/*
 * Copyright (C) 2012 Red Hat, Inc.
 *
 * This file is released under the GPL.
 */

#include "dm-cache-metadata.h"

#include "persistent-data/dm-array.h"
#include "persistent-data/dm-bitset.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/device-mapper.h>

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

#define DM_MSG_PREFIX   "cache metadata"

#define CACHE_SUPERBLOCK_MAGIC 06142003
#define CACHE_SUPERBLOCK_LOCATION 0
#define CACHE_VERSION 1
#define CACHE_METADATA_CACHE_SIZE 64

/*
 *  3 for btree insert +
 *  2 for btree lookup used within space map
 */
#define CACHE_MAX_CONCURRENT_LOCKS 5
#define SPACE_MAP_ROOT_SIZE 128

enum superblock_flag_bits {
        /* for spotting crashes that would invalidate the dirty bitset */
        CLEAN_SHUTDOWN,
};

/*
 * Each mapping from cache block -> origin block carries a set of flags.
 */
enum mapping_bits {
        /*
         * A valid mapping.  Because we're using an array we clear this
         * flag for an non existant mapping.
         */
        M_VALID = 1,

        /*
         * The data on the cache is different from that on the origin.
         */
        M_DIRTY = 2
};

struct cache_disk_superblock {
        __le32 csum;
        __le32 flags;
        __le64 blocknr;

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

        __u8 policy_name[CACHE_POLICY_NAME_SIZE];
        __le32 policy_hint_size;

        __u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
        __le64 mapping_root;
        __le64 hint_root;

        __le64 discard_root;
        __le64 discard_block_size;
        __le64 discard_nr_blocks;

        __le32 data_block_size;
        __le32 metadata_block_size;
        __le32 cache_blocks;

        __le32 compat_flags;
        __le32 compat_ro_flags;
        __le32 incompat_flags;

        __le32 read_hits;
        __le32 read_misses;
        __le32 write_hits;
        __le32 write_misses;

        __le32 policy_version[CACHE_POLICY_VERSION_SIZE];
} __packed;

struct dm_cache_metadata {
        struct block_device *bdev;
        struct dm_block_manager *bm;
        struct dm_space_map *metadata_sm;
        struct dm_transaction_manager *tm;

        struct dm_array_info info;
        struct dm_array_info hint_info;
        struct dm_disk_bitset discard_info;

        struct rw_semaphore root_lock;
        dm_block_t root;
        dm_block_t hint_root;
        dm_block_t discard_root;

        sector_t discard_block_size;
        dm_dblock_t discard_nr_blocks;

        sector_t data_block_size;
        dm_cblock_t cache_blocks;
        bool changed:1;
        bool clean_when_opened:1;

        char policy_name[CACHE_POLICY_NAME_SIZE];
        unsigned policy_version[CACHE_POLICY_VERSION_SIZE];
        size_t policy_hint_size;
        struct dm_cache_statistics stats;
};

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

#define SUPERBLOCK_CSUM_XOR 9031977

static void sb_prepare_for_write(struct dm_block_validator *v,
                                 struct dm_block *b,
                                 size_t sb_block_size)
{
        struct cache_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,
                                                      sb_block_size - sizeof(__le32),
                                                      SUPERBLOCK_CSUM_XOR));
}

static int sb_check(struct dm_block_validator *v,
                    struct dm_block *b,
                    size_t sb_block_size)
{
        struct cache_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) != CACHE_SUPERBLOCK_MAGIC) {
                DMERR("sb_check failed: magic %llu: wanted %llu",
                      le64_to_cpu(disk_super->magic),
                      (unsigned long long)CACHE_SUPERBLOCK_MAGIC);
                return -EILSEQ;
        }

        csum_le = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
                                             sb_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
};

