Btrfs: don't lock bits in the extent tree during writepage

[linux-2.6/kvm.git] / fs / btrfs / extent_io.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/writeback.h>
#include <linux/pagevec.h>
#include "extent_io.h"
#include "extent_map.h"
#include "compat.h"
#include "ctree.h"
#include "btrfs_inode.h"

static struct kmem_cache *extent_state_cache;
static struct kmem_cache *extent_buffer_cache;

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

#define LEAK_DEBUG 0
#if LEAK_DEBUG
static DEFINE_SPINLOCK(leak_lock);
#endif

#define BUFFER_LRU_MAX 64

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

struct extent_page_data {
        struct bio *bio;
        struct extent_io_tree *tree;
        get_extent_t *get_extent;

        /* tells writepage not to lock the state bits for this range
         * it still does the unlocking
         */
        unsigned int extent_locked:1;

        /* tells the submit_bio code to use a WRITE_SYNC */
        unsigned int sync_io:1;
};

int __init extent_io_init(void)
{
        extent_state_cache = kmem_cache_create("extent_state",
                        sizeof(struct extent_state), 0,
                        SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD, NULL);
        if (!extent_state_cache)
                return -ENOMEM;

        extent_buffer_cache = kmem_cache_create("extent_buffers",
                        sizeof(struct extent_buffer), 0,
                        SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD, NULL);
        if (!extent_buffer_cache)
                goto free_state_cache;
        return 0;

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

void extent_io_exit(void)
{
        struct extent_state *state;
        struct extent_buffer *eb;

        while (!list_empty(&states)) {
                state = list_entry(states.next, struct extent_state, leak_list);
                printk(KERN_ERR "btrfs state leak: start %llu end %llu "
                       "state %lu in tree %p refs %d\n",
                       (unsigned long long)state->start,
                       (unsigned long long)state->end,
                       state->state, state->tree, atomic_read(&state->refs));
                list_del(&state->leak_list);
                kmem_cache_free(extent_state_cache, state);

        }

        while (!list_empty(&buffers)) {
                eb = list_entry(buffers.next, struct extent_buffer, leak_list);
                printk(KERN_ERR "btrfs buffer leak start %llu len %lu "
                       "refs %d\n", (unsigned long long)eb->start,
                       eb->len, atomic_read(&eb->refs));
                list_del(&eb->leak_list);
                kmem_cache_free(extent_buffer_cache, eb);
        }
        if (extent_state_cache)
                kmem_cache_destroy(extent_state_cache);
        if (extent_buffer_cache)
                kmem_cache_destroy(extent_buffer_cache);
}

void extent_io_tree_init(struct extent_io_tree *tree,
                          struct address_space *mapping, gfp_t mask)
{
        tree->state.rb_node = NULL;
        tree->buffer.rb_node = NULL;
        tree->ops = NULL;
        tree->dirty_bytes = 0;
        spin_lock_init(&tree->lock);
        spin_lock_init(&tree->buffer_lock);
        tree->mapping = mapping;
}

static struct extent_state *alloc_extent_state(gfp_t mask)
{
        struct extent_state *state;
#if LEAK_DEBUG
        unsigned long flags;
#endif

        state = kmem_cache_alloc(extent_state_cache, mask);
        if (!state)
                return state;
        state->state = 0;
        state->private = 0;
        state->tree = NULL;
#if LEAK_DEBUG
        spin_lock_irqsave(&leak_lock, flags);
        list_add(&state->leak_list, &states);
        spin_unlock_irqrestore(&leak_lock, flags);
#endif
        atomic_set(&state->refs, 1);
        init_waitqueue_head(&state->wq);
        return state;
}

static void free_extent_state(struct extent_state *state)
{
        if (!state)
                return;
        if (atomic_dec_and_test(&state->refs)) {
#if LEAK_DEBUG
                unsigned long flags;
#endif
                WARN_ON(state->tree);
#if LEAK_DEBUG
                spin_lock_irqsave(&leak_lock, flags);
                list_del(&state->leak_list);
                spin_unlock_irqrestore(&leak_lock, flags);
#endif
                kmem_cache_free(extent_state_cache, 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);
        rb_link_node(node, parent, p);
        rb_insert_color(node, root);
        return NULL;
}

static struct rb_node *__etree_search(struct extent_io_tree *tree, u64 offset,
                                     struct rb_node **prev_ret,
                                     struct rb_node **next_ret)
{
        struct rb_root *root = &tree->state;
        struct rb_node *n = root->rb_node;
        struct rb_node *prev = NULL;
        struct rb_node *orig_prev = NULL;
        struct tree_entry *entry;
        struct tree_entry *prev_entry = NULL;

        while (n) {
                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) {
                orig_prev = prev;
                while (prev && offset > prev_entry->end) {
                        prev = rb_next(prev);
                        prev_entry = rb_entry(prev, struct tree_entry, rb_node);
                }
                *prev_ret = prev;
                prev = orig_prev;
        }

        if (next_ret) {
                prev_entry = rb_entry(prev, struct tree_entry, rb_node);
                while (prev && offset < prev_entry->start) {
                        prev = rb_prev(prev);
                        prev_entry = rb_entry(prev, struct tree_entry, rb_node);
                }
                *next_ret = prev;
        }
        return NULL;
}

static inline struct rb_node *tree_search(struct extent_io_tree *tree,
                                          u64 offset)
{
        struct rb_node *prev = NULL;
        struct rb_node *ret;

        ret = __etree_search(tree, offset, &prev, NULL);
        if (!ret)
                return prev;
        return ret;
}

static struct extent_buffer *buffer_tree_insert(struct extent_io_tree *tree,
                                          u64 offset, struct rb_node *node)
{
        struct rb_root *root = &tree->buffer;
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct extent_buffer *eb;

        while (*p) {
                parent = *p;
                eb = rb_entry(parent, struct extent_buffer, rb_node);

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

        rb_link_node(node, parent, p);
        rb_insert_color(node, root);
        return NULL;
}

static struct extent_buffer *buffer_search(struct extent_io_tree *tree,
                                           u64 offset)
{
        struct rb_root *root = &tree->buffer;
        struct rb_node *n = root->rb_node;
        struct extent_buffer *eb;

        while (n) {
                eb = rb_entry(n, struct extent_buffer, rb_node);
                if (offset < eb->start)
                        n = n->rb_left;
                else if (offset > eb->start)
                        n = n->rb_right;
                else
                        return eb;
        }
        return NULL;
}

/*
 * 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_io_tree *tree,
                       struct extent_state *state)
{
        struct extent_state *other;
        struct rb_node *other_node;

        if (state->state & (EXTENT_IOBITS | EXTENT_BOUNDARY))
                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->tree = NULL;
                        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->tree = NULL;
                        rb_erase(&state->rb_node, &tree->state);
                        free_extent_state(state);
                }
        }
        return 0;
}

static void set_state_cb(struct extent_io_tree *tree,
                         struct extent_state *state,
                         unsigned long bits)
{
        if (tree->ops && tree->ops->set_bit_hook) {
                tree->ops->set_bit_hook(tree->mapping->host, state->start,
                                        state->end, state->state, bits);
        }
}

static void clear_state_cb(struct extent_io_tree *tree,
                           struct extent_state *state,
                           unsigned long bits)
{
        if (tree->ops && tree->ops->clear_bit_hook) {
                tree->ops->clear_bit_hook(tree->mapping->host, state->start,
                                          state->end, state->state, bits);
        }
}

