// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 */

#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/sort.h>
#include <linux/rcupdate.h>
#include <linux/kthread.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include <linux/percpu_counter.h>
#include <linux/lockdep.h>
#include <linux/crc32c.h>
#include "misc.h"
#include "tree-log.h"
#include "disk-io.h"
#include "print-tree.h"
#include "volumes.h"
#include "raid56.h"
#include "locking.h"
#include "free-space-cache.h"
#include "free-space-tree.h"
#include "sysfs.h"
#include "qgroup.h"
#include "ref-verify.h"
#include "space-info.h"
#include "block-rsv.h"
#include "delalloc-space.h"
#include "block-group.h"
#include "discard.h"
#include "rcu-string.h"

#undef SCRAMBLE_DELAYED_REFS


static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
                               struct btrfs_delayed_ref_node *node, u64 parent,
                               u64 root_objectid, u64 owner_objectid,
                               u64 owner_offset, int refs_to_drop,
                               struct btrfs_delayed_extent_op *extra_op);
static void __run_delayed_extent_op(struct btrfs_delayed_extent_op *extent_op,
                                    struct extent_buffer *leaf,
                                    struct btrfs_extent_item *ei);
static int alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                                      u64 parent, u64 root_objectid,
                                      u64 flags, u64 owner, u64 offset,
                                      struct btrfs_key *ins, int ref_mod);
static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
                                     struct btrfs_delayed_ref_node *node,
                                     struct btrfs_delayed_extent_op *extent_op);
static int find_next_key(struct btrfs_path *path, int level,
                         struct btrfs_key *key);

static int block_group_bits(struct btrfs_block_group *cache, u64 bits)
{
        return (cache->flags & bits) == bits;
}

int btrfs_add_excluded_extent(struct btrfs_fs_info *fs_info,
                              u64 start, u64 num_bytes)
{
        u64 end = start + num_bytes - 1;
        set_extent_bits(&fs_info->excluded_extents, start, end,
                        EXTENT_UPTODATE);
        return 0;
}

void btrfs_free_excluded_extents(struct btrfs_block_group *cache)
{
        struct btrfs_fs_info *fs_info = cache->fs_info;
        u64 start, end;

        start = cache->start;
        end = start + cache->length - 1;

        clear_extent_bits(&fs_info->excluded_extents, start, end,
                          EXTENT_UPTODATE);
}

static u64 generic_ref_to_space_flags(struct btrfs_ref *ref)
{
        if (ref->type == BTRFS_REF_METADATA) {
                if (ref->tree_ref.root == BTRFS_CHUNK_TREE_OBJECTID)
                        return BTRFS_BLOCK_GROUP_SYSTEM;
                else
                        return BTRFS_BLOCK_GROUP_METADATA;
        }
        return BTRFS_BLOCK_GROUP_DATA;
}

static void add_pinned_bytes(struct btrfs_fs_info *fs_info,
                             struct btrfs_ref *ref)
{
        struct btrfs_space_info *space_info;
        u64 flags = generic_ref_to_space_flags(ref);

        space_info = btrfs_find_space_info(fs_info, flags);
        ASSERT(space_info);
        percpu_counter_add_batch(&space_info->total_bytes_pinned, ref->len,
                    BTRFS_TOTAL_BYTES_PINNED_BATCH);
}

static void sub_pinned_bytes(struct btrfs_fs_info *fs_info,
                             struct btrfs_ref *ref)
{
        struct btrfs_space_info *space_info;
        u64 flags = generic_ref_to_space_flags(ref);

        space_info = btrfs_find_space_info(fs_info, flags);
        ASSERT(space_info);
        percpu_counter_add_batch(&space_info->total_bytes_pinned, -ref->len,
                    BTRFS_TOTAL_BYTES_PINNED_BATCH);
}

/* simple helper to search for an existing data extent at a given offset */
int btrfs_lookup_data_extent(struct btrfs_fs_info *fs_info, u64 start, u64 len)
{
        int ret;
        struct btrfs_key key;
        struct btrfs_path *path;

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

        key.objectid = start;
        key.offset = len;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, path, 0, 0);
        btrfs_free_path(path);
        return ret;
}

/*
 * helper function to lookup reference count and flags of a tree block.
 *
 * the head node for delayed ref is used to store the sum of all the
 * reference count modifications queued up in the rbtree. the head
 * node may also store the extent flags to set. This way you can check
 * to see what the reference count and extent flags would be if all of
 * the delayed refs are not processed.
 */
int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
                             struct btrfs_fs_info *fs_info, u64 bytenr,
                             u64 offset, int metadata, u64 *refs, u64 *flags)
{
        struct btrfs_delayed_ref_head *head;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_path *path;
        struct btrfs_extent_item *ei;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        u32 item_size;
        u64 num_refs;
        u64 extent_flags;
        int ret;

        /*
         * If we don't have skinny metadata, don't bother doing anything
         * different
         */
        if (metadata && !btrfs_fs_incompat(fs_info, SKINNY_METADATA)) {
                offset = fs_info->nodesize;
                metadata = 0;
        }

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

        if (!trans) {
                path->skip_locking = 1;
                path->search_commit_root = 1;
        }

search_again:
        key.objectid = bytenr;
        key.offset = offset;
        if (metadata)
                key.type = BTRFS_METADATA_ITEM_KEY;
        else
                key.type = BTRFS_EXTENT_ITEM_KEY;

        ret = btrfs_search_slot(trans, fs_info->extent_root, &key, path, 0, 0);
        if (ret < 0)
                goto out_free;

        if (ret > 0 && metadata && key.type == BTRFS_METADATA_ITEM_KEY) {
                if (path->slots[0]) {
                        path->slots[0]--;
                        btrfs_item_key_to_cpu(path->nodes[0], &key,
                                              path->slots[0]);
                        if (key.objectid == bytenr &&
                            key.type == BTRFS_EXTENT_ITEM_KEY &&
                            key.offset == fs_info->nodesize)
                                ret = 0;
                }
        }

        if (ret == 0) {
                leaf = path->nodes[0];
                item_size = btrfs_item_size_nr(leaf, path->slots[0]);
                if (item_size >= sizeof(*ei)) {
                        ei = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_extent_item);
                        num_refs = btrfs_extent_refs(leaf, ei);
                        extent_flags = btrfs_extent_flags(leaf, ei);
                } else {
                        ret = -EINVAL;
                        btrfs_print_v0_err(fs_info);
                        if (trans)
                                btrfs_abort_transaction(trans, ret);
                        else
                                btrfs_handle_fs_error(fs_info, ret, NULL);

                        goto out_free;
                }

                BUG_ON(num_refs == 0);
        } else {
                num_refs = 0;
                extent_flags = 0;
                ret = 0;
        }

        if (!trans)
                goto out;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);
        head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
        if (head) {
                if (!mutex_trylock(&head->mutex)) {
                        refcount_inc(&head->refs);
                        spin_unlock(&delayed_refs->lock);

                        btrfs_release_path(path);

                        /*
                         * Mutex was contended, block until it's released and try
                         * again
                         */
                        mutex_lock(&head->mutex);
                        mutex_unlock(&head->mutex);
                        btrfs_put_delayed_ref_head(head);
                        goto search_again;
                }
                spin_lock(&head->lock);
                if (head->extent_op && head->extent_op->update_flags)
                        extent_flags |= head->extent_op->flags_to_set;
                else
                        BUG_ON(num_refs == 0);

                num_refs += head->ref_mod;
                spin_unlock(&head->lock);
                mutex_unlock(&head->mutex);
        }
        spin_unlock(&delayed_refs->lock);
out:
        WARN_ON(num_refs == 0);
        if (refs)
                *refs = num_refs;
        if (flags)
                *flags = extent_flags;
out_free:
        btrfs_free_path(path);
        return ret;
}

/*
 * Back reference rules.  Back refs have three main goals:
 *
 * 1) differentiate between all holders of references to an extent so that
 *    when a reference is dropped we can make sure it was a valid reference
 *    before freeing the extent.
 *
 * 2) Provide enough information to quickly find the holders of an extent
 *    if we notice a given block is corrupted or bad.
 *
 * 3) Make it easy to migrate blocks for FS shrinking or storage pool
 *    maintenance.  This is actually the same as #2, but with a slightly
 *    different use case.
 *
 * There are two kinds of back refs. The implicit back refs is optimized
 * for pointers in non-shared tree blocks. For a given pointer in a block,
 * back refs of this kind provide information about the block's owner tree
 * and the pointer's key. These information allow us to find the block by
 * b-tree searching. The full back refs is for pointers in tree blocks not
 * referenced by their owner trees. The location of tree block is recorded
 * in the back refs. Actually the full back refs is generic, and can be
 * used in all cases the implicit back refs is used. The major shortcoming
 * of the full back refs is its overhead. Every time a tree block gets
 * COWed, we have to update back refs entry for all pointers in it.
 *
 * For a newly allocated tree block, we use implicit back refs for
 * pointers in it. This means most tree related operations only involve
 * implicit back refs. For a tree block created in old transaction, the
 * only way to drop a reference to it is COW it. So we can detect the
 * event that tree block loses its owner tree's reference and do the
 * back refs conversion.
 *
 * When a tree block is COWed through a tree, there are four cases:
 *
 * The reference count of the block is one and the tree is the block's
 * owner tree. Nothing to do in this case.
 *
 * The reference count of the block is one and the tree is not the
 * block's owner tree. In this case, full back refs is used for pointers
 * in the block. Remove these full back refs, add implicit back refs for
 * every pointers in the new block.
 *
 * The reference count of the block is greater than one and the tree is
 * the block's owner tree. In this case, implicit back refs is used for
 * pointers in the block. Add full back refs for every pointers in the
 * block, increase lower level extents' reference counts. The original
 * implicit back refs are entailed to the new block.
 *
 * The reference count of the block is greater than one and the tree is
 * not the block's owner tree. Add implicit back refs for every pointer in
 * the new block, increase lower level extents' reference count.
 *
 * Back Reference Key composing:
 *
 * The key objectid corresponds to the first byte in the extent,
 * The key type is used to differentiate between types of back refs.
 * There are different meanings of the key offset for different types
 * of back refs.
 *
 * File extents can be referenced by:
 *
 * - multiple snapshots, subvolumes, or different generations in one subvol
 * - different files inside a single subvolume
 * - different offsets inside a file (bookend extents in file.c)
 *
 * The extent ref structure for the implicit back refs has fields for:
 *
 * - Objectid of the subvolume root
 * - objectid of the file holding the reference
 * - original offset in the file
 * - how many bookend extents
 *
 * The key offset for the implicit back refs is hash of the first
 * three fields.
 *
 * The extent ref structure for the full back refs has field for:
 *
 * - number of pointers in the tree leaf
 *
 * The key offset for the implicit back refs is the first byte of
 * the tree leaf
 *
 * When a file extent is allocated, The implicit back refs is used.
 * the fields are filled in:
 *
 *     (root_key.objectid, inode objectid, offset in file, 1)
 *
 * When a file extent is removed file truncation, we find the
 * corresponding implicit back refs and check the following fields:
 *
 *     (btrfs_header_owner(leaf), inode objectid, offset in file)
 *
 * Btree extents can be referenced by:
 *
 * - Different subvolumes
 *
 * Both the implicit back refs and the full back refs for tree blocks
 * only consist of key. The key offset for the implicit back refs is
 * objectid of block's owner tree. The key offset for the full back refs
 * is the first byte of parent block.
 *
 * When implicit back refs is used, information about the lowest key and
 * level of the tree block are required. These information are stored in
 * tree block info structure.
 */

