// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015 Facebook.  All rights reserved.
 */

#include <linux/kernel.h>
#include <linux/sched/mm.h>
#include "messages.h"
#include "ctree.h"
#include "disk-io.h"
#include "locking.h"
#include "free-space-tree.h"
#include "transaction.h"
#include "block-group.h"
#include "fs.h"
#include "accessors.h"
#include "extent-tree.h"
#include "root-tree.h"

static int __add_block_group_free_space(struct btrfs_trans_handle *trans,
                                        struct btrfs_block_group *block_group,
                                        struct btrfs_path *path);

struct btrfs_root *btrfs_free_space_root(struct btrfs_block_group *block_group)
{
        struct btrfs_key key = {
                .objectid = BTRFS_FREE_SPACE_TREE_OBJECTID,
                .type = BTRFS_ROOT_ITEM_KEY,
                .offset = 0,
        };

        if (btrfs_fs_incompat(block_group->fs_info, EXTENT_TREE_V2))
                key.offset = block_group->global_root_id;
        return btrfs_global_root(block_group->fs_info, &key);
}

void btrfs_set_free_space_tree_thresholds(struct btrfs_block_group *cache)
{
        u32 bitmap_range;
        size_t bitmap_size;
        u64 num_bitmaps, total_bitmap_size;

        if (WARN_ON(cache->length == 0))
                btrfs_warn(cache->fs_info, "block group %llu length is zero",
                           cache->start);

        /*
         * We convert to bitmaps when the disk space required for using extents
         * exceeds that required for using bitmaps.
         */
        bitmap_range = cache->fs_info->sectorsize * BTRFS_FREE_SPACE_BITMAP_BITS;
        num_bitmaps = div_u64(cache->length + bitmap_range - 1, bitmap_range);
        bitmap_size = sizeof(struct btrfs_item) + BTRFS_FREE_SPACE_BITMAP_SIZE;
        total_bitmap_size = num_bitmaps * bitmap_size;
        cache->bitmap_high_thresh = div_u64(total_bitmap_size,
                                            sizeof(struct btrfs_item));

        /*
         * We allow for a small buffer between the high threshold and low
         * threshold to avoid thrashing back and forth between the two formats.
         */
        if (cache->bitmap_high_thresh > 100)
                cache->bitmap_low_thresh = cache->bitmap_high_thresh - 100;
        else
                cache->bitmap_low_thresh = 0;
}

static int add_new_free_space_info(struct btrfs_trans_handle *trans,
                                   struct btrfs_block_group *block_group,
                                   struct btrfs_path *path)
{
        struct btrfs_root *root = btrfs_free_space_root(block_group);
        struct btrfs_free_space_info *info;
        struct btrfs_key key;
        struct extent_buffer *leaf;
        int ret;

        key.objectid = block_group->start;
        key.type = BTRFS_FREE_SPACE_INFO_KEY;
        key.offset = block_group->length;

        ret = btrfs_insert_empty_item(trans, root, path, &key, sizeof(*info));
        if (ret)
                return ret;

        leaf = path->nodes[0];
        info = btrfs_item_ptr(leaf, path->slots[0],
                              struct btrfs_free_space_info);
        btrfs_set_free_space_extent_count(leaf, info, 0);
        btrfs_set_free_space_flags(leaf, info, 0);
        btrfs_release_path(path);
        return 0;
}

struct btrfs_free_space_info *btrfs_search_free_space_info(
                struct btrfs_trans_handle *trans,
                struct btrfs_block_group *block_group,
                struct btrfs_path *path, int cow)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_root *root = btrfs_free_space_root(block_group);
        struct btrfs_key key;
        int ret;

        key.objectid = block_group->start;
        key.type = BTRFS_FREE_SPACE_INFO_KEY;
        key.offset = block_group->length;

        ret = btrfs_search_slot(trans, root, &key, path, 0, cow);
        if (ret < 0)
                return ERR_PTR(ret);
        if (ret != 0) {
                btrfs_warn(fs_info, "missing free space info for %llu",
                           block_group->start);
                DEBUG_WARN();
                return ERR_PTR(-ENOENT);
        }

        return btrfs_item_ptr(path->nodes[0], path->slots[0],
                              struct btrfs_free_space_info);
}

/*
 * btrfs_search_slot() but we're looking for the greatest key less than the
 * passed key.
 */
static int btrfs_search_prev_slot(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,
                                  struct btrfs_key *key, struct btrfs_path *p,
                                  int ins_len, int cow)
{
        int ret;

        ret = btrfs_search_slot(trans, root, key, p, ins_len, cow);
        if (ret < 0)
                return ret;

        if (unlikely(ret == 0)) {
                DEBUG_WARN();
                return -EIO;
        }

        if (unlikely(p->slots[0] == 0)) {
                DEBUG_WARN("no previous slot found");
                return -EIO;
        }
        p->slots[0]--;

        return 0;
}

static inline u32 free_space_bitmap_size(const struct btrfs_fs_info *fs_info,
                                         u64 size)
{
        return DIV_ROUND_UP(size >> fs_info->sectorsize_bits, BITS_PER_BYTE);
}

static unsigned long *alloc_bitmap(u32 bitmap_size)
{
        unsigned long *ret;
        unsigned int nofs_flag;
        u32 bitmap_rounded_size = round_up(bitmap_size, sizeof(unsigned long));

        /*
         * GFP_NOFS doesn't work with kvmalloc(), but we really can't recurse
         * into the filesystem here. All callers hold a transaction handle
         * open, so if a GFP_KERNEL allocation recurses into the filesystem
         * and triggers a transaction commit, we would deadlock.
         */
        nofs_flag = memalloc_nofs_save();
        ret = kvzalloc(bitmap_rounded_size, GFP_KERNEL);
        memalloc_nofs_restore(nofs_flag);
        return ret;
}

static void le_bitmap_set(unsigned long *map, unsigned int start, int len)
{
        u8 *p = ((u8 *)map) + BIT_BYTE(start);
        const unsigned int size = start + len;
        int bits_to_set = BITS_PER_BYTE - (start % BITS_PER_BYTE);
        u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(start);

        while (len - bits_to_set >= 0) {
                *p |= mask_to_set;
                len -= bits_to_set;
                bits_to_set = BITS_PER_BYTE;
                mask_to_set = ~0;
                p++;
        }
        if (len) {
                mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
                *p |= mask_to_set;
        }
}

