btrfs: abort transaction on generation mismatch when marking eb as dirty

[linux.git] / fs / btrfs / extent-tree.c

// 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 "ctree.h"
#include "extent-tree.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 "discard.h"
#include "rcu-string.h"
#include "zoned.h"
#include "dev-replace.h"
#include "fs.h"
#include "accessors.h"
#include "root-tree.h"
#include "file-item.h"
#include "orphan.h"
#include "tree-checker.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,
                               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;
}

/* 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)
{
        struct btrfs_root *root = btrfs_extent_root(fs_info, start);
        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, 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_root *extent_root;
        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;

        extent_root = btrfs_extent_root(fs_info, bytenr);
        ret = btrfs_search_slot(NULL, 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(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 = -EUCLEAN;
                        btrfs_err(fs_info,
                        "unexpected extent item size, has %u expect >= %zu",
                                  item_size, sizeof(*ei));
                        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;
                }
        }

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

        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 = crc32c(high_crc, &lenum, sizeof(lenum));
        lenum = cpu_to_le64(owner);
        low_crc = crc32c(low_crc, &lenum, sizeof(lenum));
        lenum = cpu_to_le64(offset);
        low_crc = 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 = btrfs_extent_root(trans->fs_info, bytenr);
        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 = btrfs_extent_root(trans->fs_info, bytenr);
        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(trans, leaf);
        ret = 0;
fail:
        btrfs_release_path(path);
        return ret;
}

static noinline int remove_extent_data_ref(struct btrfs_trans_handle *trans,
                                           struct btrfs_root *root,
                                           struct btrfs_path *path,
                                           int refs_to_drop)
{
        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 {
                btrfs_err(trans->fs_info,
                          "unrecognized backref key (%llu %u %llu)",
                          key.objectid, key.type, key.offset);
                btrfs_abort_transaction(trans, -EUCLEAN);
                return -EUCLEAN;
        }

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

        if (num_refs == 0) {
                ret = btrfs_del_item(trans, root, path);
        } 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(trans, 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]);

        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 = btrfs_extent_root(trans->fs_info, bytenr);
        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_root *root = btrfs_extent_root(trans->fs_info, bytenr);
        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, 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 = btrfs_extent_root(fs_info, bytenr);
        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;
        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->search_for_extension = 1;
                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)
                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) {
                ret = -ENOENT;
                goto out;
        } else if (WARN_ON(ret)) {
                btrfs_print_leaf(path->nodes[0]);
                btrfs_err(fs_info,
"extent item not found for insert, bytenr %llu num_bytes %llu parent %llu root_objectid %llu owner %llu offset %llu",
                          bytenr, num_bytes, parent, root_objectid, owner,
                          offset);
                ret = -EUCLEAN;
                goto out;
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size(leaf, path->slots[0]);
        if (unlikely(item_size < sizeof(*ei))) {
                ret = -EUCLEAN;
                btrfs_err(fs_info,
                          "unexpected extent item size, has %llu expect >= %zu",
                          item_size, sizeof(*ei));
                btrfs_abort_transaction(trans, ret);
                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;

        ret = -ENOENT;
        while (ptr < end) {
                iref = (struct btrfs_extent_inline_ref *)ptr;
                type = btrfs_get_extent_inline_ref_type(leaf, iref, needed);
                if (type == BTRFS_REF_TYPE_INVALID) {
                        ret = -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)) {
                                ret = 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) {
                                        ret = 0;
                                        break;
                                }
                                if (ref_offset < parent)
                                        break;
                        } else {
                                if (root_objectid == ref_offset) {
                                        ret = 0;
                                        break;
                                }
                                if (ref_offset < root_objectid)
                                        break;
                        }
                }
                ptr += btrfs_extent_inline_ref_size(type);
        }

        if (unlikely(ptr > end)) {
                ret = -EUCLEAN;
                btrfs_print_leaf(path->nodes[0]);
                btrfs_crit(fs_info,
"overrun extent record at slot %d while looking for inline extent for root %llu owner %llu offset %llu parent %llu",
                           path->slots[0], root_objectid, owner, offset, parent);
                goto out;
        }

        if (ret == -ENOENT && insert) {
                if (item_size + extra_size >=
                    BTRFS_MAX_EXTENT_ITEM_SIZE(root)) {
                        ret = -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) {
                        ret = -EAGAIN;
                        goto out;
                }
        }
        *ref_ret = (struct btrfs_extent_inline_ref *)ptr;
out:
        if (insert) {
                path->keep_locks = 0;
                path->search_for_extension = 0;
                btrfs_unlock_up_safe(path, 1);
        }
        return ret;
}

/*
 * helper to add new inline back ref
 */
static noinline_for_stack
void setup_inline_extent_backref(struct btrfs_trans_handle *trans,
                                 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(trans, 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(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(trans, 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 int update_inline_extent_backref(
                                  struct btrfs_trans_handle *trans,
                                  struct btrfs_path *path,
                                  struct btrfs_extent_inline_ref *iref,
                                  int refs_to_mod,
                                  struct btrfs_delayed_extent_op *extent_op)
{
        struct extent_buffer *leaf = path->nodes[0];
        struct btrfs_fs_info *fs_info = leaf->fs_info;
        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);
        if (unlikely(refs_to_mod < 0 && refs + refs_to_mod <= 0)) {
                struct btrfs_key key;
                u32 extent_size;

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.type == BTRFS_METADATA_ITEM_KEY)
                        extent_size = fs_info->nodesize;
                else
                        extent_size = key.offset;
                btrfs_print_leaf(leaf);
                btrfs_err(fs_info,
        "invalid refs_to_mod for extent %llu num_bytes %u, has %d expect >= -%llu",
                          key.objectid, extent_size, refs_to_mod, refs);
                return -EUCLEAN;
        }
        refs += refs_to_mod;
        btrfs_set_extent_refs(leaf, ei, refs);
        if (extent_op)
                __run_delayed_extent_op(extent_op, leaf, ei);

        type = btrfs_get_extent_inline_ref_type(leaf, iref, BTRFS_REF_TYPE_ANY);
        /*
         * Function btrfs_get_extent_inline_ref_type() has already printed
         * error messages.
         */
        if (unlikely(type == BTRFS_REF_TYPE_INVALID))
                return -EUCLEAN;

        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;
                /*
                 * For tree blocks we can only drop one ref for it, and tree
                 * blocks should not have refs > 1.
                 *
                 * Furthermore if we're inserting a new inline backref, we
                 * won't reach this path either. That would be
                 * setup_inline_extent_backref().
                 */
                if (unlikely(refs_to_mod != -1)) {
                        struct btrfs_key key;

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

                        btrfs_print_leaf(leaf);
                        btrfs_err(fs_info,
                        "invalid refs_to_mod for tree block %llu, has %d expect -1",
                                  key.objectid, refs_to_mod);
                        return -EUCLEAN;
                }
        }

        if (unlikely(refs_to_mod < 0 && refs < -refs_to_mod)) {
                struct btrfs_key key;
                u32 extent_size;

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.type == BTRFS_METADATA_ITEM_KEY)
                        extent_size = fs_info->nodesize;
                else
                        extent_size = key.offset;
                btrfs_print_leaf(leaf);
                btrfs_err(fs_info,
"invalid refs_to_mod for backref entry, iref %lu extent %llu num_bytes %u, has %d expect >= -%llu",
                          (unsigned long)iref, key.objectid, extent_size,
                          refs_to_mod, refs);
                return -EUCLEAN;
        }
        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 {
                size =  btrfs_extent_inline_ref_size(type);
                item_size = btrfs_item_size(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(trans, path, item_size, 1);
        }
        btrfs_mark_buffer_dirty(trans, leaf);
        return 0;
}

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_print_leaf(path->nodes[0]);
                        btrfs_crit(trans->fs_info,
"adding refs to an existing tree ref, bytenr %llu num_bytes %llu root_objectid %llu slot %u",
                                   bytenr, num_bytes, root_objectid, path->slots[0]);
                        return -EUCLEAN;
                }
                ret = update_inline_extent_backref(trans, path, iref,
                                                   refs_to_add, extent_op);
        } else if (ret == -ENOENT) {
                setup_inline_extent_backref(trans, 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_root *root,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref *iref,
                                 int refs_to_drop, int is_data)
{
        int ret = 0;

        BUG_ON(!is_data && refs_to_drop != 1);
        if (iref)
                ret = update_inline_extent_backref(trans, path, iref,
                                                   -refs_to_drop, NULL);
        else if (is_data)
                ret = remove_extent_data_ref(trans, root, path, refs_to_drop);
        else
                ret = btrfs_del_item(trans, 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 << SECTOR_SHIFT);

        if (WARN_ON(start != aligned_start)) {
                len -= aligned_start - start;
                len = round_down(len, 1 << SECTOR_SHIFT);
                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 >> SECTOR_SHIFT,
                                                   size >> SECTOR_SHIFT,
                                                   GFP_NOFS);
                        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 >> SECTOR_SHIFT,
                                           bytes_left >> SECTOR_SHIFT,
                                           GFP_NOFS);
                if (!ret)
                        *discarded_bytes += bytes_left;
        }
        return ret;
}

static int do_discard_extent(struct btrfs_discard_stripe *stripe, u64 *bytes)
{
        struct btrfs_device *dev = stripe->dev;
        struct btrfs_fs_info *fs_info = dev->fs_info;
        struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
        u64 phys = stripe->physical;
        u64 len = stripe->length;
        u64 discarded = 0;
        int ret = 0;

        /* Zone reset on a zoned filesystem */
        if (btrfs_can_zone_reset(dev, phys, len)) {
                u64 src_disc;

                ret = btrfs_reset_device_zone(dev, phys, len, &discarded);
                if (ret)
                        goto out;

                if (!btrfs_dev_replace_is_ongoing(dev_replace) ||
                    dev != dev_replace->srcdev)
                        goto out;

                src_disc = discarded;

                /* Send to replace target as well */
                ret = btrfs_reset_device_zone(dev_replace->tgtdev, phys, len,
                                              &discarded);
                discarded += src_disc;
        } else if (bdev_max_discard_sectors(stripe->dev->bdev)) {
                ret = btrfs_issue_discard(dev->bdev, phys, len, &discarded);
        } else {
                ret = 0;
                *bytes = 0;
        }

out:
        *bytes = discarded;
        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;

        /*
         * Avoid races with device replace and make sure the devices in the
         * stripes don't go away while we are discarding.
         */
        btrfs_bio_counter_inc_blocked(fs_info);
        while (cur < end) {
                struct btrfs_discard_stripe *stripes;
                unsigned int num_stripes;
                int i;

                num_bytes = end - cur;
                stripes = btrfs_map_discard(fs_info, cur, &num_bytes, &num_stripes);
                if (IS_ERR(stripes)) {
                        ret = PTR_ERR(stripes);
                        if (ret == -EOPNOTSUPP)
                                ret = 0;
                        break;
                }

                for (i = 0; i < num_stripes; i++) {
                        struct btrfs_discard_stripe *stripe = stripes + i;
                        u64 bytes;

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

                        if (!test_bit(BTRFS_DEV_STATE_WRITEABLE,
                                        &stripe->dev->dev_state))
                                continue;

                        ret = do_discard_extent(stripe, &bytes);
                        if (ret) {
                                /*
                                 * Keep going if discard is not supported by the
                                 * device.
                                 */
                                if (ret != -EOPNOTSUPP)
                                        break;
                                ret = 0;
                        } else {
                                discarded_bytes += bytes;
                        }
                }
                kfree(stripes);
                if (ret)
                        break;
                cur += num_bytes;
        }
        btrfs_bio_counter_dec(fs_info);
        if (actual_bytes)
                *actual_bytes = discarded_bytes;
        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 ret;

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

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

        btrfs_ref_tree_mod(fs_info, generic_ref);

        return ret;
}

/*
 * 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. Otherwise, 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.
 *
 * @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,
                                  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 refs_to_add = node->ref_mod;
        int ret;

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

        /* 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(trans, leaf);
        btrfs_release_path(path);

        /* now insert the actual backref */
        if (owner < BTRFS_FIRST_FREE_OBJECTID)
                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,
                                bool insert_reserved)
{
        int ret = 0;
        struct btrfs_delayed_data_ref *ref;
        u64 parent = 0;
        u64 flags = 0;

        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;

        if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
                struct btrfs_key key;

                if (extent_op)
                        flags |= extent_op->flags_to_set;

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

                ret = alloc_reserved_file_extent(trans, parent, ref->root,
                                                 flags, ref->objectid,
                                                 ref->offset, &key,
                                                 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,
                                             extent_op);
        } else if (node->action == BTRFS_DROP_DELAYED_REF) {
                ret = __btrfs_free_extent(trans, node, parent,
                                          ref->root, ref->objectid,
                                          ref->offset, 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_root *root;
        struct btrfs_key key;
        struct btrfs_path *path;
        struct btrfs_extent_item *ei;
        struct extent_buffer *leaf;
        u32 item_size;
        int ret;
        int metadata = 1;

        if (TRANS_ABORTED(trans))
                return 0;

        if (!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;
        }

        root = btrfs_extent_root(fs_info, key.objectid);
again:
        ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
        if (ret < 0) {
                goto out;
        } else 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 {
                        ret = -EUCLEAN;
                        btrfs_err(fs_info,
                  "missing extent item for extent %llu num_bytes %llu level %d",
                                  head->bytenr, head->num_bytes, extent_op->level);
                        goto out;
                }
        }

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

        if (unlikely(item_size < sizeof(*ei))) {
                ret = -EUCLEAN;
                btrfs_err(fs_info,
                          "unexpected extent item size, has %u expect >= %zu",
                          item_size, sizeof(*ei));
                btrfs_abort_transaction(trans, ret);
                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(trans, leaf);
out:
        btrfs_free_path(path);
        return ret;
}

static int run_delayed_tree_ref(struct btrfs_trans_handle *trans,
                                struct btrfs_delayed_ref_node *node,
                                struct btrfs_delayed_extent_op *extent_op,
                                bool 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 (unlikely(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 -EUCLEAN;
        }
        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, extent_op);
        } else if (node->action == BTRFS_DROP_DELAYED_REF) {
                ret = __btrfs_free_extent(trans, node, parent, ref_root,
                                          ref->level, 0, 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,
                               bool 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);
        if (ret < 0)
                btrfs_err(trans->fs_info,
"failed to run delayed ref for logical %llu num_bytes %llu type %u action %u ref_mod %d: %d",
                          node->bytenr, node->num_bytes, node->type,
                          node->action, node->ref_mod, ret);
        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 = false;
        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;
}

u64 btrfs_cleanup_ref_head_accounting(struct btrfs_fs_info *fs_info,
                                  struct btrfs_delayed_ref_root *delayed_refs,
                                  struct btrfs_delayed_ref_head *head)
{
        /*
         * 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->total_ref_mod < 0 && head->is_data) {
                int nr_csums;

                spin_lock(&delayed_refs->lock);
                delayed_refs->pending_csums -= head->num_bytes;
                spin_unlock(&delayed_refs->lock);
                nr_csums = btrfs_csum_bytes_to_leaves(fs_info, head->num_bytes);

                btrfs_delayed_refs_rsv_release(fs_info, 0, nr_csums);

                return btrfs_calc_delayed_ref_csum_bytes(fs_info, nr_csums);
        }

        return 0;
}

static int cleanup_ref_head(struct btrfs_trans_handle *trans,
                            struct btrfs_delayed_ref_head *head,
                            u64 *bytes_released)
{

        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) {
                        struct btrfs_root *csum_root;

                        csum_root = btrfs_csum_root(fs_info, head->bytenr);
                        ret = btrfs_del_csums(trans, csum_root, head->bytenr,
                                              head->num_bytes);
                }
        }

        *bytes_released += 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 ret;
}

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,
                                           u64 *bytes_released)
{
        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;
        bool must_insert_reserved;
        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;
                }

