fs/btrfs/extent_map.c

#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/bio.h>
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/pagemap.h>
#include <linux/page-flags.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/blkdev.h>
#include "extent_map.h"

/* temporary define until extent_map moves out of btrfs */
struct kmem_cache *btrfs_cache_create(const char *name, size_t size,
				       unsigned long extra_flags,
				       void (*ctor)(void *, struct kmem_cache *,
						    unsigned long));

static struct kmem_cache *extent_map_cache;
static struct kmem_cache *extent_state_cache;

struct tree_entry {
	u64 start;
	u64 end;
	int in_tree;
	struct rb_node rb_node;
};

/* bits for the extent state */
#define EXTENT_DIRTY 1
#define EXTENT_WRITEBACK (1 << 1)
#define EXTENT_UPTODATE (1 << 2)
#define EXTENT_LOCKED (1 << 3)
#define EXTENT_NEW (1 << 4)
#define EXTENT_DELALLOC (1 << 5)

#define EXTENT_IOBITS (EXTENT_LOCKED | EXTENT_WRITEBACK)

void __init extent_map_init(void)
{
	extent_map_cache = btrfs_cache_create("extent_map",
					    sizeof(struct extent_map),
					    SLAB_DESTROY_BY_RCU,
					    NULL);
	extent_state_cache = btrfs_cache_create("extent_state",
					    sizeof(struct extent_state),
					    SLAB_DESTROY_BY_RCU,
					    NULL);
}

void __exit extent_map_exit(void)
{
	if (extent_map_cache)
		kmem_cache_destroy(extent_map_cache);
	if (extent_state_cache)
		kmem_cache_destroy(extent_state_cache);
}

void extent_map_tree_init(struct extent_map_tree *tree,
			  struct address_space *mapping, gfp_t mask)
{
	tree->map.rb_node = NULL;
	tree->state.rb_node = NULL;
	tree->ops = NULL;
	rwlock_init(&tree->lock);
	tree->mapping = mapping;
}
EXPORT_SYMBOL(extent_map_tree_init);

struct extent_map *alloc_extent_map(gfp_t mask)
{
	struct extent_map *em;
	em = kmem_cache_alloc(extent_map_cache, mask);
	if (!em || IS_ERR(em))
		return em;
	em->in_tree = 0;
	atomic_set(&em->refs, 1);
	return em;
}
EXPORT_SYMBOL(alloc_extent_map);

void free_extent_map(struct extent_map *em)
{
	if (!em)
		return;
	if (atomic_dec_and_test(&em->refs)) {
		WARN_ON(em->in_tree);
		kmem_cache_free(extent_map_cache, em);
	}
}
EXPORT_SYMBOL(free_extent_map);


struct extent_state *alloc_extent_state(gfp_t mask)
{
	struct extent_state *state;
	state = kmem_cache_alloc(extent_state_cache, mask);
	if (!state || IS_ERR(state))
		return state;
	state->state = 0;
	state->in_tree = 0;
	state->private = 0;
	atomic_set(&state->refs, 1);
	init_waitqueue_head(&state->wq);
	return state;
}
EXPORT_SYMBOL(alloc_extent_state);

void free_extent_state(struct extent_state *state)
{
	if (!state)
		return;
	if (atomic_dec_and_test(&state->refs)) {
		WARN_ON(state->in_tree);
		kmem_cache_free(extent_state_cache, state);
	}
}
EXPORT_SYMBOL(free_extent_state);

static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
				   struct rb_node *node)
{
	struct rb_node ** p = &root->rb_node;
	struct rb_node * parent = NULL;
	struct tree_entry *entry;

	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;
	}

	entry = rb_entry(node, struct tree_entry, rb_node);
	entry->in_tree = 1;
	rb_link_node(node, parent, p);
	rb_insert_color(node, root);
	return NULL;
}

static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
				   struct rb_node **prev_ret)
{
	struct rb_node * n = root->rb_node;
	struct rb_node *prev = NULL;
	struct tree_entry *entry;
	struct tree_entry *prev_entry = NULL;

	while(n) {
		entry = rb_entry(n, struct tree_entry, rb_node);
		prev = n;
		prev_entry = entry;

		if (offset < entry->start)
			n = n->rb_left;
		else if (offset > entry->end)
			n = n->rb_right;
		else
			return n;
	}
	if (!prev_ret)
		return NULL;
	while(prev && offset > prev_entry->end) {
		prev = rb_next(prev);
		prev_entry = rb_entry(prev, struct tree_entry, rb_node);
	}
	*prev_ret = prev;
	return NULL;
}

static inline struct rb_node *tree_search(struct rb_root *root, u64 offset)
{
	struct rb_node *prev;
	struct rb_node *ret;
	ret = __tree_search(root, offset, &prev);
	if (!ret)
		return prev;
	return ret;
}

static int tree_delete(struct rb_root *root, u64 offset)
{
	struct rb_node *node;
	struct tree_entry *entry;

	node = __tree_search(root, offset, NULL);
	if (!node)
		return -ENOENT;
	entry = rb_entry(node, struct tree_entry, rb_node);
	entry->in_tree = 0;
	rb_erase(node, root);
	return 0;
}

/*
 * add_extent_mapping tries a simple backward merge with existing
 * mappings.  The extent_map struct passed in will be inserted into
 * the tree directly (no copies made, just a reference taken).
 */
int add_extent_mapping(struct extent_map_tree *tree,
		       struct extent_map *em)
{
	int ret = 0;
	struct extent_map *prev = NULL;
	struct rb_node *rb;

	write_lock_irq(&tree->lock);
	rb = tree_insert(&tree->map, em->end, &em->rb_node);
	if (rb) {
		prev = rb_entry(rb, struct extent_map, rb_node);
		printk("found extent map %Lu %Lu on insert of %Lu %Lu\n", prev->start, prev->end, em->start, em->end);
		ret = -EEXIST;
		goto out;
	}
	atomic_inc(&em->refs);
	if (em->start != 0) {
		rb = rb_prev(&em->rb_node);
		if (rb)
			prev = rb_entry(rb, struct extent_map, rb_node);
		if (prev && prev->end + 1 == em->start &&
		    ((em->block_start == 0 && prev->block_start == 0) ||
			     (em->block_start == prev->block_end + 1))) {
			em->start = prev->start;
			em->block_start = prev->block_start;
			rb_erase(&prev->rb_node, &tree->map);
			prev->in_tree = 0;
			free_extent_map(prev);
		}
	 }
out:
	write_unlock_irq(&tree->lock);
	return ret;
}
EXPORT_SYMBOL(add_extent_mapping);

