Merge branch 'foreign/josef/space-updates' into for-chris-4.6

[mirror_ubuntu-bionic-kernel.git] / fs / btrfs / extent_io.c

#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/bio.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/page-flags.h>
#include <linux/spinlock.h>
#include <linux/blkdev.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/prefetch.h>
#include <linux/cleancache.h>
#include "extent_io.h"
#include "extent_map.h"
#include "ctree.h"
#include "btrfs_inode.h"
#include "volumes.h"
#include "check-integrity.h"
#include "locking.h"
#include "rcu-string.h"
#include "backref.h"

static struct kmem_cache *extent_state_cache;
static struct kmem_cache *extent_buffer_cache;
static struct bio_set *btrfs_bioset;

static inline bool extent_state_in_tree(const struct extent_state *state)
{
        return !RB_EMPTY_NODE(&state->rb_node);
}

#ifdef CONFIG_BTRFS_DEBUG
static LIST_HEAD(buffers);
static LIST_HEAD(states);

static DEFINE_SPINLOCK(leak_lock);

static inline
void btrfs_leak_debug_add(struct list_head *new, struct list_head *head)
{
        unsigned long flags;

        spin_lock_irqsave(&leak_lock, flags);
        list_add(new, head);
        spin_unlock_irqrestore(&leak_lock, flags);
}

static inline
void btrfs_leak_debug_del(struct list_head *entry)
{
        unsigned long flags;

        spin_lock_irqsave(&leak_lock, flags);
        list_del(entry);
        spin_unlock_irqrestore(&leak_lock, flags);
}

static inline
void btrfs_leak_debug_check(void)
{
        struct extent_state *state;
        struct extent_buffer *eb;

        while (!list_empty(&states)) {
                state = list_entry(states.next, struct extent_state, leak_list);
                pr_err("BTRFS: state leak: start %llu end %llu state %u in tree %d refs %d\n",
                       state->start, state->end, state->state,
                       extent_state_in_tree(state),
                       atomic_read(&state->refs));
                list_del(&state->leak_list);
                kmem_cache_free(extent_state_cache, state);
        }

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

#define btrfs_debug_check_extent_io_range(tree, start, end)             \
        __btrfs_debug_check_extent_io_range(__func__, (tree), (start), (end))
static inline void __btrfs_debug_check_extent_io_range(const char *caller,
                struct extent_io_tree *tree, u64 start, u64 end)
{
        struct inode *inode;
        u64 isize;

        if (!tree->mapping)
                return;

        inode = tree->mapping->host;
        isize = i_size_read(inode);
        if (end >= PAGE_SIZE && (end % 2) == 0 && end != isize - 1) {
                btrfs_debug_rl(BTRFS_I(inode)->root->fs_info,
                    "%s: ino %llu isize %llu odd range [%llu,%llu]",
                                caller, btrfs_ino(inode), isize, start, end);
        }
}
#else
#define btrfs_leak_debug_add(new, head) do {} while (0)
#define btrfs_leak_debug_del(entry)     do {} while (0)
#define btrfs_leak_debug_check()        do {} while (0)
#define btrfs_debug_check_extent_io_range(c, s, e)      do {} while (0)
#endif

#define BUFFER_LRU_MAX 64

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

struct extent_page_data {
        struct bio *bio;
        struct extent_io_tree *tree;
        get_extent_t *get_extent;
        unsigned long bio_flags;

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

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

static void add_extent_changeset(struct extent_state *state, unsigned bits,
                                 struct extent_changeset *changeset,
                                 int set)
{
        int ret;

        if (!changeset)
                return;
        if (set && (state->state & bits) == bits)
                return;
        if (!set && (state->state & bits) == 0)
                return;
        changeset->bytes_changed += state->end - state->start + 1;
        ret = ulist_add(changeset->range_changed, state->start, state->end,
                        GFP_ATOMIC);
        /* ENOMEM */
        BUG_ON(ret < 0);
}

static noinline void flush_write_bio(void *data);
static inline struct btrfs_fs_info *
tree_fs_info(struct extent_io_tree *tree)
{
        if (!tree->mapping)
                return NULL;
        return btrfs_sb(tree->mapping->host->i_sb);
}

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

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

        btrfs_bioset = bioset_create(BIO_POOL_SIZE,
                                     offsetof(struct btrfs_io_bio, bio));
        if (!btrfs_bioset)
                goto free_buffer_cache;

        if (bioset_integrity_create(btrfs_bioset, BIO_POOL_SIZE))
                goto free_bioset;

        return 0;

free_bioset:
        bioset_free(btrfs_bioset);
        btrfs_bioset = NULL;

free_buffer_cache:
        kmem_cache_destroy(extent_buffer_cache);
        extent_buffer_cache = NULL;

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

void extent_io_exit(void)
{
        btrfs_leak_debug_check();

        /*
         * Make sure all delayed rcu free are flushed before we
         * destroy caches.
         */
        rcu_barrier();
        if (extent_state_cache)
                kmem_cache_destroy(extent_state_cache);
        if (extent_buffer_cache)
                kmem_cache_destroy(extent_buffer_cache);
        if (btrfs_bioset)
                bioset_free(btrfs_bioset);
}

void extent_io_tree_init(struct extent_io_tree *tree,
                         struct address_space *mapping)
{
        tree->state = RB_ROOT;
        tree->ops = NULL;
        tree->dirty_bytes = 0;
        spin_lock_init(&tree->lock);
        tree->mapping = mapping;
}

static struct extent_state *alloc_extent_state(gfp_t mask)
{
        struct extent_state *state;

        state = kmem_cache_alloc(extent_state_cache, mask);
        if (!state)
                return state;
        state->state = 0;
        state->private = 0;
        RB_CLEAR_NODE(&state->rb_node);
        btrfs_leak_debug_add(&state->leak_list, &states);
        atomic_set(&state->refs, 1);
        init_waitqueue_head(&state->wq);
        trace_alloc_extent_state(state, mask, _RET_IP_);
        return state;
}

void free_extent_state(struct extent_state *state)
{
        if (!state)
                return;
        if (atomic_dec_and_test(&state->refs)) {
                WARN_ON(extent_state_in_tree(state));
                btrfs_leak_debug_del(&state->leak_list);
                trace_free_extent_state(state, _RET_IP_);
                kmem_cache_free(extent_state_cache, state);
        }
}

static struct rb_node *tree_insert(struct rb_root *root,
                                   struct rb_node *search_start,
                                   u64 offset,
                                   struct rb_node *node,
                                   struct rb_node ***p_in,
                                   struct rb_node **parent_in)
{
        struct rb_node **p;
        struct rb_node *parent = NULL;
        struct tree_entry *entry;

        if (p_in && parent_in) {
                p = *p_in;
                parent = *parent_in;
                goto do_insert;
        }

        p = search_start ? &search_start : &root->rb_node;
        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct tree_entry, rb_node);

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

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

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

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

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

        if (p_ret)
                *p_ret = n;
        if (parent_ret)
                *parent_ret = prev;

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

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

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

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

static inline struct rb_node *tree_search(struct extent_io_tree *tree,
                                          u64 offset)
{
        return tree_search_for_insert(tree, offset, NULL, NULL);
}

static void merge_cb(struct extent_io_tree *tree, struct extent_state *new,
                     struct extent_state *other)
{
        if (tree->ops && tree->ops->merge_extent_hook)
                tree->ops->merge_extent_hook(tree->mapping->host, new,
                                             other);
}

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

        if (state->state & (EXTENT_IOBITS | EXTENT_BOUNDARY))
                return;

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

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

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

static void set_state_bits(struct extent_io_tree *tree,
                           struct extent_state *state, unsigned *bits,
                           struct extent_changeset *changeset);

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

        if (end < start)
                WARN(1, KERN_ERR "BTRFS: end < start %llu %llu\n",
                       end, start);
        state->start = start;
        state->end = end;

        set_state_bits(tree, state, bits, changeset);

        node = tree_insert(&tree->state, NULL, end, &state->rb_node, p, parent);
        if (node) {
                struct extent_state *found;
                found = rb_entry(node, struct extent_state, rb_node);
                printk(KERN_ERR "BTRFS: found node %llu %llu on insert of "
                       "%llu %llu\n",
                       found->start, found->end, start, end);
                return -EEXIST;
        }
        merge_state(tree, state);
        return 0;
}

static void split_cb(struct extent_io_tree *tree, struct extent_state *orig,
                     u64 split)
{
        if (tree->ops && tree->ops->split_extent_hook)
                tree->ops->split_extent_hook(tree->mapping->host, orig, split);
}

/*
 * split a given extent state struct in two, inserting the preallocated
 * struct 'prealloc' as the newly created second half.  'split' indicates an
 * offset inside 'orig' where it should be split.
 *
 * Before calling,
 * the tree has 'orig' at [orig->start, orig->end].  After calling, there
 * are two extent state structs in the tree:
 * prealloc: [orig->start, split - 1]
 * orig: [ split, orig->end ]
 *
 * The tree locks are not taken by this function. They need to be held
 * by the caller.
 */
static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
                       struct extent_state *prealloc, u64 split)
{
        struct rb_node *node;

        split_cb(tree, orig, split);

        prealloc->start = orig->start;
        prealloc->end = split - 1;
        prealloc->state = orig->state;
        orig->start = split;

        node = tree_insert(&tree->state, &orig->rb_node, prealloc->end,
                           &prealloc->rb_node, NULL, NULL);
        if (node) {
                free_extent_state(prealloc);
                return -EEXIST;
        }
        return 0;
}

static struct extent_state *next_state(struct extent_state *state)
{
        struct rb_node *next = rb_next(&state->rb_node);
        if (next)
                return rb_entry(next, struct extent_state, rb_node);
        else
                return NULL;
}

/*
 * utility function to clear some bits in an extent state struct.
 * it will optionally wake up any one waiting on this state (wake == 1).
 *
 * If no bits are set on the state struct after clearing things, the
 * struct is freed and removed from the tree
 */
static struct extent_state *clear_state_bit(struct extent_io_tree *tree,
                                            struct extent_state *state,
                                            unsigned *bits, int wake,
                                            struct extent_changeset *changeset)
{
        struct extent_state *next;
        unsigned bits_to_clear = *bits & ~EXTENT_CTLBITS;

        if ((bits_to_clear & EXTENT_DIRTY) && (state->state & EXTENT_DIRTY)) {
                u64 range = state->end - state->start + 1;
                WARN_ON(range > tree->dirty_bytes);
                tree->dirty_bytes -= range;
        }
        clear_state_cb(tree, state, bits);
        add_extent_changeset(state, bits_to_clear, changeset, 0);
        state->state &= ~bits_to_clear;
        if (wake)
                wake_up(&state->wq);
        if (state->state == 0) {
                next = next_state(state);
                if (extent_state_in_tree(state)) {
                        rb_erase(&state->rb_node, &tree->state);
                        RB_CLEAR_NODE(&state->rb_node);
                        free_extent_state(state);
                } else {
                        WARN_ON(1);
                }
        } else {
                merge_state(tree, state);
                next = next_state(state);
        }
        return next;
}

static struct extent_state *
alloc_extent_state_atomic(struct extent_state *prealloc)
{
        if (!prealloc)
                prealloc = alloc_extent_state(GFP_ATOMIC);

        return prealloc;
}

static void extent_io_tree_panic(struct extent_io_tree *tree, int err)
{
        btrfs_panic(tree_fs_info(tree), err, "Locking error: "
                    "Extent tree was modified by another "
                    "thread while locked.");
}