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

static int superblock_read_lock(struct dm_cache_metadata *cmd,
                                struct dm_block **sblock)
{
        return dm_bm_read_lock(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
                               &sb_validator, sblock);
}

static int superblock_lock_zero(struct dm_cache_metadata *cmd,
                                struct dm_block **sblock)
{
        return dm_bm_write_lock_zero(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
                                     &sb_validator, sblock);
}

static int superblock_lock(struct dm_cache_metadata *cmd,
                           struct dm_block **sblock)
{
        return dm_bm_write_lock(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
                                &sb_validator, sblock);
}

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

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 sb_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, CACHE_SUPERBLOCK_LOCATION, NULL, &b);
        if (r)
                return r;

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

        return dm_bm_unlock(b);
}

static void __setup_mapping_info(struct dm_cache_metadata *cmd)
{
        struct dm_btree_value_type vt;

        vt.context = NULL;
        vt.size = sizeof(__le64);
        vt.inc = NULL;
        vt.dec = NULL;
        vt.equal = NULL;
        dm_array_info_init(&cmd->info, cmd->tm, &vt);

        if (cmd->policy_hint_size) {
                vt.size = sizeof(__le32);
                dm_array_info_init(&cmd->hint_info, cmd->tm, &vt);
        }
}

static int __write_initial_superblock(struct dm_cache_metadata *cmd)
{
        int r;
        struct dm_block *sblock;
        size_t metadata_len;
        struct cache_disk_superblock *disk_super;
        sector_t bdev_size = i_size_read(cmd->bdev->bd_inode) >> SECTOR_SHIFT;

        /* FIXME: see if we can lose the max sectors limit */
        if (bdev_size > DM_CACHE_METADATA_MAX_SECTORS)
                bdev_size = DM_CACHE_METADATA_MAX_SECTORS;

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

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

        r = superblock_lock_zero(cmd, &sblock);
        if (r)
                return r;

        disk_super = dm_block_data(sblock);
        disk_super->flags = 0;
        memset(disk_super->uuid, 0, sizeof(disk_super->uuid));
        disk_super->magic = cpu_to_le64(CACHE_SUPERBLOCK_MAGIC);
        disk_super->version = cpu_to_le32(CACHE_VERSION);
        memset(disk_super->policy_name, 0, sizeof(disk_super->policy_name));
        memset(disk_super->policy_version, 0, sizeof(disk_super->policy_version));
        disk_super->policy_hint_size = 0;

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

        disk_super->mapping_root = cpu_to_le64(cmd->root);
        disk_super->hint_root = cpu_to_le64(cmd->hint_root);
        disk_super->discard_root = cpu_to_le64(cmd->discard_root);
        disk_super->discard_block_size = cpu_to_le64(cmd->discard_block_size);
        disk_super->discard_nr_blocks = cpu_to_le64(from_dblock(cmd->discard_nr_blocks));
        disk_super->metadata_block_size = cpu_to_le32(DM_CACHE_METADATA_BLOCK_SIZE >> SECTOR_SHIFT);
        disk_super->data_block_size = cpu_to_le32(cmd->data_block_size);
        disk_super->cache_blocks = cpu_to_le32(0);

        disk_super->read_hits = cpu_to_le32(0);
        disk_super->read_misses = cpu_to_le32(0);
        disk_super->write_hits = cpu_to_le32(0);
        disk_super->write_misses = cpu_to_le32(0);

        return dm_tm_commit(cmd->tm, sblock);

bad_locked:
        dm_bm_unlock(sblock);
        return r;
}

static int __format_metadata(struct dm_cache_metadata *cmd)
{
        int r;

        r = dm_tm_create_with_sm(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
                                 &cmd->tm, &cmd->metadata_sm);
        if (r < 0) {
                DMERR("tm_create_with_sm failed");
                return r;
        }

        __setup_mapping_info(cmd);

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

        dm_disk_bitset_init(cmd->tm, &cmd->discard_info);

        r = dm_bitset_empty(&cmd->discard_info, &cmd->discard_root);
        if (r < 0)
                goto bad;

        cmd->discard_block_size = 0;
        cmd->discard_nr_blocks = 0;

        r = __write_initial_superblock(cmd);
        if (r)
                goto bad;

        cmd->clean_when_opened = true;
        return 0;

bad:
        dm_tm_destroy(cmd->tm);
        dm_sm_destroy(cmd->metadata_sm);

        return r;
}

static int __check_incompat_features(struct cache_disk_superblock *disk_super,
                                     struct dm_cache_metadata *cmd)
{
        uint32_t features;

