Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 6041 insertions, 0 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
new file mode 100644
index 000000000..dabf15384
--- /dev/null
+++ b/fs/btrfs/extent_io.c
@@ -0,0 +1,6041 @@
+// 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/spinlock.h>
+#include <linux/blkdev.h>
+#include <linux/swap.h>
+#include <linux/writeback.h>
+#include <linux/pagevec.h>
+#include <linux/prefetch.h>
+#include <linux/cleancache.h>
+#include "extent_io.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"
+
+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(buffers);
+static LIST_HEAD(states);
+
+static DEFINE_SPINLOCK(leak_lock);
+
+static inline
+void btrfs_leak_debug_add(struct list_head *new, struct list_head *head)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&leak_lock, flags);
+	list_add(new, head);
+	spin_unlock_irqrestore(&leak_lock, flags);
+}
+
+static inline
+void btrfs_leak_debug_del(struct list_head *entry)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&leak_lock, flags);
+	list_del(entry);
+	spin_unlock_irqrestore(&leak_lock, flags);
+}
+
+static inline
+void btrfs_leak_debug_check(void)
+{
+	struct extent_state *state;
+	struct extent_buffer *eb;
+
+	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);
+	}
+
+	while (!list_empty(&buffers)) {
+		eb = list_entry(buffers.next, struct extent_buffer, leak_list);
+		pr_err("BTRFS: buffer leak start %llu len %lu refs %d bflags %lu\n",
+		       eb->start, eb->len, atomic_read(&eb->refs), eb->bflags);
+		list_del(&eb->leak_list);
+		kmem_cache_free(extent_buffer_cache, eb);
+	}
+}
+
+#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)
+{
+	if (tree->ops && tree->ops->check_extent_io_range)
+		tree->ops->check_extent_io_range(tree->private_data, caller,
+						 start, end);
+}
+#else
+#define btrfs_leak_debug_add(new, head)	do {} while (0)
+#define btrfs_leak_debug_del(entry)	do {} while (0)
+#define btrfs_leak_debug_check()	do {} while (0)
+#define btrfs_debug_check_extent_io_range(c, s, e)	do {} while (0)
+#endif
+
+#define BUFFER_LRU_MAX 64
+
+struct tree_entry {
+	u64 start;
+	u64 end;
+	struct rb_node rb_node;
+};
+
+struct extent_page_data {
+	struct bio *bio;
+	struct extent_io_tree *tree;
+	/* 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, unsigned 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 int __must_check submit_one_bio(struct bio *bio, int mirror_num,
+				       unsigned long bio_flags)
+{
+	blk_status_t ret = 0;
+	struct bio_vec *bvec = bio_last_bvec_all(bio);
+	struct page *page = bvec->bv_page;
+	struct extent_io_tree *tree = bio->bi_private;
+	u64 start;
+
+	start = page_offset(page) + bvec->bv_offset;
+
+	bio->bi_private = NULL;
+
+	if (tree->ops)
+		ret = tree->ops->submit_bio_hook(tree->private_data, bio,
+					   mirror_num, bio_flags, start);
+	else
+		btrfsic_submit_bio(bio);
+
+	return blk_status_to_errno(ret);
+}
+
+/* Cleanup unsubmitted bios */
+static void end_write_bio(struct extent_page_data *epd, int ret)
+{
+	if (epd->bio) {
+		epd->bio->bi_status = errno_to_blk_status(ret);
+		bio_endio(epd->bio);
+		epd->bio = NULL;
+	}
+}
+
+/*
+ * Submit bio from extent page data via submit_one_bio
+ *
+ * Return 0 if everything is OK.
+ * Return <0 for error.
+ */
+static int __must_check flush_write_bio(struct extent_page_data *epd)
+{
+	int ret = 0;
+
+	if (epd->bio) {
+		ret = submit_one_bio(epd->bio, 0, 0);
+		/*
+		 * Clean up of epd->bio is handled by its endio function.
+		 * And endio is either triggered by successful bio execution
+		 * or the error handler of submit bio hook.
+		 * So at this point, no matter what happened, we don't need
+		 * to clean up epd->bio.
+		 */
+		epd->bio = NULL;
+	}
+	return ret;
+}
+
+int __init extent_io_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;
+
+	extent_buffer_cache = kmem_cache_create("btrfs_extent_buffer",
+			sizeof(struct extent_buffer), 0,
+			SLAB_MEM_SPREAD, NULL);
+	if (!extent_buffer_cache)
+		goto free_state_cache;
+
+	if (bioset_init(&btrfs_bioset, BIO_POOL_SIZE,
+			offsetof(struct btrfs_io_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;
+
+free_state_cache:
+	kmem_cache_destroy(extent_state_cache);
+	extent_state_cache = NULL;
+	return -ENOMEM;
+}
+
+void __cold extent_io_exit(void)
+{
+	btrfs_leak_debug_check();
+
+	/*
+	 * Make sure all delayed rcu free are flushed before we
+	 * destroy caches.
+	 */
+	rcu_barrier();
+	kmem_cache_destroy(extent_state_cache);
+	kmem_cache_destroy(extent_buffer_cache);
+	bioset_exit(&btrfs_bioset);
+}
+
+void extent_io_tree_init(struct extent_io_tree *tree,
+			 void *private_data)
+{
+	tree->state = RB_ROOT;
+	tree->ops = NULL;
+	tree->dirty_bytes = 0;
+	spin_lock_init(&tree->lock);
+	tree->private_data = private_data;
+}
+
+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(&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(&state->leak_list);
+		trace_free_extent_state(state, _RET_IP_);
+		kmem_cache_free(extent_state_cache, state);
+	}
+}
+
+static struct rb_node *tree_insert(struct rb_root *root,
+				   struct rb_node *search_start,
+				   u64 offset,
+				   struct rb_node *node,
+				   struct rb_node ***p_in,
+				   struct rb_node **parent_in)
+{
+	struct rb_node **p;
+	struct rb_node *parent = NULL;
+	struct tree_entry *entry;
+
+	if (p_in && parent_in) {
+		p = *p_in;
+		parent = *parent_in;
+		goto do_insert;
+	}
+
+	p = search_start ? &search_start : &root->rb_node;
+	while (*p) {
+		parent = *p;
+		entry = rb_entry(parent, struct tree_entry, rb_node);
+
+		if (offset < entry->start)
+			p = &(*p)->rb_left;
+		else if (offset > entry->end)
+			p = &(*p)->rb_right;
+		else
+			return parent;
+	}
+
+do_insert:
+	rb_link_node(node, parent, p);
+	rb_insert_color(node, root);
+	return NULL;
+}
+
+static struct rb_node *__etree_search(struct extent_io_tree *tree, u64 offset,
+				      struct rb_node **prev_ret,
+				      struct rb_node **next_ret,
+				      struct rb_node ***p_ret,
+				      struct rb_node **parent_ret)
+{
+	struct rb_root *root = &tree->state;
+	struct rb_node **n = &root->rb_node;
+	struct rb_node *prev = NULL;
+	struct rb_node *orig_prev = NULL;
+	struct tree_entry *entry;
+	struct tree_entry *prev_entry = NULL;
+
+	while (*n) {
+		prev = *n;
+		entry = rb_entry(prev, struct tree_entry, rb_node);
+		prev_entry = entry;
+
+		if (offset < entry->start)
+			n = &(*n)->rb_left;
+		else if (offset > entry->end)
+			n = &(*n)->rb_right;
+		else
+			return *n;
+	}
+
+	if (p_ret)
+		*p_ret = n;
+	if (parent_ret)
+		*parent_ret = prev;
+
+	if (prev_ret) {
+		orig_prev = prev;
+		while (prev && offset > prev_entry->end) {
+			prev = rb_next(prev);
+			prev_entry = rb_entry(prev, struct tree_entry, rb_node);
+		}
+		*prev_ret = prev;
+		prev = orig_prev;
+	}
+
+	if (next_ret) {
+		prev_entry = rb_entry(prev, struct tree_entry, rb_node);
+		while (prev && offset < prev_entry->start) {
+			prev = rb_prev(prev);
+			prev_entry = rb_entry(prev, struct tree_entry, rb_node);
+		}
+		*next_ret = prev;
+	}
+	return NULL;
+}
+
+static inline struct rb_node *
+tree_search_for_insert(struct extent_io_tree *tree,
+		       u64 offset,
+		       struct rb_node ***p_ret,
+		       struct rb_node **parent_ret)
+{
+	struct rb_node *prev = NULL;
+	struct rb_node *ret;
+
+	ret = __etree_search(tree, offset, &prev, NULL, p_ret, parent_ret);
+	if (!ret)
+		return prev;
+	return ret;
+}
+
+static inline struct rb_node *tree_search(struct extent_io_tree *tree,
+					  u64 offset)
+{
+	return tree_search_for_insert(tree, offset, NULL, NULL);
+}
+
+static void merge_cb(struct extent_io_tree *tree, struct extent_state *new,
+		     struct extent_state *other)
+{
+	if (tree->ops && tree->ops->merge_extent_hook)
+		tree->ops->merge_extent_hook(tree->private_data, new, other);
+}
+
+/*
+ * 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_IOBITS | 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) {
+			merge_cb(tree, 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) {
+			merge_cb(tree, 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_cb(struct extent_io_tree *tree,
+			 struct extent_state *state, unsigned *bits)
+{
+	if (tree->ops && tree->ops->set_bit_hook)
+		tree->ops->set_bit_hook(tree->private_data, state, bits);
+}
+
+static void clear_state_cb(struct extent_io_tree *tree,
+			   struct extent_state *state, unsigned *bits)
+{
+	if (tree->ops && tree->ops->clear_bit_hook)
+		tree->ops->clear_bit_hook(tree->private_data, state, bits);
+}
+
+static void set_state_bits(struct extent_io_tree *tree,
+			   struct extent_state *state, unsigned *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, u64 start, u64 end,
+			struct rb_node ***p,
+			struct rb_node **parent,
+			unsigned *bits, struct extent_changeset *changeset)
+{
+	struct rb_node *node;
+
+	if (end < start)
+		WARN(1, KERN_ERR "BTRFS: end < start %llu %llu\n",
+		       end, start);
+	state->start = start;
+	state->end = end;
+
+	set_state_bits(tree, state, bits, changeset);
+
+	node = tree_insert(&tree->state, NULL, end, &state->rb_node, p, parent);
+	if (node) {
+		struct extent_state *found;
+		found = rb_entry(node, struct extent_state, rb_node);
+		pr_err("BTRFS: found node %llu %llu on insert of %llu %llu\n",
+		       found->start, found->end, start, end);
+		return -EEXIST;
+	}
+	merge_state(tree, state);
+	return 0;
+}
+
+static void split_cb(struct extent_io_tree *tree, struct extent_state *orig,
+		     u64 split)
+{
+	if (tree->ops && tree->ops->split_extent_hook)
+		tree->ops->split_extent_hook(tree->private_data, orig, split);
+}
+
+/*
+ * 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 *node;
+
+	split_cb(tree, orig, split);
+
+	prealloc->start = orig->start;
+	prealloc->end = split - 1;
+	prealloc->state = orig->state;
+	orig->start = split;
+
+	node = tree_insert(&tree->state, &orig->rb_node, prealloc->end,
+			   &prealloc->rb_node, NULL, NULL);
+	if (node) {
+		free_extent_state(prealloc);
+		return -EEXIST;
+	}
+	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 any one 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,
+					    unsigned *bits, int wake,
+					    struct extent_changeset *changeset)
+{
+	struct extent_state *next;
+	unsigned 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;
+	}
+	clear_state_cb(tree, 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)
+{
+	struct inode *inode = tree->private_data;
+
+	btrfs_panic(btrfs_sb(inode->i_sb), 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,
+			      unsigned 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);
+
+	if (bits & EXTENT_DELALLOC)
+		bits |= EXTENT_NORESERVE;
+
+	if (delete)
+		bits |= ~EXTENT_CTLBITS;
+	bits |= EXTENT_FIRST_DELALLOC;
+
+	if (bits & (EXTENT_IOBITS | 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,
+			    unsigned long 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,
+			   unsigned *bits, struct extent_changeset *changeset)
+{
+	unsigned bits_to_set = *bits & ~EXTENT_CTLBITS;
+	int ret;
+
+	set_state_cb(tree, 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_IOBITS | 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.
