dm thin metadata: introduce THIN_MAX_CONCURRENT_LOCKS

[deliverable/linux.git] / drivers / md / dm-thin-metadata.c

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

#include "dm-thin-metadata.h"
#include "persistent-data/dm-btree.h"
#include "persistent-data/dm-space-map.h"
#include "persistent-data/dm-space-map-disk.h"
#include "persistent-data/dm-transaction-manager.h"

#include <linux/list.h>
#include <linux/device-mapper.h>
#include <linux/workqueue.h>

/*--------------------------------------------------------------------------
 * As far as the metadata goes, there is:
 *
 * - A superblock in block zero, taking up fewer than 512 bytes for
 *   atomic writes.
 *
 * - A space map managing the metadata blocks.
 *
 * - A space map managing the data blocks.
 *
 * - A btree mapping our internal thin dev ids onto struct disk_device_details.
 *
 * - A hierarchical btree, with 2 levels which effectively maps (thin
 *   dev id, virtual block) -> block_time.  Block time is a 64-bit
 *   field holding the time in the low 24 bits, and block in the top 48
 *   bits.
 *
 * BTrees consist solely of btree_nodes, that fill a block.  Some are
 * internal nodes, as such their values are a __le64 pointing to other
 * nodes.  Leaf nodes can store data of any reasonable size (ie. much
 * smaller than the block size).  The nodes consist of the header,
 * followed by an array of keys, followed by an array of values.  We have
 * to binary search on the keys so they're all held together to help the
 * cpu cache.
 *
 * Space maps have 2 btrees:
 *
 * - One maps a uint64_t onto a struct index_entry.  Which points to a
 *   bitmap block, and has some details about how many free entries there
 *   are etc.
 *
 * - The bitmap blocks have a header (for the checksum).  Then the rest
 *   of the block is pairs of bits.  With the meaning being:
 *
 *   0 - ref count is 0
 *   1 - ref count is 1
 *   2 - ref count is 2
 *   3 - ref count is higher than 2
 *
 * - If the count is higher than 2 then the ref count is entered in a
 *   second btree that directly maps the block_address to a uint32_t ref
 *   count.
 *
 * The space map metadata variant doesn't have a bitmaps btree.  Instead
 * it has one single blocks worth of index_entries.  This avoids
 * recursive issues with the bitmap btree needing to allocate space in
 * order to insert.  With a small data block size such as 64k the
 * metadata support data devices that are hundreds of terrabytes.
 *
 * The space maps allocate space linearly from front to back.  Space that
 * is freed in a transaction is never recycled within that transaction.
 * To try and avoid fragmenting _free_ space the allocator always goes
 * back and fills in gaps.
 *
 * All metadata io is in THIN_METADATA_BLOCK_SIZE sized/aligned chunks
 * from the block manager.
 *--------------------------------------------------------------------------*/

#define DM_MSG_PREFIX   "thin metadata"

#define THIN_SUPERBLOCK_MAGIC 27022010
#define THIN_SUPERBLOCK_LOCATION 0
#define THIN_VERSION 1
#define THIN_METADATA_CACHE_SIZE 64
#define SECTOR_TO_BLOCK_SHIFT 3

/*
 *  3 for btree insert +
 *  2 for btree lookup used within space map
 */
#define THIN_MAX_CONCURRENT_LOCKS 5

/* This should be plenty */
#define SPACE_MAP_ROOT_SIZE 128

/*
 * Little endian on-disk superblock and device details.
 */
struct thin_disk_superblock {
        __le32 csum;    /* Checksum of superblock except for this field. */
        __le32 flags;
        __le64 blocknr; /* This block number, dm_block_t. */

        __u8 uuid[16];
        __le64 magic;
        __le32 version;
        __le32 time;

        __le64 trans_id;

        /*
         * Root held by userspace transactions.
         */
        __le64 held_root;

        __u8 data_space_map_root[SPACE_MAP_ROOT_SIZE];
        __u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];

        /*
         * 2-level btree mapping (dev_id, (dev block, time)) -> data block
         */
        __le64 data_mapping_root;

        /*
         * Device detail root mapping dev_id -> device_details
         */
        __le64 device_details_root;

        __le32 data_block_size;         /* In 512-byte sectors. */

        __le32 metadata_block_size;     /* In 512-byte sectors. */
        __le64 metadata_nr_blocks;

        __le32 compat_flags;
        __le32 compat_ro_flags;
        __le32 incompat_flags;
} __packed;

struct disk_device_details {
        __le64 mapped_blocks;
        __le64 transaction_id;          /* When created. */
        __le32 creation_time;
        __le32 snapshotted_time;
} __packed;

struct dm_pool_metadata {
        struct hlist_node hash;

        struct block_device *bdev;
        struct dm_block_manager *bm;
        struct dm_space_map *metadata_sm;
        struct dm_space_map *data_sm;
        struct dm_transaction_manager *tm;
        struct dm_transaction_manager *nb_tm;

        /*
         * Two-level btree.
         * First level holds thin_dev_t.
         * Second level holds mappings.
         */
        struct dm_btree_info info;

        /*
         * Non-blocking version of the above.
         */
        struct dm_btree_info nb_info;

        /*
         * Just the top level for deleting whole devices.
         */
        struct dm_btree_info tl_info;

        /*
         * Just the bottom level for creating new devices.
         */
        struct dm_btree_info bl_info;