/*
 * lookup_extent_mapping returns the first extent_map struct in the
 * tree that intersects the [start, end] (inclusive) range.  There may
 * be additional objects in the tree that intersect, so check the object
 * returned carefully to make sure you don't need additional lookups.
 */
struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
					 u64 start, u64 end)
{
	struct extent_map *em;
	struct rb_node *rb_node;

	read_lock_irq(&tree->lock);
	rb_node = tree_search(&tree->map, start);
	if (!rb_node) {
		em = NULL;
		goto out;
	}
	if (IS_ERR(rb_node)) {
		em = ERR_PTR(PTR_ERR(rb_node));
		goto out;
	}
	em = rb_entry(rb_node, struct extent_map, rb_node);
	if (em->end < start || em->start > end) {
		em = NULL;
		goto out;
	}
	atomic_inc(&em->refs);
out:
	read_unlock_irq(&tree->lock);
	return em;
}
EXPORT_SYMBOL(lookup_extent_mapping);

/*
 * removes an extent_map struct from the tree.  No reference counts are
 * dropped, and no checks are done to  see if the range is in use
 */
int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
{
	int ret;

	write_lock_irq(&tree->lock);
	ret = tree_delete(&tree->map, em->end);
	write_unlock_irq(&tree->lock);
	return ret;
}
EXPORT_SYMBOL(remove_extent_mapping);

/*
 * 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 int merge_state(struct extent_map_tree *tree,
		       struct extent_state *state)
{
	struct extent_state *other;
	struct rb_node *other_node;

	if (state->state & EXTENT_IOBITS)
		return 0;

	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) {
			state->start = other->start;
			other->in_tree = 0;
			rb_erase(&other->rb_node, &tree->state);
			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) {
			other->start = state->start;
			state->in_tree = 0;
			rb_erase(&state->rb_node, &tree->state);
			free_extent_state(state);
		}
	}
	return 0;
}

/*
 * 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_map_tree *tree,
			struct extent_state *state, u64 start, u64 end,
			int bits)
{
	struct rb_node *node;

	if (end < start) {
		printk("end < start %Lu %Lu\n", end, start);
		WARN_ON(1);
	}
	state->state |= bits;
	state->start = start;
	state->end = end;
	if ((end & 4095) == 0) {
		printk("insert state %Lu %Lu strange end\n", start, end);
		WARN_ON(1);
	}
	node = tree_insert(&tree->state, end, &state->rb_node);
	if (node) {
		struct extent_state *found;
		found = rb_entry(node, struct extent_state, rb_node);
		printk("found node %Lu %Lu on insert of %Lu %Lu\n", found->start, found->end, start, end);
		free_extent_state(state);
		return -EEXIST;
	}
	merge_state(tree, state);
	return 0;
}

/*
 * 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_map_tree *tree, struct extent_state *orig,
		       struct extent_state *prealloc, u64 split)
{
	struct rb_node *node;
	prealloc->start = orig->start;
	prealloc->end = split - 1;
	prealloc->state = orig->state;
	orig->start = split;
	if ((prealloc->end & 4095) == 0) {
		printk("insert state %Lu %Lu strange end\n", prealloc->start,
		       prealloc->end);
		WARN_ON(1);
	}
	node = tree_insert(&tree->state, prealloc->end, &prealloc->rb_node);
	if (node) {
		struct extent_state *found;
		found = rb_entry(node, struct extent_state, rb_node);
		printk("found node %Lu %Lu on insert of %Lu %Lu\n", found->start, found->end, prealloc->start, prealloc->end);
		free_extent_state(prealloc);
		return -EEXIST;
	}
	return 0;
}

/*
 * utility function to clear some bits in an extent state struct.
 * it will optionally wake up any one waiting on this state (wake == 1), or
 * forcibly remove the state from the tree (delete == 1).
 *
 * If no bits are set on the state struct after clearing things, the
 * struct is freed and removed from the tree
 */
static int clear_state_bit(struct extent_map_tree *tree,
			    struct extent_state *state, int bits, int wake,
			    int delete)
{
	int ret = state->state & bits;
	state->state &= ~bits;
	if (wake)
		wake_up(&state->wq);
	if (delete || state->state == 0) {
		if (state->in_tree) {
			rb_erase(&state->rb_node, &tree->state);
			state->in_tree = 0;
			free_extent_state(state);
		} else {
			WARN_ON(1);
		}
	} else {
		merge_state(tree, state);
	}
	return ret;
}

/*
 * 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 error, > 0 if any of the
 * bits were already set, or zero if none of the bits were already set.
 */
int clear_extent_bit(struct extent_map_tree *tree, u64 start, u64 end,
		     int bits, int wake, int delete, gfp_t mask)
{
	struct extent_state *state;
	struct extent_state *prealloc = NULL;
	struct rb_node *node;
	unsigned long flags;
	int err;
	int set = 0;

again:
	if (!prealloc && (mask & __GFP_WAIT)) {
		prealloc = alloc_extent_state(mask);
		if (!prealloc)
			return -ENOMEM;
	}

	write_lock_irqsave(&tree->lock, flags);
	/*
	 * this search will find the extents that end after
	 * our range starts
	 */
	node = tree_search(&tree->state, start);
	if (!node)
		goto out;
	state = rb_entry(node, struct extent_state, rb_node);
	if (state->start > end)
		goto out;
	WARN_ON(state->end < start);

