OSCL-LXR linux-6.0.1/​fs/​btrfs/​extent_io.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
 
 #include <linux/bitops.h>
 #include <linux/slab.h>
 #include <linux/bio.h>
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/page-flags.h>
 #include <linux/sched/mm.h>
 #include <linux/spinlock.h>
 #include <linux/blkdev.h>
 #include <linux/swap.h>
 #include <linux/writeback.h>
 #include <linux/pagevec.h>
 #include <linux/prefetch.h>
 #include <linux/fsverity.h>
 #include "misc.h"
 #include "extent_io.h"
 #include "extent-io-tree.h"
 #include "extent_map.h"
 #include "ctree.h"
 #include "btrfs_inode.h"
 #include "volumes.h"
 #include "check-integrity.h"
 #include "locking.h"
 #include "rcu-string.h"
 #include "backref.h"
 #include "disk-io.h"
 #include "subpage.h"
 #include "zoned.h"
 #include "block-group.h"
 #include "compression.h"
 
 static struct kmem_cache *extent_state_cache;
 static struct kmem_cache *extent_buffer_cache;
 static struct bio_set btrfs_bioset;
 
 static inline bool extent_state_in_tree(const struct extent_state *state)
 {
     return !RB_EMPTY_NODE(&state->rb_node);
 }
 
 #ifdef CONFIG_BTRFS_DEBUG
 static LIST_HEAD(states);
 static DEFINE_SPINLOCK(leak_lock);
 
 static inline void btrfs_leak_debug_add(spinlock_t *lock,
                     struct list_head *new,
                     struct list_head *head)
 {
     unsigned long flags;
 
     spin_lock_irqsave(lock, flags);
     list_add(new, head);
     spin_unlock_irqrestore(lock, flags);
 }
 
 static inline void btrfs_leak_debug_del(spinlock_t *lock,
                     struct list_head *entry)
 {
     unsigned long flags;
 
     spin_lock_irqsave(lock, flags);
     list_del(entry);
     spin_unlock_irqrestore(lock, flags);
 }
 
 void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info)
 {
     struct extent_buffer *eb;
     unsigned long flags;
 
     /*
      * If we didn't get into open_ctree our allocated_ebs will not be
      * initialized, so just skip this.
      */
     if (!fs_info->allocated_ebs.next)
         return;
 
     WARN_ON(!list_empty(&fs_info->allocated_ebs));
     spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
     while (!list_empty(&fs_info->allocated_ebs)) {
         eb = list_first_entry(&fs_info->allocated_ebs,
                       struct extent_buffer, leak_list);
         pr_err(
     "BTRFS: buffer leak start %llu len %lu refs %d bflags %lu owner %llu\n",
                eb->start, eb->len, atomic_read(&eb->refs), eb->bflags,
                btrfs_header_owner(eb));
         list_del(&eb->leak_list);
         kmem_cache_free(extent_buffer_cache, eb);
     }
     spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
 }
 
 static inline void btrfs_extent_state_leak_debug_check(void)
 {
     struct extent_state *state;
 
     while (!list_empty(&states)) {
         state = list_entry(states.next, struct extent_state, leak_list);
         pr_err("BTRFS: state leak: start %llu end %llu state %u in tree %d refs %d\n",
                state->start, state->end, state->state,
                extent_state_in_tree(state),
                refcount_read(&state->refs));
         list_del(&state->leak_list);
         kmem_cache_free(extent_state_cache, state);
     }
 }
 
 #define btrfs_debug_check_extent_io_range(tree, start, end)     \
     __btrfs_debug_check_extent_io_range(__func__, (tree), (start), (end))
 static inline void __btrfs_debug_check_extent_io_range(const char *caller,
         struct extent_io_tree *tree, u64 start, u64 end)
 {
     struct inode *inode = tree->private_data;
     u64 isize;
 
     if (!inode || !is_data_inode(inode))
         return;
 
     isize = i_size_read(inode);
     if (end >= PAGE_SIZE && (end % 2) == 0 && end != isize - 1) {
         btrfs_debug_rl(BTRFS_I(inode)->root->fs_info,
             "%s: ino %llu isize %llu odd range [%llu,%llu]",
             caller, btrfs_ino(BTRFS_I(inode)), isize, start, end);
     }
 }
 #else
 #define btrfs_leak_debug_add(lock, new, head)   do {} while (0)
 #define btrfs_leak_debug_del(lock, entry)   do {} while (0)
 #define btrfs_extent_state_leak_debug_check()   do {} while (0)
 #define btrfs_debug_check_extent_io_range(c, s, e)  do {} while (0)
 #endif
 
 struct tree_entry {
     u64 start;
     u64 end;
     struct rb_node rb_node;
 };
 
 /*
  * Structure to record info about the bio being assembled, and other info like
  * how many bytes are there before stripe/ordered extent boundary.
  */
 struct btrfs_bio_ctrl {
     struct bio *bio;
     int mirror_num;
     enum btrfs_compression_type compress_type;
     u32 len_to_stripe_boundary;
     u32 len_to_oe_boundary;
 };
 
 struct extent_page_data {
     struct btrfs_bio_ctrl bio_ctrl;
     /* tells writepage not to lock the state bits for this range
      * it still does the unlocking
      */
     unsigned int extent_locked:1;
 
     /* tells the submit_bio code to use REQ_SYNC */
     unsigned int sync_io:1;
 };
 
 static int add_extent_changeset(struct extent_state *state, u32 bits,
                  struct extent_changeset *changeset,
                  int set)
 {
     int ret;
 
     if (!changeset)
         return 0;
     if (set && (state->state & bits) == bits)
         return 0;
     if (!set && (state->state & bits) == 0)
         return 0;
     changeset->bytes_changed += state->end - state->start + 1;
     ret = ulist_add(&changeset->range_changed, state->start, state->end,
             GFP_ATOMIC);
     return ret;
 }
 
 static void submit_one_bio(struct btrfs_bio_ctrl *bio_ctrl)
 {
     struct bio *bio;
     struct bio_vec *bv;
     struct inode *inode;
     int mirror_num;
 
     if (!bio_ctrl->bio)
         return;
 
     bio = bio_ctrl->bio;
     bv = bio_first_bvec_all(bio);
     inode = bv->bv_page->mapping->host;
     mirror_num = bio_ctrl->mirror_num;
 
     /* Caller should ensure the bio has at least some range added */
     ASSERT(bio->bi_iter.bi_size);
 
     btrfs_bio(bio)->file_offset = page_offset(bv->bv_page) + bv->bv_offset;
 
     if (!is_data_inode(inode))
         btrfs_submit_metadata_bio(inode, bio, mirror_num);
     else if (btrfs_op(bio) == BTRFS_MAP_WRITE)
         btrfs_submit_data_write_bio(inode, bio, mirror_num);
     else
         btrfs_submit_data_read_bio(inode, bio, mirror_num,
                        bio_ctrl->compress_type);
 
     /* The bio is owned by the bi_end_io handler now */
     bio_ctrl->bio = NULL;
 }
 
 /*
  * Submit or fail the current bio in an extent_page_data structure.
  */
 static void submit_write_bio(struct extent_page_data *epd, int ret)
 {
     struct bio *bio = epd->bio_ctrl.bio;
 
     if (!bio)
         return;
 
     if (ret) {
         ASSERT(ret < 0);
         bio->bi_status = errno_to_blk_status(ret);
         bio_endio(bio);
         /* The bio is owned by the bi_end_io handler now */
         epd->bio_ctrl.bio = NULL;
     } else {
         submit_one_bio(&epd->bio_ctrl);
     }
 }
 
 int __init extent_state_cache_init(void)
 {
     extent_state_cache = kmem_cache_create("btrfs_extent_state",
             sizeof(struct extent_state), 0,
             SLAB_MEM_SPREAD, NULL);
     if (!extent_state_cache)
         return -ENOMEM;
     return 0;
 }
 
 int __init extent_io_init(void)
 {
     extent_buffer_cache = kmem_cache_create("btrfs_extent_buffer",
             sizeof(struct extent_buffer), 0,
             SLAB_MEM_SPREAD, NULL);
     if (!extent_buffer_cache)
         return -ENOMEM;
 
     if (bioset_init(&btrfs_bioset, BIO_POOL_SIZE,
             offsetof(struct btrfs_bio, bio),
             BIOSET_NEED_BVECS))
         goto free_buffer_cache;
 
     if (bioset_integrity_create(&btrfs_bioset, BIO_POOL_SIZE))
         goto free_bioset;
 
     return 0;
 
 free_bioset:
     bioset_exit(&btrfs_bioset);
 
 free_buffer_cache:
     kmem_cache_destroy(extent_buffer_cache);
     extent_buffer_cache = NULL;
     return -ENOMEM;
 }
 
 void __cold extent_state_cache_exit(void)
 {
     btrfs_extent_state_leak_debug_check();
     kmem_cache_destroy(extent_state_cache);
 }
 
 void __cold extent_io_exit(void)
 {
     /*
      * Make sure all delayed rcu free are flushed before we
      * destroy caches.
      */
     rcu_barrier();
     kmem_cache_destroy(extent_buffer_cache);
     bioset_exit(&btrfs_bioset);
 }
 
 /*
  * For the file_extent_tree, we want to hold the inode lock when we lookup and
  * update the disk_i_size, but lockdep will complain because our io_tree we hold
  * the tree lock and get the inode lock when setting delalloc.  These two things
  * are unrelated, so make a class for the file_extent_tree so we don't get the
  * two locking patterns mixed up.
  */
 static struct lock_class_key file_extent_tree_class;
 
 void extent_io_tree_init(struct btrfs_fs_info *fs_info,
              struct extent_io_tree *tree, unsigned int owner,
              void *private_data)
 {
     tree->fs_info = fs_info;
     tree->state = RB_ROOT;
     tree->dirty_bytes = 0;
     spin_lock_init(&tree->lock);
     tree->private_data = private_data;
     tree->owner = owner;
     if (owner == IO_TREE_INODE_FILE_EXTENT)
         lockdep_set_class(&tree->lock, &file_extent_tree_class);
 }
 
 void extent_io_tree_release(struct extent_io_tree *tree)
 {
     spin_lock(&tree->lock);
     /*
      * Do a single barrier for the waitqueue_active check here, the state
      * of the waitqueue should not change once extent_io_tree_release is
      * called.
      */
     smp_mb();
     while (!RB_EMPTY_ROOT(&tree->state)) {
         struct rb_node *node;
         struct extent_state *state;
 
         node = rb_first(&tree->state);
         state = rb_entry(node, struct extent_state, rb_node);
         rb_erase(&state->rb_node, &tree->state);
         RB_CLEAR_NODE(&state->rb_node);
         /*
          * btree io trees aren't supposed to have tasks waiting for
          * changes in the flags of extent states ever.
          */
         ASSERT(!waitqueue_active(&state->wq));
         free_extent_state(state);
 
         cond_resched_lock(&tree->lock);
     }
     spin_unlock(&tree->lock);
 }
 
 static struct extent_state *alloc_extent_state(gfp_t mask)
 {
     struct extent_state *state;
 
     /*
      * The given mask might be not appropriate for the slab allocator,
      * drop the unsupported bits
      */
     mask &= ~(__GFP_DMA32|__GFP_HIGHMEM);
     state = kmem_cache_alloc(extent_state_cache, mask);
     if (!state)
         return state;
     state->state = 0;
     state->failrec = NULL;
     RB_CLEAR_NODE(&state->rb_node);
     btrfs_leak_debug_add(&leak_lock, &state->leak_list, &states);
     refcount_set(&state->refs, 1);
     init_waitqueue_head(&state->wq);
     trace_alloc_extent_state(state, mask, _RET_IP_);
     return state;
 }
 
 void free_extent_state(struct extent_state *state)
 {
     if (!state)
         return;
     if (refcount_dec_and_test(&state->refs)) {
         WARN_ON(extent_state_in_tree(state));
         btrfs_leak_debug_del(&leak_lock, &state->leak_list);
         trace_free_extent_state(state, _RET_IP_);
         kmem_cache_free(extent_state_cache, state);
     }
 }
 
 /**
  * Search @tree for an entry that contains @offset. Such entry would have
  * entry->start <= offset && entry->end >= offset.
  *
  * @tree:       the tree to search
  * @offset:     offset that should fall within an entry in @tree
  * @node_ret:   pointer where new node should be anchored (used when inserting an
  *          entry in the tree)
  * @parent_ret: points to entry which would have been the parent of the entry,
  *               containing @offset
  *
  * Return a pointer to the entry that contains @offset byte address and don't change
  * @node_ret and @parent_ret.
  *
  * If no such entry exists, return pointer to entry that ends before @offset
  * and fill parameters @node_ret and @parent_ret, ie. does not return NULL.
  */
 static inline struct rb_node *tree_search_for_insert(struct extent_io_tree *tree,
                                  u64 offset,
                              struct rb_node ***node_ret,
                              struct rb_node **parent_ret)
 {
     struct rb_root *root = &tree->state;
     struct rb_node **node = &root->rb_node;
     struct rb_node *prev = NULL;
     struct tree_entry *entry;
 
     while (*node) {
         prev = *node;
         entry = rb_entry(prev, struct tree_entry, rb_node);
 
         if (offset < entry->start)
             node = &(*node)->rb_left;
         else if (offset > entry->end)
             node = &(*node)->rb_right;
         else
             return *node;
     }
 
     if (node_ret)
         *node_ret = node;
     if (parent_ret)
         *parent_ret = prev;
 
     /* Search neighbors until we find the first one past the end */
     while (prev && offset > entry->end) {
         prev = rb_next(prev);
         entry = rb_entry(prev, struct tree_entry, rb_node);
     }
 
     return prev;
 }
 
 /*
  * Inexact rb-tree search, return the next entry if @offset is not found
  */
 static inline struct rb_node *tree_search(struct extent_io_tree *tree, u64 offset)
 {
     return tree_search_for_insert(tree, offset, NULL, NULL);
 }
 
 /**
  * Search offset in the tree or fill neighbor rbtree node pointers.
  *
  * @tree:      the tree to search
  * @offset:    offset that should fall within an entry in @tree
  * @next_ret:  pointer to the first entry whose range ends after @offset
  * @prev_ret:  pointer to the first entry whose range begins before @offset
  *
  * Return a pointer to the entry that contains @offset byte address. If no
  * such entry exists, then return NULL and fill @prev_ret and @next_ret.
  * Otherwise return the found entry and other pointers are left untouched.
  */
 static struct rb_node *tree_search_prev_next(struct extent_io_tree *tree,
                          u64 offset,
                          struct rb_node **prev_ret,
                          struct rb_node **next_ret)
 {
     struct rb_root *root = &tree->state;
     struct rb_node **node = &root->rb_node;
     struct rb_node *prev = NULL;
     struct rb_node *orig_prev = NULL;
     struct tree_entry *entry;
 
     ASSERT(prev_ret);
     ASSERT(next_ret);
 
     while (*node) {
         prev = *node;
         entry = rb_entry(prev, struct tree_entry, rb_node);
 
         if (offset < entry->start)
             node = &(*node)->rb_left;
         else if (offset > entry->end)
             node = &(*node)->rb_right;
         else
             return *node;
     }
 
     orig_prev = prev;
     while (prev && offset > entry->end) {
         prev = rb_next(prev);
         entry = rb_entry(prev, struct tree_entry, rb_node);
     }
     *next_ret = prev;
     prev = orig_prev;
 
     entry = rb_entry(prev, struct tree_entry, rb_node);
     while (prev && offset < entry->start) {
         prev = rb_prev(prev);
         entry = rb_entry(prev, struct tree_entry, rb_node);
     }
     *prev_ret = prev;
 
     return NULL;
 }
 
 /*
  * utility function to look for merge candidates inside a given range.
  * Any extents with matching state are merged together into a single
  * extent in the tree.  Extents with EXTENT_IO in their state field
  * are not merged because the end_io handlers need to be able to do
  * operations on them without sleeping (or doing allocations/splits).
  *
  * This should be called with the tree lock held.
  */
 static void merge_state(struct extent_io_tree *tree,
                 struct extent_state *state)
 {
     struct extent_state *other;
     struct rb_node *other_node;
 
     if (state->state & (EXTENT_LOCKED | EXTENT_BOUNDARY))
         return;
 
     other_node = rb_prev(&state->rb_node);
     if (other_node) {
         other = rb_entry(other_node, struct extent_state, rb_node);
         if (other->end == state->start - 1 &&
             other->state == state->state) {
             if (tree->private_data &&
                 is_data_inode(tree->private_data))
                 btrfs_merge_delalloc_extent(tree->private_data,
                                 state, other);
             state->start = other->start;
             rb_erase(&other->rb_node, &tree->state);
             RB_CLEAR_NODE(&other->rb_node);
             free_extent_state(other);
         }
     }
     other_node = rb_next(&state->rb_node);
     if (other_node) {
         other = rb_entry(other_node, struct extent_state, rb_node);
         if (other->start == state->end + 1 &&
             other->state == state->state) {
             if (tree->private_data &&
                 is_data_inode(tree->private_data))
                 btrfs_merge_delalloc_extent(tree->private_data,
                                 state, other);
             state->end = other->end;
             rb_erase(&other->rb_node, &tree->state);
             RB_CLEAR_NODE(&other->rb_node);
             free_extent_state(other);
         }
     }
 }
 
 static void set_state_bits(struct extent_io_tree *tree,
                struct extent_state *state, u32 bits,
                struct extent_changeset *changeset);
 
 /*
  * insert an extent_state struct into the tree.  'bits' are set on the
  * struct before it is inserted.
  *
  * This may return -EEXIST if the extent is already there, in which case the
  * state struct is freed.
  *
  * The tree lock is not taken internally.  This is a utility function and
  * probably isn't what you want to call (see set/clear_extent_bit).
  */
 static int insert_state(struct extent_io_tree *tree,
             struct extent_state *state,
             u32 bits, struct extent_changeset *changeset)
 {
     struct rb_node **node;
     struct rb_node *parent;
     const u64 end = state->end;
 
     set_state_bits(tree, state, bits, changeset);
 
     node = &tree->state.rb_node;
     while (*node) {
         struct tree_entry *entry;
 
         parent = *node;
         entry = rb_entry(parent, struct tree_entry, rb_node);
 
         if (end < entry->start) {
             node = &(*node)->rb_left;
         } else if (end > entry->end) {
             node = &(*node)->rb_right;
         } else {
             btrfs_err(tree->fs_info,
                    "found node %llu %llu on insert of %llu %llu",
                    entry->start, entry->end, state->start, end);
             return -EEXIST;
         }
     }
 
     rb_link_node(&state->rb_node, parent, node);
     rb_insert_color(&state->rb_node, &tree->state);
 
     merge_state(tree, state);
     return 0;
 }
 
 /*
  * Insert state to @tree to the location given by @node and @parent.
  */
 static void insert_state_fast(struct extent_io_tree *tree,
                   struct extent_state *state, struct rb_node **node,
                   struct rb_node *parent, unsigned bits,
                   struct extent_changeset *changeset)
 {
     set_state_bits(tree, state, bits, changeset);
     rb_link_node(&state->rb_node, parent, node);
     rb_insert_color(&state->rb_node, &tree->state);
     merge_state(tree, state);
 }
 
 /*
  * split a given extent state struct in two, inserting the preallocated
  * struct 'prealloc' as the newly created second half.  'split' indicates an
  * offset inside 'orig' where it should be split.
  *
  * Before calling,
  * the tree has 'orig' at [orig->start, orig->end].  After calling, there
  * are two extent state structs in the tree:
  * prealloc: [orig->start, split - 1]
  * orig: [ split, orig->end ]
  *
  * The tree locks are not taken by this function. They need to be held
  * by the caller.
  */
 static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
                struct extent_state *prealloc, u64 split)
 {
     struct rb_node *parent = NULL;
     struct rb_node **node;
 
     if (tree->private_data && is_data_inode(tree->private_data))
         btrfs_split_delalloc_extent(tree->private_data, orig, split);
 
     prealloc->start = orig->start;
     prealloc->end = split - 1;
     prealloc->state = orig->state;
     orig->start = split;
 
     parent = &orig->rb_node;
     node = &parent;
     while (*node) {
         struct tree_entry *entry;
 
         parent = *node;
         entry = rb_entry(parent, struct tree_entry, rb_node);
 
         if (prealloc->end < entry->start) {
             node = &(*node)->rb_left;
         } else if (prealloc->end > entry->end) {
             node = &(*node)->rb_right;
         } else {
             free_extent_state(prealloc);
             return -EEXIST;
         }
     }
 
     rb_link_node(&prealloc->rb_node, parent, node);
     rb_insert_color(&prealloc->rb_node, &tree->state);
 
     return 0;
 }
 
 static struct extent_state *next_state(struct extent_state *state)
 {
     struct rb_node *next = rb_next(&state->rb_node);
     if (next)
         return rb_entry(next, struct extent_state, rb_node);
     else
         return NULL;
 }
 
 /*
  * utility function to clear some bits in an extent state struct.
  * it will optionally wake up anyone waiting on this state (wake == 1).
  *
  * If no bits are set on the state struct after clearing things, the
  * struct is freed and removed from the tree
  */
 static struct extent_state *clear_state_bit(struct extent_io_tree *tree,
                         struct extent_state *state,
                         u32 bits, int wake,
                         struct extent_changeset *changeset)
 {
     struct extent_state *next;
     u32 bits_to_clear = bits & ~EXTENT_CTLBITS;
     int ret;
 
     if ((bits_to_clear & EXTENT_DIRTY) && (state->state & EXTENT_DIRTY)) {
         u64 range = state->end - state->start + 1;
         WARN_ON(range > tree->dirty_bytes);
         tree->dirty_bytes -= range;
     }
 
     if (tree->private_data && is_data_inode(tree->private_data))
         btrfs_clear_delalloc_extent(tree->private_data, state, bits);
 
     ret = add_extent_changeset(state, bits_to_clear, changeset, 0);
     BUG_ON(ret < 0);
     state->state &= ~bits_to_clear;
     if (wake)
         wake_up(&state->wq);
     if (state->state == 0) {
         next = next_state(state);
         if (extent_state_in_tree(state)) {
             rb_erase(&state->rb_node, &tree->state);
             RB_CLEAR_NODE(&state->rb_node);
             free_extent_state(state);
         } else {
             WARN_ON(1);
         }
     } else {
         merge_state(tree, state);
         next = next_state(state);
     }
     return next;
 }
 
 static struct extent_state *
 alloc_extent_state_atomic(struct extent_state *prealloc)
 {
     if (!prealloc)
         prealloc = alloc_extent_state(GFP_ATOMIC);
 
     return prealloc;
 }
 
 static void extent_io_tree_panic(struct extent_io_tree *tree, int err)
 {
     btrfs_panic(tree->fs_info, err,
     "locking error: extent tree was modified by another thread while locked");
 }
 
 /*
  * clear some bits on a range in the tree.  This may require splitting
  * or inserting elements in the tree, so the gfp mask is used to
  * indicate which allocations or sleeping are allowed.
  *
  * pass 'wake' == 1 to kick any sleepers, and 'delete' == 1 to remove
  * the given range from the tree regardless of state (ie for truncate).
  *
  * the range [start, end] is inclusive.
  *
  * This takes the tree lock, and returns 0 on success and < 0 on error.
  */
 int __clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                u32 bits, int wake, int delete,
                struct extent_state **cached_state,
                gfp_t mask, struct extent_changeset *changeset)
 {
     struct extent_state *state;
     struct extent_state *cached;
     struct extent_state *prealloc = NULL;
     struct rb_node *node;
     u64 last_end;
     int err;
     int clear = 0;
 
     btrfs_debug_check_extent_io_range(tree, start, end);
     trace_btrfs_clear_extent_bit(tree, start, end - start + 1, bits);
 
     if (bits & EXTENT_DELALLOC)
         bits |= EXTENT_NORESERVE;
 
     if (delete)
         bits |= ~EXTENT_CTLBITS;
 
     if (bits & (EXTENT_LOCKED | EXTENT_BOUNDARY))
         clear = 1;
 again:
     if (!prealloc && gfpflags_allow_blocking(mask)) {
         /*
          * Don't care for allocation failure here because we might end
          * up not needing the pre-allocated extent state at all, which
          * is the case if we only have in the tree extent states that
          * cover our input range and don't cover too any other range.
          * If we end up needing a new extent state we allocate it later.
          */
         prealloc = alloc_extent_state(mask);
     }
 
     spin_lock(&tree->lock);
     if (cached_state) {
         cached = *cached_state;
 
         if (clear) {
             *cached_state = NULL;
             cached_state = NULL;
         }
 
         if (cached && extent_state_in_tree(cached) &&
             cached->start <= start && cached->end > start) {
             if (clear)
                 refcount_dec(&cached->refs);
             state = cached;
             goto hit_next;
         }
         if (clear)
             free_extent_state(cached);
     }
     /*
      * this search will find the extents that end after
      * our range starts
      */
     node = tree_search(tree, start);
     if (!node)
         goto out;
     state = rb_entry(node, struct extent_state, rb_node);
 hit_next:
     if (state->start > end)
         goto out;
     WARN_ON(state->end < start);
     last_end = state->end;
 
     /* the state doesn't have the wanted bits, go ahead */
     if (!(state->state & bits)) {
         state = next_state(state);
         goto next;
     }
 
     /*
      *     | ---- desired range ---- |
      *  | state | or
      *  | ------------- state -------------- |
      *
      * We need to split the extent we found, and may flip
      * bits on second half.
      *
      * If the extent we found extends past our range, we
      * just split and search again.  It'll get split again
      * the next time though.
      *
      * If the extent we found is inside our range, we clear
      * the desired bit on it.
      */
 
     if (state->start < start) {
         prealloc = alloc_extent_state_atomic(prealloc);
         BUG_ON(!prealloc);
         err = split_state(tree, state, prealloc, start);
         if (err)
             extent_io_tree_panic(tree, err);
 
         prealloc = NULL;
         if (err)
             goto out;
         if (state->end <= end) {
             state = clear_state_bit(tree, state, bits, wake, changeset);
             goto next;
         }
         goto search_again;
     }
     /*
      * | ---- desired range ---- |
      *                        | state |
      * We need to split the extent, and clear the bit
      * on the first half
      */
     if (state->start <= end && state->end > end) {
         prealloc = alloc_extent_state_atomic(prealloc);
         BUG_ON(!prealloc);
         err = split_state(tree, state, prealloc, end + 1);
         if (err)
             extent_io_tree_panic(tree, err);
 
         if (wake)
             wake_up(&state->wq);
 
         clear_state_bit(tree, prealloc, bits, wake, changeset);
 
         prealloc = NULL;
         goto out;
     }
 
     state = clear_state_bit(tree, state, bits, wake, changeset);
 next:
     if (last_end == (u64)-1)
         goto out;
     start = last_end + 1;
     if (start <= end && state && !need_resched())
         goto hit_next;
 
 search_again:
     if (start > end)
         goto out;
     spin_unlock(&tree->lock);
     if (gfpflags_allow_blocking(mask))
         cond_resched();
     goto again;
 
 out:
     spin_unlock(&tree->lock);
     if (prealloc)
         free_extent_state(prealloc);
 
     return 0;
 
 }
 
 static void wait_on_state(struct extent_io_tree *tree,
               struct extent_state *state)
         __releases(tree->lock)
         __acquires(tree->lock)
 {
     DEFINE_WAIT(wait);
     prepare_to_wait(&state->wq, &wait, TASK_UNINTERRUPTIBLE);
     spin_unlock(&tree->lock);
     schedule();
     spin_lock(&tree->lock);
     finish_wait(&state->wq, &wait);
 }
 