        /*
         * Describes the device details btree.
         */
        struct dm_btree_info details_info;

        struct rw_semaphore root_lock;
        uint32_t time;
        int need_commit;
        dm_block_t root;
        dm_block_t details_root;
        struct list_head thin_devices;
        uint64_t trans_id;
        unsigned long flags;
        sector_t data_block_size;
};

struct dm_thin_device {
        struct list_head list;
        struct dm_pool_metadata *pmd;
        dm_thin_id id;

        int open_count;
        int changed;
        uint64_t mapped_blocks;
        uint64_t transaction_id;
        uint32_t creation_time;
        uint32_t snapshotted_time;
};

/*----------------------------------------------------------------
 * superblock validator
 *--------------------------------------------------------------*/

#define SUPERBLOCK_CSUM_XOR 160774

static void sb_prepare_for_write(struct dm_block_validator *v,
                                 struct dm_block *b,
                                 size_t block_size)
{
        struct thin_disk_superblock *disk_super = dm_block_data(b);

        disk_super->blocknr = cpu_to_le64(dm_block_location(b));
        disk_super->csum = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
                                                      block_size - sizeof(__le32),
                                                      SUPERBLOCK_CSUM_XOR));
}

static int sb_check(struct dm_block_validator *v,
                    struct dm_block *b,
                    size_t block_size)
{
        struct thin_disk_superblock *disk_super = dm_block_data(b);
        __le32 csum_le;

        if (dm_block_location(b) != le64_to_cpu(disk_super->blocknr)) {
                DMERR("sb_check failed: blocknr %llu: "
                      "wanted %llu", le64_to_cpu(disk_super->blocknr),
                      (unsigned long long)dm_block_location(b));
                return -ENOTBLK;
        }

        if (le64_to_cpu(disk_super->magic) != THIN_SUPERBLOCK_MAGIC) {
                DMERR("sb_check failed: magic %llu: "
                      "wanted %llu", le64_to_cpu(disk_super->magic),
                      (unsigned long long)THIN_SUPERBLOCK_MAGIC);
                return -EILSEQ;
        }

        csum_le = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
                                             block_size - sizeof(__le32),
                                             SUPERBLOCK_CSUM_XOR));
        if (csum_le != disk_super->csum) {
                DMERR("sb_check failed: csum %u: wanted %u",
                      le32_to_cpu(csum_le), le32_to_cpu(disk_super->csum));
                return -EILSEQ;
        }

        return 0;
}

static struct dm_block_validator sb_validator = {
        .name = "superblock",
        .prepare_for_write = sb_prepare_for_write,
        .check = sb_check
};

/*----------------------------------------------------------------
 * Methods for the btree value types
 *--------------------------------------------------------------*/

static uint64_t pack_block_time(dm_block_t b, uint32_t t)
{
        return (b << 24) | t;
}

static void unpack_block_time(uint64_t v, dm_block_t *b, uint32_t *t)
{
        *b = v >> 24;
        *t = v & ((1 << 24) - 1);
}

static void data_block_inc(void *context, void *value_le)
{
        struct dm_space_map *sm = context;
        __le64 v_le;
        uint64_t b;
        uint32_t t;

        memcpy(&v_le, value_le, sizeof(v_le));
        unpack_block_time(le64_to_cpu(v_le), &b, &t);
        dm_sm_inc_block(sm, b);
}

static void data_block_dec(void *context, void *value_le)
{
        struct dm_space_map *sm = context;
        __le64 v_le;
        uint64_t b;
        uint32_t t;

        memcpy(&v_le, value_le, sizeof(v_le));
        unpack_block_time(le64_to_cpu(v_le), &b, &t);
        dm_sm_dec_block(sm, b);
}

static int data_block_equal(void *context, void *value1_le, void *value2_le)
{
        __le64 v1_le, v2_le;
        uint64_t b1, b2;
        uint32_t t;

        memcpy(&v1_le, value1_le, sizeof(v1_le));
        memcpy(&v2_le, value2_le, sizeof(v2_le));
        unpack_block_time(le64_to_cpu(v1_le), &b1, &t);
        unpack_block_time(le64_to_cpu(v2_le), &b2, &t);

        return b1 == b2;
}

static void subtree_inc(void *context, void *value)
{
        struct dm_btree_info *info = context;
        __le64 root_le;
        uint64_t root;

        memcpy(&root_le, value, sizeof(root_le));
        root = le64_to_cpu(root_le);
        dm_tm_inc(info->tm, root);
}

static void subtree_dec(void *context, void *value)
{
        struct dm_btree_info *info = context;
        __le64 root_le;
        uint64_t root;

        memcpy(&root_le, value, sizeof(root_le));
        root = le64_to_cpu(root_le);
        if (dm_btree_del(info, root))
                DMERR("btree delete failed\n");
}

static int subtree_equal(void *context, void *value1_le, void *value2_le)
{
        __le64 v1_le, v2_le;
        memcpy(&v1_le, value1_le, sizeof(v1_le));
        memcpy(&v2_le, value2_le, sizeof(v2_le));

        return v1_le == v2_le;
}

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

static int superblock_all_zeroes(struct dm_block_manager *bm, int *result)
{
        int r;
        unsigned i;
        struct dm_block *b;
        __le64 *data_le, zero = cpu_to_le64(0);
        unsigned block_size = dm_bm_block_size(bm) / sizeof(__le64);