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

        if (end < start) {
                printk(KERN_ERR "btrfs end < start %llu %llu\n",
                       (unsigned long long)end,
                       (unsigned long long)start);
                WARN_ON(1);
        }
        if (bits & EXTENT_DIRTY)
                tree->dirty_bytes += end - start + 1;
        state->start = start;
        state->end = end;
        set_state_cb(tree, state, bits);
        state->state |= bits;
        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(KERN_ERR "btrfs found node %llu %llu on insert of "
                       "%llu %llu\n", (unsigned long long)found->start,
                       (unsigned long long)found->end,
                       (unsigned long long)start, (unsigned long long)end);
                free_extent_state(state);
                return -EEXIST;
        }
        state->tree = tree;
        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_io_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) {
                free_extent_state(prealloc);
                return -EEXIST;
        }
        prealloc->tree = tree;
        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_io_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;
        }
        clear_state_cb(tree, state, bits);
        state->state &= ~bits;
        if (wake)
                wake_up(&state->wq);
        if (delete || state->state == 0) {
                if (state->tree) {
                        clear_state_cb(tree, state, state->state);
                        rb_erase(&state->rb_node, &tree->state);
                        state->tree = NULL;
                        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_io_tree *tree, u64 start, u64 end,
                     int bits, int wake, int delete,
                     struct extent_state **cached_state,
                     gfp_t mask)
{
        struct extent_state *state;
        struct extent_state *cached;
        struct extent_state *prealloc = NULL;
        struct rb_node *next_node;
        struct rb_node *node;
        u64 last_end;
        int err;
        int set = 0;

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

        spin_lock(&tree->lock);
        if (cached_state) {
                cached = *cached_state;
                *cached_state = NULL;
                if (cached->tree && cached->start == start) {
                        atomic_dec(&cached->refs);
                        state = cached;
                        last_end = state->end;
                        goto found;
                }
                free_extent_state(cached);
        }
        /*
         * this search will find the extents that end after
         * our range starts
         */
        node = tree_search(tree, start);
        if (!node)
                goto out;
        state = rb_entry(node, struct extent_state, rb_node);
hit_next:
        if (state->start > end)
                goto out;
        WARN_ON(state->end < start);
        last_end = state->end;

        /*
         *     | ---- 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) {
                if (!prealloc)
                        prealloc = alloc_extent_state(GFP_ATOMIC);
                err = split_state(tree, state, prealloc, start);
                BUG_ON(err == -EEXIST);
                prealloc = NULL;
                if (err)
                        goto out;
                if (state->end <= end) {
                        set |= clear_state_bit(tree, state, bits,
                                        wake, delete);
                        if (last_end == (u64)-1)
                                goto out;
                        start = last_end + 1;
                } 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) {
                if (!prealloc)
                        prealloc = alloc_extent_state(GFP_ATOMIC);
                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;
        }
found:
        if (state->end < end && prealloc && !need_resched())
                next_node = rb_next(&state->rb_node);
        else
                next_node = NULL;
        set |= clear_state_bit(tree, state, bits, wake, delete);
        if (last_end == (u64)-1)
                goto out;
        start = last_end + 1;
        if (start <= end && next_node) {
                state = rb_entry(next_node, struct extent_state,
                                 rb_node);
                if (state->start == start)
                        goto hit_next;
        }
        goto search_again;

out:
        spin_unlock(&tree->lock);
        if (prealloc)
                free_extent_state(prealloc);

        return set;

search_again:
        if (start > end)
                goto out;
        spin_unlock(&tree->lock);
        if (mask & __GFP_WAIT)
                cond_resched();
        goto again;
}

static int wait_on_state(struct extent_io_tree *tree,
                         struct extent_state *state)
                __releases(tree->lock)
                __acquires(tree->lock)
{
        DEFINE_WAIT(wait);
        prepare_to_wait(&state->wq, &wait, TASK_UNINTERRUPTIBLE);
        spin_unlock(&tree->lock);
        schedule();
        spin_lock(&tree->lock);
        finish_wait(&state->wq, &wait);
        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_io_tree *tree, u64 start, u64 end, int bits)
{
        struct extent_state *state;
        struct rb_node *node;

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

static void set_state_bits(struct extent_io_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;
        }
        set_state_cb(tree, state, bits);
        state->state |= bits;
}

static void cache_state(struct extent_state *state,
                        struct extent_state **cached_ptr)
{
        if (cached_ptr && !(*cached_ptr)) {
                if (state->state & (EXTENT_IOBITS | EXTENT_BOUNDARY)) {
                        *cached_ptr = state;
                        atomic_inc(&state->refs);
                }
        }
}

/*
 * set some bits on a range in the tree.  This may require allocations or
 * sleeping, so the gfp mask is used to indicate what is allowed.
 *
 * If any of the exclusive bits are set, this will fail with -EEXIST if some
 * part of the range already has the desired bits set.  The start of the
 * existing range is returned in failed_start in this case.
 *
 * [start, end] is inclusive This takes the tree lock.
 */

static int set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                          int bits, int exclusive_bits, u64 *failed_start,
                          struct extent_state **cached_state,
                          gfp_t mask)
{
        struct extent_state *state;
        struct extent_state *prealloc = NULL;
        struct rb_node *node;
        int err = 0;
        u64 last_start;
        u64 last_end;
again:
        if (!prealloc && (mask & __GFP_WAIT)) {
                prealloc = alloc_extent_state(mask);
                if (!prealloc)
                        return -ENOMEM;
        }

        spin_lock(&tree->lock);
        /*
         * this search will find all the extents that end after
         * our range starts.
         */
        node = tree_search(tree, 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);
hit_next:
        last_start = state->start;
        last_end = state->end;

        /*
         * | ---- desired range ---- |
         * | state |
         *
         * Just lock what we found and keep going
         */
        if (state->start == start && state->end <= end) {
                struct rb_node *next_node;
                if (state->state & exclusive_bits) {
                        *failed_start = state->start;
                        err = -EEXIST;
                        goto out;
                }
                set_state_bits(tree, state, bits);
                cache_state(state, cached_state);
                merge_state(tree, state);
                if (last_end == (u64)-1)
                        goto out;

                start = last_end + 1;
                if (start < end && prealloc && !need_resched()) {
                        next_node = rb_next(node);
                        if (next_node) {
                                state = rb_entry(next_node, struct extent_state,
                                                 rb_node);
                                if (state->start == start)
                                        goto hit_next;
                        }
                }
                goto search_again;
        }

        /*
         *     | ---- desired range ---- |
         * | state |
         *   or
         * | ------------- state -------------- |
         *
         * We need to split the extent we found, and may flip bits on
         * second half.
         *
         * If the extent we found extends past our
         * range, we just split and search again.  It'll get split
         * again the next time though.
         *
         * If the extent we found is inside our range, we set the
         * desired bit on it.
         */
        if (state->start < start) {
                if (state->state & exclusive_bits) {
                        *failed_start = start;
                        err = -EEXIST;
                        goto out;
                }
                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);
                        cache_state(state, cached_state);
                        merge_state(tree, state);
                        if (last_end == (u64)-1)
                                goto out;
                        start = last_end + 1;
                } 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);
                cache_state(prealloc, cached_state);
                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) {
                if (state->state & exclusive_bits) {
                        *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);
                cache_state(prealloc, cached_state);
                merge_state(tree, prealloc);
                prealloc = NULL;
                goto out;
        }

        goto search_again;

out:
        spin_unlock(&tree->lock);
        if (prealloc)
                free_extent_state(prealloc);

        return err;

search_again:
        if (start > end)
                goto out;
        spin_unlock(&tree->lock);
        if (mask & __GFP_WAIT)
                cond_resched();
        goto again;
}

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

int set_extent_ordered(struct extent_io_tree *tree, u64 start, u64 end,
                       gfp_t mask)
{
        return set_extent_bit(tree, start, end, EXTENT_ORDERED, 0, NULL, NULL,
                              mask);
}

int set_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
                    int bits, gfp_t mask)
{
        return set_extent_bit(tree, start, end, bits, 0, NULL,
                              NULL, mask);
}

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

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

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

int clear_extent_ordered(struct extent_io_tree *tree, u64 start, u64 end,
                         gfp_t mask)
{
        return clear_extent_bit(tree, start, end, EXTENT_ORDERED, 1, 0,
                                NULL, mask);
}

