// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2011 Red Hat, Inc.
 *
 * This file is released under the GPL.
 */

#include "dm-space-map-common.h"
#include "dm-transaction-manager.h"
#include "dm-btree-internal.h"
#include "dm-persistent-data-internal.h"

#include <linux/bitops.h>
#include <linux/device-mapper.h>

#define DM_MSG_PREFIX "space map common"

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

/*
 * Index validator.
 */
#define INDEX_CSUM_XOR 160478

static void index_prepare_for_write(const struct dm_block_validator *v,
                                    struct dm_block *b,
                                    size_t block_size)
{
        struct disk_metadata_index *mi_le = dm_block_data(b);

        mi_le->blocknr = cpu_to_le64(dm_block_location(b));
        mi_le->csum = cpu_to_le32(dm_bm_checksum(&mi_le->padding,
                                                 block_size - sizeof(__le32),
                                                 INDEX_CSUM_XOR));
}

static int index_check(const struct dm_block_validator *v,
                       struct dm_block *b,
                       size_t block_size)
{
        struct disk_metadata_index *mi_le = dm_block_data(b);
        __le32 csum_disk;

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

        csum_disk = cpu_to_le32(dm_bm_checksum(&mi_le->padding,
                                               block_size - sizeof(__le32),
                                               INDEX_CSUM_XOR));
        if (csum_disk != mi_le->csum) {
                DMERR_LIMIT("%s failed: csum %u != wanted %u", __func__,
                            le32_to_cpu(csum_disk), le32_to_cpu(mi_le->csum));
                return -EILSEQ;
        }

        return 0;
}

static const struct dm_block_validator index_validator = {
        .name = "index",
        .prepare_for_write = index_prepare_for_write,
        .check = index_check
};

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

/*
 * Bitmap validator
 */
#define BITMAP_CSUM_XOR 240779

static void dm_bitmap_prepare_for_write(const struct dm_block_validator *v,
                                        struct dm_block *b,
                                        size_t block_size)
{
        struct disk_bitmap_header *disk_header = dm_block_data(b);

        disk_header->blocknr = cpu_to_le64(dm_block_location(b));
        disk_header->csum = cpu_to_le32(dm_bm_checksum(&disk_header->not_used,
                                                       block_size - sizeof(__le32),
                                                       BITMAP_CSUM_XOR));
}

static int dm_bitmap_check(const struct dm_block_validator *v,
                           struct dm_block *b,
                           size_t block_size)
{
        struct disk_bitmap_header *disk_header = dm_block_data(b);
        __le32 csum_disk;

        if (dm_block_location(b) != le64_to_cpu(disk_header->blocknr)) {
                DMERR_LIMIT("bitmap check failed: blocknr %llu != wanted %llu",
                            le64_to_cpu(disk_header->blocknr), dm_block_location(b));
                return -ENOTBLK;
        }

        csum_disk = cpu_to_le32(dm_bm_checksum(&disk_header->not_used,
                                               block_size - sizeof(__le32),
                                               BITMAP_CSUM_XOR));
        if (csum_disk != disk_header->csum) {
                DMERR_LIMIT("bitmap check failed: csum %u != wanted %u",
                            le32_to_cpu(csum_disk), le32_to_cpu(disk_header->csum));
                return -EILSEQ;
        }

        return 0;
}

static const struct dm_block_validator dm_sm_bitmap_validator = {
        .name = "sm_bitmap",
        .prepare_for_write = dm_bitmap_prepare_for_write,
        .check = dm_bitmap_check,
};

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

#define ENTRIES_PER_WORD 32
#define ENTRIES_SHIFT   5

static void *dm_bitmap_data(struct dm_block *b)
{
        return dm_block_data(b) + sizeof(struct disk_bitmap_header);
}

#define WORD_MASK_HIGH 0xAAAAAAAAAAAAAAAAULL

static unsigned int dm_bitmap_word_used(void *addr, unsigned int b)
{
        __le64 *words_le = addr;
        __le64 *w_le = words_le + (b >> ENTRIES_SHIFT);

        uint64_t bits = le64_to_cpu(*w_le);
        uint64_t mask = (bits + WORD_MASK_HIGH + 1) & WORD_MASK_HIGH;

        return !(~bits & mask);
}

static unsigned int sm_lookup_bitmap(void *addr, unsigned int b)
{
        __le64 *words_le = addr;
        __le64 *w_le = words_le + (b >> ENTRIES_SHIFT);
        unsigned int hi, lo;

        b = (b & (ENTRIES_PER_WORD - 1)) << 1;
        hi = !!test_bit_le(b, (void *) w_le);
        lo = !!test_bit_le(b + 1, (void *) w_le);
        return (hi << 1) | lo;
}

