// SPDX-License-Identifier: GPL-2.0-only
#include "dm.h"
#include "persistent-data/dm-transaction-manager.h"
#include "persistent-data/dm-bitset.h"
#include "persistent-data/dm-space-map.h"

#include <linux/dm-io.h>
#include <linux/dm-kcopyd.h>
#include <linux/init.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>

#define DM_MSG_PREFIX "era"

#define SUPERBLOCK_LOCATION 0
#define SUPERBLOCK_MAGIC 2126579579
#define SUPERBLOCK_CSUM_XOR 146538381
#define MIN_ERA_VERSION 1
#define MAX_ERA_VERSION 1
#define INVALID_WRITESET_ROOT SUPERBLOCK_LOCATION
#define MIN_BLOCK_SIZE 8

/*
 *--------------------------------------------------------------
 * Writeset
 *--------------------------------------------------------------
 */
struct writeset_metadata {
        uint32_t nr_bits;
        dm_block_t root;
};

struct writeset {
        struct writeset_metadata md;

        /*
         * An in core copy of the bits to save constantly doing look ups on
         * disk.
         */
        unsigned long *bits;
};

/*
 * This does not free off the on disk bitset as this will normally be done
 * after digesting into the era array.
 */
static void writeset_free(struct writeset *ws)
{
        vfree(ws->bits);
        ws->bits = NULL;
}

static int setup_on_disk_bitset(struct dm_disk_bitset *info,
                                unsigned int nr_bits, dm_block_t *root)
{
        int r;

        r = dm_bitset_empty(info, root);
        if (r)
                return r;

        return dm_bitset_resize(info, *root, 0, nr_bits, false, root);
}

static size_t bitset_size(unsigned int nr_bits)
{
        return sizeof(unsigned long) * dm_div_up(nr_bits, BITS_PER_LONG);
}

/*
 * Allocates memory for the in core bitset.
 */
static int writeset_alloc(struct writeset *ws, dm_block_t nr_blocks)
{
        ws->bits = vzalloc(bitset_size(nr_blocks));
        if (!ws->bits) {
                DMERR("%s: couldn't allocate in memory bitset", __func__);
                return -ENOMEM;
        }

        return 0;
}

/*
 * Wipes the in-core bitset, and creates a new on disk bitset.
 */
static int writeset_init(struct dm_disk_bitset *info, struct writeset *ws,
                         dm_block_t nr_blocks)
{
        int r;

        memset(ws->bits, 0, bitset_size(nr_blocks));

        ws->md.nr_bits = nr_blocks;
        r = setup_on_disk_bitset(info, ws->md.nr_bits, &ws->md.root);
        if (r) {
                DMERR("%s: setup_on_disk_bitset failed", __func__);
                return r;
        }

        return 0;
}

static bool writeset_marked(struct writeset *ws, dm_block_t block)
{
        return test_bit(block, ws->bits);
}

static int writeset_marked_on_disk(struct dm_disk_bitset *info,
                                   struct writeset_metadata *m, dm_block_t block,
                                   bool *result)
{
        int r;
        dm_block_t old = m->root;

        /*
         * The bitset was flushed when it was archived, so we know there'll
         * be no change to the root.
         */
        r = dm_bitset_test_bit(info, m->root, block, &m->root, result);
        if (r) {
                DMERR("%s: dm_bitset_test_bit failed", __func__);
                return r;
        }

        BUG_ON(m->root != old);

        return r;
}

/*
 * Returns < 0 on error, 0 if the bit wasn't previously set, 1 if it was.
 */
static int writeset_test_and_set(struct dm_disk_bitset *info,
                                 struct writeset *ws, uint32_t block)
{
        int r;

        if (!test_bit(block, ws->bits)) {
                r = dm_bitset_set_bit(info, ws->md.root, block, &ws->md.root);
                if (r) {
                        /* FIXME: fail mode */
                        return r;
                }

                return 0;
        }

        return 1;
}

/*
 *--------------------------------------------------------------
 * On disk metadata layout
 *--------------------------------------------------------------
 */
#define SPACE_MAP_ROOT_SIZE 128
#define UUID_LEN 16

struct writeset_disk {
        __le32 nr_bits;
        __le64 root;
} __packed;

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

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

        __u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];

        __le32 data_block_size;
        __le32 metadata_block_size;
        __le32 nr_blocks;

        __le32 current_era;
        struct writeset_disk current_writeset;

        /*
         * Only these two fields are valid within the metadata snapshot.
         */
        __le64 writeset_tree_root;
        __le64 era_array_root;

        __le64 metadata_snap;
} __packed;

/*
 *--------------------------------------------------------------
 * Superblock validation
 *--------------------------------------------------------------
 */
static void sb_prepare_for_write(const struct dm_block_validator *v,
                                 struct dm_block *b,
                                 size_t sb_block_size)
{
        struct superblock_disk *disk = dm_block_data(b);

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

static int check_metadata_version(struct superblock_disk *disk)
{
        uint32_t metadata_version = le32_to_cpu(disk->version);

        if (metadata_version < MIN_ERA_VERSION || metadata_version > MAX_ERA_VERSION) {
                DMERR("Era metadata version %u found, but only versions between %u and %u supported.",
                      metadata_version, MIN_ERA_VERSION, MAX_ERA_VERSION);
                return -EINVAL;
        }

        return 0;
}

static int sb_check(const struct dm_block_validator *v,
                    struct dm_block *b,
                    size_t sb_block_size)
{
        struct superblock_disk *disk = dm_block_data(b);
        __le32 csum_le;

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

        if (le64_to_cpu(disk->magic) != SUPERBLOCK_MAGIC) {
                DMERR("%s failed: magic %llu: wanted %llu",
                      __func__, le64_to_cpu(disk->magic),
                      (unsigned long long) SUPERBLOCK_MAGIC);
                return -EILSEQ;
        }