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

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

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

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

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

/*
 * either insert or lock state struct between start and end use mask to tell
 * us if waiting is desired.
 */
int lock_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
                     int bits, struct extent_state **cached_state, gfp_t mask)
{
        int err;
        u64 failed_start;
        while (1) {
                err = set_extent_bit(tree, start, end, EXTENT_LOCKED | bits,
                                     EXTENT_LOCKED, &failed_start,
                                     cached_state, 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;
}

int lock_extent(struct extent_io_tree *tree, u64 start, u64 end, gfp_t mask)
{
        return lock_extent_bits(tree, start, end, 0, NULL, mask);
}

int try_lock_extent(struct extent_io_tree *tree, u64 start, u64 end,
                    gfp_t mask)
{
        int err;
        u64 failed_start;

        err = set_extent_bit(tree, start, end, EXTENT_LOCKED, EXTENT_LOCKED,
                             &failed_start, NULL, mask);
        if (err == -EEXIST) {
                if (failed_start > start)
                        clear_extent_bit(tree, start, failed_start - 1,
                                         EXTENT_LOCKED, 1, 0, NULL, mask);
                return 0;
        }
        return 1;
}

int unlock_extent_cached(struct extent_io_tree *tree, u64 start, u64 end,
                         struct extent_state **cached, gfp_t mask)
{
        return clear_extent_bit(tree, start, end, EXTENT_LOCKED, 1, 0, cached,
                                mask);
}

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

/*
 * helper function to set pages and extents in the tree dirty
 */
int set_range_dirty(struct extent_io_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++;
        }
        return 0;
}

/*
 * helper function to set both pages and extents in the tree writeback
 */
static int set_range_writeback(struct extent_io_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++;
        }
        return 0;
}

/*
 * find the first offset in the io tree with 'bits' set. zero is
 * returned if we find something, and *start_ret and *end_ret are
 * set to reflect the state struct that was found.
 *
 * If nothing was found, 1 is returned, < 0 on error
 */
int find_first_extent_bit(struct extent_io_tree *tree, u64 start,
                          u64 *start_ret, u64 *end_ret, int bits)
{
        struct rb_node *node;
        struct extent_state *state;
        int ret = 1;

        spin_lock(&tree->lock);
        /*
         * this search will find all the extents that end after
         * our range starts.
         */
        node = tree_search(tree, start);
        if (!node)
                goto out;

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

/* find the first state struct with 'bits' set after 'start', and
 * return it.  tree->lock must be held.  NULL will returned if
 * nothing was found after 'start'
 */
struct extent_state *find_first_extent_bit_state(struct extent_io_tree *tree,
                                                 u64 start, int bits)
{
        struct rb_node *node;
        struct extent_state *state;

        /*
         * this search will find all the extents that end after
         * our range starts.
         */
        node = tree_search(tree, start);
        if (!node)
                goto out;

        while (1) {
                state = rb_entry(node, struct extent_state, rb_node);
                if (state->end >= start && (state->state & bits))
                        return state;

                node = rb_next(node);
                if (!node)
                        break;
        }
out:
        return NULL;
}

/*
 * find a contiguous range of bytes in the file marked as delalloc, not
 * more than 'max_bytes'.  start and end are used to return the range,
 *
 * 1 is returned if we find something, 0 if nothing was in the tree
 */
static noinline u64 find_delalloc_range(struct extent_io_tree *tree,
                                        u64 *start, u64 *end, u64 max_bytes)
{
        struct rb_node *node;
        struct extent_state *state;
        u64 cur_start = *start;
        u64 found = 0;
        u64 total_bytes = 0;

        spin_lock(&tree->lock);

        /*
         * this search will find all the extents that end after
         * our range starts.
         */
        node = tree_search(tree, cur_start);
        if (!node) {
                if (!found)
                        *end = (u64)-1;
                goto out;
        }

        while (1) {
                state = rb_entry(node, struct extent_state, rb_node);
                if (found && (state->start != cur_start ||
                              (state->state & EXTENT_BOUNDARY))) {
                        goto out;
                }
                if (!(state->state & EXTENT_DELALLOC)) {
                        if (!found)
                                *end = state->end;
                        goto out;
                }
                if (!found)
                        *start = state->start;
                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:
        spin_unlock(&tree->lock);
        return found;
}

static noinline int __unlock_for_delalloc(struct inode *inode,
                                          struct page *locked_page,
                                          u64 start, u64 end)
{
        int ret;
        struct page *pages[16];
        unsigned long index = start >> PAGE_CACHE_SHIFT;
        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
        unsigned long nr_pages = end_index - index + 1;
        int i;

        if (index == locked_page->index && end_index == index)
                return 0;

        while (nr_pages > 0) {
                ret = find_get_pages_contig(inode->i_mapping, index,
                                     min_t(unsigned long, nr_pages,
                                     ARRAY_SIZE(pages)), pages);
                for (i = 0; i < ret; i++) {
                        if (pages[i] != locked_page)
                                unlock_page(pages[i]);
                        page_cache_release(pages[i]);
                }
                nr_pages -= ret;
                index += ret;
                cond_resched();
        }
        return 0;
}

static noinline int lock_delalloc_pages(struct inode *inode,
                                        struct page *locked_page,
                                        u64 delalloc_start,
                                        u64 delalloc_end)
{
        unsigned long index = delalloc_start >> PAGE_CACHE_SHIFT;
        unsigned long start_index = index;
        unsigned long end_index = delalloc_end >> PAGE_CACHE_SHIFT;
        unsigned long pages_locked = 0;
        struct page *pages[16];
        unsigned long nrpages;
        int ret;
        int i;

        /* the caller is responsible for locking the start index */
        if (index == locked_page->index && index == end_index)
                return 0;

        /* skip the page at the start index */
        nrpages = end_index - index + 1;
        while (nrpages > 0) {
                ret = find_get_pages_contig(inode->i_mapping, index,
                                     min_t(unsigned long,
                                     nrpages, ARRAY_SIZE(pages)), pages);
                if (ret == 0) {
                        ret = -EAGAIN;
                        goto done;
                }
                /* now we have an array of pages, lock them all */
                for (i = 0; i < ret; i++) {
                        /*
                         * the caller is taking responsibility for
                         * locked_page
                         */
                        if (pages[i] != locked_page) {
                                lock_page(pages[i]);
                                if (!PageDirty(pages[i]) ||
                                    pages[i]->mapping != inode->i_mapping) {
                                        ret = -EAGAIN;
                                        unlock_page(pages[i]);
                                        page_cache_release(pages[i]);
                                        goto done;
                                }
                        }
                        page_cache_release(pages[i]);
                        pages_locked++;
                }
                nrpages -= ret;
                index += ret;
                cond_resched();
        }
        ret = 0;
done:
        if (ret && pages_locked) {
                __unlock_for_delalloc(inode, locked_page,
                              delalloc_start,
                              ((u64)(start_index + pages_locked - 1)) <<
                              PAGE_CACHE_SHIFT);
        }
        return ret;
}

/*
 * find a contiguous range of bytes in the file marked as delalloc, not
 * more than 'max_bytes'.  start and end are used to return the range,
 *
 * 1 is returned if we find something, 0 if nothing was in the tree
 */
static noinline u64 find_lock_delalloc_range(struct inode *inode,
                                             struct extent_io_tree *tree,
                                             struct page *locked_page,
                                             u64 *start, u64 *end,
                                             u64 max_bytes)
{
        u64 delalloc_start;
        u64 delalloc_end;
        u64 found;
        int ret;
        int loops = 0;

again:
        /* step one, find a bunch of delalloc bytes starting at start */
        delalloc_start = *start;
        delalloc_end = 0;
        found = find_delalloc_range(tree, &delalloc_start, &delalloc_end,
                                    max_bytes);
        if (!found || delalloc_end <= *start) {
                *start = delalloc_start;
                *end = delalloc_end;
                return found;
        }

        /*
         * start comes from the offset of locked_page.  We have to lock
         * pages in order, so we can't process delalloc bytes before
         * locked_page
         */
        if (delalloc_start < *start)
                delalloc_start = *start;

        /*
         * make sure to limit the number of pages we try to lock down
         * if we're looping.
         */
        if (delalloc_end + 1 - delalloc_start > max_bytes && loops)
                delalloc_end = delalloc_start + PAGE_CACHE_SIZE - 1;