+ */
+
+static int __must_check
+__set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
+		 unsigned bits, unsigned 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);
+
+	bits |= EXTENT_FIRST_DELALLOC;
+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);
+		err = insert_state(tree, prealloc, start, end,
+				   &p, &parent, &bits, changeset);
+		if (err)
+			extent_io_tree_panic(tree, err);
+
+		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;
+		}
+
+		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.
+		 */
+		err = insert_state(tree, prealloc, start, this_end,
+				   NULL, NULL, &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;
+
+}
+
+int set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
+		   unsigned bits, u64 * failed_start,
+		   struct extent_state **cached_state, gfp_t mask)
+{
+	return __set_extent_bit(tree, start, end, bits, 0, failed_start,
+				cached_state, mask, NULL);
+}
+
+
+/**
+ * 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,
+		       unsigned bits, unsigned 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);
+
+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;
+		}
+		err = insert_state(tree, prealloc, start, end,
+				   &p, &parent, &bits, NULL);
+		if (err)
+			extent_io_tree_panic(tree, err);
+		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.
+		 */
+		err = insert_state(tree, prealloc, start, this_end,
+				   NULL, NULL, &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,
+			   unsigned 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 clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
+		     unsigned 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,
+		unsigned 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)
+{
+	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 */
+		__set_page_dirty_nobuffers(page);
+		account_page_redirty(page);
+		put_page(page);
+		index++;
+	}
+}
+
+/* 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, unsigned 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 'bits' set. zero is
+ * returned if we find something, and *start_ret and *end_ret are
+ * set to reflect the state struct that was found.
+ *
+ * If nothing was found, 1 is returned. If found something, return 0.
+ */
+int find_first_extent_bit(struct extent_io_tree *tree, u64 start,
+			  u64 *start_ret, u64 *end_ret, unsigned bits,
+			  struct extent_state **cached_state)
+{
+	struct extent_state *state;
+	struct rb_node *n;
+	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)) {
+			n = rb_next(&state->rb_node);
+			while (n) {
+				state = rb_entry(n, struct extent_state,
+						 rb_node);
+				if (state->state & bits)
+					goto got_it;
+				n = rb_next(n);
+			}
+			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 range of bytes in the file marked as delalloc, not
+ * more than 'max_bytes'.  start and end are used to return the range,
+ *
+ * 1 is returned if we find something, 0 if nothing was in the tree
+ */
+static noinline u64 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;
+	u64 found = 0;
+	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) {
+		if (!found)
+			*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++;
+		*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;
+}
+
+static int __process_pages_contig(struct address_space *mapping,
+				  struct page *locked_page,
+				  pgoff_t start_index, pgoff_t end_index,
+				  unsigned long page_ops, pgoff_t *index_ret);
+
+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, index, end_index,
+			       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 index_ret = index;
+	unsigned long end_index = delalloc_end >> PAGE_SHIFT;
+	int ret;
+
+	ASSERT(locked_page);
+	if (index == locked_page->index && index == end_index)
+		return 0;
+
+	ret = __process_pages_contig(inode->i_mapping, locked_page, index,
+				     end_index, PAGE_LOCK, &index_ret);
+	if (ret == -EAGAIN)
+		__unlock_for_delalloc(inode, locked_page, delalloc_start,
+				      (u64)index_ret << PAGE_SHIFT);
+	return ret;
+}
+
+/*
+ * 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,
+ *
+ * 1 is returned if we find something, 0 if nothing was in the tree
+ */
+STATIC u64 find_lock_delalloc_range(struct inode *inode,
+				    struct extent_io_tree *tree,
+				    struct page *locked_page, u64 *start,
+				    u64 *end, u64 max_bytes)
+{
+	u64 delalloc_start;
+	u64 delalloc_end;
+	u64 found;
+	struct extent_state *cached_state = NULL;
+	int ret;
+	int loops = 0;
+
+again:
+	/* step one, find a bunch of delalloc bytes starting at start */
+	delalloc_start = *start;
+	delalloc_end = 0;
+	found = find_delalloc_range(tree, &delalloc_start, &delalloc_end,
+				    max_bytes, &cached_state);
+	if (!found || delalloc_end <= *start) {
+		*start = delalloc_start;
+		*end = delalloc_end;
+		free_extent_state(cached_state);
+		return 0;
+	}
+
+	/*
+	 * 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);
+	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 = 0;
+			goto out_failed;
+		}
+	}
+	BUG_ON(ret); /* Only valid values are 0 and -EAGAIN */
+
+	/* 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;
+}
+
+static int __process_pages_contig(struct address_space *mapping,
+				  struct page *locked_page,
+				  pgoff_t start_index, pgoff_t end_index,
+				  unsigned long page_ops, pgoff_t *index_ret)
+{
+	unsigned long nr_pages = end_index - start_index + 1;
+	unsigned long pages_locked = 0;
+	pgoff_t index = start_index;
+	struct page *pages[16];
+	unsigned ret;
+	int err = 0;
+	int i;
+
+	if (page_ops & PAGE_LOCK) {
+		ASSERT(page_ops == PAGE_LOCK);
+		ASSERT(index_ret && *index_ret == start_index);
+	}
+
+	if ((page_ops & PAGE_SET_ERROR) && nr_pages > 0)
+		mapping_set_error(mapping, -EIO);
+
+	while (nr_pages > 0) {
+		ret = find_get_pages_contig(mapping, index,
+				     min_t(unsigned long,
+				     nr_pages, ARRAY_SIZE(pages)), pages);
+		if (ret == 0) {
+			/*
+			 * Only if we're going to lock these pages,
+			 * can we find nothing at @index.
+			 */
+			ASSERT(page_ops & PAGE_LOCK);
+			err = -EAGAIN;
+			goto out;
+		}
+
+		for (i = 0; i < ret; i++) {
+			if (page_ops & PAGE_SET_PRIVATE2)
+				SetPagePrivate2(pages[i]);
+
+			if (pages[i] == locked_page) {
+				put_page(pages[i]);
+				pages_locked++;
+				continue;
+			}
+			if (page_ops & PAGE_CLEAR_DIRTY)
+				clear_page_dirty_for_io(pages[i]);
+			if (page_ops & PAGE_SET_WRITEBACK)
+				set_page_writeback(pages[i]);
+			if (page_ops & PAGE_SET_ERROR)
+				SetPageError(pages[i]);
+			if (page_ops & PAGE_END_WRITEBACK)
+				end_page_writeback(pages[i]);
+			if (page_ops & PAGE_UNLOCK)
+				unlock_page(pages[i]);
+			if (page_ops & PAGE_LOCK) {
+				lock_page(pages[i]);
+				if (!PageDirty(pages[i]) ||
+				    pages[i]->mapping != mapping) {
+					unlock_page(pages[i]);
+					for (; i < ret; i++)
+						put_page(pages[i]);
+					err = -EAGAIN;
+					goto out;
+				}
+			}
+			put_page(pages[i]);
+			pages_locked++;
+		}
+		nr_pages -= ret;
+		index += ret;
+		cond_resched();
+	}
+out:
+	if (err && index_ret)
+		*index_ret = start_index + pages_locked - 1;
+	return err;
+}
+
+void extent_clear_unlock_delalloc(struct inode *inode, u64 start, u64 end,
+				 u64 delalloc_end, struct page *locked_page,
+				 unsigned clear_bits,
+				 unsigned long page_ops)
+{
+	clear_extent_bit(&BTRFS_I(inode)->io_tree, start, end, clear_bits, 1, 0,
+			 NULL);
+
+	__process_pages_contig(inode->i_mapping, locked_page,
+			       start >> PAGE_SHIFT, end >> PAGE_SHIFT,
+			       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,
+		     unsigned 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.
+ */
+static noinline 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;
+}
+
+static noinline int get_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;
+	}
+	*failrec = state->failrec;
+out:
+	spin_unlock(&tree->lock);
+	return ret;
+}
+
+/*
+ * 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,
+		   unsigned 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;
+}
+
+/*
+ * helper function to set a given page up to date if all the
+ * extents in the tree for that page are up to date
+ */
+static void check_page_uptodate(struct extent_io_tree *tree, struct page *page)
+{
+	u64 start = page_offset(page);
+	u64 end = start + PAGE_SIZE - 1;
+	if (test_range_bit(tree, start, end, EXTENT_UPTODATE, 1, NULL))
+		SetPageUptodate(page);
+}
+
+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.