EXPORT_FOR_TESTS
int btrfs_convert_free_space_to_bitmaps(struct btrfs_trans_handle *trans,
                                        struct btrfs_block_group *block_group,
                                        struct btrfs_path *path)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = btrfs_free_space_root(block_group);
        struct btrfs_free_space_info *info;
        struct btrfs_key key, found_key;
        struct extent_buffer *leaf;
        unsigned long *bitmap;
        char *bitmap_cursor;
        u64 start, end;
        u64 bitmap_range, i;
        u32 bitmap_size, flags, expected_extent_count;
        u32 extent_count = 0;
        int done = 0, nr;
        int ret;

        bitmap_size = free_space_bitmap_size(fs_info, block_group->length);
        bitmap = alloc_bitmap(bitmap_size);
        if (unlikely(!bitmap))
                return 0;

        start = block_group->start;
        end = btrfs_block_group_end(block_group);

        key.objectid = end - 1;
        key.type = (u8)-1;
        key.offset = (u64)-1;

        while (!done) {
                ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                leaf = path->nodes[0];
                nr = 0;
                path->slots[0]++;
                while (path->slots[0] > 0) {
                        btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0] - 1);

                        if (found_key.type == BTRFS_FREE_SPACE_INFO_KEY) {
                                ASSERT(found_key.objectid == block_group->start);
                                ASSERT(found_key.offset == block_group->length);
                                done = 1;
                                break;
                        } else if (found_key.type == BTRFS_FREE_SPACE_EXTENT_KEY) {
                                u64 first, last;

                                ASSERT(found_key.objectid >= start);
                                ASSERT(found_key.objectid < end);
                                ASSERT(found_key.objectid + found_key.offset <= end);

                                first = div_u64(found_key.objectid - start,
                                                fs_info->sectorsize);
                                last = div_u64(found_key.objectid + found_key.offset - start,
                                               fs_info->sectorsize);
                                le_bitmap_set(bitmap, first, last - first);

                                extent_count++;
                                nr++;
                                path->slots[0]--;
                        } else {
                                ASSERT(0);
                        }
                }

                ret = btrfs_del_items(trans, root, path, path->slots[0], nr);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
                btrfs_release_path(path);
        }

        info = btrfs_search_free_space_info(trans, block_group, path, 1);
        if (IS_ERR(info)) {
                ret = PTR_ERR(info);
                btrfs_abort_transaction(trans, ret);
                goto out;
        }
        leaf = path->nodes[0];
        flags = btrfs_free_space_flags(leaf, info);
        flags |= BTRFS_FREE_SPACE_USING_BITMAPS;
        block_group->using_free_space_bitmaps = true;
        block_group->using_free_space_bitmaps_cached = true;
        btrfs_set_free_space_flags(leaf, info, flags);
        expected_extent_count = btrfs_free_space_extent_count(leaf, info);
        btrfs_release_path(path);

        if (unlikely(extent_count != expected_extent_count)) {
                btrfs_err(fs_info,
                          "incorrect extent count for %llu; counted %u, expected %u",
                          block_group->start, extent_count,
                          expected_extent_count);
                ret = -EIO;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

        bitmap_cursor = (char *)bitmap;
        bitmap_range = fs_info->sectorsize * BTRFS_FREE_SPACE_BITMAP_BITS;
        i = start;
        while (i < end) {
                unsigned long ptr;
                u64 extent_size;
                u32 data_size;

                extent_size = min(end - i, bitmap_range);
                data_size = free_space_bitmap_size(fs_info, extent_size);

                key.objectid = i;
                key.type = BTRFS_FREE_SPACE_BITMAP_KEY;
                key.offset = extent_size;

                ret = btrfs_insert_empty_item(trans, root, path, &key,
                                              data_size);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                leaf = path->nodes[0];
                ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
                write_extent_buffer(leaf, bitmap_cursor, ptr,
                                    data_size);
                btrfs_release_path(path);

                i += extent_size;
                bitmap_cursor += data_size;
        }

        ret = 0;
out:
        kvfree(bitmap);
        return ret;
}

EXPORT_FOR_TESTS
int btrfs_convert_free_space_to_extents(struct btrfs_trans_handle *trans,
                                        struct btrfs_block_group *block_group,
                                        struct btrfs_path *path)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = btrfs_free_space_root(block_group);
        struct btrfs_free_space_info *info;
        struct btrfs_key key, found_key;
        struct extent_buffer *leaf;
        unsigned long *bitmap;
        u64 start, end;
        u32 bitmap_size, flags, expected_extent_count;
        unsigned long nrbits, start_bit, end_bit;
        u32 extent_count = 0;
        int done = 0, nr;
        int ret;

        bitmap_size = free_space_bitmap_size(fs_info, block_group->length);
        bitmap = alloc_bitmap(bitmap_size);
        if (unlikely(!bitmap))
                return 0;

        start = block_group->start;
        end = btrfs_block_group_end(block_group);

        key.objectid = end - 1;
        key.type = (u8)-1;
        key.offset = (u64)-1;

        while (!done) {
                ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                leaf = path->nodes[0];
                nr = 0;
                path->slots[0]++;
                while (path->slots[0] > 0) {
                        btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0] - 1);

                        if (found_key.type == BTRFS_FREE_SPACE_INFO_KEY) {
                                ASSERT(found_key.objectid == block_group->start);
                                ASSERT(found_key.offset == block_group->length);
                                done = 1;
                                break;
                        } else if (found_key.type == BTRFS_FREE_SPACE_BITMAP_KEY) {
                                unsigned long ptr;
                                char *bitmap_cursor;
                                u32 bitmap_pos, data_size;

                                ASSERT(found_key.objectid >= start);
                                ASSERT(found_key.objectid < end);
                                ASSERT(found_key.objectid + found_key.offset <= end);

                                bitmap_pos = div_u64(found_key.objectid - start,
                                                     fs_info->sectorsize *
                                                     BITS_PER_BYTE);
                                bitmap_cursor = ((char *)bitmap) + bitmap_pos;
                                data_size = free_space_bitmap_size(fs_info,
                                                                found_key.offset);

                                path->slots[0]--;
                                ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
                                read_extent_buffer(leaf, bitmap_cursor, ptr,
                                                   data_size);

                                nr++;
                        } else {
                                ASSERT(0);
                        }
                }

                ret = btrfs_del_items(trans, root, path, path->slots[0], nr);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
                btrfs_release_path(path);
        }

        info = btrfs_search_free_space_info(trans, block_group, path, 1);
        if (IS_ERR(info)) {
                ret = PTR_ERR(info);
                btrfs_abort_transaction(trans, ret);
                goto out;
        }
        leaf = path->nodes[0];
        flags = btrfs_free_space_flags(leaf, info);
        flags &= ~BTRFS_FREE_SPACE_USING_BITMAPS;
        block_group->using_free_space_bitmaps = false;
        block_group->using_free_space_bitmaps_cached = true;
        btrfs_set_free_space_flags(leaf, info, flags);
        expected_extent_count = btrfs_free_space_extent_count(leaf, info);
        btrfs_release_path(path);

        nrbits = block_group->length >> fs_info->sectorsize_bits;
        start_bit = find_next_bit_le(bitmap, nrbits, 0);

        while (start_bit < nrbits) {
                end_bit = find_next_zero_bit_le(bitmap, nrbits, start_bit);
                ASSERT(start_bit < end_bit);

                key.objectid = start + start_bit * fs_info->sectorsize;
                key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
                key.offset = (end_bit - start_bit) * fs_info->sectorsize;

                ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
                btrfs_release_path(path);

                extent_count++;

                start_bit = find_next_bit_le(bitmap, nrbits, end_bit);
        }

        if (unlikely(extent_count != expected_extent_count)) {
                btrfs_err(fs_info,
                          "incorrect extent count for %llu; counted %u, expected %u",
                          block_group->start, extent_count,
                          expected_extent_count);
                ret = -EIO;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

        ret = 0;
out:
        kvfree(bitmap);
        return ret;
}

static int update_free_space_extent_count(struct btrfs_trans_handle *trans,
                                          struct btrfs_block_group *block_group,
                                          struct btrfs_path *path,
                                          int new_extents)
{
        struct btrfs_free_space_info *info;
        u32 flags;
        u32 extent_count;
        int ret = 0;

        if (new_extents == 0)
                return 0;

        info = btrfs_search_free_space_info(trans, block_group, path, 1);
        if (IS_ERR(info))
                return PTR_ERR(info);

        flags = btrfs_free_space_flags(path->nodes[0], info);
        extent_count = btrfs_free_space_extent_count(path->nodes[0], info);

        extent_count += new_extents;
        btrfs_set_free_space_extent_count(path->nodes[0], info, extent_count);
        btrfs_release_path(path);

        if (!(flags & BTRFS_FREE_SPACE_USING_BITMAPS) &&
            extent_count > block_group->bitmap_high_thresh) {
                ret = btrfs_convert_free_space_to_bitmaps(trans, block_group, path);
        } else if ((flags & BTRFS_FREE_SPACE_USING_BITMAPS) &&
                   extent_count < block_group->bitmap_low_thresh) {
                ret = btrfs_convert_free_space_to_extents(trans, block_group, path);
        }

        return ret;
}

EXPORT_FOR_TESTS
bool btrfs_free_space_test_bit(struct btrfs_block_group *block_group,
                               struct btrfs_path *path, u64 offset)
{
        struct extent_buffer *leaf;
        struct btrfs_key key;
        u64 found_start, found_end;
        unsigned long ptr, i;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        ASSERT(key.type == BTRFS_FREE_SPACE_BITMAP_KEY);

        found_start = key.objectid;
        found_end = key.objectid + key.offset;
        ASSERT(offset >= found_start && offset < found_end);

        ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
        i = div_u64(offset - found_start,
                    block_group->fs_info->sectorsize);
        return extent_buffer_test_bit(leaf, ptr, i);
}

static void free_space_modify_bits(struct btrfs_trans_handle *trans,
                                   struct btrfs_block_group *block_group,
                                   struct btrfs_path *path, u64 *start, u64 *size,
                                   bool set_bits)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        u64 end = *start + *size;
        u64 found_start, found_end;
        unsigned long ptr, first, last;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        ASSERT(key.type == BTRFS_FREE_SPACE_BITMAP_KEY);

        found_start = key.objectid;
        found_end = key.objectid + key.offset;
        ASSERT(*start >= found_start && *start < found_end);
        ASSERT(end > found_start);

        if (end > found_end)
                end = found_end;

        ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
        first = (*start - found_start) >> fs_info->sectorsize_bits;
        last = (end - found_start) >> fs_info->sectorsize_bits;
        if (set_bits)
                extent_buffer_bitmap_set(leaf, ptr, first, last - first);
        else
                extent_buffer_bitmap_clear(leaf, ptr, first, last - first);
        btrfs_mark_buffer_dirty(trans, leaf);

        *size -= end - *start;
        *start = end;
}

/*
 * We can't use btrfs_next_item() in modify_free_space_bitmap() because
 * btrfs_next_leaf() doesn't get the path for writing. We can forgo the fancy
 * tree walking in btrfs_next_leaf() anyways because we know exactly what we're
 * looking for.
 */
static int free_space_next_bitmap(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root, struct btrfs_path *p)
{
        struct btrfs_key key;

        if (p->slots[0] + 1 < btrfs_header_nritems(p->nodes[0])) {
                p->slots[0]++;
                return 0;
        }

        btrfs_item_key_to_cpu(p->nodes[0], &key, p->slots[0]);
        btrfs_release_path(p);

        key.objectid += key.offset;
        key.type = (u8)-1;
        key.offset = (u64)-1;

        return btrfs_search_prev_slot(trans, root, &key, p, 0, 1);
}

/*
 * If remove is 1, then we are removing free space, thus clearing bits in the
 * bitmap. If remove is 0, then we are adding free space, thus setting bits in
 * the bitmap.
 */
static int modify_free_space_bitmap(struct btrfs_trans_handle *trans,
                                    struct btrfs_block_group *block_group,
                                    struct btrfs_path *path,
                                    u64 start, u64 size, bool remove)
{
        struct btrfs_root *root = btrfs_free_space_root(block_group);
        struct btrfs_key key;
        u64 end = start + size;
        u64 cur_start, cur_size;
        bool prev_bit_set = false;
        bool next_bit_set = false;
        int new_extents;
        int ret;

        /*
         * Read the bit for the block immediately before the extent of space if
         * that block is within the block group.
         */
        if (start > block_group->start) {
                u64 prev_block = start - block_group->fs_info->sectorsize;

                key.objectid = prev_block;
                key.type = (u8)-1;
                key.offset = (u64)-1;

                ret = btrfs_search_prev_slot(trans, root, &key, path, 0, 1);
                if (ret)
                        return ret;

                prev_bit_set = btrfs_free_space_test_bit(block_group, path, prev_block);

                /* The previous block may have been in the previous bitmap. */
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
                if (start >= key.objectid + key.offset) {
                        ret = free_space_next_bitmap(trans, root, path);
                        if (ret)
                                return ret;
                }
        } else {
                key.objectid = start;
                key.type = (u8)-1;
                key.offset = (u64)-1;

                ret = btrfs_search_prev_slot(trans, root, &key, path, 0, 1);
                if (ret)
                        return ret;
        }

        /*
         * Iterate over all of the bitmaps overlapped by the extent of space,
         * clearing/setting bits as required.
         */
        cur_start = start;
        cur_size = size;
        while (1) {
                free_space_modify_bits(trans, block_group, path, &cur_start,
                                       &cur_size, !remove);
                if (cur_size == 0)
                        break;
                ret = free_space_next_bitmap(trans, root, path);
                if (ret)
                        return ret;
        }