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

        return check_metadata_version(disk);
}

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

/*
 *--------------------------------------------------------------
 * Low level metadata handling
 *--------------------------------------------------------------
 */
#define DM_ERA_METADATA_BLOCK_SIZE 4096
#define ERA_MAX_CONCURRENT_LOCKS 5

struct era_metadata {
        struct block_device *bdev;
        struct dm_block_manager *bm;
        struct dm_space_map *sm;
        struct dm_transaction_manager *tm;

        dm_block_t block_size;
        uint32_t nr_blocks;

        uint32_t current_era;

        /*
         * We preallocate 2 writesets.  When an era rolls over we
         * switch between them. This means the allocation is done at
         * preresume time, rather than on the io path.
         */
        struct writeset writesets[2];
        struct writeset *current_writeset;

        dm_block_t writeset_tree_root;
        dm_block_t era_array_root;

        struct dm_disk_bitset bitset_info;
        struct dm_btree_info writeset_tree_info;
        struct dm_array_info era_array_info;

        dm_block_t metadata_snap;

        /*
         * A flag that is set whenever a writeset has been archived.
         */
        bool archived_writesets;

        /*
         * Reading the space map root can fail, so we read it into this
         * buffer before the superblock is locked and updated.
         */
        __u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
};

static int superblock_read_lock(struct era_metadata *md,
                                struct dm_block **sblock)
{
        return dm_bm_read_lock(md->bm, SUPERBLOCK_LOCATION,
                               &sb_validator, sblock);
}

static int superblock_lock_zero(struct era_metadata *md,
                                struct dm_block **sblock)
{
        return dm_bm_write_lock_zero(md->bm, SUPERBLOCK_LOCATION,
                                     &sb_validator, sblock);
}

static int superblock_lock(struct era_metadata *md,
                           struct dm_block **sblock)
{
        return dm_bm_write_lock(md->bm, SUPERBLOCK_LOCATION,
                                &sb_validator, sblock);
}

/* FIXME: duplication with cache and thin */
static int superblock_all_zeroes(struct dm_block_manager *bm, bool *result)
{
        int r;
        unsigned int i;
        struct dm_block *b;
        __le64 *data_le, zero = cpu_to_le64(0);
        unsigned int 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, SUPERBLOCK_LOCATION, NULL, &b);
        if (r)
                return r;

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

        dm_bm_unlock(b);

        return 0;
}

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

static void ws_pack(const struct writeset_metadata *core, struct writeset_disk *disk)
{
        disk->nr_bits = cpu_to_le32(core->nr_bits);
        disk->root = cpu_to_le64(core->root);
}

static void ws_unpack(const struct writeset_disk *disk, struct writeset_metadata *core)
{
        core->nr_bits = le32_to_cpu(disk->nr_bits);
        core->root = le64_to_cpu(disk->root);
}

static void ws_inc(void *context, const void *value, unsigned int count)
{
        struct era_metadata *md = context;
        struct writeset_disk ws_d;
        dm_block_t b;
        unsigned int i;

        for (i = 0; i < count; i++) {
                memcpy(&ws_d, value + (i * sizeof(ws_d)), sizeof(ws_d));
                b = le64_to_cpu(ws_d.root);
                dm_tm_inc(md->tm, b);
        }
}

static void ws_dec(void *context, const void *value, unsigned int count)
{
        struct era_metadata *md = context;
        struct writeset_disk ws_d;
        dm_block_t b;
        unsigned int i;

        for (i = 0; i < count; i++) {
                memcpy(&ws_d, value + (i * sizeof(ws_d)), sizeof(ws_d));
                b = le64_to_cpu(ws_d.root);
                dm_bitset_del(&md->bitset_info, b);
        }
}

static int ws_eq(void *context, const void *value1, const void *value2)
{
        return !memcmp(value1, value2, sizeof(struct writeset_disk));
}

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

static void setup_writeset_tree_info(struct era_metadata *md)
{
        struct dm_btree_value_type *vt = &md->writeset_tree_info.value_type;

        md->writeset_tree_info.tm = md->tm;
        md->writeset_tree_info.levels = 1;
        vt->context = md;
        vt->size = sizeof(struct writeset_disk);
        vt->inc = ws_inc;
        vt->dec = ws_dec;
        vt->equal = ws_eq;
}

static void setup_era_array_info(struct era_metadata *md)
{
        struct dm_btree_value_type vt;

        vt.context = NULL;
        vt.size = sizeof(__le32);
        vt.inc = NULL;
        vt.dec = NULL;
        vt.equal = NULL;

        dm_array_info_init(&md->era_array_info, md->tm, &vt);
}

static void setup_infos(struct era_metadata *md)
{
        dm_disk_bitset_init(md->tm, &md->bitset_info);
        setup_writeset_tree_info(md);
        setup_era_array_info(md);
}

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

static int create_fresh_metadata(struct era_metadata *md)
{
        int r;

        r = dm_tm_create_with_sm(md->bm, SUPERBLOCK_LOCATION,
                                 &md->tm, &md->sm);
        if (r < 0) {
                DMERR("dm_tm_create_with_sm failed");
                return r;
        }

        setup_infos(md);

        r = dm_btree_empty(&md->writeset_tree_info, &md->writeset_tree_root);
        if (r) {
                DMERR("couldn't create new writeset tree");
                goto bad;
        }

        r = dm_array_empty(&md->era_array_info, &md->era_array_root);
        if (r) {
                DMERR("couldn't create era array");
                goto bad;
        }

        return 0;

bad:
        dm_sm_destroy(md->sm);
        dm_tm_destroy(md->tm);

        return r;
}

static int save_sm_root(struct era_metadata *md)
{
        int r;
        size_t metadata_len;

        r = dm_sm_root_size(md->sm, &metadata_len);
        if (r < 0)
                return r;

        return dm_sm_copy_root(md->sm, &md->metadata_space_map_root,
                               metadata_len);
}

static void copy_sm_root(struct era_metadata *md, struct superblock_disk *disk)
{
        memcpy(&disk->metadata_space_map_root,
               &md->metadata_space_map_root,
               sizeof(md->metadata_space_map_root));
}

