/*
 * Copyright (C) 2008 Red Hat.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/pagemap.h>
#include <linux/sched.h>
#include <linux/math64.h>
#include "ctree.h"
#include "free-space-cache.h"
#include "transaction.h"

#define BITS_PER_BITMAP         (PAGE_CACHE_SIZE * 8)
#define MAX_CACHE_BYTES_PER_GIG (32 * 1024)

static inline unsigned long offset_to_bit(u64 bitmap_start, u64 sectorsize,
                                          u64 offset)
{
        BUG_ON(offset < bitmap_start);
        offset -= bitmap_start;
        return (unsigned long)(div64_u64(offset, sectorsize));
}

static inline unsigned long bytes_to_bits(u64 bytes, u64 sectorsize)
{
        return (unsigned long)(div64_u64(bytes, sectorsize));
}

static inline u64 offset_to_bitmap(struct btrfs_block_group_cache *block_group,
                                   u64 offset)
{
        u64 bitmap_start;
        u64 bytes_per_bitmap;

        bytes_per_bitmap = BITS_PER_BITMAP * block_group->sectorsize;
        bitmap_start = offset - block_group->key.objectid;
        bitmap_start = div64_u64(bitmap_start, bytes_per_bitmap);
        bitmap_start *= bytes_per_bitmap;
        bitmap_start += block_group->key.objectid;

        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) {
                                WARN_ON(info->bitmap);
                                p = &(*p)->rb_right;
                        } else {
                                WARN_ON(!info->bitmap);
                                p = &(*p)->rb_left;
                        }
                }
        }

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

        return 0;
}

/*
 * 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_block_group_cache *block_group,
                   u64 offset, int bitmap_only, int fuzzy)
{
        struct rb_node *n = block_group->free_space_offset.rb_node;
        struct btrfs_free_space *entry, *prev = NULL;

        /* find entry that is closest to the 'offset' */
        while (1) {
                if (!n) {
                        entry = NULL;
                        break;
                }

                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;
        }

        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 = &entry->offset_index;
                        while (1) {
                                n = rb_prev(n);
                                if (!n)
                                        break;
                                prev = rb_entry(n, struct btrfs_free_space,
                                                offset_index);
                                if (!prev->bitmap) {
                                        if (prev->offset + prev->bytes > offset)
                                                entry = prev;
                                        break;
                                }
                        }
                }
                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);
                        BUG_ON(entry->offset > offset);
                } else {
                        if (fuzzy)
                                return entry;
                        else
                                return NULL;
                }
        }

        if (entry->bitmap) {
                n = &entry->offset_index;
                while (1) {
                        n = rb_prev(n);
                        if (!n)
                                break;
                        prev = rb_entry(n, struct btrfs_free_space,
                                        offset_index);
                        if (!prev->bitmap) {
                                if (prev->offset + prev->bytes > offset)
                                        return prev;
                                break;
                        }
                }
                if (entry->offset + BITS_PER_BITMAP *
                    block_group->sectorsize > offset)
                        return entry;
        } else if (entry->offset + entry->bytes > offset)
                return entry;

        if (!fuzzy)
                return NULL;

        while (1) {
                if (entry->bitmap) {
                        if (entry->offset + BITS_PER_BITMAP *
                            block_group->sectorsize > offset)
                                break;
                } else {
                        if (entry->offset + entry->bytes > offset)
                                break;
                }

                n = rb_next(&entry->offset_index);
                if (!n)
                        return NULL;
                entry = rb_entry(n, struct btrfs_free_space, offset_index);
        }
        return entry;
}

static void unlink_free_space(struct btrfs_block_group_cache *block_group,
                              struct btrfs_free_space *info)
{
        rb_erase(&info->offset_index, &block_group->free_space_offset);
        block_group->free_extents--;
        block_group->free_space -= info->bytes;
}

static int link_free_space(struct btrfs_block_group_cache *block_group,
                           struct btrfs_free_space *info)
{
        int ret = 0;

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

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

static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
{
        u64 max_bytes;
        u64 bitmap_bytes;
        u64 extent_bytes;

