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32 results

node.c

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  • extent_io.c 147.59 KiB
    #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 "transaction.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),
    		       atomic_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);
    		printk(KERN_ERR "BTRFS: buffer leak start %llu len %lu "
    		       "refs %d\n",
    		       eb->start, eb->len, atomic_read(&eb->refs));
    		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)
    {
    	struct inode *inode;
    	u64 isize;
    
    	if (!tree->mapping)
    		return;
    
    	inode = tree->mapping->host;
    	isize = i_size_read(inode);
    	if (end >= PAGE_SIZE && (end % 2) == 0 && end != isize - 1) {
    		btrfs_debug_rl(BTRFS_I(inode)->root->fs_info,
    		    "%s: ino %llu isize %llu odd range [%llu,%llu]",
    				caller, btrfs_ino(inode), isize, 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;
    	get_extent_t *get_extent;
    	unsigned long bio_flags;
    
    	/* 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 a WRITE_SYNC */
    	unsigned int sync_io:1;
    };
    
    static void add_extent_changeset(struct extent_state *state, unsigned bits,
    				 struct extent_changeset *changeset,
    				 int set)
    {
    	int ret;
    
    	if (!changeset)
    		return;
    	if (set && (state->state & bits) == bits)
    		return;
    	if (!set && (state->state & bits) == 0)
    		return;
    	changeset->bytes_changed += state->end - state->start + 1;
    	ret = ulist_add(changeset->range_changed, state->start, state->end,
    			GFP_ATOMIC);
    	/* ENOMEM */
    	BUG_ON(ret < 0);
    }
    
    static noinline void flush_write_bio(void *data);
    static inline struct btrfs_fs_info *
    tree_fs_info(struct extent_io_tree *tree)
    {
    	if (!tree->mapping)
    		return NULL;
    	return btrfs_sb(tree->mapping->host->i_sb);
    }
    
    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;
    
    	btrfs_bioset = bioset_create(BIO_POOL_SIZE,
    				     offsetof(struct btrfs_io_bio, bio));
    	if (!btrfs_bioset)
    		goto free_buffer_cache;
    
    	if (bioset_integrity_create(btrfs_bioset, BIO_POOL_SIZE))
    		goto free_bioset;
    
    	return 0;
    
    free_bioset:
    	bioset_free(btrfs_bioset);
    	btrfs_bioset = NULL;
    
    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 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);
    	if (btrfs_bioset)
    		bioset_free(btrfs_bioset);
    }
    
    void extent_io_tree_init(struct extent_io_tree *tree,
    			 struct address_space *mapping)
    {
    	tree->state = RB_ROOT;
    	tree->ops = NULL;
    	tree->dirty_bytes = 0;
    	spin_lock_init(&tree->lock);
    	tree->mapping = mapping;
    }
    
    static struct extent_state *alloc_extent_state(gfp_t mask)
    {
    	struct extent_state *state;
    
    	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);
    	atomic_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 (atomic_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->mapping->host, 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->mapping->host, 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->mapping->host, 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);
    		printk(KERN_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->mapping->host, 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;
    
    	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);
    	add_extent_changeset(state, bits_to_clear, changeset, 0);
    	state->state &= ~bits_to_clear;
    	if (wake)
    		wake_up(&state->wq);
    	if (state->state == 0) {
    		next = next_state(state);
    		if (extent_state_in_tree(state)) {
    			rb_erase(&state->rb_node, &tree->state);
    			RB_CLEAR_NODE(&state->rb_node);
    			free_extent_state(state);
    		} else {
    			WARN_ON(1);
    		}
    	} else {
    		merge_state(tree, state);
    		next = next_state(state);
    	}
    	return next;
    }
    
    static struct extent_state *
    alloc_extent_state_atomic(struct extent_state *prealloc)
    {
    	if (!prealloc)
    		prealloc = alloc_extent_state(GFP_ATOMIC);
    
    	return prealloc;
    }
    
    static void extent_io_tree_panic(struct extent_io_tree *tree, int err)
    {
    	btrfs_panic(tree_fs_info(tree), 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.
     */
    static 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)
    				atomic_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;
    			atomic_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;
    
    	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;
    	}
    	add_extent_changeset(state, bits_to_set, changeset, 1);
    	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;
    			atomic_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, gfp_t mask)
    {
    	return __clear_extent_bit(tree, start, end, bits, wake, delete,
    				  cached, mask, 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, GFP_NOFS);
    		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++;
    	}
    }
    
    /*
     * helper function to set both pages and extents in the tree writeback
     */
    static void set_range_writeback(struct extent_io_tree *tree, 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(tree->mapping, index);
    		BUG_ON(!page); /* Pages should be in the extent_io_tree */
    		set_page_writeback(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;
    			atomic_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 noinline void __unlock_for_delalloc(struct inode *inode,
    					   struct page *locked_page,
    					   u64 start, u64 end)
    {
    	int ret;
    	struct page *pages[16];
    	unsigned long index = start >> PAGE_SHIFT;
    	unsigned long end_index = end >> PAGE_SHIFT;
    	unsigned long nr_pages = end_index - index + 1;
    	int i;
    
    	if (index == locked_page->index && end_index == index)
    		return;
    
    	while (nr_pages > 0) {
    		ret = find_get_pages_contig(inode->i_mapping, index,
    				     min_t(unsigned long, nr_pages,
    				     ARRAY_SIZE(pages)), pages);
    		for (i = 0; i < ret; i++) {
    			if (pages[i] != locked_page)
    				unlock_page(pages[i]);
    			put_page(pages[i]);
    		}
    		nr_pages -= ret;
    		index += ret;
    		cond_resched();
    	}
    }
    
    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 start_index = index;
    	unsigned long end_index = delalloc_end >> PAGE_SHIFT;
    	unsigned long pages_locked = 0;
    	struct page *pages[16];
    	unsigned long nrpages;
    	int ret;
    	int i;
    
