Btrfs: [PATCH] extent_map: fix locking for bio completion

[safe/jmp/linux-2.6] / fs / btrfs / extent_map.c

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

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

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

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

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

#define EXTENT_IOBITS (EXTENT_LOCKED | EXTENT_WRITEBACK)

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

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

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

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

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


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

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

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

        while(*p) {
                parent = *p;
                entry = rb_entry(parent, struct tree_entry, rb_node);

                if (offset < entry->start)
                        p = &(*p)->rb_left;
                else if (offset > entry->end)
                        p = &(*p)->rb_right;
                else
                        return parent;
        }

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

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

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

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

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

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

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

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

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

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

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

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

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

/*
 * utility function to look for merge candidates inside a given range.
 * Any extents with matching state are merged together into a single
 * extent in the tree.  Extents with EXTENT_IO in their state field
 * are not merged because the end_io handlers need to be able to do
 * operations on them without sleeping (or doing allocations/splits).
 *
 * This should be called with the tree lock held.
 */
static int merge_state(struct extent_map_tree *tree,
                       struct extent_state *state)
{
        struct extent_state *other;
        struct rb_node *other_node;

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

        other_node = rb_prev(&state->rb_node);
        if (other_node) {
                other = rb_entry(other_node, struct extent_state, rb_node);
                if (other->end == state->start - 1 &&
                    other->state == state->state) {
                        state->start = other->start;
                        other->in_tree = 0;
                        rb_erase(&other->rb_node, &tree->state);
                        free_extent_state(other);
                }
        }
        other_node = rb_next(&state->rb_node);
        if (other_node) {
                other = rb_entry(other_node, struct extent_state, rb_node);
                if (other->start == state->end + 1 &&
                    other->state == state->state) {
                        other->start = state->start;
                        state->in_tree = 0;
                        rb_erase(&state->rb_node, &tree->state);
                        free_extent_state(state);
                }
        }
        return 0;
}

/*
 * insert an extent_state struct into the tree.  'bits' are set on the
 * struct before it is inserted.
 *
 * This may return -EEXIST if the extent is already there, in which case the
 * state struct is freed.
 *
 * The tree lock is not taken internally.  This is a utility function and
 * probably isn't what you want to call (see set/clear_extent_bit).
 */
static int insert_state(struct extent_map_tree *tree,
                        struct extent_state *state, u64 start, u64 end,
                        int bits)
{
        struct rb_node *node;

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

/*
 * split a given extent state struct in two, inserting the preallocated
 * struct 'prealloc' as the newly created second half.  'split' indicates an
 * offset inside 'orig' where it should be split.
 *
 * Before calling,
 * the tree has 'orig' at [orig->start, orig->end].  After calling, there
 * are two extent state structs in the tree:
 * prealloc: [orig->start, split - 1]
 * orig: [ split, orig->end ]
 *
 * The tree locks are not taken by this function. They need to be held
 * by the caller.
 */
static int split_state(struct extent_map_tree *tree, struct extent_state *orig,
                       struct extent_state *prealloc, u64 split)
{
        struct rb_node *node;
        prealloc->start = orig->start;
        prealloc->end = split - 1;
        prealloc->state = orig->state;
        orig->start = split;
        if ((prealloc->end & 4095) == 0) {
                printk("insert state %Lu %Lu strange end\n", prealloc->start,
                       prealloc->end);
                WARN_ON(1);
        }
        node = tree_insert(&tree->state, prealloc->end, &prealloc->rb_node);
        if (node) {
                struct extent_state *found;
                found = rb_entry(node, struct extent_state, rb_node);
                printk("found node %Lu %Lu on insert of %Lu %Lu\n", found->start, found->end, prealloc->start, prealloc->end);
                free_extent_state(prealloc);
                return -EEXIST;
        }
        return 0;
}

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

/*
 * clear some bits on a range in the tree.  This may require splitting
 * or inserting elements in the tree, so the gfp mask is used to
 * indicate which allocations or sleeping are allowed.
 *
 * pass 'wake' == 1 to kick any sleepers, and 'delete' == 1 to remove
 * the given range from the tree regardless of state (ie for truncate).
 *
 * the range [start, end] is inclusive.
 *
 * This takes the tree lock, and returns < 0 on error, > 0 if any of the
 * bits were already set, or zero if none of the bits were already set.
 */
int clear_extent_bit(struct extent_map_tree *tree, u64 start, u64 end,
                     int bits, int wake, int delete, gfp_t mask)
{
        struct extent_state *state;
        struct extent_state *prealloc = NULL;
        struct rb_node *node;
        unsigned long flags;
        int err;
        int set = 0;