	/*
	 *     | ---- 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) {
		err = split_state(tree, state, prealloc, start);
		BUG_ON(err == -EEXIST);
		prealloc = NULL;
		if (err)
			goto out;
		if (state->end <= end) {
			start = state->end + 1;
			set |= clear_state_bit(tree, state, bits,
					wake, delete);
		} else {
			start = state->start;
		}
		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) {
		err = split_state(tree, state, prealloc, end + 1);
		BUG_ON(err == -EEXIST);

		if (wake)
			wake_up(&state->wq);
		set |= clear_state_bit(tree, prealloc, bits,
				       wake, delete);
		prealloc = NULL;
		goto out;
	}

	start = state->end + 1;
	set |= clear_state_bit(tree, state, bits, wake, delete);
	goto search_again;

out:
	write_unlock_irqrestore(&tree->lock, flags);
	if (prealloc)
		free_extent_state(prealloc);

	return set;

search_again:
	if (start >= end)
		goto out;
	write_unlock_irqrestore(&tree->lock, flags);
	if (mask & __GFP_WAIT)
		cond_resched();
	goto again;
}
EXPORT_SYMBOL(clear_extent_bit);

static int wait_on_state(struct extent_map_tree *tree,
			 struct extent_state *state)
{
	DEFINE_WAIT(wait);
	prepare_to_wait(&state->wq, &wait, TASK_UNINTERRUPTIBLE);
	read_unlock_irq(&tree->lock);
	schedule();
	read_lock_irq(&tree->lock);
	finish_wait(&state->wq, &wait);
	return 0;
}

/*
 * 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
 */
int wait_extent_bit(struct extent_map_tree *tree, u64 start, u64 end, int bits)
{
	struct extent_state *state;
	struct rb_node *node;

	read_lock_irq(&tree->lock);
again:
	while (1) {
		/*
		 * this search will find all the extents that end after
		 * our range starts
		 */
		node = tree_search(&tree->state, start);
		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 (need_resched()) {
			read_unlock_irq(&tree->lock);
			cond_resched();
			read_lock_irq(&tree->lock);
		}
	}
out:
	read_unlock_irq(&tree->lock);
	return 0;
}
EXPORT_SYMBOL(wait_extent_bit);

/*
 * 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 'exclusive' == 1, this will fail with -EEXIST if some part of the
 * range already has the desired bits set.  The start of the existing
 * range is returned in failed_start in this case.
 *
 * [start, end] is inclusive
 * This takes the tree lock.
 */
int set_extent_bit(struct extent_map_tree *tree, u64 start, u64 end, int bits,
		   int exclusive, u64 *failed_start, gfp_t mask)
{
	struct extent_state *state;
	struct extent_state *prealloc = NULL;
	struct rb_node *node;
	unsigned long flags;
	int err = 0;
	int set;
	u64 last_start;
	u64 last_end;
again:
	if (!prealloc && (mask & __GFP_WAIT)) {
		prealloc = alloc_extent_state(mask);
		if (!prealloc)
			return -ENOMEM;
	}

	write_lock_irqsave(&tree->lock, flags);
	/*
	 * this search will find all the extents that end after
	 * our range starts.
	 */
	node = tree_search(&tree->state, start);
	if (!node) {
		err = insert_state(tree, prealloc, start, end, bits);
		prealloc = NULL;
		BUG_ON(err == -EEXIST);
		goto out;
	}

	state = rb_entry(node, struct extent_state, rb_node);
	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->state & bits;
		if (set && exclusive) {
			*failed_start = state->start;
			err = -EEXIST;
			goto out;
		}
		state->state |= bits;
		start = state->end + 1;
		merge_state(tree, state);
		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) {
		set = state->state & bits;
		if (exclusive && set) {
			*failed_start = start;
			err = -EEXIST;
			goto out;
		}
		err = split_state(tree, state, prealloc, start);
		BUG_ON(err == -EEXIST);
		prealloc = NULL;
		if (err)
			goto out;
		if (state->end <= end) {
			state->state |= bits;
			start = state->end + 1;
			merge_state(tree, state);
		} else {
			start = state->start;
		}
		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;
		err = insert_state(tree, prealloc, start, this_end,
				   bits);
		prealloc = NULL;
		BUG_ON(err == -EEXIST);
		if (err)
			goto out;
		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) {
		set = state->state & bits;
		if (exclusive && set) {
			*failed_start = start;
			err = -EEXIST;
			goto out;
		}
		err = split_state(tree, state, prealloc, end + 1);
		BUG_ON(err == -EEXIST);

		prealloc->state |= bits;
		merge_state(tree, prealloc);
		prealloc = NULL;
		goto out;
	}

	goto search_again;

out:
	write_unlock_irqrestore(&tree->lock, flags);
	if (prealloc)
		free_extent_state(prealloc);

	return err;

search_again:
	if (start > end)
		goto out;
	write_unlock_irqrestore(&tree->lock, flags);
	if (mask & __GFP_WAIT)
		cond_resched();
	goto again;
}
EXPORT_SYMBOL(set_extent_bit);

/* wrappers around set/clear extent bit */
int set_extent_dirty(struct extent_map_tree *tree, u64 start, u64 end,
		     gfp_t mask)
{
	return set_extent_bit(tree, start, end, EXTENT_DIRTY, 0, NULL,
			      mask);
}
EXPORT_SYMBOL(set_extent_dirty);

int set_extent_delalloc(struct extent_map_tree *tree, u64 start, u64 end,
		     gfp_t mask)
{
	return set_extent_bit(tree, start, end,
			      EXTENT_DELALLOC | EXTENT_DIRTY, 0, NULL,
			      mask);
}
EXPORT_SYMBOL(set_extent_delalloc);

int clear_extent_dirty(struct extent_map_tree *tree, u64 start, u64 end,
		       gfp_t mask)
{
	return clear_extent_bit(tree, start, end,
				EXTENT_DIRTY | EXTENT_DELALLOC, 0, 0, mask);
}
EXPORT_SYMBOL(clear_extent_dirty);

int set_extent_new(struct extent_map_tree *tree, u64 start, u64 end,
		     gfp_t mask)
{
	return set_extent_bit(tree, start, end, EXTENT_NEW, 0, NULL,
			      mask);
}
EXPORT_SYMBOL(set_extent_new);