        /*
         * We can't use a validator here - it may be all zeroes.
         */
        r = dm_bm_read_lock(bm, THIN_SUPERBLOCK_LOCATION, NULL, &b);
        if (r)
                return r;

        data_le = dm_block_data(b);
        *result = 1;
        for (i = 0; i < block_size; i++) {
                if (data_le[i] != zero) {
                        *result = 0;
                        break;
                }
        }

        return dm_bm_unlock(b);
}

static int init_pmd(struct dm_pool_metadata *pmd,
                    struct dm_block_manager *bm,
                    dm_block_t nr_blocks, int create)
{
        int r;
        struct dm_space_map *sm, *data_sm;
        struct dm_transaction_manager *tm;
        struct dm_block *sblock;

        if (create) {
                r = dm_tm_create_with_sm(bm, THIN_SUPERBLOCK_LOCATION,
                                         &sb_validator, &tm, &sm, &sblock);
                if (r < 0) {
                        DMERR("tm_create_with_sm failed");
                        return r;
                }

                data_sm = dm_sm_disk_create(tm, nr_blocks);
                if (IS_ERR(data_sm)) {
                        DMERR("sm_disk_create failed");
                        dm_tm_unlock(tm, sblock);
                        r = PTR_ERR(data_sm);
                        goto bad;
                }
        } else {
                struct thin_disk_superblock *disk_super = NULL;
                size_t space_map_root_offset =
                        offsetof(struct thin_disk_superblock, metadata_space_map_root);

                r = dm_tm_open_with_sm(bm, THIN_SUPERBLOCK_LOCATION,
                                       &sb_validator, space_map_root_offset,
                                       SPACE_MAP_ROOT_SIZE, &tm, &sm, &sblock);
                if (r < 0) {
                        DMERR("tm_open_with_sm failed");
                        return r;
                }

                disk_super = dm_block_data(sblock);
                data_sm = dm_sm_disk_open(tm, disk_super->data_space_map_root,
                                          sizeof(disk_super->data_space_map_root));
                if (IS_ERR(data_sm)) {
                        DMERR("sm_disk_open failed");
                        r = PTR_ERR(data_sm);
                        goto bad;
                }
        }


        r = dm_tm_unlock(tm, sblock);
        if (r < 0) {
                DMERR("couldn't unlock superblock");
                goto bad_data_sm;
        }

        pmd->bm = bm;
        pmd->metadata_sm = sm;
        pmd->data_sm = data_sm;
        pmd->tm = tm;
        pmd->nb_tm = dm_tm_create_non_blocking_clone(tm);
        if (!pmd->nb_tm) {
                DMERR("could not create clone tm");
                r = -ENOMEM;
                goto bad_data_sm;
        }

        pmd->info.tm = tm;
        pmd->info.levels = 2;
        pmd->info.value_type.context = pmd->data_sm;
        pmd->info.value_type.size = sizeof(__le64);
        pmd->info.value_type.inc = data_block_inc;
        pmd->info.value_type.dec = data_block_dec;
        pmd->info.value_type.equal = data_block_equal;

        memcpy(&pmd->nb_info, &pmd->info, sizeof(pmd->nb_info));
        pmd->nb_info.tm = pmd->nb_tm;

        pmd->tl_info.tm = tm;
        pmd->tl_info.levels = 1;
        pmd->tl_info.value_type.context = &pmd->info;
        pmd->tl_info.value_type.size = sizeof(__le64);
        pmd->tl_info.value_type.inc = subtree_inc;
        pmd->tl_info.value_type.dec = subtree_dec;
        pmd->tl_info.value_type.equal = subtree_equal;

        pmd->bl_info.tm = tm;
        pmd->bl_info.levels = 1;
        pmd->bl_info.value_type.context = pmd->data_sm;
        pmd->bl_info.value_type.size = sizeof(__le64);
        pmd->bl_info.value_type.inc = data_block_inc;
        pmd->bl_info.value_type.dec = data_block_dec;
        pmd->bl_info.value_type.equal = data_block_equal;

        pmd->details_info.tm = tm;
        pmd->details_info.levels = 1;
        pmd->details_info.value_type.context = NULL;
        pmd->details_info.value_type.size = sizeof(struct disk_device_details);
        pmd->details_info.value_type.inc = NULL;
        pmd->details_info.value_type.dec = NULL;
        pmd->details_info.value_type.equal = NULL;

        pmd->root = 0;

        init_rwsem(&pmd->root_lock);
        pmd->time = 0;
        pmd->need_commit = 0;
        pmd->details_root = 0;
        pmd->trans_id = 0;
        pmd->flags = 0;
        INIT_LIST_HEAD(&pmd->thin_devices);

        return 0;

bad_data_sm:
        dm_sm_destroy(data_sm);
bad:
        dm_tm_destroy(tm);
        dm_sm_destroy(sm);

        return r;
}

static int __begin_transaction(struct dm_pool_metadata *pmd)
{
        int r;
        u32 features;
        struct thin_disk_superblock *disk_super;
        struct dm_block *sblock;

        /*
         * __maybe_commit_transaction() resets these
         */
        WARN_ON(pmd->need_commit);

