// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2008 Red Hat.  All rights reserved.
 */

#include <linux/pagemap.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/math64.h>
#include <linux/ratelimit.h>
#include <linux/error-injection.h>
#include <linux/sched/mm.h>
#include "misc.h"
#include "ctree.h"
#include "free-space-cache.h"
#include "transaction.h"
#include "disk-io.h"
#include "extent_io.h"
#include "volumes.h"
#include "space-info.h"
#include "delalloc-space.h"
#include "block-group.h"
#include "discard.h"
#include "subpage.h"
#include "inode-item.h"

#define BITS_PER_BITMAP         (PAGE_SIZE * 8UL)
#define MAX_CACHE_BYTES_PER_GIG SZ_64K
#define FORCE_EXTENT_THRESHOLD  SZ_1M

struct btrfs_trim_range {
        u64 start;
        u64 bytes;
        struct list_head list;
};

static int link_free_space(struct btrfs_free_space_ctl *ctl,
                           struct btrfs_free_space *info);
static void unlink_free_space(struct btrfs_free_space_ctl *ctl,
                              struct btrfs_free_space *info, bool update_stat);
static int search_bitmap(struct btrfs_free_space_ctl *ctl,
                         struct btrfs_free_space *bitmap_info, u64 *offset,
                         u64 *bytes, bool for_alloc);
static void free_bitmap(struct btrfs_free_space_ctl *ctl,
                        struct btrfs_free_space *bitmap_info);
static void bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
                              struct btrfs_free_space *info, u64 offset,
                              u64 bytes, bool update_stats);

static struct inode *__lookup_free_space_inode(struct btrfs_root *root,
                                               struct btrfs_path *path,
                                               u64 offset)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_key key;
        struct btrfs_key location;
        struct btrfs_disk_key disk_key;
        struct btrfs_free_space_header *header;
        struct extent_buffer *leaf;
        struct inode *inode = NULL;
        unsigned nofs_flag;
        int ret;

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

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                return ERR_PTR(ret);
        if (ret > 0) {
                btrfs_release_path(path);
                return ERR_PTR(-ENOENT);
        }

        leaf = path->nodes[0];
        header = btrfs_item_ptr(leaf, path->slots[0],
                                struct btrfs_free_space_header);
        btrfs_free_space_key(leaf, header, &disk_key);
        btrfs_disk_key_to_cpu(&location, &disk_key);
        btrfs_release_path(path);

        /*
         * We are often under a trans handle at this point, so we need to make
         * sure NOFS is set to keep us from deadlocking.
         */
        nofs_flag = memalloc_nofs_save();
        inode = btrfs_iget_path(fs_info->sb, location.objectid, root, path);
        btrfs_release_path(path);
        memalloc_nofs_restore(nofs_flag);
        if (IS_ERR(inode))
                return inode;

        mapping_set_gfp_mask(inode->i_mapping,
                        mapping_gfp_constraint(inode->i_mapping,
                        ~(__GFP_FS | __GFP_HIGHMEM)));

        return inode;
}

struct inode *lookup_free_space_inode(struct btrfs_block_group *block_group,
                struct btrfs_path *path)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct inode *inode = NULL;
        u32 flags = BTRFS_INODE_NODATASUM | BTRFS_INODE_NODATACOW;

        spin_lock(&block_group->lock);
        if (block_group->inode)
                inode = igrab(block_group->inode);
        spin_unlock(&block_group->lock);
        if (inode)
                return inode;

        inode = __lookup_free_space_inode(fs_info->tree_root, path,
                                          block_group->start);
        if (IS_ERR(inode))
                return inode;

        spin_lock(&block_group->lock);
        if (!((BTRFS_I(inode)->flags & flags) == flags)) {
                btrfs_info(fs_info, "Old style space inode found, converting.");
                BTRFS_I(inode)->flags |= BTRFS_INODE_NODATASUM |
                        BTRFS_INODE_NODATACOW;
                block_group->disk_cache_state = BTRFS_DC_CLEAR;
        }

        if (!block_group->iref) {
                block_group->inode = igrab(inode);
                block_group->iref = 1;
        }
        spin_unlock(&block_group->lock);

        return inode;
}

static int __create_free_space_inode(struct btrfs_root *root,
                                     struct btrfs_trans_handle *trans,
                                     struct btrfs_path *path,
                                     u64 ino, u64 offset)
{
        struct btrfs_key key;
        struct btrfs_disk_key disk_key;
        struct btrfs_free_space_header *header;
        struct btrfs_inode_item *inode_item;
        struct extent_buffer *leaf;
        /* We inline CRCs for the free disk space cache */
        const u64 flags = BTRFS_INODE_NOCOMPRESS | BTRFS_INODE_PREALLOC |
                          BTRFS_INODE_NODATASUM | BTRFS_INODE_NODATACOW;
        int ret;

        ret = btrfs_insert_empty_inode(trans, root, path, ino);
        if (ret)
                return ret;

        leaf = path->nodes[0];
        inode_item = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_inode_item);
        btrfs_item_key(leaf, &disk_key, path->slots[0]);
        memzero_extent_buffer(leaf, (unsigned long)inode_item,
                             sizeof(*inode_item));
        btrfs_set_inode_generation(leaf, inode_item, trans->transid);
        btrfs_set_inode_size(leaf, inode_item, 0);
        btrfs_set_inode_nbytes(leaf, inode_item, 0);
        btrfs_set_inode_uid(leaf, inode_item, 0);
        btrfs_set_inode_gid(leaf, inode_item, 0);
        btrfs_set_inode_mode(leaf, inode_item, S_IFREG | 0600);
        btrfs_set_inode_flags(leaf, inode_item, flags);
        btrfs_set_inode_nlink(leaf, inode_item, 1);
        btrfs_set_inode_transid(leaf, inode_item, trans->transid);
        btrfs_set_inode_block_group(leaf, inode_item, offset);
        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        key.objectid = BTRFS_FREE_SPACE_OBJECTID;
        key.offset = offset;
        key.type = 0;
        ret = btrfs_insert_empty_item(trans, root, path, &key,
                                      sizeof(struct btrfs_free_space_header));
        if (ret < 0) {
                btrfs_release_path(path);
                return ret;
        }

        leaf = path->nodes[0];
        header = btrfs_item_ptr(leaf, path->slots[0],
                                struct btrfs_free_space_header);
        memzero_extent_buffer(leaf, (unsigned long)header, sizeof(*header));
        btrfs_set_free_space_key(leaf, header, &disk_key);
        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        return 0;
}

int create_free_space_inode(struct btrfs_trans_handle *trans,
                            struct btrfs_block_group *block_group,
                            struct btrfs_path *path)
{
        int ret;
        u64 ino;

        ret = btrfs_get_free_objectid(trans->fs_info->tree_root, &ino);
        if (ret < 0)
                return ret;

        return __create_free_space_inode(trans->fs_info->tree_root, trans, path,
                                         ino, block_group->start);
}

/*
 * inode is an optional sink: if it is NULL, btrfs_remove_free_space_inode
 * handles lookup, otherwise it takes ownership and iputs the inode.
 * Don't reuse an inode pointer after passing it into this function.
 */
int btrfs_remove_free_space_inode(struct btrfs_trans_handle *trans,
                                  struct inode *inode,
                                  struct btrfs_block_group *block_group)
{
        struct btrfs_path *path;
        struct btrfs_key key;
        int ret = 0;

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

        if (!inode)
                inode = lookup_free_space_inode(block_group, path);
        if (IS_ERR(inode)) {
                if (PTR_ERR(inode) != -ENOENT)
                        ret = PTR_ERR(inode);
                goto out;
        }
        ret = btrfs_orphan_add(trans, BTRFS_I(inode));
        if (ret) {
                btrfs_add_delayed_iput(inode);
                goto out;
        }
        clear_nlink(inode);
        /* One for the block groups ref */
        spin_lock(&block_group->lock);
        if (block_group->iref) {
                block_group->iref = 0;
                block_group->inode = NULL;
                spin_unlock(&block_group->lock);
                iput(inode);
        } else {
                spin_unlock(&block_group->lock);
        }
        /* One for the lookup ref */
        btrfs_add_delayed_iput(inode);

        key.objectid = BTRFS_FREE_SPACE_OBJECTID;
        key.type = 0;
        key.offset = block_group->start;
        ret = btrfs_search_slot(trans, trans->fs_info->tree_root, &key, path,
                                -1, 1);
        if (ret) {
                if (ret > 0)
                        ret = 0;
                goto out;
        }
        ret = btrfs_del_item(trans, trans->fs_info->tree_root, path);
out:
        btrfs_free_path(path);
        return ret;
}

int btrfs_check_trunc_cache_free_space(struct btrfs_fs_info *fs_info,
                                       struct btrfs_block_rsv *rsv)
{
        u64 needed_bytes;
        int ret;

        /* 1 for slack space, 1 for updating the inode */
        needed_bytes = btrfs_calc_insert_metadata_size(fs_info, 1) +
                btrfs_calc_metadata_size(fs_info, 1);

        spin_lock(&rsv->lock);
        if (rsv->reserved < needed_bytes)
                ret = -ENOSPC;
        else
                ret = 0;
        spin_unlock(&rsv->lock);
        return ret;
}

int btrfs_truncate_free_space_cache(struct btrfs_trans_handle *trans,
                                    struct btrfs_block_group *block_group,
                                    struct inode *vfs_inode)
{
        struct btrfs_truncate_control control = {
                .inode = BTRFS_I(vfs_inode),
                .new_size = 0,
                .ino = btrfs_ino(BTRFS_I(vfs_inode)),
                .min_type = BTRFS_EXTENT_DATA_KEY,
                .clear_extent_range = true,
        };
        struct btrfs_inode *inode = BTRFS_I(vfs_inode);
        struct btrfs_root *root = inode->root;
        struct extent_state *cached_state = NULL;
        int ret = 0;
        bool locked = false;

        if (block_group) {
                struct btrfs_path *path = btrfs_alloc_path();

                if (!path) {
                        ret = -ENOMEM;
                        goto fail;
                }
                locked = true;
                mutex_lock(&trans->transaction->cache_write_mutex);
                if (!list_empty(&block_group->io_list)) {
                        list_del_init(&block_group->io_list);

                        btrfs_wait_cache_io(trans, block_group, path);
                        btrfs_put_block_group(block_group);
                }

                /*
                 * now that we've truncated the cache away, its no longer
                 * setup or written
                 */
                spin_lock(&block_group->lock);
                block_group->disk_cache_state = BTRFS_DC_CLEAR;
                spin_unlock(&block_group->lock);
                btrfs_free_path(path);
        }

        btrfs_i_size_write(inode, 0);
        truncate_pagecache(vfs_inode, 0);

        lock_extent_bits(&inode->io_tree, 0, (u64)-1, &cached_state);
        btrfs_drop_extent_cache(inode, 0, (u64)-1, 0);

        /*
         * We skip the throttling logic for free space cache inodes, so we don't
         * need to check for -EAGAIN.
         */
        ret = btrfs_truncate_inode_items(trans, root, &control);

        inode_sub_bytes(&inode->vfs_inode, control.sub_bytes);
        btrfs_inode_safe_disk_i_size_write(inode, control.last_size);

        unlock_extent_cached(&inode->io_tree, 0, (u64)-1, &cached_state);
        if (ret)
                goto fail;

        ret = btrfs_update_inode(trans, root, inode);

fail:
        if (locked)
                mutex_unlock(&trans->transaction->cache_write_mutex);
        if (ret)
                btrfs_abort_transaction(trans, ret);

        return ret;
}

static void readahead_cache(struct inode *inode)
{
        struct file_ra_state ra;
        unsigned long last_index;

        file_ra_state_init(&ra, inode->i_mapping);
        last_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;

        page_cache_sync_readahead(inode->i_mapping, &ra, NULL, 0, last_index);
}

static int io_ctl_init(struct btrfs_io_ctl *io_ctl, struct inode *inode,
                       int write)
{
        int num_pages;

        num_pages = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);