                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 = false;

                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_delayed_refs_rsv_release(fs_info, 1, 0);
                *bytes_released += btrfs_calc_delayed_ref_bytes(fs_info, 1);
                btrfs_free_delayed_extent_op(extent_op);
                if (ret) {
                        unselect_delayed_ref_head(delayed_refs, locked_ref);
                        btrfs_put_delayed_ref(ref);
                        return ret;
                }

                btrfs_put_delayed_ref(ref);
                cond_resched();

                spin_lock(&locked_ref->lock);
                btrfs_merge_delayed_refs(fs_info, 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,
                                             u64 min_bytes)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_ref_head *locked_ref = NULL;
        int ret;
        unsigned long count = 0;
        unsigned long max_count = 0;
        u64 bytes_processed = 0;

        delayed_refs = &trans->transaction->delayed_refs;
        if (min_bytes == 0) {
                max_count = delayed_refs->num_heads_ready;
                min_bytes = U64_MAX;
        }

        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(fs_info, delayed_refs, locked_ref);

                ret = btrfs_run_delayed_refs_for_head(trans, locked_ref, &bytes_processed);
                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, &bytes_processed);
                        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 ((min_bytes != U64_MAX && bytes_processed < min_bytes) ||
                 (max_count > 0 && count < max_count) ||
                 locked_ref);

        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

/*
 * Start processing the delayed reference count updates and extent insertions
 * we have queued up so far.
 *
 * @trans:      Transaction handle.
 * @min_bytes:  How many bytes of delayed references to process. After this
 *              many bytes we stop processing delayed references if there are
 *              any more. If 0 it means to run all existing delayed references,
 *              but not new ones added after running all existing ones.
 *              Use (u64)-1 (U64_MAX) to run all existing delayed references
 *              plus any new ones that are added.
 *
 * 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, u64 min_bytes)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret;

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

        if (min_bytes == U64_MAX) {
                btrfs_create_pending_block_groups(trans);

                spin_lock(&delayed_refs->lock);
                if (RB_EMPTY_ROOT(&delayed_refs->href_root.rb_root)) {
                        spin_unlock(&delayed_refs->lock);
                        return 0;
                }
                spin_unlock(&delayed_refs->lock);

                cond_resched();
                goto again;
        }

        return 0;
}

int btrfs_set_disk_extent_flags(struct btrfs_trans_handle *trans,
                                struct extent_buffer *eb, u64 flags)
{
        struct btrfs_delayed_extent_op *extent_op;
        int level = btrfs_header_level(eb);
        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->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)) {
                if (path->nowait) {
                        spin_unlock(&delayed_refs->lock);
                        btrfs_put_transaction(cur_trans);
                        return -EAGAIN;
                }

                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 = btrfs_extent_root(fs_info, bytenr);
        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(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;

        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_release_path(path);
        if (btrfs_is_data_reloc_root(root))
                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);
                        btrfs_init_data_ref(&generic_ref, ref_root, key.objectid,
                                            key.offset, root->root_key.objectid,
                                            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);
                        btrfs_init_tree_ref(&generic_ref, level - 1, ref_root,
                                            root->root_key.objectid, 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);
}

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)
{
        struct rb_node *leftmost;
        u64 bytenr = 0;

        read_lock(&fs_info->block_group_cache_lock);
        /* Get the block group with the lowest logical start address. */
        leftmost = rb_first_cached(&fs_info->block_group_cache_tree);
        if (leftmost) {
                struct btrfs_block_group *bg;

                bg = rb_entry(leftmost, struct btrfs_block_group, cache_node);
                bytenr = bg->start;
        }
        read_unlock(&fs_info->block_group_cache_lock);

        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);

        set_extent_bit(&trans->transaction->pinned_extents, bytenr,
                       bytenr + num_bytes - 1, EXTENT_DIRTY, NULL);
        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,
                                    const struct extent_buffer *eb)
{
        struct btrfs_block_group *cache;
        int ret;

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

        /*
         * Fully cache the free space first so that our pin removes the free space
         * from the cache.
         */
        ret = btrfs_cache_block_group(cache, true);
        if (ret)
                goto out;

        pin_down_extent(trans, cache, eb->start, eb->len, 0);

        /* remove us from the free space cache (if we're there at all) */
        ret = btrfs_remove_free_space(cache, eb->start, eb->len);
out:
        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;

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

        ret = btrfs_cache_block_group(block_group, true);
        if (ret)
                goto out;

        ret = btrfs_remove_free_space(block_group, start, num_bytes);
out:
        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);
}

/*
 * 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 (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;
                if (cache->ro) {
                        space_info->bytes_readonly += len;
                        readonly = true;
                } else if (btrfs_is_zoned(fs_info)) {
                        /* Need reset before reusing in a zoned block group */
                        space_info->bytes_zone_unusable += len;
                        readonly = true;
                }
                spin_unlock(&cache->lock);
                if (!readonly && return_free_space &&
                    global_rsv->space_info == space_info) {
                        spin_lock(&global_rsv->lock);
                        if (!global_rsv->full) {
                                u64 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);
                if (!find_first_extent_bit(unpin, 0, &start, &end,
                                           EXTENT_DIRTY, &cached_state)) {
                        mutex_unlock(&fs_info->unused_bg_unpin_mutex);
                        break;
                }

                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;
}

static int do_free_extent_accounting(struct btrfs_trans_handle *trans,
                                     u64 bytenr, u64 num_bytes, bool is_data)
{
        int ret;

        if (is_data) {
                struct btrfs_root *csum_root;

                csum_root = btrfs_csum_root(trans->fs_info, bytenr);
                ret = btrfs_del_csums(trans, csum_root, bytenr, num_bytes);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }
        }

        ret = add_to_free_space_tree(trans, bytenr, num_bytes);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        ret = btrfs_update_block_group(trans, bytenr, num_bytes, false);
        if (ret)
                btrfs_abort_transaction(trans, ret);

        return ret;
}

#define abort_and_dump(trans, path, fmt, args...)       \
({                                                      \
        btrfs_abort_transaction(trans, -EUCLEAN);       \
        btrfs_print_leaf(path->nodes[0]);               \
        btrfs_crit(trans->fs_info, fmt, ##args);        \
})

/*
 * 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
 *    node->num_bytes = 1048576
 *    root_objectid = FS_TREE
 *    owner_objectid = 866
 *    owner_offset = 0
 *    refs_to_drop = 1
 *
 * Then we should get some like:
 *
 *      item 0 key (13631488 EXTENT_ITEM 1048576) itemoff 3971 itemsize 24
 *              refs 753 gen 6 flags DATA
 *
 * And that (13631488 EXTENT_DATA_REF <HASH>) gets removed.
 */
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,
                               struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_fs_info *info = trans->fs_info;
        struct btrfs_key key;
        struct btrfs_path *path;
        struct btrfs_root *extent_root;
        struct extent_buffer *leaf;
        struct btrfs_extent_item *ei;
        struct btrfs_extent_inline_ref *iref;
        int ret;
        int is_data;
        int extent_slot = 0;
        int found_extent = 0;
        int num_to_del = 1;
        int refs_to_drop = node->ref_mod;
        u32 item_size;
        u64 refs;
        u64 bytenr = node->bytenr;
        u64 num_bytes = node->num_bytes;
        bool skinny_metadata = btrfs_fs_incompat(info, SKINNY_METADATA);

        extent_root = btrfs_extent_root(info, bytenr);
        ASSERT(extent_root);

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

        is_data = owner_objectid >= BTRFS_FIRST_FREE_OBJECTID;

        if (!is_data && refs_to_drop != 1) {
                btrfs_crit(info,
"invalid refs_to_drop, dropping more than 1 refs for tree block %llu refs_to_drop %u",
                           node->bytenr, refs_to_drop);
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

        if (is_data)
                skinny_metadata = false;

        ret = lookup_extent_backref(trans, path, &iref, bytenr, num_bytes,
                                    parent, root_objectid, owner_objectid,
                                    owner_offset);
        if (ret == 0) {
                /*
                 * Either the inline backref or the SHARED_DATA_REF/
                 * SHARED_BLOCK_REF is found
                 *
                 * Here is a quick path to locate EXTENT/METADATA_ITEM.
                 * It's possible the EXTENT/METADATA_ITEM is near current slot.
                 */
                extent_slot = path->slots[0];
                while (extent_slot >= 0) {
                        btrfs_item_key_to_cpu(path->nodes[0], &key,
                                              extent_slot);
                        if (key.objectid != bytenr)
                                break;
                        if (key.type == BTRFS_EXTENT_ITEM_KEY &&
                            key.offset == num_bytes) {
                                found_extent = 1;
                                break;
                        }
                        if (key.type == BTRFS_METADATA_ITEM_KEY &&
                            key.offset == owner_objectid) {
                                found_extent = 1;
                                break;
                        }

                        /* Quick path didn't find the EXTEMT/METADATA_ITEM */
                        if (path->slots[0] - extent_slot > 5)
                                break;
                        extent_slot--;
                }

                if (!found_extent) {
                        if (iref) {
                                abort_and_dump(trans, path,
"invalid iref slot %u, no EXTENT/METADATA_ITEM found but has inline extent ref",
                                           path->slots[0]);
                                ret = -EUCLEAN;
                                goto out;
                        }
                        /* Must be SHARED_* item, remove the backref first */
                        ret = remove_extent_backref(trans, extent_root, path,
                                                    NULL, refs_to_drop, is_data);
                        if (ret) {
                                btrfs_abort_transaction(trans, ret);
                                goto out;
                        }
                        btrfs_release_path(path);

                        /* Slow path to locate EXTENT/METADATA_ITEM */
                        key.objectid = bytenr;
                        key.type = BTRFS_EXTENT_ITEM_KEY;
                        key.offset = num_bytes;

                        if (!is_data && skinny_metadata) {
                                key.type = BTRFS_METADATA_ITEM_KEY;
                                key.offset = owner_objectid;
                        }

                        ret = btrfs_search_slot(trans, extent_root,
                                                &key, path, -1, 1);
                        if (ret > 0 && skinny_metadata && path->slots[0]) {
                                /*
                                 * Couldn't find our skinny metadata item,
                                 * see if we have ye olde extent item.
                                 */
                                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 > 0 && skinny_metadata) {
                                skinny_metadata = false;
                                key.objectid = bytenr;
                                key.type = BTRFS_EXTENT_ITEM_KEY;
                                key.offset = num_bytes;
                                btrfs_release_path(path);
                                ret = btrfs_search_slot(trans, extent_root,
                                                        &key, path, -1, 1);
                        }

                        if (ret) {
                                if (ret > 0)
                                        btrfs_print_leaf(path->nodes[0]);
                                btrfs_err(info,
                        "umm, got %d back from search, was looking for %llu, slot %d",
                                          ret, bytenr, path->slots[0]);
                        }
                        if (ret < 0) {
                                btrfs_abort_transaction(trans, ret);
                                goto out;
                        }
                        extent_slot = path->slots[0];
                }
        } else if (WARN_ON(ret == -ENOENT)) {
                abort_and_dump(trans, path,
"unable to find ref byte nr %llu parent %llu root %llu owner %llu offset %llu slot %d",
                               bytenr, parent, root_objectid, owner_objectid,
                               owner_offset, path->slots[0]);
                goto out;
        } else {
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size(leaf, extent_slot);
        if (unlikely(item_size < sizeof(*ei))) {
                ret = -EUCLEAN;
                btrfs_err(trans->fs_info,
                          "unexpected extent item size, has %u expect >= %zu",
                          item_size, sizeof(*ei));
                btrfs_abort_transaction(trans, ret);
                goto out;
        }
        ei = btrfs_item_ptr(leaf, extent_slot,
                            struct btrfs_extent_item);
        if (owner_objectid < BTRFS_FIRST_FREE_OBJECTID &&
            key.type == BTRFS_EXTENT_ITEM_KEY) {
                struct btrfs_tree_block_info *bi;

                if (item_size < sizeof(*ei) + sizeof(*bi)) {
                        abort_and_dump(trans, path,
"invalid extent item size for key (%llu, %u, %llu) slot %u owner %llu, has %u expect >= %zu",
                                       key.objectid, key.type, key.offset,
                                       path->slots[0], owner_objectid, item_size,
                                       sizeof(*ei) + sizeof(*bi));
                        ret = -EUCLEAN;
                        goto out;
                }
                bi = (struct btrfs_tree_block_info *)(ei + 1);
                WARN_ON(owner_objectid != btrfs_tree_block_level(leaf, bi));
        }

        refs = btrfs_extent_refs(leaf, ei);
        if (refs < refs_to_drop) {
                abort_and_dump(trans, path,
                "trying to drop %d refs but we only have %llu for bytenr %llu slot %u",
                               refs_to_drop, refs, bytenr, path->slots[0]);
                ret = -EUCLEAN;
                goto out;
        }
        refs -= refs_to_drop;

        if (refs > 0) {
                if (extent_op)
                        __run_delayed_extent_op(extent_op, leaf, ei);
                /*
                 * In the case of inline back ref, reference count will
                 * be updated by remove_extent_backref
                 */
                if (iref) {
                        if (!found_extent) {
                                abort_and_dump(trans, path,
"invalid iref, got inlined extent ref but no EXTENT/METADATA_ITEM found, slot %u",
                                               path->slots[0]);
                                ret = -EUCLEAN;
                                goto out;
                        }
                } else {
                        btrfs_set_extent_refs(leaf, ei, refs);
                        btrfs_mark_buffer_dirty(trans, leaf);
                }
                if (found_extent) {
                        ret = remove_extent_backref(trans, extent_root, path,
                                                    iref, refs_to_drop, is_data);
                        if (ret) {
                                btrfs_abort_transaction(trans, ret);
                                goto out;
                        }
                }
        } else {
                /* In this branch refs == 1 */
                if (found_extent) {
                        if (is_data && refs_to_drop !=
                            extent_data_ref_count(path, iref)) {
                                abort_and_dump(trans, path,
                "invalid refs_to_drop, current refs %u refs_to_drop %u slot %u",
                                               extent_data_ref_count(path, iref),
                                               refs_to_drop, path->slots[0]);
                                ret = -EUCLEAN;
                                goto out;
                        }
                        if (iref) {
                                if (path->slots[0] != extent_slot) {
                                        abort_and_dump(trans, path,
"invalid iref, extent item key (%llu %u %llu) slot %u doesn't have wanted iref",
                                                       key.objectid, key.type,
                                                       key.offset, path->slots[0]);
                                        ret = -EUCLEAN;
                                        goto out;
                                }
                        } else {
                                /*
                                 * No inline ref, we must be at SHARED_* item,
                                 * And it's single ref, it must be:
                                 * |    extent_slot       ||extent_slot + 1|
                                 * [ EXTENT/METADATA_ITEM ][ SHARED_* ITEM ]
                                 */
                                if (path->slots[0] != extent_slot + 1) {
                                        abort_and_dump(trans, path,
        "invalid SHARED_* item slot %u, previous item is not EXTENT/METADATA_ITEM",
                                                       path->slots[0]);
                                        ret = -EUCLEAN;
                                        goto out;
                                }
                                path->slots[0] = extent_slot;
                                num_to_del = 2;
                        }
                }

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

                ret = do_free_extent_accounting(trans, bytenr, num_bytes, is_data);
        }
        btrfs_release_path(path);

out:
        btrfs_free_path(path);
        return ret;
}

/*
 * when we free an block, it is possible (and likely) that we free the last
 * delayed ref for that extent as well.  This searches the delayed ref tree for
 * a given extent, and if there are no other delayed refs to be processed, it
 * removes it from the tree.
 */
static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
                                      u64 bytenr)
{
        struct btrfs_delayed_ref_head *head;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret = 0;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);
        head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
        if (!head)
                goto out_delayed_unlock;

        spin_lock(&head->lock);
        if (!RB_EMPTY_ROOT(&head->ref_tree.rb_root))
                goto out;

        if (cleanup_extent_op(head) != NULL)
                goto out;