/*
 * is_data == BTRFS_REF_TYPE_BLOCK, tree block type is required,
 * is_data == BTRFS_REF_TYPE_DATA, data type is requiried,
 * is_data == BTRFS_REF_TYPE_ANY, either type is OK.
 */
int btrfs_get_extent_inline_ref_type(const struct extent_buffer *eb,
                                     struct btrfs_extent_inline_ref *iref,
                                     enum btrfs_inline_ref_type is_data)
{
        int type = btrfs_extent_inline_ref_type(eb, iref);
        u64 offset = btrfs_extent_inline_ref_offset(eb, iref);

        if (type == BTRFS_TREE_BLOCK_REF_KEY ||
            type == BTRFS_SHARED_BLOCK_REF_KEY ||
            type == BTRFS_SHARED_DATA_REF_KEY ||
            type == BTRFS_EXTENT_DATA_REF_KEY) {
                if (is_data == BTRFS_REF_TYPE_BLOCK) {
                        if (type == BTRFS_TREE_BLOCK_REF_KEY)
                                return type;
                        if (type == BTRFS_SHARED_BLOCK_REF_KEY) {
                                ASSERT(eb->fs_info);
                                /*
                                 * Every shared one has parent tree block,
                                 * which must be aligned to sector size.
                                 */
                                if (offset &&
                                    IS_ALIGNED(offset, eb->fs_info->sectorsize))
                                        return type;
                        }
                } else if (is_data == BTRFS_REF_TYPE_DATA) {
                        if (type == BTRFS_EXTENT_DATA_REF_KEY)
                                return type;
                        if (type == BTRFS_SHARED_DATA_REF_KEY) {
                                ASSERT(eb->fs_info);
                                /*
                                 * Every shared one has parent tree block,
                                 * which must be aligned to sector size.
                                 */
                                if (offset &&
                                    IS_ALIGNED(offset, eb->fs_info->sectorsize))
                                        return type;
                        }
                } else {
                        ASSERT(is_data == BTRFS_REF_TYPE_ANY);
                        return type;
                }
        }

        btrfs_print_leaf((struct extent_buffer *)eb);
        btrfs_err(eb->fs_info,
                  "eb %llu iref 0x%lx invalid extent inline ref type %d",
                  eb->start, (unsigned long)iref, type);
        WARN_ON(1);

        return BTRFS_REF_TYPE_INVALID;
}

u64 hash_extent_data_ref(u64 root_objectid, u64 owner, u64 offset)
{
        u32 high_crc = ~(u32)0;
        u32 low_crc = ~(u32)0;
        __le64 lenum;

        lenum = cpu_to_le64(root_objectid);
        high_crc = btrfs_crc32c(high_crc, &lenum, sizeof(lenum));
        lenum = cpu_to_le64(owner);
        low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));
        lenum = cpu_to_le64(offset);
        low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));

        return ((u64)high_crc << 31) ^ (u64)low_crc;
}

static u64 hash_extent_data_ref_item(struct extent_buffer *leaf,
                                     struct btrfs_extent_data_ref *ref)
{
        return hash_extent_data_ref(btrfs_extent_data_ref_root(leaf, ref),
                                    btrfs_extent_data_ref_objectid(leaf, ref),
                                    btrfs_extent_data_ref_offset(leaf, ref));
}

static int match_extent_data_ref(struct extent_buffer *leaf,
                                 struct btrfs_extent_data_ref *ref,
                                 u64 root_objectid, u64 owner, u64 offset)
{
        if (btrfs_extent_data_ref_root(leaf, ref) != root_objectid ||
            btrfs_extent_data_ref_objectid(leaf, ref) != owner ||
            btrfs_extent_data_ref_offset(leaf, ref) != offset)
                return 0;
        return 1;
}

static noinline int lookup_extent_data_ref(struct btrfs_trans_handle *trans,
                                           struct btrfs_path *path,
                                           u64 bytenr, u64 parent,
                                           u64 root_objectid,
                                           u64 owner, u64 offset)
{
        struct btrfs_root *root = trans->fs_info->extent_root;
        struct btrfs_key key;
        struct btrfs_extent_data_ref *ref;
        struct extent_buffer *leaf;
        u32 nritems;
        int ret;
        int recow;
        int err = -ENOENT;

        key.objectid = bytenr;
        if (parent) {
                key.type = BTRFS_SHARED_DATA_REF_KEY;
                key.offset = parent;
        } else {
                key.type = BTRFS_EXTENT_DATA_REF_KEY;
                key.offset = hash_extent_data_ref(root_objectid,
                                                  owner, offset);
        }
again:
        recow = 0;
        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret < 0) {
                err = ret;
                goto fail;
        }

        if (parent) {
                if (!ret)
                        return 0;
                goto fail;
        }

        leaf = path->nodes[0];
        nritems = btrfs_header_nritems(leaf);
        while (1) {
                if (path->slots[0] >= nritems) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                err = ret;
                        if (ret)
                                goto fail;

                        leaf = path->nodes[0];
                        nritems = btrfs_header_nritems(leaf);
                        recow = 1;
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.objectid != bytenr ||
                    key.type != BTRFS_EXTENT_DATA_REF_KEY)
                        goto fail;

                ref = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_extent_data_ref);

                if (match_extent_data_ref(leaf, ref, root_objectid,
                                          owner, offset)) {
                        if (recow) {
                                btrfs_release_path(path);
                                goto again;
                        }
                        err = 0;
                        break;
                }
                path->slots[0]++;
        }
fail:
        return err;
}

static noinline int insert_extent_data_ref(struct btrfs_trans_handle *trans,
                                           struct btrfs_path *path,
                                           u64 bytenr, u64 parent,
                                           u64 root_objectid, u64 owner,
                                           u64 offset, int refs_to_add)
{
        struct btrfs_root *root = trans->fs_info->extent_root;
        struct btrfs_key key;
        struct extent_buffer *leaf;
        u32 size;
        u32 num_refs;
        int ret;

        key.objectid = bytenr;
        if (parent) {
                key.type = BTRFS_SHARED_DATA_REF_KEY;
                key.offset = parent;
                size = sizeof(struct btrfs_shared_data_ref);
        } else {
                key.type = BTRFS_EXTENT_DATA_REF_KEY;
                key.offset = hash_extent_data_ref(root_objectid,
                                                  owner, offset);
                size = sizeof(struct btrfs_extent_data_ref);
        }

        ret = btrfs_insert_empty_item(trans, root, path, &key, size);
        if (ret && ret != -EEXIST)
                goto fail;

        leaf = path->nodes[0];
        if (parent) {
                struct btrfs_shared_data_ref *ref;
                ref = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_shared_data_ref);
                if (ret == 0) {
                        btrfs_set_shared_data_ref_count(leaf, ref, refs_to_add);
                } else {
                        num_refs = btrfs_shared_data_ref_count(leaf, ref);
                        num_refs += refs_to_add;
                        btrfs_set_shared_data_ref_count(leaf, ref, num_refs);
                }
        } else {
                struct btrfs_extent_data_ref *ref;
                while (ret == -EEXIST) {
                        ref = btrfs_item_ptr(leaf, path->slots[0],
                                             struct btrfs_extent_data_ref);
                        if (match_extent_data_ref(leaf, ref, root_objectid,
                                                  owner, offset))
                                break;
                        btrfs_release_path(path);
                        key.offset++;
                        ret = btrfs_insert_empty_item(trans, root, path, &key,
                                                      size);
                        if (ret && ret != -EEXIST)
                                goto fail;

                        leaf = path->nodes[0];
                }
                ref = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_extent_data_ref);
                if (ret == 0) {
                        btrfs_set_extent_data_ref_root(leaf, ref,
                                                       root_objectid);
                        btrfs_set_extent_data_ref_objectid(leaf, ref, owner);
                        btrfs_set_extent_data_ref_offset(leaf, ref, offset);
                        btrfs_set_extent_data_ref_count(leaf, ref, refs_to_add);
                } else {
                        num_refs = btrfs_extent_data_ref_count(leaf, ref);
                        num_refs += refs_to_add;
                        btrfs_set_extent_data_ref_count(leaf, ref, num_refs);
                }
        }
        btrfs_mark_buffer_dirty(leaf);
        ret = 0;
fail:
        btrfs_release_path(path);
        return ret;
}

static noinline int remove_extent_data_ref(struct btrfs_trans_handle *trans,
                                           struct btrfs_path *path,
                                           int refs_to_drop, int *last_ref)
{
        struct btrfs_key key;
        struct btrfs_extent_data_ref *ref1 = NULL;
        struct btrfs_shared_data_ref *ref2 = NULL;
        struct extent_buffer *leaf;
        u32 num_refs = 0;
        int ret = 0;

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

        if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
                ref1 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_extent_data_ref);
                num_refs = btrfs_extent_data_ref_count(leaf, ref1);
        } else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
                ref2 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_shared_data_ref);
                num_refs = btrfs_shared_data_ref_count(leaf, ref2);
        } else if (unlikely(key.type == BTRFS_EXTENT_REF_V0_KEY)) {
                btrfs_print_v0_err(trans->fs_info);
                btrfs_abort_transaction(trans, -EINVAL);
                return -EINVAL;
        } else {
                BUG();
        }

        BUG_ON(num_refs < refs_to_drop);
        num_refs -= refs_to_drop;

        if (num_refs == 0) {
                ret = btrfs_del_item(trans, trans->fs_info->extent_root, path);
                *last_ref = 1;
        } else {
                if (key.type == BTRFS_EXTENT_DATA_REF_KEY)
                        btrfs_set_extent_data_ref_count(leaf, ref1, num_refs);
                else if (key.type == BTRFS_SHARED_DATA_REF_KEY)
                        btrfs_set_shared_data_ref_count(leaf, ref2, num_refs);
                btrfs_mark_buffer_dirty(leaf);
        }
        return ret;
}

static noinline u32 extent_data_ref_count(struct btrfs_path *path,
                                          struct btrfs_extent_inline_ref *iref)
{
        struct btrfs_key key;
        struct extent_buffer *leaf;
        struct btrfs_extent_data_ref *ref1;
        struct btrfs_shared_data_ref *ref2;
        u32 num_refs = 0;
        int type;

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

        BUG_ON(key.type == BTRFS_EXTENT_REF_V0_KEY);
        if (iref) {
                /*
                 * If type is invalid, we should have bailed out earlier than
                 * this call.
                 */
                type = btrfs_get_extent_inline_ref_type(leaf, iref, BTRFS_REF_TYPE_DATA);
                ASSERT(type != BTRFS_REF_TYPE_INVALID);
                if (type == BTRFS_EXTENT_DATA_REF_KEY) {
                        ref1 = (struct btrfs_extent_data_ref *)(&iref->offset);
                        num_refs = btrfs_extent_data_ref_count(leaf, ref1);
                } else {
                        ref2 = (struct btrfs_shared_data_ref *)(iref + 1);
                        num_refs = btrfs_shared_data_ref_count(leaf, ref2);
                }
        } else if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
                ref1 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_extent_data_ref);
                num_refs = btrfs_extent_data_ref_count(leaf, ref1);
        } else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
                ref2 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_shared_data_ref);
                num_refs = btrfs_shared_data_ref_count(leaf, ref2);
        } else {
                WARN_ON(1);
        }
        return num_refs;
}

static noinline int lookup_tree_block_ref(struct btrfs_trans_handle *trans,
                                          struct btrfs_path *path,
                                          u64 bytenr, u64 parent,
                                          u64 root_objectid)
{
        struct btrfs_root *root = trans->fs_info->extent_root;
        struct btrfs_key key;
        int ret;

        key.objectid = bytenr;
        if (parent) {
                key.type = BTRFS_SHARED_BLOCK_REF_KEY;
                key.offset = parent;
        } else {
                key.type = BTRFS_TREE_BLOCK_REF_KEY;
                key.offset = root_objectid;
        }