int clear_extent_new(struct extent_map_tree *tree, u64 start, u64 end,
		       gfp_t mask)
{
	return clear_extent_bit(tree, start, end, EXTENT_NEW, 0, 0, mask);
}
EXPORT_SYMBOL(clear_extent_new);

int set_extent_uptodate(struct extent_map_tree *tree, u64 start, u64 end,
			gfp_t mask)
{
	return set_extent_bit(tree, start, end, EXTENT_UPTODATE, 0, NULL,
			      mask);
}
EXPORT_SYMBOL(set_extent_uptodate);

int clear_extent_uptodate(struct extent_map_tree *tree, u64 start, u64 end,
			  gfp_t mask)
{
	return clear_extent_bit(tree, start, end, EXTENT_UPTODATE, 0, 0, mask);
}
EXPORT_SYMBOL(clear_extent_uptodate);

int set_extent_writeback(struct extent_map_tree *tree, u64 start, u64 end,
			 gfp_t mask)
{
	return set_extent_bit(tree, start, end, EXTENT_WRITEBACK,
			      0, NULL, mask);
}
EXPORT_SYMBOL(set_extent_writeback);

int clear_extent_writeback(struct extent_map_tree *tree, u64 start, u64 end,
			   gfp_t mask)
{
	return clear_extent_bit(tree, start, end, EXTENT_WRITEBACK, 1, 0, mask);
}
EXPORT_SYMBOL(clear_extent_writeback);

int wait_on_extent_writeback(struct extent_map_tree *tree, u64 start, u64 end)
{
	return wait_extent_bit(tree, start, end, EXTENT_WRITEBACK);
}
EXPORT_SYMBOL(wait_on_extent_writeback);

/*
 * locks a range in ascending order, waiting for any locked regions
 * it hits on the way.  [start,end] are inclusive, and this will sleep.
 */
int lock_extent(struct extent_map_tree *tree, u64 start, u64 end, gfp_t mask)
{
	int err;
	u64 failed_start;
	while (1) {
		err = set_extent_bit(tree, start, end, EXTENT_LOCKED, 1,
				     &failed_start, mask);
		if (err == -EEXIST && (mask & __GFP_WAIT)) {
			wait_extent_bit(tree, failed_start, end, EXTENT_LOCKED);
			start = failed_start;
		} else {
			break;
		}
		WARN_ON(start > end);
	}
	return err;
}
EXPORT_SYMBOL(lock_extent);

int unlock_extent(struct extent_map_tree *tree, u64 start, u64 end,
		  gfp_t mask)
{
	return clear_extent_bit(tree, start, end, EXTENT_LOCKED, 1, 0, mask);
}
EXPORT_SYMBOL(unlock_extent);

/*
 * helper function to set pages and extents in the tree dirty
 */
int set_range_dirty(struct extent_map_tree *tree, u64 start, u64 end)
{
	unsigned long index = start >> PAGE_CACHE_SHIFT;
	unsigned long end_index = end >> PAGE_CACHE_SHIFT;
	struct page *page;

	while (index <= end_index) {
		page = find_get_page(tree->mapping, index);
		BUG_ON(!page);
		__set_page_dirty_nobuffers(page);
		page_cache_release(page);
		index++;
	}
	set_extent_dirty(tree, start, end, GFP_NOFS);
	return 0;
}
EXPORT_SYMBOL(set_range_dirty);

/*
 * helper function to set both pages and extents in the tree writeback
 */
int set_range_writeback(struct extent_map_tree *tree, u64 start, u64 end)
{
	unsigned long index = start >> PAGE_CACHE_SHIFT;
	unsigned long end_index = end >> PAGE_CACHE_SHIFT;
	struct page *page;

	while (index <= end_index) {
		page = find_get_page(tree->mapping, index);
		BUG_ON(!page);
		set_page_writeback(page);
		page_cache_release(page);
		index++;
	}
	set_extent_writeback(tree, start, end, GFP_NOFS);
	return 0;
}
EXPORT_SYMBOL(set_range_writeback);

u64 find_lock_delalloc_range(struct extent_map_tree *tree,
			     u64 start, u64 lock_start, u64 *end, u64 max_bytes)
{
	struct rb_node *node;
	struct extent_state *state;
	u64 cur_start = start;
	u64 found = 0;
	u64 total_bytes = 0;

	write_lock_irq(&tree->lock);
	/*
	 * this search will find all the extents that end after
	 * our range starts.
	 */
search_again:
	node = tree_search(&tree->state, cur_start);
	if (!node || IS_ERR(node)) {
		goto out;
	}

	while(1) {
		state = rb_entry(node, struct extent_state, rb_node);
		if (state->start != cur_start) {
			goto out;
		}
		if (!(state->state & EXTENT_DELALLOC)) {
			goto out;
		}
		if (state->start >= lock_start) {
			if (state->state & EXTENT_LOCKED) {
				DEFINE_WAIT(wait);
				atomic_inc(&state->refs);
				write_unlock_irq(&tree->lock);
				schedule();
				write_lock_irq(&tree->lock);
				finish_wait(&state->wq, &wait);
				free_extent_state(state);
				goto search_again;
			}
			state->state |= EXTENT_LOCKED;
		}
		found++;
		*end = state->end;
		cur_start = state->end + 1;
		node = rb_next(node);
		if (!node)
			break;
		total_bytes = state->end - state->start + 1;
		if (total_bytes >= max_bytes)
			break;
	}
out:
	write_unlock_irq(&tree->lock);
	return found;
}

/*
 * helper function to lock both pages and extents in the tree.
 * pages must be locked first.
 */
int lock_range(struct extent_map_tree *tree, u64 start, u64 end)
{
	unsigned long index = start >> PAGE_CACHE_SHIFT;
	unsigned long end_index = end >> PAGE_CACHE_SHIFT;
	struct page *page;
	int err;

	while (index <= end_index) {
		page = grab_cache_page(tree->mapping, index);
		if (!page) {
			err = -ENOMEM;
			goto failed;
		}
		if (IS_ERR(page)) {
			err = PTR_ERR(page);
			goto failed;
		}
		index++;
	}
	lock_extent(tree, start, end, GFP_NOFS);
	return 0;

failed:
	/*
	 * we failed above in getting the page at 'index', so we undo here
	 * up to but not including the page at 'index'
	 */
	end_index = index;
	index = start >> PAGE_CACHE_SHIFT;
	while (index < end_index) {
		page = find_get_page(tree->mapping, index);
		unlock_page(page);
		page_cache_release(page);
		index++;
	}
	return err;
}
EXPORT_SYMBOL(lock_range);