        /* step two, lock all the pages after the page that has start */
        ret = lock_delalloc_pages(inode, locked_page,
                                  delalloc_start, delalloc_end);
        if (ret == -EAGAIN) {
                /* some of the pages are gone, lets avoid looping by
                 * shortening the size of the delalloc range we're searching
                 */
                if (!loops) {
                        unsigned long offset = (*start) & (PAGE_CACHE_SIZE - 1);
                        max_bytes = PAGE_CACHE_SIZE - offset;
                        loops = 1;
                        goto again;
                } else {
                        found = 0;
                        goto out_failed;
                }
        }
        BUG_ON(ret);

        /* step three, lock the state bits for the whole range */
        lock_extent(tree, delalloc_start, delalloc_end, GFP_NOFS);

        /* then test to make sure it is all still delalloc */
        ret = test_range_bit(tree, delalloc_start, delalloc_end,
                             EXTENT_DELALLOC, 1);
        if (!ret) {
                unlock_extent(tree, delalloc_start, delalloc_end, GFP_NOFS);
                __unlock_for_delalloc(inode, locked_page,
                              delalloc_start, delalloc_end);
                cond_resched();
                goto again;
        }
        *start = delalloc_start;
        *end = delalloc_end;
out_failed:
        return found;
}

int extent_clear_unlock_delalloc(struct inode *inode,
                                struct extent_io_tree *tree,
                                u64 start, u64 end, struct page *locked_page,
                                int unlock_pages,
                                int clear_unlock,
                                int clear_delalloc, int clear_dirty,
                                int set_writeback,
                                int end_writeback)
{
        int ret;
        struct page *pages[16];
        unsigned long index = start >> PAGE_CACHE_SHIFT;
        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
        unsigned long nr_pages = end_index - index + 1;
        int i;
        int clear_bits = 0;

        if (clear_unlock)
                clear_bits |= EXTENT_LOCKED;
        if (clear_dirty)
                clear_bits |= EXTENT_DIRTY;

        if (clear_delalloc)
                clear_bits |= EXTENT_DELALLOC;

        clear_extent_bit(tree, start, end, clear_bits, 1, 0, NULL, GFP_NOFS);
        if (!(unlock_pages || clear_dirty || set_writeback || end_writeback))
                return 0;

        while (nr_pages > 0) {
                ret = find_get_pages_contig(inode->i_mapping, index,
                                     min_t(unsigned long,
                                     nr_pages, ARRAY_SIZE(pages)), pages);
                for (i = 0; i < ret; i++) {
                        if (pages[i] == locked_page) {
                                page_cache_release(pages[i]);
                                continue;
                        }
                        if (clear_dirty)
                                clear_page_dirty_for_io(pages[i]);
                        if (set_writeback)
                                set_page_writeback(pages[i]);
                        if (end_writeback)
                                end_page_writeback(pages[i]);
                        if (unlock_pages)
                                unlock_page(pages[i]);
                        page_cache_release(pages[i]);
                }
                nr_pages -= ret;
                index += ret;
                cond_resched();
        }
        return 0;
}

/*
 * count the number of bytes in the tree that have a given bit(s)
 * set.  This can be fairly slow, except for EXTENT_DIRTY which is
 * cached.  The total number found is returned.
 */
u64 count_range_bits(struct extent_io_tree *tree,
                     u64 *start, u64 search_end, u64 max_bytes,
                     unsigned long bits)
{
        struct rb_node *node;
        struct extent_state *state;
        u64 cur_start = *start;
        u64 total_bytes = 0;
        int found = 0;

        if (search_end <= cur_start) {
                WARN_ON(1);
                return 0;
        }

        spin_lock(&tree->lock);
        if (cur_start == 0 && bits == EXTENT_DIRTY) {
                total_bytes = tree->dirty_bytes;
                goto out;
        }
        /*
         * this search will find all the extents that end after
         * our range starts.
         */
        node = tree_search(tree, cur_start);
        if (!node)
                goto out;

        while (1) {
                state = rb_entry(node, struct extent_state, rb_node);
                if (state->start > search_end)
                        break;
                if (state->end >= cur_start && (state->state & bits)) {
                        total_bytes += min(search_end, state->end) + 1 -
                                       max(cur_start, state->start);
                        if (total_bytes >= max_bytes)
                                break;
                        if (!found) {
                                *start = state->start;
                                found = 1;
                        }
                }
                node = rb_next(node);
                if (!node)
                        break;
        }
out:
        spin_unlock(&tree->lock);
        return total_bytes;
}

/*
 * set the private field for a given byte offset in the tree.  If there isn't
 * an extent_state there already, this does nothing.
 */
int set_state_private(struct extent_io_tree *tree, u64 start, u64 private)
{
        struct rb_node *node;
        struct extent_state *state;
        int ret = 0;

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

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

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

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

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

                if (filled && state->start > start) {
                        bitset = 0;
                        break;
                }

                if (state->start > end)
                        break;

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

/*
 * helper function to set a given page up to date if all the
 * extents in the tree for that page are up to date
 */
static int check_page_uptodate(struct extent_io_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_io_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_io_tree *tree,
                             struct page *page)
{
        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 void end_bio_extent_writepage(struct bio *bio, int err)
{
        int uptodate = err == 0;
        struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
        struct extent_io_tree *tree;
        u64 start;
        u64 end;
        int whole_page;
        int ret;

        do {
                struct page *page = bvec->bv_page;
                tree = &BTRFS_I(page->mapping->host)->io_tree;

                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 (tree->ops && tree->ops->writepage_end_io_hook) {
                        ret = tree->ops->writepage_end_io_hook(page, start,
                                                       end, NULL, uptodate);
                        if (ret)
                                uptodate = 0;
                }

                if (!uptodate && tree->ops &&
                    tree->ops->writepage_io_failed_hook) {
                        ret = tree->ops->writepage_io_failed_hook(bio, page,
                                                         start, end, NULL);
                        if (ret == 0) {
                                uptodate = (err == 0);
                                continue;
                        }
                }

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

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

        bio_put(bio);
}

/*
 * after a readpage IO is done, we need to:
 * clear the uptodate bits on error
 * set the uptodate bits if things worked
 * set the page up to date if all extents in the tree are uptodate
 * clear the lock bit in the extent tree
 * unlock the page if there are no other extents locked for it
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bio_extent_readpage(struct bio *bio, 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_io_tree *tree;
        u64 start;
        u64 end;
        int whole_page;
        int ret;

        if (err)
                uptodate = 0;

        do {
                struct page *page = bvec->bv_page;
                tree = &BTRFS_I(page->mapping->host)->io_tree;

                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,
                                                              NULL);
                        if (ret)
                                uptodate = 0;
                }
                if (!uptodate && tree->ops &&
                    tree->ops->readpage_io_failed_hook) {
                        ret = tree->ops->readpage_io_failed_hook(bio, page,
                                                         start, end, NULL);
                        if (ret == 0) {
                                uptodate =
                                        test_bit(BIO_UPTODATE, &bio->bi_flags);
                                if (err)
                                        uptodate = 0;
                                continue;
                        }
                }

                if (uptodate) {
                        set_extent_uptodate(tree, start, end,
                                            GFP_ATOMIC);
                }
                unlock_extent(tree, start, end, GFP_ATOMIC);

                if (whole_page) {
                        if (uptodate) {
                                SetPageUptodate(page);
                        } else {
                                ClearPageUptodate(page);
                                SetPageError(page);
                        }
                        unlock_page(page);
                } else {
                        if (uptodate) {
                                check_page_uptodate(tree, page);
                        } else {
                                ClearPageUptodate(page);
                                SetPageError(page);
                        }
                        check_page_locked(tree, page);
                }
        } while (bvec >= bio->bi_io_vec);

        bio_put(bio);
}

/*
 * 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 void end_bio_extent_preparewrite(struct bio *bio, 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_io_tree *tree;
        u64 start;
        u64 end;

        do {
                struct page *page = bvec->bv_page;
                tree = &BTRFS_I(page->mapping->host)->io_tree;