    	/* the caller is responsible for locking the start index */
    	if (index == locked_page->index && index == end_index)
    		return 0;
    
    	/* skip the page at the start index */
    	nrpages = end_index - index + 1;
    	while (nrpages > 0) {
    		ret = find_get_pages_contig(inode->i_mapping, index,
    				     min_t(unsigned long,
    				     nrpages, ARRAY_SIZE(pages)), pages);
    		if (ret == 0) {
    			ret = -EAGAIN;
    			goto done;
    		}
    		/* now we have an array of pages, lock them all */
    		for (i = 0; i < ret; i++) {
    			/*
    			 * the caller is taking responsibility for
    			 * locked_page
    			 */
    			if (pages[i] != locked_page) {
    				lock_page(pages[i]);
    				if (!PageDirty(pages[i]) ||
    				    pages[i]->mapping != inode->i_mapping) {
    					ret = -EAGAIN;
    					unlock_page(pages[i]);
    					put_page(pages[i]);
    					goto done;
    				}
    			}
    			put_page(pages[i]);
    			pages_locked++;
    		}
    		nrpages -= ret;
    		index += ret;
    		cond_resched();
    	}
    	ret = 0;
    done:
    	if (ret && pages_locked) {
    		__unlock_for_delalloc(inode, locked_page,
    			      delalloc_start,
    			      ((u64)(start_index + pages_locked - 1)) <<
    			      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, GFP_NOFS);
    		__unlock_for_delalloc(inode, locked_page,
    			      delalloc_start, delalloc_end);
    		cond_resched();
    		goto again;
    	}
    	free_extent_state(cached_state);
    	*start = delalloc_start;
    	*end = delalloc_end;
    out_failed:
    	return found;
    }
    
    void extent_clear_unlock_delalloc(struct inode *inode, u64 start, u64 end,
    				 struct page *locked_page,
    				 unsigned clear_bits,
    				 unsigned long page_ops)
    {
    	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
    	int ret;
    	struct page *pages[16];
    	unsigned long index = start >> PAGE_SHIFT;
    	unsigned long end_index = end >> PAGE_SHIFT;
    	unsigned long nr_pages = end_index - index + 1;
    	int i;
    
    	clear_extent_bit(tree, start, end, clear_bits, 1, 0, NULL, GFP_NOFS);
    	if (page_ops == 0)
    		return;
    
    	if ((page_ops & PAGE_SET_ERROR) && nr_pages > 0)
    		mapping_set_error(inode->i_mapping, -EIO);
    
    	while (nr_pages > 0) {
    		ret = find_get_pages_contig(inode->i_mapping, index,
    				     min_t(unsigned long,
    				     nr_pages, ARRAY_SIZE(pages)), pages);
    		for (i = 0; i < ret; i++) {
    
    			if (page_ops & PAGE_SET_PRIVATE2)
    				SetPagePrivate2(pages[i]);
    
    			if (pages[i] == locked_page) {
    				put_page(pages[i]);
    				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]);
    			put_page(pages[i]);
    		}
    		nr_pages -= ret;
    		index += ret;
    		cond_resched();
    	}
    }
    
    /*
     * 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 inode *inode, struct io_failure_record *rec)
    {
    	int ret;
    	int err = 0;
    	struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
    
    	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(&BTRFS_I(inode)->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 inode *inode, u64 start, u64 length, u64 logical,
    		      struct page *page, unsigned int pg_offset, int mirror_num)
    {
    	struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
    	struct bio *bio;
    	struct btrfs_device *dev;
    	u64 map_length = 0;
    	u64 sector;
    	struct btrfs_bio *bbio = NULL;
    	struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
    	int ret;
    
    	ASSERT(!(fs_info->sb->s_flags & MS_RDONLY));
    	BUG_ON(!mirror_num);
    
    	/* we can't repair anything in raid56 yet */
    	if (btrfs_is_parity_mirror(map_tree, logical, length, mirror_num))
    		return 0;
    
    	bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
    	if (!bio)
    		return -EIO;
    	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);
    	ret = btrfs_map_block(fs_info, 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[mirror_num-1].physical >> 9;
    	bio->bi_iter.bi_sector = sector;
    	dev = bbio->stripes[mirror_num-1].dev;
    	btrfs_put_bbio(bbio);
    	if (!dev || !dev->bdev || !dev->writeable) {
    		btrfs_bio_counter_dec(fs_info);
    		bio_put(bio);
    		return -EIO;
    	}
    	bio->bi_bdev = dev->bdev;
    	bio_set_op_attrs(bio, REQ_OP_WRITE, WRITE_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)",
    				  btrfs_ino(inode), 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_root *root, struct extent_buffer *eb,
    			 int mirror_num)
    {
    	u64 start = eb->start;
    	unsigned long i, num_pages = num_extent_pages(eb->start, eb->len);
    	int ret = 0;
    
    	if (root->fs_info->sb->s_flags & MS_RDONLY)
    		return -EROFS;
    
    	for (i = 0; i < num_pages; i++) {
    		struct page *p = eb->pages[i];
    
    		ret = repair_io_failure(root->fs_info->btree_inode, 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 inode *inode, u64 start, struct page *page,
    		     unsigned int pg_offset)
    {
    	u64 private;
    	struct io_failure_record *failrec;
    	struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
    	struct extent_state *state;
    	int num_copies;
    	int ret;
    
    	private = 0;
    	ret = count_range_bits(&BTRFS_I(inode)->io_failure_tree, &private,
    				(u64)-1, 1, EXTENT_DIRTY, 0);
    	if (!ret)
    		return 0;
    
    	ret = get_state_failrec(&BTRFS_I(inode)->io_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 */
    		pr_debug("clean_io_failure: freeing dummy error at %llu\n",
    			 failrec->start);
    		goto out;
    	}
    	if (fs_info->sb->s_flags & MS_RDONLY)
    		goto out;
    