        /*
         * The goal is to keep the total amount of memory used per 1gb of space
         * at or below 32k, so we need to adjust how much memory we allow to be
         * used by extent based free space tracking
         */
        max_bytes = MAX_CACHE_BYTES_PER_GIG *
                (div64_u64(block_group->key.offset, 1024 * 1024 * 1024));

        /*
         * we want to account for 1 more bitmap than what we have so we can make
         * sure we don't go over our overall goal of MAX_CACHE_BYTES_PER_GIG as
         * we add more bitmaps.
         */
        bitmap_bytes = (block_group->total_bitmaps + 1) * PAGE_CACHE_SIZE;

        if (bitmap_bytes >= max_bytes) {
                block_group->extents_thresh = 0;
                return;
        }

        /*
         * we want the extent entry threshold to always be at most 1/2 the maxw
         * bytes we can have, or whatever is less than that.
         */
        extent_bytes = max_bytes - bitmap_bytes;
        extent_bytes = min_t(u64, extent_bytes, div64_u64(max_bytes, 2));

        block_group->extents_thresh =
                div64_u64(extent_bytes, (sizeof(struct btrfs_free_space)));
}

static void bitmap_clear_bits(struct btrfs_block_group_cache *block_group,
                              struct btrfs_free_space *info, u64 offset,
                              u64 bytes)
{
        unsigned long start, end;
        unsigned long i;

        start = offset_to_bit(info->offset, block_group->sectorsize, offset);
        end = start + bytes_to_bits(bytes, block_group->sectorsize);
        BUG_ON(end > BITS_PER_BITMAP);

        for (i = start; i < end; i++)
                clear_bit(i, info->bitmap);

        info->bytes -= bytes;
        block_group->free_space -= bytes;
}

static void bitmap_set_bits(struct btrfs_block_group_cache *block_group,
                            struct btrfs_free_space *info, u64 offset,
                            u64 bytes)
{
        unsigned long start, end;
        unsigned long i;

        start = offset_to_bit(info->offset, block_group->sectorsize, offset);
        end = start + bytes_to_bits(bytes, block_group->sectorsize);
        BUG_ON(end > BITS_PER_BITMAP);

        for (i = start; i < end; i++)
                set_bit(i, info->bitmap);

        info->bytes += bytes;
        block_group->free_space += bytes;
}

static int search_bitmap(struct btrfs_block_group_cache *block_group,
                         struct btrfs_free_space *bitmap_info, u64 *offset,
                         u64 *bytes)
{
        unsigned long found_bits = 0;
        unsigned long bits, i;
        unsigned long next_zero;

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

        for (i = find_next_bit(bitmap_info->bitmap, BITS_PER_BITMAP, i);
             i < BITS_PER_BITMAP;
             i = find_next_bit(bitmap_info->bitmap, BITS_PER_BITMAP, i + 1)) {
                next_zero = find_next_zero_bit(bitmap_info->bitmap,
                                               BITS_PER_BITMAP, i);
                if ((next_zero - i) >= bits) {
                        found_bits = next_zero - i;
                        break;
                }
                i = next_zero;
        }

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

        return -1;
}

static struct btrfs_free_space *find_free_space(struct btrfs_block_group_cache
                                                *block_group, u64 *offset,
                                                u64 *bytes, int debug)
{
        struct btrfs_free_space *entry;
        struct rb_node *node;
        int ret;

        if (!block_group->free_space_offset.rb_node)
                return NULL;

        entry = tree_search_offset(block_group,
                                   offset_to_bitmap(block_group, *offset),
                                   0, 1);
        if (!entry)
                return NULL;

        for (node = &entry->offset_index; node; node = rb_next(node)) {
                entry = rb_entry(node, struct btrfs_free_space, offset_index);
                if (entry->bytes < *bytes)
                        continue;

                if (entry->bitmap) {
                        ret = search_bitmap(block_group, entry, offset, bytes);
                        if (!ret)
                                return entry;
                        continue;
                }