/*
 * clear some bits on a range in the tree.  This may require splitting
 * or inserting elements in the tree, so the gfp mask is used to
 * indicate which allocations or sleeping are allowed.
 *
 * pass 'wake' == 1 to kick any sleepers, and 'delete' == 1 to remove
 * the given range from the tree regardless of state (ie for truncate).
 *
 * the range [start, end] is inclusive.
 *
 * This takes the tree lock, and returns 0 on success and < 0 on error.
 */
static int __clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                              unsigned bits, int wake, int delete,
                              struct extent_state **cached_state,
                              gfp_t mask, struct extent_changeset *changeset)
{
        struct extent_state *state;
        struct extent_state *cached;
        struct extent_state *prealloc = NULL;
        struct rb_node *node;
        u64 last_end;
        int err;
        int clear = 0;

        btrfs_debug_check_extent_io_range(tree, start, end);

        if (bits & EXTENT_DELALLOC)
                bits |= EXTENT_NORESERVE;

        if (delete)
                bits |= ~EXTENT_CTLBITS;
        bits |= EXTENT_FIRST_DELALLOC;

        if (bits & (EXTENT_IOBITS | EXTENT_BOUNDARY))
                clear = 1;
again:
        if (!prealloc && gfpflags_allow_blocking(mask)) {
                /*
                 * Don't care for allocation failure here because we might end
                 * up not needing the pre-allocated extent state at all, which
                 * is the case if we only have in the tree extent states that
                 * cover our input range and don't cover too any other range.
                 * If we end up needing a new extent state we allocate it later.
                 */
                prealloc = alloc_extent_state(mask);
        }

        spin_lock(&tree->lock);
        if (cached_state) {
                cached = *cached_state;

                if (clear) {
                        *cached_state = NULL;
                        cached_state = NULL;
                }

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

        /* the state doesn't have the wanted bits, go ahead */
        if (!(state->state & bits)) {
                state = next_state(state);
                goto next;
        }

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

        if (state->start < start) {
                prealloc = alloc_extent_state_atomic(prealloc);
                BUG_ON(!prealloc);
                err = split_state(tree, state, prealloc, start);
                if (err)
                        extent_io_tree_panic(tree, err);

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

                if (wake)
                        wake_up(&state->wq);

                clear_state_bit(tree, prealloc, &bits, wake, changeset);

                prealloc = NULL;
                goto out;
        }

        state = clear_state_bit(tree, state, &bits, wake, changeset);
next:
        if (last_end == (u64)-1)
                goto out;
        start = last_end + 1;
        if (start <= end && state && !need_resched())
                goto hit_next;
        goto search_again;

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

        return 0;

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

static void wait_on_state(struct extent_io_tree *tree,
                          struct extent_state *state)
                __releases(tree->lock)
                __acquires(tree->lock)
{
        DEFINE_WAIT(wait);
        prepare_to_wait(&state->wq, &wait, TASK_UNINTERRUPTIBLE);
        spin_unlock(&tree->lock);
        schedule();
        spin_lock(&tree->lock);
        finish_wait(&state->wq, &wait);
}

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

        btrfs_debug_check_extent_io_range(tree, start, end);

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

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

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

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

                if (start > end)
                        break;

                if (!cond_resched_lock(&tree->lock)) {
                        node = rb_next(node);
                        goto process_node;
                }
        }
out:
        spin_unlock(&tree->lock);
}

static void set_state_bits(struct extent_io_tree *tree,
                           struct extent_state *state,
                           unsigned *bits, struct extent_changeset *changeset)
{
        unsigned bits_to_set = *bits & ~EXTENT_CTLBITS;

        set_state_cb(tree, state, bits);
        if ((bits_to_set & EXTENT_DIRTY) && !(state->state & EXTENT_DIRTY)) {
                u64 range = state->end - state->start + 1;
                tree->dirty_bytes += range;
        }
        add_extent_changeset(state, bits_to_set, changeset, 1);
        state->state |= bits_to_set;
}

static void cache_state_if_flags(struct extent_state *state,
                                 struct extent_state **cached_ptr,
                                 unsigned flags)
{
        if (cached_ptr && !(*cached_ptr)) {
                if (!flags || (state->state & flags)) {
                        *cached_ptr = state;
                        atomic_inc(&state->refs);
                }
        }
}

static void cache_state(struct extent_state *state,
                        struct extent_state **cached_ptr)
{
        return cache_state_if_flags(state, cached_ptr,
                                    EXTENT_IOBITS | EXTENT_BOUNDARY);
}

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

static int __must_check
__set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                 unsigned bits, unsigned exclusive_bits,
                 u64 *failed_start, struct extent_state **cached_state,
                 gfp_t mask, struct extent_changeset *changeset)
{
        struct extent_state *state;
        struct extent_state *prealloc = NULL;
        struct rb_node *node;
        struct rb_node **p;
        struct rb_node *parent;
        int err = 0;
        u64 last_start;
        u64 last_end;

        btrfs_debug_check_extent_io_range(tree, start, end);

        bits |= EXTENT_FIRST_DELALLOC;
again:
        if (!prealloc && gfpflags_allow_blocking(mask)) {
                prealloc = alloc_extent_state(mask);
                BUG_ON(!prealloc);
        }

        spin_lock(&tree->lock);
        if (cached_state && *cached_state) {
                state = *cached_state;
                if (state->start <= start && state->end > start &&
                    extent_state_in_tree(state)) {
                        node = &state->rb_node;
                        goto hit_next;
                }
        }
        /*
         * this search will find all the extents that end after
         * our range starts.
         */
        node = tree_search_for_insert(tree, start, &p, &parent);
        if (!node) {
                prealloc = alloc_extent_state_atomic(prealloc);
                BUG_ON(!prealloc);
                err = insert_state(tree, prealloc, start, end,
                                   &p, &parent, &bits, changeset);
                if (err)
                        extent_io_tree_panic(tree, err);

                cache_state(prealloc, cached_state);
                prealloc = NULL;
                goto out;
        }
        state = rb_entry(node, struct extent_state, rb_node);
hit_next:
        last_start = state->start;
        last_end = state->end;

        /*
         * | ---- desired range ---- |
         * | state |
         *
         * Just lock what we found and keep going
         */
        if (state->start == start && state->end <= end) {
                if (state->state & exclusive_bits) {
                        *failed_start = state->start;
                        err = -EEXIST;
                        goto out;
                }

                set_state_bits(tree, state, &bits, changeset);
                cache_state(state, cached_state);
                merge_state(tree, state);
                if (last_end == (u64)-1)
                        goto out;
                start = last_end + 1;
                state = next_state(state);
                if (start < end && state && state->start == start &&
                    !need_resched())
                        goto hit_next;
                goto search_again;
        }

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

                prealloc = alloc_extent_state_atomic(prealloc);
                BUG_ON(!prealloc);
                err = split_state(tree, state, prealloc, start);
                if (err)
                        extent_io_tree_panic(tree, err);

                prealloc = NULL;
                if (err)
                        goto out;
                if (state->end <= end) {
                        set_state_bits(tree, state, &bits, changeset);
                        cache_state(state, cached_state);
                        merge_state(tree, state);
                        if (last_end == (u64)-1)
                                goto out;
                        start = last_end + 1;
                        state = next_state(state);
                        if (start < end && state && state->start == start &&
                            !need_resched())
                                goto hit_next;
                }
                goto search_again;
        }
        /*
         * | ---- desired range ---- |
         *     | state | or               | state |
         *
         * There's a hole, we need to insert something in it and
         * ignore the extent we found.
         */
        if (state->start > start) {
                u64 this_end;
                if (end < last_start)
                        this_end = end;
                else
                        this_end = last_start - 1;

                prealloc = alloc_extent_state_atomic(prealloc);
                BUG_ON(!prealloc);

                /*
                 * Avoid to free 'prealloc' if it can be merged with
                 * the later extent.
                 */
                err = insert_state(tree, prealloc, start, this_end,
                                   NULL, NULL, &bits, changeset);
                if (err)
                        extent_io_tree_panic(tree, err);

                cache_state(prealloc, cached_state);
                prealloc = NULL;
                start = this_end + 1;
                goto search_again;
        }
        /*
         * | ---- desired range ---- |
         *                        | state |
         * We need to split the extent, and set the bit
         * on the first half
         */
        if (state->start <= end && state->end > end) {
                if (state->state & exclusive_bits) {
                        *failed_start = start;
                        err = -EEXIST;
                        goto out;
                }

                prealloc = alloc_extent_state_atomic(prealloc);
                BUG_ON(!prealloc);
                err = split_state(tree, state, prealloc, end + 1);
                if (err)
                        extent_io_tree_panic(tree, err);

                set_state_bits(tree, prealloc, &bits, changeset);
                cache_state(prealloc, cached_state);
                merge_state(tree, prealloc);
                prealloc = NULL;
                goto out;
        }

        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 (gfpflags_allow_blocking(mask))
                cond_resched();
        goto again;
}

int set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                   unsigned bits, u64 * failed_start,
                   struct extent_state **cached_state, gfp_t mask)
{
        return __set_extent_bit(tree, start, end, bits, 0, failed_start,
                                cached_state, mask, NULL);
}


/**
 * convert_extent_bit - convert all bits in a given range from one bit to
 *                      another
 * @tree:       the io tree to search
 * @start:      the start offset in bytes
 * @end:        the end offset in bytes (inclusive)
 * @bits:       the bits to set in this range
 * @clear_bits: the bits to clear in this range
 * @cached_state:       state that we're going to cache
 * @mask:       the allocation mask
 *
 * This will go through and set bits for the given range.  If any states exist
 * already in this range they are set with the given bit and cleared of the
 * clear_bits.  This is only meant to be used by things that are mergeable, ie
 * converting from say DELALLOC to DIRTY.  This is not meant to be used with
 * boundary bits like LOCK.
 */
int convert_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                       unsigned bits, unsigned clear_bits,
                       struct extent_state **cached_state, gfp_t mask)
{
        struct extent_state *state;
        struct extent_state *prealloc = NULL;
        struct rb_node *node;
        struct rb_node **p;
        struct rb_node *parent;
        int err = 0;
        u64 last_start;
        u64 last_end;
        bool first_iteration = true;

        btrfs_debug_check_extent_io_range(tree, start, end);

again:
        if (!prealloc && gfpflags_allow_blocking(mask)) {
                /*
                 * Best effort, don't worry if extent state allocation fails
                 * here for the first iteration. We might have a cached state
                 * that matches exactly the target range, in which case no
                 * extent state allocations are needed. We'll only know this
                 * after locking the tree.
                 */
                prealloc = alloc_extent_state(mask);
                if (!prealloc && !first_iteration)
                        return -ENOMEM;
        }

        spin_lock(&tree->lock);
        if (cached_state && *cached_state) {
                state = *cached_state;
                if (state->start <= start && state->end > start &&
                    extent_state_in_tree(state)) {
                        node = &state->rb_node;
                        goto hit_next;
                }
        }

        /*
         * this search will find all the extents that end after
         * our range starts.
         */
        node = tree_search_for_insert(tree, start, &p, &parent);
        if (!node) {
                prealloc = alloc_extent_state_atomic(prealloc);
                if (!prealloc) {
                        err = -ENOMEM;
                        goto out;
                }
                err = insert_state(tree, prealloc, start, end,
                                   &p, &parent, &bits, NULL);
                if (err)
                        extent_io_tree_panic(tree, err);
                cache_state(prealloc, cached_state);
                prealloc = NULL;
                goto out;
        }
        state = rb_entry(node, struct extent_state, rb_node);
hit_next:
        last_start = state->start;
        last_end = state->end;

        /*
         * | ---- desired range ---- |
         * | state |
         *
         * Just lock what we found and keep going
         */
        if (state->start == start && state->end <= end) {
                set_state_bits(tree, state, &bits, NULL);
                cache_state(state, cached_state);
                state = clear_state_bit(tree, state, &clear_bits, 0, NULL);
                if (last_end == (u64)-1)
                        goto out;
                start = last_end + 1;
                if (start < end && state && state->start == start &&
                    !need_resched())
                        goto hit_next;
                goto search_again;
        }