/*
 * Writes a superblock, including the static fields that don't get updated
 * with every commit (possible optimisation here).  'md' should be fully
 * constructed when this is called.
 */
static void prepare_superblock(struct era_metadata *md, struct superblock_disk *disk)
{
        disk->magic = cpu_to_le64(SUPERBLOCK_MAGIC);
        disk->flags = cpu_to_le32(0ul);

        /* FIXME: can't keep blanking the uuid (uuid is currently unused though) */
        memset(disk->uuid, 0, sizeof(disk->uuid));
        disk->version = cpu_to_le32(MAX_ERA_VERSION);

        copy_sm_root(md, disk);

        disk->data_block_size = cpu_to_le32(md->block_size);
        disk->metadata_block_size = cpu_to_le32(DM_ERA_METADATA_BLOCK_SIZE >> SECTOR_SHIFT);
        disk->nr_blocks = cpu_to_le32(md->nr_blocks);
        disk->current_era = cpu_to_le32(md->current_era);

        ws_pack(&md->current_writeset->md, &disk->current_writeset);
        disk->writeset_tree_root = cpu_to_le64(md->writeset_tree_root);
        disk->era_array_root = cpu_to_le64(md->era_array_root);
        disk->metadata_snap = cpu_to_le64(md->metadata_snap);
}

static int write_superblock(struct era_metadata *md)
{
        int r;
        struct dm_block *sblock;
        struct superblock_disk *disk;

        r = save_sm_root(md);
        if (r) {
                DMERR("%s: save_sm_root failed", __func__);
                return r;
        }

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

        disk = dm_block_data(sblock);
        prepare_superblock(md, disk);

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

/*
 * Assumes block_size and the infos are set.
 */
static int format_metadata(struct era_metadata *md)
{
        int r;

        r = create_fresh_metadata(md);
        if (r)
                return r;

        r = write_superblock(md);
        if (r) {
                dm_sm_destroy(md->sm);
                dm_tm_destroy(md->tm);
                return r;
        }

        return 0;
}

static int open_metadata(struct era_metadata *md)
{
        int r;
        struct dm_block *sblock;
        struct superblock_disk *disk;

        r = superblock_read_lock(md, &sblock);
        if (r) {
                DMERR("couldn't read_lock superblock");
                return r;
        }

        disk = dm_block_data(sblock);

        /* Verify the data block size hasn't changed */
        if (le32_to_cpu(disk->data_block_size) != md->block_size) {
                DMERR("changing the data block size (from %u to %llu) is not supported",
                      le32_to_cpu(disk->data_block_size), md->block_size);
                r = -EINVAL;
                goto bad;
        }

        r = dm_tm_open_with_sm(md->bm, SUPERBLOCK_LOCATION,
                               disk->metadata_space_map_root,
                               sizeof(disk->metadata_space_map_root),
                               &md->tm, &md->sm);
        if (r) {
                DMERR("dm_tm_open_with_sm failed");
                goto bad;
        }

        setup_infos(md);

        md->nr_blocks = le32_to_cpu(disk->nr_blocks);
        md->current_era = le32_to_cpu(disk->current_era);

        ws_unpack(&disk->current_writeset, &md->current_writeset->md);
        md->writeset_tree_root = le64_to_cpu(disk->writeset_tree_root);
        md->era_array_root = le64_to_cpu(disk->era_array_root);
        md->metadata_snap = le64_to_cpu(disk->metadata_snap);
        md->archived_writesets = true;

        dm_bm_unlock(sblock);

        return 0;

bad:
        dm_bm_unlock(sblock);
        return r;
}

static int open_or_format_metadata(struct era_metadata *md,
                                   bool may_format)
{
        int r;
        bool unformatted = false;

        r = superblock_all_zeroes(md->bm, &unformatted);
        if (r)
                return r;

        if (unformatted)
                return may_format ? format_metadata(md) : -EPERM;

        return open_metadata(md);
}

static int create_persistent_data_objects(struct era_metadata *md,
                                          bool may_format)
{
        int r;

        md->bm = dm_block_manager_create(md->bdev, DM_ERA_METADATA_BLOCK_SIZE,
                                         ERA_MAX_CONCURRENT_LOCKS);
        if (IS_ERR(md->bm)) {
                DMERR("could not create block manager");
                return PTR_ERR(md->bm);
        }

        r = open_or_format_metadata(md, may_format);
        if (r)
                dm_block_manager_destroy(md->bm);

        return r;
}

static void destroy_persistent_data_objects(struct era_metadata *md)
{
        dm_sm_destroy(md->sm);
        dm_tm_destroy(md->tm);
        dm_block_manager_destroy(md->bm);
}

/*
 * This waits until all era_map threads have picked up the new filter.
 */
static void swap_writeset(struct era_metadata *md, struct writeset *new_writeset)
{
        rcu_assign_pointer(md->current_writeset, new_writeset);
        synchronize_rcu();
}

