pool)) {
                while ((bio = bio_list_pop(&bios)))
                        bio_io_error(bio);
                return;
        }
        pool->last_commit_jiffies = jiffies;

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

static void do_worker(struct work_struct *ws)
{
        struct pool *pool = container_of(ws, struct pool, worker);

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

/*
 * We want to commit periodically so that not too much
 * unwritten data builds up.
 */
static void do_waker(struct work_struct *ws)
{
        struct pool *pool = container_of(to_delayed_work(ws), struct pool, waker);
        wake_worker(pool);
        queue_delayed_work(pool->wq, &pool->waker, COMMIT_PERIOD);
}

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

static enum pool_mode get_pool_mode(struct pool *pool)
{
        return pool->pf.mode;
}

static void set_pool_mode(struct pool *pool, enum pool_mode mode)
{
        int r;

        pool->pf.mode = mode;

        switch (mode) {
        case PM_FAIL:
                DMERR("switching pool to failure mode");
                pool->process_bio = process_bio_fail;
                pool->process_discard = process_bio_fail;
                pool->process_prepared_mapping = process_prepared_mapping_fail;
                pool->process_prepared_discard = process_prepared_discard_fail;
                break;

        case PM_READ_ONLY:
                DMERR("switching pool to read-only mode");
                r = dm_pool_abort_metadata(pool->pmd);
                if (r) {
                        DMERR("aborting transaction failed");
                        set_pool_mode(pool, PM_FAIL);
                } else {
                        dm_pool_metadata_read_only(pool->pmd);
                        pool->process_bio = process_bio_read_only;
                        pool->process_discard = process_discard;
                        pool->process_prepared_mapping = process_prepared_mapping_fail;
                        pool->process_prepared_discard = process_prepared_discard_passdown;
                }
                break;

        case PM_WRITE:
                pool->process_bio = process_bio;
                pool->process_discard = process_discard;
                pool->process_prepared_mapping = process_prepared_mapping;
                pool->process_prepared_discard = process_prepared_discard;
                break;
        }
}

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

/*
 * 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);
}

static struct dm_thin_endio_hook *thin_hook_bio(struct thin_c *tc, struct bio *bio)
{
        struct pool *pool = tc->pool;
        struct dm_thin_endio_hook *h = mempool_alloc(pool->endio_hook_pool, GFP_NOIO);

        h->tc = tc;
        h->shared_read_entry = NULL;
        h->all_io_entry = bio->bi_rw & REQ_DISCARD ? NULL : ds_inc(&pool->all_io_ds);
        h->overwrite_mapping = NULL;

        return h;
}

/*
 * 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;

        map_context->ptr = thin_hook_bio(tc, bio);

        if (get_pool_mode(tc->pool) == PM_FAIL) {
                bio_io_error(bio);
                return DM_MAPIO_SUBMITTED;
        }

        if (bio->bi_rw & (REQ_DISCARD | 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:
                if (get_pool_mode(tc->pool) == PM_READ_ONLY) {
                        /*
                         * This block isn't provisioned, and we have no way
                         * of doing so.  Just error it.
                         */
                        bio_io_error(bio);
                        r = DM_MAPIO_SUBMITTED;
                        break;
                }
                /* fall through */

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

        default:
                /*
                 * Must always call bio_io_error on failure.
                 * dm_thin_find_block can fail with -EINVAL if the
                 * pool is switched to fail-io mode.
                 */
                bio_io_error(bio);
                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 bool data_dev_supports_discard(struct pool_c *pt)
{
        struct request_queue *q = bdev_get_queue(pt->data_dev->bdev);

        return q && blk_queue_discard(q);
}

/*
 * If discard_passdown was enabled verify that the data device
 * supports discards.  Disable discard_passdown if not; otherwise
 * -EOPNOTSUPP will be returned.
 */
static void disable_passdown_if_not_supported(struct pool_c *pt,
                                              struct pool_features *pf)
{
        char buf[BDEVNAME_SIZE];

        if (!pf->discard_passdown || data_dev_supports_discard(pt))
                return;