+ */
+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 bio *bio;
+	struct btrfs_device *dev;
+	u64 map_length = 0;
+	u64 sector;
+	struct btrfs_bio *bbio = NULL;
+	int ret;
+
+	ASSERT(!(fs_info->sb->s_flags & SB_RDONLY));
+	BUG_ON(!mirror_num);
+
+	bio = btrfs_io_bio_alloc(1);
+	bio->bi_iter.bi_size = 0;
+	map_length = length;
+
+	/*
+	 * Avoid races with device replace and make sure our bbio 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, &bbio, 0);
+		if (ret) {
+			btrfs_bio_counter_dec(fs_info);
+			bio_put(bio);
+			return -EIO;
+		}
+		ASSERT(bbio->mirror_num == 1);
+	} else {
+		ret = btrfs_map_block(fs_info, BTRFS_MAP_WRITE, logical,
+				      &map_length, &bbio, mirror_num);
+		if (ret) {
+			btrfs_bio_counter_dec(fs_info);
+			bio_put(bio);
+			return -EIO;
+		}
+		BUG_ON(mirror_num != bbio->mirror_num);
+	}
+
+	sector = bbio->stripes[bbio->mirror_num - 1].physical >> 9;
+	bio->bi_iter.bi_sector = sector;
+	dev = bbio->stripes[bbio->mirror_num - 1].dev;
+	btrfs_put_bbio(bbio);
+	if (!dev || !dev->bdev ||
+	    !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state)) {
+		btrfs_bio_counter_dec(fs_info);
+		bio_put(bio);
+		return -EIO;
+	}
+	bio_set_dev(bio, dev->bdev);
+	bio->bi_opf = REQ_OP_WRITE | REQ_SYNC;
+	bio_add_page(bio, page, length, pg_offset);
+
+	if (btrfsic_submit_bio_wait(bio)) {
+		/* try to remap that extent elsewhere? */
+		btrfs_bio_counter_dec(fs_info);
+		bio_put(bio);
+		btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_WRITE_ERRS);
+		return -EIO;
+	}
+
+	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);
+	btrfs_bio_counter_dec(fs_info);
+	bio_put(bio);
+	return 0;
+}
+
+int repair_eb_io_failure(struct btrfs_fs_info *fs_info,
+			 struct extent_buffer *eb, int mirror_num)
+{
+	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;
+}
+
+/*
+ * 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 num_copies;
+	int ret;
+
+	private = 0;
+	ret = count_range_bits(failure_tree, &private, (u64)-1, 1,
+			       EXTENT_DIRTY, 0);
+	if (!ret)
+		return 0;
+
+	ret = get_state_failrec(failure_tree, start, &failrec);
+	if (ret)
+		return 0;
+
+	BUG_ON(!failrec->this_mirror);
+
+	if (failrec->in_validation) {
+		/* there was no real error, just free the record */
+		btrfs_debug(fs_info,
+			"clean_io_failure: freeing dummy error at %llu",
+			failrec->start);
+		goto out;
+	}
+	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) {
+		num_copies = btrfs_num_copies(fs_info, failrec->logical,
+					      failrec->len);
+		if (num_copies > 1)  {
+			repair_io_failure(fs_info, ino, start, failrec->len,
+					  failrec->logical, page, pg_offset,
+					  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);
+}
+
+int btrfs_get_io_failure_record(struct inode *inode, u64 start, u64 end,
+		struct io_failure_record **failrec_ret)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	struct io_failure_record *failrec;
+	struct extent_map *em;
+	struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
+	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
+	struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
+	int ret;
+	u64 logical;
+
+	ret = get_state_failrec(failure_tree, start, &failrec);
+	if (ret) {
+		failrec = kzalloc(sizeof(*failrec), GFP_NOFS);
+		if (!failrec)
+			return -ENOMEM;
+
+		failrec->start = start;
+		failrec->len = end - start + 1;
+		failrec->this_mirror = 0;
+		failrec->bio_flags = 0;
+		failrec->in_validation = 0;
+
+		read_lock(&em_tree->lock);
+		em = lookup_extent_mapping(em_tree, start, failrec->len);
+		if (!em) {
+			read_unlock(&em_tree->lock);
+			kfree(failrec);
+			return -EIO;
+		}
+
+		if (em->start > start || em->start + em->len <= start) {
+			free_extent_map(em);
+			em = NULL;
+		}
+		read_unlock(&em_tree->lock);
+		if (!em) {
+			kfree(failrec);
+			return -EIO;
+		}
+
+		logical = start - em->start;
+		logical = em->block_start + logical;
+		if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) {
+			logical = em->block_start;
+			failrec->bio_flags = EXTENT_BIO_COMPRESSED;
+			extent_set_compress_type(&failrec->bio_flags,
+						 em->compress_type);
+		}
+
+		btrfs_debug(fs_info,
+			"Get IO Failure Record: (new) logical=%llu, start=%llu, len=%llu",
+			logical, start, failrec->len);
+
+		failrec->logical = logical;
+		free_extent_map(em);
+
+		/* set the bits in the private failure tree */
+		ret = set_extent_bits(failure_tree, start, end,
+					EXTENT_LOCKED | EXTENT_DIRTY);
+		if (ret >= 0)
+			ret = set_state_failrec(failure_tree, start, failrec);
+		/* set the bits in the inode's tree */
+		if (ret >= 0)
+			ret = set_extent_bits(tree, start, end, EXTENT_DAMAGED);
+		if (ret < 0) {
+			kfree(failrec);
+			return ret;
+		}
+	} else {
+		btrfs_debug(fs_info,
+			"Get IO Failure Record: (found) logical=%llu, start=%llu, len=%llu, validation=%d",
+			failrec->logical, failrec->start, failrec->len,
+			failrec->in_validation);
+		/*
+		 * 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.
+		 */
+	}
+
+	*failrec_ret = failrec;
+
+	return 0;
+}
+
+bool btrfs_check_repairable(struct inode *inode, unsigned failed_bio_pages,
+			   struct io_failure_record *failrec, int failed_mirror)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	int num_copies;
+
+	num_copies = btrfs_num_copies(fs_info, failrec->logical, failrec->len);
+	if (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,
+			"Check Repairable: cannot repair, num_copies=%d, next_mirror %d, failed_mirror %d",
+			num_copies, failrec->this_mirror, failed_mirror);
+		return false;
+	}
+
+	/*
+	 * there are two premises:
+	 *	a) deliver good data to the caller
+	 *	b) correct the bad sectors on disk
+	 */
+	if (failed_bio_pages > 1) {
+		/*
+		 * to fulfill b), we need to know the exact failing sectors, as
+		 * we don't want to rewrite any more than the failed ones. thus,
+		 * we need separate read requests for the failed bio
+		 *
+		 * if the following BUG_ON triggers, our validation request got
+		 * merged. we need separate requests for our algorithm to work.
+		 */
+		BUG_ON(failrec->in_validation);
+		failrec->in_validation = 1;
+		failrec->this_mirror = failed_mirror;
+	} else {
+		/*
+		 * we're ready to fulfill a) and b) alongside. 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.
+		 */
+		if (failrec->in_validation) {
+			BUG_ON(failrec->this_mirror != failed_mirror);
+			failrec->in_validation = 0;
+			failrec->this_mirror = 0;
+		}
+		failrec->failed_mirror = failed_mirror;
+		failrec->this_mirror++;
+		if (failrec->this_mirror == failed_mirror)
+			failrec->this_mirror++;
+	}
+
+	if (failrec->this_mirror > num_copies) {
+		btrfs_debug(fs_info,
+			"Check Repairable: (fail) num_copies=%d, next_mirror %d, failed_mirror %d",
+			num_copies, failrec->this_mirror, failed_mirror);
+		return false;
+	}
+
+	return true;
+}
+
+
+struct bio *btrfs_create_repair_bio(struct inode *inode, struct bio *failed_bio,
+				    struct io_failure_record *failrec,
+				    struct page *page, int pg_offset, int icsum,
+				    bio_end_io_t *endio_func, void *data)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	struct bio *bio;
+	struct btrfs_io_bio *btrfs_failed_bio;
+	struct btrfs_io_bio *btrfs_bio;
+
+	bio = btrfs_io_bio_alloc(1);
+	bio->bi_end_io = endio_func;
+	bio->bi_iter.bi_sector = failrec->logical >> 9;
+	bio_set_dev(bio, fs_info->fs_devices->latest_bdev);
+	bio->bi_iter.bi_size = 0;
+	bio->bi_private = data;
+
+	btrfs_failed_bio = btrfs_io_bio(failed_bio);
+	if (btrfs_failed_bio->csum) {
+		u16 csum_size = btrfs_super_csum_size(fs_info->super_copy);
+
+		btrfs_bio = btrfs_io_bio(bio);
+		btrfs_bio->csum = btrfs_bio->csum_inline;
+		icsum *= csum_size;
+		memcpy(btrfs_bio->csum, btrfs_failed_bio->csum + icsum,
+		       csum_size);
+	}
+
+	bio_add_page(bio, page, failrec->len, pg_offset);
+
+	return bio;
+}
+
+/*
+ * this is a generic handler for readpage errors (default
+ * readpage_io_failed_hook). if other copies exist, read those and write back
+ * good data to the failed position. does not investigate in remapping the
+ * failed extent elsewhere, hoping the device will be smart enough to do this as
+ * needed
+ */
+
+static int bio_readpage_error(struct bio *failed_bio, u64 phy_offset,
+			      struct page *page, u64 start, u64 end,
+			      int failed_mirror)
+{
+	struct io_failure_record *failrec;
+	struct inode *inode = page->mapping->host;
+	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
+	struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
+	struct bio *bio;
+	int read_mode = 0;
+	blk_status_t status;
+	int ret;
+	unsigned failed_bio_pages = bio_pages_all(failed_bio);
+
+	BUG_ON(bio_op(failed_bio) == REQ_OP_WRITE);
+
+	ret = btrfs_get_io_failure_record(inode, start, end, &failrec);
+	if (ret)
+		return ret;
+
+	if (!btrfs_check_repairable(inode, failed_bio_pages, failrec,
+				    failed_mirror)) {
+		free_io_failure(failure_tree, tree, failrec);
+		return -EIO;
+	}
+
+	if (failed_bio_pages > 1)
+		read_mode |= REQ_FAILFAST_DEV;
+
+	phy_offset >>= inode->i_sb->s_blocksize_bits;
+	bio = btrfs_create_repair_bio(inode, failed_bio, failrec, page,
+				      start - page_offset(page),
+				      (int)phy_offset, failed_bio->bi_end_io,
+				      NULL);
+	bio->bi_opf = REQ_OP_READ | read_mode;
+
+	btrfs_debug(btrfs_sb(inode->i_sb),
+		"Repair Read Error: submitting new read[%#x] to this_mirror=%d, in_validation=%d",
+		read_mode, failrec->this_mirror, failrec->in_validation);
+
+	status = tree->ops->submit_bio_hook(tree->private_data, bio, failrec->this_mirror,
+					 failrec->bio_flags, 0);
+	if (status) {
+		free_io_failure(failure_tree, tree, failrec);
+		bio_put(bio);
+		ret = blk_status_to_errno(status);
+	}
+
+	return ret;
+}
+
+/* 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)
+{
+	int uptodate = (err == 0);
+	struct extent_io_tree *tree;
+	int ret = 0;
+
+	tree = &BTRFS_I(page->mapping->host)->io_tree;
+
+	if (tree->ops && tree->ops->writepage_end_io_hook)
+		tree->ops->writepage_end_io_hook(page, start, end, NULL,
+				uptodate);
+
+	if (!uptodate) {
+		ClearPageUptodate(page);
+		SetPageError(page);
+		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;
+	int i;
+
+	ASSERT(!bio_flagged(bio, BIO_CLONED));
+	bio_for_each_segment_all(bvec, bio, i) {
+		struct page *page = bvec->bv_page;
+		struct inode *inode = page->mapping->host;
+		struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+
+		/* We always issue full-page 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 nonzero offsets, and an error
+		 * if they don't add up to a full page.  */
+		if (bvec->bv_offset || bvec->bv_len != PAGE_SIZE) {
+			if (bvec->bv_offset + bvec->bv_len != PAGE_SIZE)
+				btrfs_err(fs_info,
+				   "partial page write in btrfs with offset %u and length %u",
+					bvec->bv_offset, bvec->bv_len);
+			else
+				btrfs_info(fs_info,
+				   "incomplete page write in btrfs with offset %u and length %u",
+					bvec->bv_offset, bvec->bv_len);
+		}
+
+		start = page_offset(page);
+		end = start + bvec->bv_offset + bvec->bv_len - 1;
+
+		end_extent_writepage(page, error, start, end);
+		end_page_writeback(page);
+	}
+
+	bio_put(bio);
+}
+
+static void
+endio_readpage_release_extent(struct extent_io_tree *tree, u64 start, u64 len,
+			      int uptodate)
+{
+	struct extent_state *cached = NULL;
+	u64 end = start + len - 1;
+
+	if (uptodate && tree->track_uptodate)
+		set_extent_uptodate(tree, start, end, &cached, GFP_ATOMIC);
+	unlock_extent_cached_atomic(tree, start, end, &cached);
+}
+
+/*
+ * 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;
+	int uptodate = !bio->bi_status;
+	struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
+	struct extent_io_tree *tree, *failure_tree;
+	u64 offset = 0;
+	u64 start;
+	u64 end;
+	u64 len;
+	u64 extent_start = 0;
+	u64 extent_len = 0;
+	int mirror;
+	int ret;
+	int i;
+
+	ASSERT(!bio_flagged(bio, BIO_CLONED));
+	bio_for_each_segment_all(bvec, bio, i) {
+		struct page *page = bvec->bv_page;
+		struct inode *inode = page->mapping->host;
+		struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+
+		btrfs_debug(fs_info,
+			"end_bio_extent_readpage: bi_sector=%llu, err=%d, mirror=%u",
+			(u64)bio->bi_iter.bi_sector, bio->bi_status,
+			io_bio->mirror_num);
+		tree = &BTRFS_I(inode)->io_tree;
+		failure_tree = &BTRFS_I(inode)->io_failure_tree;
+
+		/* We always issue full-page 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 nonzero offsets, and an error
+		 * if they don't add up to a full page.  */
+		if (bvec->bv_offset || bvec->bv_len != PAGE_SIZE) {
+			if (bvec->bv_offset + bvec->bv_len != PAGE_SIZE)
+				btrfs_err(fs_info,
+					"partial page read in btrfs with offset %u and length %u",
+					bvec->bv_offset, bvec->bv_len);
+			else
+				btrfs_info(fs_info,
+					"incomplete page read in btrfs with offset %u and length %u",
+					bvec->bv_offset, bvec->bv_len);
+		}
+
+		start = page_offset(page);
+		end = start + bvec->bv_offset + bvec->bv_len - 1;
+		len = bvec->bv_len;
+
+		mirror = io_bio->mirror_num;
+		if (likely(uptodate && tree->ops)) {
+			ret = tree->ops->readpage_end_io_hook(io_bio, offset,
+							      page, start, end,
+							      mirror);
+			if (ret)
+				uptodate = 0;
+			else
+				clean_io_failure(BTRFS_I(inode)->root->fs_info,
+						 failure_tree, tree, start,
+						 page,
+						 btrfs_ino(BTRFS_I(inode)), 0);
+		}
+
+		if (likely(uptodate))
+			goto readpage_ok;
+
+		if (tree->ops) {
+			ret = tree->ops->readpage_io_failed_hook(page, mirror);
+			if (ret == -EAGAIN) {
+				/*
+				 * Data inode's readpage_io_failed_hook() always
+				 * returns -EAGAIN.