    	spin_lock(&BTRFS_I(inode)->io_tree.lock);
    	state = find_first_extent_bit_state(&BTRFS_I(inode)->io_tree,
    					    failrec->start,
    					    EXTENT_LOCKED);
    	spin_unlock(&BTRFS_I(inode)->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(inode, start, failrec->len,
    					  failrec->logical, page,
    					  pg_offset, failrec->failed_mirror);
    		}
    	}
    
    out:
    	free_io_failure(inode, failrec);
    
    	return 0;
    }
    
    /*
     * Can be called when
     * - hold extent lock
     * - under ordered extent
     * - the inode is freeing
     */
    void btrfs_free_io_failure_record(struct inode *inode, u64 start, u64 end)
    {
    	struct extent_io_tree *failure_tree = &BTRFS_I(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 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);
    		}
    
    		pr_debug("Get IO Failure Record: (new) logical=%llu, start=%llu, len=%llu\n",
    			 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 {
    		pr_debug("Get IO Failure Record: (found) logical=%llu, start=%llu, len=%llu, validation=%d\n",
    			 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;
    }
    
    int btrfs_check_repairable(struct inode *inode, struct bio *failed_bio,
    			   struct io_failure_record *failrec, int failed_mirror)
    {
    	int num_copies;
    
    	num_copies = btrfs_num_copies(BTRFS_I(inode)->root->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.
    		 */
    		pr_debug("Check Repairable: cannot repair, num_copies=%d, next_mirror %d, failed_mirror %d\n",
    			 num_copies, failrec->this_mirror, failed_mirror);
    		return 0;
    	}
    
    	/*
    	 * there are two premises:
    	 *	a) deliver good data to the caller
    	 *	b) correct the bad sectors on disk
    	 */
    	if (failed_bio->bi_vcnt > 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) {
    		pr_debug("Check Repairable: (fail) num_copies=%d, next_mirror %d, failed_mirror %d\n",
    			 num_copies, failrec->this_mirror, failed_mirror);
    		return 0;
    	}
    
    	return 1;
    }
    
    
    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 bio *bio;
    	struct btrfs_io_bio *btrfs_failed_bio;
    	struct btrfs_io_bio *btrfs_bio;
    
    	bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
    	if (!bio)
    		return NULL;
    
    	bio->bi_end_io = endio_func;
    	bio->bi_iter.bi_sector = failrec->logical >> 9;
    	bio->bi_bdev = BTRFS_I(inode)->root->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) {
    		struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
    		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 bio *bio;
    	int read_mode;
    	int ret;
    
    	BUG_ON(bio_op(failed_bio) == REQ_OP_WRITE);
    
    	ret = btrfs_get_io_failure_record(inode, start, end, &failrec);
    	if (ret)
    		return ret;
    
    	ret = btrfs_check_repairable(inode, failed_bio, failrec, failed_mirror);
    	if (!ret) {
    		free_io_failure(inode, failrec);
    		return -EIO;
    	}
    
    	if (failed_bio->bi_vcnt > 1)
    		read_mode = READ_SYNC | REQ_FAILFAST_DEV;
    	else
    		read_mode = READ_SYNC;
    
    	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);
    	if (!bio) {
    		free_io_failure(inode, failrec);
    		return -EIO;
    	}
    	bio_set_op_attrs(bio, REQ_OP_READ, read_mode);
    
    	pr_debug("Repair Read Error: submitting new read[%#x] to this_mirror=%d, in_validation=%d\n",
    		 read_mode, failrec->this_mirror, failrec->in_validation);
    
    	ret = tree->ops->submit_bio_hook(inode, bio, failrec->this_mirror,
    					 failrec->bio_flags, 0);
    	if (ret) {
    		free_io_failure(inode, failrec);
    		bio_put(bio);
    	}
    
    	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) {
    		ret = tree->ops->writepage_end_io_hook(page, start,
    					       end, NULL, uptodate);
    		if (ret)
    			uptodate = 0;
    	}
    
    	if (!uptodate) {
    		ClearPageUptodate(page);
    		SetPageError(page);
    		ret = ret < 0 ? ret : -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)
    {
    	struct bio_vec *bvec;
    	u64 start;
    	u64 end;
    	int i;
    
    	bio_for_each_segment_all(bvec, bio, i) {
    		struct page *page = bvec->bv_page;
    
    		/* 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(BTRFS_I(page->mapping->host)->root->fs_info,
    				   "partial page write in btrfs with offset %u and length %u",
    					bvec->bv_offset, bvec->bv_len);
    			else
    				btrfs_info(BTRFS_I(page->mapping->host)->root->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, bio->bi_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(tree, start, end, &cached, GFP_ATOMIC);
    }
    
    /*
     * 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_error;
    	struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
    	struct extent_io_tree *tree;
    	u64 offset = 0;
    	u64 start;
    	u64 end;
    	u64 len;
    	u64 extent_start = 0;
    	u64 extent_len = 0;
    	int mirror;
    	int ret;
    	int i;
    
    	bio_for_each_segment_all(bvec, bio, i) {
    		struct page *page = bvec->bv_page;
    		struct inode *inode = page->mapping->host;
    
    		pr_debug("end_bio_extent_readpage: bi_sector=%llu, err=%d, "
    			 "mirror=%u\n", (u64)bio->bi_iter.bi_sector,
    			 bio->bi_error, io_bio->mirror_num);
    		tree = &BTRFS_I(inode)->io_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(BTRFS_I(page->mapping->host)->root->fs_info,
    				   "partial page read in btrfs with offset %u and length %u",
    					bvec->bv_offset, bvec->bv_len);
    			else
    				btrfs_info(BTRFS_I(page->mapping->host)->root->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 &&
    			   tree->ops->readpage_end_io_hook)) {
    			ret = tree->ops->readpage_end_io_hook(io_bio, offset,
    							      page, start, end,
    							      mirror);
    			if (ret)
    				uptodate = 0;
    			else
    				clean_io_failure(inode, start, page, 0);
    		}
    
    		if (likely(uptodate))
    			goto readpage_ok;
    
    		if (tree->ops && tree->ops->readpage_io_failed_hook) {
    			ret = tree->ops->readpage_io_failed_hook(page, mirror);
    			if (!ret && !bio->bi_error)
    				uptodate = 1;
    		} else {
    			/*
    			 * 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_error;
    				offset += len;
    				continue;
    			}
    		}
    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, bio->bi_error);
    	bio_put(bio);
    }
    