 /*
  * waits for one or more bits to clear on a range in the state tree.
  * The range [start, end] is inclusive.
  * The tree lock is taken by this function
  */
 static void wait_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                 u32 bits)
 {
     struct extent_state *state;
     struct rb_node *node;
 
     btrfs_debug_check_extent_io_range(tree, start, end);
 
     spin_lock(&tree->lock);
 again:
     while (1) {
         /*
          * this search will find all the extents that end after
          * our range starts
          */
         node = tree_search(tree, start);
 process_node:
         if (!node)
             break;
 
         state = rb_entry(node, struct extent_state, rb_node);
 
         if (state->start > end)
             goto out;
 
         if (state->state & bits) {
             start = state->start;
             refcount_inc(&state->refs);
             wait_on_state(tree, state);
             free_extent_state(state);
             goto again;
         }
         start = state->end + 1;
 
         if (start > end)
             break;
 
         if (!cond_resched_lock(&tree->lock)) {
             node = rb_next(node);
             goto process_node;
         }
     }
 out:
     spin_unlock(&tree->lock);
 }
 
 static void set_state_bits(struct extent_io_tree *tree,
                struct extent_state *state,
                u32 bits, struct extent_changeset *changeset)
 {
     u32 bits_to_set = bits & ~EXTENT_CTLBITS;
     int ret;
 
     if (tree->private_data && is_data_inode(tree->private_data))
         btrfs_set_delalloc_extent(tree->private_data, state, bits);
 
     if ((bits_to_set & EXTENT_DIRTY) && !(state->state & EXTENT_DIRTY)) {
         u64 range = state->end - state->start + 1;
         tree->dirty_bytes += range;
     }
     ret = add_extent_changeset(state, bits_to_set, changeset, 1);
     BUG_ON(ret < 0);
     state->state |= bits_to_set;
 }
 
 static void cache_state_if_flags(struct extent_state *state,
                  struct extent_state **cached_ptr,
                  unsigned flags)
 {
     if (cached_ptr && !(*cached_ptr)) {
         if (!flags || (state->state & flags)) {
             *cached_ptr = state;
             refcount_inc(&state->refs);
         }
     }
 }
 
 static void cache_state(struct extent_state *state,
             struct extent_state **cached_ptr)
 {
     return cache_state_if_flags(state, cached_ptr,
                     EXTENT_LOCKED | EXTENT_BOUNDARY);
 }
 
 /*
  * set some bits on a range in the tree.  This may require allocations or
  * sleeping, so the gfp mask is used to indicate what is allowed.
  *
  * If any of the exclusive bits are set, this will fail with -EEXIST if some
  * part of the range already has the desired bits set.  The start of the
  * existing range is returned in failed_start in this case.
  *
  * [start, end] is inclusive This takes the tree lock.
  */
 int set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end, u32 bits,
            u32 exclusive_bits, u64 *failed_start,
            struct extent_state **cached_state, gfp_t mask,
            struct extent_changeset *changeset)
 {
     struct extent_state *state;
     struct extent_state *prealloc = NULL;
     struct rb_node *node;
     struct rb_node **p;
     struct rb_node *parent;
     int err = 0;
     u64 last_start;
     u64 last_end;
 
     btrfs_debug_check_extent_io_range(tree, start, end);
     trace_btrfs_set_extent_bit(tree, start, end - start + 1, bits);
 
     if (exclusive_bits)
         ASSERT(failed_start);
     else
         ASSERT(failed_start == NULL);
 again:
     if (!prealloc && gfpflags_allow_blocking(mask)) {
         /*
          * Don't care for allocation failure here because we might end
          * up not needing the pre-allocated extent state at all, which
          * is the case if we only have in the tree extent states that
          * cover our input range and don't cover too any other range.
          * If we end up needing a new extent state we allocate it later.
          */
         prealloc = alloc_extent_state(mask);
     }
 
     spin_lock(&tree->lock);
     if (cached_state && *cached_state) {
         state = *cached_state;
         if (state->start <= start && state->end > start &&
             extent_state_in_tree(state)) {
             node = &state->rb_node;
             goto hit_next;
         }
     }
     /*
      * this search will find all the extents that end after
      * our range starts.
      */
     node = tree_search_for_insert(tree, start, &p, &parent);
     if (!node) {
         prealloc = alloc_extent_state_atomic(prealloc);
         BUG_ON(!prealloc);
         prealloc->start = start;
         prealloc->end = end;
         insert_state_fast(tree, prealloc, p, parent, bits, changeset);
         cache_state(prealloc, cached_state);
         prealloc = NULL;
         goto out;
     }
     state = rb_entry(node, struct extent_state, rb_node);
 hit_next:
     last_start = state->start;
     last_end = state->end;
 
     /*
      * | ---- desired range ---- |
      * | state |
      *
      * Just lock what we found and keep going
      */
     if (state->start == start && state->end <= end) {
         if (state->state & exclusive_bits) {
             *failed_start = state->start;
             err = -EEXIST;
             goto out;
         }
 
         set_state_bits(tree, state, bits, changeset);
         cache_state(state, cached_state);
         merge_state(tree, state);
         if (last_end == (u64)-1)
             goto out;
         start = last_end + 1;
         state = next_state(state);
         if (start < end && state && state->start == start &&
             !need_resched())
             goto hit_next;
         goto search_again;
     }
 
     /*
      *     | ---- desired range ---- |
      * | state |
      *   or
      * | ------------- state -------------- |
      *
      * We need to split the extent we found, and may flip bits on
      * second half.
      *
      * If the extent we found extends past our
      * range, we just split and search again.  It'll get split
      * again the next time though.
      *
      * If the extent we found is inside our range, we set the
      * desired bit on it.
      */
     if (state->start < start) {
         if (state->state & exclusive_bits) {
             *failed_start = start;
             err = -EEXIST;
             goto out;
         }
 
         /*
          * If this extent already has all the bits we want set, then
          * skip it, not necessary to split it or do anything with it.
          */
         if ((state->state & bits) == bits) {
             start = state->end + 1;
             cache_state(state, cached_state);
             goto search_again;
         }
 
         prealloc = alloc_extent_state_atomic(prealloc);
         BUG_ON(!prealloc);
         err = split_state(tree, state, prealloc, start);
         if (err)
             extent_io_tree_panic(tree, err);
 
         prealloc = NULL;
         if (err)
             goto out;
         if (state->end <= end) {
             set_state_bits(tree, state, bits, changeset);
             cache_state(state, cached_state);
             merge_state(tree, state);
             if (last_end == (u64)-1)
                 goto out;
             start = last_end + 1;
             state = next_state(state);
             if (start < end && state && state->start == start &&
                 !need_resched())
                 goto hit_next;
         }
         goto search_again;
     }
     /*
      * | ---- desired range ---- |
      *     | state | or               | state |
      *
      * There's a hole, we need to insert something in it and
      * ignore the extent we found.
      */
     if (state->start > start) {
         u64 this_end;
         if (end < last_start)
             this_end = end;
         else
             this_end = last_start - 1;
 
         prealloc = alloc_extent_state_atomic(prealloc);
         BUG_ON(!prealloc);
 
         /*
          * Avoid to free 'prealloc' if it can be merged with
          * the later extent.
          */
         prealloc->start = start;
         prealloc->end = this_end;
         err = insert_state(tree, prealloc, bits, changeset);
         if (err)
             extent_io_tree_panic(tree, err);
 
         cache_state(prealloc, cached_state);
         prealloc = NULL;
         start = this_end + 1;
         goto search_again;
     }
     /*
      * | ---- desired range ---- |
      *                        | state |
      * We need to split the extent, and set the bit
      * on the first half
      */
     if (state->start <= end && state->end > end) {
         if (state->state & exclusive_bits) {
             *failed_start = start;
             err = -EEXIST;
             goto out;
         }
 
         prealloc = alloc_extent_state_atomic(prealloc);
         BUG_ON(!prealloc);
         err = split_state(tree, state, prealloc, end + 1);
         if (err)
             extent_io_tree_panic(tree, err);
 
         set_state_bits(tree, prealloc, bits, changeset);
         cache_state(prealloc, cached_state);
         merge_state(tree, prealloc);
         prealloc = NULL;
         goto out;
     }
 
 search_again:
     if (start > end)
         goto out;
     spin_unlock(&tree->lock);
     if (gfpflags_allow_blocking(mask))
         cond_resched();
     goto again;
 
 out:
     spin_unlock(&tree->lock);
     if (prealloc)
         free_extent_state(prealloc);
 
     return err;
 
 }
 
 /**
  * convert_extent_bit - convert all bits in a given range from one bit to
  *          another
  * @tree:   the io tree to search
  * @start:  the start offset in bytes
  * @end:    the end offset in bytes (inclusive)
  * @bits:   the bits to set in this range
  * @clear_bits: the bits to clear in this range
  * @cached_state:   state that we're going to cache
  *
  * This will go through and set bits for the given range.  If any states exist
  * already in this range they are set with the given bit and cleared of the
  * clear_bits.  This is only meant to be used by things that are mergeable, ie
  * converting from say DELALLOC to DIRTY.  This is not meant to be used with
  * boundary bits like LOCK.
  *
  * All allocations are done with GFP_NOFS.
  */
 int convert_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                u32 bits, u32 clear_bits,
                struct extent_state **cached_state)
 {
     struct extent_state *state;
     struct extent_state *prealloc = NULL;
     struct rb_node *node;
     struct rb_node **p;
     struct rb_node *parent;
     int err = 0;
     u64 last_start;
     u64 last_end;
     bool first_iteration = true;
 
     btrfs_debug_check_extent_io_range(tree, start, end);
     trace_btrfs_convert_extent_bit(tree, start, end - start + 1, bits,
                        clear_bits);
 
 again:
     if (!prealloc) {
         /*
          * Best effort, don't worry if extent state allocation fails
          * here for the first iteration. We might have a cached state
          * that matches exactly the target range, in which case no
          * extent state allocations are needed. We'll only know this
          * after locking the tree.
          */
         prealloc = alloc_extent_state(GFP_NOFS);
         if (!prealloc && !first_iteration)
             return -ENOMEM;
     }
 
     spin_lock(&tree->lock);
     if (cached_state && *cached_state) {
         state = *cached_state;
         if (state->start <= start && state->end > start &&
             extent_state_in_tree(state)) {
             node = &state->rb_node;
             goto hit_next;
         }
     }
 
     /*
      * this search will find all the extents that end after
      * our range starts.
      */
     node = tree_search_for_insert(tree, start, &p, &parent);
     if (!node) {
         prealloc = alloc_extent_state_atomic(prealloc);
         if (!prealloc) {
             err = -ENOMEM;
             goto out;
         }
         prealloc->start = start;
         prealloc->end = end;
         insert_state_fast(tree, prealloc, p, parent, bits, NULL);
         cache_state(prealloc, cached_state);
         prealloc = NULL;
         goto out;
     }
     state = rb_entry(node, struct extent_state, rb_node);
 hit_next:
     last_start = state->start;
     last_end = state->end;
 
     /*
      * | ---- desired range ---- |
      * | state |
      *
      * Just lock what we found and keep going
      */
     if (state->start == start && state->end <= end) {
         set_state_bits(tree, state, bits, NULL);
         cache_state(state, cached_state);
         state = clear_state_bit(tree, state, clear_bits, 0, NULL);
         if (last_end == (u64)-1)
             goto out;
         start = last_end + 1;
         if (start < end && state && state->start == start &&
             !need_resched())
             goto hit_next;
         goto search_again;
     }
 
     /*
      *     | ---- desired range ---- |
      * | state |
      *   or
      * | ------------- state -------------- |
      *
      * We need to split the extent we found, and may flip bits on
      * second half.
      *
      * If the extent we found extends past our
      * range, we just split and search again.  It'll get split
      * again the next time though.
      *
      * If the extent we found is inside our range, we set the
      * desired bit on it.
      */
     if (state->start < start) {
         prealloc = alloc_extent_state_atomic(prealloc);
         if (!prealloc) {
             err = -ENOMEM;
             goto out;
         }
         err = split_state(tree, state, prealloc, start);
         if (err)
             extent_io_tree_panic(tree, err);
         prealloc = NULL;
         if (err)
             goto out;
         if (state->end <= end) {
             set_state_bits(tree, state, bits, NULL);
             cache_state(state, cached_state);
             state = clear_state_bit(tree, state, clear_bits, 0, NULL);
             if (last_end == (u64)-1)
                 goto out;
             start = last_end + 1;
             if (start < end && state && state->start == start &&
                 !need_resched())
                 goto hit_next;
         }
         goto search_again;
     }
     /*
      * | ---- desired range ---- |
      *     | state | or               | state |
      *
      * There's a hole, we need to insert something in it and
      * ignore the extent we found.
      */
     if (state->start > start) {
         u64 this_end;
         if (end < last_start)
             this_end = end;
         else
             this_end = last_start - 1;
 
         prealloc = alloc_extent_state_atomic(prealloc);
         if (!prealloc) {
             err = -ENOMEM;
             goto out;
         }
 
         /*
          * Avoid to free 'prealloc' if it can be merged with
          * the later extent.
          */
         prealloc->start = start;
         prealloc->end = this_end;
         err = insert_state(tree, prealloc, bits, NULL);
         if (err)
             extent_io_tree_panic(tree, err);
         cache_state(prealloc, cached_state);
         prealloc = NULL;
         start = this_end + 1;
         goto search_again;
     }
     /*
      * | ---- desired range ---- |
      *                        | state |
      * We need to split the extent, and set the bit
      * on the first half
      */
     if (state->start <= end && state->end > end) {
         prealloc = alloc_extent_state_atomic(prealloc);
         if (!prealloc) {
             err = -ENOMEM;
             goto out;
         }
 
         err = split_state(tree, state, prealloc, end + 1);
         if (err)
             extent_io_tree_panic(tree, err);
 
         set_state_bits(tree, prealloc, bits, NULL);
         cache_state(prealloc, cached_state);
         clear_state_bit(tree, prealloc, clear_bits, 0, NULL);
         prealloc = NULL;
         goto out;
     }
 
 search_again:
     if (start > end)
         goto out;
     spin_unlock(&tree->lock);
     cond_resched();
     first_iteration = false;
     goto again;
 
 out:
     spin_unlock(&tree->lock);
     if (prealloc)
         free_extent_state(prealloc);
 
     return err;
 }
 
 /* wrappers around set/clear extent bit */
 int set_record_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
                u32 bits, struct extent_changeset *changeset)
 {
     /*
      * We don't support EXTENT_LOCKED yet, as current changeset will
      * record any bits changed, so for EXTENT_LOCKED case, it will
      * either fail with -EEXIST or changeset will record the whole
      * range.
      */
     BUG_ON(bits & EXTENT_LOCKED);
 
     return set_extent_bit(tree, start, end, bits, 0, NULL, NULL, GFP_NOFS,
                   changeset);
 }
 
 int set_extent_bits_nowait(struct extent_io_tree *tree, u64 start, u64 end,
                u32 bits)
 {
     return set_extent_bit(tree, start, end, bits, 0, NULL, NULL,
                   GFP_NOWAIT, NULL);
 }
 
 int clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
              u32 bits, int wake, int delete,
              struct extent_state **cached)
 {
     return __clear_extent_bit(tree, start, end, bits, wake, delete,
                   cached, GFP_NOFS, NULL);
 }
 
 int clear_record_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
         u32 bits, struct extent_changeset *changeset)
 {
     /*
      * Don't support EXTENT_LOCKED case, same reason as
      * set_record_extent_bits().
      */
     BUG_ON(bits & EXTENT_LOCKED);
 
     return __clear_extent_bit(tree, start, end, bits, 0, 0, NULL, GFP_NOFS,
                   changeset);
 }
 
 /*
  * either insert or lock state struct between start and end use mask to tell
  * us if waiting is desired.
  */
 int lock_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
              struct extent_state **cached_state)
 {
     int err;
     u64 failed_start;
 
     while (1) {
         err = set_extent_bit(tree, start, end, EXTENT_LOCKED,
                      EXTENT_LOCKED, &failed_start,
                      cached_state, GFP_NOFS, NULL);
         if (err == -EEXIST) {
             wait_extent_bit(tree, failed_start, end, EXTENT_LOCKED);
             start = failed_start;
         } else
             break;
         WARN_ON(start > end);
     }
     return err;
 }
 
 int try_lock_extent(struct extent_io_tree *tree, u64 start, u64 end)
 {
     int err;
     u64 failed_start;
 
     err = set_extent_bit(tree, start, end, EXTENT_LOCKED, EXTENT_LOCKED,
                  &failed_start, NULL, GFP_NOFS, NULL);
     if (err == -EEXIST) {
         if (failed_start > start)
             clear_extent_bit(tree, start, failed_start - 1,
                      EXTENT_LOCKED, 1, 0, NULL);
         return 0;
     }
     return 1;
 }
 
 void extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end)
 {
     unsigned long index = start >> PAGE_SHIFT;
     unsigned long end_index = end >> PAGE_SHIFT;
     struct page *page;
 
     while (index <= end_index) {
         page = find_get_page(inode->i_mapping, index);
         BUG_ON(!page); /* Pages should be in the extent_io_tree */
         clear_page_dirty_for_io(page);
         put_page(page);
         index++;
     }
 }
 
 void extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end)
 {
     struct address_space *mapping = inode->i_mapping;
     unsigned long index = start >> PAGE_SHIFT;
     unsigned long end_index = end >> PAGE_SHIFT;
     struct folio *folio;
 
     while (index <= end_index) {
         folio = filemap_get_folio(mapping, index);
         filemap_dirty_folio(mapping, folio);
         folio_account_redirty(folio);
         index += folio_nr_pages(folio);
         folio_put(folio);
     }
 }
 
 /* find the first state struct with 'bits' set after 'start', and
  * return it.  tree->lock must be held.  NULL will returned if
  * nothing was found after 'start'
  */
 static struct extent_state *
 find_first_extent_bit_state(struct extent_io_tree *tree, u64 start, u32 bits)
 {
     struct rb_node *node;
     struct extent_state *state;
 
     /*
      * this search will find all the extents that end after
      * our range starts.
      */
     node = tree_search(tree, start);
     if (!node)
         goto out;
 
     while (1) {
         state = rb_entry(node, struct extent_state, rb_node);
         if (state->end >= start && (state->state & bits))
             return state;
 
         node = rb_next(node);
         if (!node)
             break;
     }
 out:
     return NULL;
 }
 
 /*
  * Find the first offset in the io tree with one or more @bits set.
  *
  * Note: If there are multiple bits set in @bits, any of them will match.
  *
  * Return 0 if we find something, and update @start_ret and @end_ret.
  * Return 1 if we found nothing.
  */
 int find_first_extent_bit(struct extent_io_tree *tree, u64 start,
               u64 *start_ret, u64 *end_ret, u32 bits,
               struct extent_state **cached_state)
 {
     struct extent_state *state;
     int ret = 1;
 
     spin_lock(&tree->lock);
     if (cached_state && *cached_state) {
         state = *cached_state;
         if (state->end == start - 1 && extent_state_in_tree(state)) {
             while ((state = next_state(state)) != NULL) {
                 if (state->state & bits)
                     goto got_it;
             }
             free_extent_state(*cached_state);
             *cached_state = NULL;
             goto out;
         }
         free_extent_state(*cached_state);
         *cached_state = NULL;
     }
 
     state = find_first_extent_bit_state(tree, start, bits);
 got_it:
     if (state) {
         cache_state_if_flags(state, cached_state, 0);
         *start_ret = state->start;
         *end_ret = state->end;
         ret = 0;
     }
 out:
     spin_unlock(&tree->lock);
     return ret;
 }
 
 /**
  * Find a contiguous area of bits
  *
  * @tree:      io tree to check
  * @start:     offset to start the search from
  * @start_ret: the first offset we found with the bits set
  * @end_ret:   the final contiguous range of the bits that were set
  * @bits:      bits to look for
  *
  * set_extent_bit and clear_extent_bit can temporarily split contiguous ranges
  * to set bits appropriately, and then merge them again.  During this time it
  * will drop the tree->lock, so use this helper if you want to find the actual
  * contiguous area for given bits.  We will search to the first bit we find, and
  * then walk down the tree until we find a non-contiguous area.  The area
  * returned will be the full contiguous area with the bits set.
  */
 int find_contiguous_extent_bit(struct extent_io_tree *tree, u64 start,
                    u64 *start_ret, u64 *end_ret, u32 bits)
 {
     struct extent_state *state;
     int ret = 1;
 
     spin_lock(&tree->lock);
     state = find_first_extent_bit_state(tree, start, bits);
     if (state) {
         *start_ret = state->start;
         *end_ret = state->end;
         while ((state = next_state(state)) != NULL) {
             if (state->start > (*end_ret + 1))
                 break;
             *end_ret = state->end;
         }
         ret = 0;
     }
     spin_unlock(&tree->lock);
     return ret;
 }
 
 /**
  * Find the first range that has @bits not set. This range could start before
  * @start.
  *
  * @tree:      the tree to search
  * @start:     offset at/after which the found extent should start
  * @start_ret: records the beginning of the range
  * @end_ret:   records the end of the range (inclusive)
  * @bits:      the set of bits which must be unset
  *
  * Since unallocated range is also considered one which doesn't have the bits
  * set it's possible that @end_ret contains -1, this happens in case the range
  * spans (last_range_end, end of device]. In this case it's up to the caller to
  * trim @end_ret to the appropriate size.
  */
 void find_first_clear_extent_bit(struct extent_io_tree *tree, u64 start,
                  u64 *start_ret, u64 *end_ret, u32 bits)
 {
     struct extent_state *state;
     struct rb_node *node, *prev = NULL, *next;
 
     spin_lock(&tree->lock);
 
     /* Find first extent with bits cleared */
     while (1) {
         node = tree_search_prev_next(tree, start, &prev, &next);
         if (!node && !next && !prev) {
             /*
              * Tree is completely empty, send full range and let
              * caller deal with it
              */
             *start_ret = 0;
             *end_ret = -1;
             goto out;
         } else if (!node && !next) {
             /*
              * We are past the last allocated chunk, set start at
              * the end of the last extent.
              */
             state = rb_entry(prev, struct extent_state, rb_node);
             *start_ret = state->end + 1;
             *end_ret = -1;
             goto out;
         } else if (!node) {
             node = next;
         }
         /*
          * At this point 'node' either contains 'start' or start is
          * before 'node'
          */
         state = rb_entry(node, struct extent_state, rb_node);
 
         if (in_range(start, state->start, state->end - state->start + 1)) {
             if (state->state & bits) {
                 /*
                  * |--range with bits sets--|
                  *    |
                  *    start
                  */
                 start = state->end + 1;
             } else {
                 /*
                  * 'start' falls within a range that doesn't
                  * have the bits set, so take its start as
                  * the beginning of the desired range
                  *
                  * |--range with bits cleared----|
                  *      |
                  *      start
                  */
                 *start_ret = state->start;
                 break;
             }
         } else {
             /*
              * |---prev range---|---hole/unset---|---node range---|
              *                          |
              *                        start
              *
              *                        or
              *
              * |---hole/unset--||--first node--|
              * 0   |
              *    start
              */
             if (prev) {
                 state = rb_entry(prev, struct extent_state,
                          rb_node);
                 *start_ret = state->end + 1;
             } else {
                 *start_ret = 0;
             }
             break;
         }
     }
 
     /*
      * Find the longest stretch from start until an entry which has the
      * bits set
      */
     while (1) {
         state = rb_entry(node, struct extent_state, rb_node);
         if (state->end >= start && !(state->state & bits)) {
             *end_ret = state->end;
         } else {
             *end_ret = state->start - 1;
             break;
         }
 
         node = rb_next(node);
         if (!node)
             break;
     }
 out:
     spin_unlock(&tree->lock);
 }
 
 /*
  * find a contiguous range of bytes in the file marked as delalloc, not
  * more than 'max_bytes'.  start and end are used to return the range,
  *
  * true is returned if we find something, false if nothing was in the tree
  */
 bool btrfs_find_delalloc_range(struct extent_io_tree *tree, u64 *start,
                    u64 *end, u64 max_bytes,
                    struct extent_state **cached_state)
 {
     struct rb_node *node;
     struct extent_state *state;
     u64 cur_start = *start;
     bool found = false;
     u64 total_bytes = 0;
 
     spin_lock(&tree->lock);
 
     /*
      * this search will find all the extents that end after
      * our range starts.
      */
     node = tree_search(tree, cur_start);
     if (!node) {
         *end = (u64)-1;
         goto out;
     }
 
     while (1) {
         state = rb_entry(node, struct extent_state, rb_node);
         if (found && (state->start != cur_start ||
                   (state->state & EXTENT_BOUNDARY))) {
             goto out;
         }
         if (!(state->state & EXTENT_DELALLOC)) {
             if (!found)
                 *end = state->end;
             goto out;
         }
         if (!found) {
             *start = state->start;
             *cached_state = state;
             refcount_inc(&state->refs);
         }
         found = true;
         *end = state->end;
         cur_start = state->end + 1;
         node = rb_next(node);
         total_bytes += state->end - state->start + 1;
         if (total_bytes >= max_bytes)
             break;
         if (!node)
             break;
     }
 out:
     spin_unlock(&tree->lock);
     return found;
 }
 
 /*
  * Process one page for __process_pages_contig().
  *
  * Return >0 if we hit @page == @locked_page.
  * Return 0 if we updated the page status.
  * Return -EGAIN if the we need to try again.
  * (For PAGE_LOCK case but got dirty page or page not belong to mapping)
  */
 static int process_one_page(struct btrfs_fs_info *fs_info,
                 struct address_space *mapping,
                 struct page *page, struct page *locked_page,
                 unsigned long page_ops, u64 start, u64 end)
 {
     u32 len;
 
     ASSERT(end + 1 - start != 0 && end + 1 - start < U32_MAX);
     len = end + 1 - start;
 
     if (page_ops & PAGE_SET_ORDERED)
         btrfs_page_clamp_set_ordered(fs_info, page, start, len);
     if (page_ops & PAGE_SET_ERROR)
         btrfs_page_clamp_set_error(fs_info, page, start, len);
     if (page_ops & PAGE_START_WRITEBACK) {
         btrfs_page_clamp_clear_dirty(fs_info, page, start, len);
         btrfs_page_clamp_set_writeback(fs_info, page, start, len);
     }
     if (page_ops & PAGE_END_WRITEBACK)
         btrfs_page_clamp_clear_writeback(fs_info, page, start, len);
 
     if (page == locked_page)
         return 1;
 
     if (page_ops & PAGE_LOCK) {
         int ret;
 
         ret = btrfs_page_start_writer_lock(fs_info, page, start, len);
         if (ret)
             return ret;
         if (!PageDirty(page) || page->mapping != mapping) {
             btrfs_page_end_writer_lock(fs_info, page, start, len);
             return -EAGAIN;
         }
     }
     if (page_ops & PAGE_UNLOCK)
         btrfs_page_end_writer_lock(fs_info, page, start, len);
     return 0;
 }
 
 static int __process_pages_contig(struct address_space *mapping,
                   struct page *locked_page,
                   u64 start, u64 end, unsigned long page_ops,
                   u64 *processed_end)
 {
     struct btrfs_fs_info *fs_info = btrfs_sb(mapping->host->i_sb);
     pgoff_t start_index = start >> PAGE_SHIFT;
     pgoff_t end_index = end >> PAGE_SHIFT;
     pgoff_t index = start_index;
     unsigned long nr_pages = end_index - start_index + 1;
     unsigned long pages_processed = 0;
     struct page *pages[16];
     int err = 0;
     int i;
 
     if (page_ops & PAGE_LOCK) {
         ASSERT(page_ops == PAGE_LOCK);
         ASSERT(processed_end && *processed_end == start);
     }
 
     if ((page_ops & PAGE_SET_ERROR) && nr_pages > 0)
         mapping_set_error(mapping, -EIO);
 
     while (nr_pages > 0) {
         int found_pages;
 
         found_pages = find_get_pages_contig(mapping, index,
                      min_t(unsigned long,
                      nr_pages, ARRAY_SIZE(pages)), pages);
         if (found_pages == 0) {
             /*
              * Only if we're going to lock these pages, we can find
              * nothing at @index.
              */
             ASSERT(page_ops & PAGE_LOCK);
             err = -EAGAIN;
             goto out;
         }
 
         for (i = 0; i < found_pages; i++) {
             int process_ret;
 
             process_ret = process_one_page(fs_info, mapping,
                     pages[i], locked_page, page_ops,
                     start, end);
             if (process_ret < 0) {
                 for (; i < found_pages; i++)
                     put_page(pages[i]);
                 err = -EAGAIN;
                 goto out;
             }
             put_page(pages[i]);
             pages_processed++;
         }
         nr_pages -= found_pages;
         index += found_pages;
         cond_resched();
     }
 out:
     if (err && processed_end) {
         /*
          * Update @processed_end. I know this is awful since it has
          * two different return value patterns (inclusive vs exclusive).
          *
          * But the exclusive pattern is necessary if @start is 0, or we
          * underflow and check against processed_end won't work as
          * expected.
          */
         if (pages_processed)
             *processed_end = min(end,
             ((u64)(start_index + pages_processed) << PAGE_SHIFT) - 1);
         else
             *processed_end = start;
     }
     return err;
 }
 
 static noinline void __unlock_for_delalloc(struct inode *inode,
                        struct page *locked_page,
                        u64 start, u64 end)
 {
     unsigned long index = start >> PAGE_SHIFT;
     unsigned long end_index = end >> PAGE_SHIFT;
 