        DMWARN("Discard unsupported by data device (%s): Disabling discard passdown.",
               bdevname(pt->data_dev->bdev, buf));

        pf->discard_passdown = false;
}

static int bind_control_target(struct pool *pool, struct dm_target *ti)
{
        struct pool_c *pt = ti->private;

        /*
         * We want to make sure that degraded pools are never upgraded.
         */
        enum pool_mode old_mode = pool->pf.mode;
        enum pool_mode new_mode = pt->pf.mode;

        if (old_mode > new_mode)
                new_mode = old_mode;

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

        disable_passdown_if_not_supported(pt, &pool->pf);
        set_pool_mode(pool, new_mode);

        return 0;
}

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

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

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 kmem_cache *_new_mapping_cache;
static struct kmem_cache *_endio_hook_cache;

static struct pool *pool_create(struct mapped_device *pool_md,
                                struct block_device *metadata_dev,
                                unsigned long block_size,
                                int read_only, char **error)
{
        int r;
        void *err_p;
        struct pool *pool;
        struct dm_pool_metadata *pmd;
        bool format_device = read_only ? false : true;

        pmd = dm_pool_metadata_open(metadata_dev, block_size, format_device);
        if (IS_ERR(pmd)) {
                *error = "Error creating metadata object";
                return (struct pool *)pmd;
        }

        pool = kmalloc(sizeof(*pool), GFP_KERNEL);
        if (!pool) {
                *error = "Error allocating memory for pool";
                err_p = ERR_PTR(-ENOMEM);
                goto bad_pool;
        }

        pool->pmd = pmd;
        pool->sectors_per_block = block_size;
        if (block_size & (block_size - 1))
                pool->sectors_per_block_shift = -1;
        else
                pool->sectors_per_block_shift = __ffs(block_size);
        pool->low_water_blocks = 0;
        pool_features_init(&pool->pf);
        pool->prison = 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);
        INIT_DELAYED_WORK(&pool->waker, do_waker);
        spin_lock_init(&pool->lock);
        bio_list_init(&pool->deferred_bios);
        bio_list_init(&pool->deferred_flush_bios);
        INIT_LIST_HEAD(&pool->prepared_mappings);
        INIT_LIST_HEAD(&pool->prepared_discards);
        pool->low_water_triggered = 0;
        pool->no_free_space = 0;
        bio_list_init(&pool->retry_on_resume_list);
        ds_init(&pool->shared_read_ds);
        ds_init(&pool->all_io_ds);

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

        pool->endio_hook_pool = mempool_create_slab_pool(ENDIO_HOOK_POOL_SIZE,
                                                         _endio_hook_cache);
        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->last_commit_jiffies = jiffies;
        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, int read_only,
                                char **error, int *created)
{
        struct pool *pool = __pool_table_lookup_metadata_dev(metadata_dev);

        if (pool) {
                if (pool->pool_md != pool_md) {
                        *error = "metadata device already in use by a pool";
                        return ERR_PTR(-EBUSY);
                }
                __pool_inc(pool);

        } else {
                pool = __pool_table_lookup(pool_md);
                if (pool) {
                        if (pool->md_dev != metadata_dev) {
                                *error = "different pool cannot replace a pool";
                                return ERR_PTR(-EINVAL);
                        }
                        __pool_inc(pool);

                } else {
                        pool = pool_create(pool_md, metadata_dev, block_size, read_only, error);
                        *created = 1;
                }
        }

        return pool;
}

/*----------------------------------------------------------------
 * Pool target methods
 *--------------------------------------------------------------*/
static void pool_dtr(struct dm_target *ti)
{
        struct pool_c *pt = ti->private;

        mutex_lock(&dm_thin_pool_table.mutex);

        unbind_control_target(pt->pool, ti);
        __pool_dec(pt->pool);
        dm_put_device(ti, pt->metadata_dev);
        dm_put_device(ti, pt->data_dev);
        kfree(pt);

        mutex_unlock(&dm_thin_pool_table.mutex);
}

static int parse_pool_features(struct dm_arg_set *as, struct pool_features *pf,
                               struct dm_target *ti)
{
        int r;
        unsigned argc;
        const char *arg_name;

        static struct dm_arg _args[] = {
                {0, 3, "Invalid number of pool feature arguments"},
        };

