OSCL-LXR linux-6.0.1/​fs/​btrfs/​extent-tree.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Oracle.  All rights reserved.
  */
 
 #include <linux/sched.h>
 #include <linux/sched/signal.h>
 #include <linux/pagemap.h>
 #include <linux/writeback.h>
 #include <linux/blkdev.h>
 #include <linux/sort.h>
 #include <linux/rcupdate.h>
 #include <linux/kthread.h>
 #include <linux/slab.h>
 #include <linux/ratelimit.h>
 #include <linux/percpu_counter.h>
 #include <linux/lockdep.h>
 #include <linux/crc32c.h>
 #include "misc.h"
 #include "tree-log.h"
 #include "disk-io.h"
 #include "print-tree.h"
 #include "volumes.h"
 #include "raid56.h"
 #include "locking.h"
 #include "free-space-cache.h"
 #include "free-space-tree.h"
 #include "sysfs.h"
 #include "qgroup.h"
 #include "ref-verify.h"
 #include "space-info.h"
 #include "block-rsv.h"
 #include "delalloc-space.h"
 #include "block-group.h"
 #include "discard.h"
 #include "rcu-string.h"
 #include "zoned.h"
 #include "dev-replace.h"
 
 #undef SCRAMBLE_DELAYED_REFS
 
 
 static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
                    struct btrfs_delayed_ref_node *node, u64 parent,
                    u64 root_objectid, u64 owner_objectid,
                    u64 owner_offset, int refs_to_drop,
                    struct btrfs_delayed_extent_op *extra_op);
 static void __run_delayed_extent_op(struct btrfs_delayed_extent_op *extent_op,
                     struct extent_buffer *leaf,
                     struct btrfs_extent_item *ei);
 static int alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                       u64 parent, u64 root_objectid,
                       u64 flags, u64 owner, u64 offset,
                       struct btrfs_key *ins, int ref_mod);
 static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
                      struct btrfs_delayed_ref_node *node,
                      struct btrfs_delayed_extent_op *extent_op);
 static int find_next_key(struct btrfs_path *path, int level,
              struct btrfs_key *key);
 
 static int block_group_bits(struct btrfs_block_group *cache, u64 bits)
 {
     return (cache->flags & bits) == bits;
 }
 
 int btrfs_add_excluded_extent(struct btrfs_fs_info *fs_info,
                   u64 start, u64 num_bytes)
 {
     u64 end = start + num_bytes - 1;
     set_extent_bits(&fs_info->excluded_extents, start, end,
             EXTENT_UPTODATE);
     return 0;
 }
 
 void btrfs_free_excluded_extents(struct btrfs_block_group *cache)
 {
     struct btrfs_fs_info *fs_info = cache->fs_info;
     u64 start, end;
 
     start = cache->start;
     end = start + cache->length - 1;
 
     clear_extent_bits(&fs_info->excluded_extents, start, end,
               EXTENT_UPTODATE);
 }
 
 /* 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 = -EINVAL;
             btrfs_print_v0_err(fs_info);
             if (trans)
                 btrfs_abort_transaction(trans, ret);
             else
                 btrfs_handle_fs_error(fs_info, ret, NULL);
 
             goto out_free;
         }
 
         BUG_ON(num_refs == 0);
     } else {
         num_refs = 0;
         extent_flags = 0;
         ret = 0;
     }
 
     if (!trans)
         goto out;
 
     delayed_refs = &trans->transaction->delayed_refs;
     spin_lock(&delayed_refs->lock);
     head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
     if (head) {
         if (!mutex_trylock(&head->mutex)) {
             refcount_inc(&head->refs);
             spin_unlock(&delayed_refs->lock);
 
             btrfs_release_path(path);
 
             /*
              * Mutex was contended, block until it's released and try
              * again
              */
             mutex_lock(&head->mutex);
             mutex_unlock(&head->mutex);
             btrfs_put_delayed_ref_head(head);
             goto search_again;
         }
         spin_lock(&head->lock);
         if (head->extent_op && head->extent_op->update_flags)
             extent_flags |= head->extent_op->flags_to_set;
         else
             BUG_ON(num_refs == 0);
 
         num_refs += head->ref_mod;
         spin_unlock(&head->lock);
         mutex_unlock(&head->mutex);
     }
     spin_unlock(&delayed_refs->lock);
 out:
     WARN_ON(num_refs == 0);
     if (refs)
         *refs = num_refs;
     if (flags)
         *flags = extent_flags;
 out_free:
     btrfs_free_path(path);
     return ret;
 }
 
 /*
  * Back reference rules.  Back refs have three main goals:
  *
  * 1) differentiate between all holders of references to an extent so that
  *    when a reference is dropped we can make sure it was a valid reference
  *    before freeing the extent.
  *
  * 2) Provide enough information to quickly find the holders of an extent
  *    if we notice a given block is corrupted or bad.
  *
  * 3) Make it easy to migrate blocks for FS shrinking or storage pool
  *    maintenance.  This is actually the same as #2, but with a slightly
  *    different use case.
  *
  * There are two kinds of back refs. The implicit back refs is optimized
  * for pointers in non-shared tree blocks. For a given pointer in a block,
  * back refs of this kind provide information about the block's owner tree
  * and the pointer's key. These information allow us to find the block by
  * b-tree searching. The full back refs is for pointers in tree blocks not
  * referenced by their owner trees. The location of tree block is recorded
  * in the back refs. Actually the full back refs is generic, and can be
  * used in all cases the implicit back refs is used. The major shortcoming
  * of the full back refs is its overhead. Every time a tree block gets
  * COWed, we have to update back refs entry for all pointers in it.
  *
  * For a newly allocated tree block, we use implicit back refs for
  * pointers in it. This means most tree related operations only involve
  * implicit back refs. For a tree block created in old transaction, the
  * only way to drop a reference to it is COW it. So we can detect the
  * event that tree block loses its owner tree's reference and do the
  * back refs conversion.
  *
  * When a tree block is COWed through a tree, there are four cases:
  *
  * The reference count of the block is one and the tree is the block's
  * owner tree. Nothing to do in this case.
  *
  * The reference count of the block is one and the tree is not the
  * block's owner tree. In this case, full back refs is used for pointers
  * in the block. Remove these full back refs, add implicit back refs for
  * every pointers in the new block.
  *
  * The reference count of the block is greater than one and the tree is
  * the block's owner tree. In this case, implicit back refs is used for
  * pointers in the block. Add full back refs for every pointers in the
  * block, increase lower level extents' reference counts. The original
  * implicit back refs are entailed to the new block.
  *
  * The reference count of the block is greater than one and the tree is
  * not the block's owner tree. Add implicit back refs for every pointer in
  * the new block, increase lower level extents' reference count.
  *
  * Back Reference Key composing:
  *
  * The key objectid corresponds to the first byte in the extent,
  * The key type is used to differentiate between types of back refs.
  * There are different meanings of the key offset for different types
  * of back refs.
  *
  * File extents can be referenced by:
  *
  * - multiple snapshots, subvolumes, or different generations in one subvol
  * - different files inside a single subvolume
  * - different offsets inside a file (bookend extents in file.c)
  *
  * The extent ref structure for the implicit back refs has fields for:
  *
  * - Objectid of the subvolume root
  * - objectid of the file holding the reference
  * - original offset in the file
  * - how many bookend extents
  *
  * The key offset for the implicit back refs is hash of the first
  * three fields.
  *
  * The extent ref structure for the full back refs has field for:
  *
  * - number of pointers in the tree leaf
  *
  * The key offset for the implicit back refs is the first byte of
  * the tree leaf
  *
  * When a file extent is allocated, The implicit back refs is used.
  * the fields are filled in:
  *
  *     (root_key.objectid, inode objectid, offset in file, 1)
  *
  * When a file extent is removed file truncation, we find the
  * corresponding implicit back refs and check the following fields:
  *
  *     (btrfs_header_owner(leaf), inode objectid, offset in file)
  *
  * Btree extents can be referenced by:
  *
  * - Different subvolumes
  *
  * Both the implicit back refs and the full back refs for tree blocks
  * only consist of key. The key offset for the implicit back refs is
  * objectid of block's owner tree. The key offset for the full back refs
  * is the first byte of parent block.
  *
  * When implicit back refs is used, information about the lowest key and
  * level of the tree block are required. These information are stored in
  * tree block info structure.
  */
 