     ASSERT(locked_page);
     if (index == locked_page->index && end_index == index)
         return;
 
     __process_pages_contig(inode->i_mapping, locked_page, start, end,
                    PAGE_UNLOCK, NULL);
 }
 
 static noinline int lock_delalloc_pages(struct inode *inode,
                     struct page *locked_page,
                     u64 delalloc_start,
                     u64 delalloc_end)
 {
     unsigned long index = delalloc_start >> PAGE_SHIFT;
     unsigned long end_index = delalloc_end >> PAGE_SHIFT;
     u64 processed_end = delalloc_start;
     int ret;
 
     ASSERT(locked_page);
     if (index == locked_page->index && index == end_index)
         return 0;
 
     ret = __process_pages_contig(inode->i_mapping, locked_page, delalloc_start,
                      delalloc_end, PAGE_LOCK, &processed_end);
     if (ret == -EAGAIN && processed_end > delalloc_start)
         __unlock_for_delalloc(inode, locked_page, delalloc_start,
                       processed_end);
     return ret;
 }
 
 /*
  * Find and lock a contiguous range of bytes in the file marked as delalloc, no
  * more than @max_bytes.
  *
  * @start:  The original start bytenr to search.
  *      Will store the extent range start bytenr.
  * @end:    The original end bytenr of the search range
  *      Will store the extent range end bytenr.
  *
  * Return true if we find a delalloc range which starts inside the original
  * range, and @start/@end will store the delalloc range start/end.
  *
  * Return false if we can't find any delalloc range which starts inside the
  * original range, and @start/@end will be the non-delalloc range start/end.
  */
 EXPORT_FOR_TESTS
 noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
                     struct page *locked_page, u64 *start,
                     u64 *end)
 {
     struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
     struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
     const u64 orig_start = *start;
     const u64 orig_end = *end;
     /* The sanity tests may not set a valid fs_info. */
     u64 max_bytes = fs_info ? fs_info->max_extent_size : BTRFS_MAX_EXTENT_SIZE;
     u64 delalloc_start;
     u64 delalloc_end;
     bool found;
     struct extent_state *cached_state = NULL;
     int ret;
     int loops = 0;
 
     /* Caller should pass a valid @end to indicate the search range end */
     ASSERT(orig_end > orig_start);
 
     /* The range should at least cover part of the page */
     ASSERT(!(orig_start >= page_offset(locked_page) + PAGE_SIZE ||
          orig_end <= page_offset(locked_page)));
 again:
     /* step one, find a bunch of delalloc bytes starting at start */
     delalloc_start = *start;
     delalloc_end = 0;
     found = btrfs_find_delalloc_range(tree, &delalloc_start, &delalloc_end,
                       max_bytes, &cached_state);
     if (!found || delalloc_end <= *start || delalloc_start > orig_end) {
         *start = delalloc_start;
 
         /* @delalloc_end can be -1, never go beyond @orig_end */
         *end = min(delalloc_end, orig_end);
         free_extent_state(cached_state);
         return false;
     }
 
     /*
      * start comes from the offset of locked_page.  We have to lock
      * pages in order, so we can't process delalloc bytes before
      * locked_page
      */
     if (delalloc_start < *start)
         delalloc_start = *start;
 
     /*
      * make sure to limit the number of pages we try to lock down
      */
     if (delalloc_end + 1 - delalloc_start > max_bytes)
         delalloc_end = delalloc_start + max_bytes - 1;
 
     /* step two, lock all the pages after the page that has start */
     ret = lock_delalloc_pages(inode, locked_page,
                   delalloc_start, delalloc_end);
     ASSERT(!ret || ret == -EAGAIN);
     if (ret == -EAGAIN) {
         /* some of the pages are gone, lets avoid looping by
          * shortening the size of the delalloc range we're searching
          */
         free_extent_state(cached_state);
         cached_state = NULL;
         if (!loops) {
             max_bytes = PAGE_SIZE;
             loops = 1;
             goto again;
         } else {
             found = false;
             goto out_failed;
         }
     }
 
     /* step three, lock the state bits for the whole range */
     lock_extent_bits(tree, delalloc_start, delalloc_end, &cached_state);
 
     /* then test to make sure it is all still delalloc */
     ret = test_range_bit(tree, delalloc_start, delalloc_end,
                  EXTENT_DELALLOC, 1, cached_state);
     if (!ret) {
         unlock_extent_cached(tree, delalloc_start, delalloc_end,
                      &cached_state);
         __unlock_for_delalloc(inode, locked_page,
                   delalloc_start, delalloc_end);
         cond_resched();
         goto again;
     }
     free_extent_state(cached_state);
     *start = delalloc_start;
     *end = delalloc_end;
 out_failed:
     return found;
 }
 
 void extent_clear_unlock_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
                   struct page *locked_page,
                   u32 clear_bits, unsigned long page_ops)
 {
     clear_extent_bit(&inode->io_tree, start, end, clear_bits, 1, 0, NULL);
 
     __process_pages_contig(inode->vfs_inode.i_mapping, locked_page,
                    start, end, page_ops, NULL);
 }
 
 /*
  * count the number of bytes in the tree that have a given bit(s)
  * set.  This can be fairly slow, except for EXTENT_DIRTY which is
  * cached.  The total number found is returned.
  */
 u64 count_range_bits(struct extent_io_tree *tree,
              u64 *start, u64 search_end, u64 max_bytes,
              u32 bits, int contig)
 {
     struct rb_node *node;
     struct extent_state *state;
     u64 cur_start = *start;
     u64 total_bytes = 0;
     u64 last = 0;
     int found = 0;
 
     if (WARN_ON(search_end <= cur_start))
         return 0;
 
     spin_lock(&tree->lock);
     if (cur_start == 0 && bits == EXTENT_DIRTY) {
         total_bytes = tree->dirty_bytes;
         goto out;
     }
     /*
      * this search will find all the extents that end after
      * our range starts.
      */
     node = tree_search(tree, cur_start);
     if (!node)
         goto out;
 
     while (1) {
         state = rb_entry(node, struct extent_state, rb_node);
         if (state->start > search_end)
             break;
         if (contig && found && state->start > last + 1)
             break;
         if (state->end >= cur_start && (state->state & bits) == bits) {
             total_bytes += min(search_end, state->end) + 1 -
                        max(cur_start, state->start);
             if (total_bytes >= max_bytes)
                 break;
             if (!found) {
                 *start = max(cur_start, state->start);
                 found = 1;
             }
             last = state->end;
         } else if (contig && found) {
             break;
         }
         node = rb_next(node);
         if (!node)
             break;
     }
 out:
     spin_unlock(&tree->lock);
     return total_bytes;
 }
 
 /*
  * set the private field for a given byte offset in the tree.  If there isn't
  * an extent_state there already, this does nothing.
  */
 int set_state_failrec(struct extent_io_tree *tree, u64 start,
               struct io_failure_record *failrec)
 {
     struct rb_node *node;
     struct extent_state *state;
     int ret = 0;
 
     spin_lock(&tree->lock);
     /*
      * this search will find all the extents that end after
      * our range starts.
      */
     node = tree_search(tree, start);
     if (!node) {
         ret = -ENOENT;
         goto out;
     }
     state = rb_entry(node, struct extent_state, rb_node);
     if (state->start != start) {
         ret = -ENOENT;
         goto out;
     }
     state->failrec = failrec;
 out:
     spin_unlock(&tree->lock);
     return ret;
 }
 
 struct io_failure_record *get_state_failrec(struct extent_io_tree *tree, u64 start)
 {
     struct rb_node *node;
     struct extent_state *state;
     struct io_failure_record *failrec;
 
     spin_lock(&tree->lock);
     /*
      * this search will find all the extents that end after
      * our range starts.
      */
     node = tree_search(tree, start);
     if (!node) {
         failrec = ERR_PTR(-ENOENT);
         goto out;
     }
     state = rb_entry(node, struct extent_state, rb_node);
     if (state->start != start) {
         failrec = ERR_PTR(-ENOENT);
         goto out;
     }
 
     failrec = state->failrec;
 out:
     spin_unlock(&tree->lock);
     return failrec;
 }
 
 /*
  * searches a range in the state tree for a given mask.
  * If 'filled' == 1, this returns 1 only if every extent in the tree
  * has the bits set.  Otherwise, 1 is returned if any bit in the
  * range is found set.
  */
 int test_range_bit(struct extent_io_tree *tree, u64 start, u64 end,
            u32 bits, int filled, struct extent_state *cached)
 {
     struct extent_state *state = NULL;
     struct rb_node *node;
     int bitset = 0;
 
     spin_lock(&tree->lock);
     if (cached && extent_state_in_tree(cached) && cached->start <= start &&
         cached->end > start)
         node = &cached->rb_node;
     else
         node = tree_search(tree, start);
     while (node && start <= end) {
         state = rb_entry(node, struct extent_state, rb_node);
 
         if (filled && state->start > start) {
             bitset = 0;
             break;
         }
 
         if (state->start > end)
             break;
 
         if (state->state & bits) {
             bitset = 1;
             if (!filled)
                 break;
         } else if (filled) {
             bitset = 0;
             break;
         }
 
         if (state->end == (u64)-1)
             break;
 
         start = state->end + 1;
         if (start > end)
             break;
         node = rb_next(node);
         if (!node) {
             if (filled)
                 bitset = 0;
             break;
         }
     }
     spin_unlock(&tree->lock);
     return bitset;
 }
 
 int free_io_failure(struct extent_io_tree *failure_tree,
             struct extent_io_tree *io_tree,
             struct io_failure_record *rec)
 {
     int ret;
     int err = 0;
 
     set_state_failrec(failure_tree, rec->start, NULL);
     ret = clear_extent_bits(failure_tree, rec->start,
                 rec->start + rec->len - 1,
                 EXTENT_LOCKED | EXTENT_DIRTY);
     if (ret)
         err = ret;
 
     ret = clear_extent_bits(io_tree, rec->start,
                 rec->start + rec->len - 1,
                 EXTENT_DAMAGED);
     if (ret && !err)
         err = ret;
 
     kfree(rec);
     return err;
 }
 
 /*
  * this bypasses the standard btrfs submit functions deliberately, as
  * the standard behavior is to write all copies in a raid setup. here we only
  * want to write the one bad copy. so we do the mapping for ourselves and issue
  * submit_bio directly.
  * to avoid any synchronization issues, wait for the data after writing, which
  * actually prevents the read that triggered the error from finishing.
  * currently, there can be no more than two copies of every data bit. thus,
  * exactly one rewrite is required.
  */
 static int repair_io_failure(struct btrfs_fs_info *fs_info, u64 ino, u64 start,
                  u64 length, u64 logical, struct page *page,
                  unsigned int pg_offset, int mirror_num)
 {
     struct btrfs_device *dev;
     struct bio_vec bvec;
     struct bio bio;
     u64 map_length = 0;
     u64 sector;
     struct btrfs_io_context *bioc = NULL;
     int ret = 0;
 
     ASSERT(!(fs_info->sb->s_flags & SB_RDONLY));
     BUG_ON(!mirror_num);
 
     if (btrfs_repair_one_zone(fs_info, logical))
         return 0;
 
     map_length = length;
 
     /*
      * Avoid races with device replace and make sure our bioc has devices
      * associated to its stripes that don't go away while we are doing the
      * read repair operation.
      */
     btrfs_bio_counter_inc_blocked(fs_info);
     if (btrfs_is_parity_mirror(fs_info, logical, length)) {
         /*
          * Note that we don't use BTRFS_MAP_WRITE because it's supposed
          * to update all raid stripes, but here we just want to correct
          * bad stripe, thus BTRFS_MAP_READ is abused to only get the bad
          * stripe's dev and sector.
          */
         ret = btrfs_map_block(fs_info, BTRFS_MAP_READ, logical,
                       &map_length, &bioc, 0);
         if (ret)
             goto out_counter_dec;
         ASSERT(bioc->mirror_num == 1);
     } else {
         ret = btrfs_map_block(fs_info, BTRFS_MAP_WRITE, logical,
                       &map_length, &bioc, mirror_num);
         if (ret)
             goto out_counter_dec;
         BUG_ON(mirror_num != bioc->mirror_num);
     }
 
     sector = bioc->stripes[bioc->mirror_num - 1].physical >> 9;
     dev = bioc->stripes[bioc->mirror_num - 1].dev;
     btrfs_put_bioc(bioc);
 
     if (!dev || !dev->bdev ||
         !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state)) {
         ret = -EIO;
         goto out_counter_dec;
     }
 
     bio_init(&bio, dev->bdev, &bvec, 1, REQ_OP_WRITE | REQ_SYNC);
     bio.bi_iter.bi_sector = sector;
     __bio_add_page(&bio, page, length, pg_offset);
 
     btrfsic_check_bio(&bio);
     ret = submit_bio_wait(&bio);
     if (ret) {
         /* try to remap that extent elsewhere? */
         btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_WRITE_ERRS);
         goto out_bio_uninit;
     }
 
     btrfs_info_rl_in_rcu(fs_info,
         "read error corrected: ino %llu off %llu (dev %s sector %llu)",
                   ino, start,
                   rcu_str_deref(dev->name), sector);
     ret = 0;
 
 out_bio_uninit:
     bio_uninit(&bio);
 out_counter_dec:
     btrfs_bio_counter_dec(fs_info);
     return ret;
 }
 
 int btrfs_repair_eb_io_failure(const struct extent_buffer *eb, int mirror_num)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     u64 start = eb->start;
     int i, num_pages = num_extent_pages(eb);
     int ret = 0;
 
     if (sb_rdonly(fs_info->sb))
         return -EROFS;
 
     for (i = 0; i < num_pages; i++) {
         struct page *p = eb->pages[i];
 
         ret = repair_io_failure(fs_info, 0, start, PAGE_SIZE, start, p,
                     start - page_offset(p), mirror_num);
         if (ret)
             break;
         start += PAGE_SIZE;
     }
 
     return ret;
 }
 
 static int next_mirror(const struct io_failure_record *failrec, int cur_mirror)
 {
     if (cur_mirror == failrec->num_copies)
         return cur_mirror + 1 - failrec->num_copies;
     return cur_mirror + 1;
 }
 
 static int prev_mirror(const struct io_failure_record *failrec, int cur_mirror)
 {
     if (cur_mirror == 1)
         return failrec->num_copies;
     return cur_mirror - 1;
 }
 
 /*
  * each time an IO finishes, we do a fast check in the IO failure tree
  * to see if we need to process or clean up an io_failure_record
  */
 int clean_io_failure(struct btrfs_fs_info *fs_info,
              struct extent_io_tree *failure_tree,
              struct extent_io_tree *io_tree, u64 start,
              struct page *page, u64 ino, unsigned int pg_offset)
 {
     u64 private;
     struct io_failure_record *failrec;
     struct extent_state *state;
     int mirror;
     int ret;
 
     private = 0;
     ret = count_range_bits(failure_tree, &private, (u64)-1, 1,
                    EXTENT_DIRTY, 0);
     if (!ret)
         return 0;
 
     failrec = get_state_failrec(failure_tree, start);
     if (IS_ERR(failrec))
         return 0;
 
     BUG_ON(!failrec->this_mirror);
 
     if (sb_rdonly(fs_info->sb))
         goto out;
 
     spin_lock(&io_tree->lock);
     state = find_first_extent_bit_state(io_tree,
                         failrec->start,
                         EXTENT_LOCKED);
     spin_unlock(&io_tree->lock);
 
     if (!state || state->start > failrec->start ||
         state->end < failrec->start + failrec->len - 1)
         goto out;
 
     mirror = failrec->this_mirror;
     do {
         mirror = prev_mirror(failrec, mirror);
         repair_io_failure(fs_info, ino, start, failrec->len,
                   failrec->logical, page, pg_offset, mirror);
     } while (mirror != failrec->failed_mirror);
 
 out:
     free_io_failure(failure_tree, io_tree, failrec);
     return 0;
 }
 
 /*
  * Can be called when
  * - hold extent lock
  * - under ordered extent
  * - the inode is freeing
  */
 void btrfs_free_io_failure_record(struct btrfs_inode *inode, u64 start, u64 end)
 {
     struct extent_io_tree *failure_tree = &inode->io_failure_tree;
     struct io_failure_record *failrec;
     struct extent_state *state, *next;
 
     if (RB_EMPTY_ROOT(&failure_tree->state))
         return;
 
     spin_lock(&failure_tree->lock);
     state = find_first_extent_bit_state(failure_tree, start, EXTENT_DIRTY);
     while (state) {
         if (state->start > end)
             break;
 
         ASSERT(state->end <= end);
 
         next = next_state(state);
 
         failrec = state->failrec;
         free_extent_state(state);
         kfree(failrec);
 
         state = next;
     }
     spin_unlock(&failure_tree->lock);
 }
 
 static struct io_failure_record *btrfs_get_io_failure_record(struct inode *inode,
                                  struct btrfs_bio *bbio,
                                  unsigned int bio_offset)
 {
     struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
     u64 start = bbio->file_offset + bio_offset;
     struct io_failure_record *failrec;
     struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
     struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
     const u32 sectorsize = fs_info->sectorsize;
     int ret;
 
     failrec = get_state_failrec(failure_tree, start);
     if (!IS_ERR(failrec)) {
         btrfs_debug(fs_info,
     "Get IO Failure Record: (found) logical=%llu, start=%llu, len=%llu",
             failrec->logical, failrec->start, failrec->len);
         /*
          * when data can be on disk more than twice, add to failrec here
          * (e.g. with a list for failed_mirror) to make
          * clean_io_failure() clean all those errors at once.
          */
         ASSERT(failrec->this_mirror == bbio->mirror_num);
         ASSERT(failrec->len == fs_info->sectorsize);
         return failrec;
     }
 
     failrec = kzalloc(sizeof(*failrec), GFP_NOFS);
     if (!failrec)
         return ERR_PTR(-ENOMEM);
 
     failrec->start = start;
     failrec->len = sectorsize;
     failrec->failed_mirror = bbio->mirror_num;
     failrec->this_mirror = bbio->mirror_num;
     failrec->logical = (bbio->iter.bi_sector << SECTOR_SHIFT) + bio_offset;
 
     btrfs_debug(fs_info,
             "new io failure record logical %llu start %llu",
             failrec->logical, start);
 
     failrec->num_copies = btrfs_num_copies(fs_info, failrec->logical, sectorsize);
     if (failrec->num_copies == 1) {
         /*
          * We only have a single copy of the data, so don't bother with
          * all the retry and error correction code that follows. No
          * matter what the error is, it is very likely to persist.
          */
         btrfs_debug(fs_info,
             "cannot repair logical %llu num_copies %d",
             failrec->logical, failrec->num_copies);
         kfree(failrec);
         return ERR_PTR(-EIO);
     }
 
     /* Set the bits in the private failure tree */
     ret = set_extent_bits(failure_tree, start, start + sectorsize - 1,
                   EXTENT_LOCKED | EXTENT_DIRTY);
     if (ret >= 0) {
         ret = set_state_failrec(failure_tree, start, failrec);
         /* Set the bits in the inode's tree */
         ret = set_extent_bits(tree, start, start + sectorsize - 1,
                       EXTENT_DAMAGED);
     } else if (ret < 0) {
         kfree(failrec);
         return ERR_PTR(ret);
     }
 
     return failrec;
 }
 
 int btrfs_repair_one_sector(struct inode *inode, struct btrfs_bio *failed_bbio,
                 u32 bio_offset, struct page *page, unsigned int pgoff,
                 submit_bio_hook_t *submit_bio_hook)
 {
     u64 start = failed_bbio->file_offset + bio_offset;
     struct io_failure_record *failrec;
     struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
     struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
     struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
     struct bio *failed_bio = &failed_bbio->bio;
     const int icsum = bio_offset >> fs_info->sectorsize_bits;
     struct bio *repair_bio;
     struct btrfs_bio *repair_bbio;
 
     btrfs_debug(fs_info,
            "repair read error: read error at %llu", start);
 
     BUG_ON(bio_op(failed_bio) == REQ_OP_WRITE);
 
     failrec = btrfs_get_io_failure_record(inode, failed_bbio, bio_offset);
     if (IS_ERR(failrec))
         return PTR_ERR(failrec);
 
     /*
      * There are two premises:
      * a) deliver good data to the caller
      * b) correct the bad sectors on disk
      *
      * Since we're only doing repair for one sector, we only need to get
      * a good copy of the failed sector and if we succeed, we have setup
      * everything for repair_io_failure to do the rest for us.
      */
     failrec->this_mirror = next_mirror(failrec, failrec->this_mirror);
     if (failrec->this_mirror == failrec->failed_mirror) {
         btrfs_debug(fs_info,
             "failed to repair num_copies %d this_mirror %d failed_mirror %d",
             failrec->num_copies, failrec->this_mirror, failrec->failed_mirror);
         free_io_failure(failure_tree, tree, failrec);
         return -EIO;
     }
 
     repair_bio = btrfs_bio_alloc(1);
     repair_bbio = btrfs_bio(repair_bio);
     repair_bbio->file_offset = start;
     repair_bio->bi_opf = REQ_OP_READ;
     repair_bio->bi_end_io = failed_bio->bi_end_io;
     repair_bio->bi_iter.bi_sector = failrec->logical >> 9;
     repair_bio->bi_private = failed_bio->bi_private;
 
     if (failed_bbio->csum) {
         const u32 csum_size = fs_info->csum_size;
 
         repair_bbio->csum = repair_bbio->csum_inline;
         memcpy(repair_bbio->csum,
                failed_bbio->csum + csum_size * icsum, csum_size);
     }
 
     bio_add_page(repair_bio, page, failrec->len, pgoff);
     repair_bbio->iter = repair_bio->bi_iter;
 
     btrfs_debug(btrfs_sb(inode->i_sb),
             "repair read error: submitting new read to mirror %d",
             failrec->this_mirror);
 
     /*
      * At this point we have a bio, so any errors from submit_bio_hook()
      * will be handled by the endio on the repair_bio, so we can't return an
      * error here.
      */
     submit_bio_hook(inode, repair_bio, failrec->this_mirror, 0);
     return BLK_STS_OK;
 }
 
 static void end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
 {
     struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
 
     ASSERT(page_offset(page) <= start &&
            start + len <= page_offset(page) + PAGE_SIZE);
 
     if (uptodate) {
         if (fsverity_active(page->mapping->host) &&
             !PageError(page) &&
             !PageUptodate(page) &&
             start < i_size_read(page->mapping->host) &&
             !fsverity_verify_page(page)) {
             btrfs_page_set_error(fs_info, page, start, len);
         } else {
             btrfs_page_set_uptodate(fs_info, page, start, len);
         }
     } else {
         btrfs_page_clear_uptodate(fs_info, page, start, len);
         btrfs_page_set_error(fs_info, page, start, len);
     }
 
     if (!btrfs_is_subpage(fs_info, page))
         unlock_page(page);
     else
         btrfs_subpage_end_reader(fs_info, page, start, len);
 }
 
 static void end_sector_io(struct page *page, u64 offset, bool uptodate)
 {
     struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
     const u32 sectorsize = inode->root->fs_info->sectorsize;
     struct extent_state *cached = NULL;
 
     end_page_read(page, uptodate, offset, sectorsize);
     if (uptodate)
         set_extent_uptodate(&inode->io_tree, offset,
                     offset + sectorsize - 1, &cached, GFP_ATOMIC);
     unlock_extent_cached_atomic(&inode->io_tree, offset,
                     offset + sectorsize - 1, &cached);
 }
 
 static void submit_data_read_repair(struct inode *inode,
                     struct btrfs_bio *failed_bbio,
                     u32 bio_offset, const struct bio_vec *bvec,
                     unsigned int error_bitmap)
 {
     const unsigned int pgoff = bvec->bv_offset;
     struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
     struct page *page = bvec->bv_page;
     const u64 start = page_offset(bvec->bv_page) + bvec->bv_offset;
     const u64 end = start + bvec->bv_len - 1;
     const u32 sectorsize = fs_info->sectorsize;
     const int nr_bits = (end + 1 - start) >> fs_info->sectorsize_bits;
     int i;
 
     BUG_ON(bio_op(&failed_bbio->bio) == REQ_OP_WRITE);
 
     /* This repair is only for data */
     ASSERT(is_data_inode(inode));
 
     /* We're here because we had some read errors or csum mismatch */
     ASSERT(error_bitmap);
 
     /*
      * We only get called on buffered IO, thus page must be mapped and bio
      * must not be cloned.
      */
     ASSERT(page->mapping && !bio_flagged(&failed_bbio->bio, BIO_CLONED));
 
     /* Iterate through all the sectors in the range */
     for (i = 0; i < nr_bits; i++) {
         const unsigned int offset = i * sectorsize;
         bool uptodate = false;
         int ret;
 
         if (!(error_bitmap & (1U << i))) {
             /*
              * This sector has no error, just end the page read
              * and unlock the range.
              */
             uptodate = true;
             goto next;
         }
 
         ret = btrfs_repair_one_sector(inode, failed_bbio,
                 bio_offset + offset, page, pgoff + offset,
                 btrfs_submit_data_read_bio);
         if (!ret) {
             /*
              * We have submitted the read repair, the page release
              * will be handled by the endio function of the
              * submitted repair bio.
              * Thus we don't need to do any thing here.
              */
             continue;
         }
         /*
          * Continue on failed repair, otherwise the remaining sectors
          * will not be properly unlocked.
          */
 next:
         end_sector_io(page, start + offset, uptodate);
     }
 }
 
 /* lots and lots of room for performance fixes in the end_bio funcs */
 
 void end_extent_writepage(struct page *page, int err, u64 start, u64 end)
 {
     struct btrfs_inode *inode;
     const bool uptodate = (err == 0);
     int ret = 0;
 
     ASSERT(page && page->mapping);
     inode = BTRFS_I(page->mapping->host);
     btrfs_writepage_endio_finish_ordered(inode, page, start, end, uptodate);
 
     if (!uptodate) {
         const struct btrfs_fs_info *fs_info = inode->root->fs_info;
         u32 len;
 
         ASSERT(end + 1 - start <= U32_MAX);
         len = end + 1 - start;
 
         btrfs_page_clear_uptodate(fs_info, page, start, len);
         btrfs_page_set_error(fs_info, page, start, len);
         ret = err < 0 ? err : -EIO;
         mapping_set_error(page->mapping, ret);
     }
 }
 
 /*
  * after a writepage IO is done, we need to:
  * clear the uptodate bits on error
  * clear the writeback bits in the extent tree for this IO
  * end_page_writeback if the page has no more pending IO
  *
  * Scheduling is not allowed, so the extent state tree is expected
  * to have one and only one object corresponding to this IO.
  */
 static void end_bio_extent_writepage(struct bio *bio)
 {
     int error = blk_status_to_errno(bio->bi_status);
     struct bio_vec *bvec;
     u64 start;
     u64 end;
     struct bvec_iter_all iter_all;
     bool first_bvec = true;
 
     ASSERT(!bio_flagged(bio, BIO_CLONED));
     bio_for_each_segment_all(bvec, bio, iter_all) {
         struct page *page = bvec->bv_page;
         struct inode *inode = page->mapping->host;
         struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
         const u32 sectorsize = fs_info->sectorsize;
 
         /* Our read/write should always be sector aligned. */
         if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
             btrfs_err(fs_info,
         "partial page write in btrfs with offset %u and length %u",
                   bvec->bv_offset, bvec->bv_len);
         else if (!IS_ALIGNED(bvec->bv_len, sectorsize))
             btrfs_info(fs_info,
         "incomplete page write with offset %u and length %u",
                    bvec->bv_offset, bvec->bv_len);
 
         start = page_offset(page) + bvec->bv_offset;
         end = start + bvec->bv_len - 1;
 
         if (first_bvec) {
             btrfs_record_physical_zoned(inode, start, bio);
             first_bvec = false;
         }
 
         end_extent_writepage(page, error, start, end);
 
         btrfs_page_clear_writeback(fs_info, page, start, bvec->bv_len);
     }
 
     bio_put(bio);
 }
 
 /*
  * Record previously processed extent range
  *
  * For endio_readpage_release_extent() to handle a full extent range, reducing
  * the extent io operations.
  */
 struct processed_extent {
     struct btrfs_inode *inode;
     /* Start of the range in @inode */
     u64 start;
     /* End of the range in @inode */
     u64 end;
     bool uptodate;
 };
 