        /*
         * No feature arguments supplied.
         */
        if (!as->argc)
                return 0;

        r = dm_read_arg_group(_args, as, &argc, &ti->error);
        if (r)
                return -EINVAL;

        while (argc && !r) {
                arg_name = dm_shift_arg(as);
                argc--;

                if (!strcasecmp(arg_name, "skip_block_zeroing"))
                        pf->zero_new_blocks = false;

                else if (!strcasecmp(arg_name, "ignore_discard"))
                        pf->discard_enabled = false;

                else if (!strcasecmp(arg_name, "no_discard_passdown"))
                        pf->discard_passdown = false;

                else if (!strcasecmp(arg_name, "read_only"))
                        pf->mode = PM_READ_ONLY;

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

        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.
 *           ignore_discard: disable discard
 *           no_discard_passdown: don't pass discards down to the data device
 */
static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
        int r, pool_created = 0;
        struct pool_c *pt;
        struct pool *pool;
        struct pool_features pf;
        struct dm_arg_set as;
        struct dm_dev *data_dev;
        unsigned long block_size;
        dm_block_t low_water_blocks;
        struct dm_dev *metadata_dev;
        sector_t metadata_dev_size;
        char b[BDEVNAME_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 > THIN_METADATA_MAX_SECTORS_WARNING)
                DMWARN("Metadata device %s is larger than %u sectors: excess space will not be used.",
                       bdevname(metadata_dev->bdev, b), THIN_METADATA_MAX_SECTORS);

        r = dm_get_device(ti, argv[1], FMODE_READ | FMODE_WRITE, &data_dev);
        if (r) {
                ti->error = "Error getting data device";
                goto out_metadata;
        }

        if (kstrtoul(argv[2], 10, &block_size) || !block_size ||
            block_size < DATA_DEV_BLOCK_SIZE_MIN_SECTORS ||
            block_size > DATA_DEV_BLOCK_SIZE_MAX_SECTORS ||
            block_size & (DATA_DEV_BLOCK_SIZE_MIN_SECTORS - 1)) {
                ti->error = "Invalid block size";
                r = -EINVAL;
                goto out;
        }

        if (kstrtoull(argv[3], 10, (unsigned long long *)&low_water_blocks)) {
                ti->error = "Invalid low water mark";
                r = -EINVAL;
                goto out;
        }

        /*
         * Set default pool features.
         */
        pool_features_init(&pf);

        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, pf.mode == PM_READ_ONLY, &ti->error, &pool_created);
        if (IS_ERR(pool)) {
                r = PTR_ERR(pool);
                goto out_free_pt;
        }

        /*
         * 'pool_created' reflects whether this is the first table load.
         * Top level discard support is not allowed to be changed after
         * initial load.  This would require a pool reload to trigger thin
         * device changes.
         */
        if (!pool_created && pf.discard_enabled != pool->pf.discard_enabled) {
                ti->error = "Discard support cannot be disabled once enabled";
                r = -EINVAL;
                goto out_flags_changed;
        }

        /*
         * The block layer requires discard_granularity to be a power of 2.
         */
        if (pf.discard_enabled && !is_power_of_2(block_size)) {
                ti->error = "Discard support must be disabled when the block size is not a power of 2";
                r = -EINVAL;
                goto out_flags_changed;
        }

        pt->pool = pool;
        pt->ti = ti;
        pt->metadata_dev = metadata_dev;
        pt->data_dev = data_dev;
        pt->low_water_blocks = low_water_blocks;
        pt->pf = pf;
        ti->num_flush_requests = 1;

        /*
         * Only need to enable discards if the pool should pass
         * them down to the data device.  The thin device's discard
         * processing will cause mappings to be removed from the btree.
         */
        if (pf.discard_enabled && pf.discard_passdown) {
                ti->num_discard_requests = 1;

                /*
                 * Setting 'discards_supported' circumvents the normal
                 * stacking of discard limits (this keeps the pool and
                 * thin devices' discard limits consistent).
                 */
                ti->discards_supported = true;
                ti->discard_zeroes_data_unsupported = true;
        }
        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_flags_changed:
        __pool_dec(pool);
out_free_pt:
        kfree(pt);
out:
        dm_put_device(ti, data_dev);
out_metadata:
        dm_put_device(ti, metadata_dev);
out_unlock:
        mutex_unlock(&dm_thin_pool_table.mutex);

        return r;
}

static int pool_map(struct dm_target *ti, struct bio *bio,
                    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;
        sector_t data_size = ti->len;
        dm_block_t sb_data_size;