static void sm_set_bitmap(void *addr, unsigned int b, unsigned int val)
{
        __le64 *words_le = addr;
        __le64 *w_le = words_le + (b >> ENTRIES_SHIFT);

        b = (b & (ENTRIES_PER_WORD - 1)) << 1;

        if (val & 2)
                __set_bit_le(b, (void *) w_le);
        else
                __clear_bit_le(b, (void *) w_le);

        if (val & 1)
                __set_bit_le(b + 1, (void *) w_le);
        else
                __clear_bit_le(b + 1, (void *) w_le);
}

static int sm_find_free(void *addr, unsigned int begin, unsigned int end,
                        unsigned int *result)
{
        while (begin < end) {
                if (!(begin & (ENTRIES_PER_WORD - 1)) &&
                    dm_bitmap_word_used(addr, begin)) {
                        begin += ENTRIES_PER_WORD;
                        continue;
                }

                if (!sm_lookup_bitmap(addr, begin)) {
                        *result = begin;
                        return 0;
                }

                begin++;
        }

        return -ENOSPC;
}

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

static int sm_ll_init(struct ll_disk *ll, struct dm_transaction_manager *tm)
{
        memset(ll, 0, sizeof(struct ll_disk));

        ll->tm = tm;

        ll->bitmap_info.tm = tm;
        ll->bitmap_info.levels = 1;

        /*
         * Because the new bitmap blocks are created via a shadow
         * operation, the old entry has already had its reference count
         * decremented and we don't need the btree to do any bookkeeping.
         */
        ll->bitmap_info.value_type.size = sizeof(struct disk_index_entry);
        ll->bitmap_info.value_type.inc = NULL;
        ll->bitmap_info.value_type.dec = NULL;
        ll->bitmap_info.value_type.equal = NULL;

        ll->ref_count_info.tm = tm;
        ll->ref_count_info.levels = 1;
        ll->ref_count_info.value_type.size = sizeof(uint32_t);
        ll->ref_count_info.value_type.inc = NULL;
        ll->ref_count_info.value_type.dec = NULL;
        ll->ref_count_info.value_type.equal = NULL;

        ll->block_size = dm_bm_block_size(dm_tm_get_bm(tm));

        if (ll->block_size > (1 << 30)) {
                DMERR("block size too big to hold bitmaps");
                return -EINVAL;
        }

        ll->entries_per_block = (ll->block_size - sizeof(struct disk_bitmap_header)) *
                ENTRIES_PER_BYTE;
        ll->nr_blocks = 0;
        ll->bitmap_root = 0;
        ll->ref_count_root = 0;
        ll->bitmap_index_changed = false;

        return 0;
}

int sm_ll_extend(struct ll_disk *ll, dm_block_t extra_blocks)
{
        int r;
        dm_block_t i, nr_blocks, nr_indexes;
        unsigned int old_blocks, blocks;

        nr_blocks = ll->nr_blocks + extra_blocks;
        old_blocks = dm_sector_div_up(ll->nr_blocks, ll->entries_per_block);
        blocks = dm_sector_div_up(nr_blocks, ll->entries_per_block);

        nr_indexes = dm_sector_div_up(nr_blocks, ll->entries_per_block);
        if (nr_indexes > ll->max_entries(ll)) {
                DMERR("space map too large");
                return -EINVAL;
        }

        /*
         * We need to set this before the dm_tm_new_block() call below.
         */
        ll->nr_blocks = nr_blocks;
        for (i = old_blocks; i < blocks; i++) {
                struct dm_block *b;
                struct disk_index_entry idx;

                r = dm_tm_new_block(ll->tm, &dm_sm_bitmap_validator, &b);
                if (r < 0)
                        return r;

                idx.blocknr = cpu_to_le64(dm_block_location(b));

                dm_tm_unlock(ll->tm, b);

                idx.nr_free = cpu_to_le32(ll->entries_per_block);
                idx.none_free_before = 0;

                r = ll->save_ie(ll, i, &idx);
                if (r < 0)
                        return r;
        }

        return 0;
}

int sm_ll_lookup_bitmap(struct ll_disk *ll, dm_block_t b, uint32_t *result)
{
        int r;
        dm_block_t index = b;
        struct disk_index_entry ie_disk;
        struct dm_block *blk;

        if (b >= ll->nr_blocks) {
                DMERR_LIMIT("metadata block out of bounds");
                return -EINVAL;
        }

        b = do_div(index, ll->entries_per_block);
        r = ll->load_ie(ll, index, &ie_disk);
        if (r < 0)
                return r;

        r = dm_tm_read_lock(ll->tm, le64_to_cpu(ie_disk.blocknr),
                            &dm_sm_bitmap_validator, &blk);
        if (r < 0)
                return r;