/*
 *------------------------------------------------------------------------
 * Writesets get 'digested' into the main era array.
 *
 * We're using a coroutine here so the worker thread can do the digestion,
 * thus avoiding synchronisation of the metadata.  Digesting a whole
 * writeset in one go would cause too much latency.
 *------------------------------------------------------------------------
 */
struct digest {
        uint32_t era;
        unsigned int nr_bits, current_bit;
        struct writeset_metadata writeset;
        __le32 value;
        struct dm_disk_bitset info;

        int (*step)(struct era_metadata *md, struct digest *d);
};

static int metadata_digest_lookup_writeset(struct era_metadata *md,
                                           struct digest *d);

static int metadata_digest_remove_writeset(struct era_metadata *md,
                                           struct digest *d)
{
        int r;
        uint64_t key = d->era;

        r = dm_btree_remove(&md->writeset_tree_info, md->writeset_tree_root,
                            &key, &md->writeset_tree_root);
        if (r) {
                DMERR("%s: dm_btree_remove failed", __func__);
                return r;
        }

        d->step = metadata_digest_lookup_writeset;
        return 0;
}

#define INSERTS_PER_STEP 100

static int metadata_digest_transcribe_writeset(struct era_metadata *md,
                                               struct digest *d)
{
        int r;
        bool marked;
        unsigned int b, e = min(d->current_bit + INSERTS_PER_STEP, d->nr_bits);

        for (b = d->current_bit; b < e; b++) {
                r = writeset_marked_on_disk(&d->info, &d->writeset, b, &marked);
                if (r) {
                        DMERR("%s: writeset_marked_on_disk failed", __func__);
                        return r;
                }

                if (!marked)
                        continue;

                __dm_bless_for_disk(&d->value);
                r = dm_array_set_value(&md->era_array_info, md->era_array_root,
                                       b, &d->value, &md->era_array_root);
                if (r) {
                        DMERR("%s: dm_array_set_value failed", __func__);
                        return r;
                }
        }

        if (b == d->nr_bits)
                d->step = metadata_digest_remove_writeset;
        else
                d->current_bit = b;

        return 0;
}

static int metadata_digest_lookup_writeset(struct era_metadata *md,
                                           struct digest *d)
{
        int r;
        uint64_t key;
        struct writeset_disk disk;

        r = dm_btree_find_lowest_key(&md->writeset_tree_info,
                                     md->writeset_tree_root, &key);
        if (r < 0)
                return r;

        d->era = key;

        r = dm_btree_lookup(&md->writeset_tree_info,
                            md->writeset_tree_root, &key, &disk);
        if (r) {
                if (r == -ENODATA) {
                        d->step = NULL;
                        return 0;
                }

                DMERR("%s: dm_btree_lookup failed", __func__);
                return r;
        }

        ws_unpack(&disk, &d->writeset);
        d->value = cpu_to_le32(key);

        /*
         * We initialise another bitset info to avoid any caching side effects
         * with the previous one.
         */
        dm_disk_bitset_init(md->tm, &d->info);

        d->nr_bits = min(d->writeset.nr_bits, md->nr_blocks);
        d->current_bit = 0;
        d->step = metadata_digest_transcribe_writeset;

        return 0;
}

static int metadata_digest_start(struct era_metadata *md, struct digest *d)
{
        if (d->step)
                return 0;

        memset(d, 0, sizeof(*d));
        d->step = metadata_digest_lookup_writeset;

        return 0;
}

/*
 *-----------------------------------------------------------------
 * High level metadata interface.  Target methods should use these,
 * and not the lower level ones.
 *-----------------------------------------------------------------
 */
static struct era_metadata *metadata_open(struct block_device *bdev,
                                          sector_t block_size,
                                          bool may_format)
{
        int r;
        struct era_metadata *md = kzalloc_obj(*md);

        if (!md)
                return NULL;

        md->bdev = bdev;
        md->block_size = block_size;

        md->writesets[0].md.root = INVALID_WRITESET_ROOT;
        md->writesets[1].md.root = INVALID_WRITESET_ROOT;
        md->current_writeset = &md->writesets[0];

        r = create_persistent_data_objects(md, may_format);
        if (r) {
                kfree(md);
                return ERR_PTR(r);
        }

        return md;
}

static void metadata_close(struct era_metadata *md)
{
        writeset_free(&md->writesets[0]);
        writeset_free(&md->writesets[1]);
        destroy_persistent_data_objects(md);
        kfree(md);
}

static bool valid_nr_blocks(dm_block_t n)
{
        /*
         * dm_bitset restricts us to 2^32.  test_bit & co. restrict us
         * further to 2^31 - 1
         */
        return n < (1ull << 31);
}

static int metadata_resize(struct era_metadata *md, void *arg)
{
        int r;
        dm_block_t *new_size = arg;
        __le32 value;

        if (!valid_nr_blocks(*new_size)) {
                DMERR("Invalid number of origin blocks %llu",
                      (unsigned long long) *new_size);
                return -EINVAL;
        }

        writeset_free(&md->writesets[0]);
        writeset_free(&md->writesets[1]);

        r = writeset_alloc(&md->writesets[0], *new_size);
        if (r) {
                DMERR("%s: writeset_alloc failed for writeset 0", __func__);
                return r;
        }

        r = writeset_alloc(&md->writesets[1], *new_size);
        if (r) {
                DMERR("%s: writeset_alloc failed for writeset 1", __func__);
                writeset_free(&md->writesets[0]);
                return r;
        }

        value = cpu_to_le32(0u);
        __dm_bless_for_disk(&value);
        r = dm_array_resize(&md->era_array_info, md->era_array_root,
                            md->nr_blocks, *new_size,
                            &value, &md->era_array_root);
        if (r) {
                DMERR("%s: dm_array_resize failed", __func__);
                writeset_free(&md->writesets[0]);
                writeset_free(&md->writesets[1]);
                return r;
        }

        md->nr_blocks = *new_size;
        return 0;
}

static int metadata_era_archive(struct era_metadata *md)
{
        int r;
        uint64_t keys[1];
        struct writeset_disk value;