/*
 * helper function to unlock both pages and extents in the tree.
 */
int unlock_range(struct extent_map_tree *tree, u64 start, u64 end)
{
	unsigned long index = start >> PAGE_CACHE_SHIFT;
	unsigned long end_index = end >> PAGE_CACHE_SHIFT;
	struct page *page;

	while (index <= end_index) {
		page = find_get_page(tree->mapping, index);
		unlock_page(page);
		page_cache_release(page);
		index++;
	}
	unlock_extent(tree, start, end, GFP_NOFS);
	return 0;
}
EXPORT_SYMBOL(unlock_range);

int set_state_private(struct extent_map_tree *tree, u64 start, u64 private)
{
	struct rb_node *node;
	struct extent_state *state;
	int ret = 0;

	write_lock_irq(&tree->lock);
	/*
	 * this search will find all the extents that end after
	 * our range starts.
	 */
	node = tree_search(&tree->state, start);
	if (!node || IS_ERR(node)) {
		ret = -ENOENT;
		goto out;
	}
	state = rb_entry(node, struct extent_state, rb_node);
	if (state->start != start) {
		ret = -ENOENT;
		goto out;
	}
	state->private = private;
out:
	write_unlock_irq(&tree->lock);
	return ret;

}

int get_state_private(struct extent_map_tree *tree, u64 start, u64 *private)
{
	struct rb_node *node;
	struct extent_state *state;
	int ret = 0;

	read_lock_irq(&tree->lock);
	/*
	 * this search will find all the extents that end after
	 * our range starts.
	 */
	node = tree_search(&tree->state, start);
	if (!node || IS_ERR(node)) {
		ret = -ENOENT;
		goto out;
	}
	state = rb_entry(node, struct extent_state, rb_node);
	if (state->start != start) {
		ret = -ENOENT;
		goto out;
	}
	*private = state->private;
out:
	read_unlock_irq(&tree->lock);
	return ret;
}

/*
 * searches a range in the state tree for a given mask.
 * If 'filled' == 1, this returns 1 only if ever extent in the tree
 * has the bits set.  Otherwise, 1 is returned if any bit in the
 * range is found set.
 */
static int test_range_bit(struct extent_map_tree *tree, u64 start, u64 end,
			  int bits, int filled)
{
	struct extent_state *state = NULL;
	struct rb_node *node;
	int bitset = 0;

	read_lock_irq(&tree->lock);
	node = tree_search(&tree->state, start);
	while (node && start <= end) {
		state = rb_entry(node, struct extent_state, rb_node);
		if (state->start > end)
			break;

		if (filled && state->start > start) {
			bitset = 0;
			break;
		}
		if (state->state & bits) {
			bitset = 1;
			if (!filled)
				break;
		} else if (filled) {
			bitset = 0;
			break;
		}
		start = state->end + 1;
		if (start > end)
			break;
		node = rb_next(node);
	}
	read_unlock_irq(&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 int check_page_uptodate(struct extent_map_tree *tree,
			       struct page *page)
{
	u64 start = page->index << PAGE_CACHE_SHIFT;
	u64 end = start + PAGE_CACHE_SIZE - 1;
	if (test_range_bit(tree, start, end, EXTENT_UPTODATE, 1))
		SetPageUptodate(page);
	return 0;
}

/*
 * helper function to unlock a page if all the extents in the tree
 * for that page are unlocked
 */
static int check_page_locked(struct extent_map_tree *tree,
			     struct page *page)
{
	u64 start = page->index << PAGE_CACHE_SHIFT;
	u64 end = start + PAGE_CACHE_SIZE - 1;
	if (!test_range_bit(tree, start, end, EXTENT_LOCKED, 0))
		unlock_page(page);
	return 0;
}

/*
 * helper function to end page writeback if all the extents
 * in the tree for that page are done with writeback
 */
static int check_page_writeback(struct extent_map_tree *tree,
			     struct page *page)
{
	u64 start = page->index << PAGE_CACHE_SHIFT;
	u64 end = start + PAGE_CACHE_SIZE - 1;
	if (!test_range_bit(tree, start, end, EXTENT_WRITEBACK, 0))
		end_page_writeback(page);
	return 0;
}

/* lots and lots of room for performance fixes in the end_bio funcs */

/*
 * 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 int end_bio_extent_writepage(struct bio *bio,
				   unsigned int bytes_done, int err)
{
	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
	struct extent_map_tree *tree = bio->bi_private;
	u64 start;
	u64 end;
	int whole_page;

	if (bio->bi_size)
		return 1;

	do {
		struct page *page = bvec->bv_page;
		start = (page->index << PAGE_CACHE_SHIFT) + bvec->bv_offset;
		end = start + bvec->bv_len - 1;

		if (bvec->bv_offset == 0 && bvec->bv_len == PAGE_CACHE_SIZE)
			whole_page = 1;
		else
			whole_page = 0;

		if (--bvec >= bio->bi_io_vec)
			prefetchw(&bvec->bv_page->flags);

		if (!uptodate) {
			clear_extent_uptodate(tree, start, end, GFP_ATOMIC);
			ClearPageUptodate(page);
			SetPageError(page);
		}
		clear_extent_writeback(tree, start, end, GFP_ATOMIC);

		if (whole_page)
			end_page_writeback(page);
		else
			check_page_writeback(tree, page);
		if (tree->ops && tree->ops->writepage_end_io_hook)
			tree->ops->writepage_end_io_hook(page, start, end);
	} while (bvec >= bio->bi_io_vec);