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret > 0)
                ret = -ENOENT;
        return ret;
}

static noinline int insert_tree_block_ref(struct btrfs_trans_handle *trans,
                                          struct btrfs_path *path,
                                          u64 bytenr, u64 parent,
                                          u64 root_objectid)
{
        struct btrfs_key key;
        int ret;

        key.objectid = bytenr;
        if (parent) {
                key.type = BTRFS_SHARED_BLOCK_REF_KEY;
                key.offset = parent;
        } else {
                key.type = BTRFS_TREE_BLOCK_REF_KEY;
                key.offset = root_objectid;
        }

        ret = btrfs_insert_empty_item(trans, trans->fs_info->extent_root,
                                      path, &key, 0);
        btrfs_release_path(path);
        return ret;
}

static inline int extent_ref_type(u64 parent, u64 owner)
{
        int type;
        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                if (parent > 0)
                        type = BTRFS_SHARED_BLOCK_REF_KEY;
                else
                        type = BTRFS_TREE_BLOCK_REF_KEY;
        } else {
                if (parent > 0)
                        type = BTRFS_SHARED_DATA_REF_KEY;
                else
                        type = BTRFS_EXTENT_DATA_REF_KEY;
        }
        return type;
}

static int find_next_key(struct btrfs_path *path, int level,
                         struct btrfs_key *key)

{
        for (; level < BTRFS_MAX_LEVEL; level++) {
                if (!path->nodes[level])
                        break;
                if (path->slots[level] + 1 >=
                    btrfs_header_nritems(path->nodes[level]))
                        continue;
                if (level == 0)
                        btrfs_item_key_to_cpu(path->nodes[level], key,
                                              path->slots[level] + 1);
                else
                        btrfs_node_key_to_cpu(path->nodes[level], key,
                                              path->slots[level] + 1);
                return 0;
        }
        return 1;
}

/*
 * look for inline back ref. if back ref is found, *ref_ret is set
 * to the address of inline back ref, and 0 is returned.
 *
 * if back ref isn't found, *ref_ret is set to the address where it
 * should be inserted, and -ENOENT is returned.
 *
 * if insert is true and there are too many inline back refs, the path
 * points to the extent item, and -EAGAIN is returned.
 *
 * NOTE: inline back refs are ordered in the same way that back ref
 *       items in the tree are ordered.
 */
static noinline_for_stack
int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref **ref_ret,
                                 u64 bytenr, u64 num_bytes,
                                 u64 parent, u64 root_objectid,
                                 u64 owner, u64 offset, int insert)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = fs_info->extent_root;
        struct btrfs_key key;
        struct extent_buffer *leaf;
        struct btrfs_extent_item *ei;
        struct btrfs_extent_inline_ref *iref;
        u64 flags;
        u64 item_size;
        unsigned long ptr;
        unsigned long end;
        int extra_size;
        int type;
        int want;
        int ret;
        int err = 0;
        bool skinny_metadata = btrfs_fs_incompat(fs_info, SKINNY_METADATA);
        int needed;

        key.objectid = bytenr;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        key.offset = num_bytes;

        want = extent_ref_type(parent, owner);
        if (insert) {
                extra_size = btrfs_extent_inline_ref_size(want);
                path->keep_locks = 1;
        } else
                extra_size = -1;

        /*
         * Owner is our level, so we can just add one to get the level for the
         * block we are interested in.
         */
        if (skinny_metadata && owner < BTRFS_FIRST_FREE_OBJECTID) {
                key.type = BTRFS_METADATA_ITEM_KEY;
                key.offset = owner;
        }

again:
        ret = btrfs_search_slot(trans, root, &key, path, extra_size, 1);
        if (ret < 0) {
                err = ret;
                goto out;
        }

        /*
         * We may be a newly converted file system which still has the old fat
         * extent entries for metadata, so try and see if we have one of those.
         */
        if (ret > 0 && skinny_metadata) {
                skinny_metadata = false;
                if (path->slots[0]) {
                        path->slots[0]--;
                        btrfs_item_key_to_cpu(path->nodes[0], &key,
                                              path->slots[0]);
                        if (key.objectid == bytenr &&
                            key.type == BTRFS_EXTENT_ITEM_KEY &&
                            key.offset == num_bytes)
                                ret = 0;
                }
                if (ret) {
                        key.objectid = bytenr;
                        key.type = BTRFS_EXTENT_ITEM_KEY;
                        key.offset = num_bytes;
                        btrfs_release_path(path);
                        goto again;
                }
        }

        if (ret && !insert) {
                err = -ENOENT;
                goto out;
        } else if (WARN_ON(ret)) {
                err = -EIO;
                goto out;
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        if (unlikely(item_size < sizeof(*ei))) {
                err = -EINVAL;
                btrfs_print_v0_err(fs_info);
                btrfs_abort_transaction(trans, err);
                goto out;
        }

        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        flags = btrfs_extent_flags(leaf, ei);

        ptr = (unsigned long)(ei + 1);
        end = (unsigned long)ei + item_size;

        if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK && !skinny_metadata) {
                ptr += sizeof(struct btrfs_tree_block_info);
                BUG_ON(ptr > end);
        }

        if (owner >= BTRFS_FIRST_FREE_OBJECTID)
                needed = BTRFS_REF_TYPE_DATA;
        else
                needed = BTRFS_REF_TYPE_BLOCK;

        err = -ENOENT;
        while (1) {
                if (ptr >= end) {
                        WARN_ON(ptr > end);
                        break;
                }
                iref = (struct btrfs_extent_inline_ref *)ptr;
                type = btrfs_get_extent_inline_ref_type(leaf, iref, needed);
                if (type == BTRFS_REF_TYPE_INVALID) {
                        err = -EUCLEAN;
                        goto out;
                }

                if (want < type)
                        break;
                if (want > type) {
                        ptr += btrfs_extent_inline_ref_size(type);
                        continue;
                }

                if (type == BTRFS_EXTENT_DATA_REF_KEY) {
                        struct btrfs_extent_data_ref *dref;
                        dref = (struct btrfs_extent_data_ref *)(&iref->offset);
                        if (match_extent_data_ref(leaf, dref, root_objectid,
                                                  owner, offset)) {
                                err = 0;
                                break;
                        }
                        if (hash_extent_data_ref_item(leaf, dref) <
                            hash_extent_data_ref(root_objectid, owner, offset))
                                break;
                } else {
                        u64 ref_offset;
                        ref_offset = btrfs_extent_inline_ref_offset(leaf, iref);
                        if (parent > 0) {
                                if (parent == ref_offset) {
                                        err = 0;
                                        break;
                                }
                                if (ref_offset < parent)
                                        break;
                        } else {
                                if (root_objectid == ref_offset) {
                                        err = 0;
                                        break;
                                }
                                if (ref_offset < root_objectid)
                                        break;
                        }
                }
                ptr += btrfs_extent_inline_ref_size(type);
        }
        if (err == -ENOENT && insert) {
                if (item_size + extra_size >=
                    BTRFS_MAX_EXTENT_ITEM_SIZE(root)) {
                        err = -EAGAIN;
                        goto out;
                }
                /*
                 * To add new inline back ref, we have to make sure
                 * there is no corresponding back ref item.
                 * For simplicity, we just do not add new inline back
                 * ref if there is any kind of item for this block
                 */
                if (find_next_key(path, 0, &key) == 0 &&
                    key.objectid == bytenr &&
                    key.type < BTRFS_BLOCK_GROUP_ITEM_KEY) {
                        err = -EAGAIN;
                        goto out;
                }
        }
        *ref_ret = (struct btrfs_extent_inline_ref *)ptr;
out:
        if (insert) {
                path->keep_locks = 0;
                btrfs_unlock_up_safe(path, 1);
        }

        return err;
}

/*
 * helper to add new inline back ref
 */
static noinline_for_stack
void setup_inline_extent_backref(struct btrfs_fs_info *fs_info,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref *iref,
                                 u64 parent, u64 root_objectid,
                                 u64 owner, u64 offset, int refs_to_add,
                                 struct btrfs_delayed_extent_op *extent_op)
{
        struct extent_buffer *leaf;
        struct btrfs_extent_item *ei;
        unsigned long ptr;
        unsigned long end;
        unsigned long item_offset;
        u64 refs;
        int size;
        int type;

        leaf = path->nodes[0];
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        item_offset = (unsigned long)iref - (unsigned long)ei;

        type = extent_ref_type(parent, owner);
        size = btrfs_extent_inline_ref_size(type);

        btrfs_extend_item(path, size);

        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        refs = btrfs_extent_refs(leaf, ei);
        refs += refs_to_add;
        btrfs_set_extent_refs(leaf, ei, refs);
        if (extent_op)
                __run_delayed_extent_op(extent_op, leaf, ei);

        ptr = (unsigned long)ei + item_offset;
        end = (unsigned long)ei + btrfs_item_size_nr(leaf, path->slots[0]);
        if (ptr < end - size)
                memmove_extent_buffer(leaf, ptr + size, ptr,
                                      end - size - ptr);

        iref = (struct btrfs_extent_inline_ref *)ptr;
        btrfs_set_extent_inline_ref_type(leaf, iref, type);
        if (type == BTRFS_EXTENT_DATA_REF_KEY) {
                struct btrfs_extent_data_ref *dref;
                dref = (struct btrfs_extent_data_ref *)(&iref->offset);
                btrfs_set_extent_data_ref_root(leaf, dref, root_objectid);
                btrfs_set_extent_data_ref_objectid(leaf, dref, owner);
                btrfs_set_extent_data_ref_offset(leaf, dref, offset);
                btrfs_set_extent_data_ref_count(leaf, dref, refs_to_add);
        } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
                struct btrfs_shared_data_ref *sref;
                sref = (struct btrfs_shared_data_ref *)(iref + 1);
                btrfs_set_shared_data_ref_count(leaf, sref, refs_to_add);
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
        } else if (type == BTRFS_SHARED_BLOCK_REF_KEY) {
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
        } else {
                btrfs_set_extent_inline_ref_offset(leaf, iref, root_objectid);
        }
        btrfs_mark_buffer_dirty(leaf);
}

static int lookup_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref **ref_ret,
                                 u64 bytenr, u64 num_bytes, u64 parent,
                                 u64 root_objectid, u64 owner, u64 offset)
{
        int ret;

        ret = lookup_inline_extent_backref(trans, path, ref_ret, bytenr,
                                           num_bytes, parent, root_objectid,
                                           owner, offset, 0);
        if (ret != -ENOENT)
                return ret;

        btrfs_release_path(path);
        *ref_ret = NULL;

        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                ret = lookup_tree_block_ref(trans, path, bytenr, parent,
                                            root_objectid);
        } else {
                ret = lookup_extent_data_ref(trans, path, bytenr, parent,
                                             root_objectid, owner, offset);
        }
        return ret;
}

/*
 * helper to update/remove inline back ref
 */
static noinline_for_stack
void update_inline_extent_backref(struct btrfs_path *path,
                                  struct btrfs_extent_inline_ref *iref,
                                  int refs_to_mod,
                                  struct btrfs_delayed_extent_op *extent_op,
                                  int *last_ref)
{
        struct extent_buffer *leaf = path->nodes[0];
        struct btrfs_extent_item *ei;
        struct btrfs_extent_data_ref *dref = NULL;
        struct btrfs_shared_data_ref *sref = NULL;
        unsigned long ptr;
        unsigned long end;
        u32 item_size;
        int size;
        int type;
        u64 refs;

        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        refs = btrfs_extent_refs(leaf, ei);
        WARN_ON(refs_to_mod < 0 && refs + refs_to_mod <= 0);
        refs += refs_to_mod;
        btrfs_set_extent_refs(leaf, ei, refs);
        if (extent_op)
                __run_delayed_extent_op(extent_op, leaf, ei);