 /*
  * is_data == BTRFS_REF_TYPE_BLOCK, tree block type is required,
  * is_data == BTRFS_REF_TYPE_DATA, data type is requiried,
  * is_data == BTRFS_REF_TYPE_ANY, either type is OK.
  */
 int btrfs_get_extent_inline_ref_type(const struct extent_buffer *eb,
                      struct btrfs_extent_inline_ref *iref,
                      enum btrfs_inline_ref_type is_data)
 {
     int type = btrfs_extent_inline_ref_type(eb, iref);
     u64 offset = btrfs_extent_inline_ref_offset(eb, iref);
 
     if (type == BTRFS_TREE_BLOCK_REF_KEY ||
         type == BTRFS_SHARED_BLOCK_REF_KEY ||
         type == BTRFS_SHARED_DATA_REF_KEY ||
         type == BTRFS_EXTENT_DATA_REF_KEY) {
         if (is_data == BTRFS_REF_TYPE_BLOCK) {
             if (type == BTRFS_TREE_BLOCK_REF_KEY)
                 return type;
             if (type == BTRFS_SHARED_BLOCK_REF_KEY) {
                 ASSERT(eb->fs_info);
                 /*
                  * Every shared one has parent tree block,
                  * which must be aligned to sector size.
                  */
                 if (offset &&
                     IS_ALIGNED(offset, eb->fs_info->sectorsize))
                     return type;
             }
         } else if (is_data == BTRFS_REF_TYPE_DATA) {
             if (type == BTRFS_EXTENT_DATA_REF_KEY)
                 return type;
             if (type == BTRFS_SHARED_DATA_REF_KEY) {
                 ASSERT(eb->fs_info);
                 /*
                  * Every shared one has parent tree block,
                  * which must be aligned to sector size.
                  */
                 if (offset &&
                     IS_ALIGNED(offset, eb->fs_info->sectorsize))
                     return type;
             }
         } else {
             ASSERT(is_data == BTRFS_REF_TYPE_ANY);
             return type;
         }
     }
 
     btrfs_print_leaf((struct extent_buffer *)eb);
     btrfs_err(eb->fs_info,
           "eb %llu iref 0x%lx invalid extent inline ref type %d",
           eb->start, (unsigned long)iref, type);
     WARN_ON(1);
 
     return BTRFS_REF_TYPE_INVALID;
 }
 
 u64 hash_extent_data_ref(u64 root_objectid, u64 owner, u64 offset)
 {
     u32 high_crc = ~(u32)0;
     u32 low_crc = ~(u32)0;
     __le64 lenum;
 
     lenum = cpu_to_le64(root_objectid);
     high_crc = btrfs_crc32c(high_crc, &lenum, sizeof(lenum));
     lenum = cpu_to_le64(owner);
     low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));
     lenum = cpu_to_le64(offset);
     low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));
 
     return ((u64)high_crc << 31) ^ (u64)low_crc;
 }
 
 static u64 hash_extent_data_ref_item(struct extent_buffer *leaf,
                      struct btrfs_extent_data_ref *ref)
 {
     return hash_extent_data_ref(btrfs_extent_data_ref_root(leaf, ref),
                     btrfs_extent_data_ref_objectid(leaf, ref),
                     btrfs_extent_data_ref_offset(leaf, ref));
 }
 
 static int match_extent_data_ref(struct extent_buffer *leaf,
                  struct btrfs_extent_data_ref *ref,
                  u64 root_objectid, u64 owner, u64 offset)
 {
     if (btrfs_extent_data_ref_root(leaf, ref) != root_objectid ||
         btrfs_extent_data_ref_objectid(leaf, ref) != owner ||
         btrfs_extent_data_ref_offset(leaf, ref) != offset)
         return 0;
     return 1;
 }
 
 static noinline int lookup_extent_data_ref(struct btrfs_trans_handle *trans,
                        struct btrfs_path *path,
                        u64 bytenr, u64 parent,
                        u64 root_objectid,
                        u64 owner, u64 offset)
 {
     struct btrfs_root *root = 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(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 if (unlikely(key.type == BTRFS_EXTENT_REF_V0_KEY)) {
         btrfs_print_v0_err(trans->fs_info);
         btrfs_abort_transaction(trans, -EINVAL);
         return -EINVAL;
     } else {
         BUG();
     }
 
     BUG_ON(num_refs < refs_to_drop);
     num_refs -= refs_to_drop;
 
     if (num_refs == 0) {
         ret = btrfs_del_item(trans, 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(leaf);
     }
     return ret;
 }
 
 static noinline u32 extent_data_ref_count(struct btrfs_path *path,
                       struct btrfs_extent_inline_ref *iref)
 {
     struct btrfs_key key;
     struct extent_buffer *leaf;
     struct btrfs_extent_data_ref *ref1;
     struct btrfs_shared_data_ref *ref2;
     u32 num_refs = 0;
     int type;
 
     leaf = path->nodes[0];
     btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
 
     BUG_ON(key.type == BTRFS_EXTENT_REF_V0_KEY);
     if (iref) {
         /*
          * If type is invalid, we should have bailed out earlier than
          * this call.
          */
         type = btrfs_get_extent_inline_ref_type(leaf, iref, BTRFS_REF_TYPE_DATA);
         ASSERT(type != BTRFS_REF_TYPE_INVALID);
         if (type == BTRFS_EXTENT_DATA_REF_KEY) {
             ref1 = (struct btrfs_extent_data_ref *)(&iref->offset);
             num_refs = btrfs_extent_data_ref_count(leaf, ref1);
         } else {
             ref2 = (struct btrfs_shared_data_ref *)(iref + 1);
             num_refs = btrfs_shared_data_ref_count(leaf, ref2);
         }
     } else if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
         ref1 = btrfs_item_ptr(leaf, path->slots[0],
                       struct btrfs_extent_data_ref);
         num_refs = btrfs_extent_data_ref_count(leaf, ref1);
     } else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
         ref2 = btrfs_item_ptr(leaf, path->slots[0],
                       struct btrfs_shared_data_ref);
         num_refs = btrfs_shared_data_ref_count(leaf, ref2);
     } else {
         WARN_ON(1);
     }
     return num_refs;
 }
 
 static noinline int lookup_tree_block_ref(struct btrfs_trans_handle *trans,
                       struct btrfs_path *path,
                       u64 bytenr, u64 parent,
                       u64 root_objectid)
 {
     struct btrfs_root *root = 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;
     int err = 0;
     bool skinny_metadata = btrfs_fs_incompat(fs_info, SKINNY_METADATA);
     int needed;
 
     key.objectid = bytenr;
     key.type = BTRFS_EXTENT_ITEM_KEY;
     key.offset = num_bytes;
 
     want = extent_ref_type(parent, owner);
     if (insert) {
         extra_size = btrfs_extent_inline_ref_size(want);
         path->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) {
         err = ret;
         goto out;
     }
 
     /*
      * We may be a newly converted file system which still has the old fat
      * extent entries for metadata, so try and see if we have one of those.
      */
     if (ret > 0 && skinny_metadata) {
         skinny_metadata = false;
         if (path->slots[0]) {
             path->slots[0]--;
             btrfs_item_key_to_cpu(path->nodes[0], &key,
                           path->slots[0]);
             if (key.objectid == bytenr &&
                 key.type == BTRFS_EXTENT_ITEM_KEY &&
                 key.offset == num_bytes)
                 ret = 0;
         }
         if (ret) {
             key.objectid = bytenr;
             key.type = BTRFS_EXTENT_ITEM_KEY;
             key.offset = num_bytes;
             btrfs_release_path(path);
             goto again;
         }
     }
 
     if (ret && !insert) {
         err = -ENOENT;
         goto out;
     } else if (WARN_ON(ret)) {
         err = -EIO;
         goto out;
     }
 
     leaf = path->nodes[0];
     item_size = btrfs_item_size(leaf, path->slots[0]);
     if (unlikely(item_size < sizeof(*ei))) {
         err = -EINVAL;
         btrfs_print_v0_err(fs_info);
         btrfs_abort_transaction(trans, err);
         goto out;
     }
 
     ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
     flags = btrfs_extent_flags(leaf, ei);
 
     ptr = (unsigned long)(ei + 1);
     end = (unsigned long)ei + item_size;
 
     if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK && !skinny_metadata) {
         ptr += sizeof(struct btrfs_tree_block_info);
         BUG_ON(ptr > end);
     }
 
     if (owner >= BTRFS_FIRST_FREE_OBJECTID)
         needed = BTRFS_REF_TYPE_DATA;
     else
         needed = BTRFS_REF_TYPE_BLOCK;
 
     err = -ENOENT;
     while (1) {
         if (ptr >= end) {
             if (ptr > end) {
                 err = -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);
             }
             break;
         }
         iref = (struct btrfs_extent_inline_ref *)ptr;
         type = btrfs_get_extent_inline_ref_type(leaf, iref, needed);
         if (type == BTRFS_REF_TYPE_INVALID) {
             err = -EUCLEAN;
             goto out;
         }
 
         if (want < type)
             break;
         if (want > type) {
             ptr += btrfs_extent_inline_ref_size(type);
             continue;
         }
 
         if (type == BTRFS_EXTENT_DATA_REF_KEY) {
             struct btrfs_extent_data_ref *dref;
             dref = (struct btrfs_extent_data_ref *)(&iref->offset);
             if (match_extent_data_ref(leaf, dref, root_objectid,
                           owner, offset)) {
                 err = 0;
                 break;
             }
             if (hash_extent_data_ref_item(leaf, dref) <
                 hash_extent_data_ref(root_objectid, owner, offset))
                 break;
         } else {
             u64 ref_offset;
             ref_offset = btrfs_extent_inline_ref_offset(leaf, iref);
             if (parent > 0) {
                 if (parent == ref_offset) {
                     err = 0;
                     break;
                 }
                 if (ref_offset < parent)
                     break;
             } else {
                 if (root_objectid == ref_offset) {
                     err = 0;
                     break;
                 }
                 if (ref_offset < root_objectid)
                     break;
             }
         }
         ptr += btrfs_extent_inline_ref_size(type);
     }
     if (err == -ENOENT && insert) {
         if (item_size + extra_size >=
             BTRFS_MAX_EXTENT_ITEM_SIZE(root)) {
             err = -EAGAIN;
             goto out;
         }
         /*
          * To add new inline back ref, we have to make sure
          * there is no corresponding back ref item.
          * For simplicity, we just do not add new inline back
          * ref if there is any kind of item for this block
          */
         if (find_next_key(path, 0, &key) == 0 &&
             key.objectid == bytenr &&
             key.type < BTRFS_BLOCK_GROUP_ITEM_KEY) {
             err = -EAGAIN;
             goto out;
         }
     }
     *ref_ret = (struct btrfs_extent_inline_ref *)ptr;
 out:
     if (insert) {
         path->keep_locks = 0;
         path->search_for_extension = 0;
         btrfs_unlock_up_safe(path, 1);
     }
     return err;
 }
 
 /*
  * helper to add new inline back ref
  */
 static noinline_for_stack
 void setup_inline_extent_backref(struct btrfs_fs_info *fs_info,
                  struct btrfs_path *path,
                  struct btrfs_extent_inline_ref *iref,
                  u64 parent, u64 root_objectid,
                  u64 owner, u64 offset, int refs_to_add,
                  struct btrfs_delayed_extent_op *extent_op)
 {
     struct extent_buffer *leaf;
     struct btrfs_extent_item *ei;
     unsigned long ptr;
     unsigned long end;
     unsigned long item_offset;
     u64 refs;
     int size;
     int type;
 
     leaf = path->nodes[0];
     ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
     item_offset = (unsigned long)iref - (unsigned long)ei;
 
     type = extent_ref_type(parent, owner);
     size = btrfs_extent_inline_ref_size(type);
 
     btrfs_extend_item(path, size);
 
     ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
     refs = btrfs_extent_refs(leaf, ei);
     refs += refs_to_add;
     btrfs_set_extent_refs(leaf, ei, refs);
     if (extent_op)
         __run_delayed_extent_op(extent_op, leaf, ei);
 
     ptr = (unsigned long)ei + item_offset;
     end = (unsigned long)ei + btrfs_item_size(leaf, path->slots[0]);
     if (ptr < end - size)
         memmove_extent_buffer(leaf, ptr + size, ptr,
                       end - size - ptr);
 
     iref = (struct btrfs_extent_inline_ref *)ptr;
     btrfs_set_extent_inline_ref_type(leaf, iref, type);
     if (type == BTRFS_EXTENT_DATA_REF_KEY) {
         struct btrfs_extent_data_ref *dref;
         dref = (struct btrfs_extent_data_ref *)(&iref->offset);
         btrfs_set_extent_data_ref_root(leaf, dref, root_objectid);
         btrfs_set_extent_data_ref_objectid(leaf, dref, owner);
         btrfs_set_extent_data_ref_offset(leaf, dref, offset);
         btrfs_set_extent_data_ref_count(leaf, dref, refs_to_add);
     } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
         struct btrfs_shared_data_ref *sref;
         sref = (struct btrfs_shared_data_ref *)(iref + 1);
         btrfs_set_shared_data_ref_count(leaf, sref, refs_to_add);
         btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
     } else if (type == BTRFS_SHARED_BLOCK_REF_KEY) {
         btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
     } else {
         btrfs_set_extent_inline_ref_offset(leaf, iref, root_objectid);
     }
     btrfs_mark_buffer_dirty(leaf);
 }
 
 static int lookup_extent_backref(struct btrfs_trans_handle *trans,
                  struct btrfs_path *path,
                  struct btrfs_extent_inline_ref **ref_ret,
                  u64 bytenr, u64 num_bytes, u64 parent,
                  u64 root_objectid, u64 owner, u64 offset)
 {
     int ret;
 
     ret = lookup_inline_extent_backref(trans, path, ref_ret, bytenr,
                        num_bytes, parent, root_objectid,
                        owner, offset, 0);
     if (ret != -ENOENT)
         return ret;
 
     btrfs_release_path(path);
     *ref_ret = NULL;
 
     if (owner < BTRFS_FIRST_FREE_OBJECTID) {
         ret = lookup_tree_block_ref(trans, path, bytenr, parent,
                         root_objectid);
     } else {
         ret = lookup_extent_data_ref(trans, path, bytenr, parent,
                          root_objectid, owner, offset);
     }
     return ret;
 }
 
 /*
  * helper to update/remove inline back ref
  */
 static noinline_for_stack
 void update_inline_extent_backref(struct btrfs_path *path,
                   struct btrfs_extent_inline_ref *iref,
                   int refs_to_mod,
                   struct btrfs_delayed_extent_op *extent_op)
 {
     struct extent_buffer *leaf = path->nodes[0];
     struct btrfs_extent_item *ei;
     struct btrfs_extent_data_ref *dref = NULL;
     struct btrfs_shared_data_ref *sref = NULL;
     unsigned long ptr;
     unsigned long end;
     u32 item_size;
     int size;
     int type;
     u64 refs;
 
     ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
     refs = btrfs_extent_refs(leaf, ei);
     WARN_ON(refs_to_mod < 0 && refs + refs_to_mod <= 0);
     refs += refs_to_mod;
     btrfs_set_extent_refs(leaf, ei, refs);
     if (extent_op)
         __run_delayed_extent_op(extent_op, leaf, ei);
 
     /*
      * If type is invalid, we should have bailed out after
      * lookup_inline_extent_backref().
      */
     type = btrfs_get_extent_inline_ref_type(leaf, iref, BTRFS_REF_TYPE_ANY);
     ASSERT(type != BTRFS_REF_TYPE_INVALID);
 
     if (type == BTRFS_EXTENT_DATA_REF_KEY) {
         dref = (struct btrfs_extent_data_ref *)(&iref->offset);
         refs = btrfs_extent_data_ref_count(leaf, dref);
     } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
         sref = (struct btrfs_shared_data_ref *)(iref + 1);
         refs = btrfs_shared_data_ref_count(leaf, sref);
     } else {
         refs = 1;
         BUG_ON(refs_to_mod != -1);
     }
 
     BUG_ON(refs_to_mod < 0 && refs < -refs_to_mod);
     refs += refs_to_mod;
 
     if (refs > 0) {
         if (type == BTRFS_EXTENT_DATA_REF_KEY)
             btrfs_set_extent_data_ref_count(leaf, dref, refs);
         else
             btrfs_set_shared_data_ref_count(leaf, sref, refs);
     } else {
         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(path, item_size, 1);
     }
     btrfs_mark_buffer_dirty(leaf);
 }
 
 static noinline_for_stack
 int insert_inline_extent_backref(struct btrfs_trans_handle *trans,
                  struct btrfs_path *path,
                  u64 bytenr, u64 num_bytes, u64 parent,
                  u64 root_objectid, u64 owner,
                  u64 offset, int refs_to_add,
                  struct btrfs_delayed_extent_op *extent_op)
 {
     struct btrfs_extent_inline_ref *iref;
     int ret;
 
     ret = lookup_inline_extent_backref(trans, path, &iref, bytenr,
                        num_bytes, parent, root_objectid,
                        owner, offset, 1);
     if (ret == 0) {
         /*
          * We're adding refs to a tree block we already own, this
          * should not happen at all.
          */
         if (owner < BTRFS_FIRST_FREE_OBJECTID) {
             btrfs_crit(trans->fs_info,
 "adding refs to an existing tree ref, bytenr %llu num_bytes %llu root_objectid %llu",
                    bytenr, num_bytes, root_objectid);
             if (IS_ENABLED(CONFIG_BTRFS_DEBUG)) {
                 WARN_ON(1);
                 btrfs_crit(trans->fs_info,
             "path->slots[0]=%d path->nodes[0]:", path->slots[0]);
                 btrfs_print_leaf(path->nodes[0]);
             }
             return -EUCLEAN;
         }
         update_inline_extent_backref(path, iref, refs_to_add, extent_op);
     } else if (ret == -ENOENT) {
         setup_inline_extent_backref(trans->fs_info, path, iref, parent,
                         root_objectid, owner, offset,
                         refs_to_add, extent_op);
         ret = 0;
     }
     return ret;
 }
 
 static int remove_extent_backref(struct btrfs_trans_handle *trans,
                  struct btrfs_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)
         update_inline_extent_backref(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 << 9);
 
     if (WARN_ON(start != aligned_start)) {
         len -= aligned_start - start;
         len = round_down(len, 1 << 9);
         start = aligned_start;
     }
 