+				 *
+				 * The generic bio_readpage_error handles errors
+				 * the following way: If possible, new read
+				 * requests are created and submitted and will
+				 * end up in end_bio_extent_readpage as well (if
+				 * we're lucky, not in the !uptodate case). In
+				 * that case it returns 0 and we just go on with
+				 * the next page in our bio. If it can't handle
+				 * the error it will return -EIO and we remain
+				 * responsible for that page.
+				 */
+				ret = bio_readpage_error(bio, offset, page,
+							 start, end, mirror);
+				if (ret == 0) {
+					uptodate = !bio->bi_status;
+					offset += len;
+					continue;
+				}
+			}
+
+			/*
+			 * metadata's readpage_io_failed_hook() always returns
+			 * -EIO and fixes nothing.  -EIO is also returned if
+			 * data inode error could not be fixed.
+			 */
+			ASSERT(ret == -EIO);
+		}
+readpage_ok:
+		if (likely(uptodate)) {
+			loff_t i_size = i_size_read(inode);
+			pgoff_t end_index = i_size >> PAGE_SHIFT;
+			unsigned off;
+
+			/* Zero out the end if this page straddles i_size */
+			off = i_size & (PAGE_SIZE-1);
+			if (page->index == end_index && off)
+				zero_user_segment(page, off, PAGE_SIZE);
+			SetPageUptodate(page);
+		} else {
+			ClearPageUptodate(page);
+			SetPageError(page);
+		}
+		unlock_page(page);
+		offset += len;
+
+		if (unlikely(!uptodate)) {
+			if (extent_len) {
+				endio_readpage_release_extent(tree,
+							      extent_start,
+							      extent_len, 1);
+				extent_start = 0;
+				extent_len = 0;
+			}
+			endio_readpage_release_extent(tree, start,
+						      end - start + 1, 0);
+		} else if (!extent_len) {
+			extent_start = start;
+			extent_len = end + 1 - start;
+		} else if (extent_start + extent_len == start) {
+			extent_len += end + 1 - start;
+		} else {
+			endio_readpage_release_extent(tree, extent_start,
+						      extent_len, uptodate);
+			extent_start = start;
+			extent_len = end + 1 - start;
+		}
+	}
+
+	if (extent_len)
+		endio_readpage_release_extent(tree, extent_start, extent_len,
+					      uptodate);
+	if (io_bio->end_io)
+		io_bio->end_io(io_bio, blk_status_to_errno(bio->bi_status));
+	bio_put(bio);
+}
+
+/*
+ * 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_io_bio_init(struct btrfs_io_bio *btrfs_bio)
+{
+	memset(btrfs_bio, 0, offsetof(struct btrfs_io_bio, bio));
+}
+
+/*
+ * The following helpers allocate a bio. As it's backed by a bioset, it'll
+ * never fail.  We're returning a bio right now but you can call btrfs_io_bio
+ * for the appropriate container_of magic
+ */
+struct bio *btrfs_bio_alloc(struct block_device *bdev, u64 first_byte)
+{
+	struct bio *bio;
+
+	bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, &btrfs_bioset);
+	bio_set_dev(bio, bdev);
+	bio->bi_iter.bi_sector = first_byte >> 9;
+	btrfs_io_bio_init(btrfs_io_bio(bio));
+	return bio;
+}
+
+struct bio *btrfs_bio_clone(struct bio *bio)
+{
+	struct btrfs_io_bio *btrfs_bio;
+	struct bio *new;
+
+	/* Bio allocation backed by a bioset does not fail */
+	new = bio_clone_fast(bio, GFP_NOFS, &btrfs_bioset);
+	btrfs_bio = btrfs_io_bio(new);
+	btrfs_io_bio_init(btrfs_bio);
+	btrfs_bio->iter = bio->bi_iter;
+	return new;
+}
+
+struct bio *btrfs_io_bio_alloc(unsigned int nr_iovecs)
+{
+	struct bio *bio;
+
+	/* Bio allocation backed by a bioset does not fail */
+	bio = bio_alloc_bioset(GFP_NOFS, nr_iovecs, &btrfs_bioset);
+	btrfs_io_bio_init(btrfs_io_bio(bio));
+	return bio;
+}
+
+struct bio *btrfs_bio_clone_partial(struct bio *orig, int offset, int size)
+{
+	struct bio *bio;
+	struct btrfs_io_bio *btrfs_bio;
+
+	/* this will never fail when it's backed by a bioset */
+	bio = bio_clone_fast(orig, GFP_NOFS, &btrfs_bioset);
+	ASSERT(bio);
+
+	btrfs_bio = btrfs_io_bio(bio);
+	btrfs_io_bio_init(btrfs_bio);
+
+	bio_trim(bio, offset >> 9, size >> 9);
+	btrfs_bio->iter = bio->bi_iter;
+	return bio;
+}
+
+/*
+ * @opf:	bio REQ_OP_* and REQ_* flags as one value
+ * @tree:	tree so we can call our merge_bio hook
+ * @wbc:	optional writeback control for io accounting
+ * @page:	page to add to the bio
+ * @pg_offset:	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
+ * @offset:	starting offset in the page
+ * @bdev:	attach newly created bios to this bdev
+ * @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
+ * @bio_flags:	flags of the current bio to see if we can merge them
+ */
+static int submit_extent_page(unsigned int opf, struct extent_io_tree *tree,
+			      struct writeback_control *wbc,
+			      struct page *page, u64 offset,
+			      size_t size, unsigned long pg_offset,
+			      struct block_device *bdev,
+			      struct bio **bio_ret,
+			      bio_end_io_t end_io_func,
+			      int mirror_num,
+			      unsigned long prev_bio_flags,
+			      unsigned long bio_flags,
+			      bool force_bio_submit)
+{
+	int ret = 0;
+	struct bio *bio;
+	size_t page_size = min_t(size_t, size, PAGE_SIZE);
+	sector_t sector = offset >> 9;
+
+	ASSERT(bio_ret);
+
+	if (*bio_ret) {
+		bool contig;
+		bool can_merge = true;
+
+		bio = *bio_ret;
+		if (prev_bio_flags & EXTENT_BIO_COMPRESSED)
+			contig = bio->bi_iter.bi_sector == sector;
+		else
+			contig = bio_end_sector(bio) == sector;
+
+		if (tree->ops && btrfs_merge_bio_hook(page, offset, page_size,
+						      bio, bio_flags))
+			can_merge = false;
+
+		if (prev_bio_flags != bio_flags || !contig || !can_merge ||
+		    force_bio_submit ||
+		    bio_add_page(bio, page, page_size, pg_offset) < page_size) {
+			ret = submit_one_bio(bio, mirror_num, prev_bio_flags);
+			if (ret < 0) {
+				*bio_ret = NULL;
+				return ret;
+			}
+			bio = NULL;
+		} else {
+			if (wbc)
+				wbc_account_io(wbc, page, page_size);
+			return 0;
+		}
+	}
+
+	bio = btrfs_bio_alloc(bdev, offset);
+	bio_add_page(bio, page, page_size, pg_offset);
+	bio->bi_end_io = end_io_func;
+	bio->bi_private = tree;
+	bio->bi_write_hint = page->mapping->host->i_write_hint;
+	bio->bi_opf = opf;
+	if (wbc) {
+		wbc_init_bio(wbc, bio);
+		wbc_account_io(wbc, page, page_size);
+	}
+
+	*bio_ret = bio;
+
+	return ret;
+}
+
+static void attach_extent_buffer_page(struct extent_buffer *eb,
+				      struct page *page)
+{
+	if (!PagePrivate(page)) {
+		SetPagePrivate(page);
+		get_page(page);
+		set_page_private(page, (unsigned long)eb);
+	} else {
+		WARN_ON(page->private != (unsigned long)eb);
+	}
+}
+
+void set_page_extent_mapped(struct page *page)
+{
+	if (!PagePrivate(page)) {
+		SetPagePrivate(page);
+		get_page(page);
+		set_page_private(page, EXTENT_PAGE_PRIVATE);
+	}
+}
+
+static struct extent_map *
+__get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
+		 u64 start, u64 len, get_extent_t *get_extent,
+		 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 = get_extent(BTRFS_I(inode), page, pg_offset, start, len, 0);
+	if (em_cached && !IS_ERR_OR_NULL(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 __do_readpage(struct extent_io_tree *tree,
+			 struct page *page,
+			 get_extent_t *get_extent,
+			 struct extent_map **em_cached,
+			 struct bio **bio, int mirror_num,
+			 unsigned long *bio_flags, unsigned int read_flags,
+			 u64 *prev_em_start)
+{
+	struct inode *inode = page->mapping->host;
+	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;
+	struct block_device *bdev;
+	int ret = 0;
+	int nr = 0;
+	size_t pg_offset = 0;
+	size_t iosize;
+	size_t disk_io_size;
+	size_t blocksize = inode->i_sb->s_blocksize;
+	unsigned long this_bio_flag = 0;
+
+	set_page_extent_mapped(page);
