Btrfs: Less aggressive readahead on deletes

[deliverable/linux.git] / 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 <linux/swap.h>
#include <linux/version.h>
#include <linux/writeback.h>
#include <linux/pagevec.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;
static struct kmem_cache *extent_buffer_cache;

static LIST_HEAD(buffers);
static LIST_HEAD(states);

static spinlock_t state_lock = SPIN_LOCK_UNLOCKED;
#define BUFFER_LRU_MAX 64

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

struct extent_page_data {
        struct bio *bio;
        struct extent_map_tree *tree;
        get_extent_t *get_extent;
};

int __init extent_map_init(void)
{
        extent_map_cache = btrfs_cache_create("extent_map",
                                            sizeof(struct extent_map), 0,
                                            NULL);
        if (!extent_map_cache)
                return -ENOMEM;
        extent_state_cache = btrfs_cache_create("extent_state",
                                            sizeof(struct extent_state), 0,
                                            NULL);
        if (!extent_state_cache)
                goto free_map_cache;
        extent_buffer_cache = btrfs_cache_create("extent_buffers",
                                            sizeof(struct extent_buffer), 0,
                                            NULL);
        if (!extent_buffer_cache)
                goto free_state_cache;
        return 0;

free_state_cache:
        kmem_cache_destroy(extent_state_cache);
free_map_cache:
        kmem_cache_destroy(extent_map_cache);
        return -ENOMEM;
}

void extent_map_exit(void)
{
        struct extent_state *state;

        while (!list_empty(&states)) {
                state = list_entry(states.next, struct extent_state, list);
                printk("state leak: start %Lu end %Lu state %lu in tree %d refs %d\n", state->start, state->end, state->state, state->in_tree, atomic_read(&state->refs));
                list_del(&state->list);
                kmem_cache_free(extent_state_cache, state);

        }

        if (extent_map_cache)
                kmem_cache_destroy(extent_map_cache);
        if (extent_state_cache)
                kmem_cache_destroy(extent_state_cache);
        if (extent_buffer_cache)
                kmem_cache_destroy(extent_buffer_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;
        tree->dirty_bytes = 0;
        rwlock_init(&tree->lock);
        spin_lock_init(&tree->lru_lock);
        tree->mapping = mapping;
        INIT_LIST_HEAD(&tree->buffer_lru);
        tree->lru_size = 0;
}
EXPORT_SYMBOL(extent_map_tree_init);

void extent_map_tree_empty_lru(struct extent_map_tree *tree)
{
        struct extent_buffer *eb;
        while(!list_empty(&tree->buffer_lru)) {
                eb = list_entry(tree->buffer_lru.next, struct extent_buffer,
                                lru);
                list_del_init(&eb->lru);
                free_extent_buffer(eb);
        }
}
EXPORT_SYMBOL(extent_map_tree_empty_lru);

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;
        unsigned long flags;

        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;

        spin_lock_irqsave(&state_lock, flags);
        list_add(&state->list, &states);
        spin_unlock_irqrestore(&state_lock, flags);

        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)
{
        unsigned long flags;
        if (!state)
                return;
        if (atomic_dec_and_test(&state->refs)) {
                WARN_ON(state->in_tree);
                spin_lock_irqsave(&state_lock, flags);
                list_del(&state->list);
                spin_unlock_irqrestore(&state_lock, flags);
                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 == EXTENT_MAP_HOLE &&
                      prev->block_start == EXTENT_MAP_HOLE) ||
                     (em->block_start == EXTENT_MAP_INLINE &&
                      prev->block_start == EXTENT_MAP_INLINE) ||
                     (em->block_start == EXTENT_MAP_DELALLOC &&
                      prev->block_start == EXTENT_MAP_DELALLOC) ||
                     (em->block_start < EXTENT_MAP_DELALLOC - 1 &&
                      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);
        }
        if (bits & EXTENT_DIRTY)
                tree->dirty_bytes += end - start + 1;
        state->state |= bits;
        state->start = start;
        state->end = end;
        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;

        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;

        if ((bits & EXTENT_DIRTY) && (state->state & EXTENT_DIRTY)) {
                u64 range = state->end - state->start + 1;
                WARN_ON(range > tree->dirty_bytes);
                tree->dirty_bytes -= range;
        }
        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);

static void set_state_bits(struct extent_map_tree *tree,
                           struct extent_state *state,
                           int bits)
{
        if ((bits & EXTENT_DIRTY) && !(state->state & EXTENT_DIRTY)) {
                u64 range = state->end - state->start + 1;
                tree->dirty_bytes += range;
        }
        state->state |= bits;
}

/*
 * 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;
                }
                set_state_bits(tree, 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) {
                        set_state_bits(tree, 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);

                set_state_bits(tree, prealloc, 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_bits(struct extent_map_tree *tree, u64 start, u64 end,
                    int bits, gfp_t mask)
{
        return set_extent_bit(tree, start, end, bits, 0, NULL,
                              mask);
}
EXPORT_SYMBOL(set_extent_bits);

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

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);

int find_first_extent_bit(struct extent_map_tree *tree, u64 start,
                          u64 *start_ret, u64 *end_ret, int bits)
{
        struct rb_node *node;
        struct extent_state *state;
        int ret = 1;