        *result = sm_lookup_bitmap(dm_bitmap_data(blk), b);

        dm_tm_unlock(ll->tm, blk);

        return 0;
}

static int sm_ll_lookup_big_ref_count(struct ll_disk *ll, dm_block_t b,
                                      uint32_t *result)
{
        __le32 le_rc;
        int r;

        r = dm_btree_lookup(&ll->ref_count_info, ll->ref_count_root, &b, &le_rc);
        if (r < 0)
                return r;

        *result = le32_to_cpu(le_rc);

        return r;
}

int sm_ll_lookup(struct ll_disk *ll, dm_block_t b, uint32_t *result)
{
        int r = sm_ll_lookup_bitmap(ll, b, result);

        if (r)
                return r;

        if (*result != 3)
                return r;

        return sm_ll_lookup_big_ref_count(ll, b, result);
}

int sm_ll_find_free_block(struct ll_disk *ll, dm_block_t begin,
                          dm_block_t end, dm_block_t *result)
{
        int r;
        struct disk_index_entry ie_disk;
        dm_block_t i, index_begin = begin;
        dm_block_t index_end = dm_sector_div_up(end, ll->entries_per_block);

        /*
         * FIXME: Use shifts
         */
        begin = do_div(index_begin, ll->entries_per_block);
        end = do_div(end, ll->entries_per_block);
        if (end == 0)
                end = ll->entries_per_block;

        for (i = index_begin; i < index_end; i++, begin = 0) {
                struct dm_block *blk;
                unsigned int position;
                uint32_t bit_end;

                r = ll->load_ie(ll, i, &ie_disk);
                if (r < 0)
                        return r;

                if (le32_to_cpu(ie_disk.nr_free) == 0)
                        continue;

                r = dm_tm_read_lock(ll->tm, le64_to_cpu(ie_disk.blocknr),
                                    &dm_sm_bitmap_validator, &blk);
                if (r < 0)
                        return r;

                bit_end = (i == index_end - 1) ?  end : ll->entries_per_block;

                r = sm_find_free(dm_bitmap_data(blk),
                                 max_t(unsigned int, begin, le32_to_cpu(ie_disk.none_free_before)),
                                 bit_end, &position);
                if (r == -ENOSPC) {
                        /*
                         * This might happen because we started searching
                         * part way through the bitmap.
                         */
                        dm_tm_unlock(ll->tm, blk);
                        continue;
                }

                dm_tm_unlock(ll->tm, blk);

                *result = i * ll->entries_per_block + (dm_block_t) position;
                return 0;
        }

        return -ENOSPC;
}

int sm_ll_find_common_free_block(struct ll_disk *old_ll, struct ll_disk *new_ll,
                                 dm_block_t begin, dm_block_t end, dm_block_t *b)
{
        int r;
        uint32_t count;

        do {
                r = sm_ll_find_free_block(new_ll, begin, new_ll->nr_blocks, b);
                if (r)
                        break;

                /* double check this block wasn't used in the old transaction */
                if (*b >= old_ll->nr_blocks)
                        count = 0;
                else {
                        r = sm_ll_lookup(old_ll, *b, &count);
                        if (r)
                                break;

                        if (count)
                                begin = *b + 1;
                }
        } while (count);

        return r;
}

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

int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
                 uint32_t ref_count, int32_t *nr_allocations)
{
        int r;
        uint32_t bit, old;
        struct dm_block *nb;
        dm_block_t index = b;
        struct disk_index_entry ie_disk;
        void *bm_le;
        int inc;

        bit = do_div(index, ll->entries_per_block);
        r = ll->load_ie(ll, index, &ie_disk);
        if (r < 0)
                return r;

        r = dm_tm_shadow_block(ll->tm, le64_to_cpu(ie_disk.blocknr),
                               &dm_sm_bitmap_validator, &nb, &inc);
        if (r < 0) {
                DMERR("dm_tm_shadow_block() failed");
                return r;
        }
        ie_disk.blocknr = cpu_to_le64(dm_block_location(nb));
        bm_le = dm_bitmap_data(nb);

        old = sm_lookup_bitmap(bm_le, bit);
        if (old > 2) {
                r = sm_ll_lookup_big_ref_count(ll, b, &old);
                if (r < 0) {
                        dm_tm_unlock(ll->tm, nb);
                        return r;
                }
        }

        if (r) {
                dm_tm_unlock(ll->tm, nb);
                return r;
        }

        if (ref_count <= 2) {
                sm_set_bitmap(bm_le, bit, ref_count);
                dm_tm_unlock(ll->tm, nb);

                if (old > 2) {
                        r = dm_btree_remove(&ll->ref_count_info,
                                            ll->ref_count_root,
                                            &b, &ll->ref_count_root);
                        if (r)
                                return r;
                }