     *discarded_bytes = 0;
 
     if (!len)
         return 0;
 
     end = start + len;
     bytes_left = len;
 
     /* Skip any superblocks on this device. */
     for (j = 0; j < BTRFS_SUPER_MIRROR_MAX; j++) {
         u64 sb_start = btrfs_sb_offset(j);
         u64 sb_end = sb_start + BTRFS_SUPER_INFO_SIZE;
         u64 size = sb_start - start;
 
         if (!in_range(sb_start, start, bytes_left) &&
             !in_range(sb_end, start, bytes_left) &&
             !in_range(start, sb_start, BTRFS_SUPER_INFO_SIZE))
             continue;
 
         /*
          * Superblock spans beginning of range.  Adjust start and
          * try again.
          */
         if (sb_start <= start) {
             start += sb_end - start;
             if (start > end) {
                 bytes_left = 0;
                 break;
             }
             bytes_left = end - start;
             continue;
         }
 
         if (size) {
             ret = blkdev_issue_discard(bdev, start >> 9, size >> 9,
                            GFP_NOFS);
             if (!ret)
                 *discarded_bytes += size;
             else if (ret != -EOPNOTSUPP)
                 return ret;
         }
 
         start = sb_end;
         if (start > end) {
             bytes_left = 0;
             break;
         }
         bytes_left = end - start;
     }
 
     if (bytes_left) {
         ret = blkdev_issue_discard(bdev, start >> 9, bytes_left >> 9,
                        GFP_NOFS);
         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;
 }
 
 /*
  * __btrfs_inc_extent_ref - insert backreference for a given extent
  *
  * The counterpart is in __btrfs_free_extent(), with examples and more details
  * how it works.
  *
  * @trans:      Handle of transaction
  *
  * @node:       The delayed ref node used to get the bytenr/length for
  *          extent whose references are incremented.
  *
  * @parent:     If this is a shared extent (BTRFS_SHARED_DATA_REF_KEY/
  *          BTRFS_SHARED_BLOCK_REF_KEY) then it holds the logical
  *          bytenr of the parent block. Since new extents are always
  *          created with indirect references, this will only be the case
  *          when relocating a shared extent. In that case, root_objectid
  *          will be BTRFS_TREE_RELOC_OBJECTID. 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.
  *
  * @refs_to_add     Number of references to add
  *
  * @extent_op       Pointer to a structure, holding information necessary when
  *                  updating a tree block's flags
  *
  */
 static int __btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
                   struct btrfs_delayed_ref_node *node,
                   u64 parent, u64 root_objectid,
                   u64 owner, u64 offset, int refs_to_add,
                   struct btrfs_delayed_extent_op *extent_op)
 {
     struct btrfs_path *path;
     struct extent_buffer *leaf;
     struct btrfs_extent_item *item;
     struct btrfs_key key;
     u64 bytenr = node->bytenr;
     u64 num_bytes = node->num_bytes;
     u64 refs;
     int ret;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
 
     /* this will setup the path even if it fails to insert the back ref */
     ret = insert_inline_extent_backref(trans, path, bytenr, num_bytes,
                        parent, root_objectid, owner,
                        offset, refs_to_add, extent_op);
     if ((ret < 0 && ret != -EAGAIN) || !ret)
         goto out;
 
     /*
      * Ok we had -EAGAIN which means we didn't have space to insert and
      * inline extent ref, so just update the reference count and add a
      * normal backref.
      */
     leaf = path->nodes[0];
     btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
     item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
     refs = btrfs_extent_refs(leaf, item);
     btrfs_set_extent_refs(leaf, item, refs + refs_to_add);
     if (extent_op)
         __run_delayed_extent_op(extent_op, leaf, item);
 
     btrfs_mark_buffer_dirty(leaf);
     btrfs_release_path(path);
 
     /* now insert the actual backref */
     if (owner < BTRFS_FIRST_FREE_OBJECTID) {
         BUG_ON(refs_to_add != 1);
         ret = insert_tree_block_ref(trans, path, bytenr, parent,
                         root_objectid);
     } else {
         ret = insert_extent_data_ref(trans, path, bytenr, parent,
                          root_objectid, owner, offset,
                          refs_to_add);
     }
     if (ret)
         btrfs_abort_transaction(trans, ret);
 out:
     btrfs_free_path(path);
     return ret;
 }
 
 static int run_delayed_data_ref(struct btrfs_trans_handle *trans,
                 struct btrfs_delayed_ref_node *node,
                 struct btrfs_delayed_extent_op *extent_op,
                 int insert_reserved)
 {
     int ret = 0;
     struct btrfs_delayed_data_ref *ref;
     struct btrfs_key ins;
     u64 parent = 0;
     u64 ref_root = 0;
     u64 flags = 0;
 
     ins.objectid = node->bytenr;
     ins.offset = node->num_bytes;
     ins.type = BTRFS_EXTENT_ITEM_KEY;
 
     ref = btrfs_delayed_node_to_data_ref(node);
     trace_run_delayed_data_ref(trans->fs_info, node, ref, node->action);
 
     if (node->type == BTRFS_SHARED_DATA_REF_KEY)
         parent = ref->parent;
     ref_root = ref->root;
 
     if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
         if (extent_op)
             flags |= extent_op->flags_to_set;
         ret = alloc_reserved_file_extent(trans, parent, ref_root,
                          flags, ref->objectid,
                          ref->offset, &ins,
                          node->ref_mod);
     } else if (node->action == BTRFS_ADD_DELAYED_REF) {
         ret = __btrfs_inc_extent_ref(trans, node, parent, ref_root,
                          ref->objectid, ref->offset,
                          node->ref_mod, extent_op);
     } else if (node->action == BTRFS_DROP_DELAYED_REF) {
         ret = __btrfs_free_extent(trans, node, parent,
                       ref_root, ref->objectid,
                       ref->offset, node->ref_mod,
                       extent_op);
     } else {
         BUG();
     }
     return ret;
 }
 
 static void __run_delayed_extent_op(struct btrfs_delayed_extent_op *extent_op,
                     struct extent_buffer *leaf,
                     struct btrfs_extent_item *ei)
 {
     u64 flags = btrfs_extent_flags(leaf, ei);
     if (extent_op->update_flags) {
         flags |= extent_op->flags_to_set;
         btrfs_set_extent_flags(leaf, ei, flags);
     }
 
     if (extent_op->update_key) {
         struct btrfs_tree_block_info *bi;
         BUG_ON(!(flags & BTRFS_EXTENT_FLAG_TREE_BLOCK));
         bi = (struct btrfs_tree_block_info *)(ei + 1);
         btrfs_set_tree_block_key(leaf, bi, &extent_op->key);
     }
 }
 
 static int run_delayed_extent_op(struct btrfs_trans_handle *trans,
                  struct btrfs_delayed_ref_head *head,
                  struct btrfs_delayed_extent_op *extent_op)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_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 err = 0;
     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) {
         err = ret;
         goto out;
     }
     if (ret > 0) {
         if (metadata) {
             if (path->slots[0] > 0) {
                 path->slots[0]--;
                 btrfs_item_key_to_cpu(path->nodes[0], &key,
                               path->slots[0]);
                 if (key.objectid == head->bytenr &&
                     key.type == BTRFS_EXTENT_ITEM_KEY &&
                     key.offset == head->num_bytes)
                     ret = 0;
             }
             if (ret > 0) {
                 btrfs_release_path(path);
                 metadata = 0;
 
                 key.objectid = head->bytenr;
                 key.offset = head->num_bytes;
                 key.type = BTRFS_EXTENT_ITEM_KEY;
                 goto again;
             }
         } else {
             err = -EIO;
             goto out;
         }
     }
 
     leaf = path->nodes[0];
     item_size = btrfs_item_size(leaf, path->slots[0]);
 
     if (unlikely(item_size < sizeof(*ei))) {
         err = -EINVAL;
         btrfs_print_v0_err(fs_info);
         btrfs_abort_transaction(trans, err);
         goto out;
     }
 
     ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
     __run_delayed_extent_op(extent_op, leaf, ei);
 
     btrfs_mark_buffer_dirty(leaf);
 out:
     btrfs_free_path(path);
     return err;
 }
 
 static int run_delayed_tree_ref(struct btrfs_trans_handle *trans,
                 struct btrfs_delayed_ref_node *node,
                 struct btrfs_delayed_extent_op *extent_op,
                 int insert_reserved)
 {
     int ret = 0;
     struct btrfs_delayed_tree_ref *ref;
     u64 parent = 0;
     u64 ref_root = 0;
 
     ref = btrfs_delayed_node_to_tree_ref(node);
     trace_run_delayed_tree_ref(trans->fs_info, node, ref, node->action);
 
     if (node->type == BTRFS_SHARED_BLOCK_REF_KEY)
         parent = ref->parent;
     ref_root = ref->root;
 
     if (node->ref_mod != 1) {
         btrfs_err(trans->fs_info,
     "btree block(%llu) has %d references rather than 1: action %d ref_root %llu parent %llu",
               node->bytenr, node->ref_mod, node->action, ref_root,
               parent);
         return -EIO;
     }
     if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
         BUG_ON(!extent_op || !extent_op->update_flags);
         ret = alloc_reserved_tree_block(trans, node, extent_op);
     } else if (node->action == BTRFS_ADD_DELAYED_REF) {
         ret = __btrfs_inc_extent_ref(trans, node, parent, ref_root,
                          ref->level, 0, 1, extent_op);
     } else if (node->action == BTRFS_DROP_DELAYED_REF) {
         ret = __btrfs_free_extent(trans, node, parent, ref_root,
                       ref->level, 0, 1, extent_op);
     } else {
         BUG();
     }
     return ret;
 }
 
 /* helper function to actually process a single delayed ref entry */
 static int run_one_delayed_ref(struct btrfs_trans_handle *trans,
                    struct btrfs_delayed_ref_node *node,
                    struct btrfs_delayed_extent_op *extent_op,
                    int insert_reserved)
 {
     int ret = 0;
 
     if (TRANS_ABORTED(trans)) {
         if (insert_reserved)
             btrfs_pin_extent(trans, node->bytenr, node->num_bytes, 1);
         return 0;
     }
 
     if (node->type == BTRFS_TREE_BLOCK_REF_KEY ||
         node->type == BTRFS_SHARED_BLOCK_REF_KEY)
         ret = run_delayed_tree_ref(trans, node, extent_op,
                        insert_reserved);
     else if (node->type == BTRFS_EXTENT_DATA_REF_KEY ||
          node->type == BTRFS_SHARED_DATA_REF_KEY)
         ret = run_delayed_data_ref(trans, node, extent_op,
                        insert_reserved);
     else
         BUG();
     if (ret && insert_reserved)
         btrfs_pin_extent(trans, node->bytenr, node->num_bytes, 1);
     return ret;
 }
 
 static inline struct btrfs_delayed_ref_node *
 select_delayed_ref(struct btrfs_delayed_ref_head *head)
 {
     struct btrfs_delayed_ref_node *ref;
 
     if (RB_EMPTY_ROOT(&head->ref_tree.rb_root))
         return NULL;
 
     /*
      * Select a delayed ref of type BTRFS_ADD_DELAYED_REF first.
      * This is to prevent a ref count from going down to zero, which deletes
      * the extent item from the extent tree, when there still are references
      * to add, which would fail because they would not find the extent item.
      */
     if (!list_empty(&head->ref_add_list))
         return list_first_entry(&head->ref_add_list,
                 struct btrfs_delayed_ref_node, add_list);
 
     ref = rb_entry(rb_first_cached(&head->ref_tree),
                struct btrfs_delayed_ref_node, ref_node);
     ASSERT(list_empty(&ref->add_list));
     return ref;
 }
 
 static void unselect_delayed_ref_head(struct btrfs_delayed_ref_root *delayed_refs,
                       struct btrfs_delayed_ref_head *head)
 {
     spin_lock(&delayed_refs->lock);
     head->processing = 0;
     delayed_refs->num_heads_ready++;
     spin_unlock(&delayed_refs->lock);
     btrfs_delayed_ref_unlock(head);
 }
 
 static struct btrfs_delayed_extent_op *cleanup_extent_op(
                 struct btrfs_delayed_ref_head *head)
 {
     struct btrfs_delayed_extent_op *extent_op = head->extent_op;
 
     if (!extent_op)
         return NULL;
 
     if (head->must_insert_reserved) {
         head->extent_op = NULL;
         btrfs_free_delayed_extent_op(extent_op);
         return NULL;
     }
     return extent_op;
 }
 
 static int run_and_cleanup_extent_op(struct btrfs_trans_handle *trans,
                      struct btrfs_delayed_ref_head *head)
 {
     struct btrfs_delayed_extent_op *extent_op;
     int ret;
 
     extent_op = cleanup_extent_op(head);
     if (!extent_op)
         return 0;
     head->extent_op = NULL;
     spin_unlock(&head->lock);
     ret = run_delayed_extent_op(trans, head, extent_op);
     btrfs_free_delayed_extent_op(extent_op);
     return ret ? ret : 1;
 }
 
 void btrfs_cleanup_ref_head_accounting(struct btrfs_fs_info *fs_info,
                   struct btrfs_delayed_ref_root *delayed_refs,
                   struct btrfs_delayed_ref_head *head)
 {
     int nr_items = 1;   /* Dropping this ref head update. */
 
     /*
      * 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) {
         spin_lock(&delayed_refs->lock);
         delayed_refs->pending_csums -= head->num_bytes;
         spin_unlock(&delayed_refs->lock);
         nr_items += btrfs_csum_bytes_to_leaves(fs_info, head->num_bytes);
     }
 
     btrfs_delayed_refs_rsv_release(fs_info, nr_items);
 }
 
 static int cleanup_ref_head(struct btrfs_trans_handle *trans,
                 struct btrfs_delayed_ref_head *head)
 {
 
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_delayed_ref_root *delayed_refs;
     int ret;
 
     delayed_refs = &trans->transaction->delayed_refs;
 
     ret = run_and_cleanup_extent_op(trans, head);
     if (ret < 0) {
         unselect_delayed_ref_head(delayed_refs, head);
         btrfs_debug(fs_info, "run_delayed_extent_op returned %d", ret);
         return ret;
     } else if (ret) {
         return ret;
     }
 
     /*
      * Need to drop our head ref lock and re-acquire the delayed ref lock
      * and then re-check to make sure nobody got added.
      */
     spin_unlock(&head->lock);
     spin_lock(&delayed_refs->lock);
     spin_lock(&head->lock);
     if (!RB_EMPTY_ROOT(&head->ref_tree.rb_root) || head->extent_op) {
         spin_unlock(&head->lock);
         spin_unlock(&delayed_refs->lock);
         return 1;
     }
     btrfs_delete_ref_head(delayed_refs, head);
     spin_unlock(&head->lock);
     spin_unlock(&delayed_refs->lock);
 
     if (head->must_insert_reserved) {
         btrfs_pin_extent(trans, head->bytenr, head->num_bytes, 1);
         if (head->is_data) {
             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);
         }
     }
 
     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,
                     unsigned long *run_refs)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_delayed_ref_root *delayed_refs;
     struct btrfs_delayed_extent_op *extent_op;
     struct btrfs_delayed_ref_node *ref;
     int must_insert_reserved = 0;
     int ret;
 
     delayed_refs = &trans->transaction->delayed_refs;
 
     lockdep_assert_held(&locked_ref->mutex);
     lockdep_assert_held(&locked_ref->lock);
 
     while ((ref = select_delayed_ref(locked_ref))) {
         if (ref->seq &&
             btrfs_check_delayed_seq(fs_info, ref->seq)) {
             spin_unlock(&locked_ref->lock);
             unselect_delayed_ref_head(delayed_refs, locked_ref);
             return -EAGAIN;
         }
 
         (*run_refs)++;
         ref->in_tree = 0;
         rb_erase_cached(&ref->ref_node, &locked_ref->ref_tree);
         RB_CLEAR_NODE(&ref->ref_node);
         if (!list_empty(&ref->add_list))
             list_del(&ref->add_list);
         /*
          * When we play the delayed ref, also correct the ref_mod on
          * head
          */
         switch (ref->action) {
         case BTRFS_ADD_DELAYED_REF:
         case BTRFS_ADD_DELAYED_EXTENT:
             locked_ref->ref_mod -= ref->ref_mod;
             break;
         case BTRFS_DROP_DELAYED_REF:
             locked_ref->ref_mod += ref->ref_mod;
             break;
         default:
             WARN_ON(1);
         }
         atomic_dec(&delayed_refs->num_entries);
 