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

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

        /*
         *     | ---- desired range ---- |
         *  | state | or
         *  | ------------- state -------------- |
         *
         * We need to split the extent we found, and may flip
         * bits on second half.
         *
         * If the extent we found extends past our range, we
         * just split and search again.  It'll get split again
         * the next time though.
         *
         * If the extent we found is inside our range, we clear
         * the desired bit on it.
         */

        if (state->start < start) {
                err = split_state(tree, state, prealloc, start);
                BUG_ON(err == -EEXIST);
                prealloc = NULL;
                if (err)
                        goto out;
                if (state->end <= end) {
                        start = state->end + 1;
                        set |= clear_state_bit(tree, state, bits,
                                        wake, delete);
                } else {
                        start = state->start;
                }
                goto search_again;
        }
        /*
         * | ---- desired range ---- |
         *                        | state |
         * We need to split the extent, and clear the bit
         * on the first half
         */
        if (state->start <= end && state->end > end) {
                err = split_state(tree, state, prealloc, end + 1);
                BUG_ON(err == -EEXIST);

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

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

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

        return set;

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

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

/*
 * waits for one or more bits to clear on a range in the state tree.
 * The range [start, end] is inclusive.
 * The tree lock is taken by this function
 */
int wait_extent_bit(struct extent_map_tree *tree, u64 start, u64 end, int bits)
{
        struct extent_state *state;
        struct rb_node *node;

        read_lock_irq(&tree->lock);
again:
        while (1) {
                /*
                 * this search will find all the extents that end after
                 * our range starts
                 */
                node = tree_search(&tree->state, start);
                if (!node)
                        break;

                state = rb_entry(node, struct extent_state, rb_node);

                if (state->start > end)
                        goto out;

                if (state->state & bits) {
                        start = state->start;
                        atomic_inc(&state->refs);
                        wait_on_state(tree, state);
                        free_extent_state(state);
                        goto again;
                }
                start = state->end + 1;

                if (start > end)
                        break;

                if (need_resched()) {
                        read_unlock_irq(&tree->lock);
                        cond_resched();
                        read_lock_irq(&tree->lock);
                }
        }
out:
        read_unlock_irq(&tree->lock);
        return 0;
}
EXPORT_SYMBOL(wait_extent_bit);

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

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

        state = rb_entry(node, struct extent_state, rb_node);
        last_start = state->start;
        last_end = state->end;

        /*
         * | ---- desired range ---- |
         * | state |
         *
         * Just lock what we found and keep going
         */
        if (state->start == start && state->end <= end) {
                set = state->state & bits;
                if (set && exclusive) {
                        *failed_start = state->start;
                        err = -EEXIST;
                        goto out;
                }
                state->state |= bits;
                start = state->end + 1;
                merge_state(tree, state);
                goto search_again;
        }

        /*
         *     | ---- desired range ---- |
         * | state |
         *   or
         * | ------------- state -------------- |
         *
         * We need to split the extent we found, and may flip bits on
         * second half.
         *
         * If the extent we found extends past our
         * range, we just split and search again.  It'll get split
         * again the next time though.
         *
         * If the extent we found is inside our range, we set the
         * desired bit on it.
         */
        if (state->start < start) {
                set = state->state & bits;
                if (exclusive && set) {
                        *failed_start = start;
                        err = -EEXIST;
                        goto out;
                }
                err = split_state(tree, state, prealloc, start);
                BUG_ON(err == -EEXIST);
                prealloc = NULL;
                if (err)
                        goto out;
                if (state->end <= end) {
                        state->state |= bits;
                        start = state->end + 1;
                        merge_state(tree, state);
                } else {
                        start = state->start;
                }
                goto search_again;
        }
        /*
         * | ---- desired range ---- |
         *     | state | or               | state |
         *
         * There's a hole, we need to insert something in it and
         * ignore the extent we found.
         */
        if (state->start > start) {
                u64 this_end;
                if (end < last_start)
                        this_end = end;
                else
                        this_end = last_start -1;
                err = insert_state(tree, prealloc, start, this_end,
                                   bits);
                prealloc = NULL;
                BUG_ON(err == -EEXIST);
                if (err)
                        goto out;
                start = this_end + 1;
                goto search_again;
        }
        /*
         * | ---- desired range ---- |
         *                        | state |
         * We need to split the extent, and set the bit
         * on the first half
         */
        if (state->start <= end && state->end > end) {
                set = state->state & bits;
                if (exclusive && set) {
                        *failed_start = start;
                        err = -EEXIST;
                        goto out;
                }
                err = split_state(tree, state, prealloc, end + 1);
                BUG_ON(err == -EEXIST);

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

        goto search_again;

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

        return err;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

}

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

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

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

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

                if (filled && state->start > start) {
                        bitset = 0;
                        break;
                }
                if (state->state & bits) {
                        bitset = 1;
                        if (!filled)
                                break;
                } else if (filled) {
                        bitset = 0;
                        break;
                }
                start = state->end + 1;
                if (start > end)
                        break;
                node = rb_next(node);
        }
        read_unlock_irq(&tree->lock);
        return bitset;
}

/*
 * helper function to set a given page up to date if all the
 * extents in the tree for that page are up to date
 */
static int check_page_uptodate(struct extent_map_tree *tree,
                               struct page *page)
{
        u64 start = page->index << PAGE_CACHE_SHIFT;
        u64 end = start + PAGE_CACHE_SIZE - 1;
        if (test_range_bit(tree, start, end, EXTENT_UPTODATE, 1))
                SetPageUptodate(page);
        return 0;
}