        /* Make sure we can fit our crcs and generation into the first page */
        if (write && (num_pages * sizeof(u32) + sizeof(u64)) > PAGE_SIZE)
                return -ENOSPC;

        memset(io_ctl, 0, sizeof(struct btrfs_io_ctl));

        io_ctl->pages = kcalloc(num_pages, sizeof(struct page *), GFP_NOFS);
        if (!io_ctl->pages)
                return -ENOMEM;

        io_ctl->num_pages = num_pages;
        io_ctl->fs_info = btrfs_sb(inode->i_sb);
        io_ctl->inode = inode;

        return 0;
}
ALLOW_ERROR_INJECTION(io_ctl_init, ERRNO);

static void io_ctl_free(struct btrfs_io_ctl *io_ctl)
{
        kfree(io_ctl->pages);
        io_ctl->pages = NULL;
}

static void io_ctl_unmap_page(struct btrfs_io_ctl *io_ctl)
{
        if (io_ctl->cur) {
                io_ctl->cur = NULL;
                io_ctl->orig = NULL;
        }
}

static void io_ctl_map_page(struct btrfs_io_ctl *io_ctl, int clear)
{
        ASSERT(io_ctl->index < io_ctl->num_pages);
        io_ctl->page = io_ctl->pages[io_ctl->index++];
        io_ctl->cur = page_address(io_ctl->page);
        io_ctl->orig = io_ctl->cur;
        io_ctl->size = PAGE_SIZE;
        if (clear)
                clear_page(io_ctl->cur);
}

static void io_ctl_drop_pages(struct btrfs_io_ctl *io_ctl)
{
        int i;

        io_ctl_unmap_page(io_ctl);

        for (i = 0; i < io_ctl->num_pages; i++) {
                if (io_ctl->pages[i]) {
                        btrfs_page_clear_checked(io_ctl->fs_info,
                                        io_ctl->pages[i],
                                        page_offset(io_ctl->pages[i]),
                                        PAGE_SIZE);
                        unlock_page(io_ctl->pages[i]);
                        put_page(io_ctl->pages[i]);
                }
        }
}

static int io_ctl_prepare_pages(struct btrfs_io_ctl *io_ctl, bool uptodate)
{
        struct page *page;
        struct inode *inode = io_ctl->inode;
        gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
        int i;

        for (i = 0; i < io_ctl->num_pages; i++) {
                int ret;

                page = find_or_create_page(inode->i_mapping, i, mask);
                if (!page) {
                        io_ctl_drop_pages(io_ctl);
                        return -ENOMEM;
                }

                ret = set_page_extent_mapped(page);
                if (ret < 0) {
                        unlock_page(page);
                        put_page(page);
                        io_ctl_drop_pages(io_ctl);
                        return ret;
                }

                io_ctl->pages[i] = page;
                if (uptodate && !PageUptodate(page)) {
                        btrfs_readpage(NULL, page);
                        lock_page(page);
                        if (page->mapping != inode->i_mapping) {
                                btrfs_err(BTRFS_I(inode)->root->fs_info,
                                          "free space cache page truncated");
                                io_ctl_drop_pages(io_ctl);
                                return -EIO;
                        }
                        if (!PageUptodate(page)) {
                                btrfs_err(BTRFS_I(inode)->root->fs_info,
                                           "error reading free space cache");
                                io_ctl_drop_pages(io_ctl);
                                return -EIO;
                        }
                }
        }

        for (i = 0; i < io_ctl->num_pages; i++)
                clear_page_dirty_for_io(io_ctl->pages[i]);

        return 0;
}

static void io_ctl_set_generation(struct btrfs_io_ctl *io_ctl, u64 generation)
{
        io_ctl_map_page(io_ctl, 1);

        /*
         * Skip the csum areas.  If we don't check crcs then we just have a
         * 64bit chunk at the front of the first page.
         */
        io_ctl->cur += (sizeof(u32) * io_ctl->num_pages);
        io_ctl->size -= sizeof(u64) + (sizeof(u32) * io_ctl->num_pages);

        put_unaligned_le64(generation, io_ctl->cur);
        io_ctl->cur += sizeof(u64);
}

static int io_ctl_check_generation(struct btrfs_io_ctl *io_ctl, u64 generation)
{
        u64 cache_gen;

        /*
         * Skip the crc area.  If we don't check crcs then we just have a 64bit
         * chunk at the front of the first page.
         */
        io_ctl->cur += sizeof(u32) * io_ctl->num_pages;
        io_ctl->size -= sizeof(u64) + (sizeof(u32) * io_ctl->num_pages);

        cache_gen = get_unaligned_le64(io_ctl->cur);
        if (cache_gen != generation) {
                btrfs_err_rl(io_ctl->fs_info,
                        "space cache generation (%llu) does not match inode (%llu)",
                                cache_gen, generation);
                io_ctl_unmap_page(io_ctl);
                return -EIO;
        }
        io_ctl->cur += sizeof(u64);
        return 0;
}

static void io_ctl_set_crc(struct btrfs_io_ctl *io_ctl, int index)
{
        u32 *tmp;
        u32 crc = ~(u32)0;
        unsigned offset = 0;

        if (index == 0)
                offset = sizeof(u32) * io_ctl->num_pages;

        crc = btrfs_crc32c(crc, io_ctl->orig + offset, PAGE_SIZE - offset);
        btrfs_crc32c_final(crc, (u8 *)&crc);
        io_ctl_unmap_page(io_ctl);
        tmp = page_address(io_ctl->pages[0]);
        tmp += index;
        *tmp = crc;
}

static int io_ctl_check_crc(struct btrfs_io_ctl *io_ctl, int index)
{
        u32 *tmp, val;
        u32 crc = ~(u32)0;
        unsigned offset = 0;

        if (index == 0)
                offset = sizeof(u32) * io_ctl->num_pages;

        tmp = page_address(io_ctl->pages[0]);
        tmp += index;
        val = *tmp;

        io_ctl_map_page(io_ctl, 0);
        crc = btrfs_crc32c(crc, io_ctl->orig + offset, PAGE_SIZE - offset);
        btrfs_crc32c_final(crc, (u8 *)&crc);
        if (val != crc) {
                btrfs_err_rl(io_ctl->fs_info,
                        "csum mismatch on free space cache");
                io_ctl_unmap_page(io_ctl);
                return -EIO;
        }

        return 0;
}

static int io_ctl_add_entry(struct btrfs_io_ctl *io_ctl, u64 offset, u64 bytes,
                            void *bitmap)
{
        struct btrfs_free_space_entry *entry;

        if (!io_ctl->cur)
                return -ENOSPC;

        entry = io_ctl->cur;
        put_unaligned_le64(offset, &entry->offset);
        put_unaligned_le64(bytes, &entry->bytes);
        entry->type = (bitmap) ? BTRFS_FREE_SPACE_BITMAP :
                BTRFS_FREE_SPACE_EXTENT;
        io_ctl->cur += sizeof(struct btrfs_free_space_entry);
        io_ctl->size -= sizeof(struct btrfs_free_space_entry);

        if (io_ctl->size >= sizeof(struct btrfs_free_space_entry))
                return 0;

        io_ctl_set_crc(io_ctl, io_ctl->index - 1);

        /* No more pages to map */
        if (io_ctl->index >= io_ctl->num_pages)
                return 0;

        /* map the next page */
        io_ctl_map_page(io_ctl, 1);
        return 0;
}

static int io_ctl_add_bitmap(struct btrfs_io_ctl *io_ctl, void *bitmap)
{
        if (!io_ctl->cur)
                return -ENOSPC;

        /*
         * If we aren't at the start of the current page, unmap this one and
         * map the next one if there is any left.
         */
        if (io_ctl->cur != io_ctl->orig) {
                io_ctl_set_crc(io_ctl, io_ctl->index - 1);
                if (io_ctl->index >= io_ctl->num_pages)
                        return -ENOSPC;
                io_ctl_map_page(io_ctl, 0);
        }

        copy_page(io_ctl->cur, bitmap);
        io_ctl_set_crc(io_ctl, io_ctl->index - 1);
        if (io_ctl->index < io_ctl->num_pages)
                io_ctl_map_page(io_ctl, 0);
        return 0;
}

static void io_ctl_zero_remaining_pages(struct btrfs_io_ctl *io_ctl)
{
        /*
         * If we're not on the boundary we know we've modified the page and we
         * need to crc the page.
         */
        if (io_ctl->cur != io_ctl->orig)
                io_ctl_set_crc(io_ctl, io_ctl->index - 1);
        else
                io_ctl_unmap_page(io_ctl);

        while (io_ctl->index < io_ctl->num_pages) {
                io_ctl_map_page(io_ctl, 1);
                io_ctl_set_crc(io_ctl, io_ctl->index - 1);
        }
}

static int io_ctl_read_entry(struct btrfs_io_ctl *io_ctl,
                            struct btrfs_free_space *entry, u8 *type)
{
        struct btrfs_free_space_entry *e;
        int ret;

        if (!io_ctl->cur) {
                ret = io_ctl_check_crc(io_ctl, io_ctl->index);
                if (ret)
                        return ret;
        }

        e = io_ctl->cur;
        entry->offset = get_unaligned_le64(&e->offset);
        entry->bytes = get_unaligned_le64(&e->bytes);
        *type = e->type;
        io_ctl->cur += sizeof(struct btrfs_free_space_entry);
        io_ctl->size -= sizeof(struct btrfs_free_space_entry);

        if (io_ctl->size >= sizeof(struct btrfs_free_space_entry))
                return 0;

        io_ctl_unmap_page(io_ctl);

        return 0;
}

static int io_ctl_read_bitmap(struct btrfs_io_ctl *io_ctl,
                              struct btrfs_free_space *entry)
{
        int ret;

        ret = io_ctl_check_crc(io_ctl, io_ctl->index);
        if (ret)
                return ret;

        copy_page(entry->bitmap, io_ctl->cur);
        io_ctl_unmap_page(io_ctl);

        return 0;
}

static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
{
        struct btrfs_block_group *block_group = ctl->block_group;
        u64 max_bytes;
        u64 bitmap_bytes;
        u64 extent_bytes;
        u64 size = block_group->length;
        u64 bytes_per_bg = BITS_PER_BITMAP * ctl->unit;
        u64 max_bitmaps = div64_u64(size + bytes_per_bg - 1, bytes_per_bg);

        max_bitmaps = max_t(u64, max_bitmaps, 1);

        ASSERT(ctl->total_bitmaps <= max_bitmaps);

        /*
         * We are trying to keep the total amount of memory used per 1GiB of
         * space to be MAX_CACHE_BYTES_PER_GIG.  However, with a reclamation
         * mechanism of pulling extents >= FORCE_EXTENT_THRESHOLD out of
         * bitmaps, we may end up using more memory than this.
         */
        if (size < SZ_1G)
                max_bytes = MAX_CACHE_BYTES_PER_GIG;
        else
                max_bytes = MAX_CACHE_BYTES_PER_GIG * div_u64(size, SZ_1G);

        bitmap_bytes = ctl->total_bitmaps * ctl->unit;

        /*
         * we want the extent entry threshold to always be at most 1/2 the max
         * bytes we can have, or whatever is less than that.
         */
        extent_bytes = max_bytes - bitmap_bytes;
        extent_bytes = min_t(u64, extent_bytes, max_bytes >> 1);

        ctl->extents_thresh =
                div_u64(extent_bytes, sizeof(struct btrfs_free_space));
}

static int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
                                   struct btrfs_free_space_ctl *ctl,
                                   struct btrfs_path *path, u64 offset)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_free_space_header *header;
        struct extent_buffer *leaf;
        struct btrfs_io_ctl io_ctl;
        struct btrfs_key key;
        struct btrfs_free_space *e, *n;
        LIST_HEAD(bitmaps);
        u64 num_entries;
        u64 num_bitmaps;
        u64 generation;
        u8 type;
        int ret = 0;