	bio_put(bio);
	return 0;
}

/*
 * 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 int end_bio_extent_readpage(struct bio *bio,
				   unsigned int bytes_done, int err)
{
	int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
	struct extent_map_tree *tree = bio->bi_private;
	u64 start;
	u64 end;
	int whole_page;
	int ret;

	if (bio->bi_size)
		return 1;

	do {
		struct page *page = bvec->bv_page;
		start = (page->index << PAGE_CACHE_SHIFT) + bvec->bv_offset;
		end = start + bvec->bv_len - 1;

		if (bvec->bv_offset == 0 && bvec->bv_len == PAGE_CACHE_SIZE)
			whole_page = 1;
		else
			whole_page = 0;

		if (--bvec >= bio->bi_io_vec)
			prefetchw(&bvec->bv_page->flags);

		if (uptodate && tree->ops && tree->ops->readpage_end_io_hook) {
			ret = tree->ops->readpage_end_io_hook(page, start, end);
			if (ret)
				uptodate = 0;
		}
		if (uptodate) {
			set_extent_uptodate(tree, start, end, GFP_ATOMIC);
			if (whole_page)
				SetPageUptodate(page);
			else
				check_page_uptodate(tree, page);
		} else {
			ClearPageUptodate(page);
			SetPageError(page);
		}

		unlock_extent(tree, start, end, GFP_ATOMIC);

		if (whole_page)
			unlock_page(page);
		else
			check_page_locked(tree, page);
	} while (bvec >= bio->bi_io_vec);

	bio_put(bio);
	return 0;
}

/*
 * IO done from prepare_write is pretty simple, we just unlock
 * the structs in the extent tree when done, and set the uptodate bits
 * as appropriate.
 */
static int end_bio_extent_preparewrite(struct bio *bio,
				       unsigned int bytes_done, int err)
{
	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
	struct extent_map_tree *tree = bio->bi_private;
	u64 start;
	u64 end;

	if (bio->bi_size)
		return 1;

	do {
		struct page *page = bvec->bv_page;
		start = (page->index << PAGE_CACHE_SHIFT) + bvec->bv_offset;
		end = start + bvec->bv_len - 1;

		if (--bvec >= bio->bi_io_vec)
			prefetchw(&bvec->bv_page->flags);

		if (uptodate) {
			set_extent_uptodate(tree, start, end, GFP_ATOMIC);
		} else {
			ClearPageUptodate(page);
			SetPageError(page);
		}

		unlock_extent(tree, start, end, GFP_ATOMIC);

	} while (bvec >= bio->bi_io_vec);

	bio_put(bio);
	return 0;
}

static int submit_extent_page(int rw, struct extent_map_tree *tree,
			      struct page *page, sector_t sector,
			      size_t size, unsigned long offset,
			      struct block_device *bdev,
			      bio_end_io_t end_io_func)
{
	struct bio *bio;
	int ret = 0;

	bio = bio_alloc(GFP_NOIO, 1);

	bio->bi_sector = sector;
	bio->bi_bdev = bdev;
	bio->bi_io_vec[0].bv_page = page;
	bio->bi_io_vec[0].bv_len = size;
	bio->bi_io_vec[0].bv_offset = offset;

	bio->bi_vcnt = 1;
	bio->bi_idx = 0;
	bio->bi_size = size;

	bio->bi_end_io = end_io_func;
	bio->bi_private = tree;

	bio_get(bio);
	submit_bio(rw, bio);

	if (bio_flagged(bio, BIO_EOPNOTSUPP))
		ret = -EOPNOTSUPP;

	bio_put(bio);
	return ret;
}

void set_page_extent_mapped(struct page *page)
{
	if (!PagePrivate(page)) {
		SetPagePrivate(page);
		WARN_ON(!page->mapping->a_ops->invalidatepage);
		set_page_private(page, 1);
		page_cache_get(page);
	}
}

/*
 * 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)
 */
int extent_read_full_page(struct extent_map_tree *tree, struct page *page,
			  get_extent_t *get_extent)
{
	struct inode *inode = page->mapping->host;
	u64 start = page->index << PAGE_CACHE_SHIFT;
	u64 page_end = start + PAGE_CACHE_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;
	int nr = 0;
	size_t page_offset = 0;
	size_t iosize;
	size_t blocksize = inode->i_sb->s_blocksize;

	set_page_extent_mapped(page);

	end = page_end;
	lock_extent(tree, start, end, GFP_NOFS);

	while (cur <= end) {
		if (cur >= last_byte) {
			iosize = PAGE_CACHE_SIZE - page_offset;
			zero_user_page(page, page_offset, iosize, KM_USER0);
			set_extent_uptodate(tree, cur, cur + iosize - 1,
					    GFP_NOFS);
			unlock_extent(tree, cur, cur + iosize - 1, GFP_NOFS);
			break;
		}
		em = get_extent(inode, page, page_offset, cur, end, 0);
		if (IS_ERR(em) || !em) {
			SetPageError(page);
			unlock_extent(tree, cur, end, GFP_NOFS);
			break;
		}

		extent_offset = cur - em->start;
		BUG_ON(em->end < cur);
		BUG_ON(end < cur);

		iosize = min(em->end - cur, end - cur) + 1;
		cur_end = min(em->end, end);
		iosize = (iosize + blocksize - 1) & ~((u64)blocksize - 1);
		sector = (em->block_start + extent_offset) >> 9;
		bdev = em->bdev;
		block_start = em->block_start;
		free_extent_map(em);
		em = NULL;