        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)) {
                goto out;
        }

        while(1) {
                state = rb_entry(node, struct extent_state, rb_node);
                if (state->end >= start && (state->state & bits)) {
                        *start_ret = state->start;
                        *end_ret = state->end;
                        ret = 0;
                        break;
                }
                node = rb_next(node);
                if (!node)
                        break;
        }
out:
        read_unlock_irq(&tree->lock);
        return ret;
}
EXPORT_SYMBOL(find_first_extent_bit);

u64 find_lock_delalloc_range(struct extent_map_tree *tree,
                             u64 *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)) {
                *end = (u64)-1;
                goto out;
        }

        while(1) {
                state = rb_entry(node, struct extent_state, rb_node);
                if (found && state->start != cur_start) {
                        goto out;
                }
                if (!(state->state & EXTENT_DELALLOC)) {
                        if (!found)
                                *end = state->end;
                        goto out;
                }
                if (!found) {
                        struct extent_state *prev_state;
                        struct rb_node *prev_node = node;
                        while(1) {
                                prev_node = rb_prev(prev_node);
                                if (!prev_node)
                                        break;
                                prev_state = rb_entry(prev_node,
                                                      struct extent_state,
                                                      rb_node);
                                if (!(prev_state->state & EXTENT_DELALLOC))
                                        break;
                                state = prev_state;
                                node = prev_node;
                        }
                }
                if (state->state & EXTENT_LOCKED) {
                        DEFINE_WAIT(wait);
                        atomic_inc(&state->refs);
                        prepare_to_wait(&state->wq, &wait,
                                        TASK_UNINTERRUPTIBLE);
                        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;
                if (!found)
                        *start = state->start;
                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;
}

u64 count_range_bits(struct extent_map_tree *tree,
                     u64 *start, u64 max_bytes, unsigned long bits)
{
        struct rb_node *node;
        struct extent_state *state;
        u64 cur_start = *start;
        u64 total_bytes = 0;
        int found = 0;

        write_lock_irq(&tree->lock);
        if (bits == EXTENT_DIRTY) {
                *start = 0;
                total_bytes = tree->dirty_bytes;
                goto out;
        }
        /*
         * this search will find all the extents that end after
         * our range starts.
         */
        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->state & bits)) {
                        total_bytes += state->end - state->start + 1;
                        if (total_bytes >= max_bytes)
                                break;
                        if (!found) {
                                *start = state->start;
                                found = 1;
                        }
                }
                node = rb_next(node);
                if (!node)
                        break;
        }
out:
        write_unlock_irq(&tree->lock);
        return total_bytes;
}

/*
 * 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.
 */
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 (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;
                }
                start = state->end + 1;
                if (start > end)
                        break;
                node = rb_next(node);
        }
        read_unlock_irq(&tree->lock);
        return bitset;
}
EXPORT_SYMBOL(test_range_bit);

/*
 * 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 = (u64)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 = (u64)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 = (u64)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.
 */
#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,23)
static void end_bio_extent_writepage(struct bio *bio, int err)
#else
static int end_bio_extent_writepage(struct bio *bio,
                                   unsigned int bytes_done, int err)
#endif
{
        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 LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
        if (bio->bi_size)
                return 1;
#endif

        do {
                struct page *page = bvec->bv_page;
                start = ((u64)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);
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
        return 0;
#endif
}

/*
 * 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.
 */
#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,23)
static void end_bio_extent_readpage(struct bio *bio, int err)
#else
static int end_bio_extent_readpage(struct bio *bio,
                                   unsigned int bytes_done, int err)
#endif
{
        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 LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
        if (bio->bi_size)
                return 1;
#endif

        do {
                struct page *page = bvec->bv_page;
                start = ((u64)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);
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
        return 0;
#endif
}

/*
 * 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.
 */
#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,23)
static void end_bio_extent_preparewrite(struct bio *bio, int err)
#else
static int end_bio_extent_preparewrite(struct bio *bio,
                                       unsigned int bytes_done, int err)
#endif
{
        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 LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
        if (bio->bi_size)
                return 1;
#endif

        do {
                struct page *page = bvec->bv_page;
                start = ((u64)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);
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
        return 0;
#endif
}

static struct bio *
extent_bio_alloc(struct block_device *bdev, u64 first_sector, int nr_vecs,
                 gfp_t gfp_flags)
{
        struct bio *bio;

        bio = bio_alloc(gfp_flags, nr_vecs);

        if (bio == NULL && (current->flags & PF_MEMALLOC)) {
                while (!bio && (nr_vecs /= 2))
                        bio = bio_alloc(gfp_flags, nr_vecs);
        }

        if (bio) {
                bio->bi_bdev = bdev;
                bio->bi_sector = first_sector;
        }
        return bio;
}

static int submit_one_bio(int rw, struct bio *bio)
{
        u64 maxsector;
        int ret = 0;

        bio_get(bio);

        maxsector = bio->bi_bdev->bd_inode->i_size >> 9;
        if (maxsector < bio->bi_sector) {
                printk("sector too large max %Lu got %llu\n", maxsector,
                        (unsigned long long)bio->bi_sector);
                WARN_ON(1);
        }

        submit_bio(rw, bio);
        if (bio_flagged(bio, BIO_EOPNOTSUPP))
                ret = -EOPNOTSUPP;
        bio_put(bio);
        return ret;
}