        /*
         * If type is invalid, we should have bailed out after
         * lookup_inline_extent_backref().
         */
        type = btrfs_get_extent_inline_ref_type(leaf, iref, BTRFS_REF_TYPE_ANY);
        ASSERT(type != BTRFS_REF_TYPE_INVALID);

        if (type == BTRFS_EXTENT_DATA_REF_KEY) {
                dref = (struct btrfs_extent_data_ref *)(&iref->offset);
                refs = btrfs_extent_data_ref_count(leaf, dref);
        } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
                sref = (struct btrfs_shared_data_ref *)(iref + 1);
                refs = btrfs_shared_data_ref_count(leaf, sref);
        } else {
                refs = 1;
                BUG_ON(refs_to_mod != -1);
        }

        BUG_ON(refs_to_mod < 0 && refs < -refs_to_mod);
        refs += refs_to_mod;

        if (refs > 0) {
                if (type == BTRFS_EXTENT_DATA_REF_KEY)
                        btrfs_set_extent_data_ref_count(leaf, dref, refs);
                else
                        btrfs_set_shared_data_ref_count(leaf, sref, refs);
        } else {
                *last_ref = 1;
                size =  btrfs_extent_inline_ref_size(type);
                item_size = btrfs_item_size_nr(leaf, path->slots[0]);
                ptr = (unsigned long)iref;
                end = (unsigned long)ei + item_size;
                if (ptr + size < end)
                        memmove_extent_buffer(leaf, ptr, ptr + size,
                                              end - ptr - size);
                item_size -= size;
                btrfs_truncate_item(path, item_size, 1);
        }
        btrfs_mark_buffer_dirty(leaf);
}

static noinline_for_stack
int insert_inline_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_path *path,
                                 u64 bytenr, u64 num_bytes, u64 parent,
                                 u64 root_objectid, u64 owner,
                                 u64 offset, int refs_to_add,
                                 struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_extent_inline_ref *iref;
        int ret;

        ret = lookup_inline_extent_backref(trans, path, &iref, bytenr,
                                           num_bytes, parent, root_objectid,
                                           owner, offset, 1);
        if (ret == 0) {
                /*
                 * We're adding refs to a tree block we already own, this
                 * should not happen at all.
                 */
                if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                        btrfs_crit(trans->fs_info,
"adding refs to an existing tree ref, bytenr %llu num_bytes %llu root_objectid %llu",
                                   bytenr, num_bytes, root_objectid);
                        if (IS_ENABLED(CONFIG_BTRFS_DEBUG)) {
                                WARN_ON(1);
                                btrfs_crit(trans->fs_info,
                        "path->slots[0]=%d path->nodes[0]:", path->slots[0]);
                                btrfs_print_leaf(path->nodes[0]);
                        }
                        return -EUCLEAN;
                }
                update_inline_extent_backref(path, iref, refs_to_add,
                                             extent_op, NULL);
        } else if (ret == -ENOENT) {
                setup_inline_extent_backref(trans->fs_info, path, iref, parent,
                                            root_objectid, owner, offset,
                                            refs_to_add, extent_op);
                ret = 0;
        }
        return ret;
}

static int remove_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref *iref,
                                 int refs_to_drop, int is_data, int *last_ref)
{
        int ret = 0;

        BUG_ON(!is_data && refs_to_drop != 1);
        if (iref) {
                update_inline_extent_backref(path, iref, -refs_to_drop, NULL,
                                             last_ref);
        } else if (is_data) {
                ret = remove_extent_data_ref(trans, path, refs_to_drop,
                                             last_ref);
        } else {
                *last_ref = 1;
                ret = btrfs_del_item(trans, trans->fs_info->extent_root, path);
        }
        return ret;
}

static int btrfs_issue_discard(struct block_device *bdev, u64 start, u64 len,
                               u64 *discarded_bytes)
{
        int j, ret = 0;
        u64 bytes_left, end;
        u64 aligned_start = ALIGN(start, 1 << 9);

        if (WARN_ON(start != aligned_start)) {
                len -= aligned_start - start;
                len = round_down(len, 1 << 9);
                start = aligned_start;
        }

        *discarded_bytes = 0;

        if (!len)
                return 0;

        end = start + len;
        bytes_left = len;

        /* Skip any superblocks on this device. */
        for (j = 0; j < BTRFS_SUPER_MIRROR_MAX; j++) {
                u64 sb_start = btrfs_sb_offset(j);
                u64 sb_end = sb_start + BTRFS_SUPER_INFO_SIZE;
                u64 size = sb_start - start;

                if (!in_range(sb_start, start, bytes_left) &&
                    !in_range(sb_end, start, bytes_left) &&
                    !in_range(start, sb_start, BTRFS_SUPER_INFO_SIZE))
                        continue;

                /*
                 * Superblock spans beginning of range.  Adjust start and
                 * try again.
                 */
                if (sb_start <= start) {
                        start += sb_end - start;
                        if (start > end) {
                                bytes_left = 0;
                                break;
                        }
                        bytes_left = end - start;
                        continue;
                }

                if (size) {
                        ret = blkdev_issue_discard(bdev, start >> 9, size >> 9,
                                                   GFP_NOFS, 0);
                        if (!ret)
                                *discarded_bytes += size;
                        else if (ret != -EOPNOTSUPP)
                                return ret;
                }

                start = sb_end;
                if (start > end) {
                        bytes_left = 0;
                        break;
                }
                bytes_left = end - start;
        }

        if (bytes_left) {
                ret = blkdev_issue_discard(bdev, start >> 9, bytes_left >> 9,
                                           GFP_NOFS, 0);
                if (!ret)
                        *discarded_bytes += bytes_left;
        }
        return ret;
}

int btrfs_discard_extent(struct btrfs_fs_info *fs_info, u64 bytenr,
                         u64 num_bytes, u64 *actual_bytes)
{
        int ret = 0;
        u64 discarded_bytes = 0;
        u64 end = bytenr + num_bytes;
        u64 cur = bytenr;
        struct btrfs_bio *bbio = NULL;


        /*
         * Avoid races with device replace and make sure our bbio has devices
         * associated to its stripes that don't go away while we are discarding.
         */
        btrfs_bio_counter_inc_blocked(fs_info);
        while (cur < end) {
                struct btrfs_bio_stripe *stripe;
                int i;

                num_bytes = end - cur;
                /* Tell the block device(s) that the sectors can be discarded */
                ret = btrfs_map_block(fs_info, BTRFS_MAP_DISCARD, cur,
                                      &num_bytes, &bbio, 0);
                /*
                 * Error can be -ENOMEM, -ENOENT (no such chunk mapping) or
                 * -EOPNOTSUPP. For any such error, @num_bytes is not updated,
                 * thus we can't continue anyway.
                 */
                if (ret < 0)
                        goto out;

                stripe = bbio->stripes;
                for (i = 0; i < bbio->num_stripes; i++, stripe++) {
                        u64 bytes;
                        struct request_queue *req_q;

                        if (!stripe->dev->bdev) {
                                ASSERT(btrfs_test_opt(fs_info, DEGRADED));
                                continue;
                        }
                        req_q = bdev_get_queue(stripe->dev->bdev);
                        if (!blk_queue_discard(req_q))
                                continue;

                        ret = btrfs_issue_discard(stripe->dev->bdev,
                                                  stripe->physical,
                                                  stripe->length,
                                                  &bytes);
                        if (!ret) {
                                discarded_bytes += bytes;
                        } else if (ret != -EOPNOTSUPP) {
                                /*
                                 * Logic errors or -ENOMEM, or -EIO, but
                                 * unlikely to happen.
                                 *
                                 * And since there are two loops, explicitly
                                 * go to out to avoid confusion.
                                 */
                                btrfs_put_bbio(bbio);
                                goto out;
                        }

                        /*
                         * Just in case we get back EOPNOTSUPP for some reason,
                         * just ignore the return value so we don't screw up
                         * people calling discard_extent.
                         */
                        ret = 0;
                }
                btrfs_put_bbio(bbio);
                cur += num_bytes;
        }
out:
        btrfs_bio_counter_dec(fs_info);

        if (actual_bytes)
                *actual_bytes = discarded_bytes;


        if (ret == -EOPNOTSUPP)
                ret = 0;
        return ret;
}

/* Can return -ENOMEM */
int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
                         struct btrfs_ref *generic_ref)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        int old_ref_mod, new_ref_mod;
        int ret;

        ASSERT(generic_ref->type != BTRFS_REF_NOT_SET &&
               generic_ref->action);
        BUG_ON(generic_ref->type == BTRFS_REF_METADATA &&
               generic_ref->tree_ref.root == BTRFS_TREE_LOG_OBJECTID);

        if (generic_ref->type == BTRFS_REF_METADATA)
                ret = btrfs_add_delayed_tree_ref(trans, generic_ref,
                                NULL, &old_ref_mod, &new_ref_mod);
        else
                ret = btrfs_add_delayed_data_ref(trans, generic_ref, 0,
                                                 &old_ref_mod, &new_ref_mod);

        btrfs_ref_tree_mod(fs_info, generic_ref);

        if (ret == 0 && old_ref_mod < 0 && new_ref_mod >= 0)
                sub_pinned_bytes(fs_info, generic_ref);

        return ret;
}

/*
 * __btrfs_inc_extent_ref - insert backreference for a given extent
 *
 * The counterpart is in __btrfs_free_extent(), with examples and more details
 * how it works.
 *
 * @trans:          Handle of transaction
 *
 * @node:           The delayed ref node used to get the bytenr/length for
 *                  extent whose references are incremented.
 *
 * @parent:         If this is a shared extent (BTRFS_SHARED_DATA_REF_KEY/
 *                  BTRFS_SHARED_BLOCK_REF_KEY) then it holds the logical
 *                  bytenr of the parent block. Since new extents are always
 *                  created with indirect references, this will only be the case
 *                  when relocating a shared extent. In that case, root_objectid
 *                  will be BTRFS_TREE_RELOC_OBJECTID. Otheriwse, parent must
 *                  be 0
 *
 * @root_objectid:  The id of the root where this modification has originated,
 *                  this can be either one of the well-known metadata trees or
 *                  the subvolume id which references this extent.
 *
 * @owner:          For data extents it is the inode number of the owning file.
 *                  For metadata extents this parameter holds the level in the
 *                  tree of the extent.
 *
 * @offset:         For metadata extents the offset is ignored and is currently
 *                  always passed as 0. For data extents it is the fileoffset
 *                  this extent belongs to.
 *
 * @refs_to_add     Number of references to add
 *
 * @extent_op       Pointer to a structure, holding information necessary when
 *                  updating a tree block's flags
 *
 */
static int __btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
                                  struct btrfs_delayed_ref_node *node,
                                  u64 parent, u64 root_objectid,
                                  u64 owner, u64 offset, int refs_to_add,
                                  struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_extent_item *item;
        struct btrfs_key key;
        u64 bytenr = node->bytenr;
        u64 num_bytes = node->num_bytes;
        u64 refs;
        int ret;

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

        path->leave_spinning = 1;
        /* this will setup the path even if it fails to insert the back ref */
        ret = insert_inline_extent_backref(trans, path, bytenr, num_bytes,
                                           parent, root_objectid, owner,
                                           offset, refs_to_add, extent_op);
        if ((ret < 0 && ret != -EAGAIN) || !ret)
                goto out;

        /*
         * Ok we had -EAGAIN which means we didn't have space to insert and
         * inline extent ref, so just update the reference count and add a
         * normal backref.
         */
        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        refs = btrfs_extent_refs(leaf, item);
        btrfs_set_extent_refs(leaf, item, refs + refs_to_add);
        if (extent_op)
                __run_delayed_extent_op(extent_op, leaf, item);