		/* we've found a hole, just zero and go on */
		if (block_start == 0) {
			zero_user_page(page, page_offset, iosize, KM_USER0);
			set_extent_uptodate(tree, cur, cur + iosize - 1,
					    GFP_NOFS);
			unlock_extent(tree, cur, cur + iosize - 1, GFP_NOFS);
			cur = cur + iosize;
			page_offset += iosize;
			continue;
		}
		/* the get_extent function already copied into the page */
		if (test_range_bit(tree, cur, cur_end, EXTENT_UPTODATE, 1)) {
			unlock_extent(tree, cur, cur + iosize - 1, GFP_NOFS);
			cur = cur + iosize;
			page_offset += iosize;
			continue;
		}

		ret = 0;
		if (tree->ops && tree->ops->readpage_io_hook) {
			ret = tree->ops->readpage_io_hook(page, cur,
							  cur + iosize - 1);
		}
		if (!ret) {
			ret = submit_extent_page(READ, tree, page,
						 sector, iosize, page_offset,
						 bdev, end_bio_extent_readpage);
		}
		if (ret)
			SetPageError(page);
		cur = cur + iosize;
		page_offset += iosize;
		nr++;
	}
	if (!nr) {
		if (!PageError(page))
			SetPageUptodate(page);
		unlock_page(page);
	}
	return 0;
}
EXPORT_SYMBOL(extent_read_full_page);

/*
 * 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
 */
int extent_write_full_page(struct extent_map_tree *tree, struct page *page,
			  get_extent_t *get_extent,
			  struct writeback_control *wbc)
{
	struct inode *inode = page->mapping->host;
	u64 start = page->index << PAGE_CACHE_SHIFT;
	u64 page_end = start + PAGE_CACHE_SIZE - 1;
	u64 end;
	u64 cur = start;
	u64 extent_offset;
	u64 last_byte = i_size_read(inode);
	u64 block_start;
	sector_t sector;
	struct extent_map *em;
	struct block_device *bdev;
	int ret;
	int nr = 0;
	size_t page_offset = 0;
	size_t iosize;
	size_t blocksize;
	loff_t i_size = i_size_read(inode);
	unsigned long end_index = i_size >> PAGE_CACHE_SHIFT;
	u64 nr_delalloc;
	u64 delalloc_end;

	WARN_ON(!PageLocked(page));
	if (page->index > end_index) {
		clear_extent_dirty(tree, start, page_end, GFP_NOFS);
		unlock_page(page);
		return 0;
	}

	if (page->index == end_index) {
		size_t offset = i_size & (PAGE_CACHE_SIZE - 1);
		zero_user_page(page, offset,
			       PAGE_CACHE_SIZE - offset, KM_USER0);
	}

	set_page_extent_mapped(page);

	lock_extent(tree, start, page_end, GFP_NOFS);
	nr_delalloc = find_lock_delalloc_range(tree, start, page_end + 1,
					       &delalloc_end,
					       128 * 1024 * 1024);
	if (nr_delalloc) {
		tree->ops->fill_delalloc(inode, start, delalloc_end);
		if (delalloc_end >= page_end + 1) {
			clear_extent_bit(tree, page_end + 1, delalloc_end,
					 EXTENT_LOCKED | EXTENT_DELALLOC,
					 1, 0, GFP_NOFS);
		}
		clear_extent_bit(tree, start, page_end, EXTENT_DELALLOC,
				 0, 0, GFP_NOFS);
		if (test_range_bit(tree, start, page_end, EXTENT_DELALLOC, 0)) {
			printk("found delalloc bits after clear extent_bit\n");
		}
	} else if (test_range_bit(tree, start, page_end, EXTENT_DELALLOC, 0)) {
		printk("found delalloc bits after find_delalloc_range returns 0\n");
	}

	end = page_end;
	if (test_range_bit(tree, start, page_end, EXTENT_DELALLOC, 0)) {
		printk("found delalloc bits after lock_extent\n");
	}

	if (last_byte <= start) {
		clear_extent_dirty(tree, start, page_end, GFP_NOFS);
		goto done;
	}

	set_extent_uptodate(tree, start, page_end, GFP_NOFS);
	blocksize = inode->i_sb->s_blocksize;

	while (cur <= end) {
		if (cur >= last_byte) {
			clear_extent_dirty(tree, cur, page_end, GFP_NOFS);
			break;
		}
		em = get_extent(inode, page, page_offset, cur, end, 0);
		if (IS_ERR(em) || !em) {
			SetPageError(page);
			break;
		}

		extent_offset = cur - em->start;
		BUG_ON(em->end < cur);
		BUG_ON(end < cur);
		iosize = min(em->end - cur, end - cur) + 1;
		iosize = (iosize + blocksize - 1) & ~((u64)blocksize - 1);
		sector = (em->block_start + extent_offset) >> 9;
		bdev = em->bdev;
		block_start = em->block_start;
		free_extent_map(em);
		em = NULL;

		if (block_start == 0 || block_start == EXTENT_MAP_INLINE) {
			clear_extent_dirty(tree, cur,
					   cur + iosize - 1, GFP_NOFS);
			cur = cur + iosize;
			page_offset += iosize;
			continue;
		}

		/* leave this out until we have a page_mkwrite call */
		if (0 && !test_range_bit(tree, cur, cur + iosize - 1,
				   EXTENT_DIRTY, 0)) {
			cur = cur + iosize;
			page_offset += iosize;
			continue;
		}
		clear_extent_dirty(tree, cur, cur + iosize - 1, GFP_NOFS);
		if (tree->ops && tree->ops->writepage_io_hook) {
			ret = tree->ops->writepage_io_hook(page, cur,
						cur + iosize - 1);
		} else {
			ret = 0;
		}
		if (ret)
			SetPageError(page);
		else {
			set_range_writeback(tree, cur, cur + iosize - 1);
			ret = submit_extent_page(WRITE, tree, page, sector,
						 iosize, page_offset, bdev,
						 end_bio_extent_writepage);
			if (ret)
				SetPageError(page);
		}
		cur = cur + iosize;
		page_offset += iosize;
		nr++;
	}
done:
	WARN_ON(test_range_bit(tree, start, page_end, EXTENT_DIRTY, 0));
	unlock_extent(tree, start, page_end, GFP_NOFS);
	unlock_page(page);
	return 0;
}
EXPORT_SYMBOL(extent_write_full_page);