                *offset = entry->offset;
                *bytes = entry->bytes;
                return entry;
        }

        return NULL;
}

static void add_new_bitmap(struct btrfs_block_group_cache *block_group,
                           struct btrfs_free_space *info, u64 offset)
{
        u64 bytes_per_bg = BITS_PER_BITMAP * block_group->sectorsize;
        int max_bitmaps = (int)div64_u64(block_group->key.offset +
                                         bytes_per_bg - 1, bytes_per_bg);
        BUG_ON(block_group->total_bitmaps >= max_bitmaps);

        info->offset = offset_to_bitmap(block_group, offset);
        info->bytes = 0;
        link_free_space(block_group, info);
        block_group->total_bitmaps++;

        recalculate_thresholds(block_group);
}

static noinline int remove_from_bitmap(struct btrfs_block_group_cache *block_group,
                              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 * block_group->sectorsize) - 1;

        /*
         * XXX - this can go away after a few releases.
         *
         * since the only user of btrfs_remove_free_space is the tree logging
         * stuff, and the only way to test that is under crash conditions, we
         * want to have this debug stuff here just in case somethings not
         * working.  Search the bitmap for the space we are trying to use to
         * make sure its actually there.  If its not there then we need to stop
         * because something has gone wrong.
         */
        search_start = *offset;
        search_bytes = *bytes;
        ret = search_bitmap(block_group, bitmap_info, &search_start,
                            &search_bytes);
        BUG_ON(ret < 0 || search_start != *offset);

        if (*offset > bitmap_info->offset && *offset + *bytes > end) {
                bitmap_clear_bits(block_group, bitmap_info, *offset,
                                  end - *offset + 1);
                *bytes -= end - *offset + 1;
                *offset = end + 1;
        } else if (*offset >= bitmap_info->offset && *offset + *bytes <= end) {
                bitmap_clear_bits(block_group, bitmap_info, *offset, *bytes);
                *bytes = 0;
        }

        if (*bytes) {
                struct rb_node *next = rb_next(&bitmap_info->offset_index);
                if (!bitmap_info->bytes) {
                        unlink_free_space(block_group, bitmap_info);
                        kfree(bitmap_info->bitmap);
                        kfree(bitmap_info);
                        block_group->total_bitmaps--;
                        recalculate_thresholds(block_group);
                }

                /*
                 * 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 = *bytes;
                ret = search_bitmap(block_group, bitmap_info, &search_start,
                                    &search_bytes);
                if (ret < 0 || search_start != *offset)
                        return -EAGAIN;

                goto again;
        } else if (!bitmap_info->bytes) {
                unlink_free_space(block_group, bitmap_info);
                kfree(bitmap_info->bitmap);
                kfree(bitmap_info);
                block_group->total_bitmaps--;
                recalculate_thresholds(block_group);
        }

        return 0;
}

static int insert_into_bitmap(struct btrfs_block_group_cache *block_group,
                              struct btrfs_free_space *info)
{
        struct btrfs_free_space *bitmap_info;
        int added = 0;
        u64 bytes, offset, end;
        int ret;

        /*
         * 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 (block_group->free_extents < block_group->extents_thresh &&
            info->bytes > block_group->sectorsize * 4)
                return 0;

        /*
         * some block groups are so tiny they can't be enveloped by a bitmap, so
         * don't even bother to create a bitmap for this
         */
        if (BITS_PER_BITMAP * block_group->sectorsize >
            block_group->key.offset)
                return 0;

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

again:
        bitmap_info = tree_search_offset(block_group,
                                         offset_to_bitmap(block_group, offset),
                                         1, 0);
        if (!bitmap_info) {
                BUG_ON(added);
                goto new_bitmap;
        }

        end = bitmap_info->offset +
                (u64)(BITS_PER_BITMAP * block_group->sectorsize);

        if (offset >= bitmap_info->offset && offset + bytes > end) {
                bitmap_set_bits(block_group, bitmap_info, offset,
                                end - offset);
                bytes -= end - offset;
                offset = end;
                added = 0;
        } else if (offset >= bitmap_info->offset && offset + bytes <= end) {
                bitmap_set_bits(block_group, bitmap_info, offset, bytes);
                bytes = 0;
        } else {
                BUG();
        }

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

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

                /* no pre-allocated info, allocate a new one */
                if (!info) {
                        info = kzalloc(sizeof(struct btrfs_free_space),
                                       GFP_NOFS);
                        if (!info) {
                                spin_lock(&block_group->tree_lock);
                                ret = -ENOMEM;
                                goto out;
                        }
                }