        r = dm_bitset_flush(&md->bitset_info, md->current_writeset->md.root,
                            &md->current_writeset->md.root);
        if (r) {
                DMERR("%s: dm_bitset_flush failed", __func__);
                return r;
        }

        ws_pack(&md->current_writeset->md, &value);

        keys[0] = md->current_era;
        __dm_bless_for_disk(&value);
        r = dm_btree_insert(&md->writeset_tree_info, md->writeset_tree_root,
                            keys, &value, &md->writeset_tree_root);
        if (r) {
                DMERR("%s: couldn't insert writeset into btree", __func__);
                /* FIXME: fail mode */
                return r;
        }

        md->current_writeset->md.root = INVALID_WRITESET_ROOT;
        md->archived_writesets = true;

        return 0;
}

static struct writeset *next_writeset(struct era_metadata *md)
{
        return (md->current_writeset == &md->writesets[0]) ?
                &md->writesets[1] : &md->writesets[0];
}

static int metadata_new_era(struct era_metadata *md)
{
        int r;
        struct writeset *new_writeset = next_writeset(md);

        r = writeset_init(&md->bitset_info, new_writeset, md->nr_blocks);
        if (r) {
                DMERR("%s: writeset_init failed", __func__);
                return r;
        }

        swap_writeset(md, new_writeset);
        md->current_era++;

        return 0;
}

static int metadata_era_rollover(struct era_metadata *md)
{
        int r;

        if (md->current_writeset->md.root != INVALID_WRITESET_ROOT) {
                r = metadata_era_archive(md);
                if (r) {
                        DMERR("%s: metadata_archive_era failed", __func__);
                        /* FIXME: fail mode? */
                        return r;
                }
        }

        r = metadata_new_era(md);
        if (r) {
                DMERR("%s: new era failed", __func__);
                /* FIXME: fail mode */
                return r;
        }

        return 0;
}

static bool metadata_current_marked(struct era_metadata *md, dm_block_t block)
{
        bool r;
        struct writeset *ws;

        rcu_read_lock();
        ws = rcu_dereference(md->current_writeset);
        r = writeset_marked(ws, block);
        rcu_read_unlock();

        return r;
}

static int metadata_commit(struct era_metadata *md)
{
        int r;
        struct dm_block *sblock;

        if (md->current_writeset->md.root != INVALID_WRITESET_ROOT) {
                r = dm_bitset_flush(&md->bitset_info, md->current_writeset->md.root,
                                    &md->current_writeset->md.root);
                if (r) {
                        DMERR("%s: bitset flush failed", __func__);
                        return r;
                }
        }

        r = dm_tm_pre_commit(md->tm);
        if (r) {
                DMERR("%s: pre commit failed", __func__);
                return r;
        }

        r = save_sm_root(md);
        if (r) {
                DMERR("%s: save_sm_root failed", __func__);
                return r;
        }

        r = superblock_lock(md, &sblock);
        if (r) {
                DMERR("%s: superblock lock failed", __func__);
                return r;
        }

        prepare_superblock(md, dm_block_data(sblock));

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

static int metadata_checkpoint(struct era_metadata *md)
{
        /*
         * For now we just rollover, but later I want to put a check in to
         * avoid this if the filter is still pretty fresh.
         */
        return metadata_era_rollover(md);
}

/*
 * Metadata snapshots allow userland to access era data.
 */
static int metadata_take_snap(struct era_metadata *md)
{
        int r, inc;
        struct dm_block *clone;

        if (md->metadata_snap != SUPERBLOCK_LOCATION) {
                DMERR("%s: metadata snapshot already exists", __func__);
                return -EINVAL;
        }

        r = metadata_era_rollover(md);
        if (r) {
                DMERR("%s: era rollover failed", __func__);
                return r;
        }

        r = metadata_commit(md);
        if (r) {
                DMERR("%s: pre commit failed", __func__);
                return r;
        }

        r = dm_sm_inc_block(md->sm, SUPERBLOCK_LOCATION);
        if (r) {
                DMERR("%s: couldn't increment superblock", __func__);
                return r;
        }

        r = dm_tm_shadow_block(md->tm, SUPERBLOCK_LOCATION,
                               &sb_validator, &clone, &inc);
        if (r) {
                DMERR("%s: couldn't shadow superblock", __func__);
                dm_sm_dec_block(md->sm, SUPERBLOCK_LOCATION);
                return r;
        }
        BUG_ON(!inc);

        r = dm_sm_inc_block(md->sm, md->writeset_tree_root);
        if (r) {
                DMERR("%s: couldn't inc writeset tree root", __func__);
                dm_tm_unlock(md->tm, clone);
                return r;
        }

        r = dm_sm_inc_block(md->sm, md->era_array_root);
        if (r) {
                DMERR("%s: couldn't inc era tree root", __func__);
                dm_sm_dec_block(md->sm, md->writeset_tree_root);
                dm_tm_unlock(md->tm, clone);
                return r;
        }

        md->metadata_snap = dm_block_location(clone);

        dm_tm_unlock(md->tm, clone);

        return 0;
}

static int metadata_drop_snap(struct era_metadata *md)
{
        int r;
        dm_block_t location;
        struct dm_block *clone;
        struct superblock_disk *disk;

        if (md->metadata_snap == SUPERBLOCK_LOCATION) {
                DMERR("%s: no snap to drop", __func__);
                return -EINVAL;
        }

        r = dm_tm_read_lock(md->tm, md->metadata_snap, &sb_validator, &clone);
        if (r) {
                DMERR("%s: couldn't read lock superblock clone", __func__);
                return r;
        }