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

        (void) sector_div(data_size, pool->sectors_per_block);

        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)",
                      (unsigned long long)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");
                        /* FIXME Stricter than necessary: Rollback transaction instead here */
                        set_pool_mode(pool, PM_READ_ONLY);
                        return r;
                }

                (void) commit_or_fallback(pool);
        }

        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);

        do_waker(&pool->waker.work);
}

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

        cancel_delayed_work(&pool->waker);
        flush_workqueue(pool->wq);
        (void) commit_or_fallback(pool);
}

static int check_arg_count(unsigned argc, unsigned args_required)
{
        if (argc != args_required) {
                DMWARN("Message received with %u arguments instead of %u.",
                       argc, args_required);
                return -EINVAL;
        }

        return 0;
}

static int read_dev_id(char *arg, dm_thin_id *dev_id, int warning)
{
        if (!kstrtoull(arg, 10, (unsigned long long *)dev_id) &&
            *dev_id <= MAX_DEV_ID)
                return 0;

        if (warning)
                DMWARN("Message received with invalid device id: %s", arg);

        return -EINVAL;
}

static int process_create_thin_mesg(unsigned argc, char **argv, struct pool *pool)
{
        dm_thin_id dev_id;
        int r;

        r = check_arg_count(argc, 2);
        if (r)
                return r;

        r = read_dev_id(argv[1], &dev_id, 1);
        if (r)
                return r;

        r = dm_pool_create_thin(pool->pmd, dev_id);
        if (r) {
                DMWARN("Creation of new thinly-provisioned device with id %s failed.",
                       argv[1]);
                return r;
        }

        return 0;
}

static int process_create_snap_mesg(unsigned argc, char **argv, struct pool *pool)
{
        dm_thin_id dev_id;
        dm_thin_id origin_dev_id;
        int r;

        r = check_arg_count(argc, 3);
        if (r)
                return r;

        r = read_dev_id(argv[1], &dev_id, 1);
        if (r)
                return r;

        r = read_dev_id(argv[2], &origin_dev_id, 1);
        if (r)
                return r;

        r = dm_pool_create_snap(pool->pmd, dev_id, origin_dev_id);
        if (r) {
                DMWARN("Creation of new snapshot %s of device %s failed.",
                       argv[1], argv[2]);
                return r;
        }

        return 0;
}

static int process_delete_mesg(unsigned argc, char **argv, struct pool *pool)
{
        dm_thin_id dev_id;
        int r;

        r = check_arg_count(argc, 2);
        if (r)
                return r;

        r = read_dev_id(argv[1], &dev_id, 1);
        if (r)
                return r;

        r = dm_pool_delete_thin_device(pool->pmd, dev_id);
        if (r)
                DMWARN("Deletion of thin device %s failed.", argv[1]);

        return r;
}

static int process_set_transaction_id_mesg(unsigned argc, char **argv, struct pool *pool)
{
        dm_thin_id old_id, new_id;
        int r;

        r = check_arg_count(argc, 3);
        if (r)
                return r;

        if (kstrtoull(argv[1], 10, (unsigned long long *)&old_id)) {
                DMWARN("set_transaction_id message: Unrecognised id %s.", argv[1]);
                return -EINVAL;
        }

        if (kstrtoull(argv[2], 10, (unsigned long long *)&new_id)) {
                DMWARN("set_transaction_id message: Unrecognised new id %s.", argv[2]);
                return -EINVAL;
        }

        r = dm_pool_set_metadata_transaction_id(pool->pmd, old_id, new_id);
        if (r) {
                DMWARN("Failed to change transaction id from %s to %s.",
                       argv[1], argv[2]);
                return r;
        }

        return 0;
}

static int process_reserve_metadata_snap_mesg(unsigned argc, char **argv, struct pool *pool)
{
        int r;

        r = check_arg_count(argc, 1);
        if (r)
                return r;