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,
                              struct bio **bio_ret,
                              unsigned long max_pages,
                              bio_end_io_t end_io_func)
{
        int ret = 0;
        struct bio *bio;
        int nr;

        if (bio_ret && *bio_ret) {
                bio = *bio_ret;
                if (bio->bi_sector + (bio->bi_size >> 9) != sector ||
                    bio_add_page(bio, page, size, offset) < size) {
                        ret = submit_one_bio(rw, bio);
                        bio = NULL;
                } else {
                        return 0;
                }
        }
        nr = min_t(int, max_pages, bio_get_nr_vecs(bdev));
        bio = extent_bio_alloc(bdev, sector, nr, GFP_NOFS | __GFP_HIGH);
        if (!bio) {
                printk("failed to allocate bio nr %d\n", nr);
        }
        bio_add_page(bio, page, size, offset);
        bio->bi_end_io = end_io_func;
        bio->bi_private = tree;
        if (bio_ret) {
                *bio_ret = bio;
        } else {
                ret = submit_one_bio(rw, 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, EXTENT_PAGE_PRIVATE);
                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)
 */
static int __extent_read_full_page(struct extent_map_tree *tree,
                                   struct page *page,
                                   get_extent_t *get_extent,
                                   struct bio **bio)
{
        struct inode *inode = page->mapping->host;
        u64 start = (u64)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) {
                        char *userpage;
                        iosize = PAGE_CACHE_SIZE - page_offset;
                        userpage = kmap_atomic(page, KM_USER0);
                        memset(userpage + page_offset, 0, iosize);
                        flush_dcache_page(page);
                        kunmap_atomic(userpage, 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 == EXTENT_MAP_HOLE) {
                        char *userpage;
                        userpage = kmap_atomic(page, KM_USER0);
                        memset(userpage + page_offset, 0, iosize);
                        flush_dcache_page(page);
                        kunmap_atomic(userpage, 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) {
                        unsigned long nr = (last_byte >> PAGE_CACHE_SHIFT) + 1;
                        nr -= page->index;
                        ret = submit_extent_page(READ, tree, page,
                                         sector, iosize, page_offset,
                                         bdev, bio, nr,
                                         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;
}

int extent_read_full_page(struct extent_map_tree *tree, struct page *page,
                            get_extent_t *get_extent)
{
        struct bio *bio = NULL;
        int ret;

        ret = __extent_read_full_page(tree, page, get_extent, &bio);
        if (bio)
                submit_one_bio(READ, bio);
        return ret;
}
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
 */
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;
        struct extent_map_tree *tree = epd->tree;
        u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
        u64 delalloc_start;
        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 iosize;
        sector_t sector;
        struct extent_map *em;
        struct block_device *bdev;
        int ret;
        int nr = 0;
        size_t page_offset = 0;
        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) {
                char *userpage;

                size_t offset = i_size & (PAGE_CACHE_SIZE - 1);

                userpage = kmap_atomic(page, KM_USER0);
                memset(userpage + offset, 0, PAGE_CACHE_SIZE - offset);
                flush_dcache_page(page);
                kunmap_atomic(userpage, KM_USER0);
        }

        set_page_extent_mapped(page);

        delalloc_start = start;
        delalloc_end = 0;
        while(delalloc_end < page_end) {
                nr_delalloc = find_lock_delalloc_range(tree, &delalloc_start,
                                                       &delalloc_end,
                                                       128 * 1024 * 1024);
                if (nr_delalloc == 0) {
                        delalloc_start = delalloc_end + 1;
                        continue;
                }
                tree->ops->fill_delalloc(inode, delalloc_start,
                                         delalloc_end);
                clear_extent_bit(tree, delalloc_start,
                                 delalloc_end,
                                 EXTENT_LOCKED | EXTENT_DELALLOC,
                                 1, 0, GFP_NOFS);
                delalloc_start = delalloc_end + 1;
        }
        lock_extent(tree, start, page_end, GFP_NOFS);

        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 = epd->get_extent(inode, page, page_offset, cur, end, 1);
                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 == EXTENT_MAP_HOLE ||
                    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 {
                        unsigned long max_nr = end_index + 1;
                        set_range_writeback(tree, cur, cur + iosize - 1);
                        if (!PageWriteback(page)) {
                                printk("warning page %lu not writeback, "
                                       "cur %llu end %llu\n", page->index,
                                       (unsigned long long)cur,
                                       (unsigned long long)end);
                        }

                        ret = submit_extent_page(WRITE, tree, page, sector,
                                                 iosize, page_offset, bdev,
                                                 &epd->bio, max_nr,
                                                 end_bio_extent_writepage);
                        if (ret)
                                SetPageError(page);
                }
                cur = cur + iosize;
                page_offset += iosize;
                nr++;
        }
done:
        if (nr == 0) {
                /* make sure the mapping tag for page dirty gets cleared */
                set_page_writeback(page);
                end_page_writeback(page);
        }
        unlock_extent(tree, start, page_end, GFP_NOFS);
        unlock_page(page);
        return 0;
}

#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)

/* Taken directly from 2.6.23 for 2.6.18 back port */
typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
                                void *data);

/**
 * 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 write_cache_pages(struct address_space *mapping,
                      struct writeback_control *wbc, writepage_t writepage,
                      void *data)
{
        struct backing_dev_info *bdi = mapping->backing_dev_info;
        int ret = 0;
        int done = 0;
        struct pagevec pvec;
        int nr_pages;
        pgoff_t index;
        pgoff_t end;            /* Inclusive */
        int scanned = 0;
        int range_whole = 0;

        if (wbc->nonblocking && bdi_write_congested(bdi)) {
                wbc->encountered_congestion = 1;
                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_CACHE_SHIFT;
                end = wbc->range_end >> PAGE_CACHE_SHIFT;
                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
                        range_whole = 1;
                scanned = 1;
        }
retry:
        while (!done && (index <= end) &&
               (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
                                              PAGECACHE_TAG_DIRTY,
                                              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];