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

        /*
         * Check for read-only metadata to skip the following RDWR checks.
         */
        if (get_disk_ro(cmd->bdev->bd_disk))
                return 0;

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

        return 0;
}

static int __open_metadata(struct dm_cache_metadata *cmd)
{
        int r;
        struct dm_block *sblock;
        struct cache_disk_superblock *disk_super;
        unsigned long sb_flags;

        r = superblock_read_lock(cmd, &sblock);
        if (r < 0) {
                DMERR("couldn't read lock superblock");
                return r;
        }

        disk_super = dm_block_data(sblock);

        r = __check_incompat_features(disk_super, cmd);
        if (r < 0)
                goto bad;

        r = dm_tm_open_with_sm(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
                               disk_super->metadata_space_map_root,
                               sizeof(disk_super->metadata_space_map_root),
                               &cmd->tm, &cmd->metadata_sm);
        if (r < 0) {
                DMERR("tm_open_with_sm failed");
                goto bad;
        }

        __setup_mapping_info(cmd);
        dm_disk_bitset_init(cmd->tm, &cmd->discard_info);
        sb_flags = le32_to_cpu(disk_super->flags);
        cmd->clean_when_opened = test_bit(CLEAN_SHUTDOWN, &sb_flags);
        return dm_bm_unlock(sblock);

bad:
        dm_bm_unlock(sblock);
        return r;
}

static int __open_or_format_metadata(struct dm_cache_metadata *cmd,
                                     bool format_device)
{
        int r, unformatted;

        r = __superblock_all_zeroes(cmd->bm, &unformatted);
        if (r)
                return r;

        if (unformatted)
                return format_device ? __format_metadata(cmd) : -EPERM;

        return __open_metadata(cmd);
}

static int __create_persistent_data_objects(struct dm_cache_metadata *cmd,
                                            bool may_format_device)
{
        int r;
        cmd->bm = dm_block_manager_create(cmd->bdev, DM_CACHE_METADATA_BLOCK_SIZE,
                                          CACHE_METADATA_CACHE_SIZE,
                                          CACHE_MAX_CONCURRENT_LOCKS);
        if (IS_ERR(cmd->bm)) {
                DMERR("could not create block manager");
                return PTR_ERR(cmd->bm);
        }

        r = __open_or_format_metadata(cmd, may_format_device);
        if (r)
                dm_block_manager_destroy(cmd->bm);

        return r;
}

static void __destroy_persistent_data_objects(struct dm_cache_metadata *cmd)
{
        dm_sm_destroy(cmd->metadata_sm);
        dm_tm_destroy(cmd->tm);
        dm_block_manager_destroy(cmd->bm);
}

typedef unsigned long (*flags_mutator)(unsigned long);

static void update_flags(struct cache_disk_superblock *disk_super,
                         flags_mutator mutator)
{
        uint32_t sb_flags = mutator(le32_to_cpu(disk_super->flags));
        disk_super->flags = cpu_to_le32(sb_flags);
}

static unsigned long set_clean_shutdown(unsigned long flags)
{
        set_bit(CLEAN_SHUTDOWN, &flags);
        return flags;
}

static unsigned long clear_clean_shutdown(unsigned long flags)
{
        clear_bit(CLEAN_SHUTDOWN, &flags);
        return flags;
}