+
+	if (!PageUptodate(page)) {
+		if (cleancache_get_page(page) == 0) {
+			BUG_ON(blocksize != PAGE_SIZE);
+			unlock_extent(tree, start, end);
+			goto out;
+		}
+	}
+
+	if (page->index == last_byte >> PAGE_SHIFT) {
+		char *userpage;
+		size_t zero_offset = last_byte & (PAGE_SIZE - 1);
+
+		if (zero_offset) {
+			iosize = PAGE_SIZE - zero_offset;
+			userpage = kmap_atomic(page);
+			memset(userpage + zero_offset, 0, iosize);
+			flush_dcache_page(page);
+			kunmap_atomic(userpage);
+		}
+	}
+	while (cur <= end) {
+		bool force_bio_submit = false;
+		u64 offset;
+
+		if (cur >= last_byte) {
+			char *userpage;
+			struct extent_state *cached = NULL;
+
+			iosize = PAGE_SIZE - pg_offset;
+			userpage = kmap_atomic(page);
+			memset(userpage + pg_offset, 0, iosize);
+			flush_dcache_page(page);
+			kunmap_atomic(userpage);
+			set_extent_uptodate(tree, cur, cur + iosize - 1,
+					    &cached, GFP_NOFS);
+			unlock_extent_cached(tree, cur,
+					     cur + iosize - 1, &cached);
+			break;
+		}
+		em = __get_extent_map(inode, page, pg_offset, cur,
+				      end - cur + 1, get_extent, em_cached);
+		if (IS_ERR_OR_NULL(em)) {
+			SetPageError(page);
+			unlock_extent(tree, cur, end);
+			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 |= EXTENT_BIO_COMPRESSED;
+			extent_set_compress_type(&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 & EXTENT_BIO_COMPRESSED) {
+			disk_io_size = em->block_len;
+			offset = em->block_start;
+		} else {
+			offset = em->block_start + extent_offset;
+			disk_io_size = iosize;
+		}
+		bdev = em->bdev;
+		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
+		 * 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) {
+			char *userpage;
+			struct extent_state *cached = NULL;
+
+			userpage = kmap_atomic(page);
+			memset(userpage + pg_offset, 0, iosize);
+			flush_dcache_page(page);
+			kunmap_atomic(userpage);
+
+			set_extent_uptodate(tree, cur, cur + iosize - 1,
+					    &cached, GFP_NOFS);
+			unlock_extent_cached(tree, cur,
+					     cur + iosize - 1, &cached);
+			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)) {
+			check_page_uptodate(tree, page);
+			unlock_extent(tree, cur, cur + iosize - 1);
+			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) {
+			SetPageError(page);
+			unlock_extent(tree, cur, cur + iosize - 1);
+			cur = cur + iosize;
+			pg_offset += iosize;
+			continue;
+		}
+
+		ret = submit_extent_page(REQ_OP_READ | read_flags, tree, NULL,
+					 page, offset, disk_io_size,
+					 pg_offset, bdev, bio,
+					 end_bio_extent_readpage, mirror_num,
+					 *bio_flags,
+					 this_bio_flag,
+					 force_bio_submit);
+		if (!ret) {
+			nr++;
+			*bio_flags = this_bio_flag;
+		} else {
+			SetPageError(page);
+			unlock_extent(tree, cur, cur + iosize - 1);
+			goto out;
+		}
+		cur = cur + iosize;
+		pg_offset += iosize;
+	}
+out:
+	if (!nr) {
+		if (!PageError(page))
+			SetPageUptodate(page);
+		unlock_page(page);
+	}
+	return ret;
+}
+
+static inline void __do_contiguous_readpages(struct extent_io_tree *tree,
+					     struct page *pages[], int nr_pages,
+					     u64 start, u64 end,
+					     struct extent_map **em_cached,
+					     struct bio **bio,
+					     unsigned long *bio_flags,
+					     u64 *prev_em_start)
+{
+	struct inode *inode;
+	struct btrfs_ordered_extent *ordered;
+	int index;
+
+	inode = pages[0]->mapping->host;
+	while (1) {
+		lock_extent(tree, start, end);
+		ordered = btrfs_lookup_ordered_range(BTRFS_I(inode), start,
+						     end - start + 1);
+		if (!ordered)
+			break;
+		unlock_extent(tree, start, end);
+		btrfs_start_ordered_extent(inode, ordered, 1);
+		btrfs_put_ordered_extent(ordered);
+	}
+
+	for (index = 0; index < nr_pages; index++) {
+		__do_readpage(tree, pages[index], btrfs_get_extent, em_cached,
+				bio, 0, bio_flags, REQ_RAHEAD, prev_em_start);
+		put_page(pages[index]);
+	}
+}
+
+static void __extent_readpages(struct extent_io_tree *tree,
+			       struct page *pages[],
+			       int nr_pages,
+			       struct extent_map **em_cached,
+			       struct bio **bio, unsigned long *bio_flags,
+			       u64 *prev_em_start)
+{
+	u64 start = 0;
+	u64 end = 0;
+	u64 page_start;
+	int index;
+	int first_index = 0;
+
+	for (index = 0; index < nr_pages; index++) {
+		page_start = page_offset(pages[index]);
+		if (!end) {
+			start = page_start;
+			end = start + PAGE_SIZE - 1;
+			first_index = index;
+		} else if (end + 1 == page_start) {
+			end += PAGE_SIZE;
+		} else {
+			__do_contiguous_readpages(tree, &pages[first_index],
+						  index - first_index, start,
+						  end, em_cached,
+						  bio, bio_flags,
+						  prev_em_start);
+			start = page_start;
+			end = start + PAGE_SIZE - 1;
+			first_index = index;
+		}
+	}
+
+	if (end)
+		__do_contiguous_readpages(tree, &pages[first_index],
+					  index - first_index, start,
+					  end, em_cached, bio,
+					  bio_flags, prev_em_start);
+}
+
+static int __extent_read_full_page(struct extent_io_tree *tree,
+				   struct page *page,
+				   get_extent_t *get_extent,
+				   struct bio **bio, int mirror_num,
+				   unsigned long *bio_flags,
+				   unsigned int read_flags)
+{
+	struct inode *inode = page->mapping->host;
+	struct btrfs_ordered_extent *ordered;
+	u64 start = page_offset(page);
+	u64 end = start + PAGE_SIZE - 1;
+	int ret;
+
+	while (1) {
+		lock_extent(tree, start, end);
+		ordered = btrfs_lookup_ordered_range(BTRFS_I(inode), start,
+						PAGE_SIZE);
+		if (!ordered)
+			break;
+		unlock_extent(tree, start, end);
+		btrfs_start_ordered_extent(inode, ordered, 1);
+		btrfs_put_ordered_extent(ordered);
+	}
+
+	ret = __do_readpage(tree, page, get_extent, NULL, bio, mirror_num,
+			    bio_flags, read_flags, NULL);
+	return ret;
+}
+
+int extent_read_full_page(struct extent_io_tree *tree, struct page *page,
+			    get_extent_t *get_extent, int mirror_num)
+{
+	struct bio *bio = NULL;
+	unsigned long bio_flags = 0;
+	int ret;
+
+	ret = __extent_read_full_page(tree, page, get_extent, &bio, mirror_num,
+				      &bio_flags, 0);
+	if (bio)
+		ret = submit_one_bio(bio, mirror_num, bio_flags);
+	return ret;
+}
+
+static void update_nr_written(struct writeback_control *wbc,
+			      unsigned long nr_written)
+{
+	wbc->nr_to_write -= nr_written;
+}
+
+/*
+ * 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 inode *inode,
+			      struct page *page, struct writeback_control *wbc,
+			      struct extent_page_data *epd,
+			      u64 delalloc_start,
+			      unsigned long *nr_written)
+{
+	struct extent_io_tree *tree = epd->tree;
+	u64 page_end = delalloc_start + PAGE_SIZE - 1;
+	u64 nr_delalloc;
+	u64 delalloc_to_write = 0;
+	u64 delalloc_end = 0;
+	int ret;
+	int page_started = 0;
+
+	if (epd->extent_locked)
+		return 0;
+
+	while (delalloc_end < page_end) {
+		nr_delalloc = find_lock_delalloc_range(inode, tree,
+					       page,
+					       &delalloc_start,
+					       &delalloc_end,
+					       BTRFS_MAX_EXTENT_SIZE);
+		if (nr_delalloc == 0) {
+			delalloc_start = delalloc_end + 1;
+			continue;
+		}
+		ret = btrfs_run_delalloc_range(inode, page, delalloc_start,
+				delalloc_end, &page_started, nr_written, wbc);
+		/* File system has been set read-only */
+		if (ret) {
+			SetPageError(page);
+			/*
+			 * btrfs_run_delalloc_range should return < 0 for error
+			 * but just in case, we use > 0 here meaning the IO is
+			 * started, so we don't want to return > 0 unless
+			 * things are going well.