    /*
     * this allocates from the btrfs_bioset.  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_sector, int nr_vecs,
    		gfp_t gfp_flags)
    {
    	struct btrfs_io_bio *btrfs_bio;
    	struct bio *bio;
    
    	bio = bio_alloc_bioset(gfp_flags, nr_vecs, btrfs_bioset);
    
    	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
    		while (!bio && (nr_vecs /= 2)) {
    			bio = bio_alloc_bioset(gfp_flags,
    					       nr_vecs, btrfs_bioset);
    		}
    	}
    
    	if (bio) {
    		bio->bi_bdev = bdev;
    		bio->bi_iter.bi_sector = first_sector;
    		btrfs_bio = btrfs_io_bio(bio);
    		btrfs_bio->csum = NULL;
    		btrfs_bio->csum_allocated = NULL;
    		btrfs_bio->end_io = NULL;
    	}
    	return bio;
    }
    
    struct bio *btrfs_bio_clone(struct bio *bio, gfp_t gfp_mask)
    {
    	struct btrfs_io_bio *btrfs_bio;
    	struct bio *new;
    
    	new = bio_clone_bioset(bio, gfp_mask, btrfs_bioset);
    	if (new) {
    		btrfs_bio = btrfs_io_bio(new);
    		btrfs_bio->csum = NULL;
    		btrfs_bio->csum_allocated = NULL;
    		btrfs_bio->end_io = NULL;
    	}
    	return new;
    }
    
    /* this also allocates from the btrfs_bioset */
    struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
    {
    	struct btrfs_io_bio *btrfs_bio;
    	struct bio *bio;
    
    	bio = bio_alloc_bioset(gfp_mask, nr_iovecs, btrfs_bioset);
    	if (bio) {
    		btrfs_bio = btrfs_io_bio(bio);
    		btrfs_bio->csum = NULL;
    		btrfs_bio->csum_allocated = NULL;
    		btrfs_bio->end_io = NULL;
    	}
    	return bio;
    }
    
    
    static int __must_check submit_one_bio(struct bio *bio, int mirror_num,
    				       unsigned long bio_flags)
    {
    	int ret = 0;
    	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
    	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;
    	bio_get(bio);
    
    	if (tree->ops && tree->ops->submit_bio_hook)
    		ret = tree->ops->submit_bio_hook(page->mapping->host, bio,
    					   mirror_num, bio_flags, start);
    	else
    		btrfsic_submit_bio(bio);
    
    	bio_put(bio);
    	return ret;
    }
    
    static int merge_bio(struct extent_io_tree *tree, struct page *page,
    		     unsigned long offset, size_t size, struct bio *bio,
    		     unsigned long bio_flags)
    {
    	int ret = 0;
    	if (tree->ops && tree->ops->merge_bio_hook)
    		ret = tree->ops->merge_bio_hook(page, offset, size, bio,
    						bio_flags);
    	return ret;
    
    }
    
    static int submit_extent_page(int op, int op_flags, struct extent_io_tree *tree,
    			      struct writeback_control *wbc,
    			      struct page *page, sector_t sector,
    			      size_t size, unsigned long offset,
    			      struct block_device *bdev,
    			      struct bio **bio_ret,
    			      unsigned long max_pages,
    			      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;
    	int contig = 0;
    	int old_compressed = prev_bio_flags & EXTENT_BIO_COMPRESSED;
    	size_t page_size = min_t(size_t, size, PAGE_SIZE);
    
    	if (bio_ret && *bio_ret) {
    		bio = *bio_ret;
    		if (old_compressed)
    			contig = bio->bi_iter.bi_sector == sector;
    		else
    			contig = bio_end_sector(bio) == sector;
    
    		if (prev_bio_flags != bio_flags || !contig ||
    		    force_bio_submit ||
    		    merge_bio(tree, page, offset, page_size, bio, bio_flags) ||
    		    bio_add_page(bio, page, page_size, 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, sector, BIO_MAX_PAGES,
    			GFP_NOFS | __GFP_HIGH);
    	if (!bio)
    		return -ENOMEM;
    
    	bio_add_page(bio, page, page_size, offset);
    	bio->bi_end_io = end_io_func;
    	bio->bi_private = tree;
    	bio_set_op_attrs(bio, op, op_flags);
    	if (wbc) {
    		wbc_init_bio(wbc, bio);
    		wbc_account_io(wbc, page, page_size);
    	}
    
    	if (bio_ret)
    		*bio_ret = bio;
    	else
    		ret = submit_one_bio(bio, mirror_num, bio_flags);
    
    	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)) {
    			atomic_inc(&em->refs);
    			return em;
    		}
    
    		free_extent_map(em);
    		*em_cached = NULL;
    	}
    
    	em = get_extent(inode, page, pg_offset, start, len, 0);
    	if (em_cached && !IS_ERR_OR_NULL(em)) {
    		BUG_ON(*em_cached);
    		atomic_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, int read_flags,
    			 u64 *prev_em_start)
    {
    	struct inode *inode = page->mapping->host;
    	u64 start = page_offset(page);
    	u64 page_end = start + PAGE_SIZE - 1;
    	u64 end;
    	u64 cur = start;
    	u64 extent_offset;
    	u64 last_byte = i_size_read(inode);
    	u64 block_start;
    	u64 cur_end;
    	sector_t sector;
    	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);
    
    	end = page_end;
    	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) {
    		unsigned long pnr = (last_byte >> PAGE_SHIFT) + 1;
    		bool force_bio_submit = false;
    