        /*
         *     | ---- desired range ---- |
         * | state |
         *   or
         * | ------------- state -------------- |
         *
         * We need to split the extent we found, and may flip bits on
         * second half.
         *
         * If the extent we found extends past our
         * range, we just split and search again.  It'll get split
         * again the next time though.
         *
         * If the extent we found is inside our range, we set the
         * desired bit on it.
         */
        if (state->start < start) {
                prealloc = alloc_extent_state_atomic(prealloc);
                if (!prealloc) {
                        err = -ENOMEM;
                        goto out;
                }
                err = split_state(tree, state, prealloc, start);
                if (err)
                        extent_io_tree_panic(tree, err);
                prealloc = NULL;
                if (err)
                        goto out;
                if (state->end <= end) {
                        set_state_bits(tree, state, &bits, NULL);
                        cache_state(state, cached_state);
                        state = clear_state_bit(tree, state, &clear_bits, 0,
                                                NULL);
                        if (last_end == (u64)-1)
                                goto out;
                        start = last_end + 1;
                        if (start < end && state && state->start == start &&
                            !need_resched())
                                goto hit_next;
                }
                goto search_again;
        }
        /*
         * | ---- desired range ---- |
         *     | state | or               | state |
         *
         * There's a hole, we need to insert something in it and
         * ignore the extent we found.
         */
        if (state->start > start) {
                u64 this_end;
                if (end < last_start)
                        this_end = end;
                else
                        this_end = last_start - 1;

                prealloc = alloc_extent_state_atomic(prealloc);
                if (!prealloc) {
                        err = -ENOMEM;
                        goto out;
                }

                /*
                 * Avoid to free 'prealloc' if it can be merged with
                 * the later extent.
                 */
                err = insert_state(tree, prealloc, start, this_end,
                                   NULL, NULL, &bits, NULL);
                if (err)
                        extent_io_tree_panic(tree, err);
                cache_state(prealloc, cached_state);
                prealloc = NULL;
                start = this_end + 1;
                goto search_again;
        }
        /*
         * | ---- desired range ---- |
         *                        | state |
         * We need to split the extent, and set the bit
         * on the first half
         */
        if (state->start <= end && state->end > end) {
                prealloc = alloc_extent_state_atomic(prealloc);
                if (!prealloc) {
                        err = -ENOMEM;
                        goto out;
                }

                err = split_state(tree, state, prealloc, end + 1);
                if (err)
                        extent_io_tree_panic(tree, err);

                set_state_bits(tree, prealloc, &bits, NULL);
                cache_state(prealloc, cached_state);
                clear_state_bit(tree, prealloc, &clear_bits, 0, NULL);
                prealloc = NULL;
                goto out;
        }

        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 (gfpflags_allow_blocking(mask))
                cond_resched();
        first_iteration = false;
        goto again;
}

/* wrappers around set/clear extent bit */
int set_record_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
                           unsigned bits, gfp_t mask,
                           struct extent_changeset *changeset)
{
        /*
         * We don't support EXTENT_LOCKED yet, as current changeset will
         * record any bits changed, so for EXTENT_LOCKED case, it will
         * either fail with -EEXIST or changeset will record the whole
         * range.
         */
        BUG_ON(bits & EXTENT_LOCKED);

        return __set_extent_bit(tree, start, end, bits, 0, NULL, NULL, mask,
                                changeset);
}

int clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
                     unsigned bits, int wake, int delete,
                     struct extent_state **cached, gfp_t mask)
{
        return __clear_extent_bit(tree, start, end, bits, wake, delete,
                                  cached, mask, NULL);
}

int clear_record_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
                             unsigned bits, gfp_t mask,
                             struct extent_changeset *changeset)
{
        /*
         * Don't support EXTENT_LOCKED case, same reason as
         * set_record_extent_bits().
         */
        BUG_ON(bits & EXTENT_LOCKED);

        return __clear_extent_bit(tree, start, end, bits, 0, 0, NULL, mask,
                                  changeset);
}

/*
 * either insert or lock state struct between start and end use mask to tell
 * us if waiting is desired.
 */
int lock_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
                     struct extent_state **cached_state)
{
        int err;
        u64 failed_start;

        while (1) {
                err = __set_extent_bit(tree, start, end, EXTENT_LOCKED,
                                       EXTENT_LOCKED, &failed_start,
                                       cached_state, GFP_NOFS, NULL);
                if (err == -EEXIST) {
                        wait_extent_bit(tree, failed_start, end, EXTENT_LOCKED);
                        start = failed_start;
                } else
                        break;
                WARN_ON(start > end);
        }
        return err;
}

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

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

void extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end)
{
        unsigned long index = start >> PAGE_CACHE_SHIFT;
        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
        struct page *page;

        while (index <= end_index) {
                page = find_get_page(inode->i_mapping, index);
                BUG_ON(!page); /* Pages should be in the extent_io_tree */
                clear_page_dirty_for_io(page);
                page_cache_release(page);
                index++;
        }
}

void extent_range_redirty_for_io(struct inode *inode, 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(inode->i_mapping, index);
                BUG_ON(!page); /* Pages should be in the extent_io_tree */
                __set_page_dirty_nobuffers(page);
                account_page_redirty(page);
                page_cache_release(page);
                index++;
        }
}

/*
 * helper function to set both pages and extents in the tree writeback
 */
static void set_range_writeback(struct extent_io_tree *tree, u64 start, u64 end)
{
        unsigned long index = start >> PAGE_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); /* Pages should be in the extent_io_tree */
                set_page_writeback(page);
                page_cache_release(page);
                index++;
        }
}

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

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

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

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

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

        spin_lock(&tree->lock);
        if (cached_state && *cached_state) {
                state = *cached_state;
                if (state->end == start - 1 && extent_state_in_tree(state)) {
                        n = rb_next(&state->rb_node);
                        while (n) {
                                state = rb_entry(n, struct extent_state,
                                                 rb_node);
                                if (state->state & bits)
                                        goto got_it;
                                n = rb_next(n);
                        }
                        free_extent_state(*cached_state);
                        *cached_state = NULL;
                        goto out;
                }
                free_extent_state(*cached_state);
                *cached_state = NULL;
        }

        state = find_first_extent_bit_state(tree, start, bits);
got_it:
        if (state) {
                cache_state_if_flags(state, cached_state, 0);
                *start_ret = state->start;
                *end_ret = state->end;
                ret = 0;
        }
out:
        spin_unlock(&tree->lock);
        return ret;
}

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

        spin_lock(&tree->lock);

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

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

static noinline void __unlock_for_delalloc(struct inode *inode,
                                           struct page *locked_page,
                                           u64 start, u64 end)
{
        int ret;
        struct page *pages[16];
        unsigned long index = start >> PAGE_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;

        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();
        }
}

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 u64 find_lock_delalloc_range(struct inode *inode,
                                    struct extent_io_tree *tree,
                                    struct page *locked_page, u64 *start,
                                    u64 *end, u64 max_bytes)
{
        u64 delalloc_start;
        u64 delalloc_end;
        u64 found;
        struct extent_state *cached_state = NULL;
        int ret;
        int loops = 0;

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

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

        /*
         * make sure to limit the number of pages we try to lock down
         */
        if (delalloc_end + 1 - delalloc_start > max_bytes)
                delalloc_end = delalloc_start + max_bytes - 1;

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

        /* step three, lock the state bits for the whole range */
        lock_extent_bits(tree, delalloc_start, delalloc_end, &cached_state);

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

void extent_clear_unlock_delalloc(struct inode *inode, u64 start, u64 end,
                                 struct page *locked_page,
                                 unsigned clear_bits,
                                 unsigned long page_ops)
{
        struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
        int ret;
        struct page *pages[16];
        unsigned long index = start >> PAGE_CACHE_SHIFT;
        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
        unsigned long nr_pages = end_index - index + 1;
        int i;

        clear_extent_bit(tree, start, end, clear_bits, 1, 0, NULL, GFP_NOFS);
        if (page_ops == 0)
                return;

        if ((page_ops & PAGE_SET_ERROR) && nr_pages > 0)
                mapping_set_error(inode->i_mapping, -EIO);

        while (nr_pages > 0) {
                ret = find_get_pages_contig(inode->i_mapping, index,
                                     min_t(unsigned long,
                                     nr_pages, ARRAY_SIZE(pages)), pages);
                for (i = 0; i < ret; i++) {

                        if (page_ops & PAGE_SET_PRIVATE2)
                                SetPagePrivate2(pages[i]);

                        if (pages[i] == locked_page) {
                                page_cache_release(pages[i]);
                                continue;
                        }
                        if (page_ops & PAGE_CLEAR_DIRTY)
                                clear_page_dirty_for_io(pages[i]);
                        if (page_ops & PAGE_SET_WRITEBACK)
                                set_page_writeback(pages[i]);
                        if (page_ops & PAGE_SET_ERROR)
                                SetPageError(pages[i]);
                        if (page_ops & PAGE_END_WRITEBACK)
                                end_page_writeback(pages[i]);
                        if (page_ops & PAGE_UNLOCK)
                                unlock_page(pages[i]);
                        page_cache_release(pages[i]);
                }
                nr_pages -= ret;
                index += ret;
                cond_resched();
        }
}

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

        if (WARN_ON(search_end <= cur_start))
                return 0;

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

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

/*
 * set the private field for a given byte offset in the tree.  If there isn't
 * an extent_state there already, this does nothing.
 */
static 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,
                   unsigned bits, int filled, struct extent_state *cached)
{
        struct extent_state *state = NULL;
        struct rb_node *node;
        int bitset = 0;

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

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

                if (state->start > end)
                        break;

                if (state->state & bits) {
                        bitset = 1;
                        if (!filled)
                                break;
                } else if (filled) {
                        bitset = 0;
                        break;
                }

                if (state->end == (u64)-1)
                        break;

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

/*
 * helper function to set a given page up to date if all the
 * extents in the tree for that page are up to date
 */
static void check_page_uptodate(struct extent_io_tree *tree, struct page *page)
{
        u64 start = page_offset(page);
        u64 end = start + PAGE_CACHE_SIZE - 1;
        if (test_range_bit(tree, start, end, EXTENT_UPTODATE, 1, NULL))
                SetPageUptodate(page);
}

int free_io_failure(struct inode *inode, struct io_failure_record *rec)
{
        int ret;
        int err = 0;
        struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;

        set_state_private(failure_tree, rec->start, 0);
        ret = clear_extent_bits(failure_tree, rec->start,
                                rec->start + rec->len - 1,
                                EXTENT_LOCKED | EXTENT_DIRTY, GFP_NOFS);
        if (ret)
                err = ret;

        ret = clear_extent_bits(&BTRFS_I(inode)->io_tree, rec->start,
                                rec->start + rec->len - 1,
                                EXTENT_DAMAGED, GFP_NOFS);
        if (ret && !err)
                err = ret;

        kfree(rec);
        return err;
}

/*
 * this bypasses the standard btrfs submit functions deliberately, as
 * the standard behavior is to write all copies in a raid setup. here we only
 * want to write the one bad copy. so we do the mapping for ourselves and issue
 * submit_bio directly.
 * to avoid any synchronization issues, wait for the data after writing, which
 * actually prevents the read that triggered the error from finishing.
 * currently, there can be no more than two copies of every data bit. thus,
 * exactly one rewrite is required.
 */
int repair_io_failure(struct inode *inode, u64 start, u64 length, u64 logical,
                      struct page *page, unsigned int pg_offset, int mirror_num)
{
        struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
        struct bio *bio;
        struct btrfs_device *dev;
        u64 map_length = 0;
        u64 sector;
        struct btrfs_bio *bbio = NULL;
        struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
        int ret;