        /*
         * We re-read the superblock every time.  Shouldn't need to do this
         * really.
         */
        r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
                            &sb_validator, &sblock);
        if (r)
                return r;

        disk_super = dm_block_data(sblock);
        pmd->time = le32_to_cpu(disk_super->time);
        pmd->root = le64_to_cpu(disk_super->data_mapping_root);
        pmd->details_root = le64_to_cpu(disk_super->device_details_root);
        pmd->trans_id = le64_to_cpu(disk_super->trans_id);
        pmd->flags = le32_to_cpu(disk_super->flags);
        pmd->data_block_size = le32_to_cpu(disk_super->data_block_size);

        features = le32_to_cpu(disk_super->incompat_flags) & ~THIN_FEATURE_INCOMPAT_SUPP;
        if (features) {
                DMERR("could not access metadata due to "
                      "unsupported optional features (%lx).",
                      (unsigned long)features);
                r = -EINVAL;
                goto out;
        }

        /*
         * Check for read-only metadata to skip the following RDWR checks.
         */
        if (get_disk_ro(pmd->bdev->bd_disk))
                goto out;

        features = le32_to_cpu(disk_super->compat_ro_flags) & ~THIN_FEATURE_COMPAT_RO_SUPP;
        if (features) {
                DMERR("could not access metadata RDWR due to "
                      "unsupported optional features (%lx).",
                      (unsigned long)features);
                r = -EINVAL;
        }

out:
        dm_bm_unlock(sblock);
        return r;
}

static int __write_changed_details(struct dm_pool_metadata *pmd)
{
        int r;
        struct dm_thin_device *td, *tmp;
        struct disk_device_details details;
        uint64_t key;

        list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
                if (!td->changed)
                        continue;

                key = td->id;

                details.mapped_blocks = cpu_to_le64(td->mapped_blocks);
                details.transaction_id = cpu_to_le64(td->transaction_id);
                details.creation_time = cpu_to_le32(td->creation_time);
                details.snapshotted_time = cpu_to_le32(td->snapshotted_time);
                __dm_bless_for_disk(&details);

                r = dm_btree_insert(&pmd->details_info, pmd->details_root,
                                    &key, &details, &pmd->details_root);
                if (r)
                        return r;

                if (td->open_count)
                        td->changed = 0;
                else {
                        list_del(&td->list);
                        kfree(td);
                }

                pmd->need_commit = 1;
        }

        return 0;
}

static int __commit_transaction(struct dm_pool_metadata *pmd)
{
        /*
         * FIXME: Associated pool should be made read-only on failure.
         */
        int r;
        size_t metadata_len, data_len;
        struct thin_disk_superblock *disk_super;
        struct dm_block *sblock;

        /*
         * We need to know if the thin_disk_superblock exceeds a 512-byte sector.
         */
        BUILD_BUG_ON(sizeof(struct thin_disk_superblock) > 512);

        r = __write_changed_details(pmd);
        if (r < 0)
                return r;

        if (!pmd->need_commit)
                return r;

        r = dm_sm_commit(pmd->data_sm);
        if (r < 0)
                return r;

        r = dm_tm_pre_commit(pmd->tm);
        if (r < 0)
                return r;

        r = dm_sm_root_size(pmd->metadata_sm, &metadata_len);
        if (r < 0)
                return r;

        r = dm_sm_root_size(pmd->data_sm, &data_len);
        if (r < 0)
                return r;

        r = dm_bm_write_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
                             &sb_validator, &sblock);
        if (r)
                return r;

        disk_super = dm_block_data(sblock);
        disk_super->time = cpu_to_le32(pmd->time);
        disk_super->data_mapping_root = cpu_to_le64(pmd->root);
        disk_super->device_details_root = cpu_to_le64(pmd->details_root);
        disk_super->trans_id = cpu_to_le64(pmd->trans_id);
        disk_super->flags = cpu_to_le32(pmd->flags);

        r = dm_sm_copy_root(pmd->metadata_sm, &disk_super->metadata_space_map_root,
                            metadata_len);
        if (r < 0)
                goto out_locked;

        r = dm_sm_copy_root(pmd->data_sm, &disk_super->data_space_map_root,
                            data_len);
        if (r < 0)
                goto out_locked;

        r = dm_tm_commit(pmd->tm, sblock);
        if (!r)
                pmd->need_commit = 0;

        return r;

out_locked:
        dm_bm_unlock(sblock);
        return r;
}

struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev,
                                               sector_t data_block_size)
{
        int r;
        struct thin_disk_superblock *disk_super;
        struct dm_pool_metadata *pmd;
        sector_t bdev_size = i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
        struct dm_block_manager *bm;
        int create;
        struct dm_block *sblock;

        pmd = kmalloc(sizeof(*pmd), GFP_KERNEL);
        if (!pmd) {
                DMERR("could not allocate metadata struct");
                return ERR_PTR(-ENOMEM);
        }

        bm = dm_block_manager_create(bdev, THIN_METADATA_BLOCK_SIZE,
                                     THIN_METADATA_CACHE_SIZE,
                                     THIN_MAX_CONCURRENT_LOCKS);
        if (!bm) {
                DMERR("could not create block manager");
                kfree(pmd);
                return ERR_PTR(-ENOMEM);
        }

        r = superblock_all_zeroes(bm, &create);
        if (r) {
                dm_block_manager_destroy(bm);
                kfree(pmd);
                return ERR_PTR(r);
        }


        r = init_pmd(pmd, bm, 0, create);
        if (r) {
                dm_block_manager_destroy(bm);
                kfree(pmd);
                return ERR_PTR(r);
        }
        pmd->bdev = bdev;

        if (!create) {
                r = __begin_transaction(pmd);
                if (r < 0)
                        goto bad;
                return pmd;
        }