         /*
          * Record the must_insert_reserved flag before we drop the
          * spin lock.
          */
         must_insert_reserved = locked_ref->must_insert_reserved;
         locked_ref->must_insert_reserved = 0;
 
         extent_op = locked_ref->extent_op;
         locked_ref->extent_op = NULL;
         spin_unlock(&locked_ref->lock);
 
         ret = run_one_delayed_ref(trans, ref, extent_op,
                       must_insert_reserved);
 
         btrfs_free_delayed_extent_op(extent_op);
         if (ret) {
             unselect_delayed_ref_head(delayed_refs, locked_ref);
             btrfs_put_delayed_ref(ref);
             btrfs_debug(fs_info, "run_one_delayed_ref returned %d",
                     ret);
             return ret;
         }
 
         btrfs_put_delayed_ref(ref);
         cond_resched();
 
         spin_lock(&locked_ref->lock);
         btrfs_merge_delayed_refs(trans, delayed_refs, locked_ref);
     }
 
     return 0;
 }
 
 /*
  * Returns 0 on success or if called with an already aborted transaction.
  * Returns -ENOMEM or -EIO on failure and will abort the transaction.
  */
 static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                          unsigned long nr)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_delayed_ref_root *delayed_refs;
     struct btrfs_delayed_ref_head *locked_ref = NULL;
     ktime_t start = ktime_get();
     int ret;
     unsigned long count = 0;
     unsigned long actual_count = 0;
 
     delayed_refs = &trans->transaction->delayed_refs;
     do {
         if (!locked_ref) {
             locked_ref = btrfs_obtain_ref_head(trans);
             if (IS_ERR_OR_NULL(locked_ref)) {
                 if (PTR_ERR(locked_ref) == -EAGAIN) {
                     continue;
                 } else {
                     break;
                 }
             }
             count++;
         }
         /*
          * We need to try and merge add/drops of the same ref since we
          * can run into issues with relocate dropping the implicit ref
          * and then it being added back again before the drop can
          * finish.  If we merged anything we need to re-loop so we can
          * get a good ref.
          * Or we can get node references of the same type that weren't
          * merged when created due to bumps in the tree mod seq, and
          * we need to merge them to prevent adding an inline extent
          * backref before dropping it (triggering a BUG_ON at
          * insert_inline_extent_backref()).
          */
         spin_lock(&locked_ref->lock);
         btrfs_merge_delayed_refs(trans, delayed_refs, locked_ref);
 
         ret = btrfs_run_delayed_refs_for_head(trans, locked_ref,
                               &actual_count);
         if (ret < 0 && ret != -EAGAIN) {
             /*
              * Error, btrfs_run_delayed_refs_for_head already
              * unlocked everything so just bail out
              */
             return ret;
         } else if (!ret) {
             /*
              * Success, perform the usual cleanup of a processed
              * head
              */
             ret = cleanup_ref_head(trans, locked_ref);
             if (ret > 0 ) {
                 /* We dropped our lock, we need to loop. */
                 ret = 0;
                 continue;
             } else if (ret) {
                 return ret;
             }
         }
 
         /*
          * Either success case or btrfs_run_delayed_refs_for_head
          * returned -EAGAIN, meaning we need to select another head
          */
 
         locked_ref = NULL;
         cond_resched();
     } while ((nr != -1 && count < nr) || locked_ref);
 
     /*
      * We don't want to include ref heads since we can have empty ref heads
      * and those will drastically skew our runtime down since we just do
      * accounting, no actual extent tree updates.
      */
     if (actual_count > 0) {
         u64 runtime = ktime_to_ns(ktime_sub(ktime_get(), start));
         u64 avg;
 
         /*
          * We weigh the current average higher than our current runtime
          * to avoid large swings in the average.
          */
         spin_lock(&delayed_refs->lock);
         avg = fs_info->avg_delayed_ref_runtime * 3 + runtime;
         fs_info->avg_delayed_ref_runtime = avg >> 2;    /* div by 4 */
         spin_unlock(&delayed_refs->lock);
     }
     return 0;
 }
 
 #ifdef SCRAMBLE_DELAYED_REFS
 /*
  * Normally delayed refs get processed in ascending bytenr order. This
  * correlates in most cases to the order added. To expose dependencies on this
  * order, we start to process the tree in the middle instead of the beginning
  */
 static u64 find_middle(struct rb_root *root)
 {
     struct rb_node *n = root->rb_node;
     struct btrfs_delayed_ref_node *entry;
     int alt = 1;
     u64 middle;
     u64 first = 0, last = 0;
 
     n = rb_first(root);
     if (n) {
         entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
         first = entry->bytenr;
     }
     n = rb_last(root);
     if (n) {
         entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
         last = entry->bytenr;
     }
     n = root->rb_node;
 
     while (n) {
         entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
         WARN_ON(!entry->in_tree);
 
         middle = entry->bytenr;
 
         if (alt)
             n = n->rb_left;
         else
             n = n->rb_right;
 
         alt = 1 - alt;
     }
     return middle;
 }
 #endif
 
 /*
  * this starts processing the delayed reference count updates and
  * extent insertions we have queued up so far.  count can be
  * 0, which means to process everything in the tree at the start
  * of the run (but not newly added entries), or it can be some target
  * number you'd like to process.
  *
  * Returns 0 on success or if called with an aborted transaction
  * Returns <0 on error and aborts the transaction
  */
 int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                unsigned long count)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct rb_node *node;
     struct btrfs_delayed_ref_root *delayed_refs;
     struct btrfs_delayed_ref_head *head;
     int ret;
     int run_all = count == (unsigned long)-1;
 
     /* We'll clean this up in btrfs_cleanup_transaction */
     if (TRANS_ABORTED(trans))
         return 0;
 
     if (test_bit(BTRFS_FS_CREATING_FREE_SPACE_TREE, &fs_info->flags))
         return 0;
 
     delayed_refs = &trans->transaction->delayed_refs;
     if (count == 0)
         count = delayed_refs->num_heads_ready;
 
 again:
 #ifdef SCRAMBLE_DELAYED_REFS
     delayed_refs->run_delayed_start = find_middle(&delayed_refs->root);
 #endif
     ret = __btrfs_run_delayed_refs(trans, count);
     if (ret < 0) {
         btrfs_abort_transaction(trans, ret);
         return ret;
     }
 
     if (run_all) {
         btrfs_create_pending_block_groups(trans);
 
         spin_lock(&delayed_refs->lock);
         node = rb_first_cached(&delayed_refs->href_root);
         if (!node) {
             spin_unlock(&delayed_refs->lock);
             goto out;
         }
         head = rb_entry(node, struct btrfs_delayed_ref_head,
                 href_node);
         refcount_inc(&head->refs);
         spin_unlock(&delayed_refs->lock);
 
         /* Mutex was contended, block until it's released and retry. */
         mutex_lock(&head->mutex);
         mutex_unlock(&head->mutex);
 
         btrfs_put_delayed_ref_head(head);
         cond_resched();
         goto again;
     }
 out:
     return 0;
 }
 
 int btrfs_set_disk_extent_flags(struct btrfs_trans_handle *trans,
                 struct extent_buffer *eb, u64 flags,
                 int level)
 {
     struct btrfs_delayed_extent_op *extent_op;
     int ret;
 
     extent_op = btrfs_alloc_delayed_extent_op();
     if (!extent_op)
         return -ENOMEM;
 
     extent_op->flags_to_set = flags;
     extent_op->update_flags = true;
     extent_op->update_key = false;
     extent_op->level = level;
 
     ret = btrfs_add_delayed_extent_op(trans, eb->start, eb->len, extent_op);
     if (ret)
         btrfs_free_delayed_extent_op(extent_op);
     return ret;
 }
 
 static noinline int check_delayed_ref(struct btrfs_root *root,
                       struct btrfs_path *path,
                       u64 objectid, u64 offset, u64 bytenr)
 {
     struct btrfs_delayed_ref_head *head;
     struct btrfs_delayed_ref_node *ref;
     struct btrfs_delayed_data_ref *data_ref;
     struct btrfs_delayed_ref_root *delayed_refs;
     struct btrfs_transaction *cur_trans;
     struct rb_node *node;
     int ret = 0;
 
     spin_lock(&root->fs_info->trans_lock);
     cur_trans = root->fs_info->running_transaction;
     if (cur_trans)
         refcount_inc(&cur_trans->use_count);
     spin_unlock(&root->fs_info->trans_lock);
     if (!cur_trans)
         return 0;
 
     delayed_refs = &cur_trans->delayed_refs;
     spin_lock(&delayed_refs->lock);
     head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
     if (!head) {
         spin_unlock(&delayed_refs->lock);
         btrfs_put_transaction(cur_trans);
         return 0;
     }
 
     if (!mutex_trylock(&head->mutex)) {
         refcount_inc(&head->refs);
         spin_unlock(&delayed_refs->lock);
 
         btrfs_release_path(path);
 