        /*
         * waiting for the lock here would deadlock.  If someone else has it
         * locked they are already in the process of dropping it anyway
         */
        if (!mutex_trylock(&head->mutex))
                goto out;

        btrfs_delete_ref_head(delayed_refs, head);
        head->processing = false;

        spin_unlock(&head->lock);
        spin_unlock(&delayed_refs->lock);

        BUG_ON(head->extent_op);
        if (head->must_insert_reserved)
                ret = 1;

        btrfs_cleanup_ref_head_accounting(trans->fs_info, delayed_refs, head);
        mutex_unlock(&head->mutex);
        btrfs_put_delayed_ref_head(head);
        return ret;
out:
        spin_unlock(&head->lock);

out_delayed_unlock:
        spin_unlock(&delayed_refs->lock);
        return 0;
}

void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
                           u64 root_id,
                           struct extent_buffer *buf,
                           u64 parent, int last_ref)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_ref generic_ref = { 0 };
        int ret;

        btrfs_init_generic_ref(&generic_ref, BTRFS_DROP_DELAYED_REF,
                               buf->start, buf->len, parent);
        btrfs_init_tree_ref(&generic_ref, btrfs_header_level(buf),
                            root_id, 0, false);

        if (root_id != BTRFS_TREE_LOG_OBJECTID) {
                btrfs_ref_tree_mod(fs_info, &generic_ref);
                ret = btrfs_add_delayed_tree_ref(trans, &generic_ref, NULL);
                BUG_ON(ret); /* -ENOMEM */
        }

        if (last_ref && btrfs_header_generation(buf) == trans->transid) {
                struct btrfs_block_group *cache;
                bool must_pin = false;

                if (root_id != BTRFS_TREE_LOG_OBJECTID) {
                        ret = check_ref_cleanup(trans, buf->start);
                        if (!ret) {
                                btrfs_redirty_list_add(trans->transaction, buf);
                                goto out;
                        }
                }

                cache = btrfs_lookup_block_group(fs_info, buf->start);

                if (btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
                        pin_down_extent(trans, cache, buf->start, buf->len, 1);
                        btrfs_put_block_group(cache);
                        goto out;
                }

                /*
                 * If there are tree mod log users we may have recorded mod log
                 * operations for this node.  If we re-allocate this node we
                 * could replay operations on this node that happened when it
                 * existed in a completely different root.  For example if it
                 * was part of root A, then was reallocated to root B, and we
                 * are doing a btrfs_old_search_slot(root b), we could replay
                 * operations that happened when the block was part of root A,
                 * giving us an inconsistent view of the btree.
                 *
                 * We are safe from races here because at this point no other
                 * node or root points to this extent buffer, so if after this
                 * check a new tree mod log user joins we will not have an
                 * existing log of operations on this node that we have to
                 * contend with.
                 */
                if (test_bit(BTRFS_FS_TREE_MOD_LOG_USERS, &fs_info->flags))
                        must_pin = true;

                if (must_pin || btrfs_is_zoned(fs_info)) {
                        btrfs_redirty_list_add(trans->transaction, buf);
                        pin_down_extent(trans, cache, buf->start, buf->len, 1);
                        btrfs_put_block_group(cache);
                        goto out;
                }

                WARN_ON(test_bit(EXTENT_BUFFER_DIRTY, &buf->bflags));

                btrfs_add_free_space(cache, buf->start, buf->len);
                btrfs_free_reserved_bytes(cache, buf->len, 0);
                btrfs_put_block_group(cache);
                trace_btrfs_reserved_extent_free(fs_info, buf->start, buf->len);
        }
out:
        if (last_ref) {
                /*
                 * Deleting the buffer, clear the corrupt flag since it doesn't
                 * matter anymore.
                 */
                clear_bit(EXTENT_BUFFER_CORRUPT, &buf->bflags);
        }
}

/* Can return -ENOMEM */
int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_ref *ref)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        int ret;

        if (btrfs_is_testing(fs_info))
                return 0;

        /*
         * tree log blocks never actually go into the extent allocation
         * tree, just update pinning info and exit early.
         */
        if ((ref->type == BTRFS_REF_METADATA &&
             ref->tree_ref.owning_root == BTRFS_TREE_LOG_OBJECTID) ||
            (ref->type == BTRFS_REF_DATA &&
             ref->data_ref.owning_root == BTRFS_TREE_LOG_OBJECTID)) {
                /* unlocks the pinned mutex */
                btrfs_pin_extent(trans, ref->bytenr, ref->len, 1);
                ret = 0;
        } else if (ref->type == BTRFS_REF_METADATA) {
                ret = btrfs_add_delayed_tree_ref(trans, ref, NULL);
        } else {
                ret = btrfs_add_delayed_data_ref(trans, ref, 0);
        }

        if (!((ref->type == BTRFS_REF_METADATA &&
               ref->tree_ref.owning_root == BTRFS_TREE_LOG_OBJECTID) ||
              (ref->type == BTRFS_REF_DATA &&
               ref->data_ref.owning_root == BTRFS_TREE_LOG_OBJECTID)))
                btrfs_ref_tree_mod(fs_info, ref);

        return ret;
}

enum btrfs_loop_type {
        /*
         * Start caching block groups but do not wait for progress or for them
         * to be done.
         */
        LOOP_CACHING_NOWAIT,

        /*
         * Wait for the block group free_space >= the space we're waiting for if
         * the block group isn't cached.
         */
        LOOP_CACHING_WAIT,

        /*
         * Allow allocations to happen from block groups that do not yet have a
         * size classification.
         */
        LOOP_UNSET_SIZE_CLASS,

        /*
         * Allocate a chunk and then retry the allocation.
         */
        LOOP_ALLOC_CHUNK,

        /*
         * Ignore the size class restrictions for this allocation.
         */
        LOOP_WRONG_SIZE_CLASS,

        /*
         * Ignore the empty size, only try to allocate the number of bytes
         * needed for this allocation.
         */
        LOOP_NO_EMPTY_SIZE,
};

static inline void
btrfs_lock_block_group(struct btrfs_block_group *cache,
                       int delalloc)
{
        if (delalloc)
                down_read(&cache->data_rwsem);
}

static inline void btrfs_grab_block_group(struct btrfs_block_group *cache,
                       int delalloc)
{
        btrfs_get_block_group(cache);
        if (delalloc)
                down_read(&cache->data_rwsem);
}

static struct btrfs_block_group *btrfs_lock_cluster(
                   struct btrfs_block_group *block_group,
                   struct btrfs_free_cluster *cluster,
                   int delalloc)
        __acquires(&cluster->refill_lock)
{
        struct btrfs_block_group *used_bg = NULL;

        spin_lock(&cluster->refill_lock);
        while (1) {
                used_bg = cluster->block_group;
                if (!used_bg)
                        return NULL;

                if (used_bg == block_group)
                        return used_bg;

                btrfs_get_block_group(used_bg);

                if (!delalloc)
                        return used_bg;

                if (down_read_trylock(&used_bg->data_rwsem))
                        return used_bg;

                spin_unlock(&cluster->refill_lock);

                /* We should only have one-level nested. */
                down_read_nested(&used_bg->data_rwsem, SINGLE_DEPTH_NESTING);

                spin_lock(&cluster->refill_lock);
                if (used_bg == cluster->block_group)
                        return used_bg;

                up_read(&used_bg->data_rwsem);
                btrfs_put_block_group(used_bg);
        }
}

static inline void
btrfs_release_block_group(struct btrfs_block_group *cache,
                         int delalloc)
{
        if (delalloc)
                up_read(&cache->data_rwsem);
        btrfs_put_block_group(cache);
}

/*
 * Helper function for find_free_extent().
 *
 * Return -ENOENT to inform caller that we need fallback to unclustered mode.
 * Return >0 to inform caller that we find nothing
 * Return 0 means we have found a location and set ffe_ctl->found_offset.
 */
static int find_free_extent_clustered(struct btrfs_block_group *bg,
                                      struct find_free_extent_ctl *ffe_ctl,
                                      struct btrfs_block_group **cluster_bg_ret)
{
        struct btrfs_block_group *cluster_bg;
        struct btrfs_free_cluster *last_ptr = ffe_ctl->last_ptr;
        u64 aligned_cluster;
        u64 offset;
        int ret;

        cluster_bg = btrfs_lock_cluster(bg, last_ptr, ffe_ctl->delalloc);
        if (!cluster_bg)
                goto refill_cluster;
        if (cluster_bg != bg && (cluster_bg->ro ||
            !block_group_bits(cluster_bg, ffe_ctl->flags)))
                goto release_cluster;

        offset = btrfs_alloc_from_cluster(cluster_bg, last_ptr,
                        ffe_ctl->num_bytes, cluster_bg->start,
                        &ffe_ctl->max_extent_size);
        if (offset) {
                /* We have a block, we're done */
                spin_unlock(&last_ptr->refill_lock);
                trace_btrfs_reserve_extent_cluster(cluster_bg, ffe_ctl);
                *cluster_bg_ret = cluster_bg;
                ffe_ctl->found_offset = offset;
                return 0;
        }
        WARN_ON(last_ptr->block_group != cluster_bg);

release_cluster:
        /*
         * If we are on LOOP_NO_EMPTY_SIZE, we can't set up a new clusters, so
         * lets just skip it and let the allocator find whatever block it can
         * find. If we reach this point, we will have tried the cluster
         * allocator plenty of times and not have found anything, so we are
         * likely way too fragmented for the clustering stuff to find anything.
         *
         * However, if the cluster is taken from the current block group,
         * release the cluster first, so that we stand a better chance of
         * succeeding in the unclustered allocation.
         */
        if (ffe_ctl->loop >= LOOP_NO_EMPTY_SIZE && cluster_bg != bg) {
                spin_unlock(&last_ptr->refill_lock);
                btrfs_release_block_group(cluster_bg, ffe_ctl->delalloc);
                return -ENOENT;
        }

        /* This cluster didn't work out, free it and start over */
        btrfs_return_cluster_to_free_space(NULL, last_ptr);

        if (cluster_bg != bg)
                btrfs_release_block_group(cluster_bg, ffe_ctl->delalloc);

refill_cluster:
        if (ffe_ctl->loop >= LOOP_NO_EMPTY_SIZE) {
                spin_unlock(&last_ptr->refill_lock);
                return -ENOENT;
        }

        aligned_cluster = max_t(u64,
                        ffe_ctl->empty_cluster + ffe_ctl->empty_size,
                        bg->full_stripe_len);
        ret = btrfs_find_space_cluster(bg, last_ptr, ffe_ctl->search_start,
                        ffe_ctl->num_bytes, aligned_cluster);
        if (ret == 0) {
                /* Now pull our allocation out of this cluster */
                offset = btrfs_alloc_from_cluster(bg, last_ptr,
                                ffe_ctl->num_bytes, ffe_ctl->search_start,
                                &ffe_ctl->max_extent_size);
                if (offset) {
                        /* We found one, proceed */
                        spin_unlock(&last_ptr->refill_lock);
                        ffe_ctl->found_offset = offset;
                        trace_btrfs_reserve_extent_cluster(bg, ffe_ctl);
                        return 0;
                }
        }
        /*
         * At this point we either didn't find a cluster or we weren't able to
         * allocate a block from our cluster.  Free the cluster we've been
         * trying to use, and go to the next block group.
         */
        btrfs_return_cluster_to_free_space(NULL, last_ptr);
        spin_unlock(&last_ptr->refill_lock);
        return 1;
}

/*
 * Return >0 to inform caller that we find nothing
 * Return 0 when we found an free extent and set ffe_ctrl->found_offset
 */
static int find_free_extent_unclustered(struct btrfs_block_group *bg,
                                        struct find_free_extent_ctl *ffe_ctl)
{
        struct btrfs_free_cluster *last_ptr = ffe_ctl->last_ptr;
        u64 offset;

        /*
         * We are doing an unclustered allocation, set the fragmented flag so
         * we don't bother trying to setup a cluster again until we get more
         * space.
         */
        if (unlikely(last_ptr)) {
                spin_lock(&last_ptr->lock);
                last_ptr->fragmented = 1;
                spin_unlock(&last_ptr->lock);
        }
        if (ffe_ctl->cached) {
                struct btrfs_free_space_ctl *free_space_ctl;

                free_space_ctl = bg->free_space_ctl;
                spin_lock(&free_space_ctl->tree_lock);
                if (free_space_ctl->free_space <
                    ffe_ctl->num_bytes + ffe_ctl->empty_cluster +
                    ffe_ctl->empty_size) {
                        ffe_ctl->total_free_space = max_t(u64,
                                        ffe_ctl->total_free_space,
                                        free_space_ctl->free_space);
                        spin_unlock(&free_space_ctl->tree_lock);
                        return 1;
                }
                spin_unlock(&free_space_ctl->tree_lock);
        }

        offset = btrfs_find_space_for_alloc(bg, ffe_ctl->search_start,
                        ffe_ctl->num_bytes, ffe_ctl->empty_size,
                        &ffe_ctl->max_extent_size);
        if (!offset)
                return 1;
        ffe_ctl->found_offset = offset;
        return 0;
}

static int do_allocation_clustered(struct btrfs_block_group *block_group,
                                   struct find_free_extent_ctl *ffe_ctl,
                                   struct btrfs_block_group **bg_ret)
{
        int ret;

        /* We want to try and use the cluster allocator, so lets look there */
        if (ffe_ctl->last_ptr && ffe_ctl->use_cluster) {
                ret = find_free_extent_clustered(block_group, ffe_ctl, bg_ret);
                if (ret >= 0)
                        return ret;
                /* ret == -ENOENT case falls through */
        }

        return find_free_extent_unclustered(block_group, ffe_ctl);
}

/*
 * Tree-log block group locking
 * ============================
 *
 * fs_info::treelog_bg_lock protects the fs_info::treelog_bg which
 * indicates the starting address of a block group, which is reserved only
 * for tree-log metadata.
 *
 * Lock nesting
 * ============
 *
 * space_info::lock
 *   block_group::lock
 *     fs_info::treelog_bg_lock
 */

/*
 * Simple allocator for sequential-only block group. It only allows sequential
 * allocation. No need to play with trees. This function also reserves the
 * bytes as in btrfs_add_reserved_bytes.
 */
static int do_allocation_zoned(struct btrfs_block_group *block_group,
                               struct find_free_extent_ctl *ffe_ctl,
                               struct btrfs_block_group **bg_ret)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_space_info *space_info = block_group->space_info;
        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
        u64 start = block_group->start;
        u64 num_bytes = ffe_ctl->num_bytes;
        u64 avail;
        u64 bytenr = block_group->start;
        u64 log_bytenr;
        u64 data_reloc_bytenr;
        int ret = 0;
        bool skip = false;

        ASSERT(btrfs_is_zoned(block_group->fs_info));

        /*
         * Do not allow non-tree-log blocks in the dedicated tree-log block
         * group, and vice versa.
         */
        spin_lock(&fs_info->treelog_bg_lock);
        log_bytenr = fs_info->treelog_bg;
        if (log_bytenr && ((ffe_ctl->for_treelog && bytenr != log_bytenr) ||
                           (!ffe_ctl->for_treelog && bytenr == log_bytenr)))
                skip = true;
        spin_unlock(&fs_info->treelog_bg_lock);
        if (skip)
                return 1;

        /*
         * Do not allow non-relocation blocks in the dedicated relocation block
         * group, and vice versa.
         */
        spin_lock(&fs_info->relocation_bg_lock);
        data_reloc_bytenr = fs_info->data_reloc_bg;
        if (data_reloc_bytenr &&
            ((ffe_ctl->for_data_reloc && bytenr != data_reloc_bytenr) ||
             (!ffe_ctl->for_data_reloc && bytenr == data_reloc_bytenr)))
                skip = true;
        spin_unlock(&fs_info->relocation_bg_lock);
        if (skip)
                return 1;