                        /*
                         * 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
                         */
                        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)
                                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 || (--(wbc->nr_to_write) <= 0))
                                done = 1;
                        if (wbc->nonblocking && bdi_write_congested(bdi)) {
                                wbc->encountered_congestion = 1;
                                done = 1;
                        }
                }
                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 || (range_whole && wbc->nr_to_write > 0))
                mapping->writeback_index = index;
        return ret;
}
#endif

int extent_write_full_page(struct extent_map_tree *tree, struct page *page,
                          get_extent_t *get_extent,
                          struct writeback_control *wbc)
{
        int ret;
        struct address_space *mapping = page->mapping;
        struct extent_page_data epd = {
                .bio = NULL,
                .tree = tree,
                .get_extent = get_extent,
        };
        struct writeback_control wbc_writepages = {
                .bdi            = wbc->bdi,
                .sync_mode      = WB_SYNC_NONE,
                .older_than_this = NULL,
                .nr_to_write    = 64,
                .range_start    = page_offset(page) + PAGE_CACHE_SIZE,
                .range_end      = (loff_t)-1,
        };


        ret = __extent_writepage(page, wbc, &epd);

        write_cache_pages(mapping, &wbc_writepages, __extent_writepage, &epd);
        if (epd.bio) {
                submit_one_bio(WRITE, epd.bio);
        }
        return ret;
}
EXPORT_SYMBOL(extent_write_full_page);


int extent_writepages(struct extent_map_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,
        };

        ret = write_cache_pages(mapping, wbc, __extent_writepage, &epd);
        if (epd.bio) {
                submit_one_bio(WRITE, epd.bio);
        }
        return ret;
}
EXPORT_SYMBOL(extent_writepages);

int extent_readpages(struct extent_map_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;
        struct pagevec pvec;

        pagevec_init(&pvec, 0);
        for (page_idx = 0; page_idx < nr_pages; page_idx++) {
                struct page *page = list_entry(pages->prev, struct page, lru);

                prefetchw(&page->flags);
                list_del(&page->lru);
                /*
                 * what we want to do here is call add_to_page_cache_lru,
                 * but that isn't exported, so we reproduce it here
                 */
                if (!add_to_page_cache(page, mapping,
                                        page->index, GFP_KERNEL)) {

                        /* open coding of lru_cache_add, also not exported */
                        page_cache_get(page);
                        if (!pagevec_add(&pvec, page))
                                __pagevec_lru_add(&pvec);
                        __extent_read_full_page(tree, page, get_extent, &bio);
                }
                page_cache_release(page);
        }
        if (pagevec_count(&pvec))
                __pagevec_lru_add(&pvec);
        BUG_ON(!list_empty(pages));
        if (bio)
                submit_one_bio(READ, bio);
        return 0;
}
EXPORT_SYMBOL(extent_readpages);

/*
 * 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 = ((u64)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 = (u64)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 ((em->block_start != EXTENT_MAP_HOLE &&
                     em->block_start != EXTENT_MAP_INLINE) && 
                    !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,
                                         NULL, 1,
                                         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 = (u64)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;
        sector_t sector = 0;
        struct extent_map *em;

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

        if (em->block_start == EXTENT_MAP_INLINE ||
            em->block_start == EXTENT_MAP_HOLE)
                goto out;

        sector = (em->block_start + start - em->start) >> inode->i_blkbits;
out:
        free_extent_map(em);
        return sector;
}

static int add_lru(struct extent_map_tree *tree, struct extent_buffer *eb)
{
        if (list_empty(&eb->lru)) {
                extent_buffer_get(eb);
                list_add(&eb->lru, &tree->buffer_lru);
                tree->lru_size++;
                if (tree->lru_size >= BUFFER_LRU_MAX) {
                        struct extent_buffer *rm;
                        rm = list_entry(tree->buffer_lru.prev,
                                        struct extent_buffer, lru);
                        tree->lru_size--;
                        list_del_init(&rm->lru);
                        free_extent_buffer(rm);
                }
        } else
                list_move(&eb->lru, &tree->buffer_lru);
        return 0;
}
static struct extent_buffer *find_lru(struct extent_map_tree *tree,
                                      u64 start, unsigned long len)
{
        struct list_head *lru = &tree->buffer_lru;
        struct list_head *cur = lru->next;
        struct extent_buffer *eb;

        if (list_empty(lru))
                return NULL;

        do {
                eb = list_entry(cur, struct extent_buffer, lru);
                if (eb->start == start && eb->len == len) {
                        extent_buffer_get(eb);
                        return eb;
                }
                cur = cur->next;
        } while (cur != lru);
        return NULL;
}

static inline unsigned long num_extent_pages(u64 start, u64 len)
{
        return ((start + len + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT) -
                (start >> PAGE_CACHE_SHIFT);
}

static inline struct page *extent_buffer_page(struct extent_buffer *eb,
                                              unsigned long i)
{
        struct page *p;
        struct address_space *mapping;

        if (i == 0)
                return eb->first_page;
        i += eb->start >> PAGE_CACHE_SHIFT;
        mapping = eb->first_page->mapping;
        read_lock_irq(&mapping->tree_lock);
        p = radix_tree_lookup(&mapping->page_tree, i);
        read_unlock_irq(&mapping->tree_lock);
        return p;
}