                /* allocate the bitmap */
                info->bitmap = kzalloc(PAGE_CACHE_SIZE, GFP_NOFS);
                spin_lock(&block_group->tree_lock);
                if (!info->bitmap) {
                        ret = -ENOMEM;
                        goto out;
                }
                goto again;
        }

out:
        if (info) {
                if (info->bitmap)
                        kfree(info->bitmap);
                kfree(info);
        }

        return ret;
}

int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
                         u64 offset, u64 bytes)
{
        struct btrfs_free_space *right_info = NULL;
        struct btrfs_free_space *left_info = NULL;
        struct btrfs_free_space *info = NULL;
        int ret = 0;

        info = kzalloc(sizeof(struct btrfs_free_space), GFP_NOFS);
        if (!info)
                return -ENOMEM;

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

        spin_lock(&block_group->tree_lock);

        /*
         * 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(block_group, 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
                left_info = tree_search_offset(block_group, offset - 1, 0, 0);

        /*
         * If 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
         */
        if ((!left_info || left_info->bitmap) &&
            (!right_info || right_info->bitmap)) {
                ret = insert_into_bitmap(block_group, info);

                if (ret < 0) {
                        goto out;
                } else if (ret) {
                        ret = 0;
                        goto out;
                }
        }

        if (right_info && !right_info->bitmap) {
                unlink_free_space(block_group, right_info);
                info->bytes += right_info->bytes;
                kfree(right_info);
        }

        if (left_info && !left_info->bitmap &&
            left_info->offset + left_info->bytes == offset) {
                unlink_free_space(block_group, left_info);
                info->offset = left_info->offset;
                info->bytes += left_info->bytes;
                kfree(left_info);
        }

        ret = link_free_space(block_group, info);
        if (ret)
                kfree(info);
out:
        spin_unlock(&block_group->tree_lock);

        if (ret) {
                printk(KERN_CRIT "btrfs: unable to add free space :%d\n", ret);
                BUG_ON(ret == -EEXIST);
        }

        return ret;
}

int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
                            u64 offset, u64 bytes)
{
        struct btrfs_free_space *info;
        struct btrfs_free_space *next_info = NULL;
        int ret = 0;

        spin_lock(&block_group->tree_lock);

again:
        info = tree_search_offset(block_group, 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(block_group,
                                          offset_to_bitmap(block_group, offset),
                                          1, 0);
                if (!info) {
                        WARN_ON(1);
                        goto out_lock;
                }
        }

        if (info->bytes < bytes && rb_next(&info->offset_index)) {
                u64 end;
                next_info = rb_entry(rb_next(&info->offset_index),
                                             struct btrfs_free_space,
                                             offset_index);

                if (next_info->bitmap)
                        end = next_info->offset + BITS_PER_BITMAP *
                                block_group->sectorsize - 1;
                else
                        end = next_info->offset + next_info->bytes;

                if (next_info->bytes < bytes ||
                    next_info->offset > offset || offset > end) {
                        printk(KERN_CRIT "Found free space at %llu, size %llu,"
                              " trying to use %llu\n",
                              (unsigned long long)info->offset,
                              (unsigned long long)info->bytes,
                              (unsigned long long)bytes);
                        WARN_ON(1);
                        ret = -EINVAL;
                        goto out_lock;
                }

                info = next_info;
        }

        if (info->bytes == bytes) {
                unlink_free_space(block_group, info);
                if (info->bitmap) {
                        kfree(info->bitmap);
                        block_group->total_bitmaps--;
                }
                kfree(info);
                goto out_lock;
        }

        if (!info->bitmap && info->offset == offset) {
                unlink_free_space(block_group, info);
                info->offset += bytes;
                info->bytes -= bytes;
                link_free_space(block_group, info);
                goto out_lock;
        }

        if (!info->bitmap && info->offset <= offset &&
            info->offset + info->bytes >= offset + bytes) {
                u64 old_start = info->offset;
                /*
                 * we're freeing space in the middle of the info,
                 * this can happen during tree log replay
                 *
                 * first unlink the old info and then
                 * insert it again after the hole we're creating
                 */
                unlink_free_space(block_group, info);
                if (offset + bytes < info->offset + info->bytes) {
                        u64 old_end = info->offset + info->bytes;