        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        path->leave_spinning = 1;
        /* now insert the actual backref */
        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                BUG_ON(refs_to_add != 1);
                ret = insert_tree_block_ref(trans, path, bytenr, parent,
                                            root_objectid);
        } else {
                ret = insert_extent_data_ref(trans, path, bytenr, parent,
                                             root_objectid, owner, offset,
                                             refs_to_add);
        }
        if (ret)
                btrfs_abort_transaction(trans, ret);
out:
        btrfs_free_path(path);
        return ret;
}

static int run_delayed_data_ref(struct btrfs_trans_handle *trans,
                                struct btrfs_delayed_ref_node *node,
                                struct btrfs_delayed_extent_op *extent_op,
                                int insert_reserved)
{
        int ret = 0;
        struct btrfs_delayed_data_ref *ref;
        struct btrfs_key ins;
        u64 parent = 0;
        u64 ref_root = 0;
        u64 flags = 0;

        ins.objectid = node->bytenr;
        ins.offset = node->num_bytes;
        ins.type = BTRFS_EXTENT_ITEM_KEY;

        ref = btrfs_delayed_node_to_data_ref(node);
        trace_run_delayed_data_ref(trans->fs_info, node, ref, node->action);

        if (node->type == BTRFS_SHARED_DATA_REF_KEY)
                parent = ref->parent;
        ref_root = ref->root;

        if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
                if (extent_op)
                        flags |= extent_op->flags_to_set;
                ret = alloc_reserved_file_extent(trans, parent, ref_root,
                                                 flags, ref->objectid,
                                                 ref->offset, &ins,
                                                 node->ref_mod);
        } else if (node->action == BTRFS_ADD_DELAYED_REF) {
                ret = __btrfs_inc_extent_ref(trans, node, parent, ref_root,
                                             ref->objectid, ref->offset,
                                             node->ref_mod, extent_op);
        } else if (node->action == BTRFS_DROP_DELAYED_REF) {
                ret = __btrfs_free_extent(trans, node, parent,
                                          ref_root, ref->objectid,
                                          ref->offset, node->ref_mod,
                                          extent_op);
        } else {
                BUG();
        }
        return ret;
}

static void __run_delayed_extent_op(struct btrfs_delayed_extent_op *extent_op,
                                    struct extent_buffer *leaf,
                                    struct btrfs_extent_item *ei)
{
        u64 flags = btrfs_extent_flags(leaf, ei);
        if (extent_op->update_flags) {
                flags |= extent_op->flags_to_set;
                btrfs_set_extent_flags(leaf, ei, flags);
        }

        if (extent_op->update_key) {
                struct btrfs_tree_block_info *bi;
                BUG_ON(!(flags & BTRFS_EXTENT_FLAG_TREE_BLOCK));
                bi = (struct btrfs_tree_block_info *)(ei + 1);
                btrfs_set_tree_block_key(leaf, bi, &extent_op->key);
        }
}

static int run_delayed_extent_op(struct btrfs_trans_handle *trans,
                                 struct btrfs_delayed_ref_head *head,
                                 struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_key key;
        struct btrfs_path *path;
        struct btrfs_extent_item *ei;
        struct extent_buffer *leaf;
        u32 item_size;
        int ret;
        int err = 0;
        int metadata = !extent_op->is_data;

        if (TRANS_ABORTED(trans))
                return 0;

        if (metadata && !btrfs_fs_incompat(fs_info, SKINNY_METADATA))
                metadata = 0;

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

        key.objectid = head->bytenr;

        if (metadata) {
                key.type = BTRFS_METADATA_ITEM_KEY;
                key.offset = extent_op->level;
        } else {
                key.type = BTRFS_EXTENT_ITEM_KEY;
                key.offset = head->num_bytes;
        }

again:
        path->leave_spinning = 1;
        ret = btrfs_search_slot(trans, fs_info->extent_root, &key, path, 0, 1);
        if (ret < 0) {
                err = ret;
                goto out;
        }
        if (ret > 0) {
                if (metadata) {
                        if (path->slots[0] > 0) {
                                path->slots[0]--;
                                btrfs_item_key_to_cpu(path->nodes[0], &key,
                                                      path->slots[0]);
                                if (key.objectid == head->bytenr &&
                                    key.type == BTRFS_EXTENT_ITEM_KEY &&
                                    key.offset == head->num_bytes)
                                        ret = 0;
                        }
                        if (ret > 0) {
                                btrfs_release_path(path);
                                metadata = 0;

                                key.objectid = head->bytenr;
                                key.offset = head->num_bytes;
                                key.type = BTRFS_EXTENT_ITEM_KEY;
                                goto again;
                        }
                } else {
                        err = -EIO;
                        goto out;
                }
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);

        if (unlikely(item_size < sizeof(*ei))) {
                err = -EINVAL;
                btrfs_print_v0_err(fs_info);
                btrfs_abort_transaction(trans, err);
                goto out;
        }

        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        __run_delayed_extent_op(extent_op, leaf, ei);

        btrfs_mark_buffer_dirty(leaf);
out:
        btrfs_free_path(path);
        return err;
}

static int run_delayed_tree_ref(struct btrfs_trans_handle *trans,
                                struct btrfs_delayed_ref_node *node,
                                struct btrfs_delayed_extent_op *extent_op,
                                int insert_reserved)
{
        int ret = 0;
        struct btrfs_delayed_tree_ref *ref;
        u64 parent = 0;
        u64 ref_root = 0;

        ref = btrfs_delayed_node_to_tree_ref(node);
        trace_run_delayed_tree_ref(trans->fs_info, node, ref, node->action);

        if (node->type == BTRFS_SHARED_BLOCK_REF_KEY)
                parent = ref->parent;
        ref_root = ref->root;

        if (node->ref_mod != 1) {
                btrfs_err(trans->fs_info,
        "btree block(%llu) has %d references rather than 1: action %d ref_root %llu parent %llu",
                          node->bytenr, node->ref_mod, node->action, ref_root,
                          parent);
                return -EIO;
        }
        if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
                BUG_ON(!extent_op || !extent_op->update_flags);
                ret = alloc_reserved_tree_block(trans, node, extent_op);
        } else if (node->action == BTRFS_ADD_DELAYED_REF) {
                ret = __btrfs_inc_extent_ref(trans, node, parent, ref_root,
                                             ref->level, 0, 1, extent_op);
        } else if (node->action == BTRFS_DROP_DELAYED_REF) {
                ret = __btrfs_free_extent(trans, node, parent, ref_root,
                                          ref->level, 0, 1, extent_op);
        } else {
                BUG();
        }
        return ret;
}

/* helper function to actually process a single delayed ref entry */
static int run_one_delayed_ref(struct btrfs_trans_handle *trans,
                               struct btrfs_delayed_ref_node *node,
                               struct btrfs_delayed_extent_op *extent_op,
                               int insert_reserved)
{
        int ret = 0;

        if (TRANS_ABORTED(trans)) {
                if (insert_reserved)
                        btrfs_pin_extent(trans, node->bytenr, node->num_bytes, 1);
                return 0;
        }

        if (node->type == BTRFS_TREE_BLOCK_REF_KEY ||
            node->type == BTRFS_SHARED_BLOCK_REF_KEY)
                ret = run_delayed_tree_ref(trans, node, extent_op,
                                           insert_reserved);
        else if (node->type == BTRFS_EXTENT_DATA_REF_KEY ||
                 node->type == BTRFS_SHARED_DATA_REF_KEY)
                ret = run_delayed_data_ref(trans, node, extent_op,
                                           insert_reserved);
        else
                BUG();
        if (ret && insert_reserved)
                btrfs_pin_extent(trans, node->bytenr, node->num_bytes, 1);
        return ret;
}

static inline struct btrfs_delayed_ref_node *
select_delayed_ref(struct btrfs_delayed_ref_head *head)
{
        struct btrfs_delayed_ref_node *ref;

        if (RB_EMPTY_ROOT(&head->ref_tree.rb_root))
                return NULL;

        /*
         * Select a delayed ref of type BTRFS_ADD_DELAYED_REF first.
         * This is to prevent a ref count from going down to zero, which deletes
         * the extent item from the extent tree, when there still are references
         * to add, which would fail because they would not find the extent item.
         */
        if (!list_empty(&head->ref_add_list))
                return list_first_entry(&head->ref_add_list,
                                struct btrfs_delayed_ref_node, add_list);

        ref = rb_entry(rb_first_cached(&head->ref_tree),
                       struct btrfs_delayed_ref_node, ref_node);
        ASSERT(list_empty(&ref->add_list));
        return ref;
}

static void unselect_delayed_ref_head(struct btrfs_delayed_ref_root *delayed_refs,
                                      struct btrfs_delayed_ref_head *head)
{
        spin_lock(&delayed_refs->lock);
        head->processing = 0;
        delayed_refs->num_heads_ready++;
        spin_unlock(&delayed_refs->lock);
        btrfs_delayed_ref_unlock(head);
}

static struct btrfs_delayed_extent_op *cleanup_extent_op(
                                struct btrfs_delayed_ref_head *head)
{
        struct btrfs_delayed_extent_op *extent_op = head->extent_op;

        if (!extent_op)
                return NULL;

        if (head->must_insert_reserved) {
                head->extent_op = NULL;
                btrfs_free_delayed_extent_op(extent_op);
                return NULL;
        }
        return extent_op;
}

static int run_and_cleanup_extent_op(struct btrfs_trans_handle *trans,
                                     struct btrfs_delayed_ref_head *head)
{
        struct btrfs_delayed_extent_op *extent_op;
        int ret;

        extent_op = cleanup_extent_op(head);
        if (!extent_op)
                return 0;
        head->extent_op = NULL;
        spin_unlock(&head->lock);
        ret = run_delayed_extent_op(trans, head, extent_op);
        btrfs_free_delayed_extent_op(extent_op);
        return ret ? ret : 1;
}

void btrfs_cleanup_ref_head_accounting(struct btrfs_fs_info *fs_info,
                                  struct btrfs_delayed_ref_root *delayed_refs,
                                  struct btrfs_delayed_ref_head *head)
{
        int nr_items = 1;       /* Dropping this ref head update. */

        if (head->total_ref_mod < 0) {
                struct btrfs_space_info *space_info;
                u64 flags;

                if (head->is_data)
                        flags = BTRFS_BLOCK_GROUP_DATA;
                else if (head->is_system)
                        flags = BTRFS_BLOCK_GROUP_SYSTEM;
                else
                        flags = BTRFS_BLOCK_GROUP_METADATA;
                space_info = btrfs_find_space_info(fs_info, flags);
                ASSERT(space_info);
                percpu_counter_add_batch(&space_info->total_bytes_pinned,
                                   -head->num_bytes,
                                   BTRFS_TOTAL_BYTES_PINNED_BATCH);

                /*
                 * We had csum deletions accounted for in our delayed refs rsv,
                 * we need to drop the csum leaves for this update from our
                 * delayed_refs_rsv.
                 */
                if (head->is_data) {
                        spin_lock(&delayed_refs->lock);
                        delayed_refs->pending_csums -= head->num_bytes;
                        spin_unlock(&delayed_refs->lock);
                        nr_items += btrfs_csum_bytes_to_leaves(fs_info,
                                head->num_bytes);
                }
        }

        btrfs_delayed_refs_rsv_release(fs_info, nr_items);
}

static int cleanup_ref_head(struct btrfs_trans_handle *trans,
                            struct btrfs_delayed_ref_head *head)
{

        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret;

        delayed_refs = &trans->transaction->delayed_refs;

        ret = run_and_cleanup_extent_op(trans, head);
        if (ret < 0) {
                unselect_delayed_ref_head(delayed_refs, head);
                btrfs_debug(fs_info, "run_delayed_extent_op returned %d", ret);
                return ret;
        } else if (ret) {
                return ret;
        }