                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);
}

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_size = 0;
                bio->bi_bdev = bdev;
                bio->bi_sector = first_sector;
        }
        return bio;
}

static int submit_one_bio(int rw, struct bio *bio, int mirror_num,
                          unsigned long bio_flags)
{
        int ret = 0;
        struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
        struct page *page = bvec->bv_page;
        struct extent_io_tree *tree = bio->bi_private;
        u64 start;
        u64 end;

        start = ((u64)page->index << PAGE_CACHE_SHIFT) + bvec->bv_offset;
        end = start + bvec->bv_len - 1;

        bio->bi_private = NULL;

        bio_get(bio);

        if (tree->ops && tree->ops->submit_bio_hook)
                tree->ops->submit_bio_hook(page->mapping->host, rw, bio,
                                           mirror_num, bio_flags);
        else
                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_io_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 mirror_num,
                              unsigned long prev_bio_flags,
                              unsigned long bio_flags)
{
        int ret = 0;
        struct bio *bio;
        int nr;
        int contig = 0;
        int this_compressed = bio_flags & EXTENT_BIO_COMPRESSED;
        int old_compressed = prev_bio_flags & EXTENT_BIO_COMPRESSED;
        size_t page_size = min_t(size_t, size, PAGE_CACHE_SIZE);

        if (bio_ret && *bio_ret) {
                bio = *bio_ret;
                if (old_compressed)
                        contig = bio->bi_sector == sector;
                else
                        contig = bio->bi_sector + (bio->bi_size >> 9) ==
                                sector;

                if (prev_bio_flags != bio_flags || !contig ||
                    (tree->ops && tree->ops->merge_bio_hook &&
                     tree->ops->merge_bio_hook(page, offset, page_size, bio,
                                               bio_flags)) ||
                    bio_add_page(bio, page, page_size, offset) < page_size) {
                        ret = submit_one_bio(rw, bio, mirror_num,
                                             prev_bio_flags);
                        bio = NULL;
                } else {
                        return 0;
                }
        }
        if (this_compressed)
                nr = BIO_MAX_PAGES;
        else
                nr = bio_get_nr_vecs(bdev);

        bio = extent_bio_alloc(bdev, sector, nr, GFP_NOFS | __GFP_HIGH);

        bio_add_page(bio, page, 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, mirror_num, bio_flags);

        return ret;
}

void set_page_extent_mapped(struct page *page)
{
        if (!PagePrivate(page)) {
                SetPagePrivate(page);
                page_cache_get(page);
                set_page_private(page, EXTENT_PAGE_PRIVATE);
        }
}

static void set_page_extent_head(struct page *page, unsigned long len)
{
        set_page_private(page, EXTENT_PAGE_PRIVATE_FIRST_PAGE | len << 2);
}

/*
 * 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_io_tree *tree,
                                   struct page *page,
                                   get_extent_t *get_extent,
                                   struct bio **bio, int mirror_num,
                                   unsigned long *bio_flags)
{
        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 disk_io_size;
        size_t blocksize = inode->i_sb->s_blocksize;
        unsigned long this_bio_flag = 0;

        set_page_extent_mapped(page);

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

        if (page->index == last_byte >> PAGE_CACHE_SHIFT) {
                char *userpage;
                size_t zero_offset = last_byte & (PAGE_CACHE_SIZE - 1);

                if (zero_offset) {
                        iosize = PAGE_CACHE_SIZE - zero_offset;
                        userpage = kmap_atomic(page, KM_USER0);
                        memset(userpage + zero_offset, 0, iosize);
                        flush_dcache_page(page);
                        kunmap_atomic(userpage, KM_USER0);
                }
        }
        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 - cur + 1, 0);
                if (IS_ERR(em) || !em) {
                        SetPageError(page);
                        unlock_extent(tree, cur, end, GFP_NOFS);
                        break;
                }
                extent_offset = cur - em->start;
                BUG_ON(extent_map_end(em) <= cur);
                BUG_ON(end < cur);

                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
                        this_bio_flag = EXTENT_BIO_COMPRESSED;

                iosize = min(extent_map_end(em) - cur, end - cur + 1);
                cur_end = min(extent_map_end(em) - 1, end);
                iosize = (iosize + blocksize - 1) & ~((u64)blocksize - 1);
                if (this_bio_flag & EXTENT_BIO_COMPRESSED) {
                        disk_io_size = em->block_len;
                        sector = em->block_start >> 9;
                } else {
                        sector = (em->block_start + extent_offset) >> 9;
                        disk_io_size = iosize;
                }
                bdev = em->bdev;
                block_start = em->block_start;
                if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
                        block_start = EXTENT_MAP_HOLE;
                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)) {
                        check_page_uptodate(tree, page);
                        unlock_extent(tree, cur, cur + iosize - 1, GFP_NOFS);
                        cur = cur + iosize;
                        page_offset += iosize;
                        continue;
                }
                /* we have an inline extent but it didn't get marked up
                 * to date.  Error out
                 */
                if (block_start == EXTENT_MAP_INLINE) {
                        SetPageError(page);
                        unlock_extent(tree, cur, cur + iosize - 1, 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 pnr = (last_byte >> PAGE_CACHE_SHIFT) + 1;
                        pnr -= page->index;
                        ret = submit_extent_page(READ, tree, page,
                                         sector, disk_io_size, page_offset,
                                         bdev, bio, pnr,
                                         end_bio_extent_readpage, mirror_num,
                                         *bio_flags,
                                         this_bio_flag);
                        nr++;
                        *bio_flags = this_bio_flag;
                }
                if (ret)
                        SetPageError(page);
                cur = cur + iosize;
                page_offset += iosize;
        }
        if (!nr) {
                if (!PageError(page))
                        SetPageUptodate(page);
                unlock_page(page);
        }
        return 0;
}

int extent_read_full_page(struct extent_io_tree *tree, struct page *page,
                            get_extent_t *get_extent)
{
        struct bio *bio = NULL;
        unsigned long bio_flags = 0;
        int ret;

        ret = __extent_read_full_page(tree, page, get_extent, &bio, 0,
                                      &bio_flags);
        if (bio)
                submit_one_bio(READ, bio, 0, bio_flags);
        return ret;
}

static noinline void update_nr_written(struct page *page,
                                      struct writeback_control *wbc,
                                      unsigned long nr_written)
{
        wbc->nr_to_write -= nr_written;
        if (wbc->range_cyclic || (wbc->nr_to_write > 0 &&
            wbc->range_start == 0 && wbc->range_end == LLONG_MAX))
                page->mapping->writeback_index = page->index + nr_written;
}

/*
 * 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_io_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;
        u64 unlock_start;
        sector_t sector;
        struct extent_state *cached_state = NULL;
        struct extent_map *em;
        struct block_device *bdev;
        int ret;
        int nr = 0;
        size_t pg_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;
        int page_started;
        int compressed;
        int write_flags;
        unsigned long nr_written = 0;

        if (wbc->sync_mode == WB_SYNC_ALL)
                write_flags = WRITE_SYNC_PLUG;
        else
                write_flags = WRITE;

        WARN_ON(!PageLocked(page));
        pg_offset = i_size & (PAGE_CACHE_SIZE - 1);
        if (page->index > end_index ||
           (page->index == end_index && !pg_offset)) {
                page->mapping->a_ops->invalidatepage(page, 0);
                unlock_page(page);
                return 0;
        }

        if (page->index == end_index) {
                char *userpage;

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

        set_page_extent_mapped(page);

        delalloc_start = start;
        delalloc_end = 0;
        page_started = 0;
        if (!epd->extent_locked) {
                u64 delalloc_to_write;
                /*
                 * make sure the wbc mapping index is at least updated
                 * to this page.
                 */
                update_nr_written(page, wbc, 0);

                while (delalloc_end < page_end) {
                        nr_delalloc = find_lock_delalloc_range(inode, tree,
                                                       page,
                                                       &delalloc_start,
                                                       &delalloc_end,
                                                       128 * 1024 * 1024);
                        if (nr_delalloc == 0) {
                                delalloc_start = delalloc_end + 1;
                                continue;
                        }
                        tree->ops->fill_delalloc(inode, page, delalloc_start,
                                                 delalloc_end, &page_started,
                                                 &nr_written);
                        delalloc_to_write = (delalloc_end -
                                        max_t(u64, page_offset(page),
                                              delalloc_start) + 1) >>
                                        PAGE_CACHE_SHIFT;
                        if (wbc->nr_to_write < delalloc_to_write) {
                                wbc->nr_to_write = min_t(long, 8192,
                                                 delalloc_to_write);
                        }
                        delalloc_start = delalloc_end + 1;
                }