    		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, GFP_NOFS);
    			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;
    			sector = em->block_start >> 9;
    		} else {
    			sector = (em->block_start + extent_offset) >> 9;
    			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->orig_start)
    			force_bio_submit = true;
    
    		if (prev_em_start)
    			*prev_em_start = em->orig_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, GFP_NOFS);
    			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;
    		}
    
    		pnr -= page->index;
    		ret = submit_extent_page(REQ_OP_READ, read_flags, tree, NULL,
    					 page, sector, disk_io_size, pg_offset,
    					 bdev, bio, pnr,
    					 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,
    					     get_extent_t *get_extent,
    					     struct extent_map **em_cached,
    					     struct bio **bio, int mirror_num,
    					     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(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], get_extent, em_cached, bio,
    			      mirror_num, bio_flags, 0, prev_em_start);
    		put_page(pages[index]);
    	}
    }
    
    static void __extent_readpages(struct extent_io_tree *tree,
    			       struct page *pages[],
    			       int nr_pages, get_extent_t *get_extent,
    			       struct extent_map **em_cached,
    			       struct bio **bio, int mirror_num,
    			       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, get_extent, em_cached,
    						  bio, mirror_num, 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, get_extent, em_cached, bio,
    					  mirror_num, 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, 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(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 page *page, 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 our fill_delalloc 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 || !tree->ops || !tree->ops->fill_delalloc)
    		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 = tree->ops->fill_delalloc(inode, page,
    					       delalloc_start,
    					       delalloc_end,
    					       &page_started,
    					       nr_written);
    		/* File system has been set read-only */
    		if (ret) {
    			SetPageError(page);
    			/* fill_delalloc should be 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,
    				 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;
    	sector_t sector;
    	struct extent_state *cached_state = NULL;
    	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(page, wbc, nr_written);
    			unlock_page(page);
    			ret = 1;
    			goto done_unlocked;
    		}
    	}
    
    	/*
    	 * we don't want to touch the inode after unlocking the page,
    	 * so we update the mapping writeback index now
    	 */
    	update_nr_written(page, 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;
    		unsigned long max_nr;
    
    		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 = epd->get_extent(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);
    		sector = (em->block_start + extent_offset) >> 9;
    		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;
    		}
    
    		max_nr = (i_size >> PAGE_SHIFT) + 1;
    
    		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, sector, iosize, pg_offset,
    					 bdev, &epd->bio, max_nr,
    					 end_bio_extent_writepage,
    					 0, 0, 0, false);
    		if (ret)
    			SetPageError(page);
    
    		cur = cur + iosize;
    		pg_offset += iosize;
    		nr++;
    	}
    done:
    	*nr_ret = nr;
    
    done_unlocked:
    
    	/* drop our reference on any cached states */
    	free_extent_state(cached_state);
    	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
     */
    static int __extent_writepage(struct page *page, struct writeback_control *wbc,
    			      void *data)
    {
    	struct inode *inode = page->mapping->host;
    	struct extent_page_data *epd = data;
    	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;
    	int write_flags = 0;
    	unsigned long nr_written = 0;
    
    	if (wbc->sync_mode == WB_SYNC_ALL)
    		write_flags = WRITE_SYNC;
    
    	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);
    	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 noinline_for_stack int
    lock_extent_buffer_for_io(struct extent_buffer *eb,
    			  struct btrfs_fs_info *fs_info,
    			  struct extent_page_data *epd)
    {
    	unsigned long i, num_pages;
    	int flush = 0;
    	int ret = 0;
    
    	if (!btrfs_try_tree_write_lock(eb)) {
    		flush = 1;
    		flush_write_bio(epd);
    		btrfs_tree_lock(eb);
    	}
    
    	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
    		btrfs_tree_unlock(eb);
    		if (!epd->sync_io)
    			return 0;
    		if (!flush) {
    			flush_write_bio(epd);
    			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(&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->start, eb->len);
    	for (i = 0; i < num_pages; i++) {
    		struct page *p = eb->pages[i];
    
    		if (!trylock_page(p)) {
    			if (!flush) {
    				flush_write_bio(epd);
    				flush = 1;
    			}
    			lock_page(p);
    		}
    	}
    
    	return ret;
    }
    
    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);
    }
    
    static void set_btree_ioerr(struct page *page)
    {
    	struct extent_buffer *eb = (struct extent_buffer *)page->private;
    	struct btrfs_inode *btree_ino = BTRFS_I(eb->fs_info->btree_inode);
    
    	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_INODE_BTREE_ERR, &btree_ino->runtime_flags);
    		break;
    	case 0:
    		set_bit(BTRFS_INODE_BTREE_LOG1_ERR, &btree_ino->runtime_flags);
    		break;
    	case 1:
    		set_bit(BTRFS_INODE_BTREE_LOG2_ERR, &btree_ino->runtime_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;
    
    	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_error ||
    		    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;
    	unsigned long i, num_pages;
    	unsigned long bio_flags = 0;
    	int write_flags = (epd->sync_io ? WRITE_SYNC : 0) | REQ_META;
    	int ret = 0;
    
    	clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
    	num_pages = num_extent_pages(eb->start, eb->len);
    	atomic_set(&eb->io_pages, num_pages);
    	if (btrfs_header_owner(eb) == BTRFS_TREE_LOG_OBJECTID)
    		bio_flags = EXTENT_BIO_TREE_LOG;
    
    	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 >> 9, PAGE_SIZE, 0, bdev,
    					 &epd->bio, -1,
    					 end_bio_extent_buffer_writepage,
    					 0, epd->bio_flags, bio_flags, false);
    		epd->bio_flags = bio_flags;
    		if (ret) {
    			set_btree_ioerr(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(p, 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,
    		.bio_flags = 0,
    	};
    	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, 0);
    	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_tag(&pvec, mapping, &index, tag,
    			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
    		unsigned i;
    
    		scanned = 1;
    		for (i = 0; i < nr_pages; i++) {
    			struct page *page = pvec.pages[i];
    
    			if (!PagePrivate(page))
    				continue;
    
    			if (!wbc->range_cyclic && page->index > end) {
    				done = 1;
    				break;
    			}
    