static struct extent_buffer *__alloc_extent_buffer(struct extent_map_tree *tree,
                                                   u64 start,
                                                   unsigned long len,
                                                   gfp_t mask)
{
        struct extent_buffer *eb = NULL;

        spin_lock(&tree->lru_lock);
        eb = find_lru(tree, start, len);
        spin_unlock(&tree->lru_lock);
        if (eb) {
                return eb;
        }

        eb = kmem_cache_zalloc(extent_buffer_cache, mask);
        INIT_LIST_HEAD(&eb->lru);
        eb->start = start;
        eb->len = len;
        atomic_set(&eb->refs, 1);

        return eb;
}

static void __free_extent_buffer(struct extent_buffer *eb)
{
        kmem_cache_free(extent_buffer_cache, eb);
}

struct extent_buffer *alloc_extent_buffer(struct extent_map_tree *tree,
                                          u64 start, unsigned long len,
                                          struct page *page0,
                                          gfp_t mask)
{
        unsigned long num_pages = num_extent_pages(start, len);
        unsigned long i;
        unsigned long index = start >> PAGE_CACHE_SHIFT;
        struct extent_buffer *eb;
        struct page *p;
        struct address_space *mapping = tree->mapping;
        int uptodate = 1;

        eb = __alloc_extent_buffer(tree, start, len, mask);
        if (!eb || IS_ERR(eb))
                return NULL;

        if (eb->flags & EXTENT_BUFFER_FILLED)
                goto lru_add;

        if (page0) {
                eb->first_page = page0;
                i = 1;
                index++;
                page_cache_get(page0);
                mark_page_accessed(page0);
                set_page_extent_mapped(page0);
                WARN_ON(!PageUptodate(page0));
                set_page_private(page0, EXTENT_PAGE_PRIVATE_FIRST_PAGE |
                                 len << 2);
        } else {
                i = 0;
        }
        for (; i < num_pages; i++, index++) {
                p = find_or_create_page(mapping, index, mask | __GFP_HIGHMEM);
                if (!p) {
                        WARN_ON(1);
                        goto fail;
                }
                set_page_extent_mapped(p);
                mark_page_accessed(p);
                if (i == 0) {
                        eb->first_page = p;
                        set_page_private(p, EXTENT_PAGE_PRIVATE_FIRST_PAGE |
                                         len << 2);
                } else {
                        set_page_private(p, EXTENT_PAGE_PRIVATE);
                }
                if (!PageUptodate(p))
                        uptodate = 0;
                unlock_page(p);
        }
        if (uptodate)
                eb->flags |= EXTENT_UPTODATE;
        eb->flags |= EXTENT_BUFFER_FILLED;

lru_add:
        spin_lock(&tree->lru_lock);
        add_lru(tree, eb);
        spin_unlock(&tree->lru_lock);
        return eb;

fail:
        spin_lock(&tree->lru_lock);
        list_del_init(&eb->lru);
        spin_unlock(&tree->lru_lock);
        if (!atomic_dec_and_test(&eb->refs))
                return NULL;
        for (index = 1; index < i; index++) {
                page_cache_release(extent_buffer_page(eb, index));
        }
        if (i > 0)
                page_cache_release(extent_buffer_page(eb, 0));
        __free_extent_buffer(eb);
        return NULL;
}
EXPORT_SYMBOL(alloc_extent_buffer);

struct extent_buffer *find_extent_buffer(struct extent_map_tree *tree,
                                         u64 start, unsigned long len,
                                          gfp_t mask)
{
        unsigned long num_pages = num_extent_pages(start, len);
        unsigned long i;
        unsigned long index = start >> PAGE_CACHE_SHIFT;
        struct extent_buffer *eb;
        struct page *p;
        struct address_space *mapping = tree->mapping;
        int uptodate = 1;

        eb = __alloc_extent_buffer(tree, start, len, mask);
        if (!eb || IS_ERR(eb))
                return NULL;

        if (eb->flags & EXTENT_BUFFER_FILLED)
                goto lru_add;

        for (i = 0; i < num_pages; i++, index++) {
                p = find_lock_page(mapping, index);
                if (!p) {
                        goto fail;
                }
                set_page_extent_mapped(p);
                mark_page_accessed(p);

                if (i == 0) {
                        eb->first_page = p;
                        set_page_private(p, EXTENT_PAGE_PRIVATE_FIRST_PAGE |
                                         len << 2);
                } else {
                        set_page_private(p, EXTENT_PAGE_PRIVATE);
                }

                if (!PageUptodate(p))
                        uptodate = 0;
                unlock_page(p);
        }
        if (uptodate)
                eb->flags |= EXTENT_UPTODATE;
        eb->flags |= EXTENT_BUFFER_FILLED;

lru_add:
        spin_lock(&tree->lru_lock);
        add_lru(tree, eb);
        spin_unlock(&tree->lru_lock);
        return eb;
fail:
        spin_lock(&tree->lru_lock);
        list_del_init(&eb->lru);
        spin_unlock(&tree->lru_lock);
        if (!atomic_dec_and_test(&eb->refs))
                return NULL;
        for (index = 1; index < i; index++) {
                page_cache_release(extent_buffer_page(eb, index));
        }
        if (i > 0)
                page_cache_release(extent_buffer_page(eb, 0));
        __free_extent_buffer(eb);
        return NULL;
}
EXPORT_SYMBOL(find_extent_buffer);

void free_extent_buffer(struct extent_buffer *eb)
{
        unsigned long i;
        unsigned long num_pages;

        if (!eb)
                return;

        if (!atomic_dec_and_test(&eb->refs))
                return;