        } else {
                __le32 le_rc = cpu_to_le32(ref_count);

                sm_set_bitmap(bm_le, bit, 3);
                dm_tm_unlock(ll->tm, nb);

                __dm_bless_for_disk(&le_rc);
                r = dm_btree_insert(&ll->ref_count_info, ll->ref_count_root,
                                    &b, &le_rc, &ll->ref_count_root);
                if (r < 0) {
                        DMERR("ref count insert failed");
                        return r;
                }
        }

        if (ref_count && !old) {
                *nr_allocations = 1;
                ll->nr_allocated++;
                le32_add_cpu(&ie_disk.nr_free, -1);
                if (le32_to_cpu(ie_disk.none_free_before) == bit)
                        ie_disk.none_free_before = cpu_to_le32(bit + 1);

        } else if (old && !ref_count) {
                *nr_allocations = -1;
                ll->nr_allocated--;
                le32_add_cpu(&ie_disk.nr_free, 1);
                ie_disk.none_free_before = cpu_to_le32(min(le32_to_cpu(ie_disk.none_free_before), bit));
        } else
                *nr_allocations = 0;

        return ll->save_ie(ll, index, &ie_disk);
}

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

/*
 * Holds useful intermediate results for the range based inc and dec
 * operations.
 */
struct inc_context {
        struct disk_index_entry ie_disk;
        struct dm_block *bitmap_block;
        void *bitmap;

        struct dm_block *overflow_leaf;
};

static inline void init_inc_context(struct inc_context *ic)
{
        ic->bitmap_block = NULL;
        ic->bitmap = NULL;
        ic->overflow_leaf = NULL;
}

static inline void exit_inc_context(struct ll_disk *ll, struct inc_context *ic)
{
        if (ic->bitmap_block)
                dm_tm_unlock(ll->tm, ic->bitmap_block);
        if (ic->overflow_leaf)
                dm_tm_unlock(ll->tm, ic->overflow_leaf);
}

static inline void reset_inc_context(struct ll_disk *ll, struct inc_context *ic)
{
        exit_inc_context(ll, ic);
        init_inc_context(ic);
}

/*
 * Confirms a btree node contains a particular key at an index.
 */
static bool contains_key(struct btree_node *n, uint64_t key, int index)
{
        return index >= 0 &&
                index < le32_to_cpu(n->header.nr_entries) &&
                le64_to_cpu(n->keys[index]) == key;
}

static int __sm_ll_inc_overflow(struct ll_disk *ll, dm_block_t b, struct inc_context *ic)
{
        int r;
        int index;
        struct btree_node *n;
        __le32 *v_ptr;
        uint32_t rc;

        /*
         * bitmap_block needs to be unlocked because getting the
         * overflow_leaf may need to allocate, and thus use the space map.
         */
        reset_inc_context(ll, ic);

        r = btree_get_overwrite_leaf(&ll->ref_count_info, ll->ref_count_root,
                                     b, &index, &ll->ref_count_root, &ic->overflow_leaf);
        if (r < 0)
                return r;

        n = dm_block_data(ic->overflow_leaf);

        if (!contains_key(n, b, index)) {
                DMERR("overflow btree is missing an entry");
                return -EINVAL;
        }

        v_ptr = value_ptr(n, index);
        rc = le32_to_cpu(*v_ptr) + 1;
        *v_ptr = cpu_to_le32(rc);

        return 0;
}

static int sm_ll_inc_overflow(struct ll_disk *ll, dm_block_t b, struct inc_context *ic)
{
        int index;
        struct btree_node *n;
        __le32 *v_ptr;
        uint32_t rc;

        /*
         * Do we already have the correct overflow leaf?
         */
        if (ic->overflow_leaf) {
                n = dm_block_data(ic->overflow_leaf);
                index = lower_bound(n, b);
                if (contains_key(n, b, index)) {
                        v_ptr = value_ptr(n, index);
                        rc = le32_to_cpu(*v_ptr) + 1;
                        *v_ptr = cpu_to_le32(rc);

                        return 0;
                }
        }

        return __sm_ll_inc_overflow(ll, b, ic);
}

static inline int shadow_bitmap(struct ll_disk *ll, struct inc_context *ic)
{
        int r, inc;

        r = dm_tm_shadow_block(ll->tm, le64_to_cpu(ic->ie_disk.blocknr),
                               &dm_sm_bitmap_validator, &ic->bitmap_block, &inc);
        if (r < 0) {
                DMERR("dm_tm_shadow_block() failed");
                return r;
        }
        ic->ie_disk.blocknr = cpu_to_le64(dm_block_location(ic->bitmap_block));
        ic->bitmap = dm_bitmap_data(ic->bitmap_block);
        return 0;
}