        /* Check RO and no space case before trying to activate it */
        spin_lock(&block_group->lock);
        if (block_group->ro || btrfs_zoned_bg_is_full(block_group)) {
                ret = 1;
                /*
                 * May need to clear fs_info->{treelog,data_reloc}_bg.
                 * Return the error after taking the locks.
                 */
        }
        spin_unlock(&block_group->lock);

        /* Metadata block group is activated at write time. */
        if (!ret && (block_group->flags & BTRFS_BLOCK_GROUP_DATA) &&
            !btrfs_zone_activate(block_group)) {
                ret = 1;
                /*
                 * May need to clear fs_info->{treelog,data_reloc}_bg.
                 * Return the error after taking the locks.
                 */
        }

        spin_lock(&space_info->lock);
        spin_lock(&block_group->lock);
        spin_lock(&fs_info->treelog_bg_lock);
        spin_lock(&fs_info->relocation_bg_lock);

        if (ret)
                goto out;

        ASSERT(!ffe_ctl->for_treelog ||
               block_group->start == fs_info->treelog_bg ||
               fs_info->treelog_bg == 0);
        ASSERT(!ffe_ctl->for_data_reloc ||
               block_group->start == fs_info->data_reloc_bg ||
               fs_info->data_reloc_bg == 0);

        if (block_group->ro ||
            (!ffe_ctl->for_data_reloc &&
             test_bit(BLOCK_GROUP_FLAG_ZONED_DATA_RELOC, &block_group->runtime_flags))) {
                ret = 1;
                goto out;
        }

        /*
         * Do not allow currently using block group to be tree-log dedicated
         * block group.
         */
        if (ffe_ctl->for_treelog && !fs_info->treelog_bg &&
            (block_group->used || block_group->reserved)) {
                ret = 1;
                goto out;
        }

        /*
         * Do not allow currently used block group to be the data relocation
         * dedicated block group.
         */
        if (ffe_ctl->for_data_reloc && !fs_info->data_reloc_bg &&
            (block_group->used || block_group->reserved)) {
                ret = 1;
                goto out;
        }

        WARN_ON_ONCE(block_group->alloc_offset > block_group->zone_capacity);
        avail = block_group->zone_capacity - block_group->alloc_offset;
        if (avail < num_bytes) {
                if (ffe_ctl->max_extent_size < avail) {
                        /*
                         * With sequential allocator, free space is always
                         * contiguous
                         */
                        ffe_ctl->max_extent_size = avail;
                        ffe_ctl->total_free_space = avail;
                }
                ret = 1;
                goto out;
        }

        if (ffe_ctl->for_treelog && !fs_info->treelog_bg)
                fs_info->treelog_bg = block_group->start;

        if (ffe_ctl->for_data_reloc) {
                if (!fs_info->data_reloc_bg)
                        fs_info->data_reloc_bg = block_group->start;
                /*
                 * Do not allow allocations from this block group, unless it is
                 * for data relocation. Compared to increasing the ->ro, setting
                 * the ->zoned_data_reloc_ongoing flag still allows nocow
                 * writers to come in. See btrfs_inc_nocow_writers().
                 *
                 * We need to disable an allocation to avoid an allocation of
                 * regular (non-relocation data) extent. With mix of relocation
                 * extents and regular extents, we can dispatch WRITE commands
                 * (for relocation extents) and ZONE APPEND commands (for
                 * regular extents) at the same time to the same zone, which
                 * easily break the write pointer.
                 *
                 * Also, this flag avoids this block group to be zone finished.
                 */
                set_bit(BLOCK_GROUP_FLAG_ZONED_DATA_RELOC, &block_group->runtime_flags);
        }

        ffe_ctl->found_offset = start + block_group->alloc_offset;
        block_group->alloc_offset += num_bytes;
        spin_lock(&ctl->tree_lock);
        ctl->free_space -= num_bytes;
        spin_unlock(&ctl->tree_lock);

        /*
         * We do not check if found_offset is aligned to stripesize. The
         * address is anyway rewritten when using zone append writing.
         */

        ffe_ctl->search_start = ffe_ctl->found_offset;

out:
        if (ret && ffe_ctl->for_treelog)
                fs_info->treelog_bg = 0;
        if (ret && ffe_ctl->for_data_reloc)
                fs_info->data_reloc_bg = 0;
        spin_unlock(&fs_info->relocation_bg_lock);
        spin_unlock(&fs_info->treelog_bg_lock);
        spin_unlock(&block_group->lock);
        spin_unlock(&space_info->lock);
        return ret;
}

static int do_allocation(struct btrfs_block_group *block_group,
                         struct find_free_extent_ctl *ffe_ctl,
                         struct btrfs_block_group **bg_ret)
{
        switch (ffe_ctl->policy) {
        case BTRFS_EXTENT_ALLOC_CLUSTERED:
                return do_allocation_clustered(block_group, ffe_ctl, bg_ret);
        case BTRFS_EXTENT_ALLOC_ZONED:
                return do_allocation_zoned(block_group, ffe_ctl, bg_ret);
        default:
                BUG();
        }
}

static void release_block_group(struct btrfs_block_group *block_group,
                                struct find_free_extent_ctl *ffe_ctl,
                                int delalloc)
{
        switch (ffe_ctl->policy) {
        case BTRFS_EXTENT_ALLOC_CLUSTERED:
                ffe_ctl->retry_uncached = false;
                break;
        case BTRFS_EXTENT_ALLOC_ZONED:
                /* Nothing to do */
                break;
        default:
                BUG();
        }

        BUG_ON(btrfs_bg_flags_to_raid_index(block_group->flags) !=
               ffe_ctl->index);
        btrfs_release_block_group(block_group, delalloc);
}

static void found_extent_clustered(struct find_free_extent_ctl *ffe_ctl,
                                   struct btrfs_key *ins)
{
        struct btrfs_free_cluster *last_ptr = ffe_ctl->last_ptr;

        if (!ffe_ctl->use_cluster && last_ptr) {
                spin_lock(&last_ptr->lock);
                last_ptr->window_start = ins->objectid;
                spin_unlock(&last_ptr->lock);
        }
}

static void found_extent(struct find_free_extent_ctl *ffe_ctl,
                         struct btrfs_key *ins)
{
        switch (ffe_ctl->policy) {
        case BTRFS_EXTENT_ALLOC_CLUSTERED:
                found_extent_clustered(ffe_ctl, ins);
                break;
        case BTRFS_EXTENT_ALLOC_ZONED:
                /* Nothing to do */
                break;
        default:
                BUG();
        }
}

static int can_allocate_chunk_zoned(struct btrfs_fs_info *fs_info,
                                    struct find_free_extent_ctl *ffe_ctl)
{
        /* Block group's activeness is not a requirement for METADATA block groups. */
        if (!(ffe_ctl->flags & BTRFS_BLOCK_GROUP_DATA))
                return 0;

        /* If we can activate new zone, just allocate a chunk and use it */
        if (btrfs_can_activate_zone(fs_info->fs_devices, ffe_ctl->flags))
                return 0;

        /*
         * We already reached the max active zones. Try to finish one block
         * group to make a room for a new block group. This is only possible
         * for a data block group because btrfs_zone_finish() may need to wait
         * for a running transaction which can cause a deadlock for metadata
         * allocation.
         */
        if (ffe_ctl->flags & BTRFS_BLOCK_GROUP_DATA) {
                int ret = btrfs_zone_finish_one_bg(fs_info);

                if (ret == 1)
                        return 0;
                else if (ret < 0)
                        return ret;
        }

        /*
         * If we have enough free space left in an already active block group
         * and we can't activate any other zone now, do not allow allocating a
         * new chunk and let find_free_extent() retry with a smaller size.
         */
        if (ffe_ctl->max_extent_size >= ffe_ctl->min_alloc_size)
                return -ENOSPC;

        /*
         * Even min_alloc_size is not left in any block groups. Since we cannot
         * activate a new block group, allocating it may not help. Let's tell a
         * caller to try again and hope it progress something by writing some
         * parts of the region. That is only possible for data block groups,
         * where a part of the region can be written.
         */
        if (ffe_ctl->flags & BTRFS_BLOCK_GROUP_DATA)
                return -EAGAIN;

        /*
         * We cannot activate a new block group and no enough space left in any
         * block groups. So, allocating a new block group may not help. But,
         * there is nothing to do anyway, so let's go with it.
         */
        return 0;
}

static int can_allocate_chunk(struct btrfs_fs_info *fs_info,
                              struct find_free_extent_ctl *ffe_ctl)
{
        switch (ffe_ctl->policy) {
        case BTRFS_EXTENT_ALLOC_CLUSTERED:
                return 0;
        case BTRFS_EXTENT_ALLOC_ZONED:
                return can_allocate_chunk_zoned(fs_info, ffe_ctl);
        default:
                BUG();
        }
}

/*
 * Return >0 means caller needs to re-search for free extent
 * Return 0 means we have the needed free extent.
 * Return <0 means we failed to locate any free extent.
 */
static int find_free_extent_update_loop(struct btrfs_fs_info *fs_info,
                                        struct btrfs_key *ins,
                                        struct find_free_extent_ctl *ffe_ctl,
                                        bool full_search)
{
        struct btrfs_root *root = fs_info->chunk_root;
        int ret;

        if ((ffe_ctl->loop == LOOP_CACHING_NOWAIT) &&
            ffe_ctl->have_caching_bg && !ffe_ctl->orig_have_caching_bg)
                ffe_ctl->orig_have_caching_bg = true;

        if (ins->objectid) {
                found_extent(ffe_ctl, ins);
                return 0;
        }

        if (ffe_ctl->loop >= LOOP_CACHING_WAIT && ffe_ctl->have_caching_bg)
                return 1;

        ffe_ctl->index++;
        if (ffe_ctl->index < BTRFS_NR_RAID_TYPES)
                return 1;

        /* See the comments for btrfs_loop_type for an explanation of the phases. */
        if (ffe_ctl->loop < LOOP_NO_EMPTY_SIZE) {
                ffe_ctl->index = 0;
                /*
                 * We want to skip the LOOP_CACHING_WAIT step if we don't have
                 * any uncached bgs and we've already done a full search
                 * through.
                 */
                if (ffe_ctl->loop == LOOP_CACHING_NOWAIT &&
                    (!ffe_ctl->orig_have_caching_bg && full_search))
                        ffe_ctl->loop++;
                ffe_ctl->loop++;

                if (ffe_ctl->loop == LOOP_ALLOC_CHUNK) {
                        struct btrfs_trans_handle *trans;
                        int exist = 0;

                        /* Check if allocation policy allows to create a new chunk */
                        ret = can_allocate_chunk(fs_info, ffe_ctl);
                        if (ret)
                                return ret;

                        trans = current->journal_info;
                        if (trans)
                                exist = 1;
                        else
                                trans = btrfs_join_transaction(root);

                        if (IS_ERR(trans)) {
                                ret = PTR_ERR(trans);
                                return ret;
                        }

                        ret = btrfs_chunk_alloc(trans, ffe_ctl->flags,
                                                CHUNK_ALLOC_FORCE_FOR_EXTENT);

                        /* Do not bail out on ENOSPC since we can do more. */
                        if (ret == -ENOSPC) {
                                ret = 0;
                                ffe_ctl->loop++;
                        }
                        else if (ret < 0)
                                btrfs_abort_transaction(trans, ret);
                        else
                                ret = 0;
                        if (!exist)
                                btrfs_end_transaction(trans);
                        if (ret)
                                return ret;
                }

                if (ffe_ctl->loop == LOOP_NO_EMPTY_SIZE) {
                        if (ffe_ctl->policy != BTRFS_EXTENT_ALLOC_CLUSTERED)
                                return -ENOSPC;

                        /*
                         * Don't loop again if we already have no empty_size and
                         * no empty_cluster.
                         */
                        if (ffe_ctl->empty_size == 0 &&
                            ffe_ctl->empty_cluster == 0)
                                return -ENOSPC;
                        ffe_ctl->empty_size = 0;
                        ffe_ctl->empty_cluster = 0;
                }
                return 1;
        }
        return -ENOSPC;
}

static bool find_free_extent_check_size_class(struct find_free_extent_ctl *ffe_ctl,
                                              struct btrfs_block_group *bg)
{
        if (ffe_ctl->policy == BTRFS_EXTENT_ALLOC_ZONED)
                return true;
        if (!btrfs_block_group_should_use_size_class(bg))
                return true;
        if (ffe_ctl->loop >= LOOP_WRONG_SIZE_CLASS)
                return true;
        if (ffe_ctl->loop >= LOOP_UNSET_SIZE_CLASS &&
            bg->size_class == BTRFS_BG_SZ_NONE)
                return true;
        return ffe_ctl->size_class == bg->size_class;
}

static int prepare_allocation_clustered(struct btrfs_fs_info *fs_info,
                                        struct find_free_extent_ctl *ffe_ctl,
                                        struct btrfs_space_info *space_info,
                                        struct btrfs_key *ins)
{
        /*
         * If our free space is heavily fragmented we may not be able to make
         * big contiguous allocations, so instead of doing the expensive search
         * for free space, simply return ENOSPC with our max_extent_size so we
         * can go ahead and search for a more manageable chunk.
         *
         * If our max_extent_size is large enough for our allocation simply
         * disable clustering since we will likely not be able to find enough
         * space to create a cluster and induce latency trying.
         */
        if (space_info->max_extent_size) {
                spin_lock(&space_info->lock);
                if (space_info->max_extent_size &&
                    ffe_ctl->num_bytes > space_info->max_extent_size) {
                        ins->offset = space_info->max_extent_size;
                        spin_unlock(&space_info->lock);
                        return -ENOSPC;
                } else if (space_info->max_extent_size) {
                        ffe_ctl->use_cluster = false;
                }
                spin_unlock(&space_info->lock);
        }

        ffe_ctl->last_ptr = fetch_cluster_info(fs_info, space_info,
                                               &ffe_ctl->empty_cluster);
        if (ffe_ctl->last_ptr) {
                struct btrfs_free_cluster *last_ptr = ffe_ctl->last_ptr;

                spin_lock(&last_ptr->lock);
                if (last_ptr->block_group)
                        ffe_ctl->hint_byte = last_ptr->window_start;
                if (last_ptr->fragmented) {
                        /*
                         * We still set window_start so we can keep track of the
                         * last place we found an allocation to try and save
                         * some time.
                         */
                        ffe_ctl->hint_byte = last_ptr->window_start;
                        ffe_ctl->use_cluster = false;
                }
                spin_unlock(&last_ptr->lock);
        }

        return 0;
}

static int prepare_allocation(struct btrfs_fs_info *fs_info,
                              struct find_free_extent_ctl *ffe_ctl,
                              struct btrfs_space_info *space_info,
                              struct btrfs_key *ins)
{
        switch (ffe_ctl->policy) {
        case BTRFS_EXTENT_ALLOC_CLUSTERED:
                return prepare_allocation_clustered(fs_info, ffe_ctl,
                                                    space_info, ins);
        case BTRFS_EXTENT_ALLOC_ZONED:
                if (ffe_ctl->for_treelog) {
                        spin_lock(&fs_info->treelog_bg_lock);
                        if (fs_info->treelog_bg)
                                ffe_ctl->hint_byte = fs_info->treelog_bg;
                        spin_unlock(&fs_info->treelog_bg_lock);
                }
                if (ffe_ctl->for_data_reloc) {
                        spin_lock(&fs_info->relocation_bg_lock);
                        if (fs_info->data_reloc_bg)
                                ffe_ctl->hint_byte = fs_info->data_reloc_bg;
                        spin_unlock(&fs_info->relocation_bg_lock);
                }
                return 0;
        default:
                BUG();
        }
}