        WARN_ON(!list_empty(&eb->lru));
        num_pages = num_extent_pages(eb->start, eb->len);

        for (i = 1; i < num_pages; i++) {
                page_cache_release(extent_buffer_page(eb, i));
        }
        page_cache_release(extent_buffer_page(eb, 0));
        __free_extent_buffer(eb);
}
EXPORT_SYMBOL(free_extent_buffer);

int clear_extent_buffer_dirty(struct extent_map_tree *tree,
                              struct extent_buffer *eb)
{
        int set;
        unsigned long i;
        unsigned long num_pages;
        struct page *page;

        u64 start = eb->start;
        u64 end = start + eb->len - 1;

        set = clear_extent_dirty(tree, start, end, GFP_NOFS);
        num_pages = num_extent_pages(eb->start, eb->len);

        for (i = 0; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                lock_page(page);
                /*
                 * if we're on the last page or the first page and the
                 * block isn't aligned on a page boundary, do extra checks
                 * to make sure we don't clean page that is partially dirty
                 */
                if ((i == 0 && (eb->start & (PAGE_CACHE_SIZE - 1))) ||
                    ((i == num_pages - 1) &&
                     ((eb->start + eb->len) & (PAGE_CACHE_SIZE - 1)))) {
                        start = (u64)page->index << PAGE_CACHE_SHIFT;
                        end  = start + PAGE_CACHE_SIZE - 1;
                        if (test_range_bit(tree, start, end,
                                           EXTENT_DIRTY, 0)) {
                                unlock_page(page);
                                continue;
                        }
                }
                clear_page_dirty_for_io(page);
                write_lock_irq(&page->mapping->tree_lock);
                if (!PageDirty(page)) {
                        radix_tree_tag_clear(&page->mapping->page_tree,
                                                page_index(page),
                                                PAGECACHE_TAG_DIRTY);
                }
                write_unlock_irq(&page->mapping->tree_lock);
                unlock_page(page);
        }
        return 0;
}
EXPORT_SYMBOL(clear_extent_buffer_dirty);

int wait_on_extent_buffer_writeback(struct extent_map_tree *tree,
                                    struct extent_buffer *eb)
{
        return wait_on_extent_writeback(tree, eb->start,
                                        eb->start + eb->len - 1);
}
EXPORT_SYMBOL(wait_on_extent_buffer_writeback);

int set_extent_buffer_dirty(struct extent_map_tree *tree,
                             struct extent_buffer *eb)
{
        unsigned long i;
        unsigned long num_pages;

        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++) {
                struct page *page = extent_buffer_page(eb, i);
                /* writepage may need to do something special for the
                 * first page, we have to make sure page->private is
                 * properly set.  releasepage may drop page->private
                 * on us if the page isn't already dirty.
                 */
                if (i == 0) {
                        lock_page(page);
                        set_page_private(page,
                                         EXTENT_PAGE_PRIVATE_FIRST_PAGE |
                                         eb->len << 2);
                }
                __set_page_dirty_nobuffers(extent_buffer_page(eb, i));
                if (i == 0)
                        unlock_page(page);
        }
        return set_extent_dirty(tree, eb->start,
                                eb->start + eb->len - 1, GFP_NOFS);
}
EXPORT_SYMBOL(set_extent_buffer_dirty);

int set_extent_buffer_uptodate(struct extent_map_tree *tree,
                                struct extent_buffer *eb)
{
        unsigned long i;
        struct page *page;
        unsigned long num_pages;

        num_pages = num_extent_pages(eb->start, eb->len);

        set_extent_uptodate(tree, eb->start, eb->start + eb->len - 1,
                            GFP_NOFS);
        for (i = 0; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                if ((i == 0 && (eb->start & (PAGE_CACHE_SIZE - 1))) ||
                    ((i == num_pages - 1) &&
                     ((eb->start + eb->len) & (PAGE_CACHE_SIZE - 1)))) {
                        check_page_uptodate(tree, page);
                        continue;
                }
                SetPageUptodate(page);
        }
        return 0;
}
EXPORT_SYMBOL(set_extent_buffer_uptodate);

int extent_buffer_uptodate(struct extent_map_tree *tree,
                             struct extent_buffer *eb)
{
        if (eb->flags & EXTENT_UPTODATE)
                return 1;
        return test_range_bit(tree, eb->start, eb->start + eb->len - 1,
                           EXTENT_UPTODATE, 1);
}
EXPORT_SYMBOL(extent_buffer_uptodate);

int read_extent_buffer_pages(struct extent_map_tree *tree,
                             struct extent_buffer *eb,
                             u64 start,
                             int wait)
{
        unsigned long i;
        unsigned long start_i;
        struct page *page;
        int err;
        int ret = 0;
        unsigned long num_pages;

        if (eb->flags & EXTENT_UPTODATE)
                return 0;

        if (0 && test_range_bit(tree, eb->start, eb->start + eb->len - 1,
                           EXTENT_UPTODATE, 1)) {
                return 0;
        }

        if (start) {
                WARN_ON(start < eb->start);
                start_i = (start >> PAGE_CACHE_SHIFT) -
                        (eb->start >> PAGE_CACHE_SHIFT);
        } else {
                start_i = 0;
        }