         /*
          * Mutex was contended, block until it's released and let
          * caller try again
          */
         mutex_lock(&head->mutex);
         mutex_unlock(&head->mutex);
         btrfs_put_delayed_ref_head(head);
         btrfs_put_transaction(cur_trans);
         return -EAGAIN;
     }
     spin_unlock(&delayed_refs->lock);
 
     spin_lock(&head->lock);
     /*
      * XXX: We should replace this with a proper search function in the
      * future.
      */
     for (node = rb_first_cached(&head->ref_tree); node;
          node = rb_next(node)) {
         ref = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
         /* If it's a shared ref we know a cross reference exists */
         if (ref->type != BTRFS_EXTENT_DATA_REF_KEY) {
             ret = 1;
             break;
         }
 
         data_ref = btrfs_delayed_node_to_data_ref(ref);
 
         /*
          * If our ref doesn't match the one we're currently looking at
          * then we have a cross reference.
          */
         if (data_ref->root != root->root_key.objectid ||
             data_ref->objectid != objectid ||
             data_ref->offset != offset) {
             ret = 1;
             break;
         }
     }
     spin_unlock(&head->lock);
     mutex_unlock(&head->mutex);
     btrfs_put_transaction(cur_trans);
     return ret;
 }
 
 static noinline int check_committed_ref(struct btrfs_root *root,
                     struct btrfs_path *path,
                     u64 objectid, u64 offset, u64 bytenr,
                     bool strict)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_root *extent_root = 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_dirty(&trans->transaction->pinned_extents, bytenr,
              bytenr + num_bytes - 1, GFP_NOFS | __GFP_NOFAIL);
     return 0;
 }
 
 int btrfs_pin_extent(struct btrfs_trans_handle *trans,
              u64 bytenr, u64 num_bytes, int reserved)
 {
     struct btrfs_block_group *cache;
 
     cache = btrfs_lookup_block_group(trans->fs_info, bytenr);
     BUG_ON(!cache); /* Logic error */
 
     pin_down_extent(trans, cache, bytenr, num_bytes, reserved);
 
     btrfs_put_block_group(cache);
     return 0;
 }
 
 /*
  * this function must be called within transaction
  */
 int btrfs_pin_extent_for_log_replay(struct btrfs_trans_handle *trans,
                     u64 bytenr, u64 num_bytes)
 {
     struct btrfs_block_group *cache;
     int ret;
 
     cache = btrfs_lookup_block_group(trans->fs_info, bytenr);
     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, bytenr, num_bytes, 0);
 
     /* remove us from the free space cache (if we're there at all) */
     ret = btrfs_remove_free_space(cache, bytenr, num_bytes);
 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);
 
         down_read(&fs_info->commit_root_sem);
         if (start < cache->last_byte_to_unpin && return_free_space) {
             u64 add_len = min(len, cache->last_byte_to_unpin - start);
 
             btrfs_add_free_space(cache, start, add_len);
         }
         up_read(&fs_info->commit_root_sem);
 
         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);
         ret = find_first_extent_bit(unpin, 0, &start, &end,
                         EXTENT_DIRTY, &cached_state);
         if (ret) {
             mutex_unlock(&fs_info->unused_bg_unpin_mutex);
             break;
         }
 
         if (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;
 }
 
 /*
  * 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, int refs_to_drop,
                    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;
     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) {
                 btrfs_crit(info,
 "invalid iref, no EXTENT/METADATA_ITEM found but has inline extent ref");
                 btrfs_abort_transaction(trans, -EUCLEAN);
                 goto err_dump;
             }
             /* 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) {
                 btrfs_err(info,
                       "umm, got %d back from search, was looking for %llu",
                       ret, bytenr);
                 if (ret > 0)
                     btrfs_print_leaf(path->nodes[0]);
             }
             if (ret < 0) {
                 btrfs_abort_transaction(trans, ret);
                 goto out;
             }
             extent_slot = path->slots[0];
         }
     } else if (WARN_ON(ret == -ENOENT)) {
         btrfs_print_leaf(path->nodes[0]);
         btrfs_err(info,
             "unable to find ref byte nr %llu parent %llu root %llu  owner %llu offset %llu",
             bytenr, parent, root_objectid, owner_objectid,
             owner_offset);
         btrfs_abort_transaction(trans, ret);
         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 = -EINVAL;
         btrfs_print_v0_err(info);
         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)) {
             btrfs_crit(info,
 "invalid extent item size for key (%llu, %u, %llu) owner %llu, has %u expect >= %zu",
                    key.objectid, key.type, key.offset,
                    owner_objectid, item_size,
                    sizeof(*ei) + sizeof(*bi));
             btrfs_abort_transaction(trans, -EUCLEAN);
             goto err_dump;
         }
         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) {
         btrfs_crit(info,
         "trying to drop %d refs but we only have %llu for bytenr %llu",
               refs_to_drop, refs, bytenr);
         btrfs_abort_transaction(trans, -EUCLEAN);
         goto err_dump;
     }
     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) {
                 btrfs_crit(info,
 "invalid iref, got inlined extent ref but no EXTENT/METADATA_ITEM found");
                 btrfs_abort_transaction(trans, -EUCLEAN);
                 goto err_dump;
             }
         } else {
             btrfs_set_extent_refs(leaf, ei, refs);
             btrfs_mark_buffer_dirty(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)) {
                 btrfs_crit(info,
         "invalid refs_to_drop, current refs %u refs_to_drop %u",
                        extent_data_ref_count(path, iref),
                        refs_to_drop);
                 btrfs_abort_transaction(trans, -EUCLEAN);
                 goto err_dump;
             }
             if (iref) {
                 if (path->slots[0] != extent_slot) {
                     btrfs_crit(info,
 "invalid iref, extent item key (%llu %u %llu) doesn't have wanted iref",
                            key.objectid, key.type,
                            key.offset);
                     btrfs_abort_transaction(trans, -EUCLEAN);
                     goto err_dump;
                 }
             } 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) {
                     btrfs_crit(info,
     "invalid SHARED_* item, previous item is not EXTENT/METADATA_ITEM");
                     btrfs_abort_transaction(trans, -EUCLEAN);
                     goto err_dump;
                 }
                 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;
 err_dump:
     /*
      * Leaf dump can take up a lot of log buffer, so we only do full leaf
      * dump for debug build.
      */
     if (IS_ENABLED(CONFIG_BTRFS_DEBUG)) {
         btrfs_crit(info, "path->slots[0]=%d extent_slot=%d",
                path->slots[0], extent_slot);
         btrfs_print_leaf(path->nodes[0]);
     }
 
     btrfs_free_path(path);
     return -EUCLEAN;
 }
 
 /*
  * 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 = 0;
 
     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 this is a leaf and there are tree mod log users, we may
          * have recorded mod log operations that point to this leaf.
          * So we must make sure no one reuses this leaf's extent before
          * mod log operations are applied to a node, otherwise after
          * rewinding a node using the mod log operations we get an
          * inconsistent btree, as the leaf's extent may now be used as
          * a node or leaf for another different 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, it will not be able to
          * find a node pointing to this leaf and record operations that
          * point to this leaf.
          */
         if (btrfs_header_level(buf) == 0 &&
             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 {
     LOOP_CACHING_NOWAIT,
     LOOP_CACHING_WAIT,
     LOOP_ALLOC_CHUNK,
     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);
 }
 
 enum btrfs_extent_allocation_policy {
     BTRFS_EXTENT_ALLOC_CLUSTERED,
     BTRFS_EXTENT_ALLOC_ZONED,
 };
 
 /*
  * Structure used internally for find_free_extent() function.  Wraps needed
  * parameters.
  */
 struct find_free_extent_ctl {
     /* Basic allocation info */
     u64 ram_bytes;
     u64 num_bytes;
     u64 min_alloc_size;
     u64 empty_size;
     u64 flags;
     int delalloc;
 
     /* Where to start the search inside the bg */
     u64 search_start;
 
     /* For clustered allocation */
     u64 empty_cluster;
     struct btrfs_free_cluster *last_ptr;
     bool use_cluster;
 
     bool have_caching_bg;
     bool orig_have_caching_bg;
 
     /* Allocation is called for tree-log */
     bool for_treelog;
 
     /* Allocation is called for data relocation */
     bool for_data_reloc;
 
     /* RAID index, converted from flags */
     int index;
 
     /*
      * Current loop number, check find_free_extent_update_loop() for details
      */
     int loop;
 
     /*
      * Whether we're refilling a cluster, if true we need to re-search
      * current block group but don't try to refill the cluster again.
      */
     bool retry_clustered;
 