/*
 * walks the btree of allocated extents and find a hole of a given size.
 * The key ins is changed to record the hole:
 * ins->objectid == start position
 * ins->flags = BTRFS_EXTENT_ITEM_KEY
 * ins->offset == the size of the hole.
 * Any available blocks before search_start are skipped.
 *
 * If there is no suitable free space, we will record the max size of
 * the free space extent currently.
 *
 * The overall logic and call chain:
 *
 * find_free_extent()
 * |- Iterate through all block groups
 * |  |- Get a valid block group
 * |  |- Try to do clustered allocation in that block group
 * |  |- Try to do unclustered allocation in that block group
 * |  |- Check if the result is valid
 * |  |  |- If valid, then exit
 * |  |- Jump to next block group
 * |
 * |- Push harder to find free extents
 *    |- If not found, re-iterate all block groups
 */
static noinline int find_free_extent(struct btrfs_root *root,
                                     struct btrfs_key *ins,
                                     struct find_free_extent_ctl *ffe_ctl)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        int ret = 0;
        int cache_block_group_error = 0;
        struct btrfs_block_group *block_group = NULL;
        struct btrfs_space_info *space_info;
        bool full_search = false;

        WARN_ON(ffe_ctl->num_bytes < fs_info->sectorsize);

        ffe_ctl->search_start = 0;
        /* For clustered allocation */
        ffe_ctl->empty_cluster = 0;
        ffe_ctl->last_ptr = NULL;
        ffe_ctl->use_cluster = true;
        ffe_ctl->have_caching_bg = false;
        ffe_ctl->orig_have_caching_bg = false;
        ffe_ctl->index = btrfs_bg_flags_to_raid_index(ffe_ctl->flags);
        ffe_ctl->loop = 0;
        ffe_ctl->retry_uncached = false;
        ffe_ctl->cached = 0;
        ffe_ctl->max_extent_size = 0;
        ffe_ctl->total_free_space = 0;
        ffe_ctl->found_offset = 0;
        ffe_ctl->policy = BTRFS_EXTENT_ALLOC_CLUSTERED;
        ffe_ctl->size_class = btrfs_calc_block_group_size_class(ffe_ctl->num_bytes);

        if (btrfs_is_zoned(fs_info))
                ffe_ctl->policy = BTRFS_EXTENT_ALLOC_ZONED;

        ins->type = BTRFS_EXTENT_ITEM_KEY;
        ins->objectid = 0;
        ins->offset = 0;

        trace_find_free_extent(root, ffe_ctl);

        space_info = btrfs_find_space_info(fs_info, ffe_ctl->flags);
        if (!space_info) {
                btrfs_err(fs_info, "No space info for %llu", ffe_ctl->flags);
                return -ENOSPC;
        }

        ret = prepare_allocation(fs_info, ffe_ctl, space_info, ins);
        if (ret < 0)
                return ret;

        ffe_ctl->search_start = max(ffe_ctl->search_start,
                                    first_logical_byte(fs_info));
        ffe_ctl->search_start = max(ffe_ctl->search_start, ffe_ctl->hint_byte);
        if (ffe_ctl->search_start == ffe_ctl->hint_byte) {
                block_group = btrfs_lookup_block_group(fs_info,
                                                       ffe_ctl->search_start);
                /*
                 * we don't want to use the block group if it doesn't match our
                 * allocation bits, or if its not cached.
                 *
                 * However if we are re-searching with an ideal block group
                 * picked out then we don't care that the block group is cached.
                 */
                if (block_group && block_group_bits(block_group, ffe_ctl->flags) &&
                    block_group->cached != BTRFS_CACHE_NO) {
                        down_read(&space_info->groups_sem);
                        if (list_empty(&block_group->list) ||
                            block_group->ro) {
                                /*
                                 * someone is removing this block group,
                                 * we can't jump into the have_block_group
                                 * target because our list pointers are not
                                 * valid
                                 */
                                btrfs_put_block_group(block_group);
                                up_read(&space_info->groups_sem);
                        } else {
                                ffe_ctl->index = btrfs_bg_flags_to_raid_index(
                                                        block_group->flags);
                                btrfs_lock_block_group(block_group,
                                                       ffe_ctl->delalloc);
                                ffe_ctl->hinted = true;
                                goto have_block_group;
                        }
                } else if (block_group) {
                        btrfs_put_block_group(block_group);
                }
        }
search:
        trace_find_free_extent_search_loop(root, ffe_ctl);
        ffe_ctl->have_caching_bg = false;
        if (ffe_ctl->index == btrfs_bg_flags_to_raid_index(ffe_ctl->flags) ||
            ffe_ctl->index == 0)
                full_search = true;
        down_read(&space_info->groups_sem);
        list_for_each_entry(block_group,
                            &space_info->block_groups[ffe_ctl->index], list) {
                struct btrfs_block_group *bg_ret;

                ffe_ctl->hinted = false;
                /* If the block group is read-only, we can skip it entirely. */
                if (unlikely(block_group->ro)) {
                        if (ffe_ctl->for_treelog)
                                btrfs_clear_treelog_bg(block_group);
                        if (ffe_ctl->for_data_reloc)
                                btrfs_clear_data_reloc_bg(block_group);
                        continue;
                }

                btrfs_grab_block_group(block_group, ffe_ctl->delalloc);
                ffe_ctl->search_start = block_group->start;

                /*
                 * this can happen if we end up cycling through all the
                 * raid types, but we want to make sure we only allocate
                 * for the proper type.
                 */
                if (!block_group_bits(block_group, ffe_ctl->flags)) {
                        u64 extra = BTRFS_BLOCK_GROUP_DUP |
                                BTRFS_BLOCK_GROUP_RAID1_MASK |
                                BTRFS_BLOCK_GROUP_RAID56_MASK |
                                BTRFS_BLOCK_GROUP_RAID10;

                        /*
                         * if they asked for extra copies and this block group
                         * doesn't provide them, bail.  This does allow us to
                         * fill raid0 from raid1.
                         */
                        if ((ffe_ctl->flags & extra) && !(block_group->flags & extra))
                                goto loop;

                        /*
                         * This block group has different flags than we want.
                         * It's possible that we have MIXED_GROUP flag but no
                         * block group is mixed.  Just skip such block group.
                         */
                        btrfs_release_block_group(block_group, ffe_ctl->delalloc);
                        continue;
                }

have_block_group:
                trace_find_free_extent_have_block_group(root, ffe_ctl, block_group);
                ffe_ctl->cached = btrfs_block_group_done(block_group);
                if (unlikely(!ffe_ctl->cached)) {
                        ffe_ctl->have_caching_bg = true;
                        ret = btrfs_cache_block_group(block_group, false);

                        /*
                         * If we get ENOMEM here or something else we want to
                         * try other block groups, because it may not be fatal.
                         * However if we can't find anything else we need to
                         * save our return here so that we return the actual
                         * error that caused problems, not ENOSPC.
                         */
                        if (ret < 0) {
                                if (!cache_block_group_error)
                                        cache_block_group_error = ret;
                                ret = 0;
                                goto loop;
                        }
                        ret = 0;
                }

                if (unlikely(block_group->cached == BTRFS_CACHE_ERROR)) {
                        if (!cache_block_group_error)
                                cache_block_group_error = -EIO;
                        goto loop;
                }

                if (!find_free_extent_check_size_class(ffe_ctl, block_group))
                        goto loop;

                bg_ret = NULL;
                ret = do_allocation(block_group, ffe_ctl, &bg_ret);
                if (ret > 0)
                        goto loop;

                if (bg_ret && bg_ret != block_group) {
                        btrfs_release_block_group(block_group, ffe_ctl->delalloc);
                        block_group = bg_ret;
                }

                /* Checks */
                ffe_ctl->search_start = round_up(ffe_ctl->found_offset,
                                                 fs_info->stripesize);

                /* move on to the next group */
                if (ffe_ctl->search_start + ffe_ctl->num_bytes >
                    block_group->start + block_group->length) {
                        btrfs_add_free_space_unused(block_group,
                                            ffe_ctl->found_offset,
                                            ffe_ctl->num_bytes);
                        goto loop;
                }

                if (ffe_ctl->found_offset < ffe_ctl->search_start)
                        btrfs_add_free_space_unused(block_group,
                                        ffe_ctl->found_offset,
                                        ffe_ctl->search_start - ffe_ctl->found_offset);

                ret = btrfs_add_reserved_bytes(block_group, ffe_ctl->ram_bytes,
                                               ffe_ctl->num_bytes,
                                               ffe_ctl->delalloc,
                                               ffe_ctl->loop >= LOOP_WRONG_SIZE_CLASS);
                if (ret == -EAGAIN) {
                        btrfs_add_free_space_unused(block_group,
                                        ffe_ctl->found_offset,
                                        ffe_ctl->num_bytes);
                        goto loop;
                }
                btrfs_inc_block_group_reservations(block_group);

                /* we are all good, lets return */
                ins->objectid = ffe_ctl->search_start;
                ins->offset = ffe_ctl->num_bytes;

                trace_btrfs_reserve_extent(block_group, ffe_ctl);
                btrfs_release_block_group(block_group, ffe_ctl->delalloc);
                break;
loop:
                if (!ffe_ctl->cached && ffe_ctl->loop > LOOP_CACHING_NOWAIT &&
                    !ffe_ctl->retry_uncached) {
                        ffe_ctl->retry_uncached = true;
                        btrfs_wait_block_group_cache_progress(block_group,
                                                ffe_ctl->num_bytes +
                                                ffe_ctl->empty_cluster +
                                                ffe_ctl->empty_size);
                        goto have_block_group;
                }
                release_block_group(block_group, ffe_ctl, ffe_ctl->delalloc);
                cond_resched();
        }
        up_read(&space_info->groups_sem);

        ret = find_free_extent_update_loop(fs_info, ins, ffe_ctl, full_search);
        if (ret > 0)
                goto search;

        if (ret == -ENOSPC && !cache_block_group_error) {
                /*
                 * Use ffe_ctl->total_free_space as fallback if we can't find
                 * any contiguous hole.
                 */
                if (!ffe_ctl->max_extent_size)
                        ffe_ctl->max_extent_size = ffe_ctl->total_free_space;
                spin_lock(&space_info->lock);
                space_info->max_extent_size = ffe_ctl->max_extent_size;
                spin_unlock(&space_info->lock);
                ins->offset = ffe_ctl->max_extent_size;
        } else if (ret == -ENOSPC) {
                ret = cache_block_group_error;
        }
        return ret;
}

/*
 * Entry point to the extent allocator. Tries to find a hole that is at least
 * as big as @num_bytes.
 *
 * @root           -    The root that will contain this extent
 *
 * @ram_bytes      -    The amount of space in ram that @num_bytes take. This
 *                      is used for accounting purposes. This value differs
 *                      from @num_bytes only in the case of compressed extents.
 *
 * @num_bytes      -    Number of bytes to allocate on-disk.
 *
 * @min_alloc_size -    Indicates the minimum amount of space that the
 *                      allocator should try to satisfy. In some cases
 *                      @num_bytes may be larger than what is required and if
 *                      the filesystem is fragmented then allocation fails.
 *                      However, the presence of @min_alloc_size gives a
 *                      chance to try and satisfy the smaller allocation.
 *
 * @empty_size     -    A hint that you plan on doing more COW. This is the
 *                      size in bytes the allocator should try to find free
 *                      next to the block it returns.  This is just a hint and
 *                      may be ignored by the allocator.
 *
 * @hint_byte      -    Hint to the allocator to start searching above the byte
 *                      address passed. It might be ignored.
 *
 * @ins            -    This key is modified to record the found hole. It will
 *                      have the following values:
 *                      ins->objectid == start position
 *                      ins->flags = BTRFS_EXTENT_ITEM_KEY
 *                      ins->offset == the size of the hole.
 *
 * @is_data        -    Boolean flag indicating whether an extent is
 *                      allocated for data (true) or metadata (false)
 *
 * @delalloc       -    Boolean flag indicating whether this allocation is for
 *                      delalloc or not. If 'true' data_rwsem of block groups
 *                      is going to be acquired.
 *
 *
 * Returns 0 when an allocation succeeded or < 0 when an error occurred. In
 * case -ENOSPC is returned then @ins->offset will contain the size of the
 * largest available hole the allocator managed to find.
 */
int btrfs_reserve_extent(struct btrfs_root *root, u64 ram_bytes,
                         u64 num_bytes, u64 min_alloc_size,
                         u64 empty_size, u64 hint_byte,
                         struct btrfs_key *ins, int is_data, int delalloc)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct find_free_extent_ctl ffe_ctl = {};
        bool final_tried = num_bytes == min_alloc_size;
        u64 flags;
        int ret;
        bool for_treelog = (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID);
        bool for_data_reloc = (btrfs_is_data_reloc_root(root) && is_data);

        flags = get_alloc_profile_by_root(root, is_data);
again:
        WARN_ON(num_bytes < fs_info->sectorsize);

        ffe_ctl.ram_bytes = ram_bytes;
        ffe_ctl.num_bytes = num_bytes;
        ffe_ctl.min_alloc_size = min_alloc_size;
        ffe_ctl.empty_size = empty_size;
        ffe_ctl.flags = flags;
        ffe_ctl.delalloc = delalloc;
        ffe_ctl.hint_byte = hint_byte;
        ffe_ctl.for_treelog = for_treelog;
        ffe_ctl.for_data_reloc = for_data_reloc;

        ret = find_free_extent(root, ins, &ffe_ctl);
        if (!ret && !is_data) {
                btrfs_dec_block_group_reservations(fs_info, ins->objectid);
        } else if (ret == -ENOSPC) {
                if (!final_tried && ins->offset) {
                        num_bytes = min(num_bytes >> 1, ins->offset);
                        num_bytes = round_down(num_bytes,
                                               fs_info->sectorsize);
                        num_bytes = max(num_bytes, min_alloc_size);
                        ram_bytes = num_bytes;
                        if (num_bytes == min_alloc_size)
                                final_tried = true;
                        goto again;
                } else if (btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
                        struct btrfs_space_info *sinfo;

                        sinfo = btrfs_find_space_info(fs_info, flags);
                        btrfs_err(fs_info,
        "allocation failed flags %llu, wanted %llu tree-log %d, relocation: %d",
                                  flags, num_bytes, for_treelog, for_data_reloc);
                        if (sinfo)
                                btrfs_dump_space_info(fs_info, sinfo,
                                                      num_bytes, 1);
                }
        }

        return ret;
}

int btrfs_free_reserved_extent(struct btrfs_fs_info *fs_info,
                               u64 start, u64 len, int delalloc)
{
        struct btrfs_block_group *cache;

        cache = btrfs_lookup_block_group(fs_info, start);
        if (!cache) {
                btrfs_err(fs_info, "Unable to find block group for %llu",
                          start);
                return -ENOSPC;
        }

        btrfs_add_free_space(cache, start, len);
        btrfs_free_reserved_bytes(cache, len, delalloc);
        trace_btrfs_reserved_extent_free(fs_info, start, len);

        btrfs_put_block_group(cache);
        return 0;
}

int btrfs_pin_reserved_extent(struct btrfs_trans_handle *trans,
                              const struct extent_buffer *eb)
{
        struct btrfs_block_group *cache;
        int ret = 0;

        cache = btrfs_lookup_block_group(trans->fs_info, eb->start);
        if (!cache) {
                btrfs_err(trans->fs_info, "unable to find block group for %llu",
                          eb->start);
                return -ENOSPC;
        }

        ret = pin_down_extent(trans, cache, eb->start, eb->len, 1);
        btrfs_put_block_group(cache);
        return ret;
}

static int alloc_reserved_extent(struct btrfs_trans_handle *trans, u64 bytenr,
                                 u64 num_bytes)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        int ret;

        ret = remove_from_free_space_tree(trans, bytenr, num_bytes);
        if (ret)
                return ret;

        ret = btrfs_update_block_group(trans, bytenr, num_bytes, true);
        if (ret) {
                ASSERT(!ret);
                btrfs_err(fs_info, "update block group failed for %llu %llu",
                          bytenr, num_bytes);
                return ret;
        }

        trace_btrfs_reserved_extent_alloc(fs_info, bytenr, num_bytes);
        return 0;
}