        ASSERT(!(fs_info->sb->s_flags & MS_RDONLY));
        BUG_ON(!mirror_num);

        /* we can't repair anything in raid56 yet */
        if (btrfs_is_parity_mirror(map_tree, logical, length, mirror_num))
                return 0;

        bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
        if (!bio)
                return -EIO;
        bio->bi_iter.bi_size = 0;
        map_length = length;

        ret = btrfs_map_block(fs_info, WRITE, logical,
                              &map_length, &bbio, mirror_num);
        if (ret) {
                bio_put(bio);
                return -EIO;
        }
        BUG_ON(mirror_num != bbio->mirror_num);
        sector = bbio->stripes[mirror_num-1].physical >> 9;
        bio->bi_iter.bi_sector = sector;
        dev = bbio->stripes[mirror_num-1].dev;
        btrfs_put_bbio(bbio);
        if (!dev || !dev->bdev || !dev->writeable) {
                bio_put(bio);
                return -EIO;
        }
        bio->bi_bdev = dev->bdev;
        bio_add_page(bio, page, length, pg_offset);

        if (btrfsic_submit_bio_wait(WRITE_SYNC, bio)) {
                /* try to remap that extent elsewhere? */
                bio_put(bio);
                btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_WRITE_ERRS);
                return -EIO;
        }

        btrfs_info_rl_in_rcu(fs_info,
                "read error corrected: ino %llu off %llu (dev %s sector %llu)",
                                  btrfs_ino(inode), start,
                                  rcu_str_deref(dev->name), sector);
        bio_put(bio);
        return 0;
}

int repair_eb_io_failure(struct btrfs_root *root, struct extent_buffer *eb,
                         int mirror_num)
{
        u64 start = eb->start;
        unsigned long i, num_pages = num_extent_pages(eb->start, eb->len);
        int ret = 0;

        if (root->fs_info->sb->s_flags & MS_RDONLY)
                return -EROFS;

        for (i = 0; i < num_pages; i++) {
                struct page *p = eb->pages[i];

                ret = repair_io_failure(root->fs_info->btree_inode, start,
                                        PAGE_CACHE_SIZE, start, p,
                                        start - page_offset(p), mirror_num);
                if (ret)
                        break;
                start += PAGE_CACHE_SIZE;
        }

        return ret;
}

/*
 * each time an IO finishes, we do a fast check in the IO failure tree
 * to see if we need to process or clean up an io_failure_record
 */
int clean_io_failure(struct inode *inode, u64 start, struct page *page,
                     unsigned int pg_offset)
{
        u64 private;
        u64 private_failure;
        struct io_failure_record *failrec;
        struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
        struct extent_state *state;
        int num_copies;
        int ret;

        private = 0;
        ret = count_range_bits(&BTRFS_I(inode)->io_failure_tree, &private,
                                (u64)-1, 1, EXTENT_DIRTY, 0);
        if (!ret)
                return 0;

        ret = get_state_private(&BTRFS_I(inode)->io_failure_tree, start,
                                &private_failure);
        if (ret)
                return 0;

        failrec = (struct io_failure_record *)(unsigned long) private_failure;
        BUG_ON(!failrec->this_mirror);

        if (failrec->in_validation) {
                /* there was no real error, just free the record */
                pr_debug("clean_io_failure: freeing dummy error at %llu\n",
                         failrec->start);
                goto out;
        }
        if (fs_info->sb->s_flags & MS_RDONLY)
                goto out;

        spin_lock(&BTRFS_I(inode)->io_tree.lock);
        state = find_first_extent_bit_state(&BTRFS_I(inode)->io_tree,
                                            failrec->start,
                                            EXTENT_LOCKED);
        spin_unlock(&BTRFS_I(inode)->io_tree.lock);

        if (state && state->start <= failrec->start &&
            state->end >= failrec->start + failrec->len - 1) {
                num_copies = btrfs_num_copies(fs_info, failrec->logical,
                                              failrec->len);
                if (num_copies > 1)  {
                        repair_io_failure(inode, start, failrec->len,
                                          failrec->logical, page,
                                          pg_offset, failrec->failed_mirror);
                }
        }

out:
        free_io_failure(inode, failrec);

        return 0;
}

/*
 * Can be called when
 * - hold extent lock
 * - under ordered extent
 * - the inode is freeing
 */
void btrfs_free_io_failure_record(struct inode *inode, u64 start, u64 end)
{
        struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
        struct io_failure_record *failrec;
        struct extent_state *state, *next;

        if (RB_EMPTY_ROOT(&failure_tree->state))
                return;

        spin_lock(&failure_tree->lock);
        state = find_first_extent_bit_state(failure_tree, start, EXTENT_DIRTY);
        while (state) {
                if (state->start > end)
                        break;

                ASSERT(state->end <= end);

                next = next_state(state);

                failrec = (struct io_failure_record *)(unsigned long)state->private;
                free_extent_state(state);
                kfree(failrec);

                state = next;
        }
        spin_unlock(&failure_tree->lock);
}

int btrfs_get_io_failure_record(struct inode *inode, u64 start, u64 end,
                                struct io_failure_record **failrec_ret)
{
        struct io_failure_record *failrec;
        u64 private;
        struct extent_map *em;
        struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
        struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        int ret;
        u64 logical;

        ret = get_state_private(failure_tree, start, &private);
        if (ret) {
                failrec = kzalloc(sizeof(*failrec), GFP_NOFS);
                if (!failrec)
                        return -ENOMEM;

                failrec->start = start;
                failrec->len = end - start + 1;
                failrec->this_mirror = 0;
                failrec->bio_flags = 0;
                failrec->in_validation = 0;

                read_lock(&em_tree->lock);
                em = lookup_extent_mapping(em_tree, start, failrec->len);
                if (!em) {
                        read_unlock(&em_tree->lock);
                        kfree(failrec);
                        return -EIO;
                }

                if (em->start > start || em->start + em->len <= start) {
                        free_extent_map(em);
                        em = NULL;
                }
                read_unlock(&em_tree->lock);
                if (!em) {
                        kfree(failrec);
                        return -EIO;
                }

                logical = start - em->start;
                logical = em->block_start + logical;
                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) {
                        logical = em->block_start;
                        failrec->bio_flags = EXTENT_BIO_COMPRESSED;
                        extent_set_compress_type(&failrec->bio_flags,
                                                 em->compress_type);
                }

                pr_debug("Get IO Failure Record: (new) logical=%llu, start=%llu, len=%llu\n",
                         logical, start, failrec->len);

                failrec->logical = logical;
                free_extent_map(em);

                /* set the bits in the private failure tree */
                ret = set_extent_bits(failure_tree, start, end,
                                        EXTENT_LOCKED | EXTENT_DIRTY, GFP_NOFS);
                if (ret >= 0)
                        ret = set_state_private(failure_tree, start,
                                                (u64)(unsigned long)failrec);
                /* set the bits in the inode's tree */
                if (ret >= 0)
                        ret = set_extent_bits(tree, start, end, EXTENT_DAMAGED,
                                                GFP_NOFS);
                if (ret < 0) {
                        kfree(failrec);
                        return ret;
                }
        } else {
                failrec = (struct io_failure_record *)(unsigned long)private;
                pr_debug("Get IO Failure Record: (found) logical=%llu, start=%llu, len=%llu, validation=%d\n",
                         failrec->logical, failrec->start, failrec->len,
                         failrec->in_validation);
                /*
                 * when data can be on disk more than twice, add to failrec here
                 * (e.g. with a list for failed_mirror) to make
                 * clean_io_failure() clean all those errors at once.
                 */
        }

        *failrec_ret = failrec;

        return 0;
}

int btrfs_check_repairable(struct inode *inode, struct bio *failed_bio,
                           struct io_failure_record *failrec, int failed_mirror)
{
        int num_copies;

        num_copies = btrfs_num_copies(BTRFS_I(inode)->root->fs_info,
                                      failrec->logical, failrec->len);
        if (num_copies == 1) {
                /*
                 * we only have a single copy of the data, so don't bother with
                 * all the retry and error correction code that follows. no
                 * matter what the error is, it is very likely to persist.
                 */
                pr_debug("Check Repairable: cannot repair, num_copies=%d, next_mirror %d, failed_mirror %d\n",
                         num_copies, failrec->this_mirror, failed_mirror);
                return 0;
        }

        /*
         * there are two premises:
         *      a) deliver good data to the caller
         *      b) correct the bad sectors on disk
         */
        if (failed_bio->bi_vcnt > 1) {
                /*
                 * to fulfill b), we need to know the exact failing sectors, as
                 * we don't want to rewrite any more than the failed ones. thus,
                 * we need separate read requests for the failed bio
                 *
                 * if the following BUG_ON triggers, our validation request got
                 * merged. we need separate requests for our algorithm to work.
                 */
                BUG_ON(failrec->in_validation);
                failrec->in_validation = 1;
                failrec->this_mirror = failed_mirror;
        } else {
                /*
                 * we're ready to fulfill a) and b) alongside. get a good copy
                 * of the failed sector and if we succeed, we have setup
                 * everything for repair_io_failure to do the rest for us.
                 */
                if (failrec->in_validation) {
                        BUG_ON(failrec->this_mirror != failed_mirror);
                        failrec->in_validation = 0;
                        failrec->this_mirror = 0;
                }
                failrec->failed_mirror = failed_mirror;
                failrec->this_mirror++;
                if (failrec->this_mirror == failed_mirror)
                        failrec->this_mirror++;
        }

        if (failrec->this_mirror > num_copies) {
                pr_debug("Check Repairable: (fail) num_copies=%d, next_mirror %d, failed_mirror %d\n",
                         num_copies, failrec->this_mirror, failed_mirror);
                return 0;
        }

        return 1;
}


struct bio *btrfs_create_repair_bio(struct inode *inode, struct bio *failed_bio,
                                    struct io_failure_record *failrec,
                                    struct page *page, int pg_offset, int icsum,
                                    bio_end_io_t *endio_func, void *data)
{
        struct bio *bio;
        struct btrfs_io_bio *btrfs_failed_bio;
        struct btrfs_io_bio *btrfs_bio;

        bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
        if (!bio)
                return NULL;

        bio->bi_end_io = endio_func;
        bio->bi_iter.bi_sector = failrec->logical >> 9;
        bio->bi_bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
        bio->bi_iter.bi_size = 0;
        bio->bi_private = data;

        btrfs_failed_bio = btrfs_io_bio(failed_bio);
        if (btrfs_failed_bio->csum) {
                struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
                u16 csum_size = btrfs_super_csum_size(fs_info->super_copy);

                btrfs_bio = btrfs_io_bio(bio);
                btrfs_bio->csum = btrfs_bio->csum_inline;
                icsum *= csum_size;
                memcpy(btrfs_bio->csum, btrfs_failed_bio->csum + icsum,
                       csum_size);
        }

        bio_add_page(bio, page, failrec->len, pg_offset);

        return bio;
}

/*
 * this is a generic handler for readpage errors (default
 * readpage_io_failed_hook). if other copies exist, read those and write back
 * good data to the failed position. does not investigate in remapping the
 * failed extent elsewhere, hoping the device will be smart enough to do this as
 * needed
 */

static int bio_readpage_error(struct bio *failed_bio, u64 phy_offset,
                              struct page *page, u64 start, u64 end,
                              int failed_mirror)
{
        struct io_failure_record *failrec;
        struct inode *inode = page->mapping->host;
        struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
        struct bio *bio;
        int read_mode;
        int ret;