        /*
         * Read the bit for the block immediately after the extent of space if
         * that block is within the block group.
         */
        if (end < btrfs_block_group_end(block_group)) {
                /* The next block may be in the next bitmap. */
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
                if (end >= key.objectid + key.offset) {
                        ret = free_space_next_bitmap(trans, root, path);
                        if (ret)
                                return ret;
                }

                next_bit_set = btrfs_free_space_test_bit(block_group, path, end);
        }

        if (remove) {
                new_extents = -1;
                if (prev_bit_set) {
                        /* Leftover on the left. */
                        new_extents++;
                }
                if (next_bit_set) {
                        /* Leftover on the right. */
                        new_extents++;
                }
        } else {
                new_extents = 1;
                if (prev_bit_set) {
                        /* Merging with neighbor on the left. */
                        new_extents--;
                }
                if (next_bit_set) {
                        /* Merging with neighbor on the right. */
                        new_extents--;
                }
        }

        btrfs_release_path(path);
        return update_free_space_extent_count(trans, block_group, path, new_extents);
}

static int remove_free_space_extent(struct btrfs_trans_handle *trans,
                                    struct btrfs_block_group *block_group,
                                    struct btrfs_path *path,
                                    u64 start, u64 size)
{
        struct btrfs_root *root = btrfs_free_space_root(block_group);
        struct btrfs_key key;
        u64 found_start, found_end;
        u64 end = start + size;
        int new_extents = -1;
        int ret;

        key.objectid = start;
        key.type = (u8)-1;
        key.offset = (u64)-1;

        ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
        if (ret)
                return ret;

        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);

        ASSERT(key.type == BTRFS_FREE_SPACE_EXTENT_KEY);

        found_start = key.objectid;
        found_end = key.objectid + key.offset;
        ASSERT(start >= found_start && end <= found_end);

        /*
         * Okay, now that we've found the free space extent which contains the
         * free space that we are removing, there are four cases:
         *
         * 1. We're using the whole extent: delete the key we found and
         * decrement the free space extent count.
         * 2. We are using part of the extent starting at the beginning: delete
         * the key we found and insert a new key representing the leftover at
         * the end. There is no net change in the number of extents.
         * 3. We are using part of the extent ending at the end: delete the key
         * we found and insert a new key representing the leftover at the
         * beginning. There is no net change in the number of extents.
         * 4. We are using part of the extent in the middle: delete the key we
         * found and insert two new keys representing the leftovers on each
         * side. Where we used to have one extent, we now have two, so increment
         * the extent count. We may need to convert the block group to bitmaps
         * as a result.
         */

        /* Delete the existing key (cases 1-4). */
        ret = btrfs_del_item(trans, root, path);
        if (ret)
                return ret;

        /* Add a key for leftovers at the beginning (cases 3 and 4). */
        if (start > found_start) {
                key.objectid = found_start;
                key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
                key.offset = start - found_start;

                btrfs_release_path(path);
                ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
                if (ret)
                        return ret;
                new_extents++;
        }

        /* Add a key for leftovers at the end (cases 2 and 4). */
        if (end < found_end) {
                key.objectid = end;
                key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
                key.offset = found_end - end;

                btrfs_release_path(path);
                ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
                if (ret)
                        return ret;
                new_extents++;
        }

        btrfs_release_path(path);
        return update_free_space_extent_count(trans, block_group, path, new_extents);
}

static int using_bitmaps(struct btrfs_block_group *bg, struct btrfs_path *path)
{
        struct btrfs_free_space_info *info;
        u32 flags;

        if (bg->using_free_space_bitmaps_cached)
                return bg->using_free_space_bitmaps;

        info = btrfs_search_free_space_info(NULL, bg, path, 0);
        if (IS_ERR(info))
                return PTR_ERR(info);
        flags = btrfs_free_space_flags(path->nodes[0], info);
        btrfs_release_path(path);

        bg->using_free_space_bitmaps = (flags & BTRFS_FREE_SPACE_USING_BITMAPS);
        bg->using_free_space_bitmaps_cached = true;

        return bg->using_free_space_bitmaps;
}

EXPORT_FOR_TESTS
int __btrfs_remove_from_free_space_tree(struct btrfs_trans_handle *trans,
                                        struct btrfs_block_group *block_group,
                                        struct btrfs_path *path, u64 start, u64 size)
{
        int ret;

        ret = __add_block_group_free_space(trans, block_group, path);
        if (ret)
                return ret;

        ret = using_bitmaps(block_group, path);
        if (ret < 0)
                return ret;

        if (ret)
                return modify_free_space_bitmap(trans, block_group, path,
                                                start, size, true);

        return remove_free_space_extent(trans, block_group, path, start, size);
}

int btrfs_remove_from_free_space_tree(struct btrfs_trans_handle *trans,
                                      u64 start, u64 size)
{
        struct btrfs_block_group *block_group;
        BTRFS_PATH_AUTO_FREE(path);
        int ret;

        if (!btrfs_fs_compat_ro(trans->fs_info, FREE_SPACE_TREE))
                return 0;

        path = btrfs_alloc_path();
        if (unlikely(!path)) {
                ret = -ENOMEM;
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        block_group = btrfs_lookup_block_group(trans->fs_info, start);
        if (unlikely(!block_group)) {
                DEBUG_WARN("no block group found for start=%llu", start);
                ret = -ENOENT;
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        mutex_lock(&block_group->free_space_lock);
        ret = __btrfs_remove_from_free_space_tree(trans, block_group, path, start, size);
        mutex_unlock(&block_group->free_space_lock);
        if (ret)
                btrfs_abort_transaction(trans, ret);

        btrfs_put_block_group(block_group);

        return ret;
}

static int add_free_space_extent(struct btrfs_trans_handle *trans,
                                 struct btrfs_block_group *block_group,
                                 struct btrfs_path *path,
                                 u64 start, u64 size)
{
        struct btrfs_root *root = btrfs_free_space_root(block_group);
        struct btrfs_key key, new_key;
        u64 found_start, found_end;
        u64 end = start + size;
        int new_extents = 1;
        int ret;

        /*
         * We are adding a new extent of free space, but we need to merge
         * extents. There are four cases here:
         *
         * 1. The new extent does not have any immediate neighbors to merge
         * with: add the new key and increment the free space extent count. We
         * may need to convert the block group to bitmaps as a result.
         * 2. The new extent has an immediate neighbor before it: remove the
         * previous key and insert a new key combining both of them. There is no
         * net change in the number of extents.
         * 3. The new extent has an immediate neighbor after it: remove the next
         * key and insert a new key combining both of them. There is no net
         * change in the number of extents.
         * 4. The new extent has immediate neighbors on both sides: remove both
         * of the keys and insert a new key combining all of them. Where we used
         * to have two extents, we now have one, so decrement the extent count.
         */

        new_key.objectid = start;
        new_key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
        new_key.offset = size;