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)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *extent_root;
        int ret;
        struct btrfs_extent_item *extent_item;
        struct btrfs_extent_inline_ref *iref;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        int type;
        u32 size;

        if (parent > 0)
                type = BTRFS_SHARED_DATA_REF_KEY;
        else
                type = BTRFS_EXTENT_DATA_REF_KEY;

        size = sizeof(*extent_item) + btrfs_extent_inline_ref_size(type);

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

        extent_root = btrfs_extent_root(fs_info, ins->objectid);
        ret = btrfs_insert_empty_item(trans, extent_root, path, ins, size);
        if (ret) {
                btrfs_free_path(path);
                return ret;
        }

        leaf = path->nodes[0];
        extent_item = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_extent_item);
        btrfs_set_extent_refs(leaf, extent_item, ref_mod);
        btrfs_set_extent_generation(leaf, extent_item, trans->transid);
        btrfs_set_extent_flags(leaf, extent_item,
                               flags | BTRFS_EXTENT_FLAG_DATA);

        iref = (struct btrfs_extent_inline_ref *)(extent_item + 1);
        btrfs_set_extent_inline_ref_type(leaf, iref, type);
        if (parent > 0) {
                struct btrfs_shared_data_ref *ref;
                ref = (struct btrfs_shared_data_ref *)(iref + 1);
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
                btrfs_set_shared_data_ref_count(leaf, ref, ref_mod);
        } else {
                struct btrfs_extent_data_ref *ref;
                ref = (struct btrfs_extent_data_ref *)(&iref->offset);
                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, ref_mod);
        }

        btrfs_mark_buffer_dirty(trans, path->nodes[0]);
        btrfs_free_path(path);

        return alloc_reserved_extent(trans, ins->objectid, ins->offset);
}

static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
                                     struct btrfs_delayed_ref_node *node,
                                     struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *extent_root;
        int ret;
        struct btrfs_extent_item *extent_item;
        struct btrfs_key extent_key;
        struct btrfs_tree_block_info *block_info;
        struct btrfs_extent_inline_ref *iref;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_delayed_tree_ref *ref;
        u32 size = sizeof(*extent_item) + sizeof(*iref);
        u64 flags = extent_op->flags_to_set;
        bool skinny_metadata = btrfs_fs_incompat(fs_info, SKINNY_METADATA);

        ref = btrfs_delayed_node_to_tree_ref(node);

        extent_key.objectid = node->bytenr;
        if (skinny_metadata) {
                extent_key.offset = ref->level;
                extent_key.type = BTRFS_METADATA_ITEM_KEY;
        } else {
                extent_key.offset = node->num_bytes;
                extent_key.type = BTRFS_EXTENT_ITEM_KEY;
                size += sizeof(*block_info);
        }

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

        extent_root = btrfs_extent_root(fs_info, extent_key.objectid);
        ret = btrfs_insert_empty_item(trans, extent_root, path, &extent_key,
                                      size);
        if (ret) {
                btrfs_free_path(path);
                return ret;
        }

        leaf = path->nodes[0];
        extent_item = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_extent_item);
        btrfs_set_extent_refs(leaf, extent_item, 1);
        btrfs_set_extent_generation(leaf, extent_item, trans->transid);
        btrfs_set_extent_flags(leaf, extent_item,
                               flags | BTRFS_EXTENT_FLAG_TREE_BLOCK);

        if (skinny_metadata) {
                iref = (struct btrfs_extent_inline_ref *)(extent_item + 1);
        } else {
                block_info = (struct btrfs_tree_block_info *)(extent_item + 1);
                btrfs_set_tree_block_key(leaf, block_info, &extent_op->key);
                btrfs_set_tree_block_level(leaf, block_info, ref->level);
                iref = (struct btrfs_extent_inline_ref *)(block_info + 1);
        }

        if (node->type == BTRFS_SHARED_BLOCK_REF_KEY) {
                btrfs_set_extent_inline_ref_type(leaf, iref,
                                                 BTRFS_SHARED_BLOCK_REF_KEY);
                btrfs_set_extent_inline_ref_offset(leaf, iref, ref->parent);
        } else {
                btrfs_set_extent_inline_ref_type(leaf, iref,
                                                 BTRFS_TREE_BLOCK_REF_KEY);
                btrfs_set_extent_inline_ref_offset(leaf, iref, ref->root);
        }

        btrfs_mark_buffer_dirty(trans, leaf);
        btrfs_free_path(path);

        return alloc_reserved_extent(trans, node->bytenr, fs_info->nodesize);
}

int btrfs_alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                                     struct btrfs_root *root, u64 owner,
                                     u64 offset, u64 ram_bytes,
                                     struct btrfs_key *ins)
{
        struct btrfs_ref generic_ref = { 0 };

        BUG_ON(root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID);

        btrfs_init_generic_ref(&generic_ref, BTRFS_ADD_DELAYED_EXTENT,
                               ins->objectid, ins->offset, 0);
        btrfs_init_data_ref(&generic_ref, root->root_key.objectid, owner,
                            offset, 0, false);
        btrfs_ref_tree_mod(root->fs_info, &generic_ref);

        return btrfs_add_delayed_data_ref(trans, &generic_ref, ram_bytes);
}

/*
 * this is used by the tree logging recovery code.  It records that
 * an extent has been allocated and makes sure to clear the free
 * space cache bits as well
 */
int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
                                   u64 root_objectid, u64 owner, u64 offset,
                                   struct btrfs_key *ins)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        int ret;
        struct btrfs_block_group *block_group;
        struct btrfs_space_info *space_info;

        /*
         * Mixed block groups will exclude before processing the log so we only
         * need to do the exclude dance if this fs isn't mixed.
         */
        if (!btrfs_fs_incompat(fs_info, MIXED_GROUPS)) {
                ret = __exclude_logged_extent(fs_info, ins->objectid,
                                              ins->offset);
                if (ret)
                        return ret;
        }

        block_group = btrfs_lookup_block_group(fs_info, ins->objectid);
        if (!block_group)
                return -EINVAL;

        space_info = block_group->space_info;
        spin_lock(&space_info->lock);
        spin_lock(&block_group->lock);
        space_info->bytes_reserved += ins->offset;
        block_group->reserved += ins->offset;
        spin_unlock(&block_group->lock);
        spin_unlock(&space_info->lock);

        ret = alloc_reserved_file_extent(trans, 0, root_objectid, 0, owner,
                                         offset, ins, 1);
        if (ret)
                btrfs_pin_extent(trans, ins->objectid, ins->offset, 1);
        btrfs_put_block_group(block_group);
        return ret;
}

#ifdef CONFIG_BTRFS_DEBUG
/*
 * Extra safety check in case the extent tree is corrupted and extent allocator
 * chooses to use a tree block which is already used and locked.
 */
static bool check_eb_lock_owner(const struct extent_buffer *eb)
{
        if (eb->lock_owner == current->pid) {
                btrfs_err_rl(eb->fs_info,
"tree block %llu owner %llu already locked by pid=%d, extent tree corruption detected",
                             eb->start, btrfs_header_owner(eb), current->pid);
                return true;
        }
        return false;
}
#else
static bool check_eb_lock_owner(struct extent_buffer *eb)
{
        return false;
}
#endif

static struct extent_buffer *
btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                      u64 bytenr, int level, u64 owner,
                      enum btrfs_lock_nesting nest)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct extent_buffer *buf;
        u64 lockdep_owner = owner;

        buf = btrfs_find_create_tree_block(fs_info, bytenr, owner, level);
        if (IS_ERR(buf))
                return buf;

        if (check_eb_lock_owner(buf)) {
                free_extent_buffer(buf);
                return ERR_PTR(-EUCLEAN);
        }

        /*
         * The reloc trees are just snapshots, so we need them to appear to be
         * just like any other fs tree WRT lockdep.
         *
         * The exception however is in replace_path() in relocation, where we
         * hold the lock on the original fs root and then search for the reloc
         * root.  At that point we need to make sure any reloc root buffers are
         * set to the BTRFS_TREE_RELOC_OBJECTID lockdep class in order to make
         * lockdep happy.
         */
        if (lockdep_owner == BTRFS_TREE_RELOC_OBJECTID &&
            !test_bit(BTRFS_ROOT_RESET_LOCKDEP_CLASS, &root->state))
                lockdep_owner = BTRFS_FS_TREE_OBJECTID;

        /* btrfs_clear_buffer_dirty() accesses generation field. */
        btrfs_set_header_generation(buf, trans->transid);

        /*
         * This needs to stay, because we could allocate a freed block from an
         * old tree into a new tree, so we need to make sure this new block is
         * set to the appropriate level and owner.
         */
        btrfs_set_buffer_lockdep_class(lockdep_owner, buf, level);

        __btrfs_tree_lock(buf, nest);
        btrfs_clear_buffer_dirty(trans, buf);
        clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);
        clear_bit(EXTENT_BUFFER_NO_CHECK, &buf->bflags);

        set_extent_buffer_uptodate(buf);

        memzero_extent_buffer(buf, 0, sizeof(struct btrfs_header));
        btrfs_set_header_level(buf, level);
        btrfs_set_header_bytenr(buf, buf->start);
        btrfs_set_header_generation(buf, trans->transid);
        btrfs_set_header_backref_rev(buf, BTRFS_MIXED_BACKREF_REV);
        btrfs_set_header_owner(buf, owner);
        write_extent_buffer_fsid(buf, fs_info->fs_devices->metadata_uuid);
        write_extent_buffer_chunk_tree_uuid(buf, fs_info->chunk_tree_uuid);
        if (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID) {
                buf->log_index = root->log_transid % 2;
                /*
                 * we allow two log transactions at a time, use different
                 * EXTENT bit to differentiate dirty pages.
                 */
                if (buf->log_index == 0)
                        set_extent_bit(&root->dirty_log_pages, buf->start,
                                       buf->start + buf->len - 1,
                                       EXTENT_DIRTY, NULL);
                else
                        set_extent_bit(&root->dirty_log_pages, buf->start,
                                       buf->start + buf->len - 1,
                                       EXTENT_NEW, NULL);
        } else {
                buf->log_index = -1;
                set_extent_bit(&trans->transaction->dirty_pages, buf->start,
                               buf->start + buf->len - 1, EXTENT_DIRTY, NULL);
        }
        /* this returns a buffer locked for blocking */
        return buf;
}

/*
 * finds a free extent and does all the dirty work required for allocation
 * returns the tree buffer or an ERR_PTR on error.
 */
struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
                                             struct btrfs_root *root,
                                             u64 parent, u64 root_objectid,
                                             const struct btrfs_disk_key *key,
                                             int level, u64 hint,
                                             u64 empty_size,
                                             enum btrfs_lock_nesting nest)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_key ins;
        struct btrfs_block_rsv *block_rsv;
        struct extent_buffer *buf;
        struct btrfs_delayed_extent_op *extent_op;
        struct btrfs_ref generic_ref = { 0 };
        u64 flags = 0;
        int ret;
        u32 blocksize = fs_info->nodesize;
        bool skinny_metadata = btrfs_fs_incompat(fs_info, SKINNY_METADATA);

#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
        if (btrfs_is_testing(fs_info)) {
                buf = btrfs_init_new_buffer(trans, root, root->alloc_bytenr,
                                            level, root_objectid, nest);
                if (!IS_ERR(buf))
                        root->alloc_bytenr += blocksize;
                return buf;
        }
#endif

        block_rsv = btrfs_use_block_rsv(trans, root, blocksize);
        if (IS_ERR(block_rsv))
                return ERR_CAST(block_rsv);

        ret = btrfs_reserve_extent(root, blocksize, blocksize, blocksize,
                                   empty_size, hint, &ins, 0, 0);
        if (ret)
                goto out_unuse;

        buf = btrfs_init_new_buffer(trans, root, ins.objectid, level,
                                    root_objectid, nest);
        if (IS_ERR(buf)) {
                ret = PTR_ERR(buf);
                goto out_free_reserved;
        }

        if (root_objectid == BTRFS_TREE_RELOC_OBJECTID) {
                if (parent == 0)
                        parent = ins.objectid;
                flags |= BTRFS_BLOCK_FLAG_FULL_BACKREF;
        } else
                BUG_ON(parent > 0);

        if (root_objectid != BTRFS_TREE_LOG_OBJECTID) {
                extent_op = btrfs_alloc_delayed_extent_op();
                if (!extent_op) {
                        ret = -ENOMEM;
                        goto out_free_buf;
                }
                if (key)
                        memcpy(&extent_op->key, key, sizeof(extent_op->key));
                else
                        memset(&extent_op->key, 0, sizeof(extent_op->key));
                extent_op->flags_to_set = flags;
                extent_op->update_key = skinny_metadata ? false : true;
                extent_op->update_flags = true;
                extent_op->level = level;

                btrfs_init_generic_ref(&generic_ref, BTRFS_ADD_DELAYED_EXTENT,
                                       ins.objectid, ins.offset, parent);
                btrfs_init_tree_ref(&generic_ref, level, root_objectid,
                                    root->root_key.objectid, false);
                btrfs_ref_tree_mod(fs_info, &generic_ref);
                ret = btrfs_add_delayed_tree_ref(trans, &generic_ref, extent_op);
                if (ret)
                        goto out_free_delayed;
        }
        return buf;

out_free_delayed:
        btrfs_free_delayed_extent_op(extent_op);
out_free_buf:
        btrfs_tree_unlock(buf);
        free_extent_buffer(buf);
out_free_reserved:
        btrfs_free_reserved_extent(fs_info, ins.objectid, ins.offset, 0);
out_unuse:
        btrfs_unuse_block_rsv(fs_info, block_rsv, blocksize);
        return ERR_PTR(ret);
}

struct walk_control {
        u64 refs[BTRFS_MAX_LEVEL];
        u64 flags[BTRFS_MAX_LEVEL];
        struct btrfs_key update_progress;
        struct btrfs_key drop_progress;
        int drop_level;
        int stage;
        int level;
        int shared_level;
        int update_ref;
        int keep_locks;
        int reada_slot;
        int reada_count;
        int restarted;
};

#define DROP_REFERENCE  1
#define UPDATE_BACKREF  2

static noinline void reada_walk_down(struct btrfs_trans_handle *trans,
                                     struct btrfs_root *root,
                                     struct walk_control *wc,
                                     struct btrfs_path *path)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 bytenr;
        u64 generation;
        u64 refs;
        u64 flags;
        u32 nritems;
        struct btrfs_key key;
        struct extent_buffer *eb;
        int ret;
        int slot;
        int nread = 0;

        if (path->slots[wc->level] < wc->reada_slot) {
                wc->reada_count = wc->reada_count * 2 / 3;
                wc->reada_count = max(wc->reada_count, 2);
        } else {
                wc->reada_count = wc->reada_count * 3 / 2;
                wc->reada_count = min_t(int, wc->reada_count,
                                        BTRFS_NODEPTRS_PER_BLOCK(fs_info));
        }

        eb = path->nodes[wc->level];
        nritems = btrfs_header_nritems(eb);

        for (slot = path->slots[wc->level]; slot < nritems; slot++) {
                if (nread >= wc->reada_count)
                        break;

                cond_resched();
                bytenr = btrfs_node_blockptr(eb, slot);
                generation = btrfs_node_ptr_generation(eb, slot);

                if (slot == path->slots[wc->level])
                        goto reada;

                if (wc->stage == UPDATE_BACKREF &&
                    generation <= root->root_key.offset)
                        continue;

                /* We don't lock the tree block, it's OK to be racy here */
                ret = btrfs_lookup_extent_info(trans, fs_info, bytenr,
                                               wc->level - 1, 1, &refs,
                                               &flags);
                /* We don't care about errors in readahead. */
                if (ret < 0)
                        continue;
                BUG_ON(refs == 0);

                if (wc->stage == DROP_REFERENCE) {
                        if (refs == 1)
                                goto reada;