        /*
         * Need to drop our head ref lock and re-acquire the delayed ref lock
         * and then re-check to make sure nobody got added.
         */
        spin_unlock(&head->lock);
        spin_lock(&delayed_refs->lock);
        spin_lock(&head->lock);
        if (!RB_EMPTY_ROOT(&head->ref_tree.rb_root) || head->extent_op) {
                spin_unlock(&head->lock);
                spin_unlock(&delayed_refs->lock);
                return 1;
        }
        btrfs_delete_ref_head(delayed_refs, head);
        spin_unlock(&head->lock);
        spin_unlock(&delayed_refs->lock);

        if (head->must_insert_reserved) {
                btrfs_pin_extent(trans, head->bytenr, head->num_bytes, 1);
                if (head->is_data) {
                        ret = btrfs_del_csums(trans, fs_info->csum_root,
                                              head->bytenr, head->num_bytes);
                }
        }

        btrfs_cleanup_ref_head_accounting(fs_info, delayed_refs, head);

        trace_run_delayed_ref_head(fs_info, head, 0);
        btrfs_delayed_ref_unlock(head);
        btrfs_put_delayed_ref_head(head);
        return 0;
}

static struct btrfs_delayed_ref_head *btrfs_obtain_ref_head(
                                        struct btrfs_trans_handle *trans)
{
        struct btrfs_delayed_ref_root *delayed_refs =
                &trans->transaction->delayed_refs;
        struct btrfs_delayed_ref_head *head = NULL;
        int ret;

        spin_lock(&delayed_refs->lock);
        head = btrfs_select_ref_head(delayed_refs);
        if (!head) {
                spin_unlock(&delayed_refs->lock);
                return head;
        }

        /*
         * Grab the lock that says we are going to process all the refs for
         * this head
         */
        ret = btrfs_delayed_ref_lock(delayed_refs, head);
        spin_unlock(&delayed_refs->lock);

        /*
         * We may have dropped the spin lock to get the head mutex lock, and
         * that might have given someone else time to free the head.  If that's
         * true, it has been removed from our list and we can move on.
         */
        if (ret == -EAGAIN)
                head = ERR_PTR(-EAGAIN);

        return head;
}

static int btrfs_run_delayed_refs_for_head(struct btrfs_trans_handle *trans,
                                    struct btrfs_delayed_ref_head *locked_ref,
                                    unsigned long *run_refs)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_extent_op *extent_op;
        struct btrfs_delayed_ref_node *ref;
        int must_insert_reserved = 0;
        int ret;

        delayed_refs = &trans->transaction->delayed_refs;

        lockdep_assert_held(&locked_ref->mutex);
        lockdep_assert_held(&locked_ref->lock);

        while ((ref = select_delayed_ref(locked_ref))) {
                if (ref->seq &&
                    btrfs_check_delayed_seq(fs_info, ref->seq)) {
                        spin_unlock(&locked_ref->lock);
                        unselect_delayed_ref_head(delayed_refs, locked_ref);
                        return -EAGAIN;
                }

                (*run_refs)++;
                ref->in_tree = 0;
                rb_erase_cached(&ref->ref_node, &locked_ref->ref_tree);
                RB_CLEAR_NODE(&ref->ref_node);
                if (!list_empty(&ref->add_list))
                        list_del(&ref->add_list);
                /*
                 * When we play the delayed ref, also correct the ref_mod on
                 * head
                 */
                switch (ref->action) {
                case BTRFS_ADD_DELAYED_REF:
                case BTRFS_ADD_DELAYED_EXTENT:
                        locked_ref->ref_mod -= ref->ref_mod;
                        break;
                case BTRFS_DROP_DELAYED_REF:
                        locked_ref->ref_mod += ref->ref_mod;
                        break;
                default:
                        WARN_ON(1);
                }
                atomic_dec(&delayed_refs->num_entries);

                /*
                 * Record the must_insert_reserved flag before we drop the
                 * spin lock.
                 */
                must_insert_reserved = locked_ref->must_insert_reserved;
                locked_ref->must_insert_reserved = 0;

                extent_op = locked_ref->extent_op;
                locked_ref->extent_op = NULL;
                spin_unlock(&locked_ref->lock);

                ret = run_one_delayed_ref(trans, ref, extent_op,
                                          must_insert_reserved);

                btrfs_free_delayed_extent_op(extent_op);
                if (ret) {
                        unselect_delayed_ref_head(delayed_refs, locked_ref);
                        btrfs_put_delayed_ref(ref);
                        btrfs_debug(fs_info, "run_one_delayed_ref returned %d",
                                    ret);
                        return ret;
                }

                btrfs_put_delayed_ref(ref);
                cond_resched();

                spin_lock(&locked_ref->lock);
                btrfs_merge_delayed_refs(trans, delayed_refs, locked_ref);
        }

        return 0;
}

/*
 * Returns 0 on success or if called with an already aborted transaction.
 * Returns -ENOMEM or -EIO on failure and will abort the transaction.
 */
static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,

                                             unsigned long nr)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_ref_head *locked_ref = NULL;
        ktime_t start = ktime_get();
        int ret;
        unsigned long count = 0;
        unsigned long actual_count = 0;

        delayed_refs = &trans->transaction->delayed_refs;
        do {
                if (!locked_ref) {
                        locked_ref = btrfs_obtain_ref_head(trans);
                        if (IS_ERR_OR_NULL(locked_ref)) {
                                if (PTR_ERR(locked_ref) == -EAGAIN) {
                                        continue;
                                } else {
                                        break;
                                }
                        }
                        count++;
                }
                /*
                 * We need to try and merge add/drops of the same ref since we
                 * can run into issues with relocate dropping the implicit ref
                 * and then it being added back again before the drop can
                 * finish.  If we merged anything we need to re-loop so we can
                 * get a good ref.
                 * Or we can get node references of the same type that weren't
                 * merged when created due to bumps in the tree mod seq, and
                 * we need to merge them to prevent adding an inline extent
                 * backref before dropping it (triggering a BUG_ON at
                 * insert_inline_extent_backref()).
                 */
                spin_lock(&locked_ref->lock);
                btrfs_merge_delayed_refs(trans, delayed_refs, locked_ref);

                ret = btrfs_run_delayed_refs_for_head(trans, locked_ref,
                                                      &actual_count);
                if (ret < 0 && ret != -EAGAIN) {
                        /*
                         * Error, btrfs_run_delayed_refs_for_head already
                         * unlocked everything so just bail out
                         */
                        return ret;
                } else if (!ret) {
                        /*
                         * Success, perform the usual cleanup of a processed
                         * head
                         */
                        ret = cleanup_ref_head(trans, locked_ref);
                        if (ret > 0 ) {
                                /* We dropped our lock, we need to loop. */
                                ret = 0;
                                continue;
                        } else if (ret) {
                                return ret;
                        }
                }

                /*
                 * Either success case or btrfs_run_delayed_refs_for_head
                 * returned -EAGAIN, meaning we need to select another head
                 */

                locked_ref = NULL;
                cond_resched();
        } while ((nr != -1 && count < nr) || locked_ref);

        /*
         * We don't want to include ref heads since we can have empty ref heads
         * and those will drastically skew our runtime down since we just do
         * accounting, no actual extent tree updates.
         */
        if (actual_count > 0) {
                u64 runtime = ktime_to_ns(ktime_sub(ktime_get(), start));
                u64 avg;

                /*
                 * We weigh the current average higher than our current runtime
                 * to avoid large swings in the average.
                 */
                spin_lock(&delayed_refs->lock);
                avg = fs_info->avg_delayed_ref_runtime * 3 + runtime;
                fs_info->avg_delayed_ref_runtime = avg >> 2;    /* div by 4 */
                spin_unlock(&delayed_refs->lock);
        }
        return 0;
}

#ifdef SCRAMBLE_DELAYED_REFS
/*
 * Normally delayed refs get processed in ascending bytenr order. This
 * correlates in most cases to the order added. To expose dependencies on this
 * order, we start to process the tree in the middle instead of the beginning
 */
static u64 find_middle(struct rb_root *root)
{
        struct rb_node *n = root->rb_node;
        struct btrfs_delayed_ref_node *entry;
        int alt = 1;
        u64 middle;
        u64 first = 0, last = 0;

        n = rb_first(root);
        if (n) {
                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
                first = entry->bytenr;
        }
        n = rb_last(root);
        if (n) {
                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
                last = entry->bytenr;
        }
        n = root->rb_node;

        while (n) {
                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
                WARN_ON(!entry->in_tree);

                middle = entry->bytenr;

                if (alt)
                        n = n->rb_left;
                else
                        n = n->rb_right;

                alt = 1 - alt;
        }
        return middle;
}
#endif

/*
 * Takes the number of bytes to be csumm'ed and figures out how many leaves it
 * would require to store the csums for that many bytes.
 */
u64 btrfs_csum_bytes_to_leaves(struct btrfs_fs_info *fs_info, u64 csum_bytes)
{
        u64 csum_size;
        u64 num_csums_per_leaf;
        u64 num_csums;

        csum_size = BTRFS_MAX_ITEM_SIZE(fs_info);
        num_csums_per_leaf = div64_u64(csum_size,
                        (u64)btrfs_super_csum_size(fs_info->super_copy));
        num_csums = div64_u64(csum_bytes, fs_info->sectorsize);
        num_csums += num_csums_per_leaf - 1;
        num_csums = div64_u64(num_csums, num_csums_per_leaf);
        return num_csums;
}

/*
 * this starts processing the delayed reference count updates and
 * extent insertions we have queued up so far.  count can be
 * 0, which means to process everything in the tree at the start
 * of the run (but not newly added entries), or it can be some target
 * number you'd like to process.
 *
 * Returns 0 on success or if called with an aborted transaction
 * Returns <0 on error and aborts the transaction
 */
int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                           unsigned long count)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct rb_node *node;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_ref_head *head;
        int ret;
        int run_all = count == (unsigned long)-1;

        /* We'll clean this up in btrfs_cleanup_transaction */
        if (TRANS_ABORTED(trans))
                return 0;

        if (test_bit(BTRFS_FS_CREATING_FREE_SPACE_TREE, &fs_info->flags))
                return 0;

        delayed_refs = &trans->transaction->delayed_refs;
        if (count == 0)
                count = atomic_read(&delayed_refs->num_entries) * 2;

again:
#ifdef SCRAMBLE_DELAYED_REFS
        delayed_refs->run_delayed_start = find_middle(&delayed_refs->root);
#endif
        ret = __btrfs_run_delayed_refs(trans, count);
        if (ret < 0) {
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        if (run_all) {
                btrfs_create_pending_block_groups(trans);

                spin_lock(&delayed_refs->lock);
                node = rb_first_cached(&delayed_refs->href_root);
                if (!node) {
                        spin_unlock(&delayed_refs->lock);
                        goto out;
                }
                head = rb_entry(node, struct btrfs_delayed_ref_head,
                                href_node);
                refcount_inc(&head->refs);
                spin_unlock(&delayed_refs->lock);

                /* Mutex was contended, block until it's released and retry. */
                mutex_lock(&head->mutex);
                mutex_unlock(&head->mutex);

                btrfs_put_delayed_ref_head(head);
                cond_resched();
                goto again;
        }
out:
        return 0;
}

int btrfs_set_disk_extent_flags(struct btrfs_trans_handle *trans,
                                struct extent_buffer *eb, u64 flags,
                                int level, int is_data)
{
        struct btrfs_delayed_extent_op *extent_op;
        int ret;

        extent_op = btrfs_alloc_delayed_extent_op();
        if (!extent_op)
                return -ENOMEM;

        extent_op->flags_to_set = flags;
        extent_op->update_flags = true;
        extent_op->update_key = false;
        extent_op->is_data = is_data ? true : false;
        extent_op->level = level;

        ret = btrfs_add_delayed_extent_op(trans, eb->start, eb->len, extent_op);
        if (ret)
                btrfs_free_delayed_extent_op(extent_op);
        return ret;
}

static noinline int check_delayed_ref(struct btrfs_root *root,
                                      struct btrfs_path *path,
                                      u64 objectid, u64 offset, u64 bytenr)
{
        struct btrfs_delayed_ref_head *head;
        struct btrfs_delayed_ref_node *ref;
        struct btrfs_delayed_data_ref *data_ref;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_transaction *cur_trans;
        struct rb_node *node;
        int ret = 0;

        spin_lock(&root->fs_info->trans_lock);
        cur_trans = root->fs_info->running_transaction;
        if (cur_trans)
                refcount_inc(&cur_trans->use_count);
        spin_unlock(&root->fs_info->trans_lock);
        if (!cur_trans)
                return 0;

        delayed_refs = &cur_trans->delayed_refs;
        spin_lock(&delayed_refs->lock);
        head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
        if (!head) {
                spin_unlock(&delayed_refs->lock);
                btrfs_put_transaction(cur_trans);
                return 0;
        }

        if (!mutex_trylock(&head->mutex)) {
                refcount_inc(&head->refs);
                spin_unlock(&delayed_refs->lock);

                btrfs_release_path(path);