        /* Nothing in the space cache, goodbye */
        if (!i_size_read(inode))
                return 0;

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

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                return 0;
        else if (ret > 0) {
                btrfs_release_path(path);
                return 0;
        }

        ret = -1;

        leaf = path->nodes[0];
        header = btrfs_item_ptr(leaf, path->slots[0],
                                struct btrfs_free_space_header);
        num_entries = btrfs_free_space_entries(leaf, header);
        num_bitmaps = btrfs_free_space_bitmaps(leaf, header);
        generation = btrfs_free_space_generation(leaf, header);
        btrfs_release_path(path);

        if (!BTRFS_I(inode)->generation) {
                btrfs_info(fs_info,
                           "the free space cache file (%llu) is invalid, skip it",
                           offset);
                return 0;
        }

        if (BTRFS_I(inode)->generation != generation) {
                btrfs_err(fs_info,
                          "free space inode generation (%llu) did not match free space cache generation (%llu)",
                          BTRFS_I(inode)->generation, generation);
                return 0;
        }

        if (!num_entries)
                return 0;

        ret = io_ctl_init(&io_ctl, inode, 0);
        if (ret)
                return ret;

        readahead_cache(inode);

        ret = io_ctl_prepare_pages(&io_ctl, true);
        if (ret)
                goto out;

        ret = io_ctl_check_crc(&io_ctl, 0);
        if (ret)
                goto free_cache;

        ret = io_ctl_check_generation(&io_ctl, generation);
        if (ret)
                goto free_cache;

        while (num_entries) {
                e = kmem_cache_zalloc(btrfs_free_space_cachep,
                                      GFP_NOFS);
                if (!e) {
                        ret = -ENOMEM;
                        goto free_cache;
                }

                ret = io_ctl_read_entry(&io_ctl, e, &type);
                if (ret) {
                        kmem_cache_free(btrfs_free_space_cachep, e);
                        goto free_cache;
                }

                if (!e->bytes) {
                        ret = -1;
                        kmem_cache_free(btrfs_free_space_cachep, e);
                        goto free_cache;
                }

                if (type == BTRFS_FREE_SPACE_EXTENT) {
                        spin_lock(&ctl->tree_lock);
                        ret = link_free_space(ctl, e);
                        spin_unlock(&ctl->tree_lock);
                        if (ret) {
                                btrfs_err(fs_info,
                                        "Duplicate entries in free space cache, dumping");
                                kmem_cache_free(btrfs_free_space_cachep, e);
                                goto free_cache;
                        }
                } else {
                        ASSERT(num_bitmaps);
                        num_bitmaps--;
                        e->bitmap = kmem_cache_zalloc(
                                        btrfs_free_space_bitmap_cachep, GFP_NOFS);
                        if (!e->bitmap) {
                                ret = -ENOMEM;
                                kmem_cache_free(
                                        btrfs_free_space_cachep, e);
                                goto free_cache;
                        }
                        spin_lock(&ctl->tree_lock);
                        ret = link_free_space(ctl, e);
                        ctl->total_bitmaps++;
                        recalculate_thresholds(ctl);
                        spin_unlock(&ctl->tree_lock);
                        if (ret) {
                                btrfs_err(fs_info,
                                        "Duplicate entries in free space cache, dumping");
                                kmem_cache_free(btrfs_free_space_cachep, e);
                                goto free_cache;
                        }
                        list_add_tail(&e->list, &bitmaps);
                }

                num_entries--;
        }

        io_ctl_unmap_page(&io_ctl);

        /*
         * We add the bitmaps at the end of the entries in order that
         * the bitmap entries are added to the cache.
         */
        list_for_each_entry_safe(e, n, &bitmaps, list) {
                list_del_init(&e->list);
                ret = io_ctl_read_bitmap(&io_ctl, e);
                if (ret)
                        goto free_cache;
        }

        io_ctl_drop_pages(&io_ctl);
        ret = 1;
out:
        io_ctl_free(&io_ctl);
        return ret;
free_cache:
        io_ctl_drop_pages(&io_ctl);
        __btrfs_remove_free_space_cache(ctl);
        goto out;
}

static int copy_free_space_cache(struct btrfs_block_group *block_group,
                                 struct btrfs_free_space_ctl *ctl)
{
        struct btrfs_free_space *info;
        struct rb_node *n;
        int ret = 0;

        while (!ret && (n = rb_first(&ctl->free_space_offset)) != NULL) {
                info = rb_entry(n, struct btrfs_free_space, offset_index);
                if (!info->bitmap) {
                        unlink_free_space(ctl, info, true);
                        ret = btrfs_add_free_space(block_group, info->offset,
                                                   info->bytes);
                        kmem_cache_free(btrfs_free_space_cachep, info);
                } else {
                        u64 offset = info->offset;
                        u64 bytes = ctl->unit;

                        while (search_bitmap(ctl, info, &offset, &bytes,
                                             false) == 0) {
                                ret = btrfs_add_free_space(block_group, offset,
                                                           bytes);
                                if (ret)
                                        break;
                                bitmap_clear_bits(ctl, info, offset, bytes, true);
                                offset = info->offset;
                                bytes = ctl->unit;
                        }
                        free_bitmap(ctl, info);
                }
                cond_resched();
        }
        return ret;
}

int load_free_space_cache(struct btrfs_block_group *block_group)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
        struct btrfs_free_space_ctl tmp_ctl = {};
        struct inode *inode;
        struct btrfs_path *path;
        int ret = 0;
        bool matched;
        u64 used = block_group->used;

        /*
         * Because we could potentially discard our loaded free space, we want
         * to load everything into a temporary structure first, and then if it's
         * valid copy it all into the actual free space ctl.
         */
        btrfs_init_free_space_ctl(block_group, &tmp_ctl);

        /*
         * If this block group has been marked to be cleared for one reason or
         * another then we can't trust the on disk cache, so just return.
         */
        spin_lock(&block_group->lock);
        if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
                spin_unlock(&block_group->lock);
                return 0;
        }
        spin_unlock(&block_group->lock);

        path = btrfs_alloc_path();
        if (!path)
                return 0;
        path->search_commit_root = 1;
        path->skip_locking = 1;

        /*
         * We must pass a path with search_commit_root set to btrfs_iget in
         * order to avoid a deadlock when allocating extents for the tree root.
         *
         * When we are COWing an extent buffer from the tree root, when looking
         * for a free extent, at extent-tree.c:find_free_extent(), we can find
         * block group without its free space cache loaded. When we find one
         * we must load its space cache which requires reading its free space
         * cache's inode item from the root tree. If this inode item is located
         * in the same leaf that we started COWing before, then we end up in
         * deadlock on the extent buffer (trying to read lock it when we
         * previously write locked it).
         *
         * It's safe to read the inode item using the commit root because
         * block groups, once loaded, stay in memory forever (until they are
         * removed) as well as their space caches once loaded. New block groups
         * once created get their ->cached field set to BTRFS_CACHE_FINISHED so
         * we will never try to read their inode item while the fs is mounted.
         */
        inode = lookup_free_space_inode(block_group, path);
        if (IS_ERR(inode)) {
                btrfs_free_path(path);
                return 0;
        }

        /* We may have converted the inode and made the cache invalid. */
        spin_lock(&block_group->lock);
        if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
                spin_unlock(&block_group->lock);
                btrfs_free_path(path);
                goto out;
        }
        spin_unlock(&block_group->lock);

        ret = __load_free_space_cache(fs_info->tree_root, inode, &tmp_ctl,
                                      path, block_group->start);
        btrfs_free_path(path);
        if (ret <= 0)
                goto out;

        matched = (tmp_ctl.free_space == (block_group->length - used -
                                          block_group->bytes_super));

        if (matched) {
                ret = copy_free_space_cache(block_group, &tmp_ctl);
                /*
                 * ret == 1 means we successfully loaded the free space cache,
                 * so we need to re-set it here.
                 */

                if (ret == 0)
                        ret = 1;
        } else {
                __btrfs_remove_free_space_cache(&tmp_ctl);
                btrfs_warn(fs_info,
                           "block group %llu has wrong amount of free space",
                           block_group->start);
                ret = -1;
        }
out:
        if (ret < 0) {
                /* This cache is bogus, make sure it gets cleared */
                spin_lock(&block_group->lock);
                block_group->disk_cache_state = BTRFS_DC_CLEAR;
                spin_unlock(&block_group->lock);
                ret = 0;

                btrfs_warn(fs_info,
                           "failed to load free space cache for block group %llu, rebuilding it now",
                           block_group->start);
        }

        spin_lock(&ctl->tree_lock);
        btrfs_discard_update_discardable(block_group);
        spin_unlock(&ctl->tree_lock);
        iput(inode);
        return ret;
}

static noinline_for_stack
int write_cache_extent_entries(struct btrfs_io_ctl *io_ctl,
                              struct btrfs_free_space_ctl *ctl,
                              struct btrfs_block_group *block_group,
                              int *entries, int *bitmaps,
                              struct list_head *bitmap_list)
{
        int ret;
        struct btrfs_free_cluster *cluster = NULL;
        struct btrfs_free_cluster *cluster_locked = NULL;
        struct rb_node *node = rb_first(&ctl->free_space_offset);
        struct btrfs_trim_range *trim_entry;

        /* Get the cluster for this block_group if it exists */
        if (block_group && !list_empty(&block_group->cluster_list)) {
                cluster = list_entry(block_group->cluster_list.next,
                                     struct btrfs_free_cluster,
                                     block_group_list);
        }

        if (!node && cluster) {
                cluster_locked = cluster;
                spin_lock(&cluster_locked->lock);
                node = rb_first(&cluster->root);
                cluster = NULL;
        }

        /* Write out the extent entries */
        while (node) {
                struct btrfs_free_space *e;

                e = rb_entry(node, struct btrfs_free_space, offset_index);
                *entries += 1;

                ret = io_ctl_add_entry(io_ctl, e->offset, e->bytes,
                                       e->bitmap);
                if (ret)
                        goto fail;

                if (e->bitmap) {
                        list_add_tail(&e->list, bitmap_list);
                        *bitmaps += 1;
                }
                node = rb_next(node);
                if (!node && cluster) {
                        node = rb_first(&cluster->root);
                        cluster_locked = cluster;
                        spin_lock(&cluster_locked->lock);
                        cluster = NULL;
                }
        }
        if (cluster_locked) {
                spin_unlock(&cluster_locked->lock);
                cluster_locked = NULL;
        }

        /*
         * Make sure we don't miss any range that was removed from our rbtree
         * because trimming is running. Otherwise after a umount+mount (or crash
         * after committing the transaction) we would leak free space and get
         * an inconsistent free space cache report from fsck.
         */
        list_for_each_entry(trim_entry, &ctl->trimming_ranges, list) {
                ret = io_ctl_add_entry(io_ctl, trim_entry->start,
                                       trim_entry->bytes, NULL);
                if (ret)
                        goto fail;
                *entries += 1;
        }

        return 0;
fail:
        if (cluster_locked)
                spin_unlock(&cluster_locked->lock);
        return -ENOSPC;
}

static noinline_for_stack int
update_cache_item(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root,
                  struct inode *inode,
                  struct btrfs_path *path, u64 offset,
                  int entries, int bitmaps)
{
        struct btrfs_key key;
        struct btrfs_free_space_header *header;
        struct extent_buffer *leaf;
        int ret;