        /*
         * Whatever happens now we'll commit with no record of the metadata
         * snap.
         */
        md->metadata_snap = SUPERBLOCK_LOCATION;

        disk = dm_block_data(clone);
        r = dm_btree_del(&md->writeset_tree_info,
                         le64_to_cpu(disk->writeset_tree_root));
        if (r) {
                DMERR("%s: error deleting writeset tree clone", __func__);
                dm_tm_unlock(md->tm, clone);
                return r;
        }

        r = dm_array_del(&md->era_array_info, le64_to_cpu(disk->era_array_root));
        if (r) {
                DMERR("%s: error deleting era array clone", __func__);
                dm_tm_unlock(md->tm, clone);
                return r;
        }

        location = dm_block_location(clone);
        dm_tm_unlock(md->tm, clone);

        return dm_sm_dec_block(md->sm, location);
}

struct metadata_stats {
        dm_block_t used;
        dm_block_t total;
        dm_block_t snap;
        uint32_t era;
};

static int metadata_get_stats(struct era_metadata *md, void *ptr)
{
        int r;
        struct metadata_stats *s = ptr;
        dm_block_t nr_free, nr_total;

        r = dm_sm_get_nr_free(md->sm, &nr_free);
        if (r) {
                DMERR("dm_sm_get_nr_free returned %d", r);
                return r;
        }

        r = dm_sm_get_nr_blocks(md->sm, &nr_total);
        if (r) {
                DMERR("dm_pool_get_metadata_dev_size returned %d", r);
                return r;
        }

        s->used = nr_total - nr_free;
        s->total = nr_total;
        s->snap = md->metadata_snap;
        s->era = md->current_era;

        return 0;
}

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

struct era {
        struct dm_target *ti;

        struct dm_dev *metadata_dev;
        struct dm_dev *origin_dev;

        dm_block_t nr_blocks;
        uint32_t sectors_per_block;
        int sectors_per_block_shift;
        struct era_metadata *md;

        struct workqueue_struct *wq;
        struct work_struct worker;

        spinlock_t deferred_lock;
        struct bio_list deferred_bios;

        spinlock_t rpc_lock;
        struct list_head rpc_calls;

        struct digest digest;
        atomic_t suspended;
};

struct rpc {
        struct list_head list;

        int (*fn0)(struct era_metadata *md);
        int (*fn1)(struct era_metadata *md, void *ref);
        void *arg;
        int result;

        struct completion complete;
};

/*
 *---------------------------------------------------------------
 * Remapping.
 *---------------------------------------------------------------
 */
static bool block_size_is_power_of_two(struct era *era)
{
        return era->sectors_per_block_shift >= 0;
}

static dm_block_t get_block(struct era *era, struct bio *bio)
{
        sector_t block_nr = bio->bi_iter.bi_sector;

        if (!block_size_is_power_of_two(era))
                (void) sector_div(block_nr, era->sectors_per_block);
        else
                block_nr >>= era->sectors_per_block_shift;

        return block_nr;
}

static void remap_to_origin(struct era *era, struct bio *bio)
{
        bio_set_dev(bio, era->origin_dev->bdev);
}

/*
 *--------------------------------------------------------------
 * Worker thread
 *--------------------------------------------------------------
 */
static void wake_worker(struct era *era)
{
        if (!atomic_read(&era->suspended))
                queue_work(era->wq, &era->worker);
}

static void process_old_eras(struct era *era)
{
        int r;

        if (!era->digest.step)
                return;

        r = era->digest.step(era->md, &era->digest);
        if (r < 0) {
                DMERR("%s: digest step failed, stopping digestion", __func__);
                era->digest.step = NULL;

        } else if (era->digest.step)
                wake_worker(era);
}

static void process_deferred_bios(struct era *era)
{
        int r;
        struct bio_list deferred_bios, marked_bios;
        struct bio *bio;
        struct blk_plug plug;
        bool commit_needed = false;
        bool failed = false;
        struct writeset *ws = era->md->current_writeset;

        bio_list_init(&deferred_bios);
        bio_list_init(&marked_bios);

        spin_lock(&era->deferred_lock);
        bio_list_merge_init(&deferred_bios, &era->deferred_bios);
        spin_unlock(&era->deferred_lock);

        if (bio_list_empty(&deferred_bios))
                return;

        while ((bio = bio_list_pop(&deferred_bios))) {
                r = writeset_test_and_set(&era->md->bitset_info, ws,
                                          get_block(era, bio));
                if (r < 0) {
                        /*
                         * This is bad news, we need to rollback.
                         * FIXME: finish.
                         */
                        failed = true;
                } else if (r == 0)
                        commit_needed = true;

                bio_list_add(&marked_bios, bio);
        }

        if (commit_needed) {
                r = metadata_commit(era->md);
                if (r)
                        failed = true;
        }

        if (failed)
                while ((bio = bio_list_pop(&marked_bios)))
                        bio_io_error(bio);
        else {
                blk_start_plug(&plug);
                while ((bio = bio_list_pop(&marked_bios))) {
                        /*
                         * Only update the in-core writeset if the on-disk one
                         * was updated too.
                         */
                        if (commit_needed)
                                set_bit(get_block(era, bio), ws->bits);
                        submit_bio_noacct(bio);
                }
                blk_finish_plug(&plug);
        }
}

static void process_rpc_calls(struct era *era)
{
        int r;
        bool need_commit = false;
        struct list_head calls;
        struct rpc *rpc, *tmp;