/*
 * Once shadow_bitmap has been called, which always happens at the start of inc/dec,
 * we can reopen the bitmap with a simple write lock, rather than re calling
 * dm_tm_shadow_block().
 */
static inline int ensure_bitmap(struct ll_disk *ll, struct inc_context *ic)
{
        if (!ic->bitmap_block) {
                int r = dm_bm_write_lock(dm_tm_get_bm(ll->tm), le64_to_cpu(ic->ie_disk.blocknr),
                                         &dm_sm_bitmap_validator, &ic->bitmap_block);
                if (r) {
                        DMERR("unable to re-get write lock for bitmap");
                        return r;
                }
                ic->bitmap = dm_bitmap_data(ic->bitmap_block);
        }

        return 0;
}

/*
 * Loops round incrementing entries in a single bitmap.
 */
static inline int sm_ll_inc_bitmap(struct ll_disk *ll, dm_block_t b,
                                   uint32_t bit, uint32_t bit_end,
                                   int32_t *nr_allocations, dm_block_t *new_b,
                                   struct inc_context *ic)
{
        int r;
        __le32 le_rc;
        uint32_t old;

        for (; bit != bit_end; bit++, b++) {
                /*
                 * We only need to drop the bitmap if we need to find a new btree
                 * leaf for the overflow.  So if it was dropped last iteration,
                 * we now re-get it.
                 */
                r = ensure_bitmap(ll, ic);
                if (r)
                        return r;

                old = sm_lookup_bitmap(ic->bitmap, bit);
                switch (old) {
                case 0:
                        /* inc bitmap, adjust nr_allocated */
                        sm_set_bitmap(ic->bitmap, bit, 1);
                        (*nr_allocations)++;
                        ll->nr_allocated++;
                        le32_add_cpu(&ic->ie_disk.nr_free, -1);
                        if (le32_to_cpu(ic->ie_disk.none_free_before) == bit)
                                ic->ie_disk.none_free_before = cpu_to_le32(bit + 1);
                        break;

                case 1:
                        /* inc bitmap */
                        sm_set_bitmap(ic->bitmap, bit, 2);
                        break;

                case 2:
                        /* inc bitmap and insert into overflow */
                        sm_set_bitmap(ic->bitmap, bit, 3);
                        reset_inc_context(ll, ic);

                        le_rc = cpu_to_le32(3);
                        __dm_bless_for_disk(&le_rc);
                        r = dm_btree_insert(&ll->ref_count_info, ll->ref_count_root,
                                            &b, &le_rc, &ll->ref_count_root);
                        if (r < 0) {
                                DMERR("ref count insert failed");
                                return r;
                        }
                        break;

                default:
                        /*
                         * inc within the overflow tree only.
                         */
                        r = sm_ll_inc_overflow(ll, b, ic);
                        if (r < 0)
                                return r;
                }
        }

        *new_b = b;
        return 0;
}

/*
 * Finds a bitmap that contains entries in the block range, and increments
 * them.
 */
static int __sm_ll_inc(struct ll_disk *ll, dm_block_t b, dm_block_t e,
                       int32_t *nr_allocations, dm_block_t *new_b)
{
        int r;
        struct inc_context ic;
        uint32_t bit, bit_end;
        dm_block_t index = b;

        init_inc_context(&ic);

        bit = do_div(index, ll->entries_per_block);
        r = ll->load_ie(ll, index, &ic.ie_disk);
        if (r < 0)
                return r;

        r = shadow_bitmap(ll, &ic);
        if (r)
                return r;

        bit_end = min(bit + (e - b), (dm_block_t) ll->entries_per_block);
        r = sm_ll_inc_bitmap(ll, b, bit, bit_end, nr_allocations, new_b, &ic);

        exit_inc_context(ll, &ic);

        if (r)
                return r;

        return ll->save_ie(ll, index, &ic.ie_disk);
}

int sm_ll_inc(struct ll_disk *ll, dm_block_t b, dm_block_t e,
              int32_t *nr_allocations)
{
        *nr_allocations = 0;
        while (b != e) {
                int r = __sm_ll_inc(ll, b, e, nr_allocations, &b);

                if (r)
                        return r;
        }

        return 0;
}

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

static int __sm_ll_del_overflow(struct ll_disk *ll, dm_block_t b,
                                struct inc_context *ic)
{
        reset_inc_context(ll, ic);
        return dm_btree_remove(&ll->ref_count_info, ll->ref_count_root,
                               &b, &ll->ref_count_root);
}