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

        ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
        if (ret < 0) {
                clear_extent_bit(&BTRFS_I(inode)->io_tree, 0, inode->i_size - 1,
                                 EXTENT_DELALLOC, 0, 0, NULL);
                goto fail;
        }
        leaf = path->nodes[0];
        if (ret > 0) {
                struct btrfs_key found_key;
                ASSERT(path->slots[0]);
                path->slots[0]--;
                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
                if (found_key.objectid != BTRFS_FREE_SPACE_OBJECTID ||
                    found_key.offset != offset) {
                        clear_extent_bit(&BTRFS_I(inode)->io_tree, 0,
                                         inode->i_size - 1, EXTENT_DELALLOC, 0,
                                         0, NULL);
                        btrfs_release_path(path);
                        goto fail;
                }
        }

        BTRFS_I(inode)->generation = trans->transid;
        header = btrfs_item_ptr(leaf, path->slots[0],
                                struct btrfs_free_space_header);
        btrfs_set_free_space_entries(leaf, header, entries);
        btrfs_set_free_space_bitmaps(leaf, header, bitmaps);
        btrfs_set_free_space_generation(leaf, header, trans->transid);
        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        return 0;

fail:
        return -1;
}

static noinline_for_stack int write_pinned_extent_entries(
                            struct btrfs_trans_handle *trans,
                            struct btrfs_block_group *block_group,
                            struct btrfs_io_ctl *io_ctl,
                            int *entries)
{
        u64 start, extent_start, extent_end, len;
        struct extent_io_tree *unpin = NULL;
        int ret;

        if (!block_group)
                return 0;

        /*
         * We want to add any pinned extents to our free space cache
         * so we don't leak the space
         *
         * We shouldn't have switched the pinned extents yet so this is the
         * right one
         */
        unpin = &trans->transaction->pinned_extents;

        start = block_group->start;

        while (start < block_group->start + block_group->length) {
                ret = find_first_extent_bit(unpin, start,
                                            &extent_start, &extent_end,
                                            EXTENT_DIRTY, NULL);
                if (ret)
                        return 0;

                /* This pinned extent is out of our range */
                if (extent_start >= block_group->start + block_group->length)
                        return 0;

                extent_start = max(extent_start, start);
                extent_end = min(block_group->start + block_group->length,
                                 extent_end + 1);
                len = extent_end - extent_start;

                *entries += 1;
                ret = io_ctl_add_entry(io_ctl, extent_start, len, NULL);
                if (ret)
                        return -ENOSPC;

                start = extent_end;
        }

        return 0;
}

static noinline_for_stack int
write_bitmap_entries(struct btrfs_io_ctl *io_ctl, struct list_head *bitmap_list)
{
        struct btrfs_free_space *entry, *next;
        int ret;

        /* Write out the bitmaps */
        list_for_each_entry_safe(entry, next, bitmap_list, list) {
                ret = io_ctl_add_bitmap(io_ctl, entry->bitmap);
                if (ret)
                        return -ENOSPC;
                list_del_init(&entry->list);
        }

        return 0;
}

static int flush_dirty_cache(struct inode *inode)
{
        int ret;

        ret = btrfs_wait_ordered_range(inode, 0, (u64)-1);
        if (ret)
                clear_extent_bit(&BTRFS_I(inode)->io_tree, 0, inode->i_size - 1,
                                 EXTENT_DELALLOC, 0, 0, NULL);

        return ret;
}

static void noinline_for_stack
cleanup_bitmap_list(struct list_head *bitmap_list)
{
        struct btrfs_free_space *entry, *next;

        list_for_each_entry_safe(entry, next, bitmap_list, list)
                list_del_init(&entry->list);
}

static void noinline_for_stack
cleanup_write_cache_enospc(struct inode *inode,
                           struct btrfs_io_ctl *io_ctl,
                           struct extent_state **cached_state)
{
        io_ctl_drop_pages(io_ctl);
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
                             i_size_read(inode) - 1, cached_state);
}

static int __btrfs_wait_cache_io(struct btrfs_root *root,
                                 struct btrfs_trans_handle *trans,
                                 struct btrfs_block_group *block_group,
                                 struct btrfs_io_ctl *io_ctl,
                                 struct btrfs_path *path, u64 offset)
{
        int ret;
        struct inode *inode = io_ctl->inode;

        if (!inode)
                return 0;

        /* Flush the dirty pages in the cache file. */
        ret = flush_dirty_cache(inode);
        if (ret)
                goto out;

        /* Update the cache item to tell everyone this cache file is valid. */
        ret = update_cache_item(trans, root, inode, path, offset,
                                io_ctl->entries, io_ctl->bitmaps);
out:
        if (ret) {
                invalidate_inode_pages2(inode->i_mapping);
                BTRFS_I(inode)->generation = 0;
                if (block_group)
                        btrfs_debug(root->fs_info,
          "failed to write free space cache for block group %llu error %d",
                                  block_group->start, ret);
        }
        btrfs_update_inode(trans, root, BTRFS_I(inode));

        if (block_group) {
                /* the dirty list is protected by the dirty_bgs_lock */
                spin_lock(&trans->transaction->dirty_bgs_lock);

                /* the disk_cache_state is protected by the block group lock */
                spin_lock(&block_group->lock);

                /*
                 * only mark this as written if we didn't get put back on
                 * the dirty list while waiting for IO.   Otherwise our
                 * cache state won't be right, and we won't get written again
                 */
                if (!ret && list_empty(&block_group->dirty_list))
                        block_group->disk_cache_state = BTRFS_DC_WRITTEN;
                else if (ret)
                        block_group->disk_cache_state = BTRFS_DC_ERROR;

                spin_unlock(&block_group->lock);
                spin_unlock(&trans->transaction->dirty_bgs_lock);
                io_ctl->inode = NULL;
                iput(inode);
        }

        return ret;

}

int btrfs_wait_cache_io(struct btrfs_trans_handle *trans,
                        struct btrfs_block_group *block_group,
                        struct btrfs_path *path)
{
        return __btrfs_wait_cache_io(block_group->fs_info->tree_root, trans,
                                     block_group, &block_group->io_ctl,
                                     path, block_group->start);
}

/**
 * Write out cached info to an inode
 *
 * @root:        root the inode belongs to
 * @inode:       freespace inode we are writing out
 * @ctl:         free space cache we are going to write out
 * @block_group: block_group for this cache if it belongs to a block_group
 * @io_ctl:      holds context for the io
 * @trans:       the trans handle
 *
 * This function writes out a free space cache struct to disk for quick recovery
 * on mount.  This will return 0 if it was successful in writing the cache out,
 * or an errno if it was not.
 */
static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
                                   struct btrfs_free_space_ctl *ctl,
                                   struct btrfs_block_group *block_group,
                                   struct btrfs_io_ctl *io_ctl,
                                   struct btrfs_trans_handle *trans)
{
        struct extent_state *cached_state = NULL;
        LIST_HEAD(bitmap_list);
        int entries = 0;
        int bitmaps = 0;
        int ret;
        int must_iput = 0;

        if (!i_size_read(inode))
                return -EIO;

        WARN_ON(io_ctl->pages);
        ret = io_ctl_init(io_ctl, inode, 1);
        if (ret)
                return ret;

        if (block_group && (block_group->flags & BTRFS_BLOCK_GROUP_DATA)) {
                down_write(&block_group->data_rwsem);
                spin_lock(&block_group->lock);
                if (block_group->delalloc_bytes) {
                        block_group->disk_cache_state = BTRFS_DC_WRITTEN;
                        spin_unlock(&block_group->lock);
                        up_write(&block_group->data_rwsem);
                        BTRFS_I(inode)->generation = 0;
                        ret = 0;
                        must_iput = 1;
                        goto out;
                }
                spin_unlock(&block_group->lock);
        }

        /* Lock all pages first so we can lock the extent safely. */
        ret = io_ctl_prepare_pages(io_ctl, false);
        if (ret)
                goto out_unlock;

        lock_extent_bits(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1,
                         &cached_state);

        io_ctl_set_generation(io_ctl, trans->transid);

        mutex_lock(&ctl->cache_writeout_mutex);
        /* Write out the extent entries in the free space cache */
        spin_lock(&ctl->tree_lock);
        ret = write_cache_extent_entries(io_ctl, ctl,
                                         block_group, &entries, &bitmaps,
                                         &bitmap_list);
        if (ret)
                goto out_nospc_locked;

        /*
         * Some spaces that are freed in the current transaction are pinned,
         * they will be added into free space cache after the transaction is
         * committed, we shouldn't lose them.
         *
         * If this changes while we are working we'll get added back to
         * the dirty list and redo it.  No locking needed
         */
        ret = write_pinned_extent_entries(trans, block_group, io_ctl, &entries);
        if (ret)
                goto out_nospc_locked;

        /*
         * At last, we write out all the bitmaps and keep cache_writeout_mutex
         * locked while doing it because a concurrent trim can be manipulating
         * or freeing the bitmap.
         */
        ret = write_bitmap_entries(io_ctl, &bitmap_list);
        spin_unlock(&ctl->tree_lock);
        mutex_unlock(&ctl->cache_writeout_mutex);
        if (ret)
                goto out_nospc;

        /* Zero out the rest of the pages just to make sure */
        io_ctl_zero_remaining_pages(io_ctl);

        /* Everything is written out, now we dirty the pages in the file. */
        ret = btrfs_dirty_pages(BTRFS_I(inode), io_ctl->pages,
                                io_ctl->num_pages, 0, i_size_read(inode),
                                &cached_state, false);
        if (ret)
                goto out_nospc;

        if (block_group && (block_group->flags & BTRFS_BLOCK_GROUP_DATA))
                up_write(&block_group->data_rwsem);
        /*
         * Release the pages and unlock the extent, we will flush
         * them out later
         */
        io_ctl_drop_pages(io_ctl);
        io_ctl_free(io_ctl);

        unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
                             i_size_read(inode) - 1, &cached_state);

        /*
         * at this point the pages are under IO and we're happy,
         * The caller is responsible for waiting on them and updating
         * the cache and the inode
         */
        io_ctl->entries = entries;
        io_ctl->bitmaps = bitmaps;

        ret = btrfs_fdatawrite_range(inode, 0, (u64)-1);
        if (ret)
                goto out;

        return 0;

out_nospc_locked:
        cleanup_bitmap_list(&bitmap_list);
        spin_unlock(&ctl->tree_lock);
        mutex_unlock(&ctl->cache_writeout_mutex);

out_nospc:
        cleanup_write_cache_enospc(inode, io_ctl, &cached_state);

out_unlock:
        if (block_group && (block_group->flags & BTRFS_BLOCK_GROUP_DATA))
                up_write(&block_group->data_rwsem);

out:
        io_ctl->inode = NULL;
        io_ctl_free(io_ctl);
        if (ret) {
                invalidate_inode_pages2(inode->i_mapping);
                BTRFS_I(inode)->generation = 0;
        }
        btrfs_update_inode(trans, root, BTRFS_I(inode));
        if (must_iput)
                iput(inode);
        return ret;
}

int btrfs_write_out_cache(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_free_space_ctl *ctl = block_group->free_space_ctl;
        struct inode *inode;
        int ret = 0;

        spin_lock(&block_group->lock);
        if (block_group->disk_cache_state < BTRFS_DC_SETUP) {
                spin_unlock(&block_group->lock);
                return 0;
        }
        spin_unlock(&block_group->lock);

        inode = lookup_free_space_inode(block_group, path);
        if (IS_ERR(inode))
                return 0;

        ret = __btrfs_write_out_cache(fs_info->tree_root, inode, ctl,
                                block_group, &block_group->io_ctl, trans);
        if (ret) {
                btrfs_debug(fs_info,
          "failed to write free space cache for block group %llu error %d",
                          block_group->start, ret);
                spin_lock(&block_group->lock);
                block_group->disk_cache_state = BTRFS_DC_ERROR;
                spin_unlock(&block_group->lock);

                block_group->io_ctl.inode = NULL;
                iput(inode);
        }

        /*
         * if ret == 0 the caller is expected to call btrfs_wait_cache_io
         * to wait for IO and put the inode
         */