    			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;
    			}
    
    			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;
    	}
    	flush_write_bio(&epd);
    	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
     * @writepage: function called for each page
     * @data: data passed to 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 extent_io_tree *tree,
    			     struct address_space *mapping,
    			     struct writeback_control *wbc,
    			     writepage_t writepage, void *data,
    			     void (*flush_fn)(void *))
    {
    	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, 0);
    	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;
    	}
    	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);
    	done_index = index;
    	while (!done && !nr_to_write_done && (index <= end) &&
    	       (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
    			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
    		unsigned i;
    
    		scanned = 1;
    		for (i = 0; i < nr_pages; i++) {
    			struct page *page = pvec.pages[i];
    
    			done_index = page->index;
    			/*
    			 * At this point we hold neither mapping->tree_lock nor
    			 * lock on the page itself: 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)) {
    				flush_fn(data);
    				lock_page(page);
    			}
    
    			if (unlikely(page->mapping != mapping)) {
    				unlock_page(page);
    				continue;
    			}
    
    			if (!wbc->range_cyclic && page->index > end) {
    				done = 1;
    				unlock_page(page);
    				continue;
    			}
    
    			if (wbc->sync_mode != WB_SYNC_NONE) {
    				if (PageWriteback(page))
    					flush_fn(data);
    				wait_on_page_writeback(page);
    			}
    
    			if (PageWriteback(page) ||
    			    !clear_page_dirty_for_io(page)) {
    				unlock_page(page);
    				continue;
    			}
    
    			ret = (*writepage)(page, wbc, data);
    
    			if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
    				unlock_page(page);
    				ret = 0;
    			}
    			if (ret < 0) {
    				/*
    				 * done_index is set past this page,
    				 * so media errors will not choke
    				 * background writeout for the entire
    				 * file. This has consequences for
    				 * range_cyclic semantics (ie. it may
    				 * not be suitable for data integrity
    				 * writeout).
    				 */
    				done_index = page->index + 1;
    				done = 1;
    				break;
    			}
    
    			/*
    			 * the filesystem may choose to bump up nr_to_write.
    			 * We have to make sure to honor the new nr_to_write
    			 * at any time
    			 */
    			nr_to_write_done = wbc->nr_to_write <= 0;
    		}
    		pagevec_release(&pvec);
    		cond_resched();
    	}
    	if (!scanned && !done) {
    		/*
    		 * We hit the last page and there is more work to be done: wrap
    		 * back to the start of the file
    		 */
    		scanned = 1;
    		index = 0;
    		goto retry;
    	}
    
    	if (wbc->range_cyclic || (wbc->nr_to_write > 0 && range_whole))
    		mapping->writeback_index = done_index;
    
    	btrfs_add_delayed_iput(inode);
    	return ret;
    }
    
    static void flush_epd_write_bio(struct extent_page_data *epd)
    {
    	if (epd->bio) {
    		int ret;
    
    		bio_set_op_attrs(epd->bio, REQ_OP_WRITE,
    				 epd->sync_io ? WRITE_SYNC : 0);
    
    		ret = submit_one_bio(epd->bio, 0, epd->bio_flags);
    		BUG_ON(ret < 0); /* -ENOMEM */
    		epd->bio = NULL;
    	}
    }
    
    static noinline void flush_write_bio(void *data)
    {
    	struct extent_page_data *epd = data;
    	flush_epd_write_bio(epd);
    }
    
    int extent_write_full_page(struct extent_io_tree *tree, struct page *page,
    			  get_extent_t *get_extent,
    			  struct writeback_control *wbc)
    {
    	int ret;
    	struct extent_page_data epd = {
    		.bio = NULL,
    		.tree = tree,
    		.get_extent = get_extent,
    		.extent_locked = 0,
    		.sync_io = wbc->sync_mode == WB_SYNC_ALL,
    		.bio_flags = 0,
    	};
    
    	ret = __extent_writepage(page, wbc, &epd);
    
    	flush_epd_write_bio(&epd);
    	return ret;
    }
    
    int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode,
    			      u64 start, u64 end, get_extent_t *get_extent,
    			      int mode)
    {
    	int ret = 0;
    	struct address_space *mapping = inode->i_mapping;
    	struct page *page;
    	unsigned long nr_pages = (end - start + PAGE_SIZE) >>
    		PAGE_SHIFT;
    
    	struct extent_page_data epd = {
    		.bio = NULL,
    		.tree = tree,
    		.get_extent = get_extent,
    		.extent_locked = 1,
    		.sync_io = mode == WB_SYNC_ALL,
    		.bio_flags = 0,
    	};
    	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_epd_write_bio(&epd);
    	return ret;
    }
    
    int extent_writepages(struct extent_io_tree *tree,
    		      struct address_space *mapping,
    		      get_extent_t *get_extent,
    		      struct writeback_control *wbc)
    {
    	int ret = 0;
    	struct extent_page_data epd = {
    		.bio = NULL,
    		.tree = tree,
    		.get_extent = get_extent,
    		.extent_locked = 0,
    		.sync_io = wbc->sync_mode == WB_SYNC_ALL,
    		.bio_flags = 0,
    	};
    
    	ret = extent_write_cache_pages(tree, mapping, wbc,
    				       __extent_writepage, &epd,
    				       flush_write_bio);
    	flush_epd_write_bio(&epd);
    	return ret;
    }
    
    int extent_readpages(struct extent_io_tree *tree,
    		     struct address_space *mapping,
    		     struct list_head *pages, unsigned nr_pages,
    		     get_extent_t get_extent)
    {
    	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;
    	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, get_extent, &em_cached,
    				   &bio, 0, &bio_flags, &prev_em_start);
    		nr = 0;
    	}
    	if (nr)
    		__extent_readpages(tree, pagepool, nr, get_extent, &em_cached,
    				   &bio, 0, &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, GFP_NOFS);
    	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_map_tree *map,
    				    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 {
    		if ((mask & GFP_NOFS) == GFP_NOFS)
    			mask = GFP_NOFS;
    		/*
    		 * 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);
    