 /*
  * Try to release processed extent range
  *
  * May not release the extent range right now if the current range is
  * contiguous to processed extent.
  *
  * Will release processed extent when any of @inode, @uptodate, the range is
  * no longer contiguous to the processed range.
  *
  * Passing @inode == NULL will force processed extent to be released.
  */
 static void endio_readpage_release_extent(struct processed_extent *processed,
                   struct btrfs_inode *inode, u64 start, u64 end,
                   bool uptodate)
 {
     struct extent_state *cached = NULL;
     struct extent_io_tree *tree;
 
     /* The first extent, initialize @processed */
     if (!processed->inode)
         goto update;
 
     /*
      * Contiguous to processed extent, just uptodate the end.
      *
      * Several things to notice:
      *
      * - bio can be merged as long as on-disk bytenr is contiguous
      *   This means we can have page belonging to other inodes, thus need to
      *   check if the inode still matches.
      * - bvec can contain range beyond current page for multi-page bvec
      *   Thus we need to do processed->end + 1 >= start check
      */
     if (processed->inode == inode && processed->uptodate == uptodate &&
         processed->end + 1 >= start && end >= processed->end) {
         processed->end = end;
         return;
     }
 
     tree = &processed->inode->io_tree;
     /*
      * Now we don't have range contiguous to the processed range, release
      * the processed range now.
      */
     if (processed->uptodate && tree->track_uptodate)
         set_extent_uptodate(tree, processed->start, processed->end,
                     &cached, GFP_ATOMIC);
     unlock_extent_cached_atomic(tree, processed->start, processed->end,
                     &cached);
 
 update:
     /* Update processed to current range */
     processed->inode = inode;
     processed->start = start;
     processed->end = end;
     processed->uptodate = uptodate;
 }
 
 static void begin_page_read(struct btrfs_fs_info *fs_info, struct page *page)
 {
     ASSERT(PageLocked(page));
     if (!btrfs_is_subpage(fs_info, page))
         return;
 
     ASSERT(PagePrivate(page));
     btrfs_subpage_start_reader(fs_info, page, page_offset(page), PAGE_SIZE);
 }
 
 /*
  * Find extent buffer for a givne bytenr.
  *
  * This is for end_bio_extent_readpage(), thus we can't do any unsafe locking
  * in endio context.
  */
 static struct extent_buffer *find_extent_buffer_readpage(
         struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
 {
     struct extent_buffer *eb;
 
     /*
      * For regular sectorsize, we can use page->private to grab extent
      * buffer
      */
     if (fs_info->nodesize >= PAGE_SIZE) {
         ASSERT(PagePrivate(page) && page->private);
         return (struct extent_buffer *)page->private;
     }
 
     /* For subpage case, we need to lookup buffer radix tree */
     rcu_read_lock();
     eb = radix_tree_lookup(&fs_info->buffer_radix,
                    bytenr >> fs_info->sectorsize_bits);
     rcu_read_unlock();
     ASSERT(eb);
     return eb;
 }
 
 /*
  * after a readpage IO is done, we need to:
  * clear the uptodate bits on error
  * set the uptodate bits if things worked
  * set the page up to date if all extents in the tree are uptodate
  * clear the lock bit in the extent tree
  * unlock the page if there are no other extents locked for it
  *
  * Scheduling is not allowed, so the extent state tree is expected
  * to have one and only one object corresponding to this IO.
  */
 static void end_bio_extent_readpage(struct bio *bio)
 {
     struct bio_vec *bvec;
     struct btrfs_bio *bbio = btrfs_bio(bio);
     struct extent_io_tree *tree, *failure_tree;
     struct processed_extent processed = { 0 };
     /*
      * The offset to the beginning of a bio, since one bio can never be
      * larger than UINT_MAX, u32 here is enough.
      */
     u32 bio_offset = 0;
     int mirror;
     struct bvec_iter_all iter_all;
 
     ASSERT(!bio_flagged(bio, BIO_CLONED));
     bio_for_each_segment_all(bvec, bio, iter_all) {
         bool uptodate = !bio->bi_status;
         struct page *page = bvec->bv_page;
         struct inode *inode = page->mapping->host;
         struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
         const u32 sectorsize = fs_info->sectorsize;
         unsigned int error_bitmap = (unsigned int)-1;
         bool repair = false;
         u64 start;
         u64 end;
         u32 len;
 
         btrfs_debug(fs_info,
             "end_bio_extent_readpage: bi_sector=%llu, err=%d, mirror=%u",
             bio->bi_iter.bi_sector, bio->bi_status,
             bbio->mirror_num);
         tree = &BTRFS_I(inode)->io_tree;
         failure_tree = &BTRFS_I(inode)->io_failure_tree;
 
         /*
          * We always issue full-sector reads, but if some block in a
          * page fails to read, blk_update_request() will advance
          * bv_offset and adjust bv_len to compensate.  Print a warning
          * for unaligned offsets, and an error if they don't add up to
          * a full sector.
          */
         if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
             btrfs_err(fs_info,
         "partial page read in btrfs with offset %u and length %u",
                   bvec->bv_offset, bvec->bv_len);
         else if (!IS_ALIGNED(bvec->bv_offset + bvec->bv_len,
                      sectorsize))
             btrfs_info(fs_info,
         "incomplete page read with offset %u and length %u",
                    bvec->bv_offset, bvec->bv_len);
 
         start = page_offset(page) + bvec->bv_offset;
         end = start + bvec->bv_len - 1;
         len = bvec->bv_len;
 
         mirror = bbio->mirror_num;
         if (likely(uptodate)) {
             if (is_data_inode(inode)) {
                 error_bitmap = btrfs_verify_data_csum(bbio,
                         bio_offset, page, start, end);
                 if (error_bitmap)
                     uptodate = false;
             } else {
                 if (btrfs_validate_metadata_buffer(bbio,
                         page, start, end, mirror))
                     uptodate = false;
             }
         }
 
         if (likely(uptodate)) {
             loff_t i_size = i_size_read(inode);
             pgoff_t end_index = i_size >> PAGE_SHIFT;
 
             clean_io_failure(BTRFS_I(inode)->root->fs_info,
                      failure_tree, tree, start, page,
                      btrfs_ino(BTRFS_I(inode)), 0);
 
             /*
              * Zero out the remaining part if this range straddles
              * i_size.
              *
              * Here we should only zero the range inside the bvec,
              * not touch anything else.
              *
              * NOTE: i_size is exclusive while end is inclusive.
              */
             if (page->index == end_index && i_size <= end) {
                 u32 zero_start = max(offset_in_page(i_size),
                              offset_in_page(start));
 
                 zero_user_segment(page, zero_start,
                           offset_in_page(end) + 1);
             }
         } else if (is_data_inode(inode)) {
             /*
              * Only try to repair bios that actually made it to a
              * device.  If the bio failed to be submitted mirror
              * is 0 and we need to fail it without retrying.
              *
              * This also includes the high level bios for compressed
              * extents - these never make it to a device and repair
              * is already handled on the lower compressed bio.
              */
             if (mirror > 0)
                 repair = true;
         } else {
             struct extent_buffer *eb;
 
             eb = find_extent_buffer_readpage(fs_info, page, start);
             set_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
             eb->read_mirror = mirror;
             atomic_dec(&eb->io_pages);
         }
 
         if (repair) {
             /*
              * submit_data_read_repair() will handle all the good
              * and bad sectors, we just continue to the next bvec.
              */
             submit_data_read_repair(inode, bbio, bio_offset, bvec,
                         error_bitmap);
         } else {
             /* Update page status and unlock */
             end_page_read(page, uptodate, start, len);
             endio_readpage_release_extent(&processed, BTRFS_I(inode),
                     start, end, PageUptodate(page));
         }
 
         ASSERT(bio_offset + len > bio_offset);
         bio_offset += len;
 
     }
     /* Release the last extent */
     endio_readpage_release_extent(&processed, NULL, 0, 0, false);
     btrfs_bio_free_csum(bbio);
     bio_put(bio);
 }
 
 /**
  * Populate every free slot in a provided array with pages.
  *
  * @nr_pages:   number of pages to allocate
  * @page_array: the array to fill with pages; any existing non-null entries in
  *      the array will be skipped
  *
  * Return: 0        if all pages were able to be allocated;
  *         -ENOMEM  otherwise, and the caller is responsible for freeing all
  *                  non-null page pointers in the array.
  */
 int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array)
 {
     unsigned int allocated;
 
     for (allocated = 0; allocated < nr_pages;) {
         unsigned int last = allocated;
 
         allocated = alloc_pages_bulk_array(GFP_NOFS, nr_pages, page_array);
 
         if (allocated == nr_pages)
             return 0;
 
         /*
          * During this iteration, no page could be allocated, even
          * though alloc_pages_bulk_array() falls back to alloc_page()
          * if  it could not bulk-allocate. So we must be out of memory.
          */
         if (allocated == last)
             return -ENOMEM;
 
         memalloc_retry_wait(GFP_NOFS);
     }
     return 0;
 }
 
 /*
  * Initialize the members up to but not including 'bio'. Use after allocating a
  * new bio by bio_alloc_bioset as it does not initialize the bytes outside of
  * 'bio' because use of __GFP_ZERO is not supported.
  */
 static inline void btrfs_bio_init(struct btrfs_bio *bbio)
 {
     memset(bbio, 0, offsetof(struct btrfs_bio, bio));
 }
 
 /*
  * Allocate a btrfs_io_bio, with @nr_iovecs as maximum number of iovecs.
  *
  * The bio allocation is backed by bioset and does not fail.
  */
 struct bio *btrfs_bio_alloc(unsigned int nr_iovecs)
 {
     struct bio *bio;
 
     ASSERT(0 < nr_iovecs && nr_iovecs <= BIO_MAX_VECS);
     bio = bio_alloc_bioset(NULL, nr_iovecs, 0, GFP_NOFS, &btrfs_bioset);
     btrfs_bio_init(btrfs_bio(bio));
     return bio;
 }
 
 struct bio *btrfs_bio_clone_partial(struct bio *orig, u64 offset, u64 size)
 {
     struct bio *bio;
     struct btrfs_bio *bbio;
 
     ASSERT(offset <= UINT_MAX && size <= UINT_MAX);
 
     /* this will never fail when it's backed by a bioset */
     bio = bio_alloc_clone(orig->bi_bdev, orig, GFP_NOFS, &btrfs_bioset);
     ASSERT(bio);
 
     bbio = btrfs_bio(bio);
     btrfs_bio_init(bbio);
 
     bio_trim(bio, offset >> 9, size >> 9);
     bbio->iter = bio->bi_iter;
     return bio;
 }
 
 /**
  * Attempt to add a page to bio
  *
  * @bio_ctrl:   record both the bio, and its bio_flags
  * @page:   page to add to the bio
  * @disk_bytenr:  offset of the new bio or to check whether we are adding
  *                a contiguous page to the previous one
  * @size:   portion of page that we want to write
  * @pg_offset:  starting offset in the page
  * @compress_type:   compression type of the current bio to see if we can merge them
  *
  * Attempt to add a page to bio considering stripe alignment etc.
  *
  * Return >= 0 for the number of bytes added to the bio.
  * Can return 0 if the current bio is already at stripe/zone boundary.
  * Return <0 for error.
  */
 static int btrfs_bio_add_page(struct btrfs_bio_ctrl *bio_ctrl,
                   struct page *page,
                   u64 disk_bytenr, unsigned int size,
                   unsigned int pg_offset,
                   enum btrfs_compression_type compress_type)
 {
     struct bio *bio = bio_ctrl->bio;
     u32 bio_size = bio->bi_iter.bi_size;
     u32 real_size;
     const sector_t sector = disk_bytenr >> SECTOR_SHIFT;
     bool contig = false;
     int ret;
 
     ASSERT(bio);
     /* The limit should be calculated when bio_ctrl->bio is allocated */
     ASSERT(bio_ctrl->len_to_oe_boundary && bio_ctrl->len_to_stripe_boundary);
     if (bio_ctrl->compress_type != compress_type)
         return 0;
 
 
     if (bio->bi_iter.bi_size == 0) {
         /* We can always add a page into an empty bio. */
         contig = true;
     } else if (bio_ctrl->compress_type == BTRFS_COMPRESS_NONE) {
         struct bio_vec *bvec = bio_last_bvec_all(bio);
 
         /*
          * The contig check requires the following conditions to be met:
          * 1) The pages are belonging to the same inode
          *    This is implied by the call chain.
          *
          * 2) The range has adjacent logical bytenr
          *
          * 3) The range has adjacent file offset
          *    This is required for the usage of btrfs_bio->file_offset.
          */
         if (bio_end_sector(bio) == sector &&
             page_offset(bvec->bv_page) + bvec->bv_offset +
             bvec->bv_len == page_offset(page) + pg_offset)
             contig = true;
     } else {
         /*
          * For compression, all IO should have its logical bytenr
          * set to the starting bytenr of the compressed extent.
          */
         contig = bio->bi_iter.bi_sector == sector;
     }
 
     if (!contig)
         return 0;
 
     real_size = min(bio_ctrl->len_to_oe_boundary,
             bio_ctrl->len_to_stripe_boundary) - bio_size;
     real_size = min(real_size, size);
 
     /*
      * If real_size is 0, never call bio_add_*_page(), as even size is 0,
      * bio will still execute its endio function on the page!
      */
     if (real_size == 0)
         return 0;
 
     if (bio_op(bio) == REQ_OP_ZONE_APPEND)
         ret = bio_add_zone_append_page(bio, page, real_size, pg_offset);
     else
         ret = bio_add_page(bio, page, real_size, pg_offset);
 
     return ret;
 }
 
 static int calc_bio_boundaries(struct btrfs_bio_ctrl *bio_ctrl,
                    struct btrfs_inode *inode, u64 file_offset)
 {
     struct btrfs_fs_info *fs_info = inode->root->fs_info;
     struct btrfs_io_geometry geom;
     struct btrfs_ordered_extent *ordered;
     struct extent_map *em;
     u64 logical = (bio_ctrl->bio->bi_iter.bi_sector << SECTOR_SHIFT);
     int ret;
 
     /*
      * Pages for compressed extent are never submitted to disk directly,
      * thus it has no real boundary, just set them to U32_MAX.
      *
      * The split happens for real compressed bio, which happens in
      * btrfs_submit_compressed_read/write().
      */
     if (bio_ctrl->compress_type != BTRFS_COMPRESS_NONE) {
         bio_ctrl->len_to_oe_boundary = U32_MAX;
         bio_ctrl->len_to_stripe_boundary = U32_MAX;
         return 0;
     }
     em = btrfs_get_chunk_map(fs_info, logical, fs_info->sectorsize);
     if (IS_ERR(em))
         return PTR_ERR(em);
     ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(bio_ctrl->bio),
                     logical, &geom);
     free_extent_map(em);
     if (ret < 0) {
         return ret;
     }
     if (geom.len > U32_MAX)
         bio_ctrl->len_to_stripe_boundary = U32_MAX;
     else
         bio_ctrl->len_to_stripe_boundary = (u32)geom.len;
 
     if (bio_op(bio_ctrl->bio) != REQ_OP_ZONE_APPEND) {
         bio_ctrl->len_to_oe_boundary = U32_MAX;
         return 0;
     }
 
     /* Ordered extent not yet created, so we're good */
     ordered = btrfs_lookup_ordered_extent(inode, file_offset);
     if (!ordered) {
         bio_ctrl->len_to_oe_boundary = U32_MAX;
         return 0;
     }
 
     bio_ctrl->len_to_oe_boundary = min_t(u32, U32_MAX,
         ordered->disk_bytenr + ordered->disk_num_bytes - logical);
     btrfs_put_ordered_extent(ordered);
     return 0;
 }
 
 static int alloc_new_bio(struct btrfs_inode *inode,
              struct btrfs_bio_ctrl *bio_ctrl,
              struct writeback_control *wbc,
              blk_opf_t opf,
              bio_end_io_t end_io_func,
              u64 disk_bytenr, u32 offset, u64 file_offset,
              enum btrfs_compression_type compress_type)
 {
     struct btrfs_fs_info *fs_info = inode->root->fs_info;
     struct bio *bio;
     int ret;
 
     bio = btrfs_bio_alloc(BIO_MAX_VECS);
     /*
      * For compressed page range, its disk_bytenr is always @disk_bytenr
      * passed in, no matter if we have added any range into previous bio.
      */
     if (compress_type != BTRFS_COMPRESS_NONE)
         bio->bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT;
     else
         bio->bi_iter.bi_sector = (disk_bytenr + offset) >> SECTOR_SHIFT;
     bio_ctrl->bio = bio;
     bio_ctrl->compress_type = compress_type;
     bio->bi_end_io = end_io_func;
     bio->bi_opf = opf;
     ret = calc_bio_boundaries(bio_ctrl, inode, file_offset);
     if (ret < 0)
         goto error;
 
     if (wbc) {
         /*
          * For Zone append we need the correct block_device that we are
          * going to write to set in the bio to be able to respect the
          * hardware limitation.  Look it up here:
          */
         if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
             struct btrfs_device *dev;
 
             dev = btrfs_zoned_get_device(fs_info, disk_bytenr,
                              fs_info->sectorsize);
             if (IS_ERR(dev)) {
                 ret = PTR_ERR(dev);
                 goto error;
             }
 
             bio_set_dev(bio, dev->bdev);
         } else {
             /*
              * Otherwise pick the last added device to support
              * cgroup writeback.  For multi-device file systems this
              * means blk-cgroup policies have to always be set on the
              * last added/replaced device.  This is a bit odd but has
              * been like that for a long time.
              */
             bio_set_dev(bio, fs_info->fs_devices->latest_dev->bdev);
         }
         wbc_init_bio(wbc, bio);
     } else {
         ASSERT(bio_op(bio) != REQ_OP_ZONE_APPEND);
     }
     return 0;
 error:
     bio_ctrl->bio = NULL;
     bio->bi_status = errno_to_blk_status(ret);
     bio_endio(bio);
     return ret;
 }
 
 /*
  * @opf:    bio REQ_OP_* and REQ_* flags as one value
  * @wbc:    optional writeback control for io accounting
  * @page:   page to add to the bio
  * @disk_bytenr: logical bytenr where the write will be
  * @size:   portion of page that we want to write to
  * @pg_offset:  offset of the new bio or to check whether we are adding
  *              a contiguous page to the previous one
  * @bio_ret:    must be valid pointer, newly allocated bio will be stored there
  * @end_io_func:     end_io callback for new bio
  * @mirror_num:      desired mirror to read/write
  * @prev_bio_flags:  flags of previous bio to see if we can merge the current one
  * @compress_type:   compress type for current bio
  */
 static int submit_extent_page(blk_opf_t opf,
                   struct writeback_control *wbc,
                   struct btrfs_bio_ctrl *bio_ctrl,
                   struct page *page, u64 disk_bytenr,
                   size_t size, unsigned long pg_offset,
                   bio_end_io_t end_io_func,
                   enum btrfs_compression_type compress_type,
                   bool force_bio_submit)
 {
     int ret = 0;
     struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
     unsigned int cur = pg_offset;
 
     ASSERT(bio_ctrl);
 
     ASSERT(pg_offset < PAGE_SIZE && size <= PAGE_SIZE &&
            pg_offset + size <= PAGE_SIZE);
     if (force_bio_submit)
         submit_one_bio(bio_ctrl);
 
     while (cur < pg_offset + size) {
         u32 offset = cur - pg_offset;
         int added;
 
         /* Allocate new bio if needed */
         if (!bio_ctrl->bio) {
             ret = alloc_new_bio(inode, bio_ctrl, wbc, opf,
                         end_io_func, disk_bytenr, offset,
                         page_offset(page) + cur,
                         compress_type);
             if (ret < 0)
                 return ret;
         }
         /*
          * We must go through btrfs_bio_add_page() to ensure each
          * page range won't cross various boundaries.
          */
         if (compress_type != BTRFS_COMPRESS_NONE)
             added = btrfs_bio_add_page(bio_ctrl, page, disk_bytenr,
                     size - offset, pg_offset + offset,
                     compress_type);
         else
             added = btrfs_bio_add_page(bio_ctrl, page,
                     disk_bytenr + offset, size - offset,
                     pg_offset + offset, compress_type);
 
         /* Metadata page range should never be split */
         if (!is_data_inode(&inode->vfs_inode))
             ASSERT(added == 0 || added == size - offset);
 
         /* At least we added some page, update the account */
         if (wbc && added)
             wbc_account_cgroup_owner(wbc, page, added);
 
         /* We have reached boundary, submit right now */
         if (added < size - offset) {
             /* The bio should contain some page(s) */
             ASSERT(bio_ctrl->bio->bi_iter.bi_size);
             submit_one_bio(bio_ctrl);
         }
         cur += added;
     }
     return 0;
 }
 
 static int attach_extent_buffer_page(struct extent_buffer *eb,
                      struct page *page,
                      struct btrfs_subpage *prealloc)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     int ret = 0;
 
     /*
      * If the page is mapped to btree inode, we should hold the private
      * lock to prevent race.
      * For cloned or dummy extent buffers, their pages are not mapped and
      * will not race with any other ebs.
      */
     if (page->mapping)
         lockdep_assert_held(&page->mapping->private_lock);
 
     if (fs_info->nodesize >= PAGE_SIZE) {
         if (!PagePrivate(page))
             attach_page_private(page, eb);
         else
             WARN_ON(page->private != (unsigned long)eb);
         return 0;
     }
 
     /* Already mapped, just free prealloc */
     if (PagePrivate(page)) {
         btrfs_free_subpage(prealloc);
         return 0;
     }
 
     if (prealloc)
         /* Has preallocated memory for subpage */
         attach_page_private(page, prealloc);
     else
         /* Do new allocation to attach subpage */
         ret = btrfs_attach_subpage(fs_info, page,
                        BTRFS_SUBPAGE_METADATA);
     return ret;
 }
 
 int set_page_extent_mapped(struct page *page)
 {
     struct btrfs_fs_info *fs_info;
 
     ASSERT(page->mapping);
 
     if (PagePrivate(page))
         return 0;
 
     fs_info = btrfs_sb(page->mapping->host->i_sb);
 
     if (btrfs_is_subpage(fs_info, page))
         return btrfs_attach_subpage(fs_info, page, BTRFS_SUBPAGE_DATA);
 
     attach_page_private(page, (void *)EXTENT_PAGE_PRIVATE);
     return 0;
 }
 
 void clear_page_extent_mapped(struct page *page)
 {
     struct btrfs_fs_info *fs_info;
 
     ASSERT(page->mapping);
 
     if (!PagePrivate(page))
         return;
 
     fs_info = btrfs_sb(page->mapping->host->i_sb);
     if (btrfs_is_subpage(fs_info, page))
         return btrfs_detach_subpage(fs_info, page);
 
     detach_page_private(page);
 }
 
 static struct extent_map *
 __get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
          u64 start, u64 len, struct extent_map **em_cached)
 {
     struct extent_map *em;
 
     if (em_cached && *em_cached) {
         em = *em_cached;
         if (extent_map_in_tree(em) && start >= em->start &&
             start < extent_map_end(em)) {
             refcount_inc(&em->refs);
             return em;
         }
 
         free_extent_map(em);
         *em_cached = NULL;
     }
 
     em = btrfs_get_extent(BTRFS_I(inode), page, pg_offset, start, len);
     if (em_cached && !IS_ERR(em)) {
         BUG_ON(*em_cached);
         refcount_inc(&em->refs);
         *em_cached = em;
     }
     return em;
 }
 /*
  * basic readpage implementation.  Locked extent state structs are inserted
  * into the tree that are removed when the IO is done (by the end_io
  * handlers)
  * XXX JDM: This needs looking at to ensure proper page locking
  * return 0 on success, otherwise return error
  */
 static int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
               struct btrfs_bio_ctrl *bio_ctrl,
               blk_opf_t read_flags, u64 *prev_em_start)
 {
     struct inode *inode = page->mapping->host;
     struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
     u64 start = page_offset(page);
     const u64 end = start + PAGE_SIZE - 1;
     u64 cur = start;
     u64 extent_offset;
     u64 last_byte = i_size_read(inode);
     u64 block_start;
     u64 cur_end;
     struct extent_map *em;
     int ret = 0;
     size_t pg_offset = 0;
     size_t iosize;
     size_t blocksize = inode->i_sb->s_blocksize;
     struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
 
     ret = set_page_extent_mapped(page);
     if (ret < 0) {
         unlock_extent(tree, start, end);
         btrfs_page_set_error(fs_info, page, start, PAGE_SIZE);
         unlock_page(page);
         goto out;
     }
 
     if (page->index == last_byte >> PAGE_SHIFT) {
         size_t zero_offset = offset_in_page(last_byte);
 
         if (zero_offset) {
             iosize = PAGE_SIZE - zero_offset;
             memzero_page(page, zero_offset, iosize);
         }
     }
     begin_page_read(fs_info, page);
     while (cur <= end) {
         unsigned long this_bio_flag = 0;
         bool force_bio_submit = false;
         u64 disk_bytenr;
 
         ASSERT(IS_ALIGNED(cur, fs_info->sectorsize));
         if (cur >= last_byte) {
             struct extent_state *cached = NULL;
 
             iosize = PAGE_SIZE - pg_offset;
             memzero_page(page, pg_offset, iosize);
             set_extent_uptodate(tree, cur, cur + iosize - 1,
                         &cached, GFP_NOFS);
             unlock_extent_cached(tree, cur,
                          cur + iosize - 1, &cached);
             end_page_read(page, true, cur, iosize);
             break;
         }
         em = __get_extent_map(inode, page, pg_offset, cur,
                       end - cur + 1, em_cached);
         if (IS_ERR(em)) {
             unlock_extent(tree, cur, end);
             end_page_read(page, false, cur, end + 1 - cur);
             ret = PTR_ERR(em);
             break;
         }
         extent_offset = cur - em->start;
         BUG_ON(extent_map_end(em) <= cur);
         BUG_ON(end < cur);
 
         if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
             this_bio_flag = em->compress_type;
 
         iosize = min(extent_map_end(em) - cur, end - cur + 1);
         cur_end = min(extent_map_end(em) - 1, end);
         iosize = ALIGN(iosize, blocksize);
         if (this_bio_flag != BTRFS_COMPRESS_NONE)
             disk_bytenr = em->block_start;
         else
             disk_bytenr = em->block_start + extent_offset;
         block_start = em->block_start;
         if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
             block_start = EXTENT_MAP_HOLE;
 
         /*
          * If we have a file range that points to a compressed extent
          * and it's followed by a consecutive file range that points
          * to the same compressed extent (possibly with a different
          * offset and/or length, so it either points to the whole extent
          * or only part of it), we must make sure we do not submit a
          * single bio to populate the pages for the 2 ranges because
          * this makes the compressed extent read zero out the pages
          * belonging to the 2nd range. Imagine the following scenario:
          *
          *  File layout
          *  [0 - 8K]                     [8K - 24K]
          *    |                               |
          *    |                               |
          * points to extent X,         points to extent X,
          * offset 4K, length of 8K     offset 0, length 16K
          *
          * [extent X, compressed length = 4K uncompressed length = 16K]
          *
          * If the bio to read the compressed extent covers both ranges,
          * it will decompress extent X into the pages belonging to the
          * first range and then it will stop, zeroing out the remaining
          * pages that belong to the other range that points to extent X.
          * So here we make sure we submit 2 bios, one for the first
          * range and another one for the third range. Both will target
          * the same physical extent from disk, but we can't currently
          * make the compressed bio endio callback populate the pages
          * for both ranges because each compressed bio is tightly
          * coupled with a single extent map, and each range can have
          * an extent map with a different offset value relative to the
          * uncompressed data of our extent and different lengths. This
          * is a corner case so we prioritize correctness over
          * non-optimal behavior (submitting 2 bios for the same extent).
          */
         if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags) &&
             prev_em_start && *prev_em_start != (u64)-1 &&
             *prev_em_start != em->start)
             force_bio_submit = true;
 
         if (prev_em_start)
             *prev_em_start = em->start;
 
         free_extent_map(em);
         em = NULL;
 