        return ret;
}

static inline unsigned long offset_to_bit(u64 bitmap_start, u32 unit,
                                          u64 offset)
{
        ASSERT(offset >= bitmap_start);
        offset -= bitmap_start;
        return (unsigned long)(div_u64(offset, unit));
}

static inline unsigned long bytes_to_bits(u64 bytes, u32 unit)
{
        return (unsigned long)(div_u64(bytes, unit));
}

static inline u64 offset_to_bitmap(struct btrfs_free_space_ctl *ctl,
                                   u64 offset)
{
        u64 bitmap_start;
        u64 bytes_per_bitmap;

        bytes_per_bitmap = BITS_PER_BITMAP * ctl->unit;
        bitmap_start = offset - ctl->start;
        bitmap_start = div64_u64(bitmap_start, bytes_per_bitmap);
        bitmap_start *= bytes_per_bitmap;
        bitmap_start += ctl->start;

        return bitmap_start;
}

static int tree_insert_offset(struct rb_root *root, u64 offset,
                              struct rb_node *node, int bitmap)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct btrfs_free_space *info;

        while (*p) {
                parent = *p;
                info = rb_entry(parent, struct btrfs_free_space, offset_index);

                if (offset < info->offset) {
                        p = &(*p)->rb_left;
                } else if (offset > info->offset) {
                        p = &(*p)->rb_right;
                } else {
                        /*
                         * we could have a bitmap entry and an extent entry
                         * share the same offset.  If this is the case, we want
                         * the extent entry to always be found first if we do a
                         * linear search through the tree, since we want to have
                         * the quickest allocation time, and allocating from an
                         * extent is faster than allocating from a bitmap.  So
                         * if we're inserting a bitmap and we find an entry at
                         * this offset, we want to go right, or after this entry
                         * logically.  If we are inserting an extent and we've
                         * found a bitmap, we want to go left, or before
                         * logically.
                         */
                        if (bitmap) {
                                if (info->bitmap) {
                                        WARN_ON_ONCE(1);
                                        return -EEXIST;
                                }
                                p = &(*p)->rb_right;
                        } else {
                                if (!info->bitmap) {
                                        WARN_ON_ONCE(1);
                                        return -EEXIST;
                                }
                                p = &(*p)->rb_left;
                        }
                }
        }

        rb_link_node(node, parent, p);
        rb_insert_color(node, root);

        return 0;
}

/*
 * This is a little subtle.  We *only* have ->max_extent_size set if we actually
 * searched through the bitmap and figured out the largest ->max_extent_size,
 * otherwise it's 0.  In the case that it's 0 we don't want to tell the
 * allocator the wrong thing, we want to use the actual real max_extent_size
 * we've found already if it's larger, or we want to use ->bytes.
 *
 * This matters because find_free_space() will skip entries who's ->bytes is
 * less than the required bytes.  So if we didn't search down this bitmap, we
 * may pick some previous entry that has a smaller ->max_extent_size than we
 * have.  For example, assume we have two entries, one that has
 * ->max_extent_size set to 4K and ->bytes set to 1M.  A second entry hasn't set
 * ->max_extent_size yet, has ->bytes set to 8K and it's contiguous.  We will
 *  call into find_free_space(), and return with max_extent_size == 4K, because
 *  that first bitmap entry had ->max_extent_size set, but the second one did
 *  not.  If instead we returned 8K we'd come in searching for 8K, and find the
 *  8K contiguous range.
 *
 *  Consider the other case, we have 2 8K chunks in that second entry and still
 *  don't have ->max_extent_size set.  We'll return 16K, and the next time the
 *  allocator comes in it'll fully search our second bitmap, and this time it'll
 *  get an uptodate value of 8K as the maximum chunk size.  Then we'll get the
 *  right allocation the next loop through.
 */
static inline u64 get_max_extent_size(const struct btrfs_free_space *entry)
{
        if (entry->bitmap && entry->max_extent_size)
                return entry->max_extent_size;
        return entry->bytes;
}

/*
 * We want the largest entry to be leftmost, so this is inverted from what you'd
 * normally expect.
 */
static bool entry_less(struct rb_node *node, const struct rb_node *parent)
{
        const struct btrfs_free_space *entry, *exist;

        entry = rb_entry(node, struct btrfs_free_space, bytes_index);
        exist = rb_entry(parent, struct btrfs_free_space, bytes_index);
        return get_max_extent_size(exist) < get_max_extent_size(entry);
}

/*
 * searches the tree for the given offset.
 *
 * fuzzy - If this is set, then we are trying to make an allocation, and we just
 * want a section that has at least bytes size and comes at or after the given
 * offset.
 */
static struct btrfs_free_space *
tree_search_offset(struct btrfs_free_space_ctl *ctl,
                   u64 offset, int bitmap_only, int fuzzy)
{
        struct rb_node *n = ctl->free_space_offset.rb_node;
        struct btrfs_free_space *entry = NULL, *prev = NULL;

        /* find entry that is closest to the 'offset' */
        while (n) {
                entry = rb_entry(n, struct btrfs_free_space, offset_index);
                prev = entry;

                if (offset < entry->offset)
                        n = n->rb_left;
                else if (offset > entry->offset)
                        n = n->rb_right;
                else
                        break;

                entry = NULL;
        }

        if (bitmap_only) {
                if (!entry)
                        return NULL;
                if (entry->bitmap)
                        return entry;

                /*
                 * bitmap entry and extent entry may share same offset,
                 * in that case, bitmap entry comes after extent entry.
                 */
                n = rb_next(n);
                if (!n)
                        return NULL;
                entry = rb_entry(n, struct btrfs_free_space, offset_index);
                if (entry->offset != offset)
                        return NULL;

                WARN_ON(!entry->bitmap);
                return entry;
        } else if (entry) {
                if (entry->bitmap) {
                        /*
                         * if previous extent entry covers the offset,
                         * we should return it instead of the bitmap entry
                         */
                        n = rb_prev(&entry->offset_index);
                        if (n) {
                                prev = rb_entry(n, struct btrfs_free_space,
                                                offset_index);
                                if (!prev->bitmap &&
                                    prev->offset + prev->bytes > offset)
                                        entry = prev;
                        }
                }
                return entry;
        }

        if (!prev)
                return NULL;

        /* find last entry before the 'offset' */
        entry = prev;
        if (entry->offset > offset) {
                n = rb_prev(&entry->offset_index);
                if (n) {
                        entry = rb_entry(n, struct btrfs_free_space,
                                        offset_index);
                        ASSERT(entry->offset <= offset);
                } else {
                        if (fuzzy)
                                return entry;
                        else
                                return NULL;
                }
        }

        if (entry->bitmap) {
                n = rb_prev(&entry->offset_index);
                if (n) {
                        prev = rb_entry(n, struct btrfs_free_space,
                                        offset_index);
                        if (!prev->bitmap &&
                            prev->offset + prev->bytes > offset)
                                return prev;
                }
                if (entry->offset + BITS_PER_BITMAP * ctl->unit > offset)
                        return entry;
        } else if (entry->offset + entry->bytes > offset)
                return entry;

        if (!fuzzy)
                return NULL;

        while (1) {
                n = rb_next(&entry->offset_index);
                if (!n)
                        return NULL;
                entry = rb_entry(n, struct btrfs_free_space, offset_index);
                if (entry->bitmap) {
                        if (entry->offset + BITS_PER_BITMAP *
                            ctl->unit > offset)
                                break;
                } else {
                        if (entry->offset + entry->bytes > offset)
                                break;
                }
        }
        return entry;
}

static inline void unlink_free_space(struct btrfs_free_space_ctl *ctl,
                                     struct btrfs_free_space *info,
                                     bool update_stat)
{
        rb_erase(&info->offset_index, &ctl->free_space_offset);
        rb_erase_cached(&info->bytes_index, &ctl->free_space_bytes);
        ctl->free_extents--;

        if (!info->bitmap && !btrfs_free_space_trimmed(info)) {
                ctl->discardable_extents[BTRFS_STAT_CURR]--;
                ctl->discardable_bytes[BTRFS_STAT_CURR] -= info->bytes;
        }

        if (update_stat)
                ctl->free_space -= info->bytes;
}

static int link_free_space(struct btrfs_free_space_ctl *ctl,
                           struct btrfs_free_space *info)
{
        int ret = 0;

        ASSERT(info->bytes || info->bitmap);
        ret = tree_insert_offset(&ctl->free_space_offset, info->offset,
                                 &info->offset_index, (info->bitmap != NULL));
        if (ret)
                return ret;

        rb_add_cached(&info->bytes_index, &ctl->free_space_bytes, entry_less);

        if (!info->bitmap && !btrfs_free_space_trimmed(info)) {
                ctl->discardable_extents[BTRFS_STAT_CURR]++;
                ctl->discardable_bytes[BTRFS_STAT_CURR] += info->bytes;
        }

        ctl->free_space += info->bytes;
        ctl->free_extents++;
        return ret;
}

static void relink_bitmap_entry(struct btrfs_free_space_ctl *ctl,
                                struct btrfs_free_space *info)
{
        ASSERT(info->bitmap);

        /*
         * If our entry is empty it's because we're on a cluster and we don't
         * want to re-link it into our ctl bytes index.
         */
        if (RB_EMPTY_NODE(&info->bytes_index))
                return;

        rb_erase_cached(&info->bytes_index, &ctl->free_space_bytes);
        rb_add_cached(&info->bytes_index, &ctl->free_space_bytes, entry_less);
}

static inline void bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
                                     struct btrfs_free_space *info,
                                     u64 offset, u64 bytes, bool update_stat)
{
        unsigned long start, count, end;
        int extent_delta = -1;

        start = offset_to_bit(info->offset, ctl->unit, offset);
        count = bytes_to_bits(bytes, ctl->unit);
        end = start + count;
        ASSERT(end <= BITS_PER_BITMAP);

        bitmap_clear(info->bitmap, start, count);

        info->bytes -= bytes;
        if (info->max_extent_size > ctl->unit)
                info->max_extent_size = 0;

        relink_bitmap_entry(ctl, info);

        if (start && test_bit(start - 1, info->bitmap))
                extent_delta++;

        if (end < BITS_PER_BITMAP && test_bit(end, info->bitmap))
                extent_delta++;

        info->bitmap_extents += extent_delta;
        if (!btrfs_free_space_trimmed(info)) {
                ctl->discardable_extents[BTRFS_STAT_CURR] += extent_delta;
                ctl->discardable_bytes[BTRFS_STAT_CURR] -= bytes;
        }

        if (update_stat)
                ctl->free_space -= bytes;
}

static void bitmap_set_bits(struct btrfs_free_space_ctl *ctl,
                            struct btrfs_free_space *info, u64 offset,
                            u64 bytes)
{
        unsigned long start, count, end;
        int extent_delta = 1;

        start = offset_to_bit(info->offset, ctl->unit, offset);
        count = bytes_to_bits(bytes, ctl->unit);
        end = start + count;
        ASSERT(end <= BITS_PER_BITMAP);

        bitmap_set(info->bitmap, start, count);

        /*
         * We set some bytes, we have no idea what the max extent size is
         * anymore.
         */
        info->max_extent_size = 0;
        info->bytes += bytes;
        ctl->free_space += bytes;

        relink_bitmap_entry(ctl, info);

        if (start && test_bit(start - 1, info->bitmap))
                extent_delta--;

        if (end < BITS_PER_BITMAP && test_bit(end, info->bitmap))
                extent_delta--;

        info->bitmap_extents += extent_delta;
        if (!btrfs_free_space_trimmed(info)) {
                ctl->discardable_extents[BTRFS_STAT_CURR] += extent_delta;
                ctl->discardable_bytes[BTRFS_STAT_CURR] += bytes;
        }
}