    		/* 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 extent_map_tree *map,
    			       struct extent_io_tree *tree, struct page *page,
    			       gfp_t mask)
    {
    	struct extent_map *em;
    	u64 start = page_offset(page);
    	u64 end = start + PAGE_SIZE - 1;
    
    	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)) {
    				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);
    		}
    	}
    	return try_release_extent_state(map, 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,
    						get_extent_t *get_extent)
    {
    	u64 sectorsize = BTRFS_I(inode)->root->sectorsize;
    	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 = get_extent(inode, NULL, 0, offset, len, 0);
    		if (IS_ERR_OR_NULL(em))
    			return em;
    
    		/* if this isn't a hole return it */
    		if (!test_bit(EXTENT_FLAG_VACANCY, &em->flags) &&
    		    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;
    }
    
    int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
    		__u64 start, __u64 len, get_extent_t *get_extent)
    {
    	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;
    	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_I(inode)->root->sectorsize);
    	len = round_up(max, BTRFS_I(inode)->root->sectorsize) - start;
    
    	/*
    	 * lookup the last file extent.  We're not using i_size here
    	 * because there might be preallocation past i_size
    	 */
    	ret = btrfs_lookup_file_extent(NULL, root, path, btrfs_ino(inode), -1,
    				       0);
    	if (ret < 0) {
    		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(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,
    				   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;
    		disko = 0;
    		flags = 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) {
    			struct btrfs_trans_handle *trans;
    
    			u64 bytenr = em->block_start -
    				(em->start - em->orig_start);
    
    			disko = em->block_start + offset_in_extent;
    
    			/*
    			 * We need a trans handle to get delayed refs
    			 */
    			trans = btrfs_join_transaction(root);
    			/*
    			 * It's OK if we can't start a trans we can still check
    			 * from commit_root
    			 */
    			if (IS_ERR(trans))
    				trans = NULL;
    
    			/*
    			 * 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(trans, root->fs_info,
    						 root->objectid,
    						 btrfs_ino(inode), bytenr);
    			if (trans)
    				btrfs_end_transaction(trans, root);
    			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,
    					   get_extent);
    		if (IS_ERR(em)) {
    			ret = PTR_ERR(em);
    			goto out;
    		}
    		if (!em) {
    			flags |= FIEMAP_EXTENT_LAST;
    			end = 1;
    		}
    		ret = fiemap_fill_next_extent(fieinfo, em_start, disko,
    					      em_len, flags);
    		if (ret) {
    			if (ret == 1)
    				ret = 0;
    			goto out_free;
    		}
    	}
    out_free:
    	free_extent_map(em);
    out:
    	btrfs_free_path(path);
    	unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, start + len - 1,
    			     &cached_state, GFP_NOFS);
    	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));
    }
    
    /*
     * Helper for releasing extent buffer page.
     */
    static void btrfs_release_extent_buffer_page(struct extent_buffer *eb)
    {
    	unsigned long index;
    	struct page *page;
    	int mapped = !test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);
    
    	BUG_ON(extent_buffer_under_io(eb));
    
    	index = num_extent_pages(eb->start, eb->len);
    	if (index == 0)
    		return;
    
    	do {
    		index--;
    		page = eb->pages[index];
    		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);
    	} while (index != 0);
    }
    
    /*
     * Helper for releasing the extent buffer.
     */
    static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
    {
    	btrfs_release_extent_buffer_page(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)
    {
    	unsigned long i;
    	struct page *p;
    	struct extent_buffer *new;
    	unsigned long num_pages = num_extent_pages(src->start, src->len);
    
    	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_extent_buffer(new, src, 0, 0, src->len);
    	set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags);
    	set_bit(EXTENT_BUFFER_DUMMY, &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;
    	unsigned long num_pages;
    	unsigned long i;
    
    	num_pages = num_extent_pages(start, len);
    
    	eb = __alloc_extent_buffer(fs_info, start, len);
    	if (!eb)
    		return NULL;
    
    	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_DUMMY, &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, u32 nodesize)
    {
    	unsigned long len;
    
    	if (!fs_info) {
    		/*
    		 * Called only from tests that don't always have a fs_info
    		 * available
    		 */
    		len = nodesize;
    	} else {
    		len = fs_info->tree_root->nodesize;
    	}
    
    	return __alloc_dummy_extent_buffer(fs_info, start, len);
    }
    
    static void check_buffer_tree_ref(struct extent_buffer *eb)
    {
    	int refs;
    	/* the ref bit is tricky.  We have to make sure it is set
    	 * if we have the buffer dirty.   Otherwise the
    	 * code to free a buffer can end up dropping a dirty
    	 * page
    	 *
    	 * Once the ref bit is set, it won't go away while the
    	 * buffer is dirty or in writeback, and it also won't
    	 * go away while we have the reference count on the
    	 * eb bumped.
    	 *
    	 * We can't just set the ref bit without bumping the
    	 * ref on the eb because free_extent_buffer might
    	 * see the ref bit and try to clear it.  If this happens
    	 * free_extent_buffer might end up dropping our original
    	 * ref by mistake and freeing the page before we are able
    	 * to add one more ref.
    	 *
    	 * So bump the ref count first, then set the bit.  If someone
    	 * beat us to it, drop the ref we added.
    	 */
    	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)
    {
    	unsigned long num_pages, i;
    
    	check_buffer_tree_ref(eb);
    
    	num_pages = num_extent_pages(eb->start, eb->len);
    	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, u32 nodesize)
    {
    	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, nodesize);
    	if (!eb)
    		return NULL;
    	eb->fs_info = fs_info;
    again:
    	ret = radix_tree_preload(GFP_NOFS);
    	if (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->tree_root->nodesize;
    	unsigned long num_pages = num_extent_pages(start, len);
    	unsigned long 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->tree_root->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);
    