+			 */
+			ret = ret < 0 ? ret : -EIO;
+			goto done;
+		}
+		/*
+		 * 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 the fill delalloc function 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;
+	}
+
+	ret = 0;
+
+done:
+	return ret;
+}
+
+/*
+ * 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 inode *inode,
+				 struct page *page,
+				 struct writeback_control *wbc,
+				 struct extent_page_data *epd,
+				 loff_t i_size,
+				 unsigned long nr_written,
+				 unsigned int write_flags, int *nr_ret)
+{
+	struct extent_io_tree *tree = epd->tree;
+	u64 start = page_offset(page);
+	u64 page_end = start + PAGE_SIZE - 1;
+	u64 end;
+	u64 cur = start;
+	u64 extent_offset;
+	u64 block_start;
+	u64 iosize;
+	struct extent_map *em;
+	struct block_device *bdev;
+	size_t pg_offset = 0;
+	size_t blocksize;
+	int ret = 0;
+	int nr = 0;
+	bool compressed;
+
+	if (tree->ops && tree->ops->writepage_start_hook) {
+		ret = tree->ops->writepage_start_hook(page, start,
+						      page_end);
+		if (ret) {
+			/* Fixup worker will requeue */
+			if (ret == -EBUSY)
+				wbc->pages_skipped++;
+			else
+				redirty_page_for_writepage(wbc, page);
+
+			update_nr_written(wbc, nr_written);
+			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
+	 */
+	update_nr_written(wbc, nr_written + 1);
+
+	end = page_end;
+	if (i_size <= start) {
+		if (tree->ops && tree->ops->writepage_end_io_hook)
+			tree->ops->writepage_end_io_hook(page, start,
+							 page_end, NULL, 1);
+		goto done;
+	}
+
+	blocksize = inode->i_sb->s_blocksize;
+
+	while (cur <= end) {
+		u64 em_end;
+		u64 offset;
+
+		if (cur >= i_size) {
+			if (tree->ops && tree->ops->writepage_end_io_hook)
+				tree->ops->writepage_end_io_hook(page, cur,
+							 page_end, NULL, 1);
+			break;
+		}
+		em = btrfs_get_extent(BTRFS_I(inode), page, pg_offset, cur,
+				     end - cur + 1, 1);
+		if (IS_ERR_OR_NULL(em)) {
+			SetPageError(page);
+			ret = PTR_ERR_OR_ZERO(em);
+			break;
+		}
+
+		extent_offset = cur - em->start;
+		em_end = extent_map_end(em);
+		BUG_ON(em_end <= cur);
+		BUG_ON(end < cur);
+		iosize = min(em_end - cur, end - cur + 1);
+		iosize = ALIGN(iosize, blocksize);
+		offset = em->block_start + extent_offset;
+		bdev = em->bdev;
+		block_start = em->block_start;
+		compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
+		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) {
+			/*
+			 * end_io notification does not happen here for
+			 * compressed extents
+			 */
+			if (!compressed && tree->ops &&
+			    tree->ops->writepage_end_io_hook)
+				tree->ops->writepage_end_io_hook(page, cur,
+							 cur + iosize - 1,
+							 NULL, 1);
+			else if (compressed) {
+				/* we don't want to end_page_writeback on
+				 * a compressed extent.  this happens
+				 * elsewhere
+				 */
+				nr++;
+			}
+
+			cur += iosize;
+			pg_offset += iosize;
+			continue;
+		}
+
+		btrfs_set_range_writeback(tree, cur, cur + iosize - 1);
+		if (!PageWriteback(page)) {
+			btrfs_err(BTRFS_I(inode)->root->fs_info,
+				   "page %lu not writeback, cur %llu end %llu",
+			       page->index, cur, end);
+		}
+
+		ret = submit_extent_page(REQ_OP_WRITE | write_flags, tree, wbc,
+					 page, offset, iosize, pg_offset,
+					 bdev, &epd->bio,
+					 end_bio_extent_writepage,
+					 0, 0, 0, false);
+		if (ret) {
+			SetPageError(page);
+			if (PageWriteback(page))
+				end_page_writeback(page);
+		}
+
+		cur = cur + iosize;
+		pg_offset += iosize;
+		nr++;
+	}
+done:
+	*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 inode *inode = page->mapping->host;
+	u64 start = page_offset(page);
+	u64 page_end = start + PAGE_SIZE - 1;
+	int ret;
+	int nr = 0;
+	size_t pg_offset = 0;
+	loff_t i_size = i_size_read(inode);
+	unsigned long end_index = i_size >> PAGE_SHIFT;
+	unsigned int write_flags = 0;
+	unsigned long nr_written = 0;
+
+	write_flags = wbc_to_write_flags(wbc);
+
+	trace___extent_writepage(page, inode, wbc);
+
+	WARN_ON(!PageLocked(page));
+
+	ClearPageError(page);
+
+	pg_offset = i_size & (PAGE_SIZE - 1);
+	if (page->index > end_index ||
+	   (page->index == end_index && !pg_offset)) {
+		page->mapping->a_ops->invalidatepage(page, 0, PAGE_SIZE);
+		unlock_page(page);
+		return 0;
+	}
+
+	if (page->index == end_index) {
+		char *userpage;
+
+		userpage = kmap_atomic(page);
+		memset(userpage + pg_offset, 0,
+		       PAGE_SIZE - pg_offset);
+		kunmap_atomic(userpage);
+		flush_dcache_page(page);
+	}
+
+	pg_offset = 0;
+
+	set_page_extent_mapped(page);
+
+	ret = writepage_delalloc(inode, page, wbc, epd, start, &nr_written);
+	if (ret == 1)
+		goto done_unlocked;
+	if (ret)
+		goto done;
+
+	ret = __extent_writepage_io(inode, page, wbc, epd,
+				    i_size, nr_written, write_flags, &nr);
+	if (ret == 1)
+		goto done_unlocked;
+
+done:
+	if (nr == 0) {
+		/* make sure the mapping tag for page dirty gets cleared */
+		set_page_writeback(page);
+		end_page_writeback(page);
+	}
+	if (PageError(page)) {
+		ret = ret < 0 ? ret : -EIO;
+		end_extent_writepage(page, ret, start, page_end);
+	}
+	unlock_page(page);
+	ASSERT(ret <= 0);
+	return ret;
+
+done_unlocked:
+	return 0;
+}
+
+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 eb pages and flush the bio if we can't the locks
+ *
+ * Return  0 if nothing went wrong
+ * Return >0 is same as 0, except bio is not submitted
+ * 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 btrfs_fs_info *fs_info,
+			  struct extent_page_data *epd)
+{
+	int i, num_pages, failed_page_nr;
+	int flush = 0;
+	int ret = 0;
+
+	if (!btrfs_try_tree_write_lock(eb)) {
+		ret = flush_write_bio(epd);
+		if (ret < 0)
+			return ret;
+		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) {
+			ret = flush_write_bio(epd);
+			if (ret < 0)
+				return ret;
+			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);
+
+	if (!ret)
+		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) {
+				int err;
+
+				err = flush_write_bio(epd);
+				if (err < 0) {
+					ret = err;
+					failed_page_nr = i;
+					goto err_unlock;
+				}
+				flush = 1;
+			}
+			lock_page(p);
+		}
+	}
+
+	return ret;
+err_unlock:
+	/* Unlock already locked pages */
+	for (i = 0; i < failed_page_nr; i++)
+		unlock_page(eb->pages[i]);
+	/*
+	 * Clear EXTENT_BUFFER_WRITEBACK and wake up anyone waiting on it.
+	 * Also set back EXTENT_BUFFER_DIRTY so future attempts to this eb can
+	 * be made and undo everything done before.
+	 */
+	btrfs_tree_lock(eb);
+	spin_lock(&eb->refs_lock);
+	set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);
+	end_extent_buffer_writeback(eb);
+	spin_unlock(&eb->refs_lock);
+	percpu_counter_add_batch(&fs_info->dirty_metadata_bytes, eb->len,
+				 fs_info->dirty_metadata_batch);
+	btrfs_clear_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
+	btrfs_tree_unlock(eb);
+	return ret;
+}
+
+static void set_btree_ioerr(struct page *page)
+{
+	struct extent_buffer *eb = (struct extent_buffer *)page->private;
+
+	SetPageError(page);
+	if (test_and_set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))
+		return;
+
+	/*
+	 * 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, &eb->fs_info->flags);
+		break;
+	case 0:
+		set_bit(BTRFS_FS_LOG1_ERR, &eb->fs_info->flags);
+		break;
+	case 1:
+		set_bit(BTRFS_FS_LOG2_ERR, &eb->fs_info->flags);
+		break;
+	default:
+		BUG(); /* unexpected, logic error */
+	}
+}
+
+static void end_bio_extent_buffer_writepage(struct bio *bio)
+{
+	struct bio_vec *bvec;
+	struct extent_buffer *eb;
+	int i, done;
+
+	ASSERT(!bio_flagged(bio, BIO_CLONED));
+	bio_for_each_segment_all(bvec, bio, i) {
+		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);
+		}
+
+		end_page_writeback(page);
+
+		if (!done)
+			continue;
+
+		end_extent_buffer_writeback(eb);
+	}
+
+	bio_put(bio);
+}
+
+static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
+			struct btrfs_fs_info *fs_info,
+			struct writeback_control *wbc,
+			struct extent_page_data *epd)
+{
+	struct block_device *bdev = fs_info->fs_devices->latest_bdev;
+	struct extent_io_tree *tree = &BTRFS_I(fs_info->btree_inode)->io_tree;
+	u64 offset = eb->start;
+	u32 nritems;
+	int i, num_pages;
+	unsigned long start, end;
+	unsigned int write_flags = wbc_to_write_flags(wbc) | REQ_META;
+	int ret = 0;
+
+	clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
+	num_pages = num_extent_pages(eb);
+	atomic_set(&eb->io_pages, num_pages);
+
+	/* 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(fs_info, eb);
+		memzero_extent_buffer(eb, start, end - start);
+	}
+
+	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, tree, wbc,
+					 p, offset, PAGE_SIZE, 0, bdev,
+					 &epd->bio,
+					 end_bio_extent_buffer_writepage,
+					 0, 0, 0, false);
+		if (ret) {
+			set_btree_ioerr(p);
+			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;
+		}
+		offset += PAGE_SIZE;
+		update_nr_written(wbc, 1);
+		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;
+}
+
+int btree_write_cache_pages(struct address_space *mapping,
+				   struct writeback_control *wbc)
+{
+	struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
+	struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
+	struct extent_buffer *eb, *prev_eb = NULL;
+	struct extent_page_data epd = {
+		.bio = NULL,
+		.tree = tree,
+		.extent_locked = 0,
+		.sync_io = wbc->sync_mode == WB_SYNC_ALL,
+	};
+	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;
+	int tag;
+
+	pagevec_init(&pvec);
+	if (wbc->range_cyclic) {
+		index = mapping->writeback_index; /* Start from prev offset */
+		end = -1;
+	} 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;
+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;
+
+		scanned = 1;
+		for (i = 0; i < nr_pages; i++) {
+			struct page *page = pvec.pages[i];
+
+			if (!PagePrivate(page))
+				continue;
+
+			spin_lock(&mapping->private_lock);
+			if (!PagePrivate(page)) {
+				spin_unlock(&mapping->private_lock);
+				continue;
+			}
+
+			eb = (struct extent_buffer *)page->private;
+
+			/*
+			 * Shouldn't happen and normally this would be a BUG_ON
+			 * but no sense in crashing the users box for something
+			 * we can survive anyway.
+			 */
+			if (WARN_ON(!eb)) {
+				spin_unlock(&mapping->private_lock);
+				continue;
+			}
+
+			if (eb == prev_eb) {
+				spin_unlock(&mapping->private_lock);
+				continue;
+			}
+
+			ret = atomic_inc_not_zero(&eb->refs);
+			spin_unlock(&mapping->private_lock);
+			if (!ret)
+				continue;
+
+			prev_eb = eb;
+			ret = lock_extent_buffer_for_io(eb, fs_info, &epd);
+			if (!ret) {
+				free_extent_buffer(eb);
+				continue;
+			} else if (ret < 0) {
+				done = 1;
+				free_extent_buffer(eb);
+				break;
+			}
+
+			ret = write_one_eb(eb, fs_info, wbc, &epd);
+			if (ret) {
+				done = 1;
+				free_extent_buffer(eb);
+				break;
+			}
+			free_extent_buffer(eb);
+
+			/*
+			 * 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;
+	}
+	ASSERT(ret <= 0);
+	if (ret < 0) {
+		end_write_bio(&epd, ret);
+		return ret;
+	}
+	/*
+	 * 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.
+	 */
+	if (!test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
+		ret = flush_write_bio(&epd);
+	} else {
+		ret = -EUCLEAN;
+		end_write_bio(&epd, ret);
+	}
+	return ret;
+}
+
+/**
+ * write_cache_pages - 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
+ * @data: data passed to __extent_writepage function
+ *
+ * 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;
+	int 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;
+	} 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;
+
+		scanned = 1;
+		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)) {
+				ret = flush_write_bio(epd);
+				BUG_ON(ret < 0);
+				lock_page(page);
+			}
+
+			if (unlikely(page->mapping != mapping)) {
+				unlock_page(page);
+				continue;
+			}
+
+			if (wbc->sync_mode != WB_SYNC_NONE) {
+				if (PageWriteback(page)) {
+					ret = flush_write_bio(epd);
+					BUG_ON(ret < 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 (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
+				unlock_page(page);
+				ret = 0;
+			}
+			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.