/*
 * If we can not find suitable extent, we will use bytes to record
 * the size of the max extent.
 */
static int search_bitmap(struct btrfs_free_space_ctl *ctl,
                         struct btrfs_free_space *bitmap_info, u64 *offset,
                         u64 *bytes, bool for_alloc)
{
        unsigned long found_bits = 0;
        unsigned long max_bits = 0;
        unsigned long bits, i;
        unsigned long next_zero;
        unsigned long extent_bits;

        /*
         * Skip searching the bitmap if we don't have a contiguous section that
         * is large enough for this allocation.
         */
        if (for_alloc &&
            bitmap_info->max_extent_size &&
            bitmap_info->max_extent_size < *bytes) {
                *bytes = bitmap_info->max_extent_size;
                return -1;
        }

        i = offset_to_bit(bitmap_info->offset, ctl->unit,
                          max_t(u64, *offset, bitmap_info->offset));
        bits = bytes_to_bits(*bytes, ctl->unit);

        for_each_set_bit_from(i, bitmap_info->bitmap, BITS_PER_BITMAP) {
                if (for_alloc && bits == 1) {
                        found_bits = 1;
                        break;
                }
                next_zero = find_next_zero_bit(bitmap_info->bitmap,
                                               BITS_PER_BITMAP, i);
                extent_bits = next_zero - i;
                if (extent_bits >= bits) {
                        found_bits = extent_bits;
                        break;
                } else if (extent_bits > max_bits) {
                        max_bits = extent_bits;
                }
                i = next_zero;
        }

        if (found_bits) {
                *offset = (u64)(i * ctl->unit) + bitmap_info->offset;
                *bytes = (u64)(found_bits) * ctl->unit;
                return 0;
        }

        *bytes = (u64)(max_bits) * ctl->unit;
        bitmap_info->max_extent_size = *bytes;
        relink_bitmap_entry(ctl, bitmap_info);
        return -1;
}

/* Cache the size of the max extent in bytes */
static struct btrfs_free_space *
find_free_space(struct btrfs_free_space_ctl *ctl, u64 *offset, u64 *bytes,
                unsigned long align, u64 *max_extent_size, bool use_bytes_index)
{
        struct btrfs_free_space *entry;
        struct rb_node *node;
        u64 tmp;
        u64 align_off;
        int ret;

        if (!ctl->free_space_offset.rb_node)
                goto out;
again:
        if (use_bytes_index) {
                node = rb_first_cached(&ctl->free_space_bytes);
        } else {
                entry = tree_search_offset(ctl, offset_to_bitmap(ctl, *offset),
                                           0, 1);
                if (!entry)
                        goto out;
                node = &entry->offset_index;
        }

        for (; node; node = rb_next(node)) {
                if (use_bytes_index)
                        entry = rb_entry(node, struct btrfs_free_space,
                                         bytes_index);
                else
                        entry = rb_entry(node, struct btrfs_free_space,
                                         offset_index);

                /*
                 * If we are using the bytes index then all subsequent entries
                 * in this tree are going to be < bytes, so simply set the max
                 * extent size and exit the loop.
                 *
                 * If we're using the offset index then we need to keep going
                 * through the rest of the tree.
                 */
                if (entry->bytes < *bytes) {
                        *max_extent_size = max(get_max_extent_size(entry),
                                               *max_extent_size);
                        if (use_bytes_index)
                                break;
                        continue;
                }

                /* make sure the space returned is big enough
                 * to match our requested alignment
                 */

                if (*bytes >= align) {
                        tmp = entry->offset - ctl->start + align - 1;
                        tmp = div64_u64(tmp, align);
                        tmp = tmp * align + ctl->start;
                        align_off = tmp - entry->offset;
                } else {
                        align_off = 0;
                        tmp = entry->offset;
                }

                /*
                 * We don't break here if we're using the bytes index because we
                 * may have another entry that has the correct alignment that is
                 * the right size, so we don't want to miss that possibility.
                 * At worst this adds another loop through the logic, but if we
                 * broke here we could prematurely ENOSPC.
                 */
                if (entry->bytes < *bytes + align_off) {
                        *max_extent_size = max(get_max_extent_size(entry),
                                               *max_extent_size);
                        continue;
                }

                if (entry->bitmap) {
                        struct rb_node *old_next = rb_next(node);
                        u64 size = *bytes;

                        ret = search_bitmap(ctl, entry, &tmp, &size, true);
                        if (!ret) {
                                *offset = tmp;
                                *bytes = size;
                                return entry;
                        } else {
                                *max_extent_size =
                                        max(get_max_extent_size(entry),
                                            *max_extent_size);
                        }

                        /*
                         * The bitmap may have gotten re-arranged in the space
                         * index here because the max_extent_size may have been
                         * updated.  Start from the beginning again if this
                         * happened.
                         */
                        if (use_bytes_index && old_next != rb_next(node))
                                goto again;
                        continue;
                }

                *offset = tmp;
                *bytes = entry->bytes - align_off;
                return entry;
        }
out:
        return NULL;
}

static void add_new_bitmap(struct btrfs_free_space_ctl *ctl,
                           struct btrfs_free_space *info, u64 offset)
{
        info->offset = offset_to_bitmap(ctl, offset);
        info->bytes = 0;
        info->bitmap_extents = 0;
        INIT_LIST_HEAD(&info->list);
        link_free_space(ctl, info);
        ctl->total_bitmaps++;
        recalculate_thresholds(ctl);
}

static void free_bitmap(struct btrfs_free_space_ctl *ctl,
                        struct btrfs_free_space *bitmap_info)
{
        /*
         * Normally when this is called, the bitmap is completely empty. However,
         * if we are blowing up the free space cache for one reason or another
         * via __btrfs_remove_free_space_cache(), then it may not be freed and
         * we may leave stats on the table.
         */
        if (bitmap_info->bytes && !btrfs_free_space_trimmed(bitmap_info)) {
                ctl->discardable_extents[BTRFS_STAT_CURR] -=
                        bitmap_info->bitmap_extents;
                ctl->discardable_bytes[BTRFS_STAT_CURR] -= bitmap_info->bytes;

        }
        unlink_free_space(ctl, bitmap_info, true);
        kmem_cache_free(btrfs_free_space_bitmap_cachep, bitmap_info->bitmap);
        kmem_cache_free(btrfs_free_space_cachep, bitmap_info);
        ctl->total_bitmaps--;
        recalculate_thresholds(ctl);
}

static noinline int remove_from_bitmap(struct btrfs_free_space_ctl *ctl,
                              struct btrfs_free_space *bitmap_info,
                              u64 *offset, u64 *bytes)
{
        u64 end;
        u64 search_start, search_bytes;
        int ret;

again:
        end = bitmap_info->offset + (u64)(BITS_PER_BITMAP * ctl->unit) - 1;

        /*
         * We need to search for bits in this bitmap.  We could only cover some
         * of the extent in this bitmap thanks to how we add space, so we need
         * to search for as much as it as we can and clear that amount, and then
         * go searching for the next bit.
         */
        search_start = *offset;
        search_bytes = ctl->unit;
        search_bytes = min(search_bytes, end - search_start + 1);
        ret = search_bitmap(ctl, bitmap_info, &search_start, &search_bytes,
                            false);
        if (ret < 0 || search_start != *offset)
                return -EINVAL;

        /* We may have found more bits than what we need */
        search_bytes = min(search_bytes, *bytes);

        /* Cannot clear past the end of the bitmap */
        search_bytes = min(search_bytes, end - search_start + 1);

        bitmap_clear_bits(ctl, bitmap_info, search_start, search_bytes, true);
        *offset += search_bytes;
        *bytes -= search_bytes;

        if (*bytes) {
                struct rb_node *next = rb_next(&bitmap_info->offset_index);
                if (!bitmap_info->bytes)
                        free_bitmap(ctl, bitmap_info);

                /*
                 * no entry after this bitmap, but we still have bytes to
                 * remove, so something has gone wrong.
                 */
                if (!next)
                        return -EINVAL;

                bitmap_info = rb_entry(next, struct btrfs_free_space,
                                       offset_index);

                /*
                 * if the next entry isn't a bitmap we need to return to let the
                 * extent stuff do its work.
                 */
                if (!bitmap_info->bitmap)
                        return -EAGAIN;

                /*
                 * Ok the next item is a bitmap, but it may not actually hold
                 * the information for the rest of this free space stuff, so
                 * look for it, and if we don't find it return so we can try
                 * everything over again.
                 */
                search_start = *offset;
                search_bytes = ctl->unit;
                ret = search_bitmap(ctl, bitmap_info, &search_start,
                                    &search_bytes, false);
                if (ret < 0 || search_start != *offset)
                        return -EAGAIN;

                goto again;
        } else if (!bitmap_info->bytes)
                free_bitmap(ctl, bitmap_info);

        return 0;
}

static u64 add_bytes_to_bitmap(struct btrfs_free_space_ctl *ctl,
                               struct btrfs_free_space *info, u64 offset,
                               u64 bytes, enum btrfs_trim_state trim_state)
{
        u64 bytes_to_set = 0;
        u64 end;

        /*
         * This is a tradeoff to make bitmap trim state minimal.  We mark the
         * whole bitmap untrimmed if at any point we add untrimmed regions.
         */
        if (trim_state == BTRFS_TRIM_STATE_UNTRIMMED) {
                if (btrfs_free_space_trimmed(info)) {
                        ctl->discardable_extents[BTRFS_STAT_CURR] +=
                                info->bitmap_extents;
                        ctl->discardable_bytes[BTRFS_STAT_CURR] += info->bytes;
                }
                info->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
        }

        end = info->offset + (u64)(BITS_PER_BITMAP * ctl->unit);

        bytes_to_set = min(end - offset, bytes);

        bitmap_set_bits(ctl, info, offset, bytes_to_set);

        return bytes_to_set;

}

static bool use_bitmap(struct btrfs_free_space_ctl *ctl,
                      struct btrfs_free_space *info)
{
        struct btrfs_block_group *block_group = ctl->block_group;
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        bool forced = false;

#ifdef CONFIG_BTRFS_DEBUG
        if (btrfs_should_fragment_free_space(block_group))
                forced = true;
#endif

        /* This is a way to reclaim large regions from the bitmaps. */
        if (!forced && info->bytes >= FORCE_EXTENT_THRESHOLD)
                return false;

        /*
         * If we are below the extents threshold then we can add this as an
         * extent, and don't have to deal with the bitmap
         */
        if (!forced && ctl->free_extents < ctl->extents_thresh) {
                /*
                 * If this block group has some small extents we don't want to
                 * use up all of our free slots in the cache with them, we want
                 * to reserve them to larger extents, however if we have plenty
                 * of cache left then go ahead an dadd them, no sense in adding
                 * the overhead of a bitmap if we don't have to.
                 */
                if (info->bytes <= fs_info->sectorsize * 8) {
                        if (ctl->free_extents * 3 <= ctl->extents_thresh)
                                return false;
                } else {
                        return false;
                }
        }