static void read_superblock_fields(struct dm_cache_metadata *cmd,
                                   struct cache_disk_superblock *disk_super)
{
        cmd->root = le64_to_cpu(disk_super->mapping_root);
        cmd->hint_root = le64_to_cpu(disk_super->hint_root);
        cmd->discard_root = le64_to_cpu(disk_super->discard_root);
        cmd->discard_block_size = le64_to_cpu(disk_super->discard_block_size);
        cmd->discard_nr_blocks = to_dblock(le64_to_cpu(disk_super->discard_nr_blocks));
        cmd->data_block_size = le32_to_cpu(disk_super->data_block_size);
        cmd->cache_blocks = to_cblock(le32_to_cpu(disk_super->cache_blocks));
        strncpy(cmd->policy_name, disk_super->policy_name, sizeof(cmd->policy_name));
        cmd->policy_version[0] = le32_to_cpu(disk_super->policy_version[0]);
        cmd->policy_version[1] = le32_to_cpu(disk_super->policy_version[1]);
        cmd->policy_version[2] = le32_to_cpu(disk_super->policy_version[2]);
        cmd->policy_hint_size = le32_to_cpu(disk_super->policy_hint_size);

        cmd->stats.read_hits = le32_to_cpu(disk_super->read_hits);
        cmd->stats.read_misses = le32_to_cpu(disk_super->read_misses);
        cmd->stats.write_hits = le32_to_cpu(disk_super->write_hits);
        cmd->stats.write_misses = le32_to_cpu(disk_super->write_misses);

        cmd->changed = false;
}

/*
 * The mutator updates the superblock flags.
 */
static int __begin_transaction_flags(struct dm_cache_metadata *cmd,
                                     flags_mutator mutator)
{
        int r;
        struct cache_disk_superblock *disk_super;
        struct dm_block *sblock;

        r = superblock_lock(cmd, &sblock);
        if (r)
                return r;

        disk_super = dm_block_data(sblock);
        update_flags(disk_super, mutator);
        read_superblock_fields(cmd, disk_super);

        return dm_bm_flush_and_unlock(cmd->bm, sblock);
}

static int __begin_transaction(struct dm_cache_metadata *cmd)
{
        int r;
        struct cache_disk_superblock *disk_super;
        struct dm_block *sblock;

        /*
         * We re-read the superblock every time.  Shouldn't need to do this
         * really.
         */
        r = superblock_read_lock(cmd, &sblock);
        if (r)
                return r;

        disk_super = dm_block_data(sblock);
        read_superblock_fields(cmd, disk_super);
        dm_bm_unlock(sblock);

        return 0;
}

static int __commit_transaction(struct dm_cache_metadata *cmd,
                                flags_mutator mutator)
{
        int r;
        size_t metadata_len;
        struct cache_disk_superblock *disk_super;
        struct dm_block *sblock;

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

        r = dm_bitset_flush(&cmd->discard_info, cmd->discard_root,
                            &cmd->discard_root);
        if (r)
                return r;

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

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

        r = superblock_lock(cmd, &sblock);
        if (r)
                return r;

        disk_super = dm_block_data(sblock);

        if (mutator)
                update_flags(disk_super, mutator);

        disk_super->mapping_root = cpu_to_le64(cmd->root);
        disk_super->hint_root = cpu_to_le64(cmd->hint_root);
        disk_super->discard_root = cpu_to_le64(cmd->discard_root);
        disk_super->discard_block_size = cpu_to_le64(cmd->discard_block_size);
        disk_super->discard_nr_blocks = cpu_to_le64(from_dblock(cmd->discard_nr_blocks));
        disk_super->cache_blocks = cpu_to_le32(from_cblock(cmd->cache_blocks));
        strncpy(disk_super->policy_name, cmd->policy_name, sizeof(disk_super->policy_name));
        disk_super->policy_version[0] = cpu_to_le32(cmd->policy_version[0]);
        disk_super->policy_version[1] = cpu_to_le32(cmd->policy_version[1]);
        disk_super->policy_version[2] = cpu_to_le32(cmd->policy_version[2]);

        disk_super->read_hits = cpu_to_le32(cmd->stats.read_hits);
        disk_super->read_misses = cpu_to_le32(cmd->stats.read_misses);
        disk_super->write_hits = cpu_to_le32(cmd->stats.write_hits);
        disk_super->write_misses = cpu_to_le32(cmd->stats.write_misses);