        /*
         * Create.
         */
        r = dm_bm_write_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
                             &sb_validator, &sblock);
        if (r)
                goto bad;

        if (bdev_size > THIN_METADATA_MAX_SECTORS)
                bdev_size = THIN_METADATA_MAX_SECTORS;

        disk_super = dm_block_data(sblock);
        disk_super->magic = cpu_to_le64(THIN_SUPERBLOCK_MAGIC);
        disk_super->version = cpu_to_le32(THIN_VERSION);
        disk_super->time = 0;
        disk_super->metadata_block_size = cpu_to_le32(THIN_METADATA_BLOCK_SIZE >> SECTOR_SHIFT);
        disk_super->metadata_nr_blocks = cpu_to_le64(bdev_size >> SECTOR_TO_BLOCK_SHIFT);
        disk_super->data_block_size = cpu_to_le32(data_block_size);

        r = dm_bm_unlock(sblock);
        if (r < 0)
                goto bad;

        r = dm_btree_empty(&pmd->info, &pmd->root);
        if (r < 0)
                goto bad;

        r = dm_btree_empty(&pmd->details_info, &pmd->details_root);
        if (r < 0) {
                DMERR("couldn't create devices root");
                goto bad;
        }

        pmd->flags = 0;
        pmd->need_commit = 1;
        r = dm_pool_commit_metadata(pmd);
        if (r < 0) {
                DMERR("%s: dm_pool_commit_metadata() failed, error = %d",
                      __func__, r);
                goto bad;
        }

        return pmd;

bad:
        if (dm_pool_metadata_close(pmd) < 0)
                DMWARN("%s: dm_pool_metadata_close() failed.", __func__);
        return ERR_PTR(r);
}

int dm_pool_metadata_close(struct dm_pool_metadata *pmd)
{
        int r;
        unsigned open_devices = 0;
        struct dm_thin_device *td, *tmp;

        down_read(&pmd->root_lock);
        list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
                if (td->open_count)
                        open_devices++;
                else {
                        list_del(&td->list);
                        kfree(td);
                }
        }
        up_read(&pmd->root_lock);

        if (open_devices) {
                DMERR("attempt to close pmd when %u device(s) are still open",
                       open_devices);
                return -EBUSY;
        }

        r = __commit_transaction(pmd);
        if (r < 0)
                DMWARN("%s: __commit_transaction() failed, error = %d",
                       __func__, r);

        dm_tm_destroy(pmd->tm);
        dm_tm_destroy(pmd->nb_tm);
        dm_block_manager_destroy(pmd->bm);
        dm_sm_destroy(pmd->metadata_sm);
        dm_sm_destroy(pmd->data_sm);
        kfree(pmd);

        return 0;
}

/*
 * __open_device: Returns @td corresponding to device with id @dev,
 * creating it if @create is set and incrementing @td->open_count.
 * On failure, @td is undefined.
 */
static int __open_device(struct dm_pool_metadata *pmd,
                         dm_thin_id dev, int create,
                         struct dm_thin_device **td)
{
        int r, changed = 0;
        struct dm_thin_device *td2;
        uint64_t key = dev;
        struct disk_device_details details_le;

        /*
         * If the device is already open, return it.
         */
        list_for_each_entry(td2, &pmd->thin_devices, list)
                if (td2->id == dev) {
                        /*
                         * May not create an already-open device.
                         */
                        if (create)
                                return -EEXIST;

                        td2->open_count++;
                        *td = td2;
                        return 0;
                }

        /*
         * Check the device exists.
         */
        r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
                            &key, &details_le);
        if (r) {
                if (r != -ENODATA || !create)
                        return r;

                /*
                 * Create new device.
                 */
                changed = 1;
                details_le.mapped_blocks = 0;
                details_le.transaction_id = cpu_to_le64(pmd->trans_id);
                details_le.creation_time = cpu_to_le32(pmd->time);
                details_le.snapshotted_time = cpu_to_le32(pmd->time);
        }

        *td = kmalloc(sizeof(**td), GFP_NOIO);
        if (!*td)
                return -ENOMEM;

        (*td)->pmd = pmd;
        (*td)->id = dev;
        (*td)->open_count = 1;
        (*td)->changed = changed;
        (*td)->mapped_blocks = le64_to_cpu(details_le.mapped_blocks);
        (*td)->transaction_id = le64_to_cpu(details_le.transaction_id);
        (*td)->creation_time = le32_to_cpu(details_le.creation_time);
        (*td)->snapshotted_time = le32_to_cpu(details_le.snapshotted_time);

        list_add(&(*td)->list, &pmd->thin_devices);

        return 0;
}

static void __close_device(struct dm_thin_device *td)
{
        --td->open_count;
}

static int __create_thin(struct dm_pool_metadata *pmd,
                         dm_thin_id dev)
{
        int r;
        dm_block_t dev_root;
        uint64_t key = dev;
        struct disk_device_details details_le;
        struct dm_thin_device *td;
        __le64 value;

        r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
                            &key, &details_le);
        if (!r)
                return -EEXIST;

        /*
         * Create an empty btree for the mappings.
         */
        r = dm_btree_empty(&pmd->bl_info, &dev_root);
        if (r)
                return r;