        BUG_ON(failed_bio->bi_rw & REQ_WRITE);

        ret = btrfs_get_io_failure_record(inode, start, end, &failrec);
        if (ret)
                return ret;

        ret = btrfs_check_repairable(inode, failed_bio, failrec, failed_mirror);
        if (!ret) {
                free_io_failure(inode, failrec);
                return -EIO;
        }

        if (failed_bio->bi_vcnt > 1)
                read_mode = READ_SYNC | REQ_FAILFAST_DEV;
        else
                read_mode = READ_SYNC;

        phy_offset >>= inode->i_sb->s_blocksize_bits;
        bio = btrfs_create_repair_bio(inode, failed_bio, failrec, page,
                                      start - page_offset(page),
                                      (int)phy_offset, failed_bio->bi_end_io,
                                      NULL);
        if (!bio) {
                free_io_failure(inode, failrec);
                return -EIO;
        }

        pr_debug("Repair Read Error: submitting new read[%#x] to this_mirror=%d, in_validation=%d\n",
                 read_mode, failrec->this_mirror, failrec->in_validation);

        ret = tree->ops->submit_bio_hook(inode, read_mode, bio,
                                         failrec->this_mirror,
                                         failrec->bio_flags, 0);
        if (ret) {
                free_io_failure(inode, failrec);
                bio_put(bio);
        }

        return ret;
}

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

void end_extent_writepage(struct page *page, int err, u64 start, u64 end)
{
        int uptodate = (err == 0);
        struct extent_io_tree *tree;
        int ret = 0;

        tree = &BTRFS_I(page->mapping->host)->io_tree;

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

        if (!uptodate) {
                ClearPageUptodate(page);
                SetPageError(page);
                ret = ret < 0 ? ret : -EIO;
                mapping_set_error(page->mapping, ret);
        }
}

/*
 * after a writepage IO is done, we need to:
 * clear the uptodate bits on error
 * clear the writeback bits in the extent tree for this IO
 * end_page_writeback if the page has no more pending IO
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bio_extent_writepage(struct bio *bio)
{
        struct bio_vec *bvec;
        u64 start;
        u64 end;
        int i;

        bio_for_each_segment_all(bvec, bio, i) {
                struct page *page = bvec->bv_page;

                /* We always issue full-page reads, but if some block
                 * in a page fails to read, blk_update_request() will
                 * advance bv_offset and adjust bv_len to compensate.
                 * Print a warning for nonzero offsets, and an error
                 * if they don't add up to a full page.  */
                if (bvec->bv_offset || bvec->bv_len != PAGE_CACHE_SIZE) {
                        if (bvec->bv_offset + bvec->bv_len != PAGE_CACHE_SIZE)
                                btrfs_err(BTRFS_I(page->mapping->host)->root->fs_info,
                                   "partial page write in btrfs with offset %u and length %u",
                                        bvec->bv_offset, bvec->bv_len);
                        else
                                btrfs_info(BTRFS_I(page->mapping->host)->root->fs_info,
                                   "incomplete page write in btrfs with offset %u and "
                                   "length %u",
                                        bvec->bv_offset, bvec->bv_len);
                }

                start = page_offset(page);
                end = start + bvec->bv_offset + bvec->bv_len - 1;

                end_extent_writepage(page, bio->bi_error, start, end);
                end_page_writeback(page);
        }

        bio_put(bio);
}

static void
endio_readpage_release_extent(struct extent_io_tree *tree, u64 start, u64 len,
                              int uptodate)
{
        struct extent_state *cached = NULL;
        u64 end = start + len - 1;

        if (uptodate && tree->track_uptodate)
                set_extent_uptodate(tree, start, end, &cached, GFP_ATOMIC);
        unlock_extent_cached(tree, start, end, &cached, GFP_ATOMIC);
}

/*
 * after a readpage IO is done, we need to:
 * clear the uptodate bits on error
 * set the uptodate bits if things worked
 * set the page up to date if all extents in the tree are uptodate
 * clear the lock bit in the extent tree
 * unlock the page if there are no other extents locked for it
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bio_extent_readpage(struct bio *bio)
{
        struct bio_vec *bvec;
        int uptodate = !bio->bi_error;
        struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
        struct extent_io_tree *tree;
        u64 offset = 0;
        u64 start;
        u64 end;
        u64 len;
        u64 extent_start = 0;
        u64 extent_len = 0;
        int mirror;
        int ret;
        int i;

        bio_for_each_segment_all(bvec, bio, i) {
                struct page *page = bvec->bv_page;
                struct inode *inode = page->mapping->host;

                pr_debug("end_bio_extent_readpage: bi_sector=%llu, err=%d, "
                         "mirror=%u\n", (u64)bio->bi_iter.bi_sector,
                         bio->bi_error, io_bio->mirror_num);
                tree = &BTRFS_I(inode)->io_tree;

                /* We always issue full-page reads, but if some block
                 * in a page fails to read, blk_update_request() will
                 * advance bv_offset and adjust bv_len to compensate.
                 * Print a warning for nonzero offsets, and an error
                 * if they don't add up to a full page.  */
                if (bvec->bv_offset || bvec->bv_len != PAGE_CACHE_SIZE) {
                        if (bvec->bv_offset + bvec->bv_len != PAGE_CACHE_SIZE)
                                btrfs_err(BTRFS_I(page->mapping->host)->root->fs_info,
                                   "partial page read in btrfs with offset %u and length %u",
                                        bvec->bv_offset, bvec->bv_len);
                        else
                                btrfs_info(BTRFS_I(page->mapping->host)->root->fs_info,
                                   "incomplete page read in btrfs with offset %u and "
                                   "length %u",
                                        bvec->bv_offset, bvec->bv_len);
                }

                start = page_offset(page);
                end = start + bvec->bv_offset + bvec->bv_len - 1;
                len = bvec->bv_len;

                mirror = io_bio->mirror_num;
                if (likely(uptodate && tree->ops &&
                           tree->ops->readpage_end_io_hook)) {
                        ret = tree->ops->readpage_end_io_hook(io_bio, offset,
                                                              page, start, end,
                                                              mirror);
                        if (ret)
                                uptodate = 0;
                        else
                                clean_io_failure(inode, start, page, 0);
                }

                if (likely(uptodate))
                        goto readpage_ok;

                if (tree->ops && tree->ops->readpage_io_failed_hook) {
                        ret = tree->ops->readpage_io_failed_hook(page, mirror);
                        if (!ret && !bio->bi_error)
                                uptodate = 1;
                } else {
                        /*
                         * The generic bio_readpage_error handles errors the
                         * following way: If possible, new read requests are
                         * created and submitted and will end up in
                         * end_bio_extent_readpage as well (if we're lucky, not
                         * in the !uptodate case). In that case it returns 0 and
                         * we just go on with the next page in our bio. If it
                         * can't handle the error it will return -EIO and we
                         * remain responsible for that page.
                         */
                        ret = bio_readpage_error(bio, offset, page, start, end,
                                                 mirror);
                        if (ret == 0) {
                                uptodate = !bio->bi_error;
                                offset += len;
                                continue;
                        }
                }
readpage_ok:
                if (likely(uptodate)) {
                        loff_t i_size = i_size_read(inode);
                        pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
                        unsigned off;

                        /* Zero out the end if this page straddles i_size */
                        off = i_size & (PAGE_CACHE_SIZE-1);
                        if (page->index == end_index && off)
                                zero_user_segment(page, off, PAGE_CACHE_SIZE);
                        SetPageUptodate(page);
                } else {
                        ClearPageUptodate(page);
                        SetPageError(page);
                }
                unlock_page(page);
                offset += len;

                if (unlikely(!uptodate)) {
                        if (extent_len) {
                                endio_readpage_release_extent(tree,
                                                              extent_start,
                                                              extent_len, 1);
                                extent_start = 0;
                                extent_len = 0;
                        }
                        endio_readpage_release_extent(tree, start,
                                                      end - start + 1, 0);
                } else if (!extent_len) {
                        extent_start = start;
                        extent_len = end + 1 - start;
                } else if (extent_start + extent_len == start) {
                        extent_len += end + 1 - start;
                } else {
                        endio_readpage_release_extent(tree, extent_start,
                                                      extent_len, uptodate);
                        extent_start = start;
                        extent_len = end + 1 - start;
                }
        }

        if (extent_len)
                endio_readpage_release_extent(tree, extent_start, extent_len,
                                              uptodate);
        if (io_bio->end_io)
                io_bio->end_io(io_bio, bio->bi_error);
        bio_put(bio);
}

/*
 * this allocates from the btrfs_bioset.  We're returning a bio right now
 * but you can call btrfs_io_bio for the appropriate container_of magic
 */
struct bio *
btrfs_bio_alloc(struct block_device *bdev, u64 first_sector, int nr_vecs,
                gfp_t gfp_flags)
{
        struct btrfs_io_bio *btrfs_bio;
        struct bio *bio;

        bio = bio_alloc_bioset(gfp_flags, nr_vecs, btrfs_bioset);

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

        if (bio) {
                bio->bi_bdev = bdev;
                bio->bi_iter.bi_sector = first_sector;
                btrfs_bio = btrfs_io_bio(bio);
                btrfs_bio->csum = NULL;
                btrfs_bio->csum_allocated = NULL;
                btrfs_bio->end_io = NULL;
        }
        return bio;
}

struct bio *btrfs_bio_clone(struct bio *bio, gfp_t gfp_mask)
{
        struct btrfs_io_bio *btrfs_bio;
        struct bio *new;

        new = bio_clone_bioset(bio, gfp_mask, btrfs_bioset);
        if (new) {
                btrfs_bio = btrfs_io_bio(new);
                btrfs_bio->csum = NULL;
                btrfs_bio->csum_allocated = NULL;
                btrfs_bio->end_io = NULL;

#ifdef CONFIG_BLK_CGROUP
                /* FIXME, put this into bio_clone_bioset */
                if (bio->bi_css)
                        bio_associate_blkcg(new, bio->bi_css);
#endif
        }
        return new;
}

/* this also allocates from the btrfs_bioset */
struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
{
        struct btrfs_io_bio *btrfs_bio;
        struct bio *bio;

        bio = bio_alloc_bioset(gfp_mask, nr_iovecs, btrfs_bioset);
        if (bio) {
                btrfs_bio = btrfs_io_bio(bio);
                btrfs_bio->csum = NULL;
                btrfs_bio->csum_allocated = NULL;
                btrfs_bio->end_io = NULL;
        }
        return bio;
}


static int __must_check submit_one_bio(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;

        start = page_offset(page) + bvec->bv_offset;

        bio->bi_private = NULL;

        bio_get(bio);

        if (tree->ops && tree->ops->submit_bio_hook)
                ret = tree->ops->submit_bio_hook(page->mapping->host, rw, bio,
                                           mirror_num, bio_flags, start);
        else
                btrfsic_submit_bio(rw, bio);

        bio_put(bio);
        return ret;
}

static int merge_bio(int rw, struct extent_io_tree *tree, struct page *page,
                     unsigned long offset, size_t size, struct bio *bio,
                     unsigned long bio_flags)
{
        int ret = 0;
        if (tree->ops && tree->ops->merge_bio_hook)
                ret = tree->ops->merge_bio_hook(rw, page, offset, size, bio,
                                                bio_flags);
        BUG_ON(ret < 0);
        return ret;