        /* Search for a neighbor on the left. */
        if (start == block_group->start)
                goto right;
        key.objectid = start - 1;
        key.type = (u8)-1;
        key.offset = (u64)-1;

        ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
        if (ret)
                return ret;

        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);

        if (key.type != BTRFS_FREE_SPACE_EXTENT_KEY) {
                ASSERT(key.type == BTRFS_FREE_SPACE_INFO_KEY);
                btrfs_release_path(path);
                goto right;
        }

        found_start = key.objectid;
        found_end = key.objectid + key.offset;
        ASSERT(found_start >= block_group->start &&
               found_end > block_group->start);
        ASSERT(found_start < start && found_end <= start);

        /*
         * Delete the neighbor on the left and absorb it into the new key (cases
         * 2 and 4).
         */
        if (found_end == start) {
                ret = btrfs_del_item(trans, root, path);
                if (ret)
                        return ret;
                new_key.objectid = found_start;
                new_key.offset += key.offset;
                new_extents--;
        }
        btrfs_release_path(path);

right:
        /* Search for a neighbor on the right. */
        if (end == btrfs_block_group_end(block_group))
                goto insert;
        key.objectid = end;
        key.type = (u8)-1;
        key.offset = (u64)-1;

        ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
        if (ret)
                return ret;

        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);

        if (key.type != BTRFS_FREE_SPACE_EXTENT_KEY) {
                ASSERT(key.type == BTRFS_FREE_SPACE_INFO_KEY);
                btrfs_release_path(path);
                goto insert;
        }

        found_start = key.objectid;
        found_end = key.objectid + key.offset;
        ASSERT(found_start >= block_group->start &&
               found_end > block_group->start);
        ASSERT((found_start < start && found_end <= start) ||
               (found_start >= end && found_end > end));

        /*
         * Delete the neighbor on the right and absorb it into the new key
         * (cases 3 and 4).
         */
        if (found_start == end) {
                ret = btrfs_del_item(trans, root, path);
                if (ret)
                        return ret;
                new_key.offset += key.offset;
                new_extents--;
        }
        btrfs_release_path(path);

insert:
        /* Insert the new key (cases 1-4). */
        ret = btrfs_insert_empty_item(trans, root, path, &new_key, 0);
        if (ret)
                return ret;

        btrfs_release_path(path);
        return update_free_space_extent_count(trans, block_group, path, new_extents);
}

EXPORT_FOR_TESTS
int __btrfs_add_to_free_space_tree(struct btrfs_trans_handle *trans,
                                   struct btrfs_block_group *block_group,
                                   struct btrfs_path *path, u64 start, u64 size)
{
        int ret;

        ret = __add_block_group_free_space(trans, block_group, path);
        if (ret)
                return ret;

        ret = using_bitmaps(block_group, path);
        if (ret < 0)
                return ret;

        if (ret)
                return modify_free_space_bitmap(trans, block_group, path,
                                                start, size, false);

        return add_free_space_extent(trans, block_group, path, start, size);
}

int btrfs_add_to_free_space_tree(struct btrfs_trans_handle *trans,
                                 u64 start, u64 size)
{
        struct btrfs_block_group *block_group;
        BTRFS_PATH_AUTO_FREE(path);
        int ret;

        if (!btrfs_fs_compat_ro(trans->fs_info, FREE_SPACE_TREE))
                return 0;

        path = btrfs_alloc_path();
        if (unlikely(!path)) {
                ret = -ENOMEM;
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        block_group = btrfs_lookup_block_group(trans->fs_info, start);
        if (unlikely(!block_group)) {
                DEBUG_WARN("no block group found for start=%llu", start);
                ret = -ENOENT;
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        mutex_lock(&block_group->free_space_lock);
        ret = __btrfs_add_to_free_space_tree(trans, block_group, path, start, size);
        mutex_unlock(&block_group->free_space_lock);
        if (ret)
                btrfs_abort_transaction(trans, ret);

        btrfs_put_block_group(block_group);

        return ret;
}

/*
 * Populate the free space tree by walking the extent tree. Operations on the
 * extent tree that happen as a result of writes to the free space tree will go
 * through the normal add/remove hooks.
 */
static int populate_free_space_tree(struct btrfs_trans_handle *trans,
                                    struct btrfs_block_group *block_group)
{
        struct btrfs_root *extent_root;
        BTRFS_PATH_AUTO_FREE(path);
        BTRFS_PATH_AUTO_FREE(path2);
        struct btrfs_key key;
        u64 start, end;
        int ret;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        path2 = btrfs_alloc_path();
        if (!path2)
                return -ENOMEM;

        path->reada = READA_FORWARD;

        ret = add_new_free_space_info(trans, block_group, path2);
        if (ret)
                return ret;

        extent_root = btrfs_extent_root(trans->fs_info, block_group->start);
        if (unlikely(!extent_root)) {
                btrfs_err(trans->fs_info,
                          "missing extent root for block group at offset %llu",
                          block_group->start);
                return -EUCLEAN;
        }

        mutex_lock(&block_group->free_space_lock);

        /*
         * Iterate through all of the extent and metadata items in this block
         * group, adding the free space between them and the free space at the
         * end. Note that EXTENT_ITEM and METADATA_ITEM are less than
         * BLOCK_GROUP_ITEM, so an extent may precede the block group that it's
         * contained in.
         */
        key.objectid = block_group->start;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        key.offset = 0;

        ret = btrfs_search_slot_for_read(extent_root, &key, path, 1, 0);
        if (ret < 0)
                goto out_locked;
        /*
         * If ret is 1 (no key found), it means this is an empty block group,
         * without any extents allocated from it and there's no block group
         * item (key BTRFS_BLOCK_GROUP_ITEM_KEY) located in the extent tree
         * because we are using the block group tree feature (so block group
         * items are stored in the block group tree) or this is a new block
         * group created in the current transaction and its block group item
         * was not yet inserted in the extent tree (that happens in
         * btrfs_create_pending_block_groups() -> insert_block_group_item()).
         * It also means there are no extents allocated for block groups with a
         * start offset beyond this block group's end offset (this is the last,
         * highest, block group).
         */
        start = block_group->start;
        end = btrfs_block_group_end(block_group);
        while (ret == 0) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);

                if (key.type == BTRFS_EXTENT_ITEM_KEY ||
                    key.type == BTRFS_METADATA_ITEM_KEY) {
                        if (key.objectid >= end)
                                break;