        r = dm_sm_copy_root(cmd->metadata_sm, &disk_super->metadata_space_map_root,
                            metadata_len);
        if (r < 0) {
                dm_bm_unlock(sblock);
                return r;
        }

        return dm_tm_commit(cmd->tm, sblock);
}

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

/*
 * The mappings are held in a dm-array that has 64-bit values stored in
 * little-endian format.  The index is the cblock, the high 48bits of the
 * value are the oblock and the low 16 bit the flags.
 */
#define FLAGS_MASK ((1 << 16) - 1)

static __le64 pack_value(dm_oblock_t block, unsigned flags)
{
        uint64_t value = from_oblock(block);
        value <<= 16;
        value = value | (flags & FLAGS_MASK);
        return cpu_to_le64(value);
}

static void unpack_value(__le64 value_le, dm_oblock_t *block, unsigned *flags)
{
        uint64_t value = le64_to_cpu(value_le);
        uint64_t b = value >> 16;
        *block = to_oblock(b);
        *flags = value & FLAGS_MASK;
}

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

struct dm_cache_metadata *dm_cache_metadata_open(struct block_device *bdev,
                                                 sector_t data_block_size,
                                                 bool may_format_device,
                                                 size_t policy_hint_size)
{
        int r;
        struct dm_cache_metadata *cmd;

        cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);
        if (!cmd) {
                DMERR("could not allocate metadata struct");
                return NULL;
        }

        init_rwsem(&cmd->root_lock);
        cmd->bdev = bdev;
        cmd->data_block_size = data_block_size;
        cmd->cache_blocks = 0;
        cmd->policy_hint_size = policy_hint_size;
        cmd->changed = true;

        r = __create_persistent_data_objects(cmd, may_format_device);
        if (r) {
                kfree(cmd);
                return ERR_PTR(r);
        }

        r = __begin_transaction_flags(cmd, clear_clean_shutdown);
        if (r < 0) {
                dm_cache_metadata_close(cmd);
                return ERR_PTR(r);
        }

        return cmd;
}

void dm_cache_metadata_close(struct dm_cache_metadata *cmd)
{
        __destroy_persistent_data_objects(cmd);
        kfree(cmd);
}

int dm_cache_resize(struct dm_cache_metadata *cmd, dm_cblock_t new_cache_size)
{
        int r;
        __le64 null_mapping = pack_value(0, 0);

        down_write(&cmd->root_lock);
        __dm_bless_for_disk(&null_mapping);
        r = dm_array_resize(&cmd->info, cmd->root, from_cblock(cmd->cache_blocks),
                            from_cblock(new_cache_size),
                            &null_mapping, &cmd->root);
        if (!r)
                cmd->cache_blocks = new_cache_size;
        cmd->changed = true;
        up_write(&cmd->root_lock);

        return r;
}

int dm_cache_discard_bitset_resize(struct dm_cache_metadata *cmd,
                                   sector_t discard_block_size,
                                   dm_dblock_t new_nr_entries)
{
        int r;

        down_write(&cmd->root_lock);
        r = dm_bitset_resize(&cmd->discard_info,
                             cmd->discard_root,
                             from_dblock(cmd->discard_nr_blocks),
                             from_dblock(new_nr_entries),
                             false, &cmd->discard_root);
        if (!r) {
                cmd->discard_block_size = discard_block_size;
                cmd->discard_nr_blocks = new_nr_entries;
        }

        cmd->changed = true;
        up_write(&cmd->root_lock);

        return r;
}

static int __set_discard(struct dm_cache_metadata *cmd, dm_dblock_t b)
{
        return dm_bitset_set_bit(&cmd->discard_info, cmd->discard_root,
                                 from_dblock(b), &cmd->discard_root);
}

static int __clear_discard(struct dm_cache_metadata *cmd, dm_dblock_t b)
{
        return dm_bitset_clear_bit(&cmd->discard_info, cmd->discard_root,
                                   from_dblock(b), &cmd->discard_root);
}