}

static int submit_extent_page(int rw, struct extent_io_tree *tree,
                              struct writeback_control *wbc,
                              struct page *page, sector_t sector,
                              size_t size, unsigned long offset,
                              struct block_device *bdev,
                              struct bio **bio_ret,
                              unsigned long max_pages,
                              bio_end_io_t end_io_func,
                              int mirror_num,
                              unsigned long prev_bio_flags,
                              unsigned long bio_flags,
                              bool force_bio_submit)
{
        int ret = 0;
        struct bio *bio;
        int contig = 0;
        int old_compressed = prev_bio_flags & EXTENT_BIO_COMPRESSED;
        size_t page_size = min_t(size_t, size, PAGE_CACHE_SIZE);

        if (bio_ret && *bio_ret) {
                bio = *bio_ret;
                if (old_compressed)
                        contig = bio->bi_iter.bi_sector == sector;
                else
                        contig = bio_end_sector(bio) == sector;

                if (prev_bio_flags != bio_flags || !contig ||
                    force_bio_submit ||
                    merge_bio(rw, tree, 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);
                        if (ret < 0) {
                                *bio_ret = NULL;
                                return ret;
                        }
                        bio = NULL;
                } else {
                        if (wbc)
                                wbc_account_io(wbc, page, page_size);
                        return 0;
                }
        }

        bio = btrfs_bio_alloc(bdev, sector, BIO_MAX_PAGES,
                        GFP_NOFS | __GFP_HIGH);
        if (!bio)
                return -ENOMEM;

        bio_add_page(bio, page, page_size, offset);
        bio->bi_end_io = end_io_func;
        bio->bi_private = tree;
        if (wbc) {
                wbc_init_bio(wbc, bio);
                wbc_account_io(wbc, page, page_size);
        }

        if (bio_ret)
                *bio_ret = bio;
        else
                ret = submit_one_bio(rw, bio, mirror_num, bio_flags);

        return ret;
}

static void attach_extent_buffer_page(struct extent_buffer *eb,
                                      struct page *page)
{
        if (!PagePrivate(page)) {
                SetPagePrivate(page);
                page_cache_get(page);
                set_page_private(page, (unsigned long)eb);
        } else {
                WARN_ON(page->private != (unsigned long)eb);
        }
}

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

static struct extent_map *
__get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
                 u64 start, u64 len, get_extent_t *get_extent,
                 struct extent_map **em_cached)
{
        struct extent_map *em;

        if (em_cached && *em_cached) {
                em = *em_cached;
                if (extent_map_in_tree(em) && start >= em->start &&
                    start < extent_map_end(em)) {
                        atomic_inc(&em->refs);
                        return em;
                }

                free_extent_map(em);
                *em_cached = NULL;
        }

        em = get_extent(inode, page, pg_offset, start, len, 0);
        if (em_cached && !IS_ERR_OR_NULL(em)) {
                BUG_ON(*em_cached);
                atomic_inc(&em->refs);
                *em_cached = em;
        }
        return em;
}
/*
 * basic readpage implementation.  Locked extent state structs are inserted
 * into the tree that are removed when the IO is done (by the end_io
 * handlers)
 * XXX JDM: This needs looking at to ensure proper page locking
 */
static int __do_readpage(struct extent_io_tree *tree,
                         struct page *page,
                         get_extent_t *get_extent,
                         struct extent_map **em_cached,
                         struct bio **bio, int mirror_num,
                         unsigned long *bio_flags, int rw,
                         u64 *prev_em_start)
{
        struct inode *inode = page->mapping->host;
        u64 start = page_offset(page);
        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;
        int parent_locked = *bio_flags & EXTENT_BIO_PARENT_LOCKED;
        size_t pg_offset = 0;
        size_t iosize;
        size_t disk_io_size;
        size_t blocksize = inode->i_sb->s_blocksize;
        unsigned long this_bio_flag = *bio_flags & EXTENT_BIO_PARENT_LOCKED;

        set_page_extent_mapped(page);

        end = page_end;
        if (!PageUptodate(page)) {
                if (cleancache_get_page(page) == 0) {
                        BUG_ON(blocksize != PAGE_SIZE);
                        unlock_extent(tree, start, end);
                        goto out;
                }
        }

        if (page->index == last_byte >> PAGE_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);
                        memset(userpage + zero_offset, 0, iosize);
                        flush_dcache_page(page);
                        kunmap_atomic(userpage);
                }
        }
        while (cur <= end) {
                unsigned long pnr = (last_byte >> PAGE_CACHE_SHIFT) + 1;
                bool force_bio_submit = false;

                if (cur >= last_byte) {
                        char *userpage;
                        struct extent_state *cached = NULL;

                        iosize = PAGE_CACHE_SIZE - pg_offset;
                        userpage = kmap_atomic(page);
                        memset(userpage + pg_offset, 0, iosize);
                        flush_dcache_page(page);
                        kunmap_atomic(userpage);
                        set_extent_uptodate(tree, cur, cur + iosize - 1,
                                            &cached, GFP_NOFS);
                        if (!parent_locked)
                                unlock_extent_cached(tree, cur,
                                                     cur + iosize - 1,
                                                     &cached, GFP_NOFS);
                        break;
                }
                em = __get_extent_map(inode, page, pg_offset, cur,
                                      end - cur + 1, get_extent, em_cached);
                if (IS_ERR_OR_NULL(em)) {
                        SetPageError(page);
                        if (!parent_locked)
                                unlock_extent(tree, cur, end);
                        break;
                }
                extent_offset = cur - em->start;
                BUG_ON(extent_map_end(em) <= cur);
                BUG_ON(end < cur);

                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) {
                        this_bio_flag |= EXTENT_BIO_COMPRESSED;
                        extent_set_compress_type(&this_bio_flag,
                                                 em->compress_type);
                }

                iosize = min(extent_map_end(em) - cur, end - cur + 1);
                cur_end = min(extent_map_end(em) - 1, end);
                iosize = ALIGN(iosize, blocksize);
                if (this_bio_flag & EXTENT_BIO_COMPRESSED) {
                        disk_io_size = em->block_len;
                        sector = em->block_start >> 9;
                } else {
                        sector = (em->block_start + extent_offset) >> 9;
                        disk_io_size = iosize;
                }
                bdev = em->bdev;
                block_start = em->block_start;
                if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
                        block_start = EXTENT_MAP_HOLE;

                /*
                 * If we have a file range that points to a compressed extent
                 * and it's followed by a consecutive file range that points to
                 * to the same compressed extent (possibly with a different
                 * offset and/or length, so it either points to the whole extent
                 * or only part of it), we must make sure we do not submit a
                 * single bio to populate the pages for the 2 ranges because
                 * this makes the compressed extent read zero out the pages
                 * belonging to the 2nd range. Imagine the following scenario:
                 *
                 *  File layout
                 *  [0 - 8K]                     [8K - 24K]
                 *    |                               |
                 *    |                               |
                 * points to extent X,         points to extent X,
                 * offset 4K, length of 8K     offset 0, length 16K
                 *
                 * [extent X, compressed length = 4K uncompressed length = 16K]
                 *
                 * If the bio to read the compressed extent covers both ranges,
                 * it will decompress extent X into the pages belonging to the
                 * first range and then it will stop, zeroing out the remaining
                 * pages that belong to the other range that points to extent X.
                 * So here we make sure we submit 2 bios, one for the first
                 * range and another one for the third range. Both will target
                 * the same physical extent from disk, but we can't currently
                 * make the compressed bio endio callback populate the pages
                 * for both ranges because each compressed bio is tightly
                 * coupled with a single extent map, and each range can have
                 * an extent map with a different offset value relative to the
                 * uncompressed data of our extent and different lengths. This
                 * is a corner case so we prioritize correctness over
                 * non-optimal behavior (submitting 2 bios for the same extent).
                 */
                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags) &&
                    prev_em_start && *prev_em_start != (u64)-1 &&
                    *prev_em_start != em->orig_start)
                        force_bio_submit = true;

                if (prev_em_start)
                        *prev_em_start = em->orig_start;

                free_extent_map(em);
                em = NULL;

                /* we've found a hole, just zero and go on */
                if (block_start == EXTENT_MAP_HOLE) {
                        char *userpage;
                        struct extent_state *cached = NULL;

                        userpage = kmap_atomic(page);
                        memset(userpage + pg_offset, 0, iosize);
                        flush_dcache_page(page);
                        kunmap_atomic(userpage);

                        set_extent_uptodate(tree, cur, cur + iosize - 1,
                                            &cached, GFP_NOFS);
                        if (parent_locked)
                                free_extent_state(cached);
                        else
                                unlock_extent_cached(tree, cur,
                                                     cur + iosize - 1,
                                                     &cached, GFP_NOFS);
                        cur = cur + iosize;
                        pg_offset += iosize;
                        continue;
                }
                /* the get_extent function already copied into the page */
                if (test_range_bit(tree, cur, cur_end,
                                   EXTENT_UPTODATE, 1, NULL)) {
                        check_page_uptodate(tree, page);
                        if (!parent_locked)
                                unlock_extent(tree, cur, cur + iosize - 1);
                        cur = cur + iosize;
                        pg_offset += iosize;
                        continue;
                }
                /* we have an inline extent but it didn't get marked up
                 * to date.  Error out
                 */
                if (block_start == EXTENT_MAP_INLINE) {
                        SetPageError(page);
                        if (!parent_locked)
                                unlock_extent(tree, cur, cur + iosize - 1);
                        cur = cur + iosize;
                        pg_offset += iosize;
                        continue;
                }

                pnr -= page->index;
                ret = submit_extent_page(rw, tree, NULL, page,
                                         sector, disk_io_size, pg_offset,
                                         bdev, bio, pnr,
                                         end_bio_extent_readpage, mirror_num,
                                         *bio_flags,
                                         this_bio_flag,
                                         force_bio_submit);
                if (!ret) {
                        nr++;
                        *bio_flags = this_bio_flag;
                } else {
                        SetPageError(page);
                        if (!parent_locked)
                                unlock_extent(tree, cur, cur + iosize - 1);
                }
                cur = cur + iosize;
                pg_offset += iosize;
        }
out:
        if (!nr) {
                if (!PageError(page))
                        SetPageUptodate(page);
                unlock_page(page);
        }
        return 0;
}

static inline void __do_contiguous_readpages(struct extent_io_tree *tree,
                                             struct page *pages[], int nr_pages,
                                             u64 start, u64 end,
                                             get_extent_t *get_extent,
                                             struct extent_map **em_cached,
                                             struct bio **bio, int mirror_num,
                                             unsigned long *bio_flags, int rw,
                                             u64 *prev_em_start)
{
        struct inode *inode;
        struct btrfs_ordered_extent *ordered;
        int index;

        inode = pages[0]->mapping->host;
        while (1) {
                lock_extent(tree, start, end);
                ordered = btrfs_lookup_ordered_range(inode, start,
                                                     end - start + 1);
                if (!ordered)
                        break;
                unlock_extent(tree, start, end);
                btrfs_start_ordered_extent(inode, ordered, 1);
                btrfs_put_ordered_extent(ordered);
        }

        for (index = 0; index < nr_pages; index++) {
                __do_readpage(tree, pages[index], get_extent, em_cached, bio,
                              mirror_num, bio_flags, rw, prev_em_start);
                page_cache_release(pages[index]);
        }
}

static void __extent_readpages(struct extent_io_tree *tree,
                               struct page *pages[],
                               int nr_pages, get_extent_t *get_extent,
                               struct extent_map **em_cached,
                               struct bio **bio, int mirror_num,
                               unsigned long *bio_flags, int rw,
                               u64 *prev_em_start)
{
        u64 start = 0;
        u64 end = 0;
        u64 page_start;
        int index;
        int first_index = 0;

        for (index = 0; index < nr_pages; index++) {
                page_start = page_offset(pages[index]);
                if (!end) {
                        start = page_start;
                        end = start + PAGE_CACHE_SIZE - 1;
                        first_index = index;
                } else if (end + 1 == page_start) {
                        end += PAGE_CACHE_SIZE;
                } else {
                        __do_contiguous_readpages(tree, &pages[first_index],
                                                  index - first_index, start,
                                                  end, get_extent, em_cached,
                                                  bio, mirror_num, bio_flags,
                                                  rw, prev_em_start);
                        start = page_start;
                        end = start + PAGE_CACHE_SIZE - 1;
                        first_index = index;
                }
        }

        if (end)
                __do_contiguous_readpages(tree, &pages[first_index],
                                          index - first_index, start,
                                          end, get_extent, em_cached, bio,
                                          mirror_num, bio_flags, rw,
                                          prev_em_start);
}

static int __extent_read_full_page(struct extent_io_tree *tree,
                                   struct page *page,
                                   get_extent_t *get_extent,
                                   struct bio **bio, int mirror_num,
                                   unsigned long *bio_flags, int rw)
{
        struct inode *inode = page->mapping->host;
        struct btrfs_ordered_extent *ordered;
        u64 start = page_offset(page);
        u64 end = start + PAGE_CACHE_SIZE - 1;
        int ret;

        while (1) {
                lock_extent(tree, start, end);
                ordered = btrfs_lookup_ordered_range(inode, start,
                                                PAGE_CACHE_SIZE);
                if (!ordered)
                        break;
                unlock_extent(tree, start, end);
                btrfs_start_ordered_extent(inode, ordered, 1);
                btrfs_put_ordered_extent(ordered);
        }

        ret = __do_readpage(tree, page, get_extent, NULL, bio, mirror_num,
                            bio_flags, rw, NULL);
        return ret;
}