                /* did the fill delalloc function already unlock and start
                 * the IO?
                 */
                if (page_started) {
                        ret = 0;
                        /*
                         * we've unlocked the page, so we can't update
                         * the mapping's writeback index, just update
                         * nr_to_write.
                         */
                        wbc->nr_to_write -= nr_written;
                        goto done_unlocked;
                }
        }
        if (tree->ops && tree->ops->writepage_start_hook) {
                ret = tree->ops->writepage_start_hook(page, start,
                                                      page_end);
                if (ret == -EAGAIN) {
                        redirty_page_for_writepage(wbc, page);
                        update_nr_written(page, wbc, nr_written);
                        unlock_page(page);
                        ret = 0;
                        goto done_unlocked;
                }
        }

        /*
         * we don't want to touch the inode after unlocking the page,
         * so we update the mapping writeback index now
         */
        update_nr_written(page, wbc, nr_written + 1);

        end = page_end;
        if (last_byte <= start) {
                if (tree->ops && tree->ops->writepage_end_io_hook)
                        tree->ops->writepage_end_io_hook(page, start,
                                                         page_end, NULL, 1);
                unlock_start = page_end + 1;
                goto done;
        }

        blocksize = inode->i_sb->s_blocksize;

        while (cur <= end) {
                if (cur >= last_byte) {
                        if (tree->ops && tree->ops->writepage_end_io_hook)
                                tree->ops->writepage_end_io_hook(page, cur,
                                                         page_end, NULL, 1);
                        unlock_start = page_end + 1;
                        break;
                }
                em = epd->get_extent(inode, page, pg_offset, cur,
                                     end - cur + 1, 1);
                if (IS_ERR(em) || !em) {
                        SetPageError(page);
                        break;
                }

                extent_offset = cur - em->start;
                BUG_ON(extent_map_end(em) <= cur);
                BUG_ON(end < cur);
                iosize = min(extent_map_end(em) - 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;
                compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
                free_extent_map(em);
                em = NULL;

                /*
                 * compressed and inline extents are written through other
                 * paths in the FS
                 */
                if (compressed || block_start == EXTENT_MAP_HOLE ||
                    block_start == EXTENT_MAP_INLINE) {
                        /*
                         * end_io notification does not happen here for
                         * compressed extents
                         */
                        if (!compressed && tree->ops &&
                            tree->ops->writepage_end_io_hook)
                                tree->ops->writepage_end_io_hook(page, cur,
                                                         cur + iosize - 1,
                                                         NULL, 1);
                        else if (compressed) {
                                /* we don't want to end_page_writeback on
                                 * a compressed extent.  this happens
                                 * elsewhere
                                 */
                                nr++;
                        }

                        cur += iosize;
                        pg_offset += iosize;
                        unlock_start = cur;
                        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;
                        pg_offset += iosize;
                        continue;
                }

                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(KERN_ERR "btrfs 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_flags, tree, page,
                                                 sector, iosize, pg_offset,
                                                 bdev, &epd->bio, max_nr,
                                                 end_bio_extent_writepage,
                                                 0, 0, 0);
                        if (ret)
                                SetPageError(page);
                }
                cur = cur + iosize;
                pg_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_page(page);

done_unlocked:

        /* drop our reference on any cached states */
        free_extent_state(cached_state);
        return 0;
}

/**
 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 * @writepage: function called for each page
 * @data: data passed to writepage function
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 */
static int extent_write_cache_pages(struct extent_io_tree *tree,
                             struct address_space *mapping,
                             struct writeback_control *wbc,
                             writepage_t writepage, void *data,
                             void (*flush_fn)(void *))
{
        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;

        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
                         */
                        if (tree->ops && tree->ops->write_cache_pages_lock_hook)
                                tree->ops->write_cache_pages_lock_hook(page);
                        else
                                lock_page(page);

                        if (unlikely(page->mapping != mapping)) {
                                unlock_page(page);
                                continue;
                        }

                        if (!wbc->range_cyclic && page->index > end) {
                                done = 1;
                                unlock_page(page);
                                continue;
                        }

                        if (wbc->sync_mode != WB_SYNC_NONE) {
                                if (PageWriteback(page))
                                        flush_fn(data);
                                wait_on_page_writeback(page);
                        }

                        if (PageWriteback(page) ||
                            !clear_page_dirty_for_io(page)) {
                                unlock_page(page);
                                continue;
                        }

                        ret = (*writepage)(page, wbc, data);

                        if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
                                unlock_page(page);
                                ret = 0;
                        }
                        if (ret || wbc->nr_to_write <= 0)
                                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;
        }
        return ret;
}

static void flush_epd_write_bio(struct extent_page_data *epd)
{
        if (epd->bio) {
                if (epd->sync_io)
                        submit_one_bio(WRITE_SYNC, epd->bio, 0, 0);
                else
                        submit_one_bio(WRITE, epd->bio, 0, 0);
                epd->bio = NULL;
        }
}

static noinline void flush_write_bio(void *data)
{
        struct extent_page_data *epd = data;
        flush_epd_write_bio(epd);
}

int extent_write_full_page(struct extent_io_tree *tree, struct page *page,
                          get_extent_t *get_extent,
                          struct writeback_control *wbc)
{
        int ret;
        struct address_space *mapping = page->mapping;
        struct extent_page_data epd = {
                .bio = NULL,
                .tree = tree,
                .get_extent = get_extent,
                .extent_locked = 0,
                .sync_io = wbc->sync_mode == WB_SYNC_ALL,
        };
        struct writeback_control wbc_writepages = {
                .bdi            = wbc->bdi,
                .sync_mode      = wbc->sync_mode,
                .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);

        extent_write_cache_pages(tree, mapping, &wbc_writepages,
                                 __extent_writepage, &epd, flush_write_bio);
        flush_epd_write_bio(&epd);
        return ret;
}

int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode,
                              u64 start, u64 end, get_extent_t *get_extent,
                              int mode)
{
        int ret = 0;
        struct address_space *mapping = inode->i_mapping;
        struct page *page;
        unsigned long nr_pages = (end - start + PAGE_CACHE_SIZE) >>
                PAGE_CACHE_SHIFT;

        struct extent_page_data epd = {
                .bio = NULL,
                .tree = tree,
                .get_extent = get_extent,
                .extent_locked = 1,
                .sync_io = mode == WB_SYNC_ALL,
        };
        struct writeback_control wbc_writepages = {
                .bdi            = inode->i_mapping->backing_dev_info,
                .sync_mode      = mode,
                .older_than_this = NULL,
                .nr_to_write    = nr_pages * 2,
                .range_start    = start,
                .range_end      = end + 1,
        };

        while (start <= end) {
                page = find_get_page(mapping, start >> PAGE_CACHE_SHIFT);
                if (clear_page_dirty_for_io(page))
                        ret = __extent_writepage(page, &wbc_writepages, &epd);
                else {
                        if (tree->ops && tree->ops->writepage_end_io_hook)
                                tree->ops->writepage_end_io_hook(page, start,
                                                 start + PAGE_CACHE_SIZE - 1,
                                                 NULL, 1);
                        unlock_page(page);
                }
                page_cache_release(page);
                start += PAGE_CACHE_SIZE;
        }

        flush_epd_write_bio(&epd);
        return ret;
}

int extent_writepages(struct extent_io_tree *tree,
                      struct address_space *mapping,
                      get_extent_t *get_extent,
                      struct writeback_control *wbc)
{
        int ret = 0;
        struct extent_page_data epd = {
                .bio = NULL,
                .tree = tree,
                .get_extent = get_extent,
                .extent_locked = 0,
                .sync_io = wbc->sync_mode == WB_SYNC_ALL,
        };

        ret = extent_write_cache_pages(tree, mapping, wbc,
                                       __extent_writepage, &epd,
                                       flush_write_bio);
        flush_epd_write_bio(&epd);
        return ret;
}

int extent_readpages(struct extent_io_tree *tree,
                     struct address_space *mapping,
                     struct list_head *pages, unsigned nr_pages,
                     get_extent_t get_extent)
{
        struct bio *bio = NULL;
        unsigned page_idx;
        struct pagevec pvec;
        unsigned long bio_flags = 0;