        /*
         * Insert it into the main mapping tree.
         */
        value = cpu_to_le64(dev_root);
        __dm_bless_for_disk(&value);
        r = dm_btree_insert(&pmd->tl_info, pmd->root, &key, &value, &pmd->root);
        if (r) {
                dm_btree_del(&pmd->bl_info, dev_root);
                return r;
        }

        r = __open_device(pmd, dev, 1, &td);
        if (r) {
                dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
                dm_btree_del(&pmd->bl_info, dev_root);
                return r;
        }
        __close_device(td);

        return r;
}

int dm_pool_create_thin(struct dm_pool_metadata *pmd, dm_thin_id dev)
{
        int r;

        down_write(&pmd->root_lock);
        r = __create_thin(pmd, dev);
        up_write(&pmd->root_lock);

        return r;
}

static int __set_snapshot_details(struct dm_pool_metadata *pmd,
                                  struct dm_thin_device *snap,
                                  dm_thin_id origin, uint32_t time)
{
        int r;
        struct dm_thin_device *td;

        r = __open_device(pmd, origin, 0, &td);
        if (r)
                return r;

        td->changed = 1;
        td->snapshotted_time = time;

        snap->mapped_blocks = td->mapped_blocks;
        snap->snapshotted_time = time;
        __close_device(td);

        return 0;
}

static int __create_snap(struct dm_pool_metadata *pmd,
                         dm_thin_id dev, dm_thin_id origin)
{
        int r;
        dm_block_t origin_root;
        uint64_t key = origin, dev_key = dev;
        struct dm_thin_device *td;
        struct disk_device_details details_le;
        __le64 value;

        /* check this device is unused */
        r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
                            &dev_key, &details_le);
        if (!r)
                return -EEXIST;

        /* find the mapping tree for the origin */
        r = dm_btree_lookup(&pmd->tl_info, pmd->root, &key, &value);
        if (r)
                return r;
        origin_root = le64_to_cpu(value);

        /* clone the origin, an inc will do */
        dm_tm_inc(pmd->tm, origin_root);

        /* insert into the main mapping tree */
        value = cpu_to_le64(origin_root);
        __dm_bless_for_disk(&value);
        key = dev;
        r = dm_btree_insert(&pmd->tl_info, pmd->root, &key, &value, &pmd->root);
        if (r) {
                dm_tm_dec(pmd->tm, origin_root);
                return r;
        }

        pmd->time++;

        r = __open_device(pmd, dev, 1, &td);
        if (r)
                goto bad;

        r = __set_snapshot_details(pmd, td, origin, pmd->time);
        __close_device(td);

        if (r)
                goto bad;

        return 0;

bad:
        dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
        dm_btree_remove(&pmd->details_info, pmd->details_root,
                        &key, &pmd->details_root);
        return r;
}

int dm_pool_create_snap(struct dm_pool_metadata *pmd,
                                 dm_thin_id dev,
                                 dm_thin_id origin)
{
        int r;

        down_write(&pmd->root_lock);
        r = __create_snap(pmd, dev, origin);
        up_write(&pmd->root_lock);

        return r;
}

static int __delete_device(struct dm_pool_metadata *pmd, dm_thin_id dev)
{
        int r;
        uint64_t key = dev;
        struct dm_thin_device *td;

        /* TODO: failure should mark the transaction invalid */
        r = __open_device(pmd, dev, 0, &td);
        if (r)
                return r;

        if (td->open_count > 1) {
                __close_device(td);
                return -EBUSY;
        }

        list_del(&td->list);
        kfree(td);
        r = dm_btree_remove(&pmd->details_info, pmd->details_root,
                            &key, &pmd->details_root);
        if (r)
                return r;

        r = dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
        if (r)
                return r;

        pmd->need_commit = 1;

        return 0;
}

int dm_pool_delete_thin_device(struct dm_pool_metadata *pmd,
                               dm_thin_id dev)
{
        int r;

        down_write(&pmd->root_lock);
        r = __delete_device(pmd, dev);
        up_write(&pmd->root_lock);

        return r;
}

int dm_pool_set_metadata_transaction_id(struct dm_pool_metadata *pmd,
                                        uint64_t current_id,
                                        uint64_t new_id)
{
        down_write(&pmd->root_lock);
        if (pmd->trans_id != current_id) {
                up_write(&pmd->root_lock);
                DMERR("mismatched transaction id");
                return -EINVAL;
        }

        pmd->trans_id = new_id;
        pmd->need_commit = 1;
        up_write(&pmd->root_lock);

        return 0;
}

int dm_pool_get_metadata_transaction_id(struct dm_pool_metadata *pmd,
                                        uint64_t *result)
{
        down_read(&pmd->root_lock);
        *result = pmd->trans_id;
        up_read(&pmd->root_lock);

        return 0;
}

static int __reserve_metadata_snap(struct dm_pool_metadata *pmd)
{
        int r, inc;
        struct thin_disk_superblock *disk_super;
        struct dm_block *copy, *sblock;
        dm_block_t held_root;

        /*
         * Copy the superblock.
         */
        dm_sm_inc_block(pmd->metadata_sm, THIN_SUPERBLOCK_LOCATION);
        r = dm_tm_shadow_block(pmd->tm, THIN_SUPERBLOCK_LOCATION,
                               &sb_validator, &copy, &inc);
        if (r)
                return r;

        BUG_ON(!inc);

        held_root = dm_block_location(copy);
        disk_super = dm_block_data(copy);

        if (le64_to_cpu(disk_super->held_root)) {
                DMWARN("Pool metadata snapshot already exists: release this before taking another.");

                dm_tm_dec(pmd->tm, held_root);
                dm_tm_unlock(pmd->tm, copy);
                pmd->need_commit = 1;

                return -EBUSY;
        }

        /*
         * Wipe the spacemap since we're not publishing this.
         */
        memset(&disk_super->data_space_map_root, 0,
               sizeof(disk_super->data_space_map_root));
        memset(&disk_super->metadata_space_map_root, 0,
               sizeof(disk_super->metadata_space_map_root));