                        info->offset = offset + bytes;
                        info->bytes = old_end - info->offset;
                        ret = link_free_space(block_group, info);
                        WARN_ON(ret);
                        if (ret)
                                goto out_lock;
                } else {
                        /* the hole we're creating ends at the end
                         * of the info struct, just free the info
                         */
                        kfree(info);
                }
                spin_unlock(&block_group->tree_lock);

                /* step two, insert a new info struct to cover
                 * anything before the hole
                 */
                ret = btrfs_add_free_space(block_group, old_start,
                                           offset - old_start);
                WARN_ON(ret);
                goto out;
        }

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

void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
                           u64 bytes)
{
        struct btrfs_free_space *info;
        struct rb_node *n;
        int count = 0;

        for (n = rb_first(&block_group->free_space_offset); n; n = rb_next(n)) {
                info = rb_entry(n, struct btrfs_free_space, offset_index);
                if (info->bytes >= bytes)
                        count++;
                printk(KERN_CRIT "entry offset %llu, bytes %llu, bitmap %s\n",
                       (unsigned long long)info->offset,
                       (unsigned long long)info->bytes,
                       (info->bitmap) ? "yes" : "no");
        }
        printk(KERN_INFO "block group has cluster?: %s\n",
               list_empty(&block_group->cluster_list) ? "no" : "yes");
        printk(KERN_INFO "%d blocks of free space at or bigger than bytes is"
               "\n", count);
}

u64 btrfs_block_group_free_space(struct btrfs_block_group_cache *block_group)
{
        struct btrfs_free_space *info;
        struct rb_node *n;
        u64 ret = 0;

        for (n = rb_first(&block_group->free_space_offset); n;
             n = rb_next(n)) {
                info = rb_entry(n, struct btrfs_free_space, offset_index);
                ret += info->bytes;
        }

        return ret;
}

/*
 * 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 int
__btrfs_return_cluster_to_free_space(
                             struct btrfs_block_group_cache *block_group,
                             struct btrfs_free_cluster *cluster)
{
        struct btrfs_free_space *entry;
        struct rb_node *node;
        bool bitmap;

        spin_lock(&cluster->lock);
        if (cluster->block_group != block_group)
                goto out;

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

        if (bitmap)
                goto out;

        node = rb_first(&cluster->root);
        while (node) {
                entry = rb_entry(node, struct btrfs_free_space, offset_index);
                node = rb_next(&entry->offset_index);
                rb_erase(&entry->offset_index, &cluster->root);
                BUG_ON(entry->bitmap);
                tree_insert_offset(&block_group->free_space_offset,
                                   entry->offset, &entry->offset_index, 0);
        }
        cluster->root.rb_node = NULL;

out:
        spin_unlock(&cluster->lock);
        btrfs_put_block_group(block_group);
        return 0;
}

void btrfs_remove_free_space_cache(struct btrfs_block_group_cache *block_group)
{
        struct btrfs_free_space *info;
        struct rb_node *node;
        struct btrfs_free_cluster *cluster;
        struct list_head *head;

        spin_lock(&block_group->tree_lock);
        while ((head = block_group->cluster_list.next) !=
               &block_group->cluster_list) {
                cluster = list_entry(head, struct btrfs_free_cluster,
                                     block_group_list);

                WARN_ON(cluster->block_group != block_group);
                __btrfs_return_cluster_to_free_space(block_group, cluster);
                if (need_resched()) {
                        spin_unlock(&block_group->tree_lock);
                        cond_resched();
                        spin_lock(&block_group->tree_lock);
                }
        }

        while ((node = rb_last(&block_group->free_space_offset)) != NULL) {
                info = rb_entry(node, struct btrfs_free_space, offset_index);
                unlink_free_space(block_group, info);
                if (info->bitmap)
                        kfree(info->bitmap);
                kfree(info);
                if (need_resched()) {
                        spin_unlock(&block_group->tree_lock);
                        cond_resched();
                        spin_lock(&block_group->tree_lock);
                }
        }

        spin_unlock(&block_group->tree_lock);
}

u64 btrfs_find_space_for_alloc(struct btrfs_block_group_cache *block_group,
                               u64 offset, u64 bytes, u64 empty_size)
{
        struct btrfs_free_space *entry = NULL;
        u64 bytes_search = bytes + empty_size;
        u64 ret = 0;