        INIT_LIST_HEAD(&calls);
        spin_lock(&era->rpc_lock);
        list_splice_init(&era->rpc_calls, &calls);
        spin_unlock(&era->rpc_lock);

        list_for_each_entry_safe(rpc, tmp, &calls, list) {
                rpc->result = rpc->fn0 ? rpc->fn0(era->md) : rpc->fn1(era->md, rpc->arg);
                need_commit = true;
        }

        if (need_commit) {
                r = metadata_commit(era->md);
                if (r)
                        list_for_each_entry_safe(rpc, tmp, &calls, list)
                                rpc->result = r;
        }

        list_for_each_entry_safe(rpc, tmp, &calls, list)
                complete(&rpc->complete);
}

static void kick_off_digest(struct era *era)
{
        if (era->md->archived_writesets) {
                era->md->archived_writesets = false;
                metadata_digest_start(era->md, &era->digest);
        }
}

static void do_work(struct work_struct *ws)
{
        struct era *era = container_of(ws, struct era, worker);

        kick_off_digest(era);
        process_old_eras(era);
        process_deferred_bios(era);
        process_rpc_calls(era);
}

static void defer_bio(struct era *era, struct bio *bio)
{
        spin_lock(&era->deferred_lock);
        bio_list_add(&era->deferred_bios, bio);
        spin_unlock(&era->deferred_lock);

        wake_worker(era);
}

/*
 * Make an rpc call to the worker to change the metadata.
 */
static int perform_rpc(struct era *era, struct rpc *rpc)
{
        rpc->result = 0;
        init_completion(&rpc->complete);

        spin_lock(&era->rpc_lock);
        list_add(&rpc->list, &era->rpc_calls);
        spin_unlock(&era->rpc_lock);

        wake_worker(era);
        wait_for_completion(&rpc->complete);

        return rpc->result;
}

static int in_worker0(struct era *era, int (*fn)(struct era_metadata *md))
{
        struct rpc rpc;

        rpc.fn0 = fn;
        rpc.fn1 = NULL;

        return perform_rpc(era, &rpc);
}

static int in_worker1(struct era *era,
                      int (*fn)(struct era_metadata *md, void *ref), void *arg)
{
        struct rpc rpc;

        rpc.fn0 = NULL;
        rpc.fn1 = fn;
        rpc.arg = arg;

        return perform_rpc(era, &rpc);
}

static void start_worker(struct era *era)
{
        atomic_set(&era->suspended, 0);
}

static void stop_worker(struct era *era)
{
        atomic_set(&era->suspended, 1);
        drain_workqueue(era->wq);
}

/*
 *--------------------------------------------------------------
 * Target methods
 *--------------------------------------------------------------
 */
static void era_destroy(struct era *era)
{
        if (era->md)
                metadata_close(era->md);

        if (era->wq)
                destroy_workqueue(era->wq);

        if (era->origin_dev)
                dm_put_device(era->ti, era->origin_dev);

        if (era->metadata_dev)
                dm_put_device(era->ti, era->metadata_dev);

        kfree(era);
}

static dm_block_t calc_nr_blocks(struct era *era)
{
        return dm_sector_div_up(era->ti->len, era->sectors_per_block);
}

static bool valid_block_size(dm_block_t block_size)
{
        bool greater_than_zero = block_size > 0;
        bool multiple_of_min_block_size = (block_size & (MIN_BLOCK_SIZE - 1)) == 0;

        return greater_than_zero && multiple_of_min_block_size;
}

/*
 * <metadata dev> <data dev> <data block size (sectors)>
 */
static int era_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
        int r;
        char dummy;
        struct era *era;
        struct era_metadata *md;

        if (argc != 3) {
                ti->error = "Invalid argument count";
                return -EINVAL;
        }

        era = kzalloc_obj(*era);
        if (!era) {
                ti->error = "Error allocating era structure";
                return -ENOMEM;
        }

        era->ti = ti;

        r = dm_get_device(ti, argv[0], BLK_OPEN_READ | BLK_OPEN_WRITE,
                          &era->metadata_dev);
        if (r) {
                ti->error = "Error opening metadata device";
                era_destroy(era);
                return -EINVAL;
        }

        r = dm_get_device(ti, argv[1], BLK_OPEN_READ | BLK_OPEN_WRITE,
                          &era->origin_dev);
        if (r) {
                ti->error = "Error opening data device";
                era_destroy(era);
                return -EINVAL;
        }

        r = sscanf(argv[2], "%u%c", &era->sectors_per_block, &dummy);
        if (r != 1) {
                ti->error = "Error parsing block size";
                era_destroy(era);
                return -EINVAL;
        }

        r = dm_set_target_max_io_len(ti, era->sectors_per_block);
        if (r) {
                ti->error = "could not set max io len";
                era_destroy(era);
                return -EINVAL;
        }

        if (!valid_block_size(era->sectors_per_block)) {
                ti->error = "Invalid block size";
                era_destroy(era);
                return -EINVAL;
        }
        if (era->sectors_per_block & (era->sectors_per_block - 1))
                era->sectors_per_block_shift = -1;
        else
                era->sectors_per_block_shift = __ffs(era->sectors_per_block);

        md = metadata_open(era->metadata_dev->bdev, era->sectors_per_block, true);
        if (IS_ERR(md)) {
                ti->error = "Error reading metadata";
                era_destroy(era);
                return PTR_ERR(md);
        }
        era->md = md;

        era->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
        if (!era->wq) {
                ti->error = "could not create workqueue for metadata object";
                era_destroy(era);
                return -ENOMEM;
        }
        INIT_WORK(&era->worker, do_work);

        spin_lock_init(&era->deferred_lock);
        bio_list_init(&era->deferred_bios);

        spin_lock_init(&era->rpc_lock);
        INIT_LIST_HEAD(&era->rpc_calls);

        ti->private = era;
        ti->num_flush_bios = 1;
        ti->flush_supported = true;

        ti->num_discard_bios = 1;

        return 0;
}

static void era_dtr(struct dm_target *ti)
{
        era_destroy(ti->private);
}

static int era_map(struct dm_target *ti, struct bio *bio)
{
        struct era *era = ti->private;
        dm_block_t block = get_block(era, bio);