        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_file(&pvec);
                        __extent_read_full_page(tree, page, get_extent,
                                                &bio, 0, &bio_flags);
                }
                page_cache_release(page);
        }
        if (pagevec_count(&pvec))
                __pagevec_lru_add_file(&pvec);
        BUG_ON(!list_empty(pages));
        if (bio)
                submit_one_bio(READ, bio, 0, bio_flags);
        return 0;
}

/*
 * basic invalidatepage code, this waits on any locked or writeback
 * ranges corresponding to the page, and then deletes any extent state
 * records from the tree
 */
int extent_invalidatepage(struct extent_io_tree *tree,
                          struct page *page, unsigned long offset)
{
        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_page_writeback(page);
        clear_extent_bit(tree, start, end,
                         EXTENT_LOCKED | EXTENT_DIRTY | EXTENT_DELALLOC,
                         1, 1, NULL, GFP_NOFS);
        return 0;
}

/*
 * 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_io_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;
}

int extent_prepare_write(struct extent_io_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 - block_start + 1, 1);
                if (IS_ERR(em) || !em)
                        goto err;

                cur_end = min(block_end, extent_map_end(em) - 1);
                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) &
                                ~((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, NULL, GFP_NOFS);
                        ret = submit_extent_page(READ, tree, page,
                                         sector, iosize, page_offset, em->bdev,
                                         NULL, 1,
                                         end_bio_extent_preparewrite, 0,
                                         0, 0);
                        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;
}

/*
 * a helper for releasepage, this tests for areas of the page that
 * are locked or under IO and drops the related state bits if it is safe
 * to drop the page.
 */
int try_release_extent_state(struct extent_map_tree *map,
                             struct extent_io_tree *tree, struct page *page,
                             gfp_t mask)
{
        u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
        u64 end = start + PAGE_CACHE_SIZE - 1;
        int ret = 1;

        if (test_range_bit(tree, start, end,
                           EXTENT_IOBITS | EXTENT_ORDERED, 0))
                ret = 0;
        else {
                if ((mask & GFP_NOFS) == GFP_NOFS)
                        mask = GFP_NOFS;
                clear_extent_bit(tree, start, end, EXTENT_UPTODATE,
                                 1, 1, NULL, mask);
        }
        return ret;
}

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

        if ((mask & __GFP_WAIT) &&
            page->mapping->host->i_size > 16 * 1024 * 1024) {
                u64 len;
                while (start <= end) {
                        len = end - start + 1;
                        write_lock(&map->lock);
                        em = lookup_extent_mapping(map, start, len);
                        if (!em || IS_ERR(em)) {
                                write_unlock(&map->lock);
                                break;
                        }
                        if (test_bit(EXTENT_FLAG_PINNED, &em->flags) ||
                            em->start != start) {
                                write_unlock(&map->lock);
                                free_extent_map(em);
                                break;
                        }
                        if (!test_range_bit(tree, em->start,
                                            extent_map_end(em) - 1,
                                            EXTENT_LOCKED | EXTENT_WRITEBACK |
                                            EXTENT_ORDERED,
                                            0)) {
                                remove_extent_mapping(map, em);
                                /* once for the rb tree */
                                free_extent_map(em);
                        }
                        start = extent_map_end(em);
                        write_unlock(&map->lock);

                        /* once for us */
                        free_extent_map(em);
                }
        }
        return try_release_extent_state(map, tree, page, mask);
}

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;
        sector_t sector = 0;
        size_t blksize = (1 << inode->i_blkbits);
        struct extent_map *em;

        lock_extent(&BTRFS_I(inode)->io_tree, start, start + blksize - 1,
                    GFP_NOFS);
        em = get_extent(inode, NULL, 0, start, blksize, 0);
        unlock_extent(&BTRFS_I(inode)->io_tree, start, start + blksize - 1,
                      GFP_NOFS);
        if (!em || IS_ERR(em))
                return 0;

        if (em->block_start > EXTENT_MAP_LAST_BYTE)
                goto out;

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

int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                __u64 start, __u64 len, get_extent_t *get_extent)
{
        int ret;
        u64 off = start;
        u64 max = start + len;
        u32 flags = 0;
        u64 disko = 0;
        struct extent_map *em = NULL;
        int end = 0;
        u64 em_start = 0, em_len = 0;
        unsigned long emflags;
        ret = 0;

        if (len == 0)
                return -EINVAL;

        lock_extent(&BTRFS_I(inode)->io_tree, start, start + len,
                GFP_NOFS);
        em = get_extent(inode, NULL, 0, off, max - off, 0);
        if (!em)
                goto out;
        if (IS_ERR(em)) {
                ret = PTR_ERR(em);
                goto out;
        }
        while (!end) {
                off = em->start + em->len;
                if (off >= max)
                        end = 1;

                em_start = em->start;
                em_len = em->len;

                disko = 0;
                flags = 0;

                if (em->block_start == EXTENT_MAP_LAST_BYTE) {
                        end = 1;
                        flags |= FIEMAP_EXTENT_LAST;
                } else if (em->block_start == EXTENT_MAP_HOLE) {
                        flags |= FIEMAP_EXTENT_UNWRITTEN;
                } else if (em->block_start == EXTENT_MAP_INLINE) {
                        flags |= (FIEMAP_EXTENT_DATA_INLINE |
                                  FIEMAP_EXTENT_NOT_ALIGNED);
                } else if (em->block_start == EXTENT_MAP_DELALLOC) {
                        flags |= (FIEMAP_EXTENT_DELALLOC |
                                  FIEMAP_EXTENT_UNKNOWN);
                } else {
                        disko = em->block_start;
                }
                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
                        flags |= FIEMAP_EXTENT_ENCODED;

                emflags = em->flags;
                free_extent_map(em);
                em = NULL;

                if (!end) {
                        em = get_extent(inode, NULL, 0, off, max - off, 0);
                        if (!em)
                                goto out;
                        if (IS_ERR(em)) {
                                ret = PTR_ERR(em);
                                goto out;
                        }
                        emflags = em->flags;
                }
                if (test_bit(EXTENT_FLAG_VACANCY, &emflags)) {
                        flags |= FIEMAP_EXTENT_LAST;
                        end = 1;
                }

                ret = fiemap_fill_next_extent(fieinfo, em_start, disko,
                                        em_len, flags);
                if (ret)
                        goto out_free;
        }
out_free:
        free_extent_map(em);
out:
        unlock_extent(&BTRFS_I(inode)->io_tree, start, start + len,
                        GFP_NOFS);
        return ret;
}

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;
        if (!mapping)
                return NULL;

        /*
         * extent_buffer_page is only called after pinning the page
         * by increasing the reference count.  So we know the page must
         * be in the radix tree.
         */
        rcu_read_lock();
        p = radix_tree_lookup(&mapping->page_tree, i);
        rcu_read_unlock();

        return p;
}

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 struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
                                                   u64 start,
                                                   unsigned long len,
                                                   gfp_t mask)
{
        struct extent_buffer *eb = NULL;
#if LEAK_DEBUG
        unsigned long flags;
#endif

        eb = kmem_cache_zalloc(extent_buffer_cache, mask);
        eb->start = start;
        eb->len = len;
        spin_lock_init(&eb->lock);
        init_waitqueue_head(&eb->lock_wq);