         /* we've found a hole, just zero and go on */
         if (block_start == EXTENT_MAP_HOLE) {
             struct extent_state *cached = NULL;
 
             memzero_page(page, pg_offset, iosize);
 
             set_extent_uptodate(tree, cur, cur + iosize - 1,
                         &cached, GFP_NOFS);
             unlock_extent_cached(tree, cur,
                          cur + iosize - 1, &cached);
             end_page_read(page, true, cur, iosize);
             cur = cur + iosize;
             pg_offset += iosize;
             continue;
         }
         /* the get_extent function already copied into the page */
         if (test_range_bit(tree, cur, cur_end,
                    EXTENT_UPTODATE, 1, NULL)) {
             unlock_extent(tree, cur, cur + iosize - 1);
             end_page_read(page, true, cur, iosize);
             cur = cur + iosize;
             pg_offset += iosize;
             continue;
         }
         /* we have an inline extent but it didn't get marked up
          * to date.  Error out
          */
         if (block_start == EXTENT_MAP_INLINE) {
             unlock_extent(tree, cur, cur + iosize - 1);
             end_page_read(page, false, cur, iosize);
             cur = cur + iosize;
             pg_offset += iosize;
             continue;
         }
 
         ret = submit_extent_page(REQ_OP_READ | read_flags, NULL,
                      bio_ctrl, page, disk_bytenr, iosize,
                      pg_offset, end_bio_extent_readpage,
                      this_bio_flag, force_bio_submit);
         if (ret) {
             /*
              * We have to unlock the remaining range, or the page
              * will never be unlocked.
              */
             unlock_extent(tree, cur, end);
             end_page_read(page, false, cur, end + 1 - cur);
             goto out;
         }
         cur = cur + iosize;
         pg_offset += iosize;
     }
 out:
     return ret;
 }
 
 int btrfs_read_folio(struct file *file, struct folio *folio)
 {
     struct page *page = &folio->page;
     struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
     u64 start = page_offset(page);
     u64 end = start + PAGE_SIZE - 1;
     struct btrfs_bio_ctrl bio_ctrl = { 0 };
     int ret;
 
     btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);
 
     ret = btrfs_do_readpage(page, NULL, &bio_ctrl, 0, NULL);
     /*
      * If btrfs_do_readpage() failed we will want to submit the assembled
      * bio to do the cleanup.
      */
     submit_one_bio(&bio_ctrl);
     return ret;
 }
 
 static inline void contiguous_readpages(struct page *pages[], int nr_pages,
                     u64 start, u64 end,
                     struct extent_map **em_cached,
                     struct btrfs_bio_ctrl *bio_ctrl,
                     u64 *prev_em_start)
 {
     struct btrfs_inode *inode = BTRFS_I(pages[0]->mapping->host);
     int index;
 
     btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);
 
     for (index = 0; index < nr_pages; index++) {
         btrfs_do_readpage(pages[index], em_cached, bio_ctrl,
                   REQ_RAHEAD, prev_em_start);
         put_page(pages[index]);
     }
 }
 
 /*
  * helper for __extent_writepage, doing all of the delayed allocation setup.
  *
  * This returns 1 if btrfs_run_delalloc_range function did all the work required
  * to write the page (copy into inline extent).  In this case the IO has
  * been started and the page is already unlocked.
  *
  * This returns 0 if all went well (page still locked)
  * This returns < 0 if there were errors (page still locked)
  */
 static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
         struct page *page, struct writeback_control *wbc)
 {
     const u64 page_end = page_offset(page) + PAGE_SIZE - 1;
     u64 delalloc_start = page_offset(page);
     u64 delalloc_to_write = 0;
     /* How many pages are started by btrfs_run_delalloc_range() */
     unsigned long nr_written = 0;
     int ret;
     int page_started = 0;
 
     while (delalloc_start < page_end) {
         u64 delalloc_end = page_end;
         bool found;
 
         found = find_lock_delalloc_range(&inode->vfs_inode, page,
                            &delalloc_start,
                            &delalloc_end);
         if (!found) {
             delalloc_start = delalloc_end + 1;
             continue;
         }
         ret = btrfs_run_delalloc_range(inode, page, delalloc_start,
                 delalloc_end, &page_started, &nr_written, wbc);
         if (ret) {
             btrfs_page_set_error(inode->root->fs_info, page,
                          page_offset(page), PAGE_SIZE);
             return ret;
         }
         /*
          * delalloc_end is already one less than the total length, so
          * we don't subtract one from PAGE_SIZE
          */
         delalloc_to_write += (delalloc_end - delalloc_start +
                       PAGE_SIZE) >> PAGE_SHIFT;
         delalloc_start = delalloc_end + 1;
     }
     if (wbc->nr_to_write < delalloc_to_write) {
         int thresh = 8192;
 
         if (delalloc_to_write < thresh * 2)
             thresh = delalloc_to_write;
         wbc->nr_to_write = min_t(u64, delalloc_to_write,
                      thresh);
     }
 
     /* Did btrfs_run_dealloc_range() already unlock and start the IO? */
     if (page_started) {
         /*
          * We've unlocked the page, so we can't update the mapping's
          * writeback index, just update nr_to_write.
          */
         wbc->nr_to_write -= nr_written;
         return 1;
     }
 
     return 0;
 }
 
 /*
  * Find the first byte we need to write.
  *
  * For subpage, one page can contain several sectors, and
  * __extent_writepage_io() will just grab all extent maps in the page
  * range and try to submit all non-inline/non-compressed extents.
  *
  * This is a big problem for subpage, we shouldn't re-submit already written
  * data at all.
  * This function will lookup subpage dirty bit to find which range we really
  * need to submit.
  *
  * Return the next dirty range in [@start, @end).
  * If no dirty range is found, @start will be page_offset(page) + PAGE_SIZE.
  */
 static void find_next_dirty_byte(struct btrfs_fs_info *fs_info,
                  struct page *page, u64 *start, u64 *end)
 {
     struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
     struct btrfs_subpage_info *spi = fs_info->subpage_info;
     u64 orig_start = *start;
     /* Declare as unsigned long so we can use bitmap ops */
     unsigned long flags;
     int range_start_bit;
     int range_end_bit;
 
     /*
      * For regular sector size == page size case, since one page only
      * contains one sector, we return the page offset directly.
      */
     if (!btrfs_is_subpage(fs_info, page)) {
         *start = page_offset(page);
         *end = page_offset(page) + PAGE_SIZE;
         return;
     }
 
     range_start_bit = spi->dirty_offset +
               (offset_in_page(orig_start) >> fs_info->sectorsize_bits);
 
     /* We should have the page locked, but just in case */
     spin_lock_irqsave(&subpage->lock, flags);
     bitmap_next_set_region(subpage->bitmaps, &range_start_bit, &range_end_bit,
                    spi->dirty_offset + spi->bitmap_nr_bits);
     spin_unlock_irqrestore(&subpage->lock, flags);
 
     range_start_bit -= spi->dirty_offset;
     range_end_bit -= spi->dirty_offset;
 
     *start = page_offset(page) + range_start_bit * fs_info->sectorsize;
     *end = page_offset(page) + range_end_bit * fs_info->sectorsize;
 }
 
 /*
  * helper for __extent_writepage.  This calls the writepage start hooks,
  * and does the loop to map the page into extents and bios.
  *
  * We return 1 if the IO is started and the page is unlocked,
  * 0 if all went well (page still locked)
  * < 0 if there were errors (page still locked)
  */
 static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
                  struct page *page,
                  struct writeback_control *wbc,
                  struct extent_page_data *epd,
                  loff_t i_size,
                  int *nr_ret)
 {
     struct btrfs_fs_info *fs_info = inode->root->fs_info;
     u64 cur = page_offset(page);
     u64 end = cur + PAGE_SIZE - 1;
     u64 extent_offset;
     u64 block_start;
     struct extent_map *em;
     int saved_ret = 0;
     int ret = 0;
     int nr = 0;
     enum req_op op = REQ_OP_WRITE;
     const blk_opf_t write_flags = wbc_to_write_flags(wbc);
     bool has_error = false;
     bool compressed;
 
     ret = btrfs_writepage_cow_fixup(page);
     if (ret) {
         /* Fixup worker will requeue */
         redirty_page_for_writepage(wbc, page);
         unlock_page(page);
         return 1;
     }
 
     /*
      * we don't want to touch the inode after unlocking the page,
      * so we update the mapping writeback index now
      */
     wbc->nr_to_write--;
 
     while (cur <= end) {
         u64 disk_bytenr;
         u64 em_end;
         u64 dirty_range_start = cur;
         u64 dirty_range_end;
         u32 iosize;
 
         if (cur >= i_size) {
             btrfs_writepage_endio_finish_ordered(inode, page, cur,
                                  end, true);
             /*
              * This range is beyond i_size, thus we don't need to
              * bother writing back.
              * But we still need to clear the dirty subpage bit, or
              * the next time the page gets dirtied, we will try to
              * writeback the sectors with subpage dirty bits,
              * causing writeback without ordered extent.
              */
             btrfs_page_clear_dirty(fs_info, page, cur, end + 1 - cur);
             break;
         }
 
         find_next_dirty_byte(fs_info, page, &dirty_range_start,
                      &dirty_range_end);
         if (cur < dirty_range_start) {
             cur = dirty_range_start;
             continue;
         }
 
         em = btrfs_get_extent(inode, NULL, 0, cur, end - cur + 1);
         if (IS_ERR(em)) {
             btrfs_page_set_error(fs_info, page, cur, end - cur + 1);
             ret = PTR_ERR_OR_ZERO(em);
             has_error = true;
             if (!saved_ret)
                 saved_ret = ret;
             break;
         }
 
         extent_offset = cur - em->start;
         em_end = extent_map_end(em);
         ASSERT(cur <= em_end);
         ASSERT(cur < end);
         ASSERT(IS_ALIGNED(em->start, fs_info->sectorsize));
         ASSERT(IS_ALIGNED(em->len, fs_info->sectorsize));
         block_start = em->block_start;
         compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
         disk_bytenr = em->block_start + extent_offset;
 
         /*
          * Note that em_end from extent_map_end() and dirty_range_end from
          * find_next_dirty_byte() are all exclusive
          */
         iosize = min(min(em_end, end + 1), dirty_range_end) - cur;
 
         if (btrfs_use_zone_append(inode, em->block_start))
             op = REQ_OP_ZONE_APPEND;
 
         free_extent_map(em);
         em = NULL;
 
         /*
          * compressed and inline extents are written through other
          * paths in the FS
          */
         if (compressed || block_start == EXTENT_MAP_HOLE ||
             block_start == EXTENT_MAP_INLINE) {
             if (compressed)
                 nr++;
             else
                 btrfs_writepage_endio_finish_ordered(inode,
                         page, cur, cur + iosize - 1, true);
             btrfs_page_clear_dirty(fs_info, page, cur, iosize);
             cur += iosize;
             continue;
         }
 
         btrfs_set_range_writeback(inode, cur, cur + iosize - 1);
         if (!PageWriteback(page)) {
             btrfs_err(inode->root->fs_info,
                    "page %lu not writeback, cur %llu end %llu",
                    page->index, cur, end);
         }
 
         /*
          * Although the PageDirty bit is cleared before entering this
          * function, subpage dirty bit is not cleared.
          * So clear subpage dirty bit here so next time we won't submit
          * page for range already written to disk.
          */
         btrfs_page_clear_dirty(fs_info, page, cur, iosize);
 
         ret = submit_extent_page(op | write_flags, wbc,
                      &epd->bio_ctrl, page,
                      disk_bytenr, iosize,
                      cur - page_offset(page),
                      end_bio_extent_writepage,
                      0, false);
         if (ret) {
             has_error = true;
             if (!saved_ret)
                 saved_ret = ret;
 
             btrfs_page_set_error(fs_info, page, cur, iosize);
             if (PageWriteback(page))
                 btrfs_page_clear_writeback(fs_info, page, cur,
                                iosize);
         }
 
         cur += iosize;
         nr++;
     }
     /*
      * If we finish without problem, we should not only clear page dirty,
      * but also empty subpage dirty bits
      */
     if (!has_error)
         btrfs_page_assert_not_dirty(fs_info, page);
     else
         ret = saved_ret;
     *nr_ret = nr;
     return ret;
 }
 
 /*
  * the writepage semantics are similar to regular writepage.  extent
  * records are inserted to lock ranges in the tree, and as dirty areas
  * are found, they are marked writeback.  Then the lock bits are removed
  * and the end_io handler clears the writeback ranges
  *
  * Return 0 if everything goes well.
  * Return <0 for error.
  */
 static int __extent_writepage(struct page *page, struct writeback_control *wbc,
                   struct extent_page_data *epd)
 {
     struct folio *folio = page_folio(page);
     struct inode *inode = page->mapping->host;
     struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
     const u64 page_start = page_offset(page);
     const u64 page_end = page_start + PAGE_SIZE - 1;
     int ret;
     int nr = 0;
     size_t pg_offset;
     loff_t i_size = i_size_read(inode);
     unsigned long end_index = i_size >> PAGE_SHIFT;
 
     trace___extent_writepage(page, inode, wbc);
 
     WARN_ON(!PageLocked(page));
 
     btrfs_page_clear_error(btrfs_sb(inode->i_sb), page,
                    page_offset(page), PAGE_SIZE);
 
     pg_offset = offset_in_page(i_size);
     if (page->index > end_index ||
        (page->index == end_index && !pg_offset)) {
         folio_invalidate(folio, 0, folio_size(folio));
         folio_unlock(folio);
         return 0;
     }
 
     if (page->index == end_index)
         memzero_page(page, pg_offset, PAGE_SIZE - pg_offset);
 
     ret = set_page_extent_mapped(page);
     if (ret < 0) {
         SetPageError(page);
         goto done;
     }
 
     if (!epd->extent_locked) {
         ret = writepage_delalloc(BTRFS_I(inode), page, wbc);
         if (ret == 1)
             return 0;
         if (ret)
             goto done;
     }
 
     ret = __extent_writepage_io(BTRFS_I(inode), page, wbc, epd, i_size,
                     &nr);
     if (ret == 1)
         return 0;
 
 done:
     if (nr == 0) {
         /* make sure the mapping tag for page dirty gets cleared */
         set_page_writeback(page);
         end_page_writeback(page);
     }
     /*
      * Here we used to have a check for PageError() and then set @ret and
      * call end_extent_writepage().
      *
      * But in fact setting @ret here will cause different error paths
      * between subpage and regular sectorsize.
      *
      * For regular page size, we never submit current page, but only add
      * current page to current bio.
      * The bio submission can only happen in next page.
      * Thus if we hit the PageError() branch, @ret is already set to
      * non-zero value and will not get updated for regular sectorsize.
      *
      * But for subpage case, it's possible we submit part of current page,
      * thus can get PageError() set by submitted bio of the same page,
      * while our @ret is still 0.
      *
      * So here we unify the behavior and don't set @ret.
      * Error can still be properly passed to higher layer as page will
      * be set error, here we just don't handle the IO failure.
      *
      * NOTE: This is just a hotfix for subpage.
      * The root fix will be properly ending ordered extent when we hit
      * an error during writeback.
      *
      * But that needs a bigger refactoring, as we not only need to grab the
      * submitted OE, but also need to know exactly at which bytenr we hit
      * the error.
      * Currently the full page based __extent_writepage_io() is not
      * capable of that.
      */
     if (PageError(page))
         end_extent_writepage(page, ret, page_start, page_end);
     if (epd->extent_locked) {
         /*
          * If epd->extent_locked, it's from extent_write_locked_range(),
          * the page can either be locked by lock_page() or
          * process_one_page().
          * Let btrfs_page_unlock_writer() handle both cases.
          */
         ASSERT(wbc);
         btrfs_page_unlock_writer(fs_info, page, wbc->range_start,
                      wbc->range_end + 1 - wbc->range_start);
     } else {
         unlock_page(page);
     }
     ASSERT(ret <= 0);
     return ret;
 }
 
 void wait_on_extent_buffer_writeback(struct extent_buffer *eb)
 {
     wait_on_bit_io(&eb->bflags, EXTENT_BUFFER_WRITEBACK,
                TASK_UNINTERRUPTIBLE);
 }
 
 static void end_extent_buffer_writeback(struct extent_buffer *eb)
 {
     clear_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
     smp_mb__after_atomic();
     wake_up_bit(&eb->bflags, EXTENT_BUFFER_WRITEBACK);
 }
 
 /*
  * Lock extent buffer status and pages for writeback.
  *
  * May try to flush write bio if we can't get the lock.
  *
  * Return  0 if the extent buffer doesn't need to be submitted.
  *           (E.g. the extent buffer is not dirty)
  * Return >0 is the extent buffer is submitted to bio.
  * Return <0 if something went wrong, no page is locked.
  */
 static noinline_for_stack int lock_extent_buffer_for_io(struct extent_buffer *eb,
               struct extent_page_data *epd)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     int i, num_pages;
     int flush = 0;
     int ret = 0;
 
     if (!btrfs_try_tree_write_lock(eb)) {
         submit_write_bio(epd, 0);
         flush = 1;
         btrfs_tree_lock(eb);
     }
 
     if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
         btrfs_tree_unlock(eb);
         if (!epd->sync_io)
             return 0;
         if (!flush) {
             submit_write_bio(epd, 0);
             flush = 1;
         }
         while (1) {
             wait_on_extent_buffer_writeback(eb);
             btrfs_tree_lock(eb);
             if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
                 break;
             btrfs_tree_unlock(eb);
         }
     }
 
     /*
      * We need to do this to prevent races in people who check if the eb is
      * under IO since we can end up having no IO bits set for a short period
      * of time.
      */
     spin_lock(&eb->refs_lock);
     if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
         set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
         spin_unlock(&eb->refs_lock);
         btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
         percpu_counter_add_batch(&fs_info->dirty_metadata_bytes,
                      -eb->len,
                      fs_info->dirty_metadata_batch);
         ret = 1;
     } else {
         spin_unlock(&eb->refs_lock);
     }
 
     btrfs_tree_unlock(eb);
 
     /*
      * Either we don't need to submit any tree block, or we're submitting
      * subpage eb.
      * Subpage metadata doesn't use page locking at all, so we can skip
      * the page locking.
      */
     if (!ret || fs_info->nodesize < PAGE_SIZE)
         return ret;
 
     num_pages = num_extent_pages(eb);
     for (i = 0; i < num_pages; i++) {
         struct page *p = eb->pages[i];
 
         if (!trylock_page(p)) {
             if (!flush) {
                 submit_write_bio(epd, 0);
                 flush = 1;
             }
             lock_page(p);
         }
     }
 
     return ret;
 }
 
 static void set_btree_ioerr(struct page *page, struct extent_buffer *eb)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
 
     btrfs_page_set_error(fs_info, page, eb->start, eb->len);
     if (test_and_set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))
         return;
 
     /*
      * A read may stumble upon this buffer later, make sure that it gets an
      * error and knows there was an error.
      */
     clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
 
     /*
      * We need to set the mapping with the io error as well because a write
      * error will flip the file system readonly, and then syncfs() will
      * return a 0 because we are readonly if we don't modify the err seq for
      * the superblock.
      */
     mapping_set_error(page->mapping, -EIO);
 
     /*
      * If we error out, we should add back the dirty_metadata_bytes
      * to make it consistent.
      */
     percpu_counter_add_batch(&fs_info->dirty_metadata_bytes,
                  eb->len, fs_info->dirty_metadata_batch);
 
     /*
      * If writeback for a btree extent that doesn't belong to a log tree
      * failed, increment the counter transaction->eb_write_errors.
      * We do this because while the transaction is running and before it's
      * committing (when we call filemap_fdata[write|wait]_range against
      * the btree inode), we might have
      * btree_inode->i_mapping->a_ops->writepages() called by the VM - if it
      * returns an error or an error happens during writeback, when we're
      * committing the transaction we wouldn't know about it, since the pages
      * can be no longer dirty nor marked anymore for writeback (if a
      * subsequent modification to the extent buffer didn't happen before the
      * transaction commit), which makes filemap_fdata[write|wait]_range not
      * able to find the pages tagged with SetPageError at transaction
      * commit time. So if this happens we must abort the transaction,
      * otherwise we commit a super block with btree roots that point to
      * btree nodes/leafs whose content on disk is invalid - either garbage
      * or the content of some node/leaf from a past generation that got
      * cowed or deleted and is no longer valid.
      *
      * Note: setting AS_EIO/AS_ENOSPC in the btree inode's i_mapping would
      * not be enough - we need to distinguish between log tree extents vs
      * non-log tree extents, and the next filemap_fdatawait_range() call
      * will catch and clear such errors in the mapping - and that call might
      * be from a log sync and not from a transaction commit. Also, checking
      * for the eb flag EXTENT_BUFFER_WRITE_ERR at transaction commit time is
      * not done and would not be reliable - the eb might have been released
      * from memory and reading it back again means that flag would not be
      * set (since it's a runtime flag, not persisted on disk).
      *
      * Using the flags below in the btree inode also makes us achieve the
      * goal of AS_EIO/AS_ENOSPC when writepages() returns success, started
      * writeback for all dirty pages and before filemap_fdatawait_range()
      * is called, the writeback for all dirty pages had already finished
      * with errors - because we were not using AS_EIO/AS_ENOSPC,
      * filemap_fdatawait_range() would return success, as it could not know
      * that writeback errors happened (the pages were no longer tagged for
      * writeback).
      */
     switch (eb->log_index) {
     case -1:
         set_bit(BTRFS_FS_BTREE_ERR, &fs_info->flags);
         break;
     case 0:
         set_bit(BTRFS_FS_LOG1_ERR, &fs_info->flags);
         break;
     case 1:
         set_bit(BTRFS_FS_LOG2_ERR, &fs_info->flags);
         break;
     default:
         BUG(); /* unexpected, logic error */
     }
 }
 
 /*
  * The endio specific version which won't touch any unsafe spinlock in endio
  * context.
  */
 static struct extent_buffer *find_extent_buffer_nolock(
         struct btrfs_fs_info *fs_info, u64 start)
 {
     struct extent_buffer *eb;
 
     rcu_read_lock();
     eb = radix_tree_lookup(&fs_info->buffer_radix,
                    start >> fs_info->sectorsize_bits);
     if (eb && atomic_inc_not_zero(&eb->refs)) {
         rcu_read_unlock();
         return eb;
     }
     rcu_read_unlock();
     return NULL;
 }
 
 /*
  * The endio function for subpage extent buffer write.
  *
  * Unlike end_bio_extent_buffer_writepage(), we only call end_page_writeback()
  * after all extent buffers in the page has finished their writeback.
  */
 static void end_bio_subpage_eb_writepage(struct bio *bio)
 {
     struct btrfs_fs_info *fs_info;
     struct bio_vec *bvec;
     struct bvec_iter_all iter_all;
 
     fs_info = btrfs_sb(bio_first_page_all(bio)->mapping->host->i_sb);
     ASSERT(fs_info->nodesize < PAGE_SIZE);
 
     ASSERT(!bio_flagged(bio, BIO_CLONED));
     bio_for_each_segment_all(bvec, bio, iter_all) {
         struct page *page = bvec->bv_page;
         u64 bvec_start = page_offset(page) + bvec->bv_offset;
         u64 bvec_end = bvec_start + bvec->bv_len - 1;
         u64 cur_bytenr = bvec_start;
 
         ASSERT(IS_ALIGNED(bvec->bv_len, fs_info->nodesize));
 
         /* Iterate through all extent buffers in the range */
         while (cur_bytenr <= bvec_end) {
             struct extent_buffer *eb;
             int done;
 
             /*
              * Here we can't use find_extent_buffer(), as it may
              * try to lock eb->refs_lock, which is not safe in endio
              * context.
              */
             eb = find_extent_buffer_nolock(fs_info, cur_bytenr);
             ASSERT(eb);
 
             cur_bytenr = eb->start + eb->len;
 
             ASSERT(test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags));
             done = atomic_dec_and_test(&eb->io_pages);
             ASSERT(done);
 
             if (bio->bi_status ||
                 test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) {
                 ClearPageUptodate(page);
                 set_btree_ioerr(page, eb);
             }
 
             btrfs_subpage_clear_writeback(fs_info, page, eb->start,
                               eb->len);
             end_extent_buffer_writeback(eb);
             /*
              * free_extent_buffer() will grab spinlock which is not
              * safe in endio context. Thus here we manually dec
              * the ref.
              */
             atomic_dec(&eb->refs);
         }
     }
     bio_put(bio);
 }
 
 static void end_bio_extent_buffer_writepage(struct bio *bio)
 {
     struct bio_vec *bvec;
     struct extent_buffer *eb;
     int done;
     struct bvec_iter_all iter_all;
 
     ASSERT(!bio_flagged(bio, BIO_CLONED));
     bio_for_each_segment_all(bvec, bio, iter_all) {
         struct page *page = bvec->bv_page;
 
         eb = (struct extent_buffer *)page->private;
         BUG_ON(!eb);
         done = atomic_dec_and_test(&eb->io_pages);
 
         if (bio->bi_status ||
             test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) {
             ClearPageUptodate(page);
             set_btree_ioerr(page, eb);
         }
 
         end_page_writeback(page);
 
         if (!done)
             continue;
 
         end_extent_buffer_writeback(eb);
     }
 
     bio_put(bio);
 }
 
 static void prepare_eb_write(struct extent_buffer *eb)
 {
     u32 nritems;
     unsigned long start;
     unsigned long end;
 
     clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
     atomic_set(&eb->io_pages, num_extent_pages(eb));
 
     /* Set btree blocks beyond nritems with 0 to avoid stale content */
     nritems = btrfs_header_nritems(eb);
     if (btrfs_header_level(eb) > 0) {
         end = btrfs_node_key_ptr_offset(nritems);
         memzero_extent_buffer(eb, end, eb->len - end);
     } else {
         /*
          * Leaf:
          * header 0 1 2 .. N ... data_N .. data_2 data_1 data_0
          */
         start = btrfs_item_nr_offset(nritems);
         end = BTRFS_LEAF_DATA_OFFSET + leaf_data_end(eb);
         memzero_extent_buffer(eb, start, end - start);
     }
 }
 
 /*
  * Unlike the work in write_one_eb(), we rely completely on extent locking.
  * Page locking is only utilized at minimum to keep the VMM code happy.
  */
 static int write_one_subpage_eb(struct extent_buffer *eb,
                 struct writeback_control *wbc,
                 struct extent_page_data *epd)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     struct page *page = eb->pages[0];
     blk_opf_t write_flags = wbc_to_write_flags(wbc);
     bool no_dirty_ebs = false;
     int ret;
 
     prepare_eb_write(eb);
 
     /* clear_page_dirty_for_io() in subpage helper needs page locked */
     lock_page(page);
     btrfs_subpage_set_writeback(fs_info, page, eb->start, eb->len);
 
     /* Check if this is the last dirty bit to update nr_written */
     no_dirty_ebs = btrfs_subpage_clear_and_test_dirty(fs_info, page,
                               eb->start, eb->len);
     if (no_dirty_ebs)
         clear_page_dirty_for_io(page);
 
     ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,
             &epd->bio_ctrl, page, eb->start, eb->len,
             eb->start - page_offset(page),
             end_bio_subpage_eb_writepage, 0, false);
     if (ret) {
         btrfs_subpage_clear_writeback(fs_info, page, eb->start, eb->len);
         set_btree_ioerr(page, eb);
         unlock_page(page);
 
         if (atomic_dec_and_test(&eb->io_pages))
             end_extent_buffer_writeback(eb);
         return -EIO;
     }
     unlock_page(page);
     /*
      * Submission finished without problem, if no range of the page is
      * dirty anymore, we have submitted a page.  Update nr_written in wbc.
      */
     if (no_dirty_ebs)
         wbc->nr_to_write--;
     return ret;
 }
 
 static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
             struct writeback_control *wbc,
             struct extent_page_data *epd)
 {
     u64 disk_bytenr = eb->start;
     int i, num_pages;
     blk_opf_t write_flags = wbc_to_write_flags(wbc);
     int ret = 0;
 
     prepare_eb_write(eb);
 
     num_pages = num_extent_pages(eb);
     for (i = 0; i < num_pages; i++) {
         struct page *p = eb->pages[i];
 
         clear_page_dirty_for_io(p);
         set_page_writeback(p);
         ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,
                      &epd->bio_ctrl, p, disk_bytenr,
                      PAGE_SIZE, 0,
                      end_bio_extent_buffer_writepage,
                      0, false);
         if (ret) {
             set_btree_ioerr(p, eb);
             if (PageWriteback(p))
                 end_page_writeback(p);
             if (atomic_sub_and_test(num_pages - i, &eb->io_pages))
                 end_extent_buffer_writeback(eb);
             ret = -EIO;
             break;
         }
         disk_bytenr += PAGE_SIZE;
         wbc->nr_to_write--;
         unlock_page(p);
     }
 
     if (unlikely(ret)) {
         for (; i < num_pages; i++) {
             struct page *p = eb->pages[i];
             clear_page_dirty_for_io(p);
             unlock_page(p);
         }
     }
 
     return ret;
 }
 
 /*
  * Submit one subpage btree page.
  *
  * The main difference to submit_eb_page() is:
  * - Page locking
  *   For subpage, we don't rely on page locking at all.
  *
  * - Flush write bio
  *   We only flush bio if we may be unable to fit current extent buffers into
  *   current bio.
  *
  * Return >=0 for the number of submitted extent buffers.
  * Return <0 for fatal error.
  */
 static int submit_eb_subpage(struct page *page,
                  struct writeback_control *wbc,
                  struct extent_page_data *epd)
 {
     struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
     int submitted = 0;
     u64 page_start = page_offset(page);
     int bit_start = 0;
     int sectors_per_node = fs_info->nodesize >> fs_info->sectorsize_bits;
     int ret;
 
     /* Lock and write each dirty extent buffers in the range */
     while (bit_start < fs_info->subpage_info->bitmap_nr_bits) {
         struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
         struct extent_buffer *eb;
         unsigned long flags;
         u64 start;
 
         /*
          * Take private lock to ensure the subpage won't be detached
          * in the meantime.
          */
         spin_lock(&page->mapping->private_lock);
         if (!PagePrivate(page)) {
             spin_unlock(&page->mapping->private_lock);
             break;
         }
         spin_lock_irqsave(&subpage->lock, flags);
         if (!test_bit(bit_start + fs_info->subpage_info->dirty_offset,
                   subpage->bitmaps)) {
             spin_unlock_irqrestore(&subpage->lock, flags);
             spin_unlock(&page->mapping->private_lock);
             bit_start++;
             continue;
         }
 
         start = page_start + bit_start * fs_info->sectorsize;
         bit_start += sectors_per_node;
 
         /*
          * Here we just want to grab the eb without touching extra
          * spin locks, so call find_extent_buffer_nolock().
          */
         eb = find_extent_buffer_nolock(fs_info, start);
         spin_unlock_irqrestore(&subpage->lock, flags);
         spin_unlock(&page->mapping->private_lock);
 
         /*
          * The eb has already reached 0 refs thus find_extent_buffer()
          * doesn't return it. We don't need to write back such eb
          * anyway.
          */
         if (!eb)
             continue;
 
         ret = lock_extent_buffer_for_io(eb, epd);
         if (ret == 0) {
             free_extent_buffer(eb);
             continue;
         }
         if (ret < 0) {
             free_extent_buffer(eb);
             goto cleanup;
         }
         ret = write_one_subpage_eb(eb, wbc, epd);
         free_extent_buffer(eb);
         if (ret < 0)
             goto cleanup;
         submitted++;
     }
     return submitted;
 
 cleanup:
     /* We hit error, end bio for the submitted extent buffers */
     submit_write_bio(epd, ret);
     return ret;
 }
 
 /*
  * Submit all page(s) of one extent buffer.
  *
  * @page:   the page of one extent buffer
  * @eb_context: to determine if we need to submit this page, if current page
  *      belongs to this eb, we don't need to submit
  *
  * The caller should pass each page in their bytenr order, and here we use
  * @eb_context to determine if we have submitted pages of one extent buffer.
  *
  * If we have, we just skip until we hit a new page that doesn't belong to
  * current @eb_context.
  *
  * If not, we submit all the page(s) of the extent buffer.
  *
  * Return >0 if we have submitted the extent buffer successfully.
  * Return 0 if we don't need to submit the page, as it's already submitted by
  * previous call.
  * Return <0 for fatal error.
  */
 static int submit_eb_page(struct page *page, struct writeback_control *wbc,
               struct extent_page_data *epd,
               struct extent_buffer **eb_context)
 {
     struct address_space *mapping = page->mapping;
     struct btrfs_block_group *cache = NULL;
     struct extent_buffer *eb;
     int ret;
 
     if (!PagePrivate(page))
         return 0;
 
     if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
         return submit_eb_subpage(page, wbc, epd);
 
     spin_lock(&mapping->private_lock);
     if (!PagePrivate(page)) {
         spin_unlock(&mapping->private_lock);
         return 0;
     }
 
     eb = (struct extent_buffer *)page->private;
 
     /*
      * Shouldn't happen and normally this would be a BUG_ON but no point
      * crashing the machine for something we can survive anyway.
      */
     if (WARN_ON(!eb)) {
         spin_unlock(&mapping->private_lock);
         return 0;
     }
 
     if (eb == *eb_context) {
         spin_unlock(&mapping->private_lock);
         return 0;
     }
     ret = atomic_inc_not_zero(&eb->refs);
     spin_unlock(&mapping->private_lock);
     if (!ret)
         return 0;
 
     if (!btrfs_check_meta_write_pointer(eb->fs_info, eb, &cache)) {
         /*
          * If for_sync, this hole will be filled with
          * trasnsaction commit.
          */
         if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync)
             ret = -EAGAIN;
         else
             ret = 0;
         free_extent_buffer(eb);
         return ret;
     }
 
     *eb_context = eb;
 
     ret = lock_extent_buffer_for_io(eb, epd);
     if (ret <= 0) {
         btrfs_revert_meta_write_pointer(cache, eb);
         if (cache)
             btrfs_put_block_group(cache);
         free_extent_buffer(eb);
         return ret;
     }
     if (cache) {
         /*
          * Implies write in zoned mode. Mark the last eb in a block group.
          */
         btrfs_schedule_zone_finish_bg(cache, eb);
         btrfs_put_block_group(cache);
     }
     ret = write_one_eb(eb, wbc, epd);
     free_extent_buffer(eb);
     if (ret < 0)
         return ret;
     return 1;
 }
 
 int btree_write_cache_pages(struct address_space *mapping,
                    struct writeback_control *wbc)
 {
     struct extent_buffer *eb_context = NULL;
     struct extent_page_data epd = {
         .bio_ctrl = { 0 },
         .extent_locked = 0,
         .sync_io = wbc->sync_mode == WB_SYNC_ALL,
     };
     struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
     int ret = 0;
     int done = 0;
     int nr_to_write_done = 0;
     struct pagevec pvec;
     int nr_pages;
     pgoff_t index;
     pgoff_t end;        /* Inclusive */
     int scanned = 0;
     xa_mark_t tag;
 
     pagevec_init(&pvec);
     if (wbc->range_cyclic) {
         index = mapping->writeback_index; /* Start from prev offset */
         end = -1;
         /*
          * Start from the beginning does not need to cycle over the
          * range, mark it as scanned.
          */
         scanned = (index == 0);
     } else {
         index = wbc->range_start >> PAGE_SHIFT;
         end = wbc->range_end >> PAGE_SHIFT;
         scanned = 1;
     }
     if (wbc->sync_mode == WB_SYNC_ALL)
         tag = PAGECACHE_TAG_TOWRITE;
     else
         tag = PAGECACHE_TAG_DIRTY;
     btrfs_zoned_meta_io_lock(fs_info);
 retry:
     if (wbc->sync_mode == WB_SYNC_ALL)
         tag_pages_for_writeback(mapping, index, end);
     while (!done && !nr_to_write_done && (index <= end) &&
            (nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
             tag))) {
         unsigned i;
 
         for (i = 0; i < nr_pages; i++) {
             struct page *page = pvec.pages[i];
 
             ret = submit_eb_page(page, wbc, &epd, &eb_context);
             if (ret == 0)
                 continue;
             if (ret < 0) {
                 done = 1;
                 break;
             }
 
             /*
              * the filesystem may choose to bump up nr_to_write.
              * We have to make sure to honor the new nr_to_write
              * at any time
              */
             nr_to_write_done = wbc->nr_to_write <= 0;
         }
         pagevec_release(&pvec);
         cond_resched();
     }
     if (!scanned && !done) {
         /*
          * We hit the last page and there is more work to be done: wrap
          * back to the start of the file
          */
         scanned = 1;
         index = 0;
         goto retry;
     }
     /*
      * If something went wrong, don't allow any metadata write bio to be
      * submitted.
      *
      * This would prevent use-after-free if we had dirty pages not
      * cleaned up, which can still happen by fuzzed images.
      *
      * - Bad extent tree
      *   Allowing existing tree block to be allocated for other trees.
      *
      * - Log tree operations
      *   Exiting tree blocks get allocated to log tree, bumps its
      *   generation, then get cleaned in tree re-balance.
      *   Such tree block will not be written back, since it's clean,
      *   thus no WRITTEN flag set.
      *   And after log writes back, this tree block is not traced by
      *   any dirty extent_io_tree.
      *
      * - Offending tree block gets re-dirtied from its original owner
      *   Since it has bumped generation, no WRITTEN flag, it can be
      *   reused without COWing. This tree block will not be traced
      *   by btrfs_transaction::dirty_pages.
      *
      *   Now such dirty tree block will not be cleaned by any dirty
      *   extent io tree. Thus we don't want to submit such wild eb
      *   if the fs already has error.
      *
      * We can get ret > 0 from submit_extent_page() indicating how many ebs
      * were submitted. Reset it to 0 to avoid false alerts for the caller.
      */
     if (ret > 0)
         ret = 0;
     if (!ret && BTRFS_FS_ERROR(fs_info))
         ret = -EROFS;
     submit_write_bio(&epd, ret);
 
     btrfs_zoned_meta_io_unlock(fs_info);
     return ret;
 }
 
 /**
  * Walk the list of dirty pages of the given address space and write all of them.
  *
  * @mapping: address space structure to write
  * @wbc:     subtract the number of written pages from *@wbc->nr_to_write
  * @epd:     holds context for the write, namely the bio
  *
  * If a page is already under I/O, write_cache_pages() skips it, even
  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
  * and msync() need to guarantee that all the data which was dirty at the time
  * the call was made get new I/O started against them.  If wbc->sync_mode is
  * WB_SYNC_ALL then we were called for data integrity and we must wait for
  * existing IO to complete.
  */
 static int extent_write_cache_pages(struct address_space *mapping,
                  struct writeback_control *wbc,
                  struct extent_page_data *epd)
 {
     struct inode *inode = mapping->host;
     int ret = 0;
     int done = 0;
     int nr_to_write_done = 0;
     struct pagevec pvec;
     int nr_pages;
     pgoff_t index;
     pgoff_t end;        /* Inclusive */
     pgoff_t done_index;
     int range_whole = 0;
     int scanned = 0;
     xa_mark_t tag;
 
     /*
      * We have to hold onto the inode so that ordered extents can do their
      * work when the IO finishes.  The alternative to this is failing to add
      * an ordered extent if the igrab() fails there and that is a huge pain
      * to deal with, so instead just hold onto the inode throughout the
      * writepages operation.  If it fails here we are freeing up the inode
      * anyway and we'd rather not waste our time writing out stuff that is
      * going to be truncated anyway.
      */
     if (!igrab(inode))
         return 0;
 
     pagevec_init(&pvec);
     if (wbc->range_cyclic) {
         index = mapping->writeback_index; /* Start from prev offset */
         end = -1;
         /*
          * Start from the beginning does not need to cycle over the
          * range, mark it as scanned.
          */
         scanned = (index == 0);
     } else {
         index = wbc->range_start >> PAGE_SHIFT;
         end = wbc->range_end >> PAGE_SHIFT;
         if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
             range_whole = 1;
         scanned = 1;
     }
 
     /*
      * We do the tagged writepage as long as the snapshot flush bit is set
      * and we are the first one who do the filemap_flush() on this inode.
      *
      * The nr_to_write == LONG_MAX is needed to make sure other flushers do
      * not race in and drop the bit.
      */
     if (range_whole && wbc->nr_to_write == LONG_MAX &&
         test_and_clear_bit(BTRFS_INODE_SNAPSHOT_FLUSH,
                    &BTRFS_I(inode)->runtime_flags))
         wbc->tagged_writepages = 1;
 
     if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
         tag = PAGECACHE_TAG_TOWRITE;
     else
         tag = PAGECACHE_TAG_DIRTY;
 retry:
     if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
         tag_pages_for_writeback(mapping, index, end);
     done_index = index;
     while (!done && !nr_to_write_done && (index <= end) &&
             (nr_pages = pagevec_lookup_range_tag(&pvec, mapping,
                         &index, end, tag))) {
         unsigned i;
 
         for (i = 0; i < nr_pages; i++) {
             struct page *page = pvec.pages[i];
 
             done_index = page->index + 1;
             /*
              * At this point we hold neither the i_pages lock nor
              * the page lock: the page may be truncated or
              * invalidated (changing page->mapping to NULL),
              * or even swizzled back from swapper_space to
              * tmpfs file mapping
              */
             if (!trylock_page(page)) {
                 submit_write_bio(epd, 0);
                 lock_page(page);
             }
 
             if (unlikely(page->mapping != mapping)) {
                 unlock_page(page);
                 continue;
             }
 
             if (wbc->sync_mode != WB_SYNC_NONE) {
                 if (PageWriteback(page))
                     submit_write_bio(epd, 0);
                 wait_on_page_writeback(page);
             }
 
             if (PageWriteback(page) ||
                 !clear_page_dirty_for_io(page)) {
                 unlock_page(page);
                 continue;
             }
 
             ret = __extent_writepage(page, wbc, epd);
             if (ret < 0) {
                 done = 1;
                 break;
             }
 
             /*
              * the filesystem may choose to bump up nr_to_write.
              * We have to make sure to honor the new nr_to_write
              * at any time
              */
             nr_to_write_done = wbc->nr_to_write <= 0;
         }
         pagevec_release(&pvec);
         cond_resched();
     }
     if (!scanned && !done) {
         /*
          * We hit the last page and there is more work to be done: wrap
          * back to the start of the file
          */
         scanned = 1;
         index = 0;
 
         /*
          * If we're looping we could run into a page that is locked by a
          * writer and that writer could be waiting on writeback for a
          * page in our current bio, and thus deadlock, so flush the
          * write bio here.
          */
         submit_write_bio(epd, 0);
         goto retry;
     }
 
     if (wbc->range_cyclic || (wbc->nr_to_write > 0 && range_whole))
         mapping->writeback_index = done_index;
 
     btrfs_add_delayed_iput(inode);
     return ret;
 }
 
 /*
  * Submit the pages in the range to bio for call sites which delalloc range has
  * already been ran (aka, ordered extent inserted) and all pages are still
  * locked.
  */
 int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
 {
     bool found_error = false;
     int first_error = 0;
     int ret = 0;
     struct address_space *mapping = inode->i_mapping;
     struct page *page;
     u64 cur = start;
     unsigned long nr_pages;
     const u32 sectorsize = btrfs_sb(inode->i_sb)->sectorsize;
     struct extent_page_data epd = {
         .bio_ctrl = { 0 },
         .extent_locked = 1,
         .sync_io = 1,
     };
     struct writeback_control wbc_writepages = {
         .sync_mode  = WB_SYNC_ALL,
         .range_start    = start,
         .range_end  = end + 1,
         /* We're called from an async helper function */
         .punt_to_cgroup = 1,
         .no_cgroup_owner = 1,
     };
 
     ASSERT(IS_ALIGNED(start, sectorsize) && IS_ALIGNED(end + 1, sectorsize));
     nr_pages = (round_up(end, PAGE_SIZE) - round_down(start, PAGE_SIZE)) >>
            PAGE_SHIFT;
     wbc_writepages.nr_to_write = nr_pages * 2;
 
     wbc_attach_fdatawrite_inode(&wbc_writepages, inode);
     while (cur <= end) {
         u64 cur_end = min(round_down(cur, PAGE_SIZE) + PAGE_SIZE - 1, end);
 
         page = find_get_page(mapping, cur >> PAGE_SHIFT);
         /*
          * All pages in the range are locked since
          * btrfs_run_delalloc_range(), thus there is no way to clear
          * the page dirty flag.
          */
         ASSERT(PageLocked(page));
         ASSERT(PageDirty(page));
         clear_page_dirty_for_io(page);
         ret = __extent_writepage(page, &wbc_writepages, &epd);
         ASSERT(ret <= 0);
         if (ret < 0) {
             found_error = true;
             first_error = ret;
         }
         put_page(page);
         cur = cur_end + 1;
     }
 
     submit_write_bio(&epd, found_error ? ret : 0);
 
     wbc_detach_inode(&wbc_writepages);
     if (found_error)
         return first_error;
     return ret;
 }
 
 int extent_writepages(struct address_space *mapping,
               struct writeback_control *wbc)
 {
     struct inode *inode = mapping->host;
     int ret = 0;
     struct extent_page_data epd = {
         .bio_ctrl = { 0 },
         .extent_locked = 0,
         .sync_io = wbc->sync_mode == WB_SYNC_ALL,
     };
 
     /*
      * Allow only a single thread to do the reloc work in zoned mode to
      * protect the write pointer updates.
      */
     btrfs_zoned_data_reloc_lock(BTRFS_I(inode));
     ret = extent_write_cache_pages(mapping, wbc, &epd);
     submit_write_bio(&epd, ret);
     btrfs_zoned_data_reloc_unlock(BTRFS_I(inode));
     return ret;
 }
 
 void extent_readahead(struct readahead_control *rac)
 {
     struct btrfs_bio_ctrl bio_ctrl = { 0 };
     struct page *pagepool[16];
     struct extent_map *em_cached = NULL;
     u64 prev_em_start = (u64)-1;
     int nr;
 
     while ((nr = readahead_page_batch(rac, pagepool))) {
         u64 contig_start = readahead_pos(rac);
         u64 contig_end = contig_start + readahead_batch_length(rac) - 1;
 
         contiguous_readpages(pagepool, nr, contig_start, contig_end,
                 &em_cached, &bio_ctrl, &prev_em_start);
     }
 
     if (em_cached)
         free_extent_map(em_cached);
     submit_one_bio(&bio_ctrl);
 }
 
 /*
  * basic invalidate_folio code, this waits on any locked or writeback
  * ranges corresponding to the folio, and then deletes any extent state
  * records from the tree
  */
 int extent_invalidate_folio(struct extent_io_tree *tree,
               struct folio *folio, size_t offset)
 {
     struct extent_state *cached_state = NULL;
     u64 start = folio_pos(folio);
     u64 end = start + folio_size(folio) - 1;
     size_t blocksize = folio->mapping->host->i_sb->s_blocksize;
 
     /* This function is only called for the btree inode */
     ASSERT(tree->owner == IO_TREE_BTREE_INODE_IO);
 
     start += ALIGN(offset, blocksize);
     if (start > end)
         return 0;
 
     lock_extent_bits(tree, start, end, &cached_state);
     folio_wait_writeback(folio);
 
     /*
      * Currently for btree io tree, only EXTENT_LOCKED is utilized,
      * so here we only need to unlock the extent range to free any
      * existing extent state.
      */
     unlock_extent_cached(tree, start, end, &cached_state);
     return 0;
 }
 
 /*
  * a helper for release_folio, this tests for areas of the page that
  * are locked or under IO and drops the related state bits if it is safe
  * to drop the page.
  */
 static int try_release_extent_state(struct extent_io_tree *tree,
                     struct page *page, gfp_t mask)
 {
     u64 start = page_offset(page);
     u64 end = start + PAGE_SIZE - 1;
     int ret = 1;
 
     if (test_range_bit(tree, start, end, EXTENT_LOCKED, 0, NULL)) {
         ret = 0;
     } else {
         /*
          * At this point we can safely clear everything except the
          * locked bit, the nodatasum bit and the delalloc new bit.
          * The delalloc new bit will be cleared by ordered extent
          * completion.
          */
         ret = __clear_extent_bit(tree, start, end,
              ~(EXTENT_LOCKED | EXTENT_NODATASUM | EXTENT_DELALLOC_NEW),
              0, 0, NULL, mask, NULL);
 
         /* if clear_extent_bit failed for enomem reasons,
          * we can't allow the release to continue.
          */
         if (ret < 0)
             ret = 0;
         else
             ret = 1;
     }
     return ret;
 }
 
 /*
  * a helper for release_folio.  As long as there are no locked extents
  * in the range corresponding to the page, both state records and extent
  * map records are removed
  */
 int try_release_extent_mapping(struct page *page, gfp_t mask)
 {
     struct extent_map *em;
     u64 start = page_offset(page);
     u64 end = start + PAGE_SIZE - 1;
     struct btrfs_inode *btrfs_inode = BTRFS_I(page->mapping->host);
     struct extent_io_tree *tree = &btrfs_inode->io_tree;
     struct extent_map_tree *map = &btrfs_inode->extent_tree;
 
     if (gfpflags_allow_blocking(mask) &&
         page->mapping->host->i_size > SZ_16M) {
         u64 len;
         while (start <= end) {
             struct btrfs_fs_info *fs_info;
             u64 cur_gen;
 
             len = end - start + 1;
             write_lock(&map->lock);
             em = lookup_extent_mapping(map, start, len);
             if (!em) {
                 write_unlock(&map->lock);
                 break;
             }
             if (test_bit(EXTENT_FLAG_PINNED, &em->flags) ||
                 em->start != start) {
                 write_unlock(&map->lock);
                 free_extent_map(em);
                 break;
             }
             if (test_range_bit(tree, em->start,
                        extent_map_end(em) - 1,
                        EXTENT_LOCKED, 0, NULL))
                 goto next;
             /*
              * If it's not in the list of modified extents, used
              * by a fast fsync, we can remove it. If it's being
              * logged we can safely remove it since fsync took an
              * extra reference on the em.
              */
             if (list_empty(&em->list) ||
                 test_bit(EXTENT_FLAG_LOGGING, &em->flags))
                 goto remove_em;
             /*
              * If it's in the list of modified extents, remove it
              * only if its generation is older then the current one,
              * in which case we don't need it for a fast fsync.
              * Otherwise don't remove it, we could be racing with an
              * ongoing fast fsync that could miss the new extent.
              */
             fs_info = btrfs_inode->root->fs_info;
             spin_lock(&fs_info->trans_lock);
             cur_gen = fs_info->generation;
             spin_unlock(&fs_info->trans_lock);
             if (em->generation >= cur_gen)
                 goto next;
 remove_em:
             /*
              * We only remove extent maps that are not in the list of
              * modified extents or that are in the list but with a
              * generation lower then the current generation, so there
              * is no need to set the full fsync flag on the inode (it
              * hurts the fsync performance for workloads with a data
              * size that exceeds or is close to the system's memory).
              */
             remove_extent_mapping(map, em);
             /* once for the rb tree */
             free_extent_map(em);
 next:
             start = extent_map_end(em);
             write_unlock(&map->lock);
 
             /* once for us */
             free_extent_map(em);
 
             cond_resched(); /* Allow large-extent preemption. */
         }
     }
     return try_release_extent_state(tree, page, mask);
 }
 
 /*
  * helper function for fiemap, which doesn't want to see any holes.
  * This maps until we find something past 'last'
  */
 static struct extent_map *get_extent_skip_holes(struct btrfs_inode *inode,
                         u64 offset, u64 last)
 {
     u64 sectorsize = btrfs_inode_sectorsize(inode);
     struct extent_map *em;
     u64 len;
 
     if (offset >= last)
         return NULL;
 
     while (1) {
         len = last - offset;
         if (len == 0)
             break;
         len = ALIGN(len, sectorsize);
         em = btrfs_get_extent_fiemap(inode, offset, len);
         if (IS_ERR(em))
             return em;
 
         /* if this isn't a hole return it */
         if (em->block_start != EXTENT_MAP_HOLE)
             return em;
 
         /* this is a hole, advance to the next extent */
         offset = extent_map_end(em);
         free_extent_map(em);
         if (offset >= last)
             break;
     }
     return NULL;
 }
 
 /*
  * To cache previous fiemap extent
  *
  * Will be used for merging fiemap extent
  */
 struct fiemap_cache {
     u64 offset;
     u64 phys;
     u64 len;
     u32 flags;
     bool cached;
 };
 
 /*
  * Helper to submit fiemap extent.
  *
  * Will try to merge current fiemap extent specified by @offset, @phys,
  * @len and @flags with cached one.
  * And only when we fails to merge, cached one will be submitted as
  * fiemap extent.
  *
  * Return value is the same as fiemap_fill_next_extent().
  */
 static int emit_fiemap_extent(struct fiemap_extent_info *fieinfo,
                 struct fiemap_cache *cache,
                 u64 offset, u64 phys, u64 len, u32 flags)
 {
     int ret = 0;
 
     if (!cache->cached)
         goto assign;
 
     /*
      * Sanity check, extent_fiemap() should have ensured that new
      * fiemap extent won't overlap with cached one.
      * Not recoverable.
      *
      * NOTE: Physical address can overlap, due to compression
      */
     if (cache->offset + cache->len > offset) {
         WARN_ON(1);
         return -EINVAL;
     }
 
     /*
      * Only merges fiemap extents if
      * 1) Their logical addresses are continuous
      *
      * 2) Their physical addresses are continuous
      *    So truly compressed (physical size smaller than logical size)
      *    extents won't get merged with each other
      *
      * 3) Share same flags except FIEMAP_EXTENT_LAST
      *    So regular extent won't get merged with prealloc extent
      */
     if (cache->offset + cache->len  == offset &&
         cache->phys + cache->len == phys  &&
         (cache->flags & ~FIEMAP_EXTENT_LAST) ==
             (flags & ~FIEMAP_EXTENT_LAST)) {
         cache->len += len;
         cache->flags |= flags;
         goto try_submit_last;
     }
 
     /* Not mergeable, need to submit cached one */
     ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
                       cache->len, cache->flags);
     cache->cached = false;
     if (ret)
         return ret;
 assign:
     cache->cached = true;
     cache->offset = offset;
     cache->phys = phys;
     cache->len = len;
     cache->flags = flags;
 try_submit_last:
     if (cache->flags & FIEMAP_EXTENT_LAST) {
         ret = fiemap_fill_next_extent(fieinfo, cache->offset,
                 cache->phys, cache->len, cache->flags);
         cache->cached = false;
     }
     return ret;
 }
 
 /*
  * Emit last fiemap cache
  *
  * The last fiemap cache may still be cached in the following case:
  * 0              4k            8k
  * |<- Fiemap range ->|
  * |<------------  First extent ----------->|
  *
  * In this case, the first extent range will be cached but not emitted.
  * So we must emit it before ending extent_fiemap().
  */
 static int emit_last_fiemap_cache(struct fiemap_extent_info *fieinfo,
                   struct fiemap_cache *cache)
 {
     int ret;
 
     if (!cache->cached)
         return 0;
 
     ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
                       cache->len, cache->flags);
     cache->cached = false;
     if (ret > 0)
         ret = 0;
     return ret;
 }
 
 int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
           u64 start, u64 len)
 {
     int ret = 0;
     u64 off;
     u64 max = start + len;
     u32 flags = 0;
     u32 found_type;
     u64 last;
     u64 last_for_get_extent = 0;
     u64 disko = 0;
     u64 isize = i_size_read(&inode->vfs_inode);
     struct btrfs_key found_key;
     struct extent_map *em = NULL;
     struct extent_state *cached_state = NULL;
     struct btrfs_path *path;
     struct btrfs_root *root = inode->root;
     struct fiemap_cache cache = { 0 };
     struct ulist *roots;
     struct ulist *tmp_ulist;
     int end = 0;
     u64 em_start = 0;
     u64 em_len = 0;
     u64 em_end = 0;
 
     if (len == 0)
         return -EINVAL;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
 
     roots = ulist_alloc(GFP_KERNEL);
     tmp_ulist = ulist_alloc(GFP_KERNEL);
     if (!roots || !tmp_ulist) {
         ret = -ENOMEM;
         goto out_free_ulist;
     }
 
     /*
      * We can't initialize that to 'start' as this could miss extents due
      * to extent item merging
      */
     off = 0;
     start = round_down(start, btrfs_inode_sectorsize(inode));
     len = round_up(max, btrfs_inode_sectorsize(inode)) - start;
 