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

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

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

        ret = __do_readpage(tree, page, get_extent, NULL, &bio, mirror_num,
                            &bio_flags, READ, NULL);
        if (bio)
                ret = submit_one_bio(READ, bio, mirror_num, 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;
}

/*
 * helper for __extent_writepage, doing all of the delayed allocation setup.
 *
 * This returns 1 if our fill_delalloc function did all the work required
 * to write the page (copy into inline extent).  In this case the IO has
 * been started and the page is already unlocked.
 *
 * This returns 0 if all went well (page still locked)
 * This returns < 0 if there were errors (page still locked)
 */
static noinline_for_stack int writepage_delalloc(struct inode *inode,
                              struct page *page, struct writeback_control *wbc,
                              struct extent_page_data *epd,
                              u64 delalloc_start,
                              unsigned long *nr_written)
{
        struct extent_io_tree *tree = epd->tree;
        u64 page_end = delalloc_start + PAGE_CACHE_SIZE - 1;
        u64 nr_delalloc;
        u64 delalloc_to_write = 0;
        u64 delalloc_end = 0;
        int ret;
        int page_started = 0;

        if (epd->extent_locked || !tree->ops || !tree->ops->fill_delalloc)
                return 0;

        while (delalloc_end < page_end) {
                nr_delalloc = find_lock_delalloc_range(inode, tree,
                                               page,
                                               &delalloc_start,
                                               &delalloc_end,
                                               BTRFS_MAX_EXTENT_SIZE);
                if (nr_delalloc == 0) {
                        delalloc_start = delalloc_end + 1;
                        continue;
                }
                ret = tree->ops->fill_delalloc(inode, page,
                                               delalloc_start,
                                               delalloc_end,
                                               &page_started,
                                               nr_written);
                /* File system has been set read-only */
                if (ret) {
                        SetPageError(page);
                        /* fill_delalloc should be return < 0 for error
                         * but just in case, we use > 0 here meaning the
                         * IO is started, so we don't want to return > 0
                         * unless things are going well.
                         */
                        ret = ret < 0 ? ret : -EIO;
                        goto done;
                }
                /*
                 * delalloc_end is already one less than the total
                 * length, so we don't subtract one from
                 * PAGE_CACHE_SIZE
                 */
                delalloc_to_write += (delalloc_end - delalloc_start +
                                      PAGE_CACHE_SIZE) >>
                                      PAGE_CACHE_SHIFT;
                delalloc_start = delalloc_end + 1;
        }
        if (wbc->nr_to_write < delalloc_to_write) {
                int thresh = 8192;

                if (delalloc_to_write < thresh * 2)
                        thresh = delalloc_to_write;
                wbc->nr_to_write = min_t(u64, delalloc_to_write,
                                         thresh);
        }

        /* did the fill delalloc function already unlock and start
         * the IO?
         */
        if (page_started) {
                /*
                 * we've unlocked the page, so we can't update
                 * the mapping's writeback index, just update
                 * nr_to_write.
                 */
                wbc->nr_to_write -= *nr_written;
                return 1;
        }

        ret = 0;

done:
        return ret;
}

/*
 * helper for __extent_writepage.  This calls the writepage start hooks,
 * and does the loop to map the page into extents and bios.
 *
 * We return 1 if the IO is started and the page is unlocked,
 * 0 if all went well (page still locked)
 * < 0 if there were errors (page still locked)
 */
static noinline_for_stack int __extent_writepage_io(struct inode *inode,
                                 struct page *page,
                                 struct writeback_control *wbc,
                                 struct extent_page_data *epd,
                                 loff_t i_size,
                                 unsigned long nr_written,
                                 int write_flags, int *nr_ret)
{
        struct extent_io_tree *tree = epd->tree;
        u64 start = page_offset(page);
        u64 page_end = start + PAGE_CACHE_SIZE - 1;
        u64 end;
        u64 cur = start;
        u64 extent_offset;
        u64 block_start;
        u64 iosize;
        sector_t sector;
        struct extent_state *cached_state = NULL;
        struct extent_map *em;
        struct block_device *bdev;
        size_t pg_offset = 0;
        size_t blocksize;
        int ret = 0;
        int nr = 0;
        bool compressed;

        if (tree->ops && tree->ops->writepage_start_hook) {
                ret = tree->ops->writepage_start_hook(page, start,
                                                      page_end);
                if (ret) {
                        /* Fixup worker will requeue */
                        if (ret == -EBUSY)
                                wbc->pages_skipped++;
                        else
                                redirty_page_for_writepage(wbc, page);

                        update_nr_written(page, wbc, nr_written);
                        unlock_page(page);
                        ret = 1;
                        goto done_unlocked;
                }
        }

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

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

        blocksize = inode->i_sb->s_blocksize;

        while (cur <= end) {
                u64 em_end;
                if (cur >= i_size) {
                        if (tree->ops && tree->ops->writepage_end_io_hook)
                                tree->ops->writepage_end_io_hook(page, cur,
                                                         page_end, NULL, 1);
                        break;
                }
                em = epd->get_extent(inode, page, pg_offset, cur,
                                     end - cur + 1, 1);
                if (IS_ERR_OR_NULL(em)) {
                        SetPageError(page);
                        ret = PTR_ERR_OR_ZERO(em);
                        break;
                }

                extent_offset = cur - em->start;
                em_end = extent_map_end(em);
                BUG_ON(em_end <= cur);
                BUG_ON(end < cur);
                iosize = min(em_end - cur, end - cur + 1);
                iosize = ALIGN(iosize, blocksize);
                sector = (em->block_start + extent_offset) >> 9;
                bdev = em->bdev;
                block_start = em->block_start;
                compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
                free_extent_map(em);
                em = NULL;

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

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

                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 = (i_size >> PAGE_CACHE_SHIFT) + 1;

                        set_range_writeback(tree, cur, cur + iosize - 1);
                        if (!PageWriteback(page)) {
                                btrfs_err(BTRFS_I(inode)->root->fs_info,
                                           "page %lu not writeback, cur %llu end %llu",
                                       page->index, cur, end);
                        }

                        ret = submit_extent_page(write_flags, tree, wbc, page,
                                                 sector, iosize, pg_offset,
                                                 bdev, &epd->bio, max_nr,
                                                 end_bio_extent_writepage,
                                                 0, 0, 0, false);
                        if (ret)
                                SetPageError(page);
                }
                cur = cur + iosize;
                pg_offset += iosize;
                nr++;
        }
done:
        *nr_ret = nr;

done_unlocked:

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

/*
 * the writepage semantics are similar to regular writepage.  extent
 * records are inserted to lock ranges in the tree, and as dirty areas
 * are found, they are marked writeback.  Then the lock bits are removed
 * and the end_io handler clears the writeback ranges
 */
static int __extent_writepage(struct page *page, struct writeback_control *wbc,
                              void *data)
{
        struct inode *inode = page->mapping->host;
        struct extent_page_data *epd = data;
        u64 start = page_offset(page);
        u64 page_end = start + PAGE_CACHE_SIZE - 1;
        int ret;
        int nr = 0;
        size_t pg_offset = 0;
        loff_t i_size = i_size_read(inode);
        unsigned long end_index = i_size >> PAGE_CACHE_SHIFT;
        int write_flags;
        unsigned long nr_written = 0;

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

        trace___extent_writepage(page, inode, wbc);

        WARN_ON(!PageLocked(page));

        ClearPageError(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, PAGE_CACHE_SIZE);
                unlock_page(page);
                return 0;
        }

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

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

        pg_offset = 0;

        set_page_extent_mapped(page);

        ret = writepage_delalloc(inode, page, wbc, epd, start, &nr_written);
        if (ret == 1)
                goto done_unlocked;
        if (ret)
                goto done;

        ret = __extent_writepage_io(inode, page, wbc, epd,
                                    i_size, nr_written, write_flags, &nr);
        if (ret == 1)
                goto done_unlocked;

done:
        if (nr == 0) {
                /* make sure the mapping tag for page dirty gets cleared */
                set_page_writeback(page);
                end_page_writeback(page);
        }
        if (PageError(page)) {
                ret = ret < 0 ? ret : -EIO;
                end_extent_writepage(page, ret, start, page_end);
        }
        unlock_page(page);
        return ret;

done_unlocked:
        return 0;
}

void wait_on_extent_buffer_writeback(struct extent_buffer *eb)
{
        wait_on_bit_io(&eb->bflags, EXTENT_BUFFER_WRITEBACK,
                       TASK_UNINTERRUPTIBLE);
}

static noinline_for_stack int
lock_extent_buffer_for_io(struct extent_buffer *eb,
                          struct btrfs_fs_info *fs_info,
                          struct extent_page_data *epd)
{
        unsigned long i, num_pages;
        int flush = 0;
        int ret = 0;

        if (!btrfs_try_tree_write_lock(eb)) {
                flush = 1;
                flush_write_bio(epd);
                btrfs_tree_lock(eb);
        }

        if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
                btrfs_tree_unlock(eb);
                if (!epd->sync_io)
                        return 0;
                if (!flush) {
                        flush_write_bio(epd);
                        flush = 1;
                }
                while (1) {
                        wait_on_extent_buffer_writeback(eb);
                        btrfs_tree_lock(eb);
                        if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
                                break;
                        btrfs_tree_unlock(eb);
                }
        }

        /*
         * We need to do this to prevent races in people who check if the eb is
         * under IO since we can end up having no IO bits set for a short period
         * of time.
         */
        spin_lock(&eb->refs_lock);
        if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
                set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
                spin_unlock(&eb->refs_lock);
                btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
                __percpu_counter_add(&fs_info->dirty_metadata_bytes,
                                     -eb->len,
                                     fs_info->dirty_metadata_batch);
                ret = 1;
        } else {
                spin_unlock(&eb->refs_lock);
        }

        btrfs_tree_unlock(eb);

        if (!ret)
                return ret;

        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++) {
                struct page *p = eb->pages[i];

                if (!trylock_page(p)) {
                        if (!flush) {
                                flush_write_bio(epd);
                                flush = 1;
                        }
                        lock_page(p);
                }
        }

        return ret;
}

static void end_extent_buffer_writeback(struct extent_buffer *eb)
{
        clear_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
        smp_mb__after_atomic();
        wake_up_bit(&eb->bflags, EXTENT_BUFFER_WRITEBACK);
}

static void set_btree_ioerr(struct page *page)
{
        struct extent_buffer *eb = (struct extent_buffer *)page->private;
        struct btrfs_inode *btree_ino = BTRFS_I(eb->fs_info->btree_inode);

        SetPageError(page);
        if (test_and_set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))
                return;