        /*
         * Increment the data structures that need to be preserved.
         */
        dm_tm_inc(pmd->tm, le64_to_cpu(disk_super->data_mapping_root));
        dm_tm_inc(pmd->tm, le64_to_cpu(disk_super->device_details_root));
        dm_tm_unlock(pmd->tm, copy);

        /*
         * Write the held root into the superblock.
         */
        r = dm_bm_write_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
                             &sb_validator, &sblock);
        if (r) {
                dm_tm_dec(pmd->tm, held_root);
                pmd->need_commit = 1;
                return r;
        }

        disk_super = dm_block_data(sblock);
        disk_super->held_root = cpu_to_le64(held_root);
        dm_bm_unlock(sblock);

        pmd->need_commit = 1;

        return 0;
}

int dm_pool_reserve_metadata_snap(struct dm_pool_metadata *pmd)
{
        int r;

        down_write(&pmd->root_lock);
        r = __reserve_metadata_snap(pmd);
        up_write(&pmd->root_lock);

        return r;
}

static int __release_metadata_snap(struct dm_pool_metadata *pmd)
{
        int r;
        struct thin_disk_superblock *disk_super;
        struct dm_block *sblock, *copy;
        dm_block_t held_root;

        r = dm_bm_write_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
                             &sb_validator, &sblock);
        if (r)
                return r;

        disk_super = dm_block_data(sblock);
        held_root = le64_to_cpu(disk_super->held_root);
        disk_super->held_root = cpu_to_le64(0);
        pmd->need_commit = 1;

        dm_bm_unlock(sblock);

        if (!held_root) {
                DMWARN("No pool metadata snapshot found: nothing to release.");
                return -EINVAL;
        }

        r = dm_tm_read_lock(pmd->tm, held_root, &sb_validator, &copy);
        if (r)
                return r;

        disk_super = dm_block_data(copy);
        dm_sm_dec_block(pmd->metadata_sm, le64_to_cpu(disk_super->data_mapping_root));
        dm_sm_dec_block(pmd->metadata_sm, le64_to_cpu(disk_super->device_details_root));
        dm_sm_dec_block(pmd->metadata_sm, held_root);

        return dm_tm_unlock(pmd->tm, copy);
}

int dm_pool_release_metadata_snap(struct dm_pool_metadata *pmd)
{
        int r;

        down_write(&pmd->root_lock);
        r = __release_metadata_snap(pmd);
        up_write(&pmd->root_lock);

        return r;
}

static int __get_metadata_snap(struct dm_pool_metadata *pmd,
                               dm_block_t *result)
{
        int r;
        struct thin_disk_superblock *disk_super;
        struct dm_block *sblock;

        r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
                            &sb_validator, &sblock);
        if (r)
                return r;

        disk_super = dm_block_data(sblock);
        *result = le64_to_cpu(disk_super->held_root);

        return dm_bm_unlock(sblock);
}

int dm_pool_get_metadata_snap(struct dm_pool_metadata *pmd,
                              dm_block_t *result)
{
        int r;

        down_read(&pmd->root_lock);
        r = __get_metadata_snap(pmd, result);
        up_read(&pmd->root_lock);

        return r;
}

int dm_pool_open_thin_device(struct dm_pool_metadata *pmd, dm_thin_id dev,
                             struct dm_thin_device **td)
{
        int r;

        down_write(&pmd->root_lock);
        r = __open_device(pmd, dev, 0, td);
        up_write(&pmd->root_lock);

        return r;
}

int dm_pool_close_thin_device(struct dm_thin_device *td)
{
        down_write(&td->pmd->root_lock);
        __close_device(td);
        up_write(&td->pmd->root_lock);

        return 0;
}

dm_thin_id dm_thin_dev_id(struct dm_thin_device *td)
{
        return td->id;
}

static bool __snapshotted_since(struct dm_thin_device *td, uint32_t time)
{
        return td->snapshotted_time > time;
}

int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
                       int can_block, struct dm_thin_lookup_result *result)
{
        int r;
        uint64_t block_time = 0;
        __le64 value;
        struct dm_pool_metadata *pmd = td->pmd;
        dm_block_t keys[2] = { td->id, block };

        if (can_block) {
                down_read(&pmd->root_lock);
                r = dm_btree_lookup(&pmd->info, pmd->root, keys, &value);
                if (!r)
                        block_time = le64_to_cpu(value);
                up_read(&pmd->root_lock);

        } else if (down_read_trylock(&pmd->root_lock)) {
                r = dm_btree_lookup(&pmd->nb_info, pmd->root, keys, &value);
                if (!r)
                        block_time = le64_to_cpu(value);
                up_read(&pmd->root_lock);