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

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

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

/*
 * after a writepage IO is done, we need to:
 * clear the uptodate bits on error
 * clear the writeback bits in the extent tree for this IO
 * end_page_writeback if the page has no more pending IO
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static int end_bio_extent_writepage(struct bio *bio,
                                   unsigned int bytes_done, int err)
{
        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
        struct extent_map_tree *tree = bio->bi_private;
        u64 start;
        u64 end;
        int whole_page;

        if (bio->bi_size)
                return 1;

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

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

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

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

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

        bio_put(bio);
        return 0;
}

/*
 * after a readpage IO is done, we need to:
 * clear the uptodate bits on error
 * set the uptodate bits if things worked
 * set the page up to date if all extents in the tree are uptodate
 * clear the lock bit in the extent tree
 * unlock the page if there are no other extents locked for it
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static int end_bio_extent_readpage(struct bio *bio,
                                   unsigned int bytes_done, int err)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
        struct extent_map_tree *tree = bio->bi_private;
        u64 start;
        u64 end;
        int whole_page;
        int ret;

        if (bio->bi_size)
                return 1;

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

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

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

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

                unlock_extent(tree, start, end, GFP_ATOMIC);

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

        bio_put(bio);
        return 0;
}

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

        if (bio->bi_size)
                return 1;

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

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

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

                unlock_extent(tree, start, end, GFP_ATOMIC);

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

        bio_put(bio);
        return 0;
}

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

        bio = bio_alloc(GFP_NOIO, 1);

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

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

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

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

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

        bio_put(bio);
        return ret;
}

/*
 * basic readpage implementation.  Locked extent state structs are inserted
 * into the tree that are removed when the IO is done (by the end_io
 * handlers)
 */
int extent_read_full_page(struct extent_map_tree *tree, struct page *page,
                          get_extent_t *get_extent)
{
        struct inode *inode = page->mapping->host;
        u64 start = page->index << PAGE_CACHE_SHIFT;
        u64 page_end = start + PAGE_CACHE_SIZE - 1;
        u64 end;
        u64 cur = start;
        u64 extent_offset;
        u64 last_byte = i_size_read(inode);
        u64 block_start;
        u64 cur_end;
        sector_t sector;
        struct extent_map *em;
        struct block_device *bdev;
        int ret;
        int nr = 0;
        size_t page_offset = 0;
        size_t iosize;
        size_t blocksize = inode->i_sb->s_blocksize;

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

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

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

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

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

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

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

/*
 * the writepage semantics are similar to regular writepage.  extent
 * records are inserted to lock ranges in the tree, and as dirty areas
 * are found, they are marked writeback.  Then the lock bits are removed
 * and the end_io handler clears the writeback ranges
 */
int extent_write_full_page(struct extent_map_tree *tree, struct page *page,
                          get_extent_t *get_extent,
                          struct writeback_control *wbc)
{
        struct inode *inode = page->mapping->host;
        u64 start = page->index << PAGE_CACHE_SHIFT;
        u64 page_end = start + PAGE_CACHE_SIZE - 1;
        u64 end;
        u64 cur = start;
        u64 extent_offset;
        u64 last_byte = i_size_read(inode);
        u64 block_start;
        sector_t sector;
        struct extent_map *em;
        struct block_device *bdev;
        int ret;
        int nr = 0;
        size_t page_offset = 0;
        size_t iosize;
        size_t blocksize;
        loff_t i_size = i_size_read(inode);
        unsigned long end_index = i_size >> PAGE_CACHE_SHIFT;
        u64 nr_delalloc;
        u64 delalloc_end;

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

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

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

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

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

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

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

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

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

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

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

/*
 * basic invalidatepage code, this waits on any locked or writeback
 * ranges corresponding to the page, and then deletes any extent state
 * records from the tree
 */
int extent_invalidatepage(struct extent_map_tree *tree,
                          struct page *page, unsigned long offset)
{
        u64 start = (page->index << PAGE_CACHE_SHIFT);
        u64 end = start + PAGE_CACHE_SIZE - 1;
        size_t blocksize = page->mapping->host->i_sb->s_blocksize;

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

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

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

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

        set_page_dirty(page);

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

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

        if (!PagePrivate(page)) {
                SetPagePrivate(page);
                set_page_private(page, 1);
                WARN_ON(!page->mapping->a_ops->invalidatepage);
                page_cache_get(page);
        }
        block_start = (page_start + from) & ~((u64)blocksize - 1);
        block_end = (page_start + to - 1) | (blocksize - 1);
        orig_block_start = block_start;

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

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

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

/*
 * a helper for releasepage.  As long as there are no locked extents
 * in the range corresponding to the page, both state records and extent
 * map records are removed
 */
int try_release_extent_mapping(struct extent_map_tree *tree, struct page *page)
{
        struct extent_map *em;
        u64 start = page->index << PAGE_CACHE_SHIFT;
        u64 end = start + PAGE_CACHE_SIZE - 1;
        u64 orig_start = start;
        int ret = 1;

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