#if LEAK_DEBUG
        spin_lock_irqsave(&leak_lock, flags);
        list_add(&eb->leak_list, &buffers);
        spin_unlock_irqrestore(&leak_lock, flags);
#endif
        atomic_set(&eb->refs, 1);

        return eb;
}

static void __free_extent_buffer(struct extent_buffer *eb)
{
#if LEAK_DEBUG
        unsigned long flags;
        spin_lock_irqsave(&leak_lock, flags);
        list_del(&eb->leak_list);
        spin_unlock_irqrestore(&leak_lock, flags);
#endif
        kmem_cache_free(extent_buffer_cache, eb);
}

struct extent_buffer *alloc_extent_buffer(struct extent_io_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 extent_buffer *exists = NULL;
        struct page *p;
        struct address_space *mapping = tree->mapping;
        int uptodate = 1;

        spin_lock(&tree->buffer_lock);
        eb = buffer_search(tree, start);
        if (eb) {
                atomic_inc(&eb->refs);
                spin_unlock(&tree->buffer_lock);
                mark_page_accessed(eb->first_page);
                return eb;
        }
        spin_unlock(&tree->buffer_lock);

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

        if (page0) {
                eb->first_page = page0;
                i = 1;
                index++;
                page_cache_get(page0);
                mark_page_accessed(page0);
                set_page_extent_mapped(page0);
                set_page_extent_head(page0, len);
                uptodate = PageUptodate(page0);
        } 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 free_eb;
                }
                set_page_extent_mapped(p);
                mark_page_accessed(p);
                if (i == 0) {
                        eb->first_page = p;
                        set_page_extent_head(p, len);
                } else {
                        set_page_private(p, EXTENT_PAGE_PRIVATE);
                }
                if (!PageUptodate(p))
                        uptodate = 0;
                unlock_page(p);
        }
        if (uptodate)
                set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);

        spin_lock(&tree->buffer_lock);
        exists = buffer_tree_insert(tree, start, &eb->rb_node);
        if (exists) {
                /* add one reference for the caller */
                atomic_inc(&exists->refs);
                spin_unlock(&tree->buffer_lock);
                goto free_eb;
        }
        spin_unlock(&tree->buffer_lock);

        /* add one reference for the tree */
        atomic_inc(&eb->refs);
        return eb;

free_eb:
        if (!atomic_dec_and_test(&eb->refs))
                return exists;
        for (index = 1; index < i; index++)
                page_cache_release(extent_buffer_page(eb, index));
        page_cache_release(extent_buffer_page(eb, 0));
        __free_extent_buffer(eb);
        return exists;
}

struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
                                         u64 start, unsigned long len,
                                          gfp_t mask)
{
        struct extent_buffer *eb;

        spin_lock(&tree->buffer_lock);
        eb = buffer_search(tree, start);
        if (eb)
                atomic_inc(&eb->refs);
        spin_unlock(&tree->buffer_lock);

        if (eb)
                mark_page_accessed(eb->first_page);

        return eb;
}

void free_extent_buffer(struct extent_buffer *eb)
{
        if (!eb)
                return;

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

        WARN_ON(1);
}

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

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

        for (i = 0; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                if (!PageDirty(page))
                        continue;

                lock_page(page);
                if (i == 0)
                        set_page_extent_head(page, eb->len);
                else
                        set_page_private(page, EXTENT_PAGE_PRIVATE);

                clear_page_dirty_for_io(page);
                spin_lock_irq(&page->mapping->tree_lock);
                if (!PageDirty(page)) {
                        radix_tree_tag_clear(&page->mapping->page_tree,
                                                page_index(page),
                                                PAGECACHE_TAG_DIRTY);
                }
                spin_unlock_irq(&page->mapping->tree_lock);
                unlock_page(page);
        }
        return 0;
}

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

int set_extent_buffer_dirty(struct extent_io_tree *tree,
                             struct extent_buffer *eb)
{
        unsigned long i;
        unsigned long num_pages;
        int was_dirty = 0;

        was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);
        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++)
                __set_page_dirty_nobuffers(extent_buffer_page(eb, i));
        return was_dirty;
}

int clear_extent_buffer_uptodate(struct extent_io_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);
        clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);

        clear_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 (page)
                        ClearPageUptodate(page);
        }
        return 0;
}

int set_extent_buffer_uptodate(struct extent_io_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;
}

int extent_range_uptodate(struct extent_io_tree *tree,
                          u64 start, u64 end)
{
        struct page *page;
        int ret;
        int pg_uptodate = 1;
        int uptodate;
        unsigned long index;

        ret = test_range_bit(tree, start, end, EXTENT_UPTODATE, 1);
        if (ret)
                return 1;
        while (start <= end) {
                index = start >> PAGE_CACHE_SHIFT;
                page = find_get_page(tree->mapping, index);
                uptodate = PageUptodate(page);
                page_cache_release(page);
                if (!uptodate) {
                        pg_uptodate = 0;
                        break;
                }
                start += PAGE_CACHE_SIZE;
        }
        return pg_uptodate;
}

int extent_buffer_uptodate(struct extent_io_tree *tree,
                           struct extent_buffer *eb)
{
        int ret = 0;
        unsigned long num_pages;
        unsigned long i;
        struct page *page;
        int pg_uptodate = 1;

        if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
                return 1;

        ret = test_range_bit(tree, eb->start, eb->start + eb->len - 1,
                           EXTENT_UPTODATE, 1);
        if (ret)
                return ret;

        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                if (!PageUptodate(page)) {
                        pg_uptodate = 0;
                        break;
                }
        }
        return pg_uptodate;
}

int read_extent_buffer_pages(struct extent_io_tree *tree,
                             struct extent_buffer *eb,
                             u64 start, int wait,
                             get_extent_t *get_extent, int mirror_num)
{
        unsigned long i;
        unsigned long start_i;
        struct page *page;
        int err;
        int ret = 0;
        int locked_pages = 0;
        int all_uptodate = 1;
        int inc_all_pages = 0;
        unsigned long num_pages;
        struct bio *bio = NULL;
        unsigned long bio_flags = 0;

        if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
                return 0;

        if (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 (!wait) {
                        if (!trylock_page(page))
                                goto unlock_exit;
                } else {
                        lock_page(page);
                }
                locked_pages++;
                if (!PageUptodate(page))
                        all_uptodate = 0;
        }
        if (all_uptodate) {
                if (start_i == 0)
                        set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
                goto unlock_exit;
        }

        for (i = start_i; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                if (inc_all_pages)
                        page_cache_get(page);
                if (!PageUptodate(page)) {
                        if (start_i == 0)
                                inc_all_pages = 1;
                        ClearPageError(page);
                        err = __extent_read_full_page(tree, page,
                                                      get_extent, &bio,
                                                      mirror_num, &bio_flags);
                        if (err)
                                ret = err;
                } else {
                        unlock_page(page);
                }
        }

        if (bio)
                submit_one_bio(READ, bio, mirror_num, bio_flags);

        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)
                set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
        return ret;

unlock_exit:
        i = start_i;
        while (locked_pages > 0) {
                page = extent_buffer_page(eb, i);
                i++;
                unlock_page(page);
                locked_pages--;
        }
        return ret;
}

void read_extent_buffer(struct extent_buffer *eb, void *dstv,
                        unsigned long start,
                        unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char *dst = (char *)dstv;
        size_t start_offset = eb->start & ((u64)PAGE_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);

                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++;
        }
}

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(KERN_ERR "btrfs bad mapping eb start %llu len %lu, "
                       "wanted %lu %lu\n", (unsigned long long)eb->start,
                       eb->len, start, min_len);
                WARN_ON(1);
        }

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

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;
}

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

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);

                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;
}

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++;
        }
}

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++;
        }
}

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++;
        }
}

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

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(KERN_ERR "btrfs 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(KERN_ERR "btrfs 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;
        }
}

int try_release_extent_buffer(struct extent_io_tree *tree, struct page *page)
{
        u64 start = page_offset(page);
        struct extent_buffer *eb;
        int ret = 1;
        unsigned long i;
        unsigned long num_pages;

        spin_lock(&tree->buffer_lock);
        eb = buffer_search(tree, start);
        if (!eb)
                goto out;

        if (atomic_read(&eb->refs) > 1) {
                ret = 0;
                goto out;
        }
        if (test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
                ret = 0;
                goto out;
        }
        /* at this point we can safely release the extent buffer */
        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++)
                page_cache_release(extent_buffer_page(eb, i));
        rb_erase(&eb->rb_node, &tree->buffer);
        __free_extent_buffer(eb);
out:
        spin_unlock(&tree->buffer_lock);
        return ret;
}