     /*
      * lookup the last file extent.  We're not using i_size here
      * because there might be preallocation past i_size
      */
     ret = btrfs_lookup_file_extent(NULL, root, path, btrfs_ino(inode), -1,
                        0);
     if (ret < 0) {
         goto out_free_ulist;
     } else {
         WARN_ON(!ret);
         if (ret == 1)
             ret = 0;
     }
 
     path->slots[0]--;
     btrfs_item_key_to_cpu(path->nodes[0], &found_key, path->slots[0]);
     found_type = found_key.type;
 
     /* No extents, but there might be delalloc bits */
     if (found_key.objectid != btrfs_ino(inode) ||
         found_type != BTRFS_EXTENT_DATA_KEY) {
         /* have to trust i_size as the end */
         last = (u64)-1;
         last_for_get_extent = isize;
     } else {
         /*
          * remember the start of the last extent.  There are a
          * bunch of different factors that go into the length of the
          * extent, so its much less complex to remember where it started
          */
         last = found_key.offset;
         last_for_get_extent = last + 1;
     }
     btrfs_release_path(path);
 
     /*
      * we might have some extents allocated but more delalloc past those
      * extents.  so, we trust isize unless the start of the last extent is
      * beyond isize
      */
     if (last < isize) {
         last = (u64)-1;
         last_for_get_extent = isize;
     }
 
     lock_extent_bits(&inode->io_tree, start, start + len - 1,
              &cached_state);
 
     em = get_extent_skip_holes(inode, start, last_for_get_extent);
     if (!em)
         goto out;
     if (IS_ERR(em)) {
         ret = PTR_ERR(em);
         goto out;
     }
 
     while (!end) {
         u64 offset_in_extent = 0;
 
         /* break if the extent we found is outside the range */
         if (em->start >= max || extent_map_end(em) < off)
             break;
 
         /*
          * get_extent may return an extent that starts before our
          * requested range.  We have to make sure the ranges
          * we return to fiemap always move forward and don't
          * overlap, so adjust the offsets here
          */
         em_start = max(em->start, off);
 
         /*
          * record the offset from the start of the extent
          * for adjusting the disk offset below.  Only do this if the
          * extent isn't compressed since our in ram offset may be past
          * what we have actually allocated on disk.
          */
         if (!test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
             offset_in_extent = em_start - em->start;
         em_end = extent_map_end(em);
         em_len = em_end - em_start;
         flags = 0;
         if (em->block_start < EXTENT_MAP_LAST_BYTE)
             disko = em->block_start + offset_in_extent;
         else
             disko = 0;
 
         /*
          * bump off for our next call to get_extent
          */
         off = extent_map_end(em);
         if (off >= max)
             end = 1;
 
         if (em->block_start == EXTENT_MAP_LAST_BYTE) {
             end = 1;
             flags |= FIEMAP_EXTENT_LAST;
         } else if (em->block_start == EXTENT_MAP_INLINE) {
             flags |= (FIEMAP_EXTENT_DATA_INLINE |
                   FIEMAP_EXTENT_NOT_ALIGNED);
         } else if (em->block_start == EXTENT_MAP_DELALLOC) {
             flags |= (FIEMAP_EXTENT_DELALLOC |
                   FIEMAP_EXTENT_UNKNOWN);
         } else if (fieinfo->fi_extents_max) {
             u64 bytenr = em->block_start -
                 (em->start - em->orig_start);
 
             /*
              * As btrfs supports shared space, this information
              * can be exported to userspace tools via
              * flag FIEMAP_EXTENT_SHARED.  If fi_extents_max == 0
              * then we're just getting a count and we can skip the
              * lookup stuff.
              */
             ret = btrfs_check_shared(root, btrfs_ino(inode),
                          bytenr, roots, tmp_ulist);
             if (ret < 0)
                 goto out_free;
             if (ret)
                 flags |= FIEMAP_EXTENT_SHARED;
             ret = 0;
         }
         if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
             flags |= FIEMAP_EXTENT_ENCODED;
         if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
             flags |= FIEMAP_EXTENT_UNWRITTEN;
 
         free_extent_map(em);
         em = NULL;
         if ((em_start >= last) || em_len == (u64)-1 ||
            (last == (u64)-1 && isize <= em_end)) {
             flags |= FIEMAP_EXTENT_LAST;
             end = 1;
         }
 
         /* now scan forward to see if this is really the last extent. */
         em = get_extent_skip_holes(inode, off, last_for_get_extent);
         if (IS_ERR(em)) {
             ret = PTR_ERR(em);
             goto out;
         }
         if (!em) {
             flags |= FIEMAP_EXTENT_LAST;
             end = 1;
         }
         ret = emit_fiemap_extent(fieinfo, &cache, em_start, disko,
                        em_len, flags);
         if (ret) {
             if (ret == 1)
                 ret = 0;
             goto out_free;
         }
     }
 out_free:
     if (!ret)
         ret = emit_last_fiemap_cache(fieinfo, &cache);
     free_extent_map(em);
 out:
     unlock_extent_cached(&inode->io_tree, start, start + len - 1,
                  &cached_state);
 
 out_free_ulist:
     btrfs_free_path(path);
     ulist_free(roots);
     ulist_free(tmp_ulist);
     return ret;
 }
 
 static void __free_extent_buffer(struct extent_buffer *eb)
 {
     kmem_cache_free(extent_buffer_cache, eb);
 }
 
 int extent_buffer_under_io(const struct extent_buffer *eb)
 {
     return (atomic_read(&eb->io_pages) ||
         test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
         test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
 }
 
 static bool page_range_has_eb(struct btrfs_fs_info *fs_info, struct page *page)
 {
     struct btrfs_subpage *subpage;
 
     lockdep_assert_held(&page->mapping->private_lock);
 
     if (PagePrivate(page)) {
         subpage = (struct btrfs_subpage *)page->private;
         if (atomic_read(&subpage->eb_refs))
             return true;
         /*
          * Even there is no eb refs here, we may still have
          * end_page_read() call relying on page::private.
          */
         if (atomic_read(&subpage->readers))
             return true;
     }
     return false;
 }
 
 static void detach_extent_buffer_page(struct extent_buffer *eb, struct page *page)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     const bool mapped = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
 
     /*
      * For mapped eb, we're going to change the page private, which should
      * be done under the private_lock.
      */
     if (mapped)
         spin_lock(&page->mapping->private_lock);
 
     if (!PagePrivate(page)) {
         if (mapped)
             spin_unlock(&page->mapping->private_lock);
         return;
     }
 
     if (fs_info->nodesize >= PAGE_SIZE) {
         /*
          * We do this since we'll remove the pages after we've
          * removed the eb from the radix tree, so we could race
          * and have this page now attached to the new eb.  So
          * only clear page_private if it's still connected to
          * this eb.
          */
         if (PagePrivate(page) &&
             page->private == (unsigned long)eb) {
             BUG_ON(test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
             BUG_ON(PageDirty(page));
             BUG_ON(PageWriteback(page));
             /*
              * We need to make sure we haven't be attached
              * to a new eb.
              */
             detach_page_private(page);
         }
         if (mapped)
             spin_unlock(&page->mapping->private_lock);
         return;
     }
 
     /*
      * For subpage, we can have dummy eb with page private.  In this case,
      * we can directly detach the private as such page is only attached to
      * one dummy eb, no sharing.
      */
     if (!mapped) {
         btrfs_detach_subpage(fs_info, page);
         return;
     }
 
     btrfs_page_dec_eb_refs(fs_info, page);
 
     /*
      * We can only detach the page private if there are no other ebs in the
      * page range and no unfinished IO.
      */
     if (!page_range_has_eb(fs_info, page))
         btrfs_detach_subpage(fs_info, page);
 
     spin_unlock(&page->mapping->private_lock);
 }
 
 /* Release all pages attached to the extent buffer */
 static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
 {
     int i;
     int num_pages;
 
     ASSERT(!extent_buffer_under_io(eb));
 
     num_pages = num_extent_pages(eb);
     for (i = 0; i < num_pages; i++) {
         struct page *page = eb->pages[i];
 
         if (!page)
             continue;
 
         detach_extent_buffer_page(eb, page);
 
         /* One for when we allocated the page */
         put_page(page);
     }
 }
 
 /*
  * Helper for releasing the extent buffer.
  */
 static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
 {
     btrfs_release_extent_buffer_pages(eb);
     btrfs_leak_debug_del(&eb->fs_info->eb_leak_lock, &eb->leak_list);
     __free_extent_buffer(eb);
 }
 
 static struct extent_buffer *
 __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
               unsigned long len)
 {
     struct extent_buffer *eb = NULL;
 
     eb = kmem_cache_zalloc(extent_buffer_cache, GFP_NOFS|__GFP_NOFAIL);
     eb->start = start;
     eb->len = len;
     eb->fs_info = fs_info;
     eb->bflags = 0;
     init_rwsem(&eb->lock);
 
     btrfs_leak_debug_add(&fs_info->eb_leak_lock, &eb->leak_list,
                  &fs_info->allocated_ebs);
     INIT_LIST_HEAD(&eb->release_list);
 
     spin_lock_init(&eb->refs_lock);
     atomic_set(&eb->refs, 1);
     atomic_set(&eb->io_pages, 0);
 
     ASSERT(len <= BTRFS_MAX_METADATA_BLOCKSIZE);
 
     return eb;
 }
 
 struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src)
 {
     int i;
     struct extent_buffer *new;
     int num_pages = num_extent_pages(src);
     int ret;
 
     new = __alloc_extent_buffer(src->fs_info, src->start, src->len);
     if (new == NULL)
         return NULL;
 
     /*
      * Set UNMAPPED before calling btrfs_release_extent_buffer(), as
      * btrfs_release_extent_buffer() have different behavior for
      * UNMAPPED subpage extent buffer.
      */
     set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags);
 
     memset(new->pages, 0, sizeof(*new->pages) * num_pages);
     ret = btrfs_alloc_page_array(num_pages, new->pages);
     if (ret) {
         btrfs_release_extent_buffer(new);
         return NULL;
     }
 
     for (i = 0; i < num_pages; i++) {
         int ret;
         struct page *p = new->pages[i];
 
         ret = attach_extent_buffer_page(new, p, NULL);
         if (ret < 0) {
             btrfs_release_extent_buffer(new);
             return NULL;
         }
         WARN_ON(PageDirty(p));
         copy_page(page_address(p), page_address(src->pages[i]));
     }
     set_extent_buffer_uptodate(new);
 
     return new;
 }
 
 struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
                           u64 start, unsigned long len)
 {
     struct extent_buffer *eb;
     int num_pages;
     int i;
     int ret;
 
     eb = __alloc_extent_buffer(fs_info, start, len);
     if (!eb)
         return NULL;
 
     num_pages = num_extent_pages(eb);
     ret = btrfs_alloc_page_array(num_pages, eb->pages);
     if (ret)
         goto err;
 
     for (i = 0; i < num_pages; i++) {
         struct page *p = eb->pages[i];
 
         ret = attach_extent_buffer_page(eb, p, NULL);
         if (ret < 0)
             goto err;
     }
 
     set_extent_buffer_uptodate(eb);
     btrfs_set_header_nritems(eb, 0);
     set_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
 
     return eb;
 err:
     for (i = 0; i < num_pages; i++) {
         if (eb->pages[i]) {
             detach_extent_buffer_page(eb, eb->pages[i]);
             __free_page(eb->pages[i]);
         }
     }
     __free_extent_buffer(eb);
     return NULL;
 }
 
 struct extent_buffer *alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
                         u64 start)
 {
     return __alloc_dummy_extent_buffer(fs_info, start, fs_info->nodesize);
 }
 
 static void check_buffer_tree_ref(struct extent_buffer *eb)
 {
     int refs;
     /*
      * The TREE_REF bit is first set when the extent_buffer is added
      * to the radix tree. It is also reset, if unset, when a new reference
      * is created by find_extent_buffer.
      *
      * It is only cleared in two cases: freeing the last non-tree
      * reference to the extent_buffer when its STALE bit is set or
      * calling release_folio when the tree reference is the only reference.
      *
      * In both cases, care is taken to ensure that the extent_buffer's
      * pages are not under io. However, release_folio can be concurrently
      * called with creating new references, which is prone to race
      * conditions between the calls to check_buffer_tree_ref in those
      * codepaths and clearing TREE_REF in try_release_extent_buffer.
      *
      * The actual lifetime of the extent_buffer in the radix tree is
      * adequately protected by the refcount, but the TREE_REF bit and
      * its corresponding reference are not. To protect against this
      * class of races, we call check_buffer_tree_ref from the codepaths
      * which trigger io after they set eb->io_pages. Note that once io is
      * initiated, TREE_REF can no longer be cleared, so that is the
      * moment at which any such race is best fixed.
      */
     refs = atomic_read(&eb->refs);
     if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
         return;
 
     spin_lock(&eb->refs_lock);
     if (!test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
         atomic_inc(&eb->refs);
     spin_unlock(&eb->refs_lock);
 }
 
 static void mark_extent_buffer_accessed(struct extent_buffer *eb,
         struct page *accessed)
 {
     int num_pages, i;
 
     check_buffer_tree_ref(eb);
 
     num_pages = num_extent_pages(eb);
     for (i = 0; i < num_pages; i++) {
         struct page *p = eb->pages[i];
 
         if (p != accessed)
             mark_page_accessed(p);
     }
 }
 
 struct extent_buffer *find_extent_buffer(struct btrfs_fs_info *fs_info,
                      u64 start)
 {
     struct extent_buffer *eb;
 
     eb = find_extent_buffer_nolock(fs_info, start);
     if (!eb)
         return NULL;
     /*
      * Lock our eb's refs_lock to avoid races with free_extent_buffer().
      * When we get our eb it might be flagged with EXTENT_BUFFER_STALE and
      * another task running free_extent_buffer() might have seen that flag
      * set, eb->refs == 2, that the buffer isn't under IO (dirty and
      * writeback flags not set) and it's still in the tree (flag
      * EXTENT_BUFFER_TREE_REF set), therefore being in the process of
      * decrementing the extent buffer's reference count twice.  So here we
      * could race and increment the eb's reference count, clear its stale
      * flag, mark it as dirty and drop our reference before the other task
      * finishes executing free_extent_buffer, which would later result in
      * an attempt to free an extent buffer that is dirty.
      */
     if (test_bit(EXTENT_BUFFER_STALE, &eb->bflags)) {
         spin_lock(&eb->refs_lock);
         spin_unlock(&eb->refs_lock);
     }
     mark_extent_buffer_accessed(eb, NULL);
     return eb;
 }
 
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
                     u64 start)
 {
     struct extent_buffer *eb, *exists = NULL;
     int ret;
 
     eb = find_extent_buffer(fs_info, start);
     if (eb)
         return eb;
     eb = alloc_dummy_extent_buffer(fs_info, start);
     if (!eb)
         return ERR_PTR(-ENOMEM);
     eb->fs_info = fs_info;
 again:
     ret = radix_tree_preload(GFP_NOFS);
     if (ret) {
         exists = ERR_PTR(ret);
         goto free_eb;
     }
     spin_lock(&fs_info->buffer_lock);
     ret = radix_tree_insert(&fs_info->buffer_radix,
                 start >> fs_info->sectorsize_bits, eb);
     spin_unlock(&fs_info->buffer_lock);
     radix_tree_preload_end();
     if (ret == -EEXIST) {
         exists = find_extent_buffer(fs_info, start);
         if (exists)
             goto free_eb;
         else
             goto again;
     }
     check_buffer_tree_ref(eb);
     set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
 
     return eb;
 free_eb:
     btrfs_release_extent_buffer(eb);
     return exists;
 }
 #endif
 
 static struct extent_buffer *grab_extent_buffer(
         struct btrfs_fs_info *fs_info, struct page *page)
 {
     struct extent_buffer *exists;
 
     /*
      * For subpage case, we completely rely on radix tree to ensure we
      * don't try to insert two ebs for the same bytenr.  So here we always
      * return NULL and just continue.
      */
     if (fs_info->nodesize < PAGE_SIZE)
         return NULL;
 
     /* Page not yet attached to an extent buffer */
     if (!PagePrivate(page))
         return NULL;
 
     /*
      * We could have already allocated an eb for this page and attached one
      * so lets see if we can get a ref on the existing eb, and if we can we
      * know it's good and we can just return that one, else we know we can
      * just overwrite page->private.
      */
     exists = (struct extent_buffer *)page->private;
     if (atomic_inc_not_zero(&exists->refs))
         return exists;
 
     WARN_ON(PageDirty(page));
     detach_page_private(page);
     return NULL;
 }
 
 static int check_eb_alignment(struct btrfs_fs_info *fs_info, u64 start)
 {
     if (!IS_ALIGNED(start, fs_info->sectorsize)) {
         btrfs_err(fs_info, "bad tree block start %llu", start);
         return -EINVAL;
     }
 
     if (fs_info->nodesize < PAGE_SIZE &&
         offset_in_page(start) + fs_info->nodesize > PAGE_SIZE) {
         btrfs_err(fs_info,
         "tree block crosses page boundary, start %llu nodesize %u",
               start, fs_info->nodesize);
         return -EINVAL;
     }
     if (fs_info->nodesize >= PAGE_SIZE &&
         !PAGE_ALIGNED(start)) {
         btrfs_err(fs_info,
         "tree block is not page aligned, start %llu nodesize %u",
               start, fs_info->nodesize);
         return -EINVAL;
     }
     return 0;
 }
 
 struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
                       u64 start, u64 owner_root, int level)
 {
     unsigned long len = fs_info->nodesize;
     int num_pages;
     int i;
     unsigned long index = start >> PAGE_SHIFT;
     struct extent_buffer *eb;
     struct extent_buffer *exists = NULL;
     struct page *p;
     struct address_space *mapping = fs_info->btree_inode->i_mapping;
     u64 lockdep_owner = owner_root;
     int uptodate = 1;
     int ret;
 
     if (check_eb_alignment(fs_info, start))
         return ERR_PTR(-EINVAL);
 
 #if BITS_PER_LONG == 32
     if (start >= MAX_LFS_FILESIZE) {
         btrfs_err_rl(fs_info,
         "extent buffer %llu is beyond 32bit page cache limit", start);
         btrfs_err_32bit_limit(fs_info);
         return ERR_PTR(-EOVERFLOW);
     }
     if (start >= BTRFS_32BIT_EARLY_WARN_THRESHOLD)
         btrfs_warn_32bit_limit(fs_info);
 #endif
 
     eb = find_extent_buffer(fs_info, start);
     if (eb)
         return eb;
 
     eb = __alloc_extent_buffer(fs_info, start, len);
     if (!eb)
         return ERR_PTR(-ENOMEM);
 
     /*
      * The reloc trees are just snapshots, so we need them to appear to be
      * just like any other fs tree WRT lockdep.
      */
     if (lockdep_owner == BTRFS_TREE_RELOC_OBJECTID)
         lockdep_owner = BTRFS_FS_TREE_OBJECTID;
 
     btrfs_set_buffer_lockdep_class(lockdep_owner, eb, level);
 
     num_pages = num_extent_pages(eb);
     for (i = 0; i < num_pages; i++, index++) {
         struct btrfs_subpage *prealloc = NULL;
 
         p = find_or_create_page(mapping, index, GFP_NOFS|__GFP_NOFAIL);
         if (!p) {
             exists = ERR_PTR(-ENOMEM);
             goto free_eb;
         }
 
         /*
          * Preallocate page->private for subpage case, so that we won't
          * allocate memory with private_lock hold.  The memory will be
          * freed by attach_extent_buffer_page() or freed manually if
          * we exit earlier.
          *
          * Although we have ensured one subpage eb can only have one
          * page, but it may change in the future for 16K page size
          * support, so we still preallocate the memory in the loop.
          */
         if (fs_info->nodesize < PAGE_SIZE) {
             prealloc = btrfs_alloc_subpage(fs_info, BTRFS_SUBPAGE_METADATA);
             if (IS_ERR(prealloc)) {
                 ret = PTR_ERR(prealloc);
                 unlock_page(p);
                 put_page(p);
                 exists = ERR_PTR(ret);
                 goto free_eb;
             }
         }
 
         spin_lock(&mapping->private_lock);
         exists = grab_extent_buffer(fs_info, p);
         if (exists) {
             spin_unlock(&mapping->private_lock);
             unlock_page(p);
             put_page(p);
             mark_extent_buffer_accessed(exists, p);
             btrfs_free_subpage(prealloc);
             goto free_eb;
         }
         /* Should not fail, as we have preallocated the memory */
         ret = attach_extent_buffer_page(eb, p, prealloc);
         ASSERT(!ret);
         /*
          * To inform we have extra eb under allocation, so that
          * detach_extent_buffer_page() won't release the page private
          * when the eb hasn't yet been inserted into radix tree.
          *
          * The ref will be decreased when the eb released the page, in
          * detach_extent_buffer_page().
          * Thus needs no special handling in error path.
          */
         btrfs_page_inc_eb_refs(fs_info, p);
         spin_unlock(&mapping->private_lock);
 
         WARN_ON(btrfs_page_test_dirty(fs_info, p, eb->start, eb->len));
         eb->pages[i] = p;
         if (!PageUptodate(p))
             uptodate = 0;
 
         /*
          * We can't unlock the pages just yet since the extent buffer
          * hasn't been properly inserted in the radix tree, this
          * opens a race with btree_release_folio which can free a page
          * while we are still filling in all pages for the buffer and
          * we could crash.
          */
     }
     if (uptodate)
         set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
 again:
     ret = radix_tree_preload(GFP_NOFS);
     if (ret) {
         exists = ERR_PTR(ret);
         goto free_eb;
     }
 
     spin_lock(&fs_info->buffer_lock);
     ret = radix_tree_insert(&fs_info->buffer_radix,
                 start >> fs_info->sectorsize_bits, eb);
     spin_unlock(&fs_info->buffer_lock);
     radix_tree_preload_end();
     if (ret == -EEXIST) {
         exists = find_extent_buffer(fs_info, start);
         if (exists)
             goto free_eb;
         else
             goto again;
     }
     /* add one reference for the tree */
     check_buffer_tree_ref(eb);
     set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
 
     /*
      * Now it's safe to unlock the pages because any calls to
      * btree_release_folio will correctly detect that a page belongs to a
      * live buffer and won't free them prematurely.
      */
     for (i = 0; i < num_pages; i++)
         unlock_page(eb->pages[i]);
     return eb;
 
 free_eb:
     WARN_ON(!atomic_dec_and_test(&eb->refs));
     for (i = 0; i < num_pages; i++) {
         if (eb->pages[i])
             unlock_page(eb->pages[i]);
     }
 
     btrfs_release_extent_buffer(eb);
     return exists;
 }
 
 static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
 {
     struct extent_buffer *eb =
             container_of(head, struct extent_buffer, rcu_head);
 
     __free_extent_buffer(eb);
 }
 
 static int release_extent_buffer(struct extent_buffer *eb)
     __releases(&eb->refs_lock)
 {
     lockdep_assert_held(&eb->refs_lock);
 
     WARN_ON(atomic_read(&eb->refs) == 0);
     if (atomic_dec_and_test(&eb->refs)) {
         if (test_and_clear_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags)) {
             struct btrfs_fs_info *fs_info = eb->fs_info;
 
             spin_unlock(&eb->refs_lock);
 
             spin_lock(&fs_info->buffer_lock);
             radix_tree_delete(&fs_info->buffer_radix,
                       eb->start >> fs_info->sectorsize_bits);
             spin_unlock(&fs_info->buffer_lock);
         } else {
             spin_unlock(&eb->refs_lock);
         }
 
         btrfs_leak_debug_del(&eb->fs_info->eb_leak_lock, &eb->leak_list);
         /* Should be safe to release our pages at this point */
         btrfs_release_extent_buffer_pages(eb);
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
         if (unlikely(test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags))) {
             __free_extent_buffer(eb);
             return 1;
         }
 #endif
         call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
         return 1;
     }
     spin_unlock(&eb->refs_lock);
 
     return 0;
 }
 
 void free_extent_buffer(struct extent_buffer *eb)
 {
     int refs;
     int old;
     if (!eb)
         return;
 
     while (1) {
         refs = atomic_read(&eb->refs);
         if ((!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) && refs <= 3)
             || (test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) &&
             refs == 1))
             break;
         old = atomic_cmpxchg(&eb->refs, refs, refs - 1);
         if (old == refs)
             return;
     }
 
     spin_lock(&eb->refs_lock);
     if (atomic_read(&eb->refs) == 2 &&
         test_bit(EXTENT_BUFFER_STALE, &eb->bflags) &&
         !extent_buffer_under_io(eb) &&
         test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
         atomic_dec(&eb->refs);
 
     /*
      * I know this is terrible, but it's temporary until we stop tracking
      * the uptodate bits and such for the extent buffers.
      */
     release_extent_buffer(eb);
 }
 
 void free_extent_buffer_stale(struct extent_buffer *eb)
 {
     if (!eb)
         return;
 
     spin_lock(&eb->refs_lock);
     set_bit(EXTENT_BUFFER_STALE, &eb->bflags);
 
     if (atomic_read(&eb->refs) == 2 && !extent_buffer_under_io(eb) &&
         test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
         atomic_dec(&eb->refs);
     release_extent_buffer(eb);
 }
 
 static void btree_clear_page_dirty(struct page *page)
 {
     ASSERT(PageDirty(page));
     ASSERT(PageLocked(page));
     clear_page_dirty_for_io(page);
     xa_lock_irq(&page->mapping->i_pages);
     if (!PageDirty(page))
         __xa_clear_mark(&page->mapping->i_pages,
                 page_index(page), PAGECACHE_TAG_DIRTY);
     xa_unlock_irq(&page->mapping->i_pages);
 }
 
 static void clear_subpage_extent_buffer_dirty(const struct extent_buffer *eb)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     struct page *page = eb->pages[0];
     bool last;
 
     /* btree_clear_page_dirty() needs page locked */
     lock_page(page);
     last = btrfs_subpage_clear_and_test_dirty(fs_info, page, eb->start,
                           eb->len);
     if (last)
         btree_clear_page_dirty(page);
     unlock_page(page);
     WARN_ON(atomic_read(&eb->refs) == 0);
 }
 
 void clear_extent_buffer_dirty(const struct extent_buffer *eb)
 {
     int i;
     int num_pages;
     struct page *page;
 
     if (eb->fs_info->nodesize < PAGE_SIZE)
         return clear_subpage_extent_buffer_dirty(eb);
 
     num_pages = num_extent_pages(eb);
 
     for (i = 0; i < num_pages; i++) {
         page = eb->pages[i];
         if (!PageDirty(page))
             continue;
         lock_page(page);
         btree_clear_page_dirty(page);
         ClearPageError(page);
         unlock_page(page);
     }
     WARN_ON(atomic_read(&eb->refs) == 0);
 }
 
 bool set_extent_buffer_dirty(struct extent_buffer *eb)
 {
     int i;
     int num_pages;
     bool was_dirty;
 
     check_buffer_tree_ref(eb);
 
     was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);
 
     num_pages = num_extent_pages(eb);
     WARN_ON(atomic_read(&eb->refs) == 0);
     WARN_ON(!test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags));
 
     if (!was_dirty) {
         bool subpage = eb->fs_info->nodesize < PAGE_SIZE;
 
         /*
          * For subpage case, we can have other extent buffers in the
          * same page, and in clear_subpage_extent_buffer_dirty() we
          * have to clear page dirty without subpage lock held.
          * This can cause race where our page gets dirty cleared after
          * we just set it.
          *
          * Thankfully, clear_subpage_extent_buffer_dirty() has locked
          * its page for other reasons, we can use page lock to prevent
          * the above race.
          */
         if (subpage)
             lock_page(eb->pages[0]);
         for (i = 0; i < num_pages; i++)
             btrfs_page_set_dirty(eb->fs_info, eb->pages[i],
                          eb->start, eb->len);
         if (subpage)
             unlock_page(eb->pages[0]);
     }
 #ifdef CONFIG_BTRFS_DEBUG
     for (i = 0; i < num_pages; i++)
         ASSERT(PageDirty(eb->pages[i]));
 #endif
 
     return was_dirty;
 }
 
 void clear_extent_buffer_uptodate(struct extent_buffer *eb)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     struct page *page;
     int num_pages;
     int i;
 
     clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
     num_pages = num_extent_pages(eb);
     for (i = 0; i < num_pages; i++) {
         page = eb->pages[i];
         if (!page)
             continue;
 