     /*
      * Whether we're updating free space cache, if true we need to re-search
      * current block group but don't try updating free space cache again.
      */
     bool retry_unclustered;
 
     /* If current block group is cached */
     int cached;
 
     /* Max contiguous hole found */
     u64 max_extent_size;
 
     /* Total free space from free space cache, not always contiguous */
     u64 total_free_space;
 
     /* Found result */
     u64 found_offset;
 
     /* Hint where to start looking for an empty space */
     u64 hint_byte;
 
     /* Allocation policy */
     enum btrfs_extent_allocation_policy policy;
 };
 
 
 /*
  * Helper function for find_free_extent().
  *
  * Return -ENOENT to inform caller that we need fallback to unclustered mode.
  * Return -EAGAIN to inform caller that we need to re-search this block group
  * 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->search_start, ffe_ctl->num_bytes);
         *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);
             trace_btrfs_reserve_extent_cluster(bg,
                     ffe_ctl->search_start,
                     ffe_ctl->num_bytes);
             ffe_ctl->found_offset = offset;
             return 0;
         }
     } else if (!ffe_ctl->cached && ffe_ctl->loop > LOOP_CACHING_NOWAIT &&
            !ffe_ctl->retry_clustered) {
         spin_unlock(&last_ptr->refill_lock);
 
         ffe_ctl->retry_clustered = true;
         btrfs_wait_block_group_cache_progress(bg, ffe_ctl->num_bytes +
                 ffe_ctl->empty_cluster + ffe_ctl->empty_size);
         return -EAGAIN;
     }
     /*
      * 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
  * Return -EAGAIN to inform caller that we need to re-search this block group
  */
 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 we didn't find a chunk, and we haven't failed on this block group
      * before, and this block group is in the middle of caching and we are
      * ok with waiting, then go ahead and wait for progress to be made, and
      * set @retry_unclustered to true.
      *
      * If @retry_unclustered is true then we've already waited on this
      * block group once and should move on to the next block group.
      */
     if (!offset && !ffe_ctl->retry_unclustered && !ffe_ctl->cached &&
         ffe_ctl->loop > LOOP_CACHING_NOWAIT) {
         btrfs_wait_block_group_cache_progress(bg, ffe_ctl->num_bytes +
                               ffe_ctl->empty_size);
         ffe_ctl->retry_unclustered = true;
         return -EAGAIN;
     } else 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 || ret == -EAGAIN)
             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);
 
     if (!ret && !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 || block_group->zoned_data_reloc_ongoing) {
         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 && !fs_info->data_reloc_bg)
         fs_info->data_reloc_bg = block_group->start;
 
     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 == block_group->start) {
         /*
          * Do not allow further allocations from this block group.
          * 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.
          */
         block_group->zoned_data_reloc_ongoing = 1;
         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_clustered = false;
         ffe_ctl->retry_unclustered = 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)
 {
     /* 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();
     }
 }
 
 static int chunk_allocation_failed(struct find_free_extent_ctl *ffe_ctl)
 {
     switch (ffe_ctl->policy) {
     case BTRFS_EXTENT_ALLOC_CLUSTERED:
         /*
          * If we can't allocate a new chunk we've already looped through
          * at least once, move on to the NO_EMPTY_SIZE case.
          */
         ffe_ctl->loop = LOOP_NO_EMPTY_SIZE;
         return 0;
     case BTRFS_EXTENT_ALLOC_ZONED:
         /* Give up here */
         return -ENOSPC;
     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;
 
     /*
      * LOOP_CACHING_NOWAIT, search partially cached block groups, kicking
      *          caching kthreads as we move along
      * LOOP_CACHING_WAIT, search everything, and wait if our bg is caching
      * LOOP_ALLOC_CHUNK, force a chunk allocation and try again
      * LOOP_NO_EMPTY_SIZE, set empty_size and empty_cluster to 0 and try
      *             again
      */
     if (ffe_ctl->loop < LOOP_NO_EMPTY_SIZE) {
         ffe_ctl->index = 0;
         if (ffe_ctl->loop == LOOP_CACHING_NOWAIT) {
             /*
              * 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->orig_have_caching_bg || !full_search)
                 ffe_ctl->loop = LOOP_CACHING_WAIT;
             else
                 ffe_ctl->loop = LOOP_ALLOC_CHUNK;
         } else {
             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 = chunk_allocation_failed(ffe_ctl);
             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 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;
     /* For clustered allocation */
     ffe_ctl->retry_clustered = false;
     ffe_ctl->retry_unclustered = 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;
 
     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->num_bytes, ffe_ctl->empty_size,
                    ffe_ctl->flags);
 
     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);
                 goto have_block_group;
             }
         } else if (block_group) {
             btrfs_put_block_group(block_group);
         }
     }
 search:
     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;
 
         /* 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:
         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))
             goto loop;
 
         bg_ret = NULL;
         ret = do_allocation(block_group, ffe_ctl, &bg_ret);
         if (ret == 0) {
             if (bg_ret && bg_ret != block_group) {
                 btrfs_release_block_group(block_group,
                               ffe_ctl->delalloc);
                 block_group = bg_ret;
             }
         } else if (ret == -EAGAIN) {
             goto have_block_group;
         } else if (ret > 0) {
             goto loop;
         }
 
         /* 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);
         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->search_start,
                        ffe_ctl->num_bytes);
         btrfs_release_block_group(block_group, ffe_ctl->delalloc);
         break;
 loop:
         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;
 }
 
 /*
  * btrfs_reserve_extent - 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, u64 start,
                   u64 len)
 {
     struct btrfs_block_group *cache;
     int ret = 0;
 
     cache = btrfs_lookup_block_group(trans->fs_info, start);
     if (!cache) {
         btrfs_err(trans->fs_info, "unable to find block group for %llu",
               start);
         return -ENOSPC;
     }
 
     ret = pin_down_extent(trans, cache, start, 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(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(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;
 }
 
 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;
 
     /*
      * 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.
      */
     if (buf->lock_owner == current->pid) {
         btrfs_err_rl(fs_info,
 "tree block %llu owner %llu already locked by pid=%d, extent tree corruption detected",
             buf->start, btrfs_header_owner(buf), current->pid);
         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;
 
     /*
      * 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_clean_tree_block(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_dirty(&root->dirty_log_pages, buf->start,
                     buf->start + buf->len - 1, GFP_NOFS);
         else
             set_extent_new(&root->dirty_log_pages, buf->start,
                     buf->start + buf->len - 1);
     } else {
         buf->log_index = -1;
         set_extent_dirty(&trans->transaction->dirty_pages, buf->start,
              buf->start + buf->len - 1, GFP_NOFS);
     }
     /* 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,
                           btrfs_header_level(eb));
         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_key key;
     struct btrfs_key first_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]);
     btrfs_node_key_to_cpu(path->nodes[level], &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, root->root_key.objectid,
                        generation, level - 1, &first_key);
         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_clean_tree_block happy */
         if (!path->locks[level] &&
             btrfs_header_generation(eb) == trans->transid) {
             btrfs_tree_lock(eb);
             path->locks[level] = BTRFS_WRITE_LOCK;
         }
         btrfs_clean_tree_block(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;
 
     while (level >= 0) {
         ret = walk_down_proc(trans, root, path, wc, lookup_info);
         if (ret > 0)
             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)
             return ret;
         level = wc->level;
     }
     return 0;
 }
 
 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)
 {
     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) {
             err = ret;
             break;
         }
 
         ret = walk_up_tree(trans, root, path, wc, BTRFS_MAX_LEVEL);
         if (ret < 0) {
             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;
             }
 
             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 (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID) {
         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:
     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;
 }
 
 /*
  * helper to account the unused space of all the readonly block group in the
  * space_info. takes mirrors into account.
  */
 u64 btrfs_account_ro_block_groups_free_space(struct btrfs_space_info *sinfo)
 {
     struct btrfs_block_group *block_group;
     u64 free_bytes = 0;
     int factor;
 
     /* It's df, we don't care if it's racy */
     if (list_empty(&sinfo->ro_bgs))
         return 0;
 
     spin_lock(&sinfo->lock);
     list_for_each_entry(block_group, &sinfo->ro_bgs, ro_list) {
         spin_lock(&block_group->lock);
 
         if (!block_group->ro) {
             spin_unlock(&block_group->lock);
             continue;
         }
 
         factor = btrfs_bg_type_to_factor(block_group->flags);
         free_bytes += (block_group->length -
                    block_group->used) * factor;
 
         spin_unlock(&block_group->lock);
     }
     spin_unlock(&sinfo->lock);
 
     return free_bytes;
 }
 
 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,
                       rcu_str_deref(device->name),
                       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_bits(&device->alloc_state, start,
                     start + bytes - 1,
                     CHUNK_TRIMMED);
         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;
 }