                        if (start < key.objectid) {
                                ret = __btrfs_add_to_free_space_tree(trans,
                                                                     block_group,
                                                                     path2, start,
                                                                     key.objectid -
                                                                     start);
                                if (ret)
                                        goto out_locked;
                        }
                        start = key.objectid;
                        if (key.type == BTRFS_METADATA_ITEM_KEY)
                                start += trans->fs_info->nodesize;
                        else
                                start += key.offset;
                } else if (key.type == BTRFS_BLOCK_GROUP_ITEM_KEY) {
                        if (key.objectid != block_group->start)
                                break;
                }

                ret = btrfs_next_item(extent_root, path);
                if (ret < 0)
                        goto out_locked;
        }
        if (start < end) {
                ret = __btrfs_add_to_free_space_tree(trans, block_group, path2,
                                                     start, end - start);
                if (ret)
                        goto out_locked;
        }

        ret = 0;
out_locked:
        mutex_unlock(&block_group->free_space_lock);

        return ret;
}

int btrfs_create_free_space_tree(struct btrfs_fs_info *fs_info)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_root *tree_root = fs_info->tree_root;
        struct btrfs_root *free_space_root;
        struct btrfs_block_group *block_group;
        struct rb_node *node;
        int ret;

        trans = btrfs_start_transaction(tree_root, 0);
        if (IS_ERR(trans))
                return PTR_ERR(trans);

        set_bit(BTRFS_FS_CREATING_FREE_SPACE_TREE, &fs_info->flags);
        set_bit(BTRFS_FS_FREE_SPACE_TREE_UNTRUSTED, &fs_info->flags);
        free_space_root = btrfs_create_tree(trans,
                                            BTRFS_FREE_SPACE_TREE_OBJECTID);
        if (IS_ERR(free_space_root)) {
                ret = PTR_ERR(free_space_root);
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
                goto out_clear;
        }
        ret = btrfs_global_root_insert(free_space_root);
        if (unlikely(ret)) {
                btrfs_put_root(free_space_root);
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
                goto out_clear;
        }

        node = rb_first_cached(&fs_info->block_group_cache_tree);
        while (node) {
                block_group = rb_entry(node, struct btrfs_block_group,
                                       cache_node);
                ret = populate_free_space_tree(trans, block_group);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        btrfs_end_transaction(trans);
                        goto out_clear;
                }
                node = rb_next(node);
        }

        btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE);
        btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID);
        clear_bit(BTRFS_FS_CREATING_FREE_SPACE_TREE, &fs_info->flags);
        ret = btrfs_commit_transaction(trans);

        /*
         * Now that we've committed the transaction any reading of our commit
         * root will be safe, so we can cache from the free space tree now.
         */
        clear_bit(BTRFS_FS_FREE_SPACE_TREE_UNTRUSTED, &fs_info->flags);
        return ret;

out_clear:
        clear_bit(BTRFS_FS_CREATING_FREE_SPACE_TREE, &fs_info->flags);
        clear_bit(BTRFS_FS_FREE_SPACE_TREE_UNTRUSTED, &fs_info->flags);
        return ret;
}

static int clear_free_space_tree(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root)
{
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct rb_node *node;
        int nr;
        int ret;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        key.objectid = 0;
        key.type = 0;
        key.offset = 0;

        while (1) {
                ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
                if (ret < 0)
                        return ret;

                nr = btrfs_header_nritems(path->nodes[0]);
                if (!nr)
                        break;

                path->slots[0] = 0;
                ret = btrfs_del_items(trans, root, path, 0, nr);
                if (ret)
                        return ret;

                btrfs_release_path(path);
        }

        node = rb_first_cached(&trans->fs_info->block_group_cache_tree);
        while (node) {
                struct btrfs_block_group *bg;

                bg = rb_entry(node, struct btrfs_block_group, cache_node);
                clear_bit(BLOCK_GROUP_FLAG_FREE_SPACE_ADDED, &bg->runtime_flags);
                node = rb_next(node);
                cond_resched();
        }

        return 0;
}

int btrfs_delete_free_space_tree(struct btrfs_fs_info *fs_info)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_root *tree_root = fs_info->tree_root;
        struct btrfs_key key = {
                .objectid = BTRFS_FREE_SPACE_TREE_OBJECTID,
                .type = BTRFS_ROOT_ITEM_KEY,
                .offset = 0,
        };
        struct btrfs_root *free_space_root = btrfs_global_root(fs_info, &key);
        int ret;

        trans = btrfs_start_transaction(tree_root, 0);
        if (IS_ERR(trans))
                return PTR_ERR(trans);

        btrfs_clear_fs_compat_ro(fs_info, FREE_SPACE_TREE);
        btrfs_clear_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID);

        ret = clear_free_space_tree(trans, free_space_root);
        if (unlikely(ret)) {
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
                return ret;
        }

        ret = btrfs_del_root(trans, &free_space_root->root_key);
        if (unlikely(ret)) {
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
                return ret;
        }

        btrfs_global_root_delete(free_space_root);

        spin_lock(&fs_info->trans_lock);
        list_del(&free_space_root->dirty_list);
        spin_unlock(&fs_info->trans_lock);

        btrfs_tree_lock(free_space_root->node);
        btrfs_clear_buffer_dirty(trans, free_space_root->node);
        btrfs_tree_unlock(free_space_root->node);
        ret = btrfs_free_tree_block(trans, btrfs_root_id(free_space_root),
                                    free_space_root->node, 0, 1);
        btrfs_put_root(free_space_root);
        if (unlikely(ret < 0)) {
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
                return ret;
        }

        return btrfs_commit_transaction(trans);
}

int btrfs_rebuild_free_space_tree(struct btrfs_fs_info *fs_info)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_key key = {
                .objectid = BTRFS_FREE_SPACE_TREE_OBJECTID,
                .type = BTRFS_ROOT_ITEM_KEY,
                .offset = 0,
        };
        struct btrfs_root *free_space_root = btrfs_global_root(fs_info, &key);
        struct rb_node *node;
        int ret;

        trans = btrfs_start_transaction(free_space_root, 1);
        if (IS_ERR(trans))
                return PTR_ERR(trans);

        set_bit(BTRFS_FS_CREATING_FREE_SPACE_TREE, &fs_info->flags);
        set_bit(BTRFS_FS_FREE_SPACE_TREE_UNTRUSTED, &fs_info->flags);

        ret = clear_free_space_tree(trans, free_space_root);
        if (unlikely(ret)) {
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
                return ret;
        }

        node = rb_first_cached(&fs_info->block_group_cache_tree);
        while (node) {
                struct btrfs_block_group *block_group;

                block_group = rb_entry(node, struct btrfs_block_group,
                                       cache_node);

                if (test_bit(BLOCK_GROUP_FLAG_FREE_SPACE_ADDED,
                             &block_group->runtime_flags))
                        goto next;