/*
 * 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_map_tree *tree,
			  struct page *page, unsigned long offset)
{
	u64 start = (page->index << PAGE_CACHE_SHIFT);
	u64 end = start + PAGE_CACHE_SIZE - 1;
	size_t blocksize = page->mapping->host->i_sb->s_blocksize;

	start += (offset + blocksize -1) & ~(blocksize - 1);
	if (start > end)
		return 0;

	lock_extent(tree, start, end, GFP_NOFS);
	wait_on_extent_writeback(tree, start, end);
	clear_extent_bit(tree, start, end,
			 EXTENT_LOCKED | EXTENT_DIRTY | EXTENT_DELALLOC,
			 1, 1, GFP_NOFS);
	return 0;
}
EXPORT_SYMBOL(extent_invalidatepage);

/*
 * simple commit_write call, set_range_dirty is used to mark both
 * the pages and the extent records as dirty
 */
int extent_commit_write(struct extent_map_tree *tree,
			struct inode *inode, struct page *page,
			unsigned from, unsigned to)
{
	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;

	set_page_extent_mapped(page);
	set_page_dirty(page);

	if (pos > inode->i_size) {
		i_size_write(inode, pos);
		mark_inode_dirty(inode);
	}
	return 0;
}
EXPORT_SYMBOL(extent_commit_write);

int extent_prepare_write(struct extent_map_tree *tree,
			 struct inode *inode, struct page *page,
			 unsigned from, unsigned to, get_extent_t *get_extent)
{
	u64 page_start = page->index << PAGE_CACHE_SHIFT;
	u64 page_end = page_start + PAGE_CACHE_SIZE - 1;
	u64 block_start;
	u64 orig_block_start;
	u64 block_end;
	u64 cur_end;
	struct extent_map *em;
	unsigned blocksize = 1 << inode->i_blkbits;
	size_t page_offset = 0;
	size_t block_off_start;
	size_t block_off_end;
	int err = 0;
	int iocount = 0;
	int ret = 0;
	int isnew;

	set_page_extent_mapped(page);

	block_start = (page_start + from) & ~((u64)blocksize - 1);
	block_end = (page_start + to - 1) | (blocksize - 1);
	orig_block_start = block_start;

	lock_extent(tree, page_start, page_end, GFP_NOFS);
	while(block_start <= block_end) {
		em = get_extent(inode, page, page_offset, block_start,
				block_end, 1);
		if (IS_ERR(em) || !em) {
			goto err;
		}
		cur_end = min(block_end, em->end);
		block_off_start = block_start & (PAGE_CACHE_SIZE - 1);
		block_off_end = block_off_start + blocksize;
		isnew = clear_extent_new(tree, block_start, cur_end, GFP_NOFS);

		if (!PageUptodate(page) && isnew &&
		    (block_off_end > to || block_off_start < from)) {
			void *kaddr;

			kaddr = kmap_atomic(page, KM_USER0);
			if (block_off_end > to)
				memset(kaddr + to, 0, block_off_end - to);
			if (block_off_start < from)
				memset(kaddr + block_off_start, 0,
				       from - block_off_start);
			flush_dcache_page(page);
			kunmap_atomic(kaddr, KM_USER0);
		}
		if (!isnew && !PageUptodate(page) &&
		    (block_off_end > to || block_off_start < from) &&
		    !test_range_bit(tree, block_start, cur_end,
				    EXTENT_UPTODATE, 1)) {
			u64 sector;
			u64 extent_offset = block_start - em->start;
			size_t iosize;
			sector = (em->block_start + extent_offset) >> 9;
			iosize = (cur_end - block_start + blocksize - 1) &
				~((u64)blocksize - 1);
			/*
			 * we've already got the extent locked, but we
			 * need to split the state such that our end_bio
			 * handler can clear the lock.
			 */
			set_extent_bit(tree, block_start,
				       block_start + iosize - 1,
				       EXTENT_LOCKED, 0, NULL, GFP_NOFS);
			ret = submit_extent_page(READ, tree, page,
					 sector, iosize, page_offset, em->bdev,
					 end_bio_extent_preparewrite);
			iocount++;
			block_start = block_start + iosize;
		} else {
			set_extent_uptodate(tree, block_start, cur_end,
					    GFP_NOFS);
			unlock_extent(tree, block_start, cur_end, GFP_NOFS);
			block_start = cur_end + 1;
		}
		page_offset = block_start & (PAGE_CACHE_SIZE - 1);
		free_extent_map(em);
	}
	if (iocount) {
		wait_extent_bit(tree, orig_block_start,
				block_end, EXTENT_LOCKED);
	}
	check_page_uptodate(tree, page);
err:
	/* FIXME, zero out newly allocated blocks on error */
	return err;
}
EXPORT_SYMBOL(extent_prepare_write);

/*
 * 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 *tree, struct page *page)
{
	struct extent_map *em;
	u64 start = page->index << PAGE_CACHE_SHIFT;
	u64 end = start + PAGE_CACHE_SIZE - 1;
	u64 orig_start = start;
	int ret = 1;

	while (start <= end) {
		em = lookup_extent_mapping(tree, start, end);
		if (!em || IS_ERR(em))
			break;
		if (!test_range_bit(tree, em->start, em->end,
				    EXTENT_LOCKED, 0)) {
			remove_extent_mapping(tree, em);
			/* once for the rb tree */
			free_extent_map(em);
		}
		start = em->end + 1;
		/* once for us */
		free_extent_map(em);
	}
	if (test_range_bit(tree, orig_start, end, EXTENT_LOCKED, 0))
		ret = 0;
	else
		clear_extent_bit(tree, orig_start, end, EXTENT_UPTODATE,
				 1, 1, GFP_NOFS);
	return ret;
}
EXPORT_SYMBOL(try_release_extent_mapping);

sector_t extent_bmap(struct address_space *mapping, sector_t iblock,
		get_extent_t *get_extent)
{
	struct inode *inode = mapping->host;
	u64 start = iblock << inode->i_blkbits;
	u64 end = start + (1 << inode->i_blkbits) - 1;
	struct extent_map *em;

	em = get_extent(inode, NULL, 0, start, end, 0);
	if (!em || IS_ERR(em))
		return 0;

	// XXX(hch): block 0 is valid in some cases, e.g. XFS RT device
	if (em->block_start == EXTENT_MAP_INLINE ||
	    em->block_start == 0)
	    	return 0;

	return (em->block_start + start - em->start) >> inode->i_blkbits;
}