+		 */
+		ret = flush_write_bio(epd);
+		if (!ret)
+			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;
+}
+
+int extent_write_full_page(struct page *page, struct writeback_control *wbc)
+{
+	int ret;
+	struct extent_page_data epd = {
+		.bio = NULL,
+		.tree = &BTRFS_I(page->mapping->host)->io_tree,
+		.extent_locked = 0,
+		.sync_io = wbc->sync_mode == WB_SYNC_ALL,
+	};
+
+	ret = __extent_writepage(page, wbc, &epd);
+	ASSERT(ret <= 0);
+	if (ret < 0) {
+		end_write_bio(&epd, ret);
+		return ret;
+	}
+
+	ret = flush_write_bio(&epd);
+	ASSERT(ret <= 0);
+	return ret;
+}
+
+int extent_write_locked_range(struct inode *inode, u64 start, u64 end,
+			      int mode)
+{
+	int ret = 0;
+	int flush_ret;
+	struct address_space *mapping = inode->i_mapping;
+	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
+	struct page *page;
+	unsigned long nr_pages = (end - start + PAGE_SIZE) >>
+		PAGE_SHIFT;
+
+	struct extent_page_data epd = {
+		.bio = NULL,
+		.tree = tree,
+		.extent_locked = 1,
+		.sync_io = mode == WB_SYNC_ALL,
+	};
+	struct writeback_control wbc_writepages = {
+		.sync_mode	= mode,
+		.nr_to_write	= nr_pages * 2,
+		.range_start	= start,
+		.range_end	= end + 1,
+	};
+
+	while (start <= end) {
+		page = find_get_page(mapping, start >> PAGE_SHIFT);
+		if (clear_page_dirty_for_io(page))
+			ret = __extent_writepage(page, &wbc_writepages, &epd);
+		else {
+			if (tree->ops && tree->ops->writepage_end_io_hook)
+				tree->ops->writepage_end_io_hook(page, start,
+						 start + PAGE_SIZE - 1,
+						 NULL, 1);
+			unlock_page(page);
+		}
+		put_page(page);
+		start += PAGE_SIZE;
+	}
+
+	flush_ret = flush_write_bio(&epd);
+	BUG_ON(flush_ret < 0);
+	return ret;
+}
+
+int extent_writepages(struct address_space *mapping,
+		      struct writeback_control *wbc)
+{
+	int ret = 0;
+	int flush_ret;
+	struct extent_page_data epd = {
+		.bio = NULL,
+		.tree = &BTRFS_I(mapping->host)->io_tree,
+		.extent_locked = 0,
+		.sync_io = wbc->sync_mode == WB_SYNC_ALL,
+	};
+
+	ret = extent_write_cache_pages(mapping, wbc, &epd);
+	flush_ret = flush_write_bio(&epd);
+	BUG_ON(flush_ret < 0);
+	return ret;
+}
+
+int extent_readpages(struct address_space *mapping, struct list_head *pages,
+		     unsigned nr_pages)
+{
+	struct bio *bio = NULL;
+	unsigned page_idx;
+	unsigned long bio_flags = 0;
+	struct page *pagepool[16];
+	struct page *page;
+	struct extent_map *em_cached = NULL;
+	struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
+	int nr = 0;
+	u64 prev_em_start = (u64)-1;
+
+	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
+		page = list_entry(pages->prev, struct page, lru);
+
+		prefetchw(&page->flags);
+		list_del(&page->lru);
+		if (add_to_page_cache_lru(page, mapping,
+					page->index,
+					readahead_gfp_mask(mapping))) {
+			put_page(page);
+			continue;
+		}
+
+		pagepool[nr++] = page;
+		if (nr < ARRAY_SIZE(pagepool))
+			continue;
+		__extent_readpages(tree, pagepool, nr, &em_cached, &bio,
+				&bio_flags, &prev_em_start);
+		nr = 0;
+	}
+	if (nr)
+		__extent_readpages(tree, pagepool, nr, &em_cached, &bio,
+				&bio_flags, &prev_em_start);
+
+	if (em_cached)
+		free_extent_map(em_cached);
+
+	BUG_ON(!list_empty(pages));
+	if (bio)
+		return submit_one_bio(bio, 0, bio_flags);
+	return 0;
+}
+
+/*
+ * basic invalidatepage code, this waits on any locked or writeback
+ * ranges corresponding to the page, and then deletes any extent state
+ * records from the tree
+ */
+int extent_invalidatepage(struct extent_io_tree *tree,
+			  struct page *page, unsigned long offset)
+{
+	struct extent_state *cached_state = NULL;
+	u64 start = page_offset(page);
+	u64 end = start + PAGE_SIZE - 1;
+	size_t blocksize = page->mapping->host->i_sb->s_blocksize;
+
+	start += ALIGN(offset, blocksize);
+	if (start > end)
+		return 0;
+
+	lock_extent_bits(tree, start, end, &cached_state);
+	wait_on_page_writeback(page);
+	clear_extent_bit(tree, start, end,
+			 EXTENT_LOCKED | EXTENT_DIRTY | EXTENT_DELALLOC |
+			 EXTENT_DO_ACCOUNTING,
+			 1, 1, &cached_state);
+	return 0;
+}
+
+/*
+ * a helper for releasepage, 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_IOBITS, 0, NULL))
+		ret = 0;
+	else {
+		/*
+		 * at this point we can safely clear everything except the
+		 * locked bit and the nodatasum bit
+		 */
+		ret = __clear_extent_bit(tree, start, end,
+				 ~(EXTENT_LOCKED | EXTENT_NODATASUM),
+				 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 releasepage.  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) {
+			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 | EXTENT_WRITEBACK,
+					    0, NULL)) {
+				set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
+					&btrfs_inode->runtime_flags);
+				remove_extent_mapping(map, em);
+				/* once for the rb tree */
+				free_extent_map(em);
+			}
+			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 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(BTRFS_I(inode), NULL, 0, offset,
+				len, 0);
+		if (IS_ERR_OR_NULL(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 cahced 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 btrfs_fs_info *fs_info,
+				  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 inode *inode, struct fiemap_extent_info *fieinfo,
+		__u64 start, __u64 len)
+{
+	int ret = 0;
+	u64 off = start;
+	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);
+	struct btrfs_key found_key;
+	struct extent_map *em = NULL;
+	struct extent_state *cached_state = NULL;
+	struct btrfs_path *path;
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	struct fiemap_cache cache = { 0 };
+	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;
+	path->leave_spinning = 1;
+
+	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(BTRFS_I(inode)), -1, 0);
+	if (ret < 0) {
+		btrfs_free_path(path);
+		return ret;
+	} 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(BTRFS_I(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(&BTRFS_I(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(BTRFS_I(inode)),
+						 bytenr);
+			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(root->fs_info, fieinfo, &cache);
+	free_extent_map(em);
+out:
+	btrfs_free_path(path);
+	unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, start + len - 1,
+			     &cached_state);
+	return ret;
+}
+
+static void __free_extent_buffer(struct extent_buffer *eb)
+{
+	btrfs_leak_debug_del(&eb->leak_list);
+	kmem_cache_free(extent_buffer_cache, eb);
+}
+
+int extent_buffer_under_io(struct extent_buffer *eb)
+{
+	return (atomic_read(&eb->io_pages) ||
+		test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
+		test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+}
+
+/*
+ * Release all pages attached to the extent buffer.
+ */
+static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
+{
+	int i;
+	int num_pages;
+	int mapped = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
+
+	BUG_ON(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;
+		if (mapped)
+			spin_lock(&page->mapping->private_lock);
+		/*
+		 * 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.
+			 */
+			ClearPagePrivate(page);
+			set_page_private(page, 0);
+			/* One for the page private */
+			put_page(page);
+		}
+
+		if (mapped)
+			spin_unlock(&page->mapping->private_lock);
+
+		/* 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);
+	__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;
+	rwlock_init(&eb->lock);
+	atomic_set(&eb->write_locks, 0);
+	atomic_set(&eb->read_locks, 0);
+	atomic_set(&eb->blocking_readers, 0);
+	atomic_set(&eb->blocking_writers, 0);
+	atomic_set(&eb->spinning_readers, 0);
+	atomic_set(&eb->spinning_writers, 0);
+	eb->lock_nested = 0;
+	init_waitqueue_head(&eb->write_lock_wq);
+	init_waitqueue_head(&eb->read_lock_wq);
+
+	btrfs_leak_debug_add(&eb->leak_list, &buffers);
+
+	spin_lock_init(&eb->refs_lock);
+	atomic_set(&eb->refs, 1);
+	atomic_set(&eb->io_pages, 0);
+
+	/*
+	 * Sanity checks, currently the maximum is 64k covered by 16x 4k pages
+	 */
+	BUILD_BUG_ON(BTRFS_MAX_METADATA_BLOCKSIZE
+		> MAX_INLINE_EXTENT_BUFFER_SIZE);
+	BUG_ON(len > MAX_INLINE_EXTENT_BUFFER_SIZE);
+
+	return eb;
+}
+
+struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src)
+{
+	int i;
+	struct page *p;
+	struct extent_buffer *new;
+	int num_pages = num_extent_pages(src);
+
+	new = __alloc_extent_buffer(src->fs_info, src->start, src->len);
+	if (new == NULL)
+		return NULL;
+
+	for (i = 0; i < num_pages; i++) {
+		p = alloc_page(GFP_NOFS);
+		if (!p) {
+			btrfs_release_extent_buffer(new);
+			return NULL;
+		}
+		attach_extent_buffer_page(new, p);
+		WARN_ON(PageDirty(p));
+		SetPageUptodate(p);
+		new->pages[i] = p;
+		copy_page(page_address(p), page_address(src->pages[i]));
+	}
+
+	set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags);
+	set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags);
+
+	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;
+
+	eb = __alloc_extent_buffer(fs_info, start, len);
+	if (!eb)
+		return NULL;
+
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++) {
+		eb->pages[i] = alloc_page(GFP_NOFS);
+		if (!eb->pages[i])
+			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--)
+		__free_page(eb->pages[i - 1]);
+	__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 releasepage 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, releasepage 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;
+
+	rcu_read_lock();
+	eb = radix_tree_lookup(&fs_info->buffer_radix,
+			       start >> PAGE_SHIFT);
+	if (eb && atomic_inc_not_zero(&eb->refs)) {
+		rcu_read_unlock();
+		/*
+		 * 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;
+	}
+	rcu_read_unlock();
+
+	return NULL;
+}
+
+#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 >> PAGE_SHIFT, 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);
+
+	/*
+	 * We will free dummy extent buffer's if they come into
+	 * free_extent_buffer with a ref count of 2, but if we are using this we
+	 * want the buffers to stay in memory until we're done with them, so
+	 * bump the ref count again.
+	 */
+	atomic_inc(&eb->refs);
+	return eb;
+free_eb:
+	btrfs_release_extent_buffer(eb);
+	return exists;
+}
+#endif
+
+struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
+					  u64 start)
+{
+	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;
+	int uptodate = 1;
+	int ret;
+
+	if (!IS_ALIGNED(start, fs_info->sectorsize)) {
+		btrfs_err(fs_info, "bad tree block start %llu", start);
+		return ERR_PTR(-EINVAL);
+	}
+
+	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);
+
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++, index++) {
+		p = find_or_create_page(mapping, index, GFP_NOFS|__GFP_NOFAIL);
+		if (!p) {
+			exists = ERR_PTR(-ENOMEM);
+			goto free_eb;
+		}
+
+		spin_lock(&mapping->private_lock);
+		if (PagePrivate(p)) {
+			/*
+			 * 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 *)p->private;
+			if (atomic_inc_not_zero(&exists->refs)) {
+				spin_unlock(&mapping->private_lock);
+				unlock_page(p);
+				put_page(p);
+				mark_extent_buffer_accessed(exists, p);
+				goto free_eb;
+			}
+			exists = NULL;
+
+			/*
+			 * Do this so attach doesn't complain and we need to
+			 * drop the ref the old guy had.