                /*
                 * Mutex was contended, block until it's released and let
                 * caller try again
                 */
                mutex_lock(&head->mutex);
                mutex_unlock(&head->mutex);
                btrfs_put_delayed_ref_head(head);
                btrfs_put_transaction(cur_trans);
                return -EAGAIN;
        }
        spin_unlock(&delayed_refs->lock);

        spin_lock(&head->lock);
        /*
         * XXX: We should replace this with a proper search function in the
         * future.
         */
        for (node = rb_first_cached(&head->ref_tree); node;
             node = rb_next(node)) {
                ref = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
                /* If it's a shared ref we know a cross reference exists */
                if (ref->type != BTRFS_EXTENT_DATA_REF_KEY) {
                        ret = 1;
                        break;
                }

                data_ref = btrfs_delayed_node_to_data_ref(ref);

                /*
                 * If our ref doesn't match the one we're currently looking at
                 * then we have a cross reference.
                 */
                if (data_ref->root != root->root_key.objectid ||
                    data_ref->objectid != objectid ||
                    data_ref->offset != offset) {
                        ret = 1;
                        break;
                }
        }
        spin_unlock(&head->lock);
        mutex_unlock(&head->mutex);
        btrfs_put_transaction(cur_trans);
        return ret;
}

static noinline int check_committed_ref(struct btrfs_root *root,
                                        struct btrfs_path *path,
                                        u64 objectid, u64 offset, u64 bytenr,
                                        bool strict)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_root *extent_root = fs_info->extent_root;
        struct extent_buffer *leaf;
        struct btrfs_extent_data_ref *ref;
        struct btrfs_extent_inline_ref *iref;
        struct btrfs_extent_item *ei;
        struct btrfs_key key;
        u32 item_size;
        int type;
        int ret;

        key.objectid = bytenr;
        key.offset = (u64)-1;
        key.type = BTRFS_EXTENT_ITEM_KEY;

        ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
        if (ret < 0)
                goto out;
        BUG_ON(ret == 0); /* Corruption */

        ret = -ENOENT;
        if (path->slots[0] == 0)
                goto out;

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

        if (key.objectid != bytenr || key.type != BTRFS_EXTENT_ITEM_KEY)
                goto out;

        ret = 1;
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);

        /* If extent item has more than 1 inline ref then it's shared */
        if (item_size != sizeof(*ei) +
            btrfs_extent_inline_ref_size(BTRFS_EXTENT_DATA_REF_KEY))
                goto out;

        /*
         * If extent created before last snapshot => it's shared unless the
         * snapshot has been deleted. Use the heuristic if strict is false.
         */
        if (!strict &&
            (btrfs_extent_generation(leaf, ei) <=
             btrfs_root_last_snapshot(&root->root_item)))
                goto out;

        iref = (struct btrfs_extent_inline_ref *)(ei + 1);

        /* If this extent has SHARED_DATA_REF then it's shared */
        type = btrfs_get_extent_inline_ref_type(leaf, iref, BTRFS_REF_TYPE_DATA);
        if (type != BTRFS_EXTENT_DATA_REF_KEY)
                goto out;

        ref = (struct btrfs_extent_data_ref *)(&iref->offset);
        if (btrfs_extent_refs(leaf, ei) !=
            btrfs_extent_data_ref_count(leaf, ref) ||
            btrfs_extent_data_ref_root(leaf, ref) !=
            root->root_key.objectid ||
            btrfs_extent_data_ref_objectid(leaf, ref) != objectid ||
            btrfs_extent_data_ref_offset(leaf, ref) != offset)
                goto out;

        ret = 0;
out:
        return ret;
}

int btrfs_cross_ref_exist(struct btrfs_root *root, u64 objectid, u64 offset,
                          u64 bytenr, bool strict)
{
        struct btrfs_path *path;
        int ret;

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

        do {
                ret = check_committed_ref(root, path, objectid,
                                          offset, bytenr, strict);
                if (ret && ret != -ENOENT)
                        goto out;

                ret = check_delayed_ref(root, path, objectid, offset, bytenr);
        } while (ret == -EAGAIN);

out:
        btrfs_free_path(path);
        if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID)
                WARN_ON(ret > 0);
        return ret;
}

static int __btrfs_mod_ref(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct extent_buffer *buf,
                           int full_backref, int inc)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 bytenr;
        u64 num_bytes;
        u64 parent;
        u64 ref_root;
        u32 nritems;
        struct btrfs_key key;
        struct btrfs_file_extent_item *fi;
        struct btrfs_ref generic_ref = { 0 };
        bool for_reloc = btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC);
        int i;
        int action;
        int level;
        int ret = 0;

        if (btrfs_is_testing(fs_info))
                return 0;

        ref_root = btrfs_header_owner(buf);
        nritems = btrfs_header_nritems(buf);
        level = btrfs_header_level(buf);

        if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state) && level == 0)
                return 0;

        if (full_backref)
                parent = buf->start;
        else
                parent = 0;
        if (inc)
                action = BTRFS_ADD_DELAYED_REF;
        else
                action = BTRFS_DROP_DELAYED_REF;

        for (i = 0; i < nritems; i++) {
                if (level == 0) {
                        btrfs_item_key_to_cpu(buf, &key, i);
                        if (key.type != BTRFS_EXTENT_DATA_KEY)
                                continue;
                        fi = btrfs_item_ptr(buf, i,
                                            struct btrfs_file_extent_item);
                        if (btrfs_file_extent_type(buf, fi) ==
                            BTRFS_FILE_EXTENT_INLINE)
                                continue;
                        bytenr = btrfs_file_extent_disk_bytenr(buf, fi);
                        if (bytenr == 0)
                                continue;

                        num_bytes = btrfs_file_extent_disk_num_bytes(buf, fi);
                        key.offset -= btrfs_file_extent_offset(buf, fi);
                        btrfs_init_generic_ref(&generic_ref, action, bytenr,
                                               num_bytes, parent);
                        generic_ref.real_root = root->root_key.objectid;
                        btrfs_init_data_ref(&generic_ref, ref_root, key.objectid,
                                            key.offset);
                        generic_ref.skip_qgroup = for_reloc;
                        if (inc)
                                ret = btrfs_inc_extent_ref(trans, &generic_ref);
                        else
                                ret = btrfs_free_extent(trans, &generic_ref);
                        if (ret)
                                goto fail;
                } else {
                        bytenr = btrfs_node_blockptr(buf, i);
                        num_bytes = fs_info->nodesize;
                        btrfs_init_generic_ref(&generic_ref, action, bytenr,
                                               num_bytes, parent);
                        generic_ref.real_root = root->root_key.objectid;
                        btrfs_init_tree_ref(&generic_ref, level - 1, ref_root);
                        generic_ref.skip_qgroup = for_reloc;
                        if (inc)
                                ret = btrfs_inc_extent_ref(trans, &generic_ref);
                        else
                                ret = btrfs_free_extent(trans, &generic_ref);
                        if (ret)
                                goto fail;
                }
        }
        return 0;
fail:
        return ret;
}

int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                  struct extent_buffer *buf, int full_backref)
{
        return __btrfs_mod_ref(trans, root, buf, full_backref, 1);
}

int btrfs_dec_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                  struct extent_buffer *buf, int full_backref)
{
        return __btrfs_mod_ref(trans, root, buf, full_backref, 0);
}

int btrfs_extent_readonly(struct btrfs_fs_info *fs_info, u64 bytenr)
{
        struct btrfs_block_group *block_group;
        int readonly = 0;

        block_group = btrfs_lookup_block_group(fs_info, bytenr);
        if (!block_group || block_group->ro)
                readonly = 1;
        if (block_group)
                btrfs_put_block_group(block_group);
        return readonly;
}

static u64 get_alloc_profile_by_root(struct btrfs_root *root, int data)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 flags;
        u64 ret;

        if (data)
                flags = BTRFS_BLOCK_GROUP_DATA;
        else if (root == fs_info->chunk_root)
                flags = BTRFS_BLOCK_GROUP_SYSTEM;
        else
                flags = BTRFS_BLOCK_GROUP_METADATA;

        ret = btrfs_get_alloc_profile(fs_info, flags);
        return ret;
}

static u64 first_logical_byte(struct btrfs_fs_info *fs_info, u64 search_start)
{
        struct btrfs_block_group *cache;
        u64 bytenr;

        spin_lock(&fs_info->block_group_cache_lock);
        bytenr = fs_info->first_logical_byte;
        spin_unlock(&fs_info->block_group_cache_lock);

        if (bytenr < (u64)-1)
                return bytenr;

        cache = btrfs_lookup_first_block_group(fs_info, search_start);
        if (!cache)
                return 0;

        bytenr = cache->start;
        btrfs_put_block_group(cache);

        return bytenr;
}

static int pin_down_extent(struct btrfs_trans_handle *trans,
                           struct btrfs_block_group *cache,
                           u64 bytenr, u64 num_bytes, int reserved)
{
        struct btrfs_fs_info *fs_info = cache->fs_info;

        spin_lock(&cache->space_info->lock);
        spin_lock(&cache->lock);
        cache->pinned += num_bytes;
        btrfs_space_info_update_bytes_pinned(fs_info, cache->space_info,
                                             num_bytes);
        if (reserved) {
                cache->reserved -= num_bytes;
                cache->space_info->bytes_reserved -= num_bytes;
        }
        spin_unlock(&cache->lock);
        spin_unlock(&cache->space_info->lock);

        percpu_counter_add_batch(&cache->space_info->total_bytes_pinned,
                    num_bytes, BTRFS_TOTAL_BYTES_PINNED_BATCH);
        set_extent_dirty(&trans->transaction->pinned_extents, bytenr,
                         bytenr + num_bytes - 1, GFP_NOFS | __GFP_NOFAIL);
        return 0;
}

int btrfs_pin_extent(struct btrfs_trans_handle *trans,
                     u64 bytenr, u64 num_bytes, int reserved)
{
        struct btrfs_block_group *cache;

        cache = btrfs_lookup_block_group(trans->fs_info, bytenr);
        BUG_ON(!cache); /* Logic error */

        pin_down_extent(trans, cache, bytenr, num_bytes, reserved);

        btrfs_put_block_group(cache);
        return 0;
}

/*
 * this function must be called within transaction
 */
int btrfs_pin_extent_for_log_replay(struct btrfs_trans_handle *trans,
                                    u64 bytenr, u64 num_bytes)
{
        struct btrfs_block_group *cache;
        int ret;

        btrfs_add_excluded_extent(trans->fs_info, bytenr, num_bytes);

        cache = btrfs_lookup_block_group(trans->fs_info, bytenr);
        if (!cache)
                return -EINVAL;

        /*
         * pull in the free space cache (if any) so that our pin
         * removes the free space from the cache.  We have load_only set
         * to one because the slow code to read in the free extents does check
         * the pinned extents.
         */
        btrfs_cache_block_group(cache, 1);

        pin_down_extent(trans, cache, bytenr, num_bytes, 0);