static int __is_discarded(struct dm_cache_metadata *cmd, dm_dblock_t b,
                          bool *is_discarded)
{
        return dm_bitset_test_bit(&cmd->discard_info, cmd->discard_root,
                                  from_dblock(b), &cmd->discard_root,
                                  is_discarded);
}

static int __discard(struct dm_cache_metadata *cmd,
                     dm_dblock_t dblock, bool discard)
{
        int r;

        r = (discard ? __set_discard : __clear_discard)(cmd, dblock);
        if (r)
                return r;

        cmd->changed = true;
        return 0;
}

int dm_cache_set_discard(struct dm_cache_metadata *cmd,
                         dm_dblock_t dblock, bool discard)
{
        int r;

        down_write(&cmd->root_lock);
        r = __discard(cmd, dblock, discard);
        up_write(&cmd->root_lock);

        return r;
}

static int __load_discards(struct dm_cache_metadata *cmd,
                           load_discard_fn fn, void *context)
{
        int r = 0;
        dm_block_t b;
        bool discard;

        for (b = 0; b < from_dblock(cmd->discard_nr_blocks); b++) {
                dm_dblock_t dblock = to_dblock(b);

                if (cmd->clean_when_opened) {
                        r = __is_discarded(cmd, dblock, &discard);
                        if (r)
                                return r;
                } else
                        discard = false;

                r = fn(context, cmd->discard_block_size, dblock, discard);
                if (r)
                        break;
        }

        return r;
}

int dm_cache_load_discards(struct dm_cache_metadata *cmd,
                           load_discard_fn fn, void *context)
{
        int r;

        down_read(&cmd->root_lock);
        r = __load_discards(cmd, fn, context);
        up_read(&cmd->root_lock);

        return r;
}

dm_cblock_t dm_cache_size(struct dm_cache_metadata *cmd)
{
        dm_cblock_t r;

        down_read(&cmd->root_lock);
        r = cmd->cache_blocks;
        up_read(&cmd->root_lock);

        return r;
}

static int __remove(struct dm_cache_metadata *cmd, dm_cblock_t cblock)
{
        int r;
        __le64 value = pack_value(0, 0);

        __dm_bless_for_disk(&value);
        r = dm_array_set_value(&cmd->info, cmd->root, from_cblock(cblock),
                               &value, &cmd->root);
        if (r)
                return r;

        cmd->changed = true;
        return 0;
}

int dm_cache_remove_mapping(struct dm_cache_metadata *cmd, dm_cblock_t cblock)
{
        int r;

        down_write(&cmd->root_lock);
        r = __remove(cmd, cblock);
        up_write(&cmd->root_lock);

        return r;
}

static int __insert(struct dm_cache_metadata *cmd,
                    dm_cblock_t cblock, dm_oblock_t oblock)
{
        int r;
        __le64 value = pack_value(oblock, M_VALID);
        __dm_bless_for_disk(&value);

        r = dm_array_set_value(&cmd->info, cmd->root, from_cblock(cblock),
                               &value, &cmd->root);
        if (r)
                return r;

        cmd->changed = true;
        return 0;
}

int dm_cache_insert_mapping(struct dm_cache_metadata *cmd,
                            dm_cblock_t cblock, dm_oblock_t oblock)
{
        int r;

        down_write(&cmd->root_lock);
        r = __insert(cmd, cblock, oblock);
        up_write(&cmd->root_lock);

        return r;
}

struct thunk {
        load_mapping_fn fn;
        void *context;

        struct dm_cache_metadata *cmd;
        bool respect_dirty_flags;
        bool hints_valid;
};

static bool policy_unchanged(struct dm_cache_metadata *cmd,
                             struct dm_cache_policy *policy)
{
        const char *policy_name = dm_cache_policy_get_name(policy);
        const unsigned *policy_version = dm_cache_policy_get_version(policy);
        size_t policy_hint_size = dm_cache_policy_get_hint_size(policy);

        /*
         * Ensure policy names match.
         */
        if (strncmp(cmd->policy_name, policy_name, sizeof(cmd->policy_name)))
                return false;

        /*
         * Ensure policy major versions match.
         */
        if (cmd->policy_version[0] != policy_version[0])
                return false;