        (void) commit_or_fallback(pool);

        r = dm_pool_reserve_metadata_snap(pool->pmd);
        if (r)
                DMWARN("reserve_metadata_snap message failed.");

        return r;
}

static int process_release_metadata_snap_mesg(unsigned argc, char **argv, struct pool *pool)
{
        int r;

        r = check_arg_count(argc, 1);
        if (r)
                return r;

        r = dm_pool_release_metadata_snap(pool->pmd);
        if (r)
                DMWARN("release_metadata_snap message failed.");

        return r;
}

/*
 * Messages supported:
 *   create_thin        <dev_id>
 *   create_snap        <dev_id> <origin_id>
 *   delete             <dev_id>
 *   trim               <dev_id> <new_size_in_sectors>
 *   set_transaction_id <current_trans_id> <new_trans_id>
 *   reserve_metadata_snap
 *   release_metadata_snap
 */
static int pool_message(struct dm_target *ti, unsigned argc, char **argv)
{
        int r = -EINVAL;
        struct pool_c *pt = ti->private;
        struct pool *pool = pt->pool;

        if (!strcasecmp(argv[0], "create_thin"))
                r = process_create_thin_mesg(argc, argv, pool);

        else if (!strcasecmp(argv[0], "create_snap"))
                r = process_create_snap_mesg(argc, argv, pool);

        else if (!strcasecmp(argv[0], "delete"))
                r = process_delete_mesg(argc, argv, pool);

        else if (!strcasecmp(argv[0], "set_transaction_id"))
                r = process_set_transaction_id_mesg(argc, argv, pool);

        else if (!strcasecmp(argv[0], "reserve_metadata_snap"))
                r = process_reserve_metadata_snap_mesg(argc, argv, pool);

        else if (!strcasecmp(argv[0], "release_metadata_snap"))
                r = process_release_metadata_snap_mesg(argc, argv, pool);

        else
                DMWARN("Unrecognised thin pool target message received: %s", argv[0]);

        if (!r)
                (void) commit_or_fallback(pool);

        return r;
}

static void emit_flags(struct pool_features *pf, char *result,
                       unsigned sz, unsigned maxlen)
{
        unsigned count = !pf->zero_new_blocks + !pf->discard_enabled +
                !pf->discard_passdown + (pf->mode == PM_READ_ONLY);
        DMEMIT("%u ", count);

        if (!pf->zero_new_blocks)
                DMEMIT("skip_block_zeroing ");

        if (!pf->discard_enabled)
                DMEMIT("ignore_discard ");

        if (!pf->discard_passdown)
                DMEMIT("no_discard_passdown ");

        if (pf->mode == PM_READ_ONLY)
                DMEMIT("read_only ");
}

/*
 * 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,
                       unsigned status_flags, char *result, unsigned maxlen)
{
        int r;
        unsigned sz = 0;
        uint64_t transaction_id;
        dm_block_t nr_free_blocks_data;
        dm_block_t nr_free_blocks_metadata;
        dm_block_t nr_blocks_data;
        dm_block_t nr_blocks_metadata;
        dm_block_t held_root;
        char buf[BDEVNAME_SIZE];
        char buf2[BDEVNAME_SIZE];
        struct pool_c *pt = ti->private;
        struct pool *pool = pt->pool;

        switch (type) {
        case STATUSTYPE_INFO:
                if (get_pool_mode(pool) == PM_FAIL) {
                        DMEMIT("Fail");
                        break;
                }

                /* Commit to ensure statistics aren't out-of-date */
                if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti))
                        (void) commit_or_fallback(pool);

                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_metadata_snap(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("- ");

                if (pool->pf.mode == PM_READ_ONLY)
                        DMEMIT("ro ");
                else
                        DMEMIT("rw ");

                if (pool->pf.discard_enabled && pool->pf.discard_passdown)
                        DMEMIT("discard_passdown");
                else
                        DMEMIT("no_discard_passdown");

                break;

        case STATUSTYPE_TABLE:
                DMEMIT("%s %s %lu %llu ",
                       format_dev_t(buf, pt->metadata_dev->bdev->bd_dev),
                       format_dev_t(buf2, pt->data_dev->bdev->bd_dev),
                       (unsigned long)pool->sectors_per_block,
                       (unsigned long long)pt->low_water_blocks);
                emit_flags(&pt->pf, result, sz, maxlen);
                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 set_discard_limits(struct pool *pool, struct queue_limits *limits)
{
        /*
         * FIXME: these limits may be incompatible with the pool's data device
         */
        limits->max_discard_sectors = pool->sectors_per_block;