        } else
                return -EWOULDBLOCK;

        if (!r) {
                dm_block_t exception_block;
                uint32_t exception_time;
                unpack_block_time(block_time, &exception_block,
                                  &exception_time);
                result->block = exception_block;
                result->shared = __snapshotted_since(td, exception_time);
        }

        return r;
}

static int __insert(struct dm_thin_device *td, dm_block_t block,
                    dm_block_t data_block)
{
        int r, inserted;
        __le64 value;
        struct dm_pool_metadata *pmd = td->pmd;
        dm_block_t keys[2] = { td->id, block };

        pmd->need_commit = 1;
        value = cpu_to_le64(pack_block_time(data_block, pmd->time));
        __dm_bless_for_disk(&value);

        r = dm_btree_insert_notify(&pmd->info, pmd->root, keys, &value,
                                   &pmd->root, &inserted);
        if (r)
                return r;

        if (inserted) {
                td->mapped_blocks++;
                td->changed = 1;
        }

        return 0;
}

int dm_thin_insert_block(struct dm_thin_device *td, dm_block_t block,
                         dm_block_t data_block)
{
        int r;

        down_write(&td->pmd->root_lock);
        r = __insert(td, block, data_block);
        up_write(&td->pmd->root_lock);

        return r;
}

static int __remove(struct dm_thin_device *td, dm_block_t block)
{
        int r;
        struct dm_pool_metadata *pmd = td->pmd;
        dm_block_t keys[2] = { td->id, block };

        r = dm_btree_remove(&pmd->info, pmd->root, keys, &pmd->root);
        if (r)
                return r;

        td->mapped_blocks--;
        td->changed = 1;
        pmd->need_commit = 1;

        return 0;
}

int dm_thin_remove_block(struct dm_thin_device *td, dm_block_t block)
{
        int r;

        down_write(&td->pmd->root_lock);
        r = __remove(td, block);
        up_write(&td->pmd->root_lock);

        return r;
}

int dm_pool_alloc_data_block(struct dm_pool_metadata *pmd, dm_block_t *result)
{
        int r;

        down_write(&pmd->root_lock);

        r = dm_sm_new_block(pmd->data_sm, result);
        pmd->need_commit = 1;

        up_write(&pmd->root_lock);

        return r;
}

int dm_pool_commit_metadata(struct dm_pool_metadata *pmd)
{
        int r;

        down_write(&pmd->root_lock);

        r = __commit_transaction(pmd);
        if (r <= 0)
                goto out;

        /*
         * Open the next transaction.
         */
        r = __begin_transaction(pmd);
out:
        up_write(&pmd->root_lock);
        return r;
}

int dm_pool_get_free_block_count(struct dm_pool_metadata *pmd, dm_block_t *result)
{
        int r;

        down_read(&pmd->root_lock);
        r = dm_sm_get_nr_free(pmd->data_sm, result);
        up_read(&pmd->root_lock);

        return r;
}

int dm_pool_get_free_metadata_block_count(struct dm_pool_metadata *pmd,
                                          dm_block_t *result)
{
        int r;

        down_read(&pmd->root_lock);
        r = dm_sm_get_nr_free(pmd->metadata_sm, result);
        up_read(&pmd->root_lock);

        return r;
}

int dm_pool_get_metadata_dev_size(struct dm_pool_metadata *pmd,
                                  dm_block_t *result)
{
        int r;

        down_read(&pmd->root_lock);
        r = dm_sm_get_nr_blocks(pmd->metadata_sm, result);
        up_read(&pmd->root_lock);

        return r;
}

int dm_pool_get_data_block_size(struct dm_pool_metadata *pmd, sector_t *result)
{
        down_read(&pmd->root_lock);
        *result = pmd->data_block_size;
        up_read(&pmd->root_lock);

        return 0;
}

int dm_pool_get_data_dev_size(struct dm_pool_metadata *pmd, dm_block_t *result)
{
        int r;

        down_read(&pmd->root_lock);
        r = dm_sm_get_nr_blocks(pmd->data_sm, result);
        up_read(&pmd->root_lock);

        return r;
}

int dm_thin_get_mapped_count(struct dm_thin_device *td, dm_block_t *result)
{
        struct dm_pool_metadata *pmd = td->pmd;

        down_read(&pmd->root_lock);
        *result = td->mapped_blocks;
        up_read(&pmd->root_lock);

        return 0;
}

static int __highest_block(struct dm_thin_device *td, dm_block_t *result)
{
        int r;
        __le64 value_le;
        dm_block_t thin_root;
        struct dm_pool_metadata *pmd = td->pmd;

        r = dm_btree_lookup(&pmd->tl_info, pmd->root, &td->id, &value_le);
        if (r)
                return r;

        thin_root = le64_to_cpu(value_le);

        return dm_btree_find_highest_key(&pmd->bl_info, thin_root, result);
}

int dm_thin_get_highest_mapped_block(struct dm_thin_device *td,
                                     dm_block_t *result)
{
        int r;
        struct dm_pool_metadata *pmd = td->pmd;

        down_read(&pmd->root_lock);
        r = __highest_block(td, result);
        up_read(&pmd->root_lock);

        return r;
}

static int __resize_data_dev(struct dm_pool_metadata *pmd, dm_block_t new_count)
{
        int r;
        dm_block_t old_count;

        r = dm_sm_get_nr_blocks(pmd->data_sm, &old_count);
        if (r)
                return r;

        if (new_count == old_count)
                return 0;

        if (new_count < old_count) {
                DMERR("cannot reduce size of data device");
                return -EINVAL;
        }

        r = dm_sm_extend(pmd->data_sm, new_count - old_count);
        if (!r)
                pmd->need_commit = 1;

        return r;
}

int dm_pool_resize_data_dev(struct dm_pool_metadata *pmd, dm_block_t new_count)
{
        int r;

        down_write(&pmd->root_lock);
        r = __resize_data_dev(pmd, new_count);
        up_write(&pmd->root_lock);

        return r;
}