        /*
         * Ensure policy hint sizes match.
         */
        if (cmd->policy_hint_size != policy_hint_size)
                return false;

        return true;
}

static bool hints_array_initialized(struct dm_cache_metadata *cmd)
{
        return cmd->hint_root && cmd->policy_hint_size;
}

static bool hints_array_available(struct dm_cache_metadata *cmd,
                                  struct dm_cache_policy *policy)
{
        return cmd->clean_when_opened && policy_unchanged(cmd, policy) &&
                hints_array_initialized(cmd);
}

static int __load_mapping(void *context, uint64_t cblock, void *leaf)
{
        int r = 0;
        bool dirty;
        __le64 value;
        __le32 hint_value = 0;
        dm_oblock_t oblock;
        unsigned flags;
        struct thunk *thunk = context;
        struct dm_cache_metadata *cmd = thunk->cmd;

        memcpy(&value, leaf, sizeof(value));
        unpack_value(value, &oblock, &flags);

        if (flags & M_VALID) {
                if (thunk->hints_valid) {
                        r = dm_array_get_value(&cmd->hint_info, cmd->hint_root,
                                               cblock, &hint_value);
                        if (r && r != -ENODATA)
                                return r;
                }

                dirty = thunk->respect_dirty_flags ? (flags & M_DIRTY) : true;
                r = thunk->fn(thunk->context, oblock, to_cblock(cblock),
                              dirty, le32_to_cpu(hint_value), thunk->hints_valid);
        }

        return r;
}

static int __load_mappings(struct dm_cache_metadata *cmd,
                           struct dm_cache_policy *policy,
                           load_mapping_fn fn, void *context)
{
        struct thunk thunk;

        thunk.fn = fn;
        thunk.context = context;

        thunk.cmd = cmd;
        thunk.respect_dirty_flags = cmd->clean_when_opened;
        thunk.hints_valid = hints_array_available(cmd, policy);

        return dm_array_walk(&cmd->info, cmd->root, __load_mapping, &thunk);
}

int dm_cache_load_mappings(struct dm_cache_metadata *cmd,
                           struct dm_cache_policy *policy,
                           load_mapping_fn fn, void *context)
{
        int r;

        down_read(&cmd->root_lock);
        r = __load_mappings(cmd, policy, fn, context);
        up_read(&cmd->root_lock);

        return r;
}

static int __dump_mapping(void *context, uint64_t cblock, void *leaf)
{
        int r = 0;
        __le64 value;
        dm_oblock_t oblock;
        unsigned flags;

        memcpy(&value, leaf, sizeof(value));
        unpack_value(value, &oblock, &flags);

        return r;
}

static int __dump_mappings(struct dm_cache_metadata *cmd)
{
        return dm_array_walk(&cmd->info, cmd->root, __dump_mapping, NULL);
}

void dm_cache_dump(struct dm_cache_metadata *cmd)
{
        down_read(&cmd->root_lock);
        __dump_mappings(cmd);
        up_read(&cmd->root_lock);
}

int dm_cache_changed_this_transaction(struct dm_cache_metadata *cmd)
{
        int r;

        down_read(&cmd->root_lock);
        r = cmd->changed;
        up_read(&cmd->root_lock);

        return r;
}

static int __dirty(struct dm_cache_metadata *cmd, dm_cblock_t cblock, bool dirty)
{
        int r;
        unsigned flags;
        dm_oblock_t oblock;
        __le64 value;

        r = dm_array_get_value(&cmd->info, cmd->root, from_cblock(cblock), &value);
        if (r)
                return r;

        unpack_value(value, &oblock, &flags);

        if (((flags & M_DIRTY) && dirty) || (!(flags & M_DIRTY) && !dirty))
                /* nothing to be done */
                return 0;

        value = pack_value(oblock, (flags & ~M_DIRTY) | (dirty ? M_DIRTY : 0));
        __dm_bless_for_disk(&value);

        r = dm_array_set_value(&cmd->info, cmd->root, from_cblock(cblock),
                               &value, &cmd->root);
        if (r)
                return r;

        cmd->changed = true;
        return 0;