                        if (wc->level == 1 &&
                            (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                                continue;
                        if (!wc->update_ref ||
                            generation <= root->root_key.offset)
                                continue;
                        btrfs_node_key_to_cpu(eb, &key, slot);
                        ret = btrfs_comp_cpu_keys(&key,
                                                  &wc->update_progress);
                        if (ret < 0)
                                continue;
                } else {
                        if (wc->level == 1 &&
                            (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                                continue;
                }
reada:
                btrfs_readahead_node_child(eb, slot);
                nread++;
        }
        wc->reada_slot = slot;
}

/*
 * helper to process tree block while walking down the tree.
 *
 * when wc->stage == UPDATE_BACKREF, this function updates
 * back refs for pointers in the block.
 *
 * NOTE: return value 1 means we should stop walking down.
 */
static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   struct btrfs_path *path,
                                   struct walk_control *wc, int lookup_info)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        int level = wc->level;
        struct extent_buffer *eb = path->nodes[level];
        u64 flag = BTRFS_BLOCK_FLAG_FULL_BACKREF;
        int ret;

        if (wc->stage == UPDATE_BACKREF &&
            btrfs_header_owner(eb) != root->root_key.objectid)
                return 1;

        /*
         * when reference count of tree block is 1, it won't increase
         * again. once full backref flag is set, we never clear it.
         */
        if (lookup_info &&
            ((wc->stage == DROP_REFERENCE && wc->refs[level] != 1) ||
             (wc->stage == UPDATE_BACKREF && !(wc->flags[level] & flag)))) {
                BUG_ON(!path->locks[level]);
                ret = btrfs_lookup_extent_info(trans, fs_info,
                                               eb->start, level, 1,
                                               &wc->refs[level],
                                               &wc->flags[level]);
                BUG_ON(ret == -ENOMEM);
                if (ret)
                        return ret;
                BUG_ON(wc->refs[level] == 0);
        }

        if (wc->stage == DROP_REFERENCE) {
                if (wc->refs[level] > 1)
                        return 1;

                if (path->locks[level] && !wc->keep_locks) {
                        btrfs_tree_unlock_rw(eb, path->locks[level]);
                        path->locks[level] = 0;
                }
                return 0;
        }

        /* wc->stage == UPDATE_BACKREF */
        if (!(wc->flags[level] & flag)) {
                BUG_ON(!path->locks[level]);
                ret = btrfs_inc_ref(trans, root, eb, 1);
                BUG_ON(ret); /* -ENOMEM */
                ret = btrfs_dec_ref(trans, root, eb, 0);
                BUG_ON(ret); /* -ENOMEM */
                ret = btrfs_set_disk_extent_flags(trans, eb, flag);
                BUG_ON(ret); /* -ENOMEM */
                wc->flags[level] |= flag;
        }

        /*
         * the block is shared by multiple trees, so it's not good to
         * keep the tree lock
         */
        if (path->locks[level] && level > 0) {
                btrfs_tree_unlock_rw(eb, path->locks[level]);
                path->locks[level] = 0;
        }
        return 0;
}

/*
 * This is used to verify a ref exists for this root to deal with a bug where we
 * would have a drop_progress key that hadn't been updated properly.
 */
static int check_ref_exists(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root, u64 bytenr, u64 parent,
                            int level)
{
        struct btrfs_path *path;
        struct btrfs_extent_inline_ref *iref;
        int ret;

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

        ret = lookup_extent_backref(trans, path, &iref, bytenr,
                                    root->fs_info->nodesize, parent,
                                    root->root_key.objectid, level, 0);
        btrfs_free_path(path);
        if (ret == -ENOENT)
                return 0;
        if (ret < 0)
                return ret;
        return 1;
}

/*
 * helper to process tree block pointer.
 *
 * when wc->stage == DROP_REFERENCE, this function checks
 * reference count of the block pointed to. if the block
 * is shared and we need update back refs for the subtree
 * rooted at the block, this function changes wc->stage to
 * UPDATE_BACKREF. if the block is shared and there is no
 * need to update back, this function drops the reference
 * to the block.
 *
 * NOTE: return value 1 means we should stop walking down.
 */
static noinline int do_walk_down(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct walk_control *wc, int *lookup_info)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 bytenr;
        u64 generation;
        u64 parent;
        struct btrfs_tree_parent_check check = { 0 };
        struct btrfs_key key;
        struct btrfs_ref ref = { 0 };
        struct extent_buffer *next;
        int level = wc->level;
        int reada = 0;
        int ret = 0;
        bool need_account = false;

        generation = btrfs_node_ptr_generation(path->nodes[level],
                                               path->slots[level]);
        /*
         * if the lower level block was created before the snapshot
         * was created, we know there is no need to update back refs
         * for the subtree
         */
        if (wc->stage == UPDATE_BACKREF &&
            generation <= root->root_key.offset) {
                *lookup_info = 1;
                return 1;
        }

        bytenr = btrfs_node_blockptr(path->nodes[level], path->slots[level]);

        check.level = level - 1;
        check.transid = generation;
        check.owner_root = root->root_key.objectid;
        check.has_first_key = true;
        btrfs_node_key_to_cpu(path->nodes[level], &check.first_key,
                              path->slots[level]);

        next = find_extent_buffer(fs_info, bytenr);
        if (!next) {
                next = btrfs_find_create_tree_block(fs_info, bytenr,
                                root->root_key.objectid, level - 1);
                if (IS_ERR(next))
                        return PTR_ERR(next);
                reada = 1;
        }
        btrfs_tree_lock(next);

        ret = btrfs_lookup_extent_info(trans, fs_info, bytenr, level - 1, 1,
                                       &wc->refs[level - 1],
                                       &wc->flags[level - 1]);
        if (ret < 0)
                goto out_unlock;

        if (unlikely(wc->refs[level - 1] == 0)) {
                btrfs_err(fs_info, "Missing references.");
                ret = -EIO;
                goto out_unlock;
        }
        *lookup_info = 0;

        if (wc->stage == DROP_REFERENCE) {
                if (wc->refs[level - 1] > 1) {
                        need_account = true;
                        if (level == 1 &&
                            (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                                goto skip;

                        if (!wc->update_ref ||
                            generation <= root->root_key.offset)
                                goto skip;

                        btrfs_node_key_to_cpu(path->nodes[level], &key,
                                              path->slots[level]);
                        ret = btrfs_comp_cpu_keys(&key, &wc->update_progress);
                        if (ret < 0)
                                goto skip;

                        wc->stage = UPDATE_BACKREF;
                        wc->shared_level = level - 1;
                }
        } else {
                if (level == 1 &&
                    (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                        goto skip;
        }

        if (!btrfs_buffer_uptodate(next, generation, 0)) {
                btrfs_tree_unlock(next);
                free_extent_buffer(next);
                next = NULL;
                *lookup_info = 1;
        }

        if (!next) {
                if (reada && level == 1)
                        reada_walk_down(trans, root, wc, path);
                next = read_tree_block(fs_info, bytenr, &check);
                if (IS_ERR(next)) {
                        return PTR_ERR(next);
                } else if (!extent_buffer_uptodate(next)) {
                        free_extent_buffer(next);
                        return -EIO;
                }
                btrfs_tree_lock(next);
        }

        level--;
        ASSERT(level == btrfs_header_level(next));
        if (level != btrfs_header_level(next)) {
                btrfs_err(root->fs_info, "mismatched level");
                ret = -EIO;
                goto out_unlock;
        }
        path->nodes[level] = next;
        path->slots[level] = 0;
        path->locks[level] = BTRFS_WRITE_LOCK;
        wc->level = level;
        if (wc->level == 1)
                wc->reada_slot = 0;
        return 0;
skip:
        wc->refs[level - 1] = 0;
        wc->flags[level - 1] = 0;
        if (wc->stage == DROP_REFERENCE) {
                if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF) {
                        parent = path->nodes[level]->start;
                } else {
                        ASSERT(root->root_key.objectid ==
                               btrfs_header_owner(path->nodes[level]));
                        if (root->root_key.objectid !=
                            btrfs_header_owner(path->nodes[level])) {
                                btrfs_err(root->fs_info,
                                                "mismatched block owner");
                                ret = -EIO;
                                goto out_unlock;
                        }
                        parent = 0;
                }

                /*
                 * If we had a drop_progress we need to verify the refs are set
                 * as expected.  If we find our ref then we know that from here
                 * on out everything should be correct, and we can clear the
                 * ->restarted flag.
                 */
                if (wc->restarted) {
                        ret = check_ref_exists(trans, root, bytenr, parent,
                                               level - 1);
                        if (ret < 0)
                                goto out_unlock;
                        if (ret == 0)
                                goto no_delete;
                        ret = 0;
                        wc->restarted = 0;
                }

                /*
                 * Reloc tree doesn't contribute to qgroup numbers, and we have
                 * already accounted them at merge time (replace_path),
                 * thus we could skip expensive subtree trace here.
                 */
                if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID &&
                    need_account) {
                        ret = btrfs_qgroup_trace_subtree(trans, next,
                                                         generation, level - 1);
                        if (ret) {
                                btrfs_err_rl(fs_info,
                                             "Error %d accounting shared subtree. Quota is out of sync, rescan required.",
                                             ret);
                        }
                }

                /*
                 * We need to update the next key in our walk control so we can
                 * update the drop_progress key accordingly.  We don't care if
                 * find_next_key doesn't find a key because that means we're at
                 * the end and are going to clean up now.
                 */
                wc->drop_level = level;
                find_next_key(path, level, &wc->drop_progress);

                btrfs_init_generic_ref(&ref, BTRFS_DROP_DELAYED_REF, bytenr,
                                       fs_info->nodesize, parent);
                btrfs_init_tree_ref(&ref, level - 1, root->root_key.objectid,
                                    0, false);
                ret = btrfs_free_extent(trans, &ref);
                if (ret)
                        goto out_unlock;
        }
no_delete:
        *lookup_info = 1;
        ret = 1;

out_unlock:
        btrfs_tree_unlock(next);
        free_extent_buffer(next);

        return ret;
}

/*
 * helper to process tree block while walking up the tree.
 *
 * when wc->stage == DROP_REFERENCE, this function drops
 * reference count on the block.
 *
 * when wc->stage == UPDATE_BACKREF, this function changes
 * wc->stage back to DROP_REFERENCE if we changed wc->stage
 * to UPDATE_BACKREF previously while processing the block.
 *
 * NOTE: return value 1 means we should stop walking up.
 */
static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct walk_control *wc)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        int ret;
        int level = wc->level;
        struct extent_buffer *eb = path->nodes[level];
        u64 parent = 0;

        if (wc->stage == UPDATE_BACKREF) {
                BUG_ON(wc->shared_level < level);
                if (level < wc->shared_level)
                        goto out;

                ret = find_next_key(path, level + 1, &wc->update_progress);
                if (ret > 0)
                        wc->update_ref = 0;

                wc->stage = DROP_REFERENCE;
                wc->shared_level = -1;
                path->slots[level] = 0;

                /*
                 * check reference count again if the block isn't locked.
                 * we should start walking down the tree again if reference
                 * count is one.
                 */
                if (!path->locks[level]) {
                        BUG_ON(level == 0);
                        btrfs_tree_lock(eb);
                        path->locks[level] = BTRFS_WRITE_LOCK;

                        ret = btrfs_lookup_extent_info(trans, fs_info,
                                                       eb->start, level, 1,
                                                       &wc->refs[level],
                                                       &wc->flags[level]);
                        if (ret < 0) {
                                btrfs_tree_unlock_rw(eb, path->locks[level]);
                                path->locks[level] = 0;
                                return ret;
                        }
                        BUG_ON(wc->refs[level] == 0);
                        if (wc->refs[level] == 1) {
                                btrfs_tree_unlock_rw(eb, path->locks[level]);
                                path->locks[level] = 0;
                                return 1;
                        }
                }
        }

        /* wc->stage == DROP_REFERENCE */
        BUG_ON(wc->refs[level] > 1 && !path->locks[level]);

        if (wc->refs[level] == 1) {
                if (level == 0) {
                        if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
                                ret = btrfs_dec_ref(trans, root, eb, 1);
                        else
                                ret = btrfs_dec_ref(trans, root, eb, 0);
                        BUG_ON(ret); /* -ENOMEM */
                        if (is_fstree(root->root_key.objectid)) {
                                ret = btrfs_qgroup_trace_leaf_items(trans, eb);
                                if (ret) {
                                        btrfs_err_rl(fs_info,
        "error %d accounting leaf items, quota is out of sync, rescan required",
                                             ret);
                                }
                        }
                }
                /* Make block locked assertion in btrfs_clear_buffer_dirty happy. */
                if (!path->locks[level]) {
                        btrfs_tree_lock(eb);
                        path->locks[level] = BTRFS_WRITE_LOCK;
                }
                btrfs_clear_buffer_dirty(trans, eb);
        }

        if (eb == root->node) {
                if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
                        parent = eb->start;
                else if (root->root_key.objectid != btrfs_header_owner(eb))
                        goto owner_mismatch;
        } else {
                if (wc->flags[level + 1] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
                        parent = path->nodes[level + 1]->start;
                else if (root->root_key.objectid !=
                         btrfs_header_owner(path->nodes[level + 1]))
                        goto owner_mismatch;
        }

        btrfs_free_tree_block(trans, btrfs_root_id(root), eb, parent,
                              wc->refs[level] == 1);
out:
        wc->refs[level] = 0;
        wc->flags[level] = 0;
        return 0;

owner_mismatch:
        btrfs_err_rl(fs_info, "unexpected tree owner, have %llu expect %llu",
                     btrfs_header_owner(eb), root->root_key.objectid);
        return -EUCLEAN;
}

static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   struct btrfs_path *path,
                                   struct walk_control *wc)
{
        int level = wc->level;
        int lookup_info = 1;
        int ret = 0;

        while (level >= 0) {
                ret = walk_down_proc(trans, root, path, wc, lookup_info);
                if (ret)
                        break;

                if (level == 0)
                        break;

                if (path->slots[level] >=
                    btrfs_header_nritems(path->nodes[level]))
                        break;

                ret = do_walk_down(trans, root, path, wc, &lookup_info);
                if (ret > 0) {
                        path->slots[level]++;
                        continue;
                } else if (ret < 0)
                        break;
                level = wc->level;
        }
        return (ret == 1) ? 0 : ret;
}

static noinline int walk_up_tree(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct walk_control *wc, int max_level)
{
        int level = wc->level;
        int ret;

        path->slots[level] = btrfs_header_nritems(path->nodes[level]);
        while (level < max_level && path->nodes[level]) {
                wc->level = level;
                if (path->slots[level] + 1 <
                    btrfs_header_nritems(path->nodes[level])) {
                        path->slots[level]++;
                        return 0;
                } else {
                        ret = walk_up_proc(trans, root, path, wc);
                        if (ret > 0)
                                return 0;
                        if (ret < 0)
                                return ret;

                        if (path->locks[level]) {
                                btrfs_tree_unlock_rw(path->nodes[level],
                                                     path->locks[level]);
                                path->locks[level] = 0;
                        }
                        free_extent_buffer(path->nodes[level]);
                        path->nodes[level] = NULL;
                        level++;
                }
        }
        return 1;
}