static int __sm_ll_dec_overflow(struct ll_disk *ll, dm_block_t b,
                                struct inc_context *ic, uint32_t *old_rc)
{
        int r;
        int index = -1;
        struct btree_node *n;
        __le32 *v_ptr;
        uint32_t rc;

        reset_inc_context(ll, ic);
        r = btree_get_overwrite_leaf(&ll->ref_count_info, ll->ref_count_root,
                                     b, &index, &ll->ref_count_root, &ic->overflow_leaf);
        if (r < 0)
                return r;

        n = dm_block_data(ic->overflow_leaf);

        if (!contains_key(n, b, index)) {
                DMERR("overflow btree is missing an entry");
                return -EINVAL;
        }

        v_ptr = value_ptr(n, index);
        rc = le32_to_cpu(*v_ptr);
        *old_rc = rc;

        if (rc == 3)
                return __sm_ll_del_overflow(ll, b, ic);

        rc--;
        *v_ptr = cpu_to_le32(rc);
        return 0;
}

static int sm_ll_dec_overflow(struct ll_disk *ll, dm_block_t b,
                              struct inc_context *ic, uint32_t *old_rc)
{
        /*
         * Do we already have the correct overflow leaf?
         */
        if (ic->overflow_leaf) {
                int index;
                struct btree_node *n;
                __le32 *v_ptr;
                uint32_t rc;

                n = dm_block_data(ic->overflow_leaf);
                index = lower_bound(n, b);
                if (contains_key(n, b, index)) {
                        v_ptr = value_ptr(n, index);
                        rc = le32_to_cpu(*v_ptr);
                        *old_rc = rc;

                        if (rc > 3) {
                                rc--;
                                *v_ptr = cpu_to_le32(rc);
                                return 0;
                        } else {
                                return __sm_ll_del_overflow(ll, b, ic);
                        }

                }
        }

        return __sm_ll_dec_overflow(ll, b, ic, old_rc);
}

/*
 * Loops round incrementing entries in a single bitmap.
 */
static inline int sm_ll_dec_bitmap(struct ll_disk *ll, dm_block_t b,
                                   uint32_t bit, uint32_t bit_end,
                                   struct inc_context *ic,
                                   int32_t *nr_allocations, dm_block_t *new_b)
{
        int r;
        uint32_t old;

        for (; bit != bit_end; bit++, b++) {
                /*
                 * We only need to drop the bitmap if we need to find a new btree
                 * leaf for the overflow.  So if it was dropped last iteration,
                 * we now re-get it.
                 */
                r = ensure_bitmap(ll, ic);
                if (r)
                        return r;

                old = sm_lookup_bitmap(ic->bitmap, bit);
                switch (old) {
                case 0:
                        DMERR("unable to decrement block");
                        return -EINVAL;

                case 1:
                        /* dec bitmap */
                        sm_set_bitmap(ic->bitmap, bit, 0);
                        (*nr_allocations)--;
                        ll->nr_allocated--;
                        le32_add_cpu(&ic->ie_disk.nr_free, 1);
                        ic->ie_disk.none_free_before =
                                cpu_to_le32(min(le32_to_cpu(ic->ie_disk.none_free_before), bit));
                        break;

                case 2:
                        /* dec bitmap and insert into overflow */
                        sm_set_bitmap(ic->bitmap, bit, 1);
                        break;

                case 3:
                        r = sm_ll_dec_overflow(ll, b, ic, &old);
                        if (r < 0)
                                return r;

                        if (old == 3) {
                                r = ensure_bitmap(ll, ic);
                                if (r)
                                        return r;

                                sm_set_bitmap(ic->bitmap, bit, 2);
                        }
                        break;
                }
        }

        *new_b = b;
        return 0;
}

static int __sm_ll_dec(struct ll_disk *ll, dm_block_t b, dm_block_t e,
                       int32_t *nr_allocations, dm_block_t *new_b)
{
        int r;
        uint32_t bit, bit_end;
        struct inc_context ic;
        dm_block_t index = b;

        init_inc_context(&ic);

        bit = do_div(index, ll->entries_per_block);
        r = ll->load_ie(ll, index, &ic.ie_disk);
        if (r < 0)
                return r;

        r = shadow_bitmap(ll, &ic);
        if (r)
                return r;

        bit_end = min(bit + (e - b), (dm_block_t) ll->entries_per_block);
        r = sm_ll_dec_bitmap(ll, b, bit, bit_end, &ic, nr_allocations, new_b);
        exit_inc_context(ll, &ic);