        spin_lock(&block_group->tree_lock);
        entry = find_free_space(block_group, &offset, &bytes_search, 0);
        if (!entry)
                goto out;

        ret = offset;
        if (entry->bitmap) {
                bitmap_clear_bits(block_group, entry, offset, bytes);
                if (!entry->bytes) {
                        unlink_free_space(block_group, entry);
                        kfree(entry->bitmap);
                        kfree(entry);
                        block_group->total_bitmaps--;
                        recalculate_thresholds(block_group);
                }
        } else {
                unlink_free_space(block_group, entry);
                entry->offset += bytes;
                entry->bytes -= bytes;
                if (!entry->bytes)
                        kfree(entry);
                else
                        link_free_space(block_group, entry);
        }

out:
        spin_unlock(&block_group->tree_lock);

        return ret;
}

/*
 * given a cluster, put all of its extents back into the free space
 * cache.  If a block group is passed, this function will only free
 * a cluster that belongs to the passed block group.
 *
 * Otherwise, it'll get a reference on the block group pointed to by the
 * cluster and remove the cluster from it.
 */
int btrfs_return_cluster_to_free_space(
                               struct btrfs_block_group_cache *block_group,
                               struct btrfs_free_cluster *cluster)
{
        int ret;

        /* first, get a safe pointer to the block group */
        spin_lock(&cluster->lock);
        if (!block_group) {
                block_group = cluster->block_group;
                if (!block_group) {
                        spin_unlock(&cluster->lock);
                        return 0;
                }
        } else if (cluster->block_group != block_group) {
                /* someone else has already freed it don't redo their work */
                spin_unlock(&cluster->lock);
                return 0;
        }
        atomic_inc(&block_group->count);
        spin_unlock(&cluster->lock);

        /* now return any extents the cluster had on it */
        spin_lock(&block_group->tree_lock);
        ret = __btrfs_return_cluster_to_free_space(block_group, cluster);
        spin_unlock(&block_group->tree_lock);

        /* finally drop our ref */
        btrfs_put_block_group(block_group);
        return ret;
}

static u64 btrfs_alloc_from_bitmap(struct btrfs_block_group_cache *block_group,
                                   struct btrfs_free_cluster *cluster,
                                   u64 bytes, u64 min_start)
{

        struct btrfs_free_space *entry;
        int err;
        u64 search_start = cluster->window_start;
        u64 search_bytes = bytes;
        u64 ret = 0;

        spin_lock(&block_group->tree_lock);
        spin_lock(&cluster->lock);

        if (!cluster->points_to_bitmap)
                goto out;

        if (cluster->block_group != block_group)
                goto out;

        /*
         * search_start is the beginning of the bitmap, but at some point it may
         * be a good idea to point to the actual start of the free area in the
         * bitmap, so do the offset_to_bitmap trick anyway, and set bitmap_only
         * to 1 to make sure we get the bitmap entry
         */
        entry = tree_search_offset(block_group,
                                   offset_to_bitmap(block_group, search_start),
                                   1, 0);
        if (!entry || !entry->bitmap)
                goto out;

        search_start = min_start;
        search_bytes = bytes;

        err = search_bitmap(block_group, entry, &search_start,
                            &search_bytes);
        if (err)
                goto out;

        ret = search_start;
        bitmap_clear_bits(block_group, entry, ret, bytes);
out:
        spin_unlock(&cluster->lock);
        spin_unlock(&block_group->tree_lock);

        return ret;
}

/*
 * given a cluster, try to allocate 'bytes' from it, returns 0
 * if it couldn't find anything suitably large, or a logical disk offset
 * if things worked out
 */
u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group,
                             struct btrfs_free_cluster *cluster, u64 bytes,
                             u64 min_start)
{
        struct btrfs_free_space *entry = NULL;
        struct rb_node *node;
        u64 ret = 0;

        if (cluster->points_to_bitmap)
                return btrfs_alloc_from_bitmap(block_group, cluster, bytes,
                                               min_start);

        spin_lock(&cluster->lock);
        if (bytes > cluster->max_size)
                goto out;

        if (cluster->block_group != block_group)
                goto out;

        node = rb_first(&cluster->root);
        if (!node)
                goto out;

        entry = rb_entry(node, struct btrfs_free_space, offset_index);

        while(1) {
                if (entry->bytes < bytes || entry->offset < min_start) {
                        struct rb_node *node;