        /*
         * This is just a hint, and not enforced.  We have to cope with
         * bios that cover a block partially.  A discard that spans a block
         * boundary is not sent to this target.
         */
        limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
}

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);
        if (pool->pf.discard_enabled)
                set_discard_limits(pool, limits);
}

static struct target_type pool_target = {
        .name = "thin-pool",
        .features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
                    DM_TARGET_IMMUTABLE,
        .version = {1, 3, 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);
        if (tc->origin_dev)
                dm_put_device(ti, tc->origin_dev);
        kfree(tc);

        mutex_unlock(&dm_thin_pool_table.mutex);
}

/*
 * Thin target parameters:
 *
 * <pool_dev> <dev_id> [origin_dev]
 *
 * pool_dev: the path to the pool (eg, /dev/mapper/my_pool)
 * dev_id: the internal device identifier
 * origin_dev: a device external to the pool that should act as the origin
 *
 * If the pool device has discards disabled, they get disabled for the thin
 * device as well.
 */
static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
        int r;
        struct thin_c *tc;
        struct dm_dev *pool_dev, *origin_dev;
        struct mapped_device *pool_md;

        mutex_lock(&dm_thin_pool_table.mutex);

        if (argc != 2 && argc != 3) {
                ti->error = "Invalid argument count";
                r = -EINVAL;
                goto out_unlock;
        }

        tc = ti->private = kzalloc(sizeof(*tc), GFP_KERNEL);
        if (!tc) {
                ti->error = "Out of memory";
                r = -ENOMEM;
                goto out_unlock;
        }

        if (argc == 3) {
                r = dm_get_device(ti, argv[2], FMODE_READ, &origin_dev);
                if (r) {
                        ti->error = "Error opening origin device";
                        goto bad_origin_dev;
                }
                tc->origin_dev = origin_dev;
        }

        r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &pool_dev);
        if (r) {
                ti->error = "Error opening pool device";
                goto bad_pool_dev;
        }
        tc->pool_dev = pool_dev;

        if (read_dev_id(argv[1], (unsigned long long *)&tc->dev_id, 0)) {
                ti->error = "Invalid device id";
                r = -EINVAL;
                goto bad_common;
        }

        pool_md = dm_get_md(tc->pool_dev->bdev->bd_dev);
        if (!pool_md) {
                ti->error = "Couldn't get pool mapped device";
                r = -EINVAL;
                goto bad_common;
        }

        tc->pool = __pool_table_lookup(pool_md);
        if (!tc->pool) {
                ti->error = "Couldn't find pool object";
                r = -EINVAL;
                goto bad_pool_lookup;
        }
        __pool_inc(tc->pool);

        if (get_pool_mode(tc->pool) == PM_FAIL) {
                ti->error = "Couldn't open thin device, Pool is in fail mode";
                goto bad_thin_open;
        }

        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;
        }

        r = dm_set_target_max_io_len(ti, tc->pool->sectors_per_block);
        if (r)
                goto bad_thin_open;

        ti->num_flush_requests = 1;
        ti->flush_supported = true;

        /* In case the pool supports discards, pass them on. */
        if (tc->pool->pf.discard_enabled) {
                ti->discards_supported = true;
                ti->num_discard_requests = 1;
                ti->discard_zeroes_data_unsupported = true;
                /* Discard requests must be split on a block boundary */
                ti->split_discard_requests = true;
        }