        /* remove us from the free space cache (if we're there at all) */
        ret = btrfs_remove_free_space(cache, bytenr, num_bytes);
        btrfs_put_block_group(cache);
        return ret;
}

static int __exclude_logged_extent(struct btrfs_fs_info *fs_info,
                                   u64 start, u64 num_bytes)
{
        int ret;
        struct btrfs_block_group *block_group;
        struct btrfs_caching_control *caching_ctl;

        block_group = btrfs_lookup_block_group(fs_info, start);
        if (!block_group)
                return -EINVAL;

        btrfs_cache_block_group(block_group, 0);
        caching_ctl = btrfs_get_caching_control(block_group);

        if (!caching_ctl) {
                /* Logic error */
                BUG_ON(!btrfs_block_group_done(block_group));
                ret = btrfs_remove_free_space(block_group, start, num_bytes);
        } else {
                mutex_lock(&caching_ctl->mutex);

                if (start >= caching_ctl->progress) {
                        ret = btrfs_add_excluded_extent(fs_info, start,
                                                        num_bytes);
                } else if (start + num_bytes <= caching_ctl->progress) {
                        ret = btrfs_remove_free_space(block_group,
                                                      start, num_bytes);
                } else {
                        num_bytes = caching_ctl->progress - start;
                        ret = btrfs_remove_free_space(block_group,
                                                      start, num_bytes);
                        if (ret)
                                goto out_lock;

                        num_bytes = (start + num_bytes) -
                                caching_ctl->progress;
                        start = caching_ctl->progress;
                        ret = btrfs_add_excluded_extent(fs_info, start,
                                                        num_bytes);
                }
out_lock:
                mutex_unlock(&caching_ctl->mutex);
                btrfs_put_caching_control(caching_ctl);
        }
        btrfs_put_block_group(block_group);
        return ret;
}

int btrfs_exclude_logged_extents(struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct btrfs_file_extent_item *item;
        struct btrfs_key key;
        int found_type;
        int i;
        int ret = 0;

        if (!btrfs_fs_incompat(fs_info, MIXED_GROUPS))
                return 0;

        for (i = 0; i < btrfs_header_nritems(eb); i++) {
                btrfs_item_key_to_cpu(eb, &key, i);
                if (key.type != BTRFS_EXTENT_DATA_KEY)
                        continue;
                item = btrfs_item_ptr(eb, i, struct btrfs_file_extent_item);
                found_type = btrfs_file_extent_type(eb, item);
                if (found_type == BTRFS_FILE_EXTENT_INLINE)
                        continue;
                if (btrfs_file_extent_disk_bytenr(eb, item) == 0)
                        continue;
                key.objectid = btrfs_file_extent_disk_bytenr(eb, item);
                key.offset = btrfs_file_extent_disk_num_bytes(eb, item);
                ret = __exclude_logged_extent(fs_info, key.objectid, key.offset);
                if (ret)
                        break;
        }

        return ret;
}

static void
btrfs_inc_block_group_reservations(struct btrfs_block_group *bg)
{
        atomic_inc(&bg->reservations);
}

void btrfs_prepare_extent_commit(struct btrfs_fs_info *fs_info)
{
        struct btrfs_caching_control *next;
        struct btrfs_caching_control *caching_ctl;
        struct btrfs_block_group *cache;

        down_write(&fs_info->commit_root_sem);

        list_for_each_entry_safe(caching_ctl, next,
                                 &fs_info->caching_block_groups, list) {
                cache = caching_ctl->block_group;
                if (btrfs_block_group_done(cache)) {
                        cache->last_byte_to_unpin = (u64)-1;
                        list_del_init(&caching_ctl->list);
                        btrfs_put_caching_control(caching_ctl);
                } else {
                        cache->last_byte_to_unpin = caching_ctl->progress;
                }
        }

        up_write(&fs_info->commit_root_sem);

        btrfs_update_global_block_rsv(fs_info);
}

/*
 * Returns the free cluster for the given space info and sets empty_cluster to
 * what it should be based on the mount options.
 */
static struct btrfs_free_cluster *
fetch_cluster_info(struct btrfs_fs_info *fs_info,
                   struct btrfs_space_info *space_info, u64 *empty_cluster)
{
        struct btrfs_free_cluster *ret = NULL;

        *empty_cluster = 0;
        if (btrfs_mixed_space_info(space_info))
                return ret;

        if (space_info->flags & BTRFS_BLOCK_GROUP_METADATA) {
                ret = &fs_info->meta_alloc_cluster;
                if (btrfs_test_opt(fs_info, SSD))
                        *empty_cluster = SZ_2M;
                else
                        *empty_cluster = SZ_64K;
        } else if ((space_info->flags & BTRFS_BLOCK_GROUP_DATA) &&
                   btrfs_test_opt(fs_info, SSD_SPREAD)) {
                *empty_cluster = SZ_2M;
                ret = &fs_info->data_alloc_cluster;
        }

        return ret;
}

static int unpin_extent_range(struct btrfs_fs_info *fs_info,
                              u64 start, u64 end,
                              const bool return_free_space)
{
        struct btrfs_block_group *cache = NULL;
        struct btrfs_space_info *space_info;
        struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
        struct btrfs_free_cluster *cluster = NULL;
        u64 len;
        u64 total_unpinned = 0;
        u64 empty_cluster = 0;
        bool readonly;

        while (start <= end) {
                readonly = false;
                if (!cache ||
                    start >= cache->start + cache->length) {
                        if (cache)
                                btrfs_put_block_group(cache);
                        total_unpinned = 0;
                        cache = btrfs_lookup_block_group(fs_info, start);
                        BUG_ON(!cache); /* Logic error */

                        cluster = fetch_cluster_info(fs_info,
                                                     cache->space_info,
                                                     &empty_cluster);
                        empty_cluster <<= 1;
                }

                len = cache->start + cache->length - start;
                len = min(len, end + 1 - start);

                if (start < cache->last_byte_to_unpin) {
                        len = min(len, cache->last_byte_to_unpin - start);
                        if (return_free_space)
                                btrfs_add_free_space(cache, start, len);
                }

                start += len;
                total_unpinned += len;
                space_info = cache->space_info;

                /*
                 * If this space cluster has been marked as fragmented and we've
                 * unpinned enough in this block group to potentially allow a
                 * cluster to be created inside of it go ahead and clear the
                 * fragmented check.
                 */
                if (cluster && cluster->fragmented &&
                    total_unpinned > empty_cluster) {
                        spin_lock(&cluster->lock);
                        cluster->fragmented = 0;
                        spin_unlock(&cluster->lock);
                }

                spin_lock(&space_info->lock);
                spin_lock(&cache->lock);
                cache->pinned -= len;
                btrfs_space_info_update_bytes_pinned(fs_info, space_info, -len);
                space_info->max_extent_size = 0;
                percpu_counter_add_batch(&space_info->total_bytes_pinned,
                            -len, BTRFS_TOTAL_BYTES_PINNED_BATCH);
                if (cache->ro) {
                        space_info->bytes_readonly += len;
                        readonly = true;
                }
                spin_unlock(&cache->lock);
                if (!readonly && return_free_space &&
                    global_rsv->space_info == space_info) {
                        u64 to_add = len;

                        spin_lock(&global_rsv->lock);
                        if (!global_rsv->full) {
                                to_add = min(len, global_rsv->size -
                                             global_rsv->reserved);
                                global_rsv->reserved += to_add;
                                btrfs_space_info_update_bytes_may_use(fs_info,
                                                space_info, to_add);
                                if (global_rsv->reserved >= global_rsv->size)
                                        global_rsv->full = 1;
                                len -= to_add;
                        }
                        spin_unlock(&global_rsv->lock);
                }
                /* Add to any tickets we may have */
                if (!readonly && return_free_space && len)
                        btrfs_try_granting_tickets(fs_info, space_info);
                spin_unlock(&space_info->lock);
        }

        if (cache)
                btrfs_put_block_group(cache);
        return 0;
}

int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_block_group *block_group, *tmp;
        struct list_head *deleted_bgs;
        struct extent_io_tree *unpin;
        u64 start;
        u64 end;
        int ret;

        unpin = &trans->transaction->pinned_extents;

        while (!TRANS_ABORTED(trans)) {
                struct extent_state *cached_state = NULL;

                mutex_lock(&fs_info->unused_bg_unpin_mutex);
                ret = find_first_extent_bit(unpin, 0, &start, &end,
                                            EXTENT_DIRTY, &cached_state);
                if (ret) {
                        mutex_unlock(&fs_info->unused_bg_unpin_mutex);
                        break;
                }
                if (test_bit(BTRFS_FS_LOG_RECOVERING, &fs_info->flags))
                        clear_extent_bits(&fs_info->excluded_extents, start,
                                          end, EXTENT_UPTODATE);

                if (btrfs_test_opt(fs_info, DISCARD_SYNC))
                        ret = btrfs_discard_extent(fs_info, start,
                                                   end + 1 - start, NULL);

                clear_extent_dirty(unpin, start, end, &cached_state);
                unpin_extent_range(fs_info, start, end, true);
                mutex_unlock(&fs_info->unused_bg_unpin_mutex);
                free_extent_state(cached_state);
                cond_resched();
        }

        if (btrfs_test_opt(fs_info, DISCARD_ASYNC)) {
                btrfs_discard_calc_delay(&fs_info->discard_ctl);
                btrfs_discard_schedule_work(&fs_info->discard_ctl, true);
        }

        /*
         * Transaction is finished.  We don't need the lock anymore.  We
         * do need to clean up the block groups in case of a transaction
         * abort.
         */
        deleted_bgs = &trans->transaction->deleted_bgs;
        list_for_each_entry_safe(block_group, tmp, deleted_bgs, bg_list) {
                u64 trimmed = 0;

                ret = -EROFS;
                if (!TRANS_ABORTED(trans))
                        ret = btrfs_discard_extent(fs_info,
                                                   block_group->start,
                                                   block_group->length,
                                                   &trimmed);

                list_del_init(&block_group->bg_list);
                btrfs_unfreeze_block_group(block_group);
                btrfs_put_block_group(block_group);

                if (ret) {
                        const char *errstr = btrfs_decode_error(ret);
                        btrfs_warn(fs_info,
                           "discard failed while removing blockgroup: errno=%d %s",
                                   ret, errstr);
                }
        }

        return 0;
}

/*
 * Drop one or more refs of @node.
 *
 * 1. Locate the extent refs.
 *    It's either inline in EXTENT/METADATA_ITEM or in keyed SHARED_* item.
 *    Locate it, then reduce the refs number or remove the ref line completely.
 *
 * 2. Update the refs count in EXTENT/METADATA_ITEM
 *
 * Inline backref case:
 *
 * in extent tree we have:
 *
 *      item 0 key (13631488 EXTENT_ITEM 1048576) itemoff 16201 itemsize 82
 *              refs 2 gen 6 flags DATA
 *              extent data backref root FS_TREE objectid 258 offset 0 count 1
 *              extent data backref root FS_TREE objectid 257 offset 0 count 1
 *
 * This function gets called with:
 *
 *    node->bytenr = 13631488
 *    node->num_bytes = 1048576
 *    root_objectid = FS_TREE
 *    owner_objectid = 257
 *    owner_offset = 0
 *    refs_to_drop = 1
 *
 * Then we should get some like:
 *
 *      item 0 key (13631488 EXTENT_ITEM 1048576) itemoff 16201 itemsize 82
 *              refs 1 gen 6 flags DATA
 *              extent data backref root FS_TREE objectid 258 offset 0 count 1
 *
 * Keyed backref case:
 *
 * in extent tree we have:
 *
 *      item 0 key (13631488 EXTENT_ITEM 1048576) itemoff 3971 itemsize 24
 *              refs 754 gen 6 flags DATA
 *      [...]
 *      item 2 key (13631488 EXTENT_DATA_REF <HASH>) itemoff 3915 itemsize 28
 *              extent data backref root FS_TREE objectid 866 offset 0 count 1
 *
 * This function get called with:
 *
 *    node->bytenr = 13631488