                        node = rb_next(&entry->offset_index);
                        if (!node)
                                break;
                        entry = rb_entry(node, struct btrfs_free_space,
                                         offset_index);
                        continue;
                }
                ret = entry->offset;

                entry->offset += bytes;
                entry->bytes -= bytes;

                if (entry->bytes == 0) {
                        rb_erase(&entry->offset_index, &cluster->root);
                        kfree(entry);
                }
                break;
        }
out:
        spin_unlock(&cluster->lock);

        return ret;
}

static int btrfs_bitmap_cluster(struct btrfs_block_group_cache *block_group,
                                struct btrfs_free_space *entry,
                                struct btrfs_free_cluster *cluster,
                                u64 offset, u64 bytes, u64 min_bytes)
{
        unsigned long next_zero;
        unsigned long i;
        unsigned long search_bits;
        unsigned long total_bits;
        unsigned long found_bits;
        unsigned long start = 0;
        unsigned long total_found = 0;
        bool found = false;

        i = offset_to_bit(entry->offset, block_group->sectorsize,
                          max_t(u64, offset, entry->offset));
        search_bits = bytes_to_bits(min_bytes, block_group->sectorsize);
        total_bits = bytes_to_bits(bytes, block_group->sectorsize);

again:
        found_bits = 0;
        for (i = find_next_bit(entry->bitmap, BITS_PER_BITMAP, i);
             i < BITS_PER_BITMAP;
             i = find_next_bit(entry->bitmap, BITS_PER_BITMAP, i + 1)) {
                next_zero = find_next_zero_bit(entry->bitmap,
                                               BITS_PER_BITMAP, i);
                if (next_zero - i >= search_bits) {
                        found_bits = next_zero - i;
                        break;
                }
                i = next_zero;
        }

        if (!found_bits)
                return -1;

        if (!found) {
                start = i;
                found = true;
        }

        total_found += found_bits;

        if (cluster->max_size < found_bits * block_group->sectorsize)
                cluster->max_size = found_bits * block_group->sectorsize;

        if (total_found < total_bits) {
                i = find_next_bit(entry->bitmap, BITS_PER_BITMAP, next_zero);
                if (i - start > total_bits * 2) {
                        total_found = 0;
                        cluster->max_size = 0;
                        found = false;
                }
                goto again;
        }

        cluster->window_start = start * block_group->sectorsize +
                entry->offset;
        cluster->points_to_bitmap = true;

        return 0;
}

/*
 * here we try to find a cluster of blocks in a block group.  The goal
 * is to find at least bytes free and up to empty_size + bytes free.
 * We might not find them all in one contiguous area.
 *
 * returns zero and sets up cluster if things worked out, otherwise
 * it returns -enospc
 */
int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root,
                             struct btrfs_block_group_cache *block_group,
                             struct btrfs_free_cluster *cluster,
                             u64 offset, u64 bytes, u64 empty_size)
{
        struct btrfs_free_space *entry = NULL;
        struct rb_node *node;
        struct btrfs_free_space *next;
        struct btrfs_free_space *last = NULL;
        u64 min_bytes;
        u64 window_start;
        u64 window_free;
        u64 max_extent = 0;
        bool found_bitmap = false;
        int ret;

        /* for metadata, allow allocates with more holes */
        if (btrfs_test_opt(root, SSD_SPREAD)) {
                min_bytes = bytes + empty_size;
        } else if (block_group->flags & BTRFS_BLOCK_GROUP_METADATA) {
                /*
                 * we want to do larger allocations when we are
                 * flushing out the delayed refs, it helps prevent
                 * making more work as we go along.
                 */
                if (trans->transaction->delayed_refs.flushing)
                        min_bytes = max(bytes, (bytes + empty_size) >> 1);
                else
                        min_bytes = max(bytes, (bytes + empty_size) >> 4);
        } else
                min_bytes = max(bytes, (bytes + empty_size) >> 2);

        spin_lock(&block_group->tree_lock);
        spin_lock(&cluster->lock);