        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:
        if (tc->origin_dev)
                dm_put_device(ti, tc->origin_dev);
bad_origin_dev:
        kfree(tc);
out_unlock:
        mutex_unlock(&dm_thin_pool_table.mutex);

        return r;
}

static int thin_map(struct dm_target *ti, struct bio *bio,
                    union map_info *map_context)
{
        bio->bi_sector = dm_target_offset(ti, bio->bi_sector);

        return thin_bio_map(ti, bio, map_context);
}

static int thin_endio(struct dm_target *ti,
                      struct bio *bio, int err,
                      union map_info *map_context)
{
        unsigned long flags;
        struct dm_thin_endio_hook *h = map_context->ptr;
        struct list_head work;
        struct dm_thin_new_mapping *m, *tmp;
        struct pool *pool = h->tc->pool;

        if (h->shared_read_entry) {
                INIT_LIST_HEAD(&work);
                ds_dec(h->shared_read_entry, &work);

                spin_lock_irqsave(&pool->lock, flags);
                list_for_each_entry_safe(m, tmp, &work, list) {
                        list_del(&m->list);
                        m->quiesced = 1;
                        __maybe_add_mapping(m);
                }
                spin_unlock_irqrestore(&pool->lock, flags);
        }

        if (h->all_io_entry) {
                INIT_LIST_HEAD(&work);
                ds_dec(h->all_io_entry, &work);
                spin_lock_irqsave(&pool->lock, flags);
                list_for_each_entry_safe(m, tmp, &work, list)
                        list_add(&m->list, &pool->prepared_discards);
                spin_unlock_irqrestore(&pool->lock, flags);
        }

        mempool_free(h, pool->endio_hook_pool);

        return 0;
}

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,
                       unsigned status_flags, char *result, unsigned maxlen)
{
        int r;
        ssize_t sz = 0;
        dm_block_t mapped, highest;
        char buf[BDEVNAME_SIZE];
        struct thin_c *tc = ti->private;

        if (get_pool_mode(tc->pool) == PM_FAIL) {
                DMEMIT("Fail");
                return 0;
        }

        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);
                        if (tc->origin_dev)
                                DMEMIT(" %s", format_dev_t(buf, tc->origin_dev->bdev->bd_dev));
                        break;
                }
        }

        return 0;
}

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

        /*
         * We can't call dm_pool_get_data_dev_size() since that blocks.  So
         * we follow a more convoluted path through to the pool's target.
         */
        if (!pool->ti)
                return 0;       /* nothing is bound */

        blocks = pool->ti->len;
        (void) sector_div(blocks, pool->sectors_per_block);
        if (blocks)
                return fn(ti, tc->pool_dev, 0, pool->sectors_per_block * blocks, data);

        return 0;
}

static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
{
        struct thin_c *tc = ti->private;
        struct pool *pool = tc->pool;

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

static struct target_type thin_target = {
        .name = "thin",
        .version = {1, 3, 0},
        .module = THIS_MODULE,
        .ctr = thin_ctr,
        .dtr = thin_dtr,
        .map = thin_map,
        .end_io = thin_endio,
        .postsuspend = thin_postsuspend,
        .status = thin_status,
        .iterate_devices = thin_iterate_devices,
        .io_hints = thin_io_hints,
};

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

static int __init dm_thin_init(void)
{
        int r;

        pool_table_init();

        r = dm_register_target(&thin_target);
        if (r)
                return r;

        r = dm_register_target(&pool_target);
        if (r)
                goto bad_pool_target;

        r = -ENOMEM;

        _cell_cache = KMEM_CACHE(dm_bio_prison_cell, 0);
        if (!_cell_cache)
                goto bad_cell_cache;

        _new_mapping_cache = KMEM_CACHE(dm_thin_new_mapping, 0);
        if (!_new_mapping_cache)
                goto bad_new_mapping_cache;

        _endio_hook_cache = KMEM_CACHE(dm_thin_endio_hook, 0);
        if (!_endio_hook_cache)
                goto bad_endio_hook_cache;

        return 0;

bad_endio_hook_cache:
        kmem_cache_destroy(_new_mapping_cache);
bad_new_mapping_cache:
        kmem_cache_destroy(_cell_cache);
bad_cell_cache:
        dm_unregister_target(&pool_target);
bad_pool_target:
        dm_unregister_target(&thin_target);

        return r;
}

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

        kmem_cache_destroy(_cell_cache);
        kmem_cache_destroy(_new_mapping_cache);
        kmem_cache_destroy(_endio_hook_cache);
}

module_init(dm_thin_init);
module_exit(dm_thin_exit);

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