        /*
         * The original block groups from mkfs can be really small, like 8
         * megabytes, so don't bother with a bitmap for those entries.  However
         * some block groups can be smaller than what a bitmap would cover but
         * are still large enough that they could overflow the 32k memory limit,
         * so allow those block groups to still be allowed to have a bitmap
         * entry.
         */
        if (((BITS_PER_BITMAP * ctl->unit) >> 1) > block_group->length)
                return false;

        return true;
}

static const struct btrfs_free_space_op free_space_op = {
        .use_bitmap             = use_bitmap,
};

static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl,
                              struct btrfs_free_space *info)
{
        struct btrfs_free_space *bitmap_info;
        struct btrfs_block_group *block_group = NULL;
        int added = 0;
        u64 bytes, offset, bytes_added;
        enum btrfs_trim_state trim_state;
        int ret;

        bytes = info->bytes;
        offset = info->offset;
        trim_state = info->trim_state;

        if (!ctl->op->use_bitmap(ctl, info))
                return 0;

        if (ctl->op == &free_space_op)
                block_group = ctl->block_group;
again:
        /*
         * Since we link bitmaps right into the cluster we need to see if we
         * have a cluster here, and if so and it has our bitmap we need to add
         * the free space to that bitmap.
         */
        if (block_group && !list_empty(&block_group->cluster_list)) {
                struct btrfs_free_cluster *cluster;
                struct rb_node *node;
                struct btrfs_free_space *entry;

                cluster = list_entry(block_group->cluster_list.next,
                                     struct btrfs_free_cluster,
                                     block_group_list);
                spin_lock(&cluster->lock);
                node = rb_first(&cluster->root);
                if (!node) {
                        spin_unlock(&cluster->lock);
                        goto no_cluster_bitmap;
                }

                entry = rb_entry(node, struct btrfs_free_space, offset_index);
                if (!entry->bitmap) {
                        spin_unlock(&cluster->lock);
                        goto no_cluster_bitmap;
                }

                if (entry->offset == offset_to_bitmap(ctl, offset)) {
                        bytes_added = add_bytes_to_bitmap(ctl, entry, offset,
                                                          bytes, trim_state);
                        bytes -= bytes_added;
                        offset += bytes_added;
                }
                spin_unlock(&cluster->lock);
                if (!bytes) {
                        ret = 1;
                        goto out;
                }
        }

no_cluster_bitmap:
        bitmap_info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                                         1, 0);
        if (!bitmap_info) {
                ASSERT(added == 0);
                goto new_bitmap;
        }

        bytes_added = add_bytes_to_bitmap(ctl, bitmap_info, offset, bytes,
                                          trim_state);
        bytes -= bytes_added;
        offset += bytes_added;
        added = 0;

        if (!bytes) {
                ret = 1;
                goto out;
        } else
                goto again;

new_bitmap:
        if (info && info->bitmap) {
                add_new_bitmap(ctl, info, offset);
                added = 1;
                info = NULL;
                goto again;
        } else {
                spin_unlock(&ctl->tree_lock);

                /* no pre-allocated info, allocate a new one */
                if (!info) {
                        info = kmem_cache_zalloc(btrfs_free_space_cachep,
                                                 GFP_NOFS);
                        if (!info) {
                                spin_lock(&ctl->tree_lock);
                                ret = -ENOMEM;
                                goto out;
                        }
                }

                /* allocate the bitmap */
                info->bitmap = kmem_cache_zalloc(btrfs_free_space_bitmap_cachep,
                                                 GFP_NOFS);
                info->trim_state = BTRFS_TRIM_STATE_TRIMMED;
                spin_lock(&ctl->tree_lock);
                if (!info->bitmap) {
                        ret = -ENOMEM;
                        goto out;
                }
                goto again;
        }

out:
        if (info) {
                if (info->bitmap)
                        kmem_cache_free(btrfs_free_space_bitmap_cachep,
                                        info->bitmap);
                kmem_cache_free(btrfs_free_space_cachep, info);
        }

        return ret;
}

/*
 * Free space merging rules:
 *  1) Merge trimmed areas together
 *  2) Let untrimmed areas coalesce with trimmed areas
 *  3) Always pull neighboring regions from bitmaps
 *
 * The above rules are for when we merge free space based on btrfs_trim_state.
 * Rules 2 and 3 are subtle because they are suboptimal, but are done for the
 * same reason: to promote larger extent regions which makes life easier for
 * find_free_extent().  Rule 2 enables coalescing based on the common path
 * being returning free space from btrfs_finish_extent_commit().  So when free
 * space is trimmed, it will prevent aggregating trimmed new region and
 * untrimmed regions in the rb_tree.  Rule 3 is purely to obtain larger extents
 * and provide find_free_extent() with the largest extents possible hoping for
 * the reuse path.
 */
static bool try_merge_free_space(struct btrfs_free_space_ctl *ctl,
                          struct btrfs_free_space *info, bool update_stat)
{
        struct btrfs_free_space *left_info = NULL;
        struct btrfs_free_space *right_info;
        bool merged = false;
        u64 offset = info->offset;
        u64 bytes = info->bytes;
        const bool is_trimmed = btrfs_free_space_trimmed(info);

        /*
         * first we want to see if there is free space adjacent to the range we
         * are adding, if there is remove that struct and add a new one to
         * cover the entire range
         */
        right_info = tree_search_offset(ctl, offset + bytes, 0, 0);
        if (right_info && rb_prev(&right_info->offset_index))
                left_info = rb_entry(rb_prev(&right_info->offset_index),
                                     struct btrfs_free_space, offset_index);
        else if (!right_info)
                left_info = tree_search_offset(ctl, offset - 1, 0, 0);

        /* See try_merge_free_space() comment. */
        if (right_info && !right_info->bitmap &&
            (!is_trimmed || btrfs_free_space_trimmed(right_info))) {
                unlink_free_space(ctl, right_info, update_stat);
                info->bytes += right_info->bytes;
                kmem_cache_free(btrfs_free_space_cachep, right_info);
                merged = true;
        }

        /* See try_merge_free_space() comment. */
        if (left_info && !left_info->bitmap &&
            left_info->offset + left_info->bytes == offset &&
            (!is_trimmed || btrfs_free_space_trimmed(left_info))) {
                unlink_free_space(ctl, left_info, update_stat);
                info->offset = left_info->offset;
                info->bytes += left_info->bytes;
                kmem_cache_free(btrfs_free_space_cachep, left_info);
                merged = true;
        }

        return merged;
}

static bool steal_from_bitmap_to_end(struct btrfs_free_space_ctl *ctl,
                                     struct btrfs_free_space *info,
                                     bool update_stat)
{
        struct btrfs_free_space *bitmap;
        unsigned long i;
        unsigned long j;
        const u64 end = info->offset + info->bytes;
        const u64 bitmap_offset = offset_to_bitmap(ctl, end);
        u64 bytes;

        bitmap = tree_search_offset(ctl, bitmap_offset, 1, 0);
        if (!bitmap)
                return false;

        i = offset_to_bit(bitmap->offset, ctl->unit, end);
        j = find_next_zero_bit(bitmap->bitmap, BITS_PER_BITMAP, i);
        if (j == i)
                return false;
        bytes = (j - i) * ctl->unit;
        info->bytes += bytes;

        /* See try_merge_free_space() comment. */
        if (!btrfs_free_space_trimmed(bitmap))
                info->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;

        bitmap_clear_bits(ctl, bitmap, end, bytes, update_stat);

        if (!bitmap->bytes)
                free_bitmap(ctl, bitmap);

        return true;
}

static bool steal_from_bitmap_to_front(struct btrfs_free_space_ctl *ctl,
                                       struct btrfs_free_space *info,
                                       bool update_stat)
{
        struct btrfs_free_space *bitmap;
        u64 bitmap_offset;
        unsigned long i;
        unsigned long j;
        unsigned long prev_j;
        u64 bytes;

        bitmap_offset = offset_to_bitmap(ctl, info->offset);
        /* If we're on a boundary, try the previous logical bitmap. */
        if (bitmap_offset == info->offset) {
                if (info->offset == 0)
                        return false;
                bitmap_offset = offset_to_bitmap(ctl, info->offset - 1);
        }

        bitmap = tree_search_offset(ctl, bitmap_offset, 1, 0);
        if (!bitmap)
                return false;

        i = offset_to_bit(bitmap->offset, ctl->unit, info->offset) - 1;
        j = 0;
        prev_j = (unsigned long)-1;
        for_each_clear_bit_from(j, bitmap->bitmap, BITS_PER_BITMAP) {
                if (j > i)
                        break;
                prev_j = j;
        }
        if (prev_j == i)
                return false;

        if (prev_j == (unsigned long)-1)
                bytes = (i + 1) * ctl->unit;
        else
                bytes = (i - prev_j) * ctl->unit;

        info->offset -= bytes;
        info->bytes += bytes;

        /* See try_merge_free_space() comment. */
        if (!btrfs_free_space_trimmed(bitmap))
                info->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;

        bitmap_clear_bits(ctl, bitmap, info->offset, bytes, update_stat);

        if (!bitmap->bytes)
                free_bitmap(ctl, bitmap);

        return true;
}

/*
 * We prefer always to allocate from extent entries, both for clustered and
 * non-clustered allocation requests. So when attempting to add a new extent
 * entry, try to see if there's adjacent free space in bitmap entries, and if
 * there is, migrate that space from the bitmaps to the extent.
 * Like this we get better chances of satisfying space allocation requests
 * because we attempt to satisfy them based on a single cache entry, and never
 * on 2 or more entries - even if the entries represent a contiguous free space
 * region (e.g. 1 extent entry + 1 bitmap entry starting where the extent entry
 * ends).
 */
static void steal_from_bitmap(struct btrfs_free_space_ctl *ctl,
                              struct btrfs_free_space *info,
                              bool update_stat)
{
        /*
         * Only work with disconnected entries, as we can change their offset,
         * and must be extent entries.
         */
        ASSERT(!info->bitmap);
        ASSERT(RB_EMPTY_NODE(&info->offset_index));

        if (ctl->total_bitmaps > 0) {
                bool stole_end;
                bool stole_front = false;

                stole_end = steal_from_bitmap_to_end(ctl, info, update_stat);
                if (ctl->total_bitmaps > 0)
                        stole_front = steal_from_bitmap_to_front(ctl, info,
                                                                 update_stat);

                if (stole_end || stole_front)
                        try_merge_free_space(ctl, info, update_stat);
        }
}

int __btrfs_add_free_space(struct btrfs_block_group *block_group,
                           u64 offset, u64 bytes,
                           enum btrfs_trim_state trim_state)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
        struct btrfs_free_space *info;
        int ret = 0;
        u64 filter_bytes = bytes;

        ASSERT(!btrfs_is_zoned(fs_info));

        info = kmem_cache_zalloc(btrfs_free_space_cachep, GFP_NOFS);
        if (!info)
                return -ENOMEM;

        info->offset = offset;
        info->bytes = bytes;
        info->trim_state = trim_state;
        RB_CLEAR_NODE(&info->offset_index);
        RB_CLEAR_NODE(&info->bytes_index);

        spin_lock(&ctl->tree_lock);

        if (try_merge_free_space(ctl, info, true))
                goto link;

        /*
         * There was no extent directly to the left or right of this new
         * extent then we know we're going to have to allocate a new extent, so
         * before we do that see if we need to drop this into a bitmap
         */
        ret = insert_into_bitmap(ctl, info);
        if (ret < 0) {
                goto out;
        } else if (ret) {
                ret = 0;
                goto out;
        }
link:
        /*
         * Only steal free space from adjacent bitmaps if we're sure we're not
         * going to add the new free space to existing bitmap entries - because
         * that would mean unnecessary work that would be reverted. Therefore
         * attempt to steal space from bitmaps if we're adding an extent entry.
         */
        steal_from_bitmap(ctl, info, true);

        filter_bytes = max(filter_bytes, info->bytes);

        ret = link_free_space(ctl, info);
        if (ret)
                kmem_cache_free(btrfs_free_space_cachep, info);
out:
        btrfs_discard_update_discardable(block_group);
        spin_unlock(&ctl->tree_lock);

        if (ret) {
                btrfs_crit(fs_info, "unable to add free space :%d", ret);
                ASSERT(ret != -EEXIST);
        }

        if (trim_state != BTRFS_TRIM_STATE_TRIMMED) {
                btrfs_discard_check_filter(block_group, filter_bytes);
                btrfs_discard_queue_work(&fs_info->discard_ctl, block_group);
        }

        return ret;
}

static int __btrfs_add_free_space_zoned(struct btrfs_block_group *block_group,
                                        u64 bytenr, u64 size, bool used)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
        u64 offset = bytenr - block_group->start;
        u64 to_free, to_unusable;
        const int bg_reclaim_threshold = READ_ONCE(fs_info->bg_reclaim_threshold);
        bool initial = (size == block_group->length);
        u64 reclaimable_unusable;