        /* someone already found a cluster, hooray */
        if (cluster->block_group) {
                ret = 0;
                goto out;
        }
again:
        entry = tree_search_offset(block_group, offset, found_bitmap, 1);
        if (!entry) {
                ret = -ENOSPC;
                goto out;
        }

        /*
         * If found_bitmap is true, we exhausted our search for extent entries,
         * and we just want to search all of the bitmaps that we can find, and
         * ignore any extent entries we find.
         */
        while (entry->bitmap || found_bitmap ||
               (!entry->bitmap && entry->bytes < min_bytes)) {
                struct rb_node *node = rb_next(&entry->offset_index);

                if (entry->bitmap && entry->bytes > bytes + empty_size) {
                        ret = btrfs_bitmap_cluster(block_group, entry, cluster,
                                                   offset, bytes + empty_size,
                                                   min_bytes);
                        if (!ret)
                                goto got_it;
                }

                if (!node) {
                        ret = -ENOSPC;
                        goto out;
                }
                entry = rb_entry(node, struct btrfs_free_space, offset_index);
        }

        /*
         * We already searched all the extent entries from the passed in offset
         * to the end and didn't find enough space for the cluster, and we also
         * didn't find any bitmaps that met our criteria, just go ahead and exit
         */
        if (found_bitmap) {
                ret = -ENOSPC;
                goto out;
        }

        cluster->points_to_bitmap = false;
        window_start = entry->offset;
        window_free = entry->bytes;
        last = entry;
        max_extent = entry->bytes;

        while (1) {
                /* out window is just right, lets fill it */
                if (window_free >= bytes + empty_size)
                        break;

                node = rb_next(&last->offset_index);
                if (!node) {
                        if (found_bitmap)
                                goto again;
                        ret = -ENOSPC;
                        goto out;
                }
                next = rb_entry(node, struct btrfs_free_space, offset_index);

                /*
                 * we found a bitmap, so if this search doesn't result in a
                 * cluster, we know to go and search again for the bitmaps and
                 * start looking for space there
                 */
                if (next->bitmap) {
                        if (!found_bitmap)
                                offset = next->offset;
                        found_bitmap = true;
                        last = next;
                        continue;
                }

                /*
                 * we haven't filled the empty size and the window is
                 * very large.  reset and try again
                 */
                if (next->offset - (last->offset + last->bytes) > 128 * 1024 ||
                    next->offset - window_start > (bytes + empty_size) * 2) {
                        entry = next;
                        window_start = entry->offset;
                        window_free = entry->bytes;
                        last = entry;
                        max_extent = entry->bytes;
                } else {
                        last = next;
                        window_free += next->bytes;
                        if (entry->bytes > max_extent)
                                max_extent = entry->bytes;
                }
        }

        cluster->window_start = entry->offset;

        /*
         * now we've found our entries, pull them out of the free space
         * cache and put them into the cluster rbtree
         *
         * The cluster includes an rbtree, but only uses the offset index
         * of each free space cache entry.
         */
        while (1) {
                node = rb_next(&entry->offset_index);
                if (entry->bitmap && node) {
                        entry = rb_entry(node, struct btrfs_free_space,
                                         offset_index);
                        continue;
                } else if (entry->bitmap && !node) {
                        break;
                }

                rb_erase(&entry->offset_index, &block_group->free_space_offset);
                ret = tree_insert_offset(&cluster->root, entry->offset,
                                         &entry->offset_index, 0);
                BUG_ON(ret);

                if (!node || entry == last)
                        break;

                entry = rb_entry(node, struct btrfs_free_space, offset_index);
        }

        cluster->max_size = max_extent;
got_it:
        ret = 0;
        atomic_inc(&block_group->count);
        list_add_tail(&cluster->block_group_list, &block_group->cluster_list);
        cluster->block_group = block_group;
out:
        spin_unlock(&cluster->lock);
        spin_unlock(&block_group->tree_lock);

        return ret;
}

/*
 * simple code to zero out a cluster
 */
void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
{
        spin_lock_init(&cluster->lock);
        spin_lock_init(&cluster->refill_lock);
        cluster->root.rb_node = NULL;
        cluster->max_size = 0;
        cluster->points_to_bitmap = false;
        INIT_LIST_HEAD(&cluster->block_group_list);
        cluster->block_group = NULL;
}