    	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;
    
    		/*
    		 * see below about how we avoid a nasty race with release page
    		 * and why we unlock later
    		 */
    	}
    	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);
    
    	/*
    	 * there is a race where release page may have
    	 * tried to find this extent buffer in the radix
    	 * but failed.  It will tell the VM it is safe to
    	 * reclaim the, and it will clear the page private bit.
    	 * We must make sure to set the page private bit properly
    	 * after the extent buffer is in the radix tree so
    	 * it doesn't get lost
    	 */
    	SetPageChecked(eb->pages[0]);
    	for (i = 1; i < num_pages; i++) {
    		p = eb->pages[i];
    		ClearPageChecked(p);
    		unlock_page(p);
    	}
    	unlock_page(eb->pages[0]);
    	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);
    }
    
    /* Expects to have eb->eb_lock already held */
    static int release_extent_buffer(struct extent_buffer *eb)
    {
    	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_page(eb);
    #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
    		if (unlikely(test_bit(EXTENT_BUFFER_DUMMY, &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_DUMMY, &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)
    {
    	unsigned long i;
    	unsigned long num_pages;
    	struct page *page;
    
    	num_pages = num_extent_pages(eb->start, eb->len);
    
    	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);
    		spin_lock_irq(&page->mapping->tree_lock);
    		if (!PageDirty(page)) {
    			radix_tree_tag_clear(&page->mapping->page_tree,
    						page_index(page),
    						PAGECACHE_TAG_DIRTY);
    		}
    		spin_unlock_irq(&page->mapping->tree_lock);
    		ClearPageError(page);
    		unlock_page(page);
    	}
    	WARN_ON(atomic_read(&eb->refs) == 0);
    }
    
    int set_extent_buffer_dirty(struct extent_buffer *eb)
    {
    	unsigned long i;
    	unsigned long 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->start, eb->len);
    	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)
    {
    	unsigned long i;
    	struct page *page;
    	unsigned long num_pages;
    
    	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
    	num_pages = num_extent_pages(eb->start, eb->len);
    	for (i = 0; i < num_pages; i++) {
    		page = eb->pages[i];
    		if (page)
    			ClearPageUptodate(page);
    	}
    }
    
    void set_extent_buffer_uptodate(struct extent_buffer *eb)
    {
    	unsigned long i;
    	struct page *page;
    	unsigned long num_pages;
    
    	set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
    	num_pages = num_extent_pages(eb->start, eb->len);
    	for (i = 0; i < num_pages; i++) {
    		page = eb->pages[i];
    		SetPageUptodate(page);
    	}
    }
    
    int extent_buffer_uptodate(struct extent_buffer *eb)
    {
    	return test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
    }
    
    int read_extent_buffer_pages(struct extent_io_tree *tree,
    			     struct extent_buffer *eb, u64 start, int wait,
    			     get_extent_t *get_extent, int mirror_num)
    {
    	unsigned long i;
    	unsigned long start_i;
    	struct page *page;
    	int err;
    	int ret = 0;
    	int locked_pages = 0;
    	int all_uptodate = 1;
    	unsigned long 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;
    
    	if (start) {
    		WARN_ON(start < eb->start);
    		start_i = (start >> PAGE_SHIFT) -
    			(eb->start >> PAGE_SHIFT);
    	} else {
    		start_i = 0;
    	}
    
    	num_pages = num_extent_pages(eb->start, eb->len);
    	for (i = start_i; 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++;
    		if (!PageUptodate(page)) {
    			num_reads++;
    			all_uptodate = 0;
    		}
    	}
    	if (all_uptodate) {
    		if (start_i == 0)
    			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);
    	for (i = start_i; 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,
    						      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 = start_i; i < num_pages; i++) {
    		page = eb->pages[i];
    		wait_on_page_locked(page);
    		if (!PageUptodate(page))
    			ret = -EIO;
    	}
    
    	return ret;
    
    unlock_exit:
    	i = start_i;
    	while (locked_pages > 0) {
    		page = eb->pages[i];
    		i++;
    		unlock_page(page);
    		locked_pages--;
    	}
    	return ret;
    }
    
    void read_extent_buffer(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;
    
    	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);
    		memcpy(dst, kaddr + offset, cur);
    
    		dst += cur;
    		len -= cur;
    		offset = 0;
    		i++;
    	}
    }
    
    int read_extent_buffer_to_user(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 (copy_to_user(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(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 (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;
    	}
    
    	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;
    	}
    
    	p = eb->pages[i];
    	kaddr = page_address(p);
    	*map = kaddr + offset;
    	*map_len = PAGE_SIZE - offset;
    	return 0;
    }
    
    int memcmp_extent_buffer(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(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 memset_extent_buffer(struct extent_buffer *eb, char c,
    			  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, c, cur);
    
    		len -= cur;
    		offset = 0;
    		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++;
    	}
    }
    
    /*
     * The extent buffer bitmap operations are done with byte granularity because
     * bitmap items are not guaranteed to be aligned to a word and therefore a
     * single word in a bitmap may straddle two pages in the extent buffer.
     */
    #define BIT_BYTE(nr) ((nr) / BITS_PER_BYTE)
    #define BYTE_MASK ((1 << BITS_PER_BYTE) - 1)
    #define BITMAP_FIRST_BYTE_MASK(start) \
    	((BYTE_MASK << ((start) & (BITS_PER_BYTE - 1))) & BYTE_MASK)
    #define BITMAP_LAST_BYTE_MASK(nbits) \
    	(BYTE_MASK >> (-(nbits) & (BITS_PER_BYTE - 1)))
    
    /*
     * 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)
    {
    	char *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)
    {
    	char *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);
    	unsigned int 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 = ~0U;
    		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)
    {
    	char *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);
    	unsigned int 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 = ~0U;
    		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)
    {
    	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(dst->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(dst->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)
    {
    	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(dst->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(dst->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);
    }