        WARN_ON(!initial && offset + size > block_group->zone_capacity);

        spin_lock(&ctl->tree_lock);
        if (!used)
                to_free = size;
        else if (initial)
                to_free = block_group->zone_capacity;
        else if (offset >= block_group->alloc_offset)
                to_free = size;
        else if (offset + size <= block_group->alloc_offset)
                to_free = 0;
        else
                to_free = offset + size - block_group->alloc_offset;
        to_unusable = size - to_free;

        ctl->free_space += to_free;
        /*
         * If the block group is read-only, we should account freed space into
         * bytes_readonly.
         */
        if (!block_group->ro)
                block_group->zone_unusable += to_unusable;
        spin_unlock(&ctl->tree_lock);
        if (!used) {
                spin_lock(&block_group->lock);
                block_group->alloc_offset -= size;
                spin_unlock(&block_group->lock);
        }

        reclaimable_unusable = block_group->zone_unusable -
                               (block_group->length - block_group->zone_capacity);
        /* All the region is now unusable. Mark it as unused and reclaim */
        if (block_group->zone_unusable == block_group->length) {
                btrfs_mark_bg_unused(block_group);
        } else if (bg_reclaim_threshold &&
                   reclaimable_unusable >=
                   div_factor_fine(block_group->zone_capacity,
                                   bg_reclaim_threshold)) {
                btrfs_mark_bg_to_reclaim(block_group);
        }

        return 0;
}

int btrfs_add_free_space(struct btrfs_block_group *block_group,
                         u64 bytenr, u64 size)
{
        enum btrfs_trim_state trim_state = BTRFS_TRIM_STATE_UNTRIMMED;

        if (btrfs_is_zoned(block_group->fs_info))
                return __btrfs_add_free_space_zoned(block_group, bytenr, size,
                                                    true);

        if (btrfs_test_opt(block_group->fs_info, DISCARD_SYNC))
                trim_state = BTRFS_TRIM_STATE_TRIMMED;

        return __btrfs_add_free_space(block_group, bytenr, size, trim_state);
}

int btrfs_add_free_space_unused(struct btrfs_block_group *block_group,
                                u64 bytenr, u64 size)
{
        if (btrfs_is_zoned(block_group->fs_info))
                return __btrfs_add_free_space_zoned(block_group, bytenr, size,
                                                    false);

        return btrfs_add_free_space(block_group, bytenr, size);
}

/*
 * This is a subtle distinction because when adding free space back in general,
 * we want it to be added as untrimmed for async. But in the case where we add
 * it on loading of a block group, we want to consider it trimmed.
 */
int btrfs_add_free_space_async_trimmed(struct btrfs_block_group *block_group,
                                       u64 bytenr, u64 size)
{
        enum btrfs_trim_state trim_state = BTRFS_TRIM_STATE_UNTRIMMED;

        if (btrfs_is_zoned(block_group->fs_info))
                return __btrfs_add_free_space_zoned(block_group, bytenr, size,
                                                    true);

        if (btrfs_test_opt(block_group->fs_info, DISCARD_SYNC) ||
            btrfs_test_opt(block_group->fs_info, DISCARD_ASYNC))
                trim_state = BTRFS_TRIM_STATE_TRIMMED;

        return __btrfs_add_free_space(block_group, bytenr, size, trim_state);
}

int btrfs_remove_free_space(struct btrfs_block_group *block_group,
                            u64 offset, u64 bytes)
{
        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
        struct btrfs_free_space *info;
        int ret;
        bool re_search = false;

        if (btrfs_is_zoned(block_group->fs_info)) {
                /*
                 * This can happen with conventional zones when replaying log.
                 * Since the allocation info of tree-log nodes are not recorded
                 * to the extent-tree, calculate_alloc_pointer() failed to
                 * advance the allocation pointer after last allocated tree log
                 * node blocks.
                 *
                 * This function is called from
                 * btrfs_pin_extent_for_log_replay() when replaying the log.
                 * Advance the pointer not to overwrite the tree-log nodes.
                 */
                if (block_group->start + block_group->alloc_offset <
                    offset + bytes) {
                        block_group->alloc_offset =
                                offset + bytes - block_group->start;
                }
                return 0;
        }

        spin_lock(&ctl->tree_lock);

again:
        ret = 0;
        if (!bytes)
                goto out_lock;

        info = tree_search_offset(ctl, offset, 0, 0);
        if (!info) {
                /*
                 * oops didn't find an extent that matched the space we wanted
                 * to remove, look for a bitmap instead
                 */
                info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                                          1, 0);
                if (!info) {
                        /*
                         * If we found a partial bit of our free space in a
                         * bitmap but then couldn't find the other part this may
                         * be a problem, so WARN about it.
                         */
                        WARN_ON(re_search);
                        goto out_lock;
                }
        }

        re_search = false;
        if (!info->bitmap) {
                unlink_free_space(ctl, info, true);
                if (offset == info->offset) {
                        u64 to_free = min(bytes, info->bytes);

                        info->bytes -= to_free;
                        info->offset += to_free;
                        if (info->bytes) {
                                ret = link_free_space(ctl, info);
                                WARN_ON(ret);
                        } else {
                                kmem_cache_free(btrfs_free_space_cachep, info);
                        }

                        offset += to_free;
                        bytes -= to_free;
                        goto again;
                } else {
                        u64 old_end = info->bytes + info->offset;

                        info->bytes = offset - info->offset;
                        ret = link_free_space(ctl, info);
                        WARN_ON(ret);
                        if (ret)
                                goto out_lock;

                        /* Not enough bytes in this entry to satisfy us */
                        if (old_end < offset + bytes) {
                                bytes -= old_end - offset;
                                offset = old_end;
                                goto again;
                        } else if (old_end == offset + bytes) {
                                /* all done */
                                goto out_lock;
                        }
                        spin_unlock(&ctl->tree_lock);

                        ret = __btrfs_add_free_space(block_group,
                                                     offset + bytes,
                                                     old_end - (offset + bytes),
                                                     info->trim_state);
                        WARN_ON(ret);
                        goto out;
                }
        }

        ret = remove_from_bitmap(ctl, info, &offset, &bytes);
        if (ret == -EAGAIN) {
                re_search = true;
                goto again;
        }
out_lock:
        btrfs_discard_update_discardable(block_group);
        spin_unlock(&ctl->tree_lock);
out:
        return ret;
}

void btrfs_dump_free_space(struct btrfs_block_group *block_group,
                           u64 bytes)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
        struct btrfs_free_space *info;
        struct rb_node *n;
        int count = 0;

        /*
         * Zoned btrfs does not use free space tree and cluster. Just print
         * out the free space after the allocation offset.
         */
        if (btrfs_is_zoned(fs_info)) {
                btrfs_info(fs_info, "free space %llu active %d",
                           block_group->zone_capacity - block_group->alloc_offset,
                           block_group->zone_is_active);
                return;
        }

        spin_lock(&ctl->tree_lock);
        for (n = rb_first(&ctl->free_space_offset); n; n = rb_next(n)) {
                info = rb_entry(n, struct btrfs_free_space, offset_index);
                if (info->bytes >= bytes && !block_group->ro)
                        count++;
                btrfs_crit(fs_info, "entry offset %llu, bytes %llu, bitmap %s",
                           info->offset, info->bytes,
                       (info->bitmap) ? "yes" : "no");
        }
        spin_unlock(&ctl->tree_lock);
        btrfs_info(fs_info, "block group has cluster?: %s",
               list_empty(&block_group->cluster_list) ? "no" : "yes");
        btrfs_info(fs_info,
                   "%d blocks of free space at or bigger than bytes is", count);
}

void btrfs_init_free_space_ctl(struct btrfs_block_group *block_group,
                               struct btrfs_free_space_ctl *ctl)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;

        spin_lock_init(&ctl->tree_lock);
        ctl->unit = fs_info->sectorsize;
        ctl->start = block_group->start;
        ctl->block_group = block_group;
        ctl->op = &free_space_op;
        ctl->free_space_bytes = RB_ROOT_CACHED;
        INIT_LIST_HEAD(&ctl->trimming_ranges);
        mutex_init(&ctl->cache_writeout_mutex);

        /*
         * we only want to have 32k of ram per block group for keeping
         * track of free space, and if we pass 1/2 of that we want to
         * start converting things over to using bitmaps
         */
        ctl->extents_thresh = (SZ_32K / 2) / sizeof(struct btrfs_free_space);
}

/*
 * for a given cluster, put all of its extents back into the free
 * space cache.  If the block group passed doesn't match the block group
 * pointed to by the cluster, someone else raced in and freed the
 * cluster already.  In that case, we just return without changing anything
 */
static void __btrfs_return_cluster_to_free_space(
                             struct btrfs_block_group *block_group,
                             struct btrfs_free_cluster *cluster)
{
        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
        struct btrfs_free_space *entry;
        struct rb_node *node;

        spin_lock(&cluster->lock);
        if (cluster->block_group != block_group) {
                spin_unlock(&cluster->lock);
                return;
        }

        cluster->block_group = NULL;
        cluster->window_start = 0;
        list_del_init(&cluster->block_group_list);

        node = rb_first(&cluster->root);
        while (node) {
                bool bitmap;

                entry = rb_entry(node, struct btrfs_free_space, offset_index);
                node = rb_next(&entry->offset_index);
                rb_erase(&entry->offset_index, &cluster->root);
                RB_CLEAR_NODE(&entry->offset_index);

                bitmap = (entry->bitmap != NULL);
                if (!bitmap) {
                        /* Merging treats extents as if they were new */
                        if (!btrfs_free_space_trimmed(entry)) {
                                ctl->discardable_extents[BTRFS_STAT_CURR]--;
                                ctl->discardable_bytes[BTRFS_STAT_CURR] -=
                                        entry->bytes;
                        }

                        try_merge_free_space(ctl, entry, false);
                        steal_from_bitmap(ctl, entry, false);

                        /* As we insert directly, update these statistics */
                        if (!btrfs_free_space_trimmed(entry)) {
                                ctl->discardable_extents[BTRFS_STAT_CURR]++;
                                ctl->discardable_bytes[BTRFS_STAT_CURR] +=
                                        entry->bytes;
                        }
                }
                tree_insert_offset(&ctl->free_space_offset,
                                   entry->offset, &entry->offset_index, bitmap);
                rb_add_cached(&entry->bytes_index, &ctl->free_space_bytes,
                              entry_less);
        }
        cluster->root = RB_ROOT;
        spin_unlock(&cluster->lock);
        btrfs_put_block_group(block_group);
}

static void __btrfs_remove_free_space_cache_locked(
                                struct btrfs_free_space_ctl *ctl)
{
        struct btrfs_free_space *info;
        struct rb_node *node;

        while ((node = rb_last(&ctl->free_space_offset)) != NULL) {
                info = rb_entry(node, struct btrfs_free_space, offset_index);
                if (!info->bitmap) {
                        unlink_free_space(ctl, info, true);
                        kmem_cache_free(btrfs_free_space_cachep, info);
                } else {
                        free_bitmap(ctl, info);
                }

                cond_resched_lock(&ctl->tree_lock);
        }
}

void __btrfs_remove_free_space_cache(struct btrfs_free_space_ctl *ctl)
{
        spin_lock(&ctl->tree_lock);
        __btrfs_remove_free_space_cache_locked(ctl);
        if (ctl->block_group)
                btrfs_discard_update_discardable(ctl->block_group);
        spin_unlock(&ctl->tree_lock);
}

void btrfs_remove_free_space_cache(struct btrfs_block_group *block_group)
{
        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
        struct btrfs_free_cluster *cluster;
        struct list_head *head;

        spin_lock(&ctl->tree_lock);
        while ((head = block_group->cluster_list.next) !=
               &block_group->cluster_list) {