                ret = populate_free_space_tree(trans, block_group);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        btrfs_end_transaction(trans);
                        return ret;
                }
next:
                if (btrfs_should_end_transaction(trans)) {
                        btrfs_end_transaction(trans);
                        trans = btrfs_start_transaction(free_space_root, 1);
                        if (IS_ERR(trans))
                                return PTR_ERR(trans);
                }
                node = rb_next(node);
        }

        btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE);
        btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID);
        clear_bit(BTRFS_FS_CREATING_FREE_SPACE_TREE, &fs_info->flags);

        ret = btrfs_commit_transaction(trans);
        clear_bit(BTRFS_FS_FREE_SPACE_TREE_UNTRUSTED, &fs_info->flags);
        return ret;
}

static int __add_block_group_free_space(struct btrfs_trans_handle *trans,
                                        struct btrfs_block_group *block_group,
                                        struct btrfs_path *path)
{
        bool own_path = false;
        int ret;

        if (!test_and_clear_bit(BLOCK_GROUP_FLAG_NEEDS_FREE_SPACE,
                                &block_group->runtime_flags))
                return 0;

        /*
         * While rebuilding the free space tree we may allocate new metadata
         * block groups while modifying the free space tree.
         *
         * Because during the rebuild (at btrfs_rebuild_free_space_tree()) we
         * can use multiple transactions, every time btrfs_end_transaction() is
         * called at btrfs_rebuild_free_space_tree() we finish the creation of
         * new block groups by calling btrfs_create_pending_block_groups(), and
         * that in turn calls us, through btrfs_add_block_group_free_space(),
         * to add a free space info item and a free space extent item for the
         * block group.
         *
         * Then later btrfs_rebuild_free_space_tree() may find such new block
         * groups and processes them with populate_free_space_tree(), which can
         * fail with EEXIST since there are already items for the block group in
         * the free space tree. Notice that we say "may find" because a new
         * block group may be added to the block groups rbtree in a node before
         * or after the block group currently being processed by the rebuild
         * process. So signal the rebuild process to skip such new block groups
         * if it finds them.
         */
        set_bit(BLOCK_GROUP_FLAG_FREE_SPACE_ADDED, &block_group->runtime_flags);

        if (!path) {
                path = btrfs_alloc_path();
                if (unlikely(!path)) {
                        btrfs_abort_transaction(trans, -ENOMEM);
                        return -ENOMEM;
                }
                own_path = true;
        }

        ret = add_new_free_space_info(trans, block_group, path);
        if (unlikely(ret)) {
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

        ret = __btrfs_add_to_free_space_tree(trans, block_group, path,
                                             block_group->start, block_group->length);
        if (ret)
                btrfs_abort_transaction(trans, ret);

out:
        if (own_path)
                btrfs_free_path(path);

        return ret;
}

int btrfs_add_block_group_free_space(struct btrfs_trans_handle *trans,
                                     struct btrfs_block_group *block_group)
{
        int ret;

        if (!btrfs_fs_compat_ro(trans->fs_info, FREE_SPACE_TREE))
                return 0;

        mutex_lock(&block_group->free_space_lock);
        ret = __add_block_group_free_space(trans, block_group, NULL);
        mutex_unlock(&block_group->free_space_lock);
        return ret;
}

int btrfs_remove_block_group_free_space(struct btrfs_trans_handle *trans,
                                        struct btrfs_block_group *block_group)
{
        struct btrfs_root *root = btrfs_free_space_root(block_group);
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key, found_key;
        struct extent_buffer *leaf;
        u64 start, end;
        int done = 0, nr;
        int ret;

        if (!btrfs_fs_compat_ro(trans->fs_info, FREE_SPACE_TREE))
                return 0;

        if (test_bit(BLOCK_GROUP_FLAG_NEEDS_FREE_SPACE, &block_group->runtime_flags)) {
                /* We never added this block group to the free space tree. */
                return 0;
        }

        path = btrfs_alloc_path();
        if (unlikely(!path)) {
                ret = -ENOMEM;
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        start = block_group->start;
        end = btrfs_block_group_end(block_group);

        key.objectid = end - 1;
        key.type = (u8)-1;
        key.offset = (u64)-1;

        while (!done) {
                ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }

                leaf = path->nodes[0];
                nr = 0;
                path->slots[0]++;
                while (path->slots[0] > 0) {
                        btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0] - 1);

                        if (found_key.type == BTRFS_FREE_SPACE_INFO_KEY) {
                                ASSERT(found_key.objectid == block_group->start);
                                ASSERT(found_key.offset == block_group->length);
                                done = 1;
                                nr++;
                                path->slots[0]--;
                                break;
                        } else if (found_key.type == BTRFS_FREE_SPACE_EXTENT_KEY ||
                                   found_key.type == BTRFS_FREE_SPACE_BITMAP_KEY) {
                                ASSERT(found_key.objectid >= start);
                                ASSERT(found_key.objectid < end);
                                ASSERT(found_key.objectid + found_key.offset <= end);
                                nr++;
                                path->slots[0]--;
                        } else {
                                ASSERT(0);
                        }
                }

                ret = btrfs_del_items(trans, root, path, path->slots[0], nr);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }
                btrfs_release_path(path);
        }

        return 0;
}

static int load_free_space_bitmaps(struct btrfs_caching_control *caching_ctl,
                                   struct btrfs_path *path,
                                   u32 expected_extent_count)
{
        struct btrfs_block_group *block_group = caching_ctl->block_group;
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_root *root;
        struct btrfs_key key;
        bool prev_bit_set = false;
        /* Initialize to silence GCC. */
        u64 extent_start = 0;
        const u64 end = btrfs_block_group_end(block_group);
        u64 offset;
        u64 total_found = 0;
        u32 extent_count = 0;
        int ret;

        root = btrfs_free_space_root(block_group);

        while (1) {
                ret = btrfs_next_item(root, path);
                if (ret < 0)
                        return ret;
                if (ret)
                        break;

                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);

                if (key.type == BTRFS_FREE_SPACE_INFO_KEY)
                        break;

                ASSERT(key.type == BTRFS_FREE_SPACE_BITMAP_KEY);
                ASSERT(key.objectid < end && key.objectid + key.offset <= end);

                offset = key.objectid;
                while (offset < key.objectid + key.offset) {
                        bool bit_set;

                        bit_set = btrfs_free_space_test_bit(block_group, path, offset);
                        if (!prev_bit_set && bit_set) {
                                extent_start = offset;
                        } else if (prev_bit_set && !bit_set) {
                                u64 space_added;