        /*
         * If writeback for a btree extent that doesn't belong to a log tree
         * failed, increment the counter transaction->eb_write_errors.
         * We do this because while the transaction is running and before it's
         * committing (when we call filemap_fdata[write|wait]_range against
         * the btree inode), we might have
         * btree_inode->i_mapping->a_ops->writepages() called by the VM - if it
         * returns an error or an error happens during writeback, when we're
         * committing the transaction we wouldn't know about it, since the pages
         * can be no longer dirty nor marked anymore for writeback (if a
         * subsequent modification to the extent buffer didn't happen before the
         * transaction commit), which makes filemap_fdata[write|wait]_range not
         * able to find the pages tagged with SetPageError at transaction
         * commit time. So if this happens we must abort the transaction,
         * otherwise we commit a super block with btree roots that point to
         * btree nodes/leafs whose content on disk is invalid - either garbage
         * or the content of some node/leaf from a past generation that got
         * cowed or deleted and is no longer valid.
         *
         * Note: setting AS_EIO/AS_ENOSPC in the btree inode's i_mapping would
         * not be enough - we need to distinguish between log tree extents vs
         * non-log tree extents, and the next filemap_fdatawait_range() call
         * will catch and clear such errors in the mapping - and that call might
         * be from a log sync and not from a transaction commit. Also, checking
         * for the eb flag EXTENT_BUFFER_WRITE_ERR at transaction commit time is
         * not done and would not be reliable - the eb might have been released
         * from memory and reading it back again means that flag would not be
         * set (since it's a runtime flag, not persisted on disk).
         *
         * Using the flags below in the btree inode also makes us achieve the
         * goal of AS_EIO/AS_ENOSPC when writepages() returns success, started
         * writeback for all dirty pages and before filemap_fdatawait_range()
         * is called, the writeback for all dirty pages had already finished
         * with errors - because we were not using AS_EIO/AS_ENOSPC,
         * filemap_fdatawait_range() would return success, as it could not know
         * that writeback errors happened (the pages were no longer tagged for
         * writeback).
         */
        switch (eb->log_index) {
        case -1:
                set_bit(BTRFS_INODE_BTREE_ERR, &btree_ino->runtime_flags);
                break;
        case 0:
                set_bit(BTRFS_INODE_BTREE_LOG1_ERR, &btree_ino->runtime_flags);
                break;
        case 1:
                set_bit(BTRFS_INODE_BTREE_LOG2_ERR, &btree_ino->runtime_flags);
                break;
        default:
                BUG(); /* unexpected, logic error */
        }
}

static void end_bio_extent_buffer_writepage(struct bio *bio)
{
        struct bio_vec *bvec;
        struct extent_buffer *eb;
        int i, done;

        bio_for_each_segment_all(bvec, bio, i) {
                struct page *page = bvec->bv_page;

                eb = (struct extent_buffer *)page->private;
                BUG_ON(!eb);
                done = atomic_dec_and_test(&eb->io_pages);

                if (bio->bi_error ||
                    test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) {
                        ClearPageUptodate(page);
                        set_btree_ioerr(page);
                }

                end_page_writeback(page);

                if (!done)
                        continue;

                end_extent_buffer_writeback(eb);
        }

        bio_put(bio);
}

static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
                        struct btrfs_fs_info *fs_info,
                        struct writeback_control *wbc,
                        struct extent_page_data *epd)
{
        struct block_device *bdev = fs_info->fs_devices->latest_bdev;
        struct extent_io_tree *tree = &BTRFS_I(fs_info->btree_inode)->io_tree;
        u64 offset = eb->start;
        unsigned long i, num_pages;
        unsigned long bio_flags = 0;
        int rw = (epd->sync_io ? WRITE_SYNC : WRITE) | REQ_META;
        int ret = 0;

        clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
        num_pages = num_extent_pages(eb->start, eb->len);
        atomic_set(&eb->io_pages, num_pages);
        if (btrfs_header_owner(eb) == BTRFS_TREE_LOG_OBJECTID)
                bio_flags = EXTENT_BIO_TREE_LOG;

        for (i = 0; i < num_pages; i++) {
                struct page *p = eb->pages[i];

                clear_page_dirty_for_io(p);
                set_page_writeback(p);
                ret = submit_extent_page(rw, tree, wbc, p, offset >> 9,
                                         PAGE_CACHE_SIZE, 0, bdev, &epd->bio,
                                         -1, end_bio_extent_buffer_writepage,
                                         0, epd->bio_flags, bio_flags, false);
                epd->bio_flags = bio_flags;
                if (ret) {
                        set_btree_ioerr(p);
                        end_page_writeback(p);
                        if (atomic_sub_and_test(num_pages - i, &eb->io_pages))
                                end_extent_buffer_writeback(eb);
                        ret = -EIO;
                        break;
                }
                offset += PAGE_CACHE_SIZE;
                update_nr_written(p, wbc, 1);
                unlock_page(p);
        }

        if (unlikely(ret)) {
                for (; i < num_pages; i++) {
                        struct page *p = eb->pages[i];
                        clear_page_dirty_for_io(p);
                        unlock_page(p);
                }
        }

        return ret;
}

int btree_write_cache_pages(struct address_space *mapping,
                                   struct writeback_control *wbc)
{
        struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
        struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
        struct extent_buffer *eb, *prev_eb = NULL;
        struct extent_page_data epd = {
                .bio = NULL,
                .tree = tree,
                .extent_locked = 0,
                .sync_io = wbc->sync_mode == WB_SYNC_ALL,
                .bio_flags = 0,
        };
        int ret = 0;
        int done = 0;
        int nr_to_write_done = 0;
        struct pagevec pvec;
        int nr_pages;
        pgoff_t index;
        pgoff_t end;            /* Inclusive */
        int scanned = 0;
        int tag;

        pagevec_init(&pvec, 0);
        if (wbc->range_cyclic) {
                index = mapping->writeback_index; /* Start from prev offset */
                end = -1;
        } else {
                index = wbc->range_start >> PAGE_CACHE_SHIFT;
                end = wbc->range_end >> PAGE_CACHE_SHIFT;
                scanned = 1;
        }
        if (wbc->sync_mode == WB_SYNC_ALL)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;
retry:
        if (wbc->sync_mode == WB_SYNC_ALL)
                tag_pages_for_writeback(mapping, index, end);
        while (!done && !nr_to_write_done && (index <= end) &&
               (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
                        min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
                unsigned i;

                scanned = 1;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        if (!PagePrivate(page))
                                continue;

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

                        spin_lock(&mapping->private_lock);
                        if (!PagePrivate(page)) {
                                spin_unlock(&mapping->private_lock);
                                continue;
                        }

                        eb = (struct extent_buffer *)page->private;

                        /*
                         * Shouldn't happen and normally this would be a BUG_ON
                         * but no sense in crashing the users box for something
                         * we can survive anyway.
                         */
                        if (WARN_ON(!eb)) {
                                spin_unlock(&mapping->private_lock);
                                continue;
                        }

                        if (eb == prev_eb) {
                                spin_unlock(&mapping->private_lock);
                                continue;
                        }

                        ret = atomic_inc_not_zero(&eb->refs);
                        spin_unlock(&mapping->private_lock);
                        if (!ret)
                                continue;

                        prev_eb = eb;
                        ret = lock_extent_buffer_for_io(eb, fs_info, &epd);
                        if (!ret) {
                                free_extent_buffer(eb);
                                continue;
                        }

                        ret = write_one_eb(eb, fs_info, wbc, &epd);
                        if (ret) {
                                done = 1;
                                free_extent_buffer(eb);
                                break;
                        }
                        free_extent_buffer(eb);

                        /*
                         * the filesystem may choose to bump up nr_to_write.
                         * We have to make sure to honor the new nr_to_write
                         * at any time
                         */
                        nr_to_write_done = wbc->nr_to_write <= 0;
                }
                pagevec_release(&pvec);
                cond_resched();
        }
        if (!scanned && !done) {
                /*
                 * We hit the last page and there is more work to be done: wrap
                 * back to the start of the file
                 */
                scanned = 1;
                index = 0;
                goto retry;
        }
        flush_write_bio(&epd);
        return ret;
}

/**
 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 * @writepage: function called for each page
 * @data: data passed to writepage function
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 */
static int extent_write_cache_pages(struct extent_io_tree *tree,
                             struct address_space *mapping,
                             struct writeback_control *wbc,
                             writepage_t writepage, void *data,
                             void (*flush_fn)(void *))
{
        struct inode *inode = mapping->host;
        int ret = 0;
        int done = 0;
        int err = 0;
        int nr_to_write_done = 0;
        struct pagevec pvec;
        int nr_pages;
        pgoff_t index;
        pgoff_t end;            /* Inclusive */
        int scanned = 0;
        int tag;

        /*
         * We have to hold onto the inode so that ordered extents can do their
         * work when the IO finishes.  The alternative to this is failing to add
         * an ordered extent if the igrab() fails there and that is a huge pain
         * to deal with, so instead just hold onto the inode throughout the
         * writepages operation.  If it fails here we are freeing up the inode
         * anyway and we'd rather not waste our time writing out stuff that is
         * going to be truncated anyway.
         */
        if (!igrab(inode))
                return 0;

        pagevec_init(&pvec, 0);
        if (wbc->range_cyclic) {
                index = mapping->writeback_index; /* Start from prev offset */
                end = -1;
        } else {
                index = wbc->range_start >> PAGE_CACHE_SHIFT;
                end = wbc->range_end >> PAGE_CACHE_SHIFT;
                scanned = 1;
        }
        if (wbc->sync_mode == WB_SYNC_ALL)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;
retry:
        if (wbc->sync_mode == WB_SYNC_ALL)
                tag_pages_for_writeback(mapping, index, end);
        while (!done && !nr_to_write_done && (index <= end) &&
               (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
                        min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
                unsigned i;

                scanned = 1;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        /*
                         * At this point we hold neither mapping->tree_lock nor
                         * lock on the page itself: the page may be truncated or
                         * invalidated (changing page->mapping to NULL), or even
                         * swizzled back from swapper_space to tmpfs file
                         * mapping
                         */
                        if (!trylock_page(page)) {
                                flush_fn(data);
                                lock_page(page);
                        }

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

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

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

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

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

                        if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
                                unlock_page(page);
                                ret = 0;
                        }
                        if (!err && ret < 0)
                                err = ret;

                        /*
                         * the filesystem may choose to bump up nr_to_write.
                         * We have to make sure to honor the new nr_to_write
                         * at any time
                         */
                        nr_to_write_done = wbc->nr_to_write <= 0;
                }
                pagevec_release(&pvec);
                cond_resched();
        }
        if (!scanned && !done && !err) {
                /*
                 * 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;
        }
        btrfs_add_delayed_iput(inode);
        return err;
}

static void flush_epd_write_bio(struct extent_page_data *epd)
{
        if (epd->bio) {
                int rw = WRITE;
                int ret;

                if (epd->sync_io)
                        rw = WRITE_SYNC;

                ret = submit_one_bio(rw, epd->bio, 0, epd->bio_flags);
                BUG_ON(ret < 0); /* -ENOMEM */
                epd->bio = NULL;
        }
}

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

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

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

        flush_epd_write_bio(&epd);
        return ret;
}

int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode,
                              u64 start, u64 end, get_extent_t *get_extent,
                              int mode)
{
        int ret = 0;
        struct address_space *mapping = inode->i_mapping;
        struct page *page;
        unsigned long nr_pages = (end - start + PAGE_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,
                .bio_flags = 0,
        };
        struct writeback_control wbc_writepages = {
                .sync_mode      = mode,
                .nr_to_write    = nr_pages * 2,
                .range_start    = start,
                .range_end      = end + 1,
        };

        while (start <= end) {
                page = find_get_page(mapping, start >> PAGE_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,
                .bio_flags = 0,
        };

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

int extent_readpages