        if (r)
                return r;

        return ll->save_ie(ll, index, &ic.ie_disk);
}

int sm_ll_dec(struct ll_disk *ll, dm_block_t b, dm_block_t e,
              int32_t *nr_allocations)
{
        *nr_allocations = 0;
        while (b != e) {
                int r = __sm_ll_dec(ll, b, e, nr_allocations, &b);

                if (r)
                        return r;
        }

        return 0;
}

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

int sm_ll_commit(struct ll_disk *ll)
{
        int r = 0;

        if (ll->bitmap_index_changed) {
                r = ll->commit(ll);
                if (!r)
                        ll->bitmap_index_changed = false;
        }

        return r;
}

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

static int metadata_ll_load_ie(struct ll_disk *ll, dm_block_t index,
                               struct disk_index_entry *ie)
{
        memcpy(ie, ll->mi_le.index + index, sizeof(*ie));
        return 0;
}

static int metadata_ll_save_ie(struct ll_disk *ll, dm_block_t index,
                               struct disk_index_entry *ie)
{
        ll->bitmap_index_changed = true;
        memcpy(ll->mi_le.index + index, ie, sizeof(*ie));
        return 0;
}

static int metadata_ll_init_index(struct ll_disk *ll)
{
        int r;
        struct dm_block *b;

        r = dm_tm_new_block(ll->tm, &index_validator, &b);
        if (r < 0)
                return r;

        ll->bitmap_root = dm_block_location(b);

        dm_tm_unlock(ll->tm, b);

        return 0;
}

static int metadata_ll_open(struct ll_disk *ll)
{
        int r;
        struct dm_block *block;

        r = dm_tm_read_lock(ll->tm, ll->bitmap_root,
                            &index_validator, &block);
        if (r)
                return r;

        memcpy(&ll->mi_le, dm_block_data(block), sizeof(ll->mi_le));
        dm_tm_unlock(ll->tm, block);

        return 0;
}

static dm_block_t metadata_ll_max_entries(struct ll_disk *ll)
{
        return MAX_METADATA_BITMAPS;
}

static int metadata_ll_commit(struct ll_disk *ll)
{
        int r, inc;
        struct dm_block *b;

        r = dm_tm_shadow_block(ll->tm, ll->bitmap_root, &index_validator, &b, &inc);
        if (r)
                return r;

        memcpy(dm_block_data(b), &ll->mi_le, sizeof(ll->mi_le));
        ll->bitmap_root = dm_block_location(b);

        dm_tm_unlock(ll->tm, b);

        return 0;
}

int sm_ll_new_metadata(struct ll_disk *ll, struct dm_transaction_manager *tm)
{
        int r;

        r = sm_ll_init(ll, tm);
        if (r < 0)
                return r;

        ll->load_ie = metadata_ll_load_ie;
        ll->save_ie = metadata_ll_save_ie;
        ll->init_index = metadata_ll_init_index;
        ll->open_index = metadata_ll_open;
        ll->max_entries = metadata_ll_max_entries;
        ll->commit = metadata_ll_commit;

        ll->nr_blocks = 0;
        ll->nr_allocated = 0;

        r = ll->init_index(ll);
        if (r < 0)
                return r;

        r = dm_btree_empty(&ll->ref_count_info, &ll->ref_count_root);
        if (r < 0)
                return r;

        return 0;
}

int sm_ll_open_metadata(struct ll_disk *ll, struct dm_transaction_manager *tm,
                        void *root_le, size_t len)
{
        int r;
        struct disk_sm_root smr;

        if (len < sizeof(struct disk_sm_root)) {
                DMERR("sm_metadata root too small");
                return -ENOMEM;
        }

        /*
         * We don't know the alignment of the root_le buffer, so need to
         * copy into a new structure.
         */
        memcpy(&smr, root_le, sizeof(smr));

        r = sm_ll_init(ll, tm);
        if (r < 0)
                return r;

        ll->load_ie = metadata_ll_load_ie;
        ll->save_ie = metadata_ll_save_ie;
        ll->init_index = metadata_ll_init_index;
        ll->open_index = metadata_ll_open;
        ll->max_entries = metadata_ll_max_entries;
        ll->commit = metadata_ll_commit;

        ll->nr_blocks = le64_to_cpu(smr.nr_blocks);
        ll->nr_allocated = le64_to_cpu(smr.nr_allocated);
        ll->bitmap_root = le64_to_cpu(smr.bitmap_root);
        ll->ref_count_root = le64_to_cpu(smr.ref_count_root);