         /*
          * This is special handling for metadata subpage, as regular
          * btrfs_is_subpage() can not handle cloned/dummy metadata.
          */
         if (fs_info->nodesize >= PAGE_SIZE)
             ClearPageUptodate(page);
         else
             btrfs_subpage_clear_uptodate(fs_info, page, eb->start,
                              eb->len);
     }
 }
 
 void set_extent_buffer_uptodate(struct extent_buffer *eb)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     struct page *page;
     int num_pages;
     int i;
 
     set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
     num_pages = num_extent_pages(eb);
     for (i = 0; i < num_pages; i++) {
         page = eb->pages[i];
 
         /*
          * This is special handling for metadata subpage, as regular
          * btrfs_is_subpage() can not handle cloned/dummy metadata.
          */
         if (fs_info->nodesize >= PAGE_SIZE)
             SetPageUptodate(page);
         else
             btrfs_subpage_set_uptodate(fs_info, page, eb->start,
                            eb->len);
     }
 }
 
 static int read_extent_buffer_subpage(struct extent_buffer *eb, int wait,
                       int mirror_num)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
     struct extent_io_tree *io_tree;
     struct page *page = eb->pages[0];
     struct btrfs_bio_ctrl bio_ctrl = {
         .mirror_num = mirror_num,
     };
     int ret = 0;
 
     ASSERT(!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags));
     ASSERT(PagePrivate(page));
     io_tree = &BTRFS_I(fs_info->btree_inode)->io_tree;
 
     if (wait == WAIT_NONE) {
         if (!try_lock_extent(io_tree, eb->start, eb->start + eb->len - 1))
             return -EAGAIN;
     } else {
         ret = lock_extent(io_tree, eb->start, eb->start + eb->len - 1);
         if (ret < 0)
             return ret;
     }
 
     ret = 0;
     if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags) ||
         PageUptodate(page) ||
         btrfs_subpage_test_uptodate(fs_info, page, eb->start, eb->len)) {
         set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
         unlock_extent(io_tree, eb->start, eb->start + eb->len - 1);
         return ret;
     }
 
     clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
     eb->read_mirror = 0;
     atomic_set(&eb->io_pages, 1);
     check_buffer_tree_ref(eb);
     btrfs_subpage_clear_error(fs_info, page, eb->start, eb->len);
 
     btrfs_subpage_start_reader(fs_info, page, eb->start, eb->len);
     ret = submit_extent_page(REQ_OP_READ, NULL, &bio_ctrl,
                  page, eb->start, eb->len,
                  eb->start - page_offset(page),
                  end_bio_extent_readpage, 0, true);
     if (ret) {
         /*
          * In the endio function, if we hit something wrong we will
          * increase the io_pages, so here we need to decrease it for
          * error path.
          */
         atomic_dec(&eb->io_pages);
     }
     submit_one_bio(&bio_ctrl);
     if (ret || wait != WAIT_COMPLETE)
         return ret;
 
     wait_extent_bit(io_tree, eb->start, eb->start + eb->len - 1, EXTENT_LOCKED);
     if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
         ret = -EIO;
     return ret;
 }
 
 int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num)
 {
     int i;
     struct page *page;
     int err;
     int ret = 0;
     int locked_pages = 0;
     int all_uptodate = 1;
     int num_pages;
     unsigned long num_reads = 0;
     struct btrfs_bio_ctrl bio_ctrl = {
         .mirror_num = mirror_num,
     };
 
     if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
         return 0;
 
     /*
      * We could have had EXTENT_BUFFER_UPTODATE cleared by the write
      * operation, which could potentially still be in flight.  In this case
      * we simply want to return an error.
      */
     if (unlikely(test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)))
         return -EIO;
 
     if (eb->fs_info->nodesize < PAGE_SIZE)
         return read_extent_buffer_subpage(eb, wait, mirror_num);
 
     num_pages = num_extent_pages(eb);
     for (i = 0; i < num_pages; i++) {
         page = eb->pages[i];
         if (wait == WAIT_NONE) {
             /*
              * WAIT_NONE is only utilized by readahead. If we can't
              * acquire the lock atomically it means either the eb
              * is being read out or under modification.
              * Either way the eb will be or has been cached,
              * readahead can exit safely.
              */
             if (!trylock_page(page))
                 goto unlock_exit;
         } else {
             lock_page(page);
         }
         locked_pages++;
     }
     /*
      * We need to firstly lock all pages to make sure that
      * the uptodate bit of our pages won't be affected by
      * clear_extent_buffer_uptodate().
      */
     for (i = 0; i < num_pages; i++) {
         page = eb->pages[i];
         if (!PageUptodate(page)) {
             num_reads++;
             all_uptodate = 0;
         }
     }
 
     if (all_uptodate) {
         set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
         goto unlock_exit;
     }
 
     clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
     eb->read_mirror = 0;
     atomic_set(&eb->io_pages, num_reads);
     /*
      * It is possible for release_folio to clear the TREE_REF bit before we
      * set io_pages. See check_buffer_tree_ref for a more detailed comment.
      */
     check_buffer_tree_ref(eb);
     for (i = 0; i < num_pages; i++) {
         page = eb->pages[i];
 
         if (!PageUptodate(page)) {
             if (ret) {
                 atomic_dec(&eb->io_pages);
                 unlock_page(page);
                 continue;
             }
 
             ClearPageError(page);
             err = submit_extent_page(REQ_OP_READ, NULL,
                      &bio_ctrl, page, page_offset(page),
                      PAGE_SIZE, 0, end_bio_extent_readpage,
                      0, false);
             if (err) {
                 /*
                  * We failed to submit the bio so it's the
                  * caller's responsibility to perform cleanup
                  * i.e unlock page/set error bit.
                  */
                 ret = err;
                 SetPageError(page);
                 unlock_page(page);
                 atomic_dec(&eb->io_pages);
             }
         } else {
             unlock_page(page);
         }
     }
 
     submit_one_bio(&bio_ctrl);
 
     if (ret || wait != WAIT_COMPLETE)
         return ret;
 
     for (i = 0; i < num_pages; i++) {
         page = eb->pages[i];
         wait_on_page_locked(page);
         if (!PageUptodate(page))
             ret = -EIO;
     }
 
     return ret;
 
 unlock_exit:
     while (locked_pages > 0) {
         locked_pages--;
         page = eb->pages[locked_pages];
         unlock_page(page);
     }
     return ret;
 }
 
 static bool report_eb_range(const struct extent_buffer *eb, unsigned long start,
                 unsigned long len)
 {
     btrfs_warn(eb->fs_info,
         "access to eb bytenr %llu len %lu out of range start %lu len %lu",
         eb->start, eb->len, start, len);
     WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
 
     return true;
 }
 
 /*
  * Check if the [start, start + len) range is valid before reading/writing
  * the eb.
  * NOTE: @start and @len are offset inside the eb, not logical address.
  *
  * Caller should not touch the dst/src memory if this function returns error.
  */
 static inline int check_eb_range(const struct extent_buffer *eb,
                  unsigned long start, unsigned long len)
 {
     unsigned long offset;
 
     /* start, start + len should not go beyond eb->len nor overflow */
     if (unlikely(check_add_overflow(start, len, &offset) || offset > eb->len))
         return report_eb_range(eb, start, len);
 
     return false;
 }
 
 void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
             unsigned long start, unsigned long len)
 {
     size_t cur;
     size_t offset;
     struct page *page;
     char *kaddr;
     char *dst = (char *)dstv;
     unsigned long i = get_eb_page_index(start);
 
     if (check_eb_range(eb, start, len))
         return;
 
     offset = get_eb_offset_in_page(eb, start);
 
     while (len > 0) {
         page = eb->pages[i];
 
         cur = min(len, (PAGE_SIZE - offset));
         kaddr = page_address(page);
         memcpy(dst, kaddr + offset, cur);
 
         dst += cur;
         len -= cur;
         offset = 0;
         i++;
     }
 }
 
 int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb,
                        void __user *dstv,
                        unsigned long start, unsigned long len)
 {
     size_t cur;
     size_t offset;
     struct page *page;
     char *kaddr;
     char __user *dst = (char __user *)dstv;
     unsigned long i = get_eb_page_index(start);
     int ret = 0;
 
     WARN_ON(start > eb->len);
     WARN_ON(start + len > eb->start + eb->len);
 
     offset = get_eb_offset_in_page(eb, start);
 
     while (len > 0) {
         page = eb->pages[i];
 
         cur = min(len, (PAGE_SIZE - offset));
         kaddr = page_address(page);
         if (copy_to_user_nofault(dst, kaddr + offset, cur)) {
             ret = -EFAULT;
             break;
         }
 
         dst += cur;
         len -= cur;
         offset = 0;
         i++;
     }
 
     return ret;
 }
 
 int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
              unsigned long start, unsigned long len)
 {
     size_t cur;
     size_t offset;
     struct page *page;
     char *kaddr;
     char *ptr = (char *)ptrv;
     unsigned long i = get_eb_page_index(start);
     int ret = 0;
 
     if (check_eb_range(eb, start, len))
         return -EINVAL;
 
     offset = get_eb_offset_in_page(eb, start);
 
     while (len > 0) {
         page = eb->pages[i];
 
         cur = min(len, (PAGE_SIZE - offset));
 
         kaddr = page_address(page);
         ret = memcmp(ptr, kaddr + offset, cur);
         if (ret)
             break;
 
         ptr += cur;
         len -= cur;
         offset = 0;
         i++;
     }
     return ret;
 }
 
 /*
  * Check that the extent buffer is uptodate.
  *
  * For regular sector size == PAGE_SIZE case, check if @page is uptodate.
  * For subpage case, check if the range covered by the eb has EXTENT_UPTODATE.
  */
 static void assert_eb_page_uptodate(const struct extent_buffer *eb,
                     struct page *page)
 {
     struct btrfs_fs_info *fs_info = eb->fs_info;
 
     /*
      * If we are using the commit root we could potentially clear a page
      * Uptodate while we're using the extent buffer that we've previously
      * looked up.  We don't want to complain in this case, as the page was
      * valid before, we just didn't write it out.  Instead we want to catch
      * the case where we didn't actually read the block properly, which
      * would have !PageUptodate && !PageError, as we clear PageError before
      * reading.
      */
     if (fs_info->nodesize < PAGE_SIZE) {
         bool uptodate, error;
 
         uptodate = btrfs_subpage_test_uptodate(fs_info, page,
                                eb->start, eb->len);
         error = btrfs_subpage_test_error(fs_info, page, eb->start, eb->len);
         WARN_ON(!uptodate && !error);
     } else {
         WARN_ON(!PageUptodate(page) && !PageError(page));
     }
 }
 
 void write_extent_buffer_chunk_tree_uuid(const struct extent_buffer *eb,
         const void *srcv)
 {
     char *kaddr;
 
     assert_eb_page_uptodate(eb, eb->pages[0]);
     kaddr = page_address(eb->pages[0]) +
         get_eb_offset_in_page(eb, offsetof(struct btrfs_header,
                            chunk_tree_uuid));
     memcpy(kaddr, srcv, BTRFS_FSID_SIZE);
 }
 
 void write_extent_buffer_fsid(const struct extent_buffer *eb, const void *srcv)
 {
     char *kaddr;
 
     assert_eb_page_uptodate(eb, eb->pages[0]);
     kaddr = page_address(eb->pages[0]) +
         get_eb_offset_in_page(eb, offsetof(struct btrfs_header, fsid));
     memcpy(kaddr, srcv, BTRFS_FSID_SIZE);
 }
 
 void write_extent_buffer(const struct extent_buffer *eb, const void *srcv,
              unsigned long start, unsigned long len)
 {
     size_t cur;
     size_t offset;
     struct page *page;
     char *kaddr;
     char *src = (char *)srcv;
     unsigned long i = get_eb_page_index(start);
 
     WARN_ON(test_bit(EXTENT_BUFFER_NO_CHECK, &eb->bflags));
 
     if (check_eb_range(eb, start, len))
         return;
 
     offset = get_eb_offset_in_page(eb, start);
 
     while (len > 0) {
         page = eb->pages[i];
         assert_eb_page_uptodate(eb, page);
 
         cur = min(len, PAGE_SIZE - offset);
         kaddr = page_address(page);
         memcpy(kaddr + offset, src, cur);
 
         src += cur;
         len -= cur;
         offset = 0;
         i++;
     }
 }
 
 void memzero_extent_buffer(const struct extent_buffer *eb, unsigned long start,
         unsigned long len)
 {
     size_t cur;
     size_t offset;
     struct page *page;
     char *kaddr;
     unsigned long i = get_eb_page_index(start);
 
     if (check_eb_range(eb, start, len))
         return;
 
     offset = get_eb_offset_in_page(eb, start);
 
     while (len > 0) {
         page = eb->pages[i];
         assert_eb_page_uptodate(eb, page);
 
         cur = min(len, PAGE_SIZE - offset);
         kaddr = page_address(page);
         memset(kaddr + offset, 0, cur);
 
         len -= cur;
         offset = 0;
         i++;
     }
 }
 
 void copy_extent_buffer_full(const struct extent_buffer *dst,
                  const struct extent_buffer *src)
 {
     int i;
     int num_pages;
 
     ASSERT(dst->len == src->len);
 
     if (dst->fs_info->nodesize >= PAGE_SIZE) {
         num_pages = num_extent_pages(dst);
         for (i = 0; i < num_pages; i++)
             copy_page(page_address(dst->pages[i]),
                   page_address(src->pages[i]));
     } else {
         size_t src_offset = get_eb_offset_in_page(src, 0);
         size_t dst_offset = get_eb_offset_in_page(dst, 0);
 
         ASSERT(src->fs_info->nodesize < PAGE_SIZE);
         memcpy(page_address(dst->pages[0]) + dst_offset,
                page_address(src->pages[0]) + src_offset,
                src->len);
     }
 }
 
 void copy_extent_buffer(const struct extent_buffer *dst,
             const struct extent_buffer *src,
             unsigned long dst_offset, unsigned long src_offset,
             unsigned long len)
 {
     u64 dst_len = dst->len;
     size_t cur;
     size_t offset;
     struct page *page;
     char *kaddr;
     unsigned long i = get_eb_page_index(dst_offset);
 
     if (check_eb_range(dst, dst_offset, len) ||
         check_eb_range(src, src_offset, len))
         return;
 
     WARN_ON(src->len != dst_len);
 
     offset = get_eb_offset_in_page(dst, dst_offset);
 
     while (len > 0) {
         page = dst->pages[i];
         assert_eb_page_uptodate(dst, page);
 
         cur = min(len, (unsigned long)(PAGE_SIZE - offset));
 
         kaddr = page_address(page);
         read_extent_buffer(src, kaddr + offset, src_offset, cur);
 
         src_offset += cur;
         len -= cur;
         offset = 0;
         i++;
     }
 }
 
 /*
  * eb_bitmap_offset() - calculate the page and offset of the byte containing the
  * given bit number
  * @eb: the extent buffer
  * @start: offset of the bitmap item in the extent buffer
  * @nr: bit number
  * @page_index: return index of the page in the extent buffer that contains the
  * given bit number
  * @page_offset: return offset into the page given by page_index
  *
  * This helper hides the ugliness of finding the byte in an extent buffer which
  * contains a given bit.
  */
 static inline void eb_bitmap_offset(const struct extent_buffer *eb,
                     unsigned long start, unsigned long nr,
                     unsigned long *page_index,
                     size_t *page_offset)
 {
     size_t byte_offset = BIT_BYTE(nr);
     size_t offset;
 
     /*
      * The byte we want is the offset of the extent buffer + the offset of
      * the bitmap item in the extent buffer + the offset of the byte in the
      * bitmap item.
      */
     offset = start + offset_in_page(eb->start) + byte_offset;
 
     *page_index = offset >> PAGE_SHIFT;
     *page_offset = offset_in_page(offset);
 }
 
 /**
  * extent_buffer_test_bit - determine whether a bit in a bitmap item is set
  * @eb: the extent buffer
  * @start: offset of the bitmap item in the extent buffer
  * @nr: bit number to test
  */
 int extent_buffer_test_bit(const struct extent_buffer *eb, unsigned long start,
                unsigned long nr)
 {
     u8 *kaddr;
     struct page *page;
     unsigned long i;
     size_t offset;
 
     eb_bitmap_offset(eb, start, nr, &i, &offset);
     page = eb->pages[i];
     assert_eb_page_uptodate(eb, page);
     kaddr = page_address(page);
     return 1U & (kaddr[offset] >> (nr & (BITS_PER_BYTE - 1)));
 }
 
 /**
  * extent_buffer_bitmap_set - set an area of a bitmap
  * @eb: the extent buffer
  * @start: offset of the bitmap item in the extent buffer
  * @pos: bit number of the first bit
  * @len: number of bits to set
  */
 void extent_buffer_bitmap_set(const struct extent_buffer *eb, unsigned long start,
                   unsigned long pos, unsigned long len)
 {
     u8 *kaddr;
     struct page *page;
     unsigned long i;
     size_t offset;
     const unsigned int size = pos + len;
     int bits_to_set = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
     u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(pos);
 
     eb_bitmap_offset(eb, start, pos, &i, &offset);
     page = eb->pages[i];
     assert_eb_page_uptodate(eb, page);
     kaddr = page_address(page);
 
     while (len >= bits_to_set) {
         kaddr[offset] |= mask_to_set;
         len -= bits_to_set;
         bits_to_set = BITS_PER_BYTE;
         mask_to_set = ~0;
         if (++offset >= PAGE_SIZE && len > 0) {
             offset = 0;
             page = eb->pages[++i];
             assert_eb_page_uptodate(eb, page);
             kaddr = page_address(page);
         }
     }
     if (len) {
         mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
         kaddr[offset] |= mask_to_set;
     }
 }
 
 
 /**
  * extent_buffer_bitmap_clear - clear an area of a bitmap
  * @eb: the extent buffer
  * @start: offset of the bitmap item in the extent buffer
  * @pos: bit number of the first bit
  * @len: number of bits to clear
  */
 void extent_buffer_bitmap_clear(const struct extent_buffer *eb,
                 unsigned long start, unsigned long pos,
                 unsigned long len)
 {
     u8 *kaddr;
     struct page *page;
     unsigned long i;
     size_t offset;
     const unsigned int size = pos + len;
     int bits_to_clear = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
     u8 mask_to_clear = BITMAP_FIRST_BYTE_MASK(pos);
 
     eb_bitmap_offset(eb, start, pos, &i, &offset);
     page = eb->pages[i];
     assert_eb_page_uptodate(eb, page);
     kaddr = page_address(page);
 
     while (len >= bits_to_clear) {
         kaddr[offset] &= ~mask_to_clear;
         len -= bits_to_clear;
         bits_to_clear = BITS_PER_BYTE;
         mask_to_clear = ~0;
         if (++offset >= PAGE_SIZE && len > 0) {
             offset = 0;
             page = eb->pages[++i];
             assert_eb_page_uptodate(eb, page);
             kaddr = page_address(page);
         }
     }
     if (len) {
         mask_to_clear &= BITMAP_LAST_BYTE_MASK(size);
         kaddr[offset] &= ~mask_to_clear;
     }
 }
 
 static inline bool areas_overlap(unsigned long src, unsigned long dst, unsigned long len)
 {
     unsigned long distance = (src > dst) ? src - dst : dst - src;
     return distance < len;
 }
 
 static void copy_pages(struct page *dst_page, struct page *src_page,
                unsigned long dst_off, unsigned long src_off,
                unsigned long len)
 {
     char *dst_kaddr = page_address(dst_page);
     char *src_kaddr;
     int must_memmove = 0;
 
     if (dst_page != src_page) {
         src_kaddr = page_address(src_page);
     } else {
         src_kaddr = dst_kaddr;
         if (areas_overlap(src_off, dst_off, len))
             must_memmove = 1;
     }
 
     if (must_memmove)
         memmove(dst_kaddr + dst_off, src_kaddr + src_off, len);
     else
         memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
 }
 
 void memcpy_extent_buffer(const struct extent_buffer *dst,
               unsigned long dst_offset, unsigned long src_offset,
               unsigned long len)
 {
     size_t cur;
     size_t dst_off_in_page;
     size_t src_off_in_page;
     unsigned long dst_i;
     unsigned long src_i;
 
     if (check_eb_range(dst, dst_offset, len) ||
         check_eb_range(dst, src_offset, len))
         return;
 
     while (len > 0) {
         dst_off_in_page = get_eb_offset_in_page(dst, dst_offset);
         src_off_in_page = get_eb_offset_in_page(dst, src_offset);
 
         dst_i = get_eb_page_index(dst_offset);
         src_i = get_eb_page_index(src_offset);
 
         cur = min(len, (unsigned long)(PAGE_SIZE -
                            src_off_in_page));
         cur = min_t(unsigned long, cur,
             (unsigned long)(PAGE_SIZE - dst_off_in_page));
 
         copy_pages(dst->pages[dst_i], dst->pages[src_i],
                dst_off_in_page, src_off_in_page, cur);
 
         src_offset += cur;
         dst_offset += cur;
         len -= cur;
     }
 }
 
 void memmove_extent_buffer(const struct extent_buffer *dst,
                unsigned long dst_offset, unsigned long src_offset,
                unsigned long len)
 {
     size_t cur;
     size_t dst_off_in_page;
     size_t src_off_in_page;
     unsigned long dst_end = dst_offset + len - 1;
     unsigned long src_end = src_offset + len - 1;
     unsigned long dst_i;
     unsigned long src_i;
 
     if (check_eb_range(dst, dst_offset, len) ||
         check_eb_range(dst, src_offset, len))
         return;
     if (dst_offset < src_offset) {
         memcpy_extent_buffer(dst, dst_offset, src_offset, len);
         return;
     }
     while (len > 0) {
         dst_i = get_eb_page_index(dst_end);
         src_i = get_eb_page_index(src_end);
 
         dst_off_in_page = get_eb_offset_in_page(dst, dst_end);
         src_off_in_page = get_eb_offset_in_page(dst, src_end);
 
         cur = min_t(unsigned long, len, src_off_in_page + 1);
         cur = min(cur, dst_off_in_page + 1);
         copy_pages(dst->pages[dst_i], dst->pages[src_i],
                dst_off_in_page - cur + 1,
                src_off_in_page - cur + 1, cur);
 
         dst_end -= cur;
         src_end -= cur;
         len -= cur;
     }
 }
 
 #define GANG_LOOKUP_SIZE    16
 static struct extent_buffer *get_next_extent_buffer(
         struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
 {
     struct extent_buffer *gang[GANG_LOOKUP_SIZE];
     struct extent_buffer *found = NULL;
     u64 page_start = page_offset(page);
     u64 cur = page_start;
 
     ASSERT(in_range(bytenr, page_start, PAGE_SIZE));
     lockdep_assert_held(&fs_info->buffer_lock);
 
     while (cur < page_start + PAGE_SIZE) {
         int ret;
         int i;
 
         ret = radix_tree_gang_lookup(&fs_info->buffer_radix,
                 (void **)gang, cur >> fs_info->sectorsize_bits,
                 min_t(unsigned int, GANG_LOOKUP_SIZE,
                       PAGE_SIZE / fs_info->nodesize));
         if (ret == 0)
             goto out;
         for (i = 0; i < ret; i++) {
             /* Already beyond page end */
             if (gang[i]->start >= page_start + PAGE_SIZE)
                 goto out;
             /* Found one */
             if (gang[i]->start >= bytenr) {
                 found = gang[i];
                 goto out;
             }
         }
         cur = gang[ret - 1]->start + gang[ret - 1]->len;
     }
 out:
     return found;
 }
 
 static int try_release_subpage_extent_buffer(struct page *page)
 {
     struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
     u64 cur = page_offset(page);
     const u64 end = page_offset(page) + PAGE_SIZE;
     int ret;
 
     while (cur < end) {
         struct extent_buffer *eb = NULL;
 
         /*
          * Unlike try_release_extent_buffer() which uses page->private
          * to grab buffer, for subpage case we rely on radix tree, thus
          * we need to ensure radix tree consistency.
          *
          * We also want an atomic snapshot of the radix tree, thus go
          * with spinlock rather than RCU.
          */
         spin_lock(&fs_info->buffer_lock);
         eb = get_next_extent_buffer(fs_info, page, cur);
         if (!eb) {
             /* No more eb in the page range after or at cur */
             spin_unlock(&fs_info->buffer_lock);
             break;
         }
         cur = eb->start + eb->len;
 
         /*
          * The same as try_release_extent_buffer(), to ensure the eb
          * won't disappear out from under us.
          */
         spin_lock(&eb->refs_lock);
         if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
             spin_unlock(&eb->refs_lock);
             spin_unlock(&fs_info->buffer_lock);
             break;
         }
         spin_unlock(&fs_info->buffer_lock);
 
         /*
          * If tree ref isn't set then we know the ref on this eb is a
          * real ref, so just return, this eb will likely be freed soon
          * anyway.
          */
         if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
             spin_unlock(&eb->refs_lock);
             break;
         }
 
         /*
          * Here we don't care about the return value, we will always
          * check the page private at the end.  And
          * release_extent_buffer() will release the refs_lock.
          */
         release_extent_buffer(eb);
     }
     /*
      * Finally to check if we have cleared page private, as if we have
      * released all ebs in the page, the page private should be cleared now.
      */
     spin_lock(&page->mapping->private_lock);
     if (!PagePrivate(page))
         ret = 1;
     else
         ret = 0;
     spin_unlock(&page->mapping->private_lock);
     return ret;
 
 }
 
 int try_release_extent_buffer(struct page *page)
 {
     struct extent_buffer *eb;
 
     if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
         return try_release_subpage_extent_buffer(page);
 
     /*
      * We need to make sure nobody is changing page->private, as we rely on
      * page->private as the pointer to extent buffer.
      */
     spin_lock(&page->mapping->private_lock);
     if (!PagePrivate(page)) {
         spin_unlock(&page->mapping->private_lock);
         return 1;
     }
 
     eb = (struct extent_buffer *)page->private;
     BUG_ON(!eb);
 
     /*
      * This is a little awful but should be ok, we need to make sure that
      * the eb doesn't disappear out from under us while we're looking at
      * this page.
      */
     spin_lock(&eb->refs_lock);
     if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
         spin_unlock(&eb->refs_lock);
         spin_unlock(&page->mapping->private_lock);
         return 0;
     }
     spin_unlock(&page->mapping->private_lock);
 
     /*
      * If tree ref isn't set then we know the ref on this eb is a real ref,
      * so just return, this page will likely be freed soon anyway.
      */
     if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
         spin_unlock(&eb->refs_lock);
         return 0;
     }
 
     return release_extent_buffer(eb);
 }
 
 /*
  * btrfs_readahead_tree_block - attempt to readahead a child block
  * @fs_info:    the fs_info
  * @bytenr: bytenr to read
  * @owner_root: objectid of the root that owns this eb
  * @gen:    generation for the uptodate check, can be 0
  * @level:  level for the eb
  *
  * Attempt to readahead a tree block at @bytenr.  If @gen is 0 then we do a
  * normal uptodate check of the eb, without checking the generation.  If we have
  * to read the block we will not block on anything.
  */
 void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
                 u64 bytenr, u64 owner_root, u64 gen, int level)
 {
     struct extent_buffer *eb;
     int ret;
 
     eb = btrfs_find_create_tree_block(fs_info, bytenr, owner_root, level);
     if (IS_ERR(eb))
         return;
 
     if (btrfs_buffer_uptodate(eb, gen, 1)) {
         free_extent_buffer(eb);
         return;
     }
 
     ret = read_extent_buffer_pages(eb, WAIT_NONE, 0);
     if (ret < 0)
         free_extent_buffer_stale(eb);
     else
         free_extent_buffer(eb);
 }
 
 /*
  * btrfs_readahead_node_child - readahead a node's child block
  * @node:   parent node we're reading from
  * @slot:   slot in the parent node for the child we want to read
  *
  * A helper for btrfs_readahead_tree_block, we simply read the bytenr pointed at
  * the slot in the node provided.
  */
 void btrfs_readahead_node_child(struct extent_buffer *node, int slot)
 {
     btrfs_readahead_tree_block(node->fs_info,
                    btrfs_node_blockptr(node, slot),
                    btrfs_header_owner(node),
                    btrfs_node_ptr_generation(node, slot),
                    btrfs_header_level(node) - 1);
 }