}

int dm_cache_set_dirty(struct dm_cache_metadata *cmd,
                       dm_cblock_t cblock, bool dirty)
{
        int r;

        down_write(&cmd->root_lock);
        r = __dirty(cmd, cblock, dirty);
        up_write(&cmd->root_lock);

        return r;
}

void dm_cache_metadata_get_stats(struct dm_cache_metadata *cmd,
                                 struct dm_cache_statistics *stats)
{
        down_read(&cmd->root_lock);
        *stats = cmd->stats;
        up_read(&cmd->root_lock);
}

void dm_cache_metadata_set_stats(struct dm_cache_metadata *cmd,
                                 struct dm_cache_statistics *stats)
{
        down_write(&cmd->root_lock);
        cmd->stats = *stats;
        up_write(&cmd->root_lock);
}

int dm_cache_commit(struct dm_cache_metadata *cmd, bool clean_shutdown)
{
        int r;
        flags_mutator mutator = (clean_shutdown ? set_clean_shutdown :
                                 clear_clean_shutdown);

        down_write(&cmd->root_lock);
        r = __commit_transaction(cmd, mutator);
        if (r)
                goto out;

        r = __begin_transaction(cmd);

out:
        up_write(&cmd->root_lock);
        return r;
}

int dm_cache_get_free_metadata_block_count(struct dm_cache_metadata *cmd,
                                           dm_block_t *result)
{
        int r = -EINVAL;

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

        return r;
}

int dm_cache_get_metadata_dev_size(struct dm_cache_metadata *cmd,
                                   dm_block_t *result)
{
        int r = -EINVAL;

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

        return r;
}

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

static int begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
{
        int r;
        __le32 value;
        size_t hint_size;
        const char *policy_name = dm_cache_policy_get_name(policy);
        const unsigned *policy_version = dm_cache_policy_get_version(policy);

        if (!policy_name[0] ||
            (strlen(policy_name) > sizeof(cmd->policy_name) - 1))
                return -EINVAL;

        if (!policy_unchanged(cmd, policy)) {
                strncpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name));
                memcpy(cmd->policy_version, policy_version, sizeof(cmd->policy_version));

                hint_size = dm_cache_policy_get_hint_size(policy);
                if (!hint_size)
                        return 0; /* short-circuit hints initialization */
                cmd->policy_hint_size = hint_size;

                if (cmd->hint_root) {
                        r = dm_array_del(&cmd->hint_info, cmd->hint_root);
                        if (r)
                                return r;
                }

                r = dm_array_empty(&cmd->hint_info, &cmd->hint_root);
                if (r)
                        return r;

                value = cpu_to_le32(0);
                __dm_bless_for_disk(&value);
                r = dm_array_resize(&cmd->hint_info, cmd->hint_root, 0,
                                    from_cblock(cmd->cache_blocks),
                                    &value, &cmd->hint_root);
                if (r)
                        return r;
        }

        return 0;
}

int dm_cache_begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
{
        int r;

        down_write(&cmd->root_lock);
        r = begin_hints(cmd, policy);
        up_write(&cmd->root_lock);

        return r;
}

static int save_hint(struct dm_cache_metadata *cmd, dm_cblock_t cblock,
                     uint32_t hint)
{
        int r;
        __le32 value = cpu_to_le32(hint);
        __dm_bless_for_disk(&value);

        r = dm_array_set_value(&cmd->hint_info, cmd->hint_root,
                               from_cblock(cblock), &value, &cmd->hint_root);
        cmd->changed = true;

        return r;
}

int dm_cache_save_hint(struct dm_cache_metadata *cmd, dm_cblock_t cblock,
                       uint32_t hint)
{
        int r;

        if (!hints_array_initialized(cmd))
                return 0;

        down_write(&cmd->root_lock);
        r = save_hint(cmd, cblock, hint);
        up_write(&cmd->root_lock);

        return r;
}