        return ll->open_index(ll);
}

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

static inline int ie_cache_writeback(struct ll_disk *ll, struct ie_cache *iec)
{
        iec->dirty = false;
        __dm_bless_for_disk(iec->ie);
        return dm_btree_insert(&ll->bitmap_info, ll->bitmap_root,
                               &iec->index, &iec->ie, &ll->bitmap_root);
}

static inline unsigned int hash_index(dm_block_t index)
{
        return dm_hash_block(index, IE_CACHE_MASK);
}

static int disk_ll_load_ie(struct ll_disk *ll, dm_block_t index,
                           struct disk_index_entry *ie)
{
        int r;
        unsigned int h = hash_index(index);
        struct ie_cache *iec = ll->ie_cache + h;

        if (iec->valid) {
                if (iec->index == index) {
                        memcpy(ie, &iec->ie, sizeof(*ie));
                        return 0;
                }

                if (iec->dirty) {
                        r = ie_cache_writeback(ll, iec);
                        if (r)
                                return r;
                }
        }

        r = dm_btree_lookup(&ll->bitmap_info, ll->bitmap_root, &index, ie);
        if (!r) {
                iec->valid = true;
                iec->dirty = false;
                iec->index = index;
                memcpy(&iec->ie, ie, sizeof(*ie));
        }

        return r;
}

static int disk_ll_save_ie(struct ll_disk *ll, dm_block_t index,
                           struct disk_index_entry *ie)
{
        int r;
        unsigned int h = hash_index(index);
        struct ie_cache *iec = ll->ie_cache + h;

        ll->bitmap_index_changed = true;
        if (iec->valid) {
                if (iec->index == index) {
                        memcpy(&iec->ie, ie, sizeof(*ie));
                        iec->dirty = true;
                        return 0;
                }

                if (iec->dirty) {
                        r = ie_cache_writeback(ll, iec);
                        if (r)
                                return r;
                }
        }

        iec->valid = true;
        iec->dirty = true;
        iec->index = index;
        memcpy(&iec->ie, ie, sizeof(*ie));
        return 0;
}

static int disk_ll_init_index(struct ll_disk *ll)
{
        unsigned int i;

        for (i = 0; i < IE_CACHE_SIZE; i++) {
                struct ie_cache *iec = ll->ie_cache + i;

                iec->valid = false;
                iec->dirty = false;
        }
        return dm_btree_empty(&ll->bitmap_info, &ll->bitmap_root);
}

static int disk_ll_open(struct ll_disk *ll)
{
        return 0;
}

static dm_block_t disk_ll_max_entries(struct ll_disk *ll)
{
        return -1ULL;
}

static int disk_ll_commit(struct ll_disk *ll)
{
        int r = 0;
        unsigned int i;

        for (i = 0; i < IE_CACHE_SIZE; i++) {
                struct ie_cache *iec = ll->ie_cache + i;

                if (iec->valid && iec->dirty)
                        r = ie_cache_writeback(ll, iec);
        }

        return r;
}

int sm_ll_new_disk(struct ll_disk *ll, struct dm_transaction_manager *tm)
{
        int r;

        r = sm_ll_init(ll, tm);
        if (r < 0)
                return r;

        ll->load_ie = disk_ll_load_ie;
        ll->save_ie = disk_ll_save_ie;
        ll->init_index = disk_ll_init_index;
        ll->open_index = disk_ll_open;
        ll->max_entries = disk_ll_max_entries;
        ll->commit = disk_ll_commit;

        ll->nr_blocks = 0;
        ll->nr_allocated = 0;

        r = ll->init_index(ll);
        if (r < 0)
                return r;

        r = dm_btree_empty(&ll->ref_count_info, &ll->ref_count_root);
        if (r < 0)
                return r;

        return 0;
}

int sm_ll_open_disk(struct ll_disk *ll, struct dm_transaction_manager *tm,
                    void *root_le, size_t len)
{
        int r;
        struct disk_sm_root *smr = root_le;

        if (len < sizeof(struct disk_sm_root)) {
                DMERR("sm_metadata root too small");
                return -ENOMEM;
        }

        r = sm_ll_init(ll, tm);
        if (r < 0)
                return r;

        ll->load_ie = disk_ll_load_ie;
        ll->save_ie = disk_ll_save_ie;
        ll->init_index = disk_ll_init_index;
        ll->open_index = disk_ll_open;
        ll->max_entries = disk_ll_max_entries;
        ll->commit = disk_ll_commit;

        ll->nr_blocks = le64_to_cpu(smr->nr_blocks);
        ll->nr_allocated = le64_to_cpu(smr->nr_allocated);
        ll->bitmap_root = le64_to_cpu(smr->bitmap_root);
        ll->ref_count_root = le64_to_cpu(smr->ref_count_root);

        return ll->open_index(ll);
}

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