        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = start_i; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                if (PageUptodate(page)) {
                        continue;
                }
                if (!wait) {
                        if (TestSetPageLocked(page)) {
                                continue;
                        }
                } else {
                        lock_page(page);
                }
                if (!PageUptodate(page)) {
                        err = page->mapping->a_ops->readpage(NULL, page);
                        if (err) {
                                ret = err;
                        }
                } else {
                        unlock_page(page);
                }
        }

        if (ret || !wait) {
                return ret;
        }

        for (i = start_i; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                wait_on_page_locked(page);
                if (!PageUptodate(page)) {
                        ret = -EIO;
                }
        }
        if (!ret)
                eb->flags |= EXTENT_UPTODATE;
        return ret;
}
EXPORT_SYMBOL(read_extent_buffer_pages);

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_CACHE_SIZE - 1);
        unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
        unsigned long num_pages = num_extent_pages(eb->start, eb->len);

        WARN_ON(start > eb->len);
        WARN_ON(start + len > eb->start + eb->len);

        offset = (start_offset + start) & ((unsigned long)PAGE_CACHE_SIZE - 1);

        while(len > 0) {
                page = extent_buffer_page(eb, i);
                if (!PageUptodate(page)) {
                        printk("page %lu not up to date i %lu, total %lu, len %lu\n", page->index, i, num_pages, eb->len);
                        WARN_ON(1);
                }
                WARN_ON(!PageUptodate(page));

                cur = min(len, (PAGE_CACHE_SIZE - offset));
                kaddr = kmap_atomic(page, KM_USER1);
                memcpy(dst, kaddr + offset, cur);
                kunmap_atomic(kaddr, KM_USER1);

                dst += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}
EXPORT_SYMBOL(read_extent_buffer);

int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
                               unsigned long min_len, char **token, char **map,
                               unsigned long *map_start,
                               unsigned long *map_len, int km)
{
        size_t offset = start & (PAGE_CACHE_SIZE - 1);
        char *kaddr;
        struct page *p;
        size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
        unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
        unsigned long end_i = (start_offset + start + min_len - 1) >>
                PAGE_CACHE_SHIFT;

        if (i != end_i)
                return -EINVAL;

        if (i == 0) {
                offset = start_offset;
                *map_start = 0;
        } else {
                offset = 0;
                *map_start = ((u64)i << PAGE_CACHE_SHIFT) - start_offset;
        }
        if (start + min_len > eb->len) {
printk("bad mapping eb start %Lu len %lu, wanted %lu %lu\n", eb->start, eb->len, start, min_len);
                WARN_ON(1);
        }

        p = extent_buffer_page(eb, i);
        WARN_ON(!PageUptodate(p));
        kaddr = kmap_atomic(p, km);
        *token = kaddr;
        *map = kaddr + offset;
        *map_len = PAGE_CACHE_SIZE - offset;
        return 0;
}
EXPORT_SYMBOL(map_private_extent_buffer);

int map_extent_buffer(struct extent_buffer *eb, unsigned long start,
                      unsigned long min_len,
                      char **token, char **map,
                      unsigned long *map_start,
                      unsigned long *map_len, int km)
{
        int err;
        int save = 0;
        if (eb->map_token) {
                unmap_extent_buffer(eb, eb->map_token, km);
                eb->map_token = NULL;
                save = 1;
        }
        err = map_private_extent_buffer(eb, start, min_len, token, map,
                                       map_start, map_len, km);
        if (!err && save) {
                eb->map_token = *token;
                eb->kaddr = *map;
                eb->map_start = *map_start;
                eb->map_len = *map_len;
        }
        return err;
}
EXPORT_SYMBOL(map_extent_buffer);

void unmap_extent_buffer(struct extent_buffer *eb, char *token, int km)
{
        kunmap_atomic(token, km);
}
EXPORT_SYMBOL(unmap_extent_buffer);

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_CACHE_SIZE - 1);
        unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
        int ret = 0;

        WARN_ON(start > eb->len);
        WARN_ON(start + len > eb->start + eb->len);

        offset = (start_offset + start) & ((unsigned long)PAGE_CACHE_SIZE - 1);

        while(len > 0) {
                page = extent_buffer_page(eb, i);
                WARN_ON(!PageUptodate(page));

                cur = min(len, (PAGE_CACHE_SIZE - offset));

                kaddr = kmap_atomic(page, KM_USER0);
                ret = memcmp(ptr, kaddr + offset, cur);
                kunmap_atomic(kaddr, KM_USER0);
                if (ret)
                        break;

                ptr += cur;
                len -= cur;
                offset = 0;
                i++;
        }
        return ret;
}
EXPORT_SYMBOL(memcmp_extent_buffer);

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_CACHE_SIZE - 1);
        unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;

        WARN_ON(start > eb->len);
        WARN_ON(start + len > eb->start + eb->len);

        offset = (start_offset + start) & ((unsigned long)PAGE_CACHE_SIZE - 1);

        while(len > 0) {
                page = extent_buffer_page(eb, i);
                WARN_ON(!PageUptodate(page));

                cur = min(len, PAGE_CACHE_SIZE - offset);
                kaddr = kmap_atomic(page, KM_USER1);
                memcpy(kaddr + offset, src, cur);
                kunmap_atomic(kaddr, KM_USER1);

                src += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}
EXPORT_SYMBOL(write_extent_buffer);