/*
 * drop a subvolume tree.
 *
 * this function traverses the tree freeing any blocks that only
 * referenced by the tree.
 *
 * when a shared tree block is found. this function decreases its
 * reference count by one. if update_ref is true, this function
 * also make sure backrefs for the shared block and all lower level
 * blocks are properly updated.
 *
 * If called with for_reloc == 0, may exit early with -EAGAIN
 */
int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc)
{
        const bool is_reloc_root = (root->root_key.objectid ==
                                    BTRFS_TREE_RELOC_OBJECTID);
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_path *path;
        struct btrfs_trans_handle *trans;
        struct btrfs_root *tree_root = fs_info->tree_root;
        struct btrfs_root_item *root_item = &root->root_item;
        struct walk_control *wc;
        struct btrfs_key key;
        int err = 0;
        int ret;
        int level;
        bool root_dropped = false;
        bool unfinished_drop = false;

        btrfs_debug(fs_info, "Drop subvolume %llu", root->root_key.objectid);

        path = btrfs_alloc_path();
        if (!path) {
                err = -ENOMEM;
                goto out;
        }

        wc = kzalloc(sizeof(*wc), GFP_NOFS);
        if (!wc) {
                btrfs_free_path(path);
                err = -ENOMEM;
                goto out;
        }

        /*
         * Use join to avoid potential EINTR from transaction start. See
         * wait_reserve_ticket and the whole reservation callchain.
         */
        if (for_reloc)
                trans = btrfs_join_transaction(tree_root);
        else
                trans = btrfs_start_transaction(tree_root, 0);
        if (IS_ERR(trans)) {
                err = PTR_ERR(trans);
                goto out_free;
        }

        err = btrfs_run_delayed_items(trans);
        if (err)
                goto out_end_trans;

        /*
         * This will help us catch people modifying the fs tree while we're
         * dropping it.  It is unsafe to mess with the fs tree while it's being
         * dropped as we unlock the root node and parent nodes as we walk down
         * the tree, assuming nothing will change.  If something does change
         * then we'll have stale information and drop references to blocks we've
         * already dropped.
         */
        set_bit(BTRFS_ROOT_DELETING, &root->state);
        unfinished_drop = test_bit(BTRFS_ROOT_UNFINISHED_DROP, &root->state);

        if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
                level = btrfs_header_level(root->node);
                path->nodes[level] = btrfs_lock_root_node(root);
                path->slots[level] = 0;
                path->locks[level] = BTRFS_WRITE_LOCK;
                memset(&wc->update_progress, 0,
                       sizeof(wc->update_progress));
        } else {
                btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);
                memcpy(&wc->update_progress, &key,
                       sizeof(wc->update_progress));

                level = btrfs_root_drop_level(root_item);
                BUG_ON(level == 0);
                path->lowest_level = level;
                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                path->lowest_level = 0;
                if (ret < 0) {
                        err = ret;
                        goto out_end_trans;
                }
                WARN_ON(ret > 0);

                /*
                 * unlock our path, this is safe because only this
                 * function is allowed to delete this snapshot
                 */
                btrfs_unlock_up_safe(path, 0);

                level = btrfs_header_level(root->node);
                while (1) {
                        btrfs_tree_lock(path->nodes[level]);
                        path->locks[level] = BTRFS_WRITE_LOCK;

                        ret = btrfs_lookup_extent_info(trans, fs_info,
                                                path->nodes[level]->start,
                                                level, 1, &wc->refs[level],
                                                &wc->flags[level]);
                        if (ret < 0) {
                                err = ret;
                                goto out_end_trans;
                        }
                        BUG_ON(wc->refs[level] == 0);

                        if (level == btrfs_root_drop_level(root_item))
                                break;

                        btrfs_tree_unlock(path->nodes[level]);
                        path->locks[level] = 0;
                        WARN_ON(wc->refs[level] != 1);
                        level--;
                }
        }

        wc->restarted = test_bit(BTRFS_ROOT_DEAD_TREE, &root->state);
        wc->level = level;
        wc->shared_level = -1;
        wc->stage = DROP_REFERENCE;
        wc->update_ref = update_ref;
        wc->keep_locks = 0;
        wc->reada_count = BTRFS_NODEPTRS_PER_BLOCK(fs_info);

        while (1) {

                ret = walk_down_tree(trans, root, path, wc);
                if (ret < 0) {
                        btrfs_abort_transaction(trans, ret);
                        err = ret;
                        break;
                }

                ret = walk_up_tree(trans, root, path, wc, BTRFS_MAX_LEVEL);
                if (ret < 0) {
                        btrfs_abort_transaction(trans, ret);
                        err = ret;
                        break;
                }

                if (ret > 0) {
                        BUG_ON(wc->stage != DROP_REFERENCE);
                        break;
                }

                if (wc->stage == DROP_REFERENCE) {
                        wc->drop_level = wc->level;
                        btrfs_node_key_to_cpu(path->nodes[wc->drop_level],
                                              &wc->drop_progress,
                                              path->slots[wc->drop_level]);
                }
                btrfs_cpu_key_to_disk(&root_item->drop_progress,
                                      &wc->drop_progress);
                btrfs_set_root_drop_level(root_item, wc->drop_level);

                BUG_ON(wc->level == 0);
                if (btrfs_should_end_transaction(trans) ||
                    (!for_reloc && btrfs_need_cleaner_sleep(fs_info))) {
                        ret = btrfs_update_root(trans, tree_root,
                                                &root->root_key,
                                                root_item);
                        if (ret) {
                                btrfs_abort_transaction(trans, ret);
                                err = ret;
                                goto out_end_trans;
                        }

                        if (!is_reloc_root)
                                btrfs_set_last_root_drop_gen(fs_info, trans->transid);

                        btrfs_end_transaction_throttle(trans);
                        if (!for_reloc && btrfs_need_cleaner_sleep(fs_info)) {
                                btrfs_debug(fs_info,
                                            "drop snapshot early exit");
                                err = -EAGAIN;
                                goto out_free;
                        }

                       /*
                        * Use join to avoid potential EINTR from transaction
                        * start. See wait_reserve_ticket and the whole
                        * reservation callchain.
                        */
                        if (for_reloc)
                                trans = btrfs_join_transaction(tree_root);
                        else
                                trans = btrfs_start_transaction(tree_root, 0);
                        if (IS_ERR(trans)) {
                                err = PTR_ERR(trans);
                                goto out_free;
                        }
                }
        }
        btrfs_release_path(path);
        if (err)
                goto out_end_trans;

        ret = btrfs_del_root(trans, &root->root_key);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                err = ret;
                goto out_end_trans;
        }

        if (!is_reloc_root) {
                ret = btrfs_find_root(tree_root, &root->root_key, path,
                                      NULL, NULL);
                if (ret < 0) {
                        btrfs_abort_transaction(trans, ret);
                        err = ret;
                        goto out_end_trans;
                } else if (ret > 0) {
                        /* if we fail to delete the orphan item this time
                         * around, it'll get picked up the next time.
                         *
                         * The most common failure here is just -ENOENT.
                         */
                        btrfs_del_orphan_item(trans, tree_root,
                                              root->root_key.objectid);
                }
        }

        /*
         * This subvolume is going to be completely dropped, and won't be
         * recorded as dirty roots, thus pertrans meta rsv will not be freed at
         * commit transaction time.  So free it here manually.
         */
        btrfs_qgroup_convert_reserved_meta(root, INT_MAX);
        btrfs_qgroup_free_meta_all_pertrans(root);

        if (test_bit(BTRFS_ROOT_IN_RADIX, &root->state))
                btrfs_add_dropped_root(trans, root);
        else
                btrfs_put_root(root);
        root_dropped = true;
out_end_trans:
        if (!is_reloc_root)
                btrfs_set_last_root_drop_gen(fs_info, trans->transid);

        btrfs_end_transaction_throttle(trans);
out_free:
        kfree(wc);
        btrfs_free_path(path);
out:
        /*
         * We were an unfinished drop root, check to see if there are any
         * pending, and if not clear and wake up any waiters.
         */
        if (!err && unfinished_drop)
                btrfs_maybe_wake_unfinished_drop(fs_info);

        /*
         * So if we need to stop dropping the snapshot for whatever reason we
         * need to make sure to add it back to the dead root list so that we
         * keep trying to do the work later.  This also cleans up roots if we
         * don't have it in the radix (like when we recover after a power fail
         * or unmount) so we don't leak memory.
         */
        if (!for_reloc && !root_dropped)
                btrfs_add_dead_root(root);
        return err;
}

/*
 * drop subtree rooted at tree block 'node'.
 *
 * NOTE: this function will unlock and release tree block 'node'
 * only used by relocation code
 */
int btrfs_drop_subtree(struct btrfs_trans_handle *trans,
                        struct btrfs_root *root,
                        struct extent_buffer *node,
                        struct extent_buffer *parent)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_path *path;
        struct walk_control *wc;
        int level;
        int parent_level;
        int ret = 0;
        int wret;

        BUG_ON(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID);

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

        wc = kzalloc(sizeof(*wc), GFP_NOFS);
        if (!wc) {
                btrfs_free_path(path);
                return -ENOMEM;
        }

        btrfs_assert_tree_write_locked(parent);
        parent_level = btrfs_header_level(parent);
        atomic_inc(&parent->refs);
        path->nodes[parent_level] = parent;
        path->slots[parent_level] = btrfs_header_nritems(parent);

        btrfs_assert_tree_write_locked(node);
        level = btrfs_header_level(node);
        path->nodes[level] = node;
        path->slots[level] = 0;
        path->locks[level] = BTRFS_WRITE_LOCK;

        wc->refs[parent_level] = 1;
        wc->flags[parent_level] = BTRFS_BLOCK_FLAG_FULL_BACKREF;
        wc->level = level;
        wc->shared_level = -1;
        wc->stage = DROP_REFERENCE;
        wc->update_ref = 0;
        wc->keep_locks = 1;
        wc->reada_count = BTRFS_NODEPTRS_PER_BLOCK(fs_info);

        while (1) {
                wret = walk_down_tree(trans, root, path, wc);
                if (wret < 0) {
                        ret = wret;
                        break;
                }

                wret = walk_up_tree(trans, root, path, wc, parent_level);
                if (wret < 0)
                        ret = wret;
                if (wret != 0)
                        break;
        }

        kfree(wc);
        btrfs_free_path(path);
        return ret;
}

int btrfs_error_unpin_extent_range(struct btrfs_fs_info *fs_info,
                                   u64 start, u64 end)
{
        return unpin_extent_range(fs_info, start, end, false);
}

/*
 * It used to be that old block groups would be left around forever.
 * Iterating over them would be enough to trim unused space.  Since we
 * now automatically remove them, we also need to iterate over unallocated
 * space.
 *
 * We don't want a transaction for this since the discard may take a
 * substantial amount of time.  We don't require that a transaction be
 * running, but we do need to take a running transaction into account
 * to ensure that we're not discarding chunks that were released or
 * allocated in the current transaction.
 *
 * Holding the chunks lock will prevent other threads from allocating
 * or releasing chunks, but it won't prevent a running transaction
 * from committing and releasing the memory that the pending chunks
 * list head uses.  For that, we need to take a reference to the
 * transaction and hold the commit root sem.  We only need to hold
 * it while performing the free space search since we have already
 * held back allocations.
 */
static int btrfs_trim_free_extents(struct btrfs_device *device, u64 *trimmed)
{
        u64 start = BTRFS_DEVICE_RANGE_RESERVED, len = 0, end = 0;
        int ret;

        *trimmed = 0;

        /* Discard not supported = nothing to do. */
        if (!bdev_max_discard_sectors(device->bdev))
                return 0;

        /* Not writable = nothing to do. */
        if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
                return 0;

        /* No free space = nothing to do. */
        if (device->total_bytes <= device->bytes_used)
                return 0;

        ret = 0;

        while (1) {
                struct btrfs_fs_info *fs_info = device->fs_info;
                u64 bytes;

                ret = mutex_lock_interruptible(&fs_info->chunk_mutex);
                if (ret)
                        break;

                find_first_clear_extent_bit(&device->alloc_state, start,
                                            &start, &end,
                                            CHUNK_TRIMMED | CHUNK_ALLOCATED);

                /* Check if there are any CHUNK_* bits left */
                if (start > device->total_bytes) {
                        WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
                        btrfs_warn_in_rcu(fs_info,
"ignoring attempt to trim beyond device size: offset %llu length %llu device %s device size %llu",
                                          start, end - start + 1,
                                          btrfs_dev_name(device),
                                          device->total_bytes);
                        mutex_unlock(&fs_info->chunk_mutex);
                        ret = 0;
                        break;
                }

                /* Ensure we skip the reserved space on each device. */
                start = max_t(u64, start, BTRFS_DEVICE_RANGE_RESERVED);

                /*
                 * If find_first_clear_extent_bit find a range that spans the
                 * end of the device it will set end to -1, in this case it's up
                 * to the caller to trim the value to the size of the device.
                 */
                end = min(end, device->total_bytes - 1);

                len = end - start + 1;

                /* We didn't find any extents */
                if (!len) {
                        mutex_unlock(&fs_info->chunk_mutex);
                        ret = 0;
                        break;
                }

                ret = btrfs_issue_discard(device->bdev, start, len,
                                          &bytes);
                if (!ret)
                        set_extent_bit(&device->alloc_state, start,
                                       start + bytes - 1, CHUNK_TRIMMED, NULL);
                mutex_unlock(&fs_info->chunk_mutex);

                if (ret)
                        break;

                start += len;
                *trimmed += bytes;

                if (fatal_signal_pending(current)) {
                        ret = -ERESTARTSYS;
                        break;
                }

                cond_resched();
        }

        return ret;
}

/*
 * Trim the whole filesystem by:
 * 1) trimming the free space in each block group
 * 2) trimming the unallocated space on each device
 *
 * This will also continue trimming even if a block group or device encounters
 * an error.  The return value will be the last error, or 0 if nothing bad
 * happens.
 */
int btrfs_trim_fs(struct btrfs_fs_info *fs_info, struct fstrim_range *range)
{
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        struct btrfs_block_group *cache = NULL;
        struct btrfs_device *device;
        u64 group_trimmed;
        u64 range_end = U64_MAX;
        u64 start;
        u64 end;
        u64 trimmed = 0;
        u64 bg_failed = 0;
        u64 dev_failed = 0;
        int bg_ret = 0;
        int dev_ret = 0;
        int ret = 0;

        if (range->start == U64_MAX)
                return -EINVAL;

        /*
         * Check range overflow if range->len is set.
         * The default range->len is U64_MAX.
         */
        if (range->len != U64_MAX &&
            check_add_overflow(range->start, range->len, &range_end))
                return -EINVAL;

        cache = btrfs_lookup_first_block_group(fs_info, range->start);
        for (; cache; cache = btrfs_next_block_group(cache)) {
                if (cache->start >= range_end) {
                        btrfs_put_block_group(cache);
                        break;
                }

                start = max(range->start, cache->start);
                end = min(range_end, cache->start + cache->length);

                if (end - start >= range->minlen) {
                        if (!btrfs_block_group_done(cache)) {
                                ret = btrfs_cache_block_group(cache, true);
                                if (ret) {
                                        bg_failed++;
                                        bg_ret = ret;
                                        continue;
                                }
                        }
                        ret = btrfs_trim_block_group(cache,
                                                     &group_trimmed,
                                                     start,
                                                     end,
                                                     range->minlen);

                        trimmed += group_trimmed;
                        if (ret) {
                                bg_failed++;
                                bg_ret = ret;
                                continue;
                        }
                }
        }

        if (bg_failed)
                btrfs_warn(fs_info,
                        "failed to trim %llu block group(s), last error %d",
                        bg_failed, bg_ret);

        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry(device, &fs_devices->devices, dev_list) {
                if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
                        continue;

                ret = btrfs_trim_free_extents(device, &group_trimmed);
                if (ret) {
                        dev_failed++;
                        dev_ret = ret;
                        break;
                }

                trimmed += group_trimmed;
        }
        mutex_unlock(&fs_devices->device_list_mutex);

        if (dev_failed)
                btrfs_warn(fs_info,
                        "failed to trim %llu device(s), last error %d",
                        dev_failed, dev_ret);
        range->len = trimmed;
        if (bg_ret)
                return bg_ret;
        return dev_ret;
}