                                ret = btrfs_add_new_free_space(block_group,
                                                               extent_start,
                                                               offset,
                                                               &space_added);
                                if (ret)
                                        return ret;
                                total_found += space_added;
                                if (total_found > CACHING_CTL_WAKE_UP) {
                                        total_found = 0;
                                        wake_up(&caching_ctl->wait);
                                }
                                extent_count++;
                        }
                        prev_bit_set = bit_set;
                        offset += fs_info->sectorsize;
                }
        }
        if (prev_bit_set) {
                ret = btrfs_add_new_free_space(block_group, extent_start, end, NULL);
                if (ret)
                        return ret;
                extent_count++;
        }

        if (unlikely(extent_count != expected_extent_count)) {
                btrfs_err(fs_info,
                          "incorrect extent count for %llu; counted %u, expected %u",
                          block_group->start, extent_count,
                          expected_extent_count);
                DEBUG_WARN();
                return -EIO;
        }

        return 0;
}

static int load_free_space_extents(struct btrfs_caching_control *caching_ctl,
                                   struct btrfs_path *path,
                                   u32 expected_extent_count)
{
        struct btrfs_block_group *block_group = caching_ctl->block_group;
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_root *root;
        struct btrfs_key key;
        const u64 end = btrfs_block_group_end(block_group);
        u64 total_found = 0;
        u32 extent_count = 0;
        int ret;

        root = btrfs_free_space_root(block_group);

        while (1) {
                u64 space_added;

                ret = btrfs_next_item(root, path);
                if (ret < 0)
                        return ret;
                if (ret)
                        break;

                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);

                if (key.type == BTRFS_FREE_SPACE_INFO_KEY)
                        break;

                ASSERT(key.type == BTRFS_FREE_SPACE_EXTENT_KEY);
                ASSERT(key.objectid < end && key.objectid + key.offset <= end);

                ret = btrfs_add_new_free_space(block_group, key.objectid,
                                               key.objectid + key.offset,
                                               &space_added);
                if (ret)
                        return ret;
                total_found += space_added;
                if (total_found > CACHING_CTL_WAKE_UP) {
                        total_found = 0;
                        wake_up(&caching_ctl->wait);
                }
                extent_count++;
        }

        if (unlikely(extent_count != expected_extent_count)) {
                btrfs_err(fs_info,
                          "incorrect extent count for %llu; counted %u, expected %u",
                          block_group->start, extent_count,
                          expected_extent_count);
                DEBUG_WARN();
                return -EIO;
        }

        return 0;
}

int btrfs_load_free_space_tree(struct btrfs_caching_control *caching_ctl)
{
        struct btrfs_block_group *block_group;
        struct btrfs_free_space_info *info;
        BTRFS_PATH_AUTO_FREE(path);
        u32 extent_count, flags;

        block_group = caching_ctl->block_group;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /*
         * Just like caching_thread() doesn't want to deadlock on the extent
         * tree, we don't want to deadlock on the free space tree.
         */
        path->skip_locking = true;
        path->search_commit_root = true;
        path->reada = READA_FORWARD;

        info = btrfs_search_free_space_info(NULL, block_group, path, 0);
        if (IS_ERR(info))
                return PTR_ERR(info);

        extent_count = btrfs_free_space_extent_count(path->nodes[0], info);
        flags = btrfs_free_space_flags(path->nodes[0], info);

        /*
         * We left path pointing to the free space info item, so now
         * load_free_space_foo can just iterate through the free space tree from
         * there.
         */
        if (flags & BTRFS_FREE_SPACE_USING_BITMAPS)
                return load_free_space_bitmaps(caching_ctl, path, extent_count);
        else
                return load_free_space_extents(caching_ctl, path, extent_count);
}

static int delete_orphan_free_space_entries(struct btrfs_root *fst_root,
                                            struct btrfs_path *path,
                                            u64 first_bg_bytenr)
{
        struct btrfs_trans_handle *trans;
        int ret;

        trans = btrfs_start_transaction(fst_root, 1);
        if (IS_ERR(trans))
                return PTR_ERR(trans);

        while (true) {
                struct btrfs_key key = { 0 };
                int i;

                ret = btrfs_search_slot(trans, fst_root, &key, path, -1, 1);
                if (ret < 0)
                        break;
                ASSERT(ret > 0);
                ret = 0;
                for (i = 0; i < btrfs_header_nritems(path->nodes[0]); i++) {
                        btrfs_item_key_to_cpu(path->nodes[0], &key, i);
                        if (key.objectid >= first_bg_bytenr) {
                                /*
                                 * Only break the for() loop and continue to
                                 * delete items.
                                 */
                                break;
                        }
                }
                /* No items to delete, finished. */
                if (i == 0)
                        break;

                ret = btrfs_del_items(trans, fst_root, path, 0, i);
                if (ret < 0)
                        break;
                btrfs_release_path(path);
        }
        btrfs_release_path(path);
        btrfs_end_transaction(trans);
        if (ret == 0)
                btrfs_info(fst_root->fs_info, "deleted orphan free space tree entries");
        return ret;
}

/* Remove any free space entry before the first block group. */
int btrfs_delete_orphan_free_space_entries(struct btrfs_fs_info *fs_info)
{
        BTRFS_PATH_AUTO_RELEASE(path);
        struct btrfs_key key = {
                .objectid = BTRFS_FREE_SPACE_TREE_OBJECTID,
                .type = BTRFS_ROOT_ITEM_KEY,
                .offset = 0,
        };
        struct btrfs_root *root;
        struct btrfs_block_group *bg;
        u64 first_bg_bytenr;
        int ret;

        /*
         * Extent tree v2 has multiple global roots based on the block group.
         * This means we cannot easily grab the global free space tree and locate
         * orphan items.  Furthermore this is still experimental, all users
         * should use the latest btrfs-progs anyway.
         */
        if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2))
                return 0;
        if (!btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE))
                return 0;
        root = btrfs_global_root(fs_info, &key);
        if (!root)
                return 0;

        key.objectid = 0;
        key.type = 0;
        key.offset = 0;

        bg = btrfs_lookup_first_block_group(fs_info, 0);
        if (unlikely(!bg)) {
                btrfs_err(fs_info, "no block group found");
                return -EUCLEAN;
        }
        first_bg_bytenr = bg->start;
        btrfs_put_block_group(bg);

        ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
        if (ret < 0)
                return ret;
        /* There should not be an all-zero key in fst. */
        ASSERT(ret > 0);

        /* Empty free space tree. */
        if (path.slots[0] >= btrfs_header_nritems(path.nodes[0]))
                return 0;

        btrfs_item_key_to_cpu(path.nodes[0], &key, path.slots[0]);
        if (key.objectid >= first_bg_bytenr)
                return 0;
        btrfs_release_path(&path);
        return delete_orphan_free_space_entries(root, &path, first_bg_bytenr);
}