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_CACHE_SIZE - 1);
        unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;

        WARN_ON(start > eb->len);
        WARN_ON(start + len > eb->start + eb->len);

        offset = (start_offset + start) & ((unsigned long)PAGE_CACHE_SIZE - 1);

        while(len > 0) {
                page = extent_buffer_page(eb, i);
                WARN_ON(!PageUptodate(page));

                cur = min(len, PAGE_CACHE_SIZE - offset);
                kaddr = kmap_atomic(page, KM_USER0);
                memset(kaddr + offset, c, cur);
                kunmap_atomic(kaddr, KM_USER0);

                len -= cur;
                offset = 0;
                i++;
        }
}
EXPORT_SYMBOL(memset_extent_buffer);

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_CACHE_SIZE - 1);
        unsigned long i = (start_offset + dst_offset) >> PAGE_CACHE_SHIFT;

        WARN_ON(src->len != dst_len);

        offset = (start_offset + dst_offset) &
                ((unsigned long)PAGE_CACHE_SIZE - 1);

        while(len > 0) {
                page = extent_buffer_page(dst, i);
                WARN_ON(!PageUptodate(page));

                cur = min(len, (unsigned long)(PAGE_CACHE_SIZE - offset));

                kaddr = kmap_atomic(page, KM_USER0);
                read_extent_buffer(src, kaddr + offset, src_offset, cur);
                kunmap_atomic(kaddr, KM_USER0);

                src_offset += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}
EXPORT_SYMBOL(copy_extent_buffer);

static void move_pages(struct page *dst_page, struct page *src_page,
                       unsigned long dst_off, unsigned long src_off,
                       unsigned long len)
{
        char *dst_kaddr = kmap_atomic(dst_page, KM_USER0);
        if (dst_page == src_page) {
                memmove(dst_kaddr + dst_off, dst_kaddr + src_off, len);
        } else {
                char *src_kaddr = kmap_atomic(src_page, KM_USER1);
                char *p = dst_kaddr + dst_off + len;
                char *s = src_kaddr + src_off + len;

                while (len--)
                        *--p = *--s;

                kunmap_atomic(src_kaddr, KM_USER1);
        }
        kunmap_atomic(dst_kaddr, KM_USER0);
}

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 = kmap_atomic(dst_page, KM_USER0);
        char *src_kaddr;

        if (dst_page != src_page)
                src_kaddr = kmap_atomic(src_page, KM_USER1);
        else
                src_kaddr = dst_kaddr;

        memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
        kunmap_atomic(dst_kaddr, KM_USER0);
        if (dst_page != src_page)
                kunmap_atomic(src_kaddr, KM_USER1);
}

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_CACHE_SIZE - 1);
        unsigned long dst_i;
        unsigned long src_i;

        if (src_offset + len > dst->len) {
                printk("memmove bogus src_offset %lu move len %lu len %lu\n",
                       src_offset, len, dst->len);
                BUG_ON(1);
        }
        if (dst_offset + len > dst->len) {
                printk("memmove bogus dst_offset %lu move len %lu len %lu\n",
                       dst_offset, len, dst->len);
                BUG_ON(1);
        }

        while(len > 0) {
                dst_off_in_page = (start_offset + dst_offset) &
                        ((unsigned long)PAGE_CACHE_SIZE - 1);
                src_off_in_page = (start_offset + src_offset) &
                        ((unsigned long)PAGE_CACHE_SIZE - 1);

                dst_i = (start_offset + dst_offset) >> PAGE_CACHE_SHIFT;
                src_i = (start_offset + src_offset) >> PAGE_CACHE_SHIFT;

                cur = min(len, (unsigned long)(PAGE_CACHE_SIZE -
                                               src_off_in_page));
                cur = min_t(unsigned long, cur,
                        (unsigned long)(PAGE_CACHE_SIZE - dst_off_in_page));

                copy_pages(extent_buffer_page(dst, dst_i),
                           extent_buffer_page(dst, src_i),
                           dst_off_in_page, src_off_in_page, cur);

                src_offset += cur;
                dst_offset += cur;
                len -= cur;
        }
}
EXPORT_SYMBOL(memcpy_extent_buffer);

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_CACHE_SIZE - 1);
        unsigned long dst_i;
        unsigned long src_i;

        if (src_offset + len > dst->len) {
                printk("memmove bogus src_offset %lu move len %lu len %lu\n",
                       src_offset, len, dst->len);
                BUG_ON(1);
        }
        if (dst_offset + len > dst->len) {
                printk("memmove bogus dst_offset %lu move len %lu len %lu\n",
                       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_CACHE_SHIFT;
                src_i = (start_offset + src_end) >> PAGE_CACHE_SHIFT;

                dst_off_in_page = (start_offset + dst_end) &
                        ((unsigned long)PAGE_CACHE_SIZE - 1);
                src_off_in_page = (start_offset + src_end) &
                        ((unsigned long)PAGE_CACHE_SIZE - 1);

                cur = min_t(unsigned long, len, src_off_in_page + 1);
                cur = min(cur, dst_off_in_page + 1);
                move_pages(extent_buffer_page(dst, dst_i),
                           extent_buffer_page(dst, src_i),
                           dst_off_in_page - cur + 1,
                           src_off_in_page - cur + 1, cur);

                dst_end -= cur;
                src_end -= cur;
                len -= cur;
        }
}
EXPORT_SYMBOL(memmove_extent_buffer);