        /*
         * All bios get remapped to the origin device.  We do this now, but
         * it may not get issued until later.  Depending on whether the
         * block is marked in this era.
         */
        remap_to_origin(era, bio);

        /*
         * REQ_PREFLUSH bios carry no data, so we're not interested in them.
         */
        if (!(bio->bi_opf & REQ_PREFLUSH) &&
            (bio_data_dir(bio) == WRITE) &&
            !metadata_current_marked(era->md, block)) {
                defer_bio(era, bio);
                return DM_MAPIO_SUBMITTED;
        }

        return DM_MAPIO_REMAPPED;
}

static void era_postsuspend(struct dm_target *ti)
{
        int r;
        struct era *era = ti->private;

        r = in_worker0(era, metadata_era_archive);
        if (r) {
                DMERR("%s: couldn't archive current era", __func__);
                /* FIXME: fail mode */
        }

        stop_worker(era);

        r = metadata_commit(era->md);
        if (r) {
                DMERR("%s: metadata_commit failed", __func__);
                /* FIXME: fail mode */
        }
}

static int era_preresume(struct dm_target *ti)
{
        int r;
        struct era *era = ti->private;
        dm_block_t new_size = calc_nr_blocks(era);

        if (era->nr_blocks != new_size) {
                r = metadata_resize(era->md, &new_size);
                if (r) {
                        DMERR("%s: metadata_resize failed", __func__);
                        return r;
                }

                r = metadata_commit(era->md);
                if (r) {
                        DMERR("%s: metadata_commit failed", __func__);
                        return r;
                }

                era->nr_blocks = new_size;
        }

        start_worker(era);

        r = in_worker0(era, metadata_era_rollover);
        if (r) {
                DMERR("%s: metadata_era_rollover failed", __func__);
                return r;
        }

        return 0;
}

/*
 * Status format:
 *
 * <metadata block size> <#used metadata blocks>/<#total metadata blocks>
 * <current era> <held metadata root | '-'>
 */
static void era_status(struct dm_target *ti, status_type_t type,
                       unsigned int status_flags, char *result, unsigned int maxlen)
{
        int r;
        struct era *era = ti->private;
        ssize_t sz = 0;
        struct metadata_stats stats;
        char buf[BDEVNAME_SIZE];

        switch (type) {
        case STATUSTYPE_INFO:
                r = in_worker1(era, metadata_get_stats, &stats);
                if (r)
                        goto err;

                DMEMIT("%u %llu/%llu %u",
                       (unsigned int) (DM_ERA_METADATA_BLOCK_SIZE >> SECTOR_SHIFT),
                       (unsigned long long) stats.used,
                       (unsigned long long) stats.total,
                       (unsigned int) stats.era);

                if (stats.snap != SUPERBLOCK_LOCATION)
                        DMEMIT(" %llu", stats.snap);
                else
                        DMEMIT(" -");
                break;

        case STATUSTYPE_TABLE:
                format_dev_t(buf, era->metadata_dev->bdev->bd_dev);
                DMEMIT("%s ", buf);
                format_dev_t(buf, era->origin_dev->bdev->bd_dev);
                DMEMIT("%s %u", buf, era->sectors_per_block);
                break;

        case STATUSTYPE_IMA:
                *result = '\0';
                break;
        }

        return;

err:
        DMEMIT("Error");
}

static int era_message(struct dm_target *ti, unsigned int argc, char **argv,
                       char *result, unsigned int maxlen)
{
        struct era *era = ti->private;

        if (argc != 1) {
                DMERR("incorrect number of message arguments");
                return -EINVAL;
        }

        if (!strcasecmp(argv[0], "checkpoint"))
                return in_worker0(era, metadata_checkpoint);

        if (!strcasecmp(argv[0], "take_metadata_snap"))
                return in_worker0(era, metadata_take_snap);

        if (!strcasecmp(argv[0], "drop_metadata_snap"))
                return in_worker0(era, metadata_drop_snap);

        DMERR("unsupported message '%s'", argv[0]);
        return -EINVAL;
}

static sector_t get_dev_size(struct dm_dev *dev)
{
        return bdev_nr_sectors(dev->bdev);
}

static int era_iterate_devices(struct dm_target *ti,
                               iterate_devices_callout_fn fn, void *data)
{
        struct era *era = ti->private;

        return fn(ti, era->origin_dev, 0, get_dev_size(era->origin_dev), data);
}

static void era_io_hints(struct dm_target *ti, struct queue_limits *limits)
{
        struct era *era = ti->private;
        uint64_t io_opt_sectors = limits->io_opt >> SECTOR_SHIFT;

        /*
         * If the system-determined stacked limits are compatible with the
         * era device's blocksize (io_opt is a factor) do not override them.
         */
        if (io_opt_sectors < era->sectors_per_block ||
            do_div(io_opt_sectors, era->sectors_per_block)) {
                limits->io_min = 0;
                limits->io_opt = era->sectors_per_block << SECTOR_SHIFT;
        }
}

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

static struct target_type era_target = {
        .name = "era",
        .version = {1, 0, 0},
        .module = THIS_MODULE,
        .ctr = era_ctr,
        .dtr = era_dtr,
        .map = era_map,
        .postsuspend = era_postsuspend,
        .preresume = era_preresume,
        .status = era_status,
        .message = era_message,
        .iterate_devices = era_iterate_devices,
        .io_hints = era_io_hints
};
module_dm(era);

MODULE_DESCRIPTION(DM_NAME " era target");
MODULE_AUTHOR("Joe Thornber <ejt@redhat.com>");
MODULE_LICENSE("GPL");