+			 */
+			ClearPagePrivate(p);
+			WARN_ON(PageDirty(p));
+			put_page(p);
+		}
+		attach_extent_buffer_page(eb, p);
+		spin_unlock(&mapping->private_lock);
+		WARN_ON(PageDirty(p));
+		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_releasepage 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 >> PAGE_SHIFT, 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_releasepage 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)
+{
+	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 >> PAGE_SHIFT);
+			spin_unlock(&fs_info->buffer_lock);
+		} else {
+			spin_unlock(&eb->refs_lock);
+		}
+
+		/* 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 (refs <= 3)
+			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_UNMAPPED, &eb->bflags))
+		atomic_dec(&eb->refs);
+
+	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);
+}
+
+void clear_extent_buffer_dirty(struct extent_buffer *eb)
+{
+	int i;
+	int num_pages;
+	struct page *page;
+
+	num_pages = num_extent_pages(eb);
+
+	for (i = 0; i < num_pages; i++) {
+		page = eb->pages[i];
+		if (!PageDirty(page))
+			continue;
+
+		lock_page(page);
+		WARN_ON(!PagePrivate(page));
+
+		clear_page_dirty_for_io(page);
+		xa_lock_irq(&page->mapping->i_pages);
+		if (!PageDirty(page)) {
+			radix_tree_tag_clear(&page->mapping->i_pages,
+						page_index(page),
+						PAGECACHE_TAG_DIRTY);
+		}
+		xa_unlock_irq(&page->mapping->i_pages);
+		ClearPageError(page);
+		unlock_page(page);
+	}
+	WARN_ON(atomic_read(&eb->refs) == 0);
+}
+
+int set_extent_buffer_dirty(struct extent_buffer *eb)
+{
+	int i;
+	int num_pages;
+	int was_dirty = 0;
+
+	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));
+
+	for (i = 0; i < num_pages; i++)
+		set_page_dirty(eb->pages[i]);
+	return was_dirty;
+}
+
+void clear_extent_buffer_uptodate(struct extent_buffer *eb)
+{
+	int i;
+	struct page *page;
+	int num_pages;
+
+	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)
+			ClearPageUptodate(page);
+	}
+}
+
+void set_extent_buffer_uptodate(struct extent_buffer *eb)
+{
+	int i;
+	struct page *page;
+	int num_pages;
+
+	set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++) {
+		page = eb->pages[i];
+		SetPageUptodate(page);
+	}
+}
+
+int read_extent_buffer_pages(struct extent_io_tree *tree,
+			     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 bio *bio = NULL;
+	unsigned long bio_flags = 0;
+
+	if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
+		return 0;
+
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++) {
+		page = eb->pages[i];
+		if (wait == WAIT_NONE) {
+			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 releasepage 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 = __extent_read_full_page(tree, page,
+						      btree_get_extent, &bio,
+						      mirror_num, &bio_flags,
+						      REQ_META);
+			if (err) {
+				ret = err;
+				/*
+				 * We use &bio in above __extent_read_full_page,
+				 * so we ensure that if it returns error, the
+				 * current page fails to add itself to bio and
+				 * it's been unlocked.
+				 *
+				 * We must dec io_pages by ourselves.
+				 */
+				atomic_dec(&eb->io_pages);
+			}
+		} else {
+			unlock_page(page);
+		}
+	}
+
+	if (bio) {
+		err = submit_one_bio(bio, mirror_num, bio_flags);
+		if (err)
+			return err;
+	}
+
+	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;
+}
+
+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;
+	size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
+	unsigned long i = (start_offset + start) >> PAGE_SHIFT;
+
+	if (start + len > eb->len) {
+		WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, wanted %lu %lu\n",
+		     eb->start, eb->len, start, len);
+		memset(dst, 0, len);
+		return;
+	}
+
+	offset = (start_offset + start) & (PAGE_SIZE - 1);
+
+	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;
+	size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
+	unsigned long i = (start_offset + start) >> PAGE_SHIFT;
+	int ret = 0;
+
+	WARN_ON(start > eb->len);
+	WARN_ON(start + len > eb->start + eb->len);
+
+	offset = (start_offset + start) & (PAGE_SIZE - 1);
+
+	while (len > 0) {
+		page = eb->pages[i];
+
+		cur = min(len, (PAGE_SIZE - offset));
+		kaddr = page_address(page);
+		if (probe_user_write(dst, kaddr + offset, cur)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		dst += cur;
+		len -= cur;
+		offset = 0;
+		i++;
+	}
+
+	return ret;
+}
+
+/*
+ * return 0 if the item is found within a page.
+ * return 1 if the item spans two pages.
+ * return -EINVAL otherwise.
+ */
+int map_private_extent_buffer(const struct extent_buffer *eb,
+			      unsigned long start, unsigned long min_len,
+			      char **map, unsigned long *map_start,
+			      unsigned long *map_len)
+{
+	size_t offset = start & (PAGE_SIZE - 1);
+	char *kaddr;
+	struct page *p;
+	size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
+	unsigned long i = (start_offset + start) >> PAGE_SHIFT;
+	unsigned long end_i = (start_offset + start + min_len - 1) >>
+		PAGE_SHIFT;
+
+	if (start + min_len > eb->len) {
+		WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, wanted %lu %lu\n",
+		       eb->start, eb->len, start, min_len);
+		return -EINVAL;
+	}
+
+	if (i != end_i)
+		return 1;
+
+	if (i == 0) {
+		offset = start_offset;
+		*map_start = 0;
+	} else {
+		offset = 0;
+		*map_start = ((u64)i << PAGE_SHIFT) - start_offset;
+	}
+
+	p = eb->pages[i];
+	kaddr = page_address(p);
+	*map = kaddr + offset;
+	*map_len = PAGE_SIZE - offset;
+	return 0;
+}
+
+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;
+	size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
+	unsigned long i = (start_offset + start) >> PAGE_SHIFT;
+	int ret = 0;
+
+	WARN_ON(start > eb->len);
+	WARN_ON(start + len > eb->start + eb->len);
+
+	offset = (start_offset + start) & (PAGE_SIZE - 1);
+
+	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;
+}
+
+void write_extent_buffer_chunk_tree_uuid(struct extent_buffer *eb,
+		const void *srcv)
+{
+	char *kaddr;
+
+	WARN_ON(!PageUptodate(eb->pages[0]));
+	kaddr = page_address(eb->pages[0]);
+	memcpy(kaddr + offsetof(struct btrfs_header, chunk_tree_uuid), srcv,
+			BTRFS_FSID_SIZE);
+}
+
+void write_extent_buffer_fsid(struct extent_buffer *eb, const void *srcv)
+{
+	char *kaddr;
+
+	WARN_ON(!PageUptodate(eb->pages[0]));
+	kaddr = page_address(eb->pages[0]);
+	memcpy(kaddr + offsetof(struct btrfs_header, fsid), srcv,
+			BTRFS_FSID_SIZE);
+}
+
+void write_extent_buffer(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;
+	size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
+	unsigned long i = (start_offset + start) >> PAGE_SHIFT;
+
+	WARN_ON(start > eb->len);
+	WARN_ON(start + len > eb->start + eb->len);
+
+	offset = (start_offset + start) & (PAGE_SIZE - 1);
+
+	while (len > 0) {
+		page = eb->pages[i];
+		WARN_ON(!PageUptodate(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(struct extent_buffer *eb, unsigned long start,
+		unsigned long len)
+{
+	size_t cur;
+	size_t offset;
+	struct page *page;
+	char *kaddr;
+	size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
+	unsigned long i = (start_offset + start) >> PAGE_SHIFT;
+
+	WARN_ON(start > eb->len);
+	WARN_ON(start + len > eb->start + eb->len);
+
+	offset = (start_offset + start) & (PAGE_SIZE - 1);
+
+	while (len > 0) {
+		page = eb->pages[i];
+		WARN_ON(!PageUptodate(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(struct extent_buffer *dst,
+			     struct extent_buffer *src)
+{
+	int i;
+	int num_pages;
+
+	ASSERT(dst->len == src->len);
+
+	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]));
+}
+
+void copy_extent_buffer(struct extent_buffer *dst, 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;
+	size_t start_offset = dst->start & ((u64)PAGE_SIZE - 1);
+	unsigned long i = (start_offset + dst_offset) >> PAGE_SHIFT;
+
+	WARN_ON(src->len != dst_len);
+
+	offset = (start_offset + dst_offset) &
+		(PAGE_SIZE - 1);
+
+	while (len > 0) {
+		page = dst->pages[i];
+		WARN_ON(!PageUptodate(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(struct extent_buffer *eb,
+				    unsigned long start, unsigned long nr,
+				    unsigned long *page_index,
+				    size_t *page_offset)
+{
+	size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
+	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 + start + byte_offset;
+
+	*page_index = offset >> PAGE_SHIFT;
+	*page_offset = offset & (PAGE_SIZE - 1);
+}
+
+/**
+ * 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(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];
+	WARN_ON(!PageUptodate(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(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];
+	WARN_ON(!PageUptodate(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];
+			WARN_ON(!PageUptodate(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(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];
+	WARN_ON(!PageUptodate(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];
+			WARN_ON(!PageUptodate(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(struct extent_buffer *dst, unsigned long dst_offset,
+			   unsigned long src_offset, unsigned long len)
+{
+	struct btrfs_fs_info *fs_info = dst->fs_info;
+	size_t cur;
+	size_t dst_off_in_page;
+	size_t src_off_in_page;
+	size_t start_offset = dst->start & ((u64)PAGE_SIZE - 1);
+	unsigned long dst_i;
+	unsigned long src_i;
+
+	if (src_offset + len > dst->len) {
+		btrfs_err(fs_info,
+			"memmove bogus src_offset %lu move len %lu dst len %lu",
+			 src_offset, len, dst->len);
+		BUG_ON(1);
+	}
+	if (dst_offset + len > dst->len) {
+		btrfs_err(fs_info,
+			"memmove bogus dst_offset %lu move len %lu dst len %lu",
+			 dst_offset, len, dst->len);
+		BUG_ON(1);
+	}
+
+	while (len > 0) {
+		dst_off_in_page = (start_offset + dst_offset) &
+			(PAGE_SIZE - 1);
+		src_off_in_page = (start_offset + src_offset) &
+			(PAGE_SIZE - 1);
+
+		dst_i = (start_offset + dst_offset) >> PAGE_SHIFT;
+		src_i = (start_offset + src_offset) >> PAGE_SHIFT;
+
+		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(struct extent_buffer *dst, unsigned long dst_offset,
+			   unsigned long src_offset, unsigned long len)
+{
+	struct btrfs_fs_info *fs_info = dst->fs_info;
+	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;
+	size_t start_offset = dst->start & ((u64)PAGE_SIZE - 1);
+	unsigned long dst_i;
+	unsigned long src_i;
+
+	if (src_offset + len > dst->len) {
+		btrfs_err(fs_info,
+			  "memmove bogus src_offset %lu move len %lu len %lu",
+			  src_offset, len, dst->len);
+		BUG_ON(1);
+	}
+	if (dst_offset + len > dst->len) {
+		btrfs_err(fs_info,
+			  "memmove bogus dst_offset %lu move len %lu len %lu",
+			  dst_offset, len, dst->len);
+		BUG_ON(1);
+	}
+	if (dst_offset < src_offset) {
+		memcpy_extent_buffer(dst, dst_offset, src_offset, len);
+		return;
+	}
+	while (len > 0) {
+		dst_i = (start_offset + dst_end) >> PAGE_SHIFT;
+		src_i = (start_offset + src_end) >> PAGE_SHIFT;
+
+		dst_off_in_page = (start_offset + dst_end) &
+			(PAGE_SIZE - 1);
+		src_off_in_page = (start_offset + src_end) &
+			(PAGE_SIZE - 1);
+
+		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;
+	}
+}
+
+int try_release_extent_buffer(struct page *page)
+{
+	struct extent_buffer *eb;
+
+	/*
+	 * We need to make sure nobody is attaching this page to an eb right
+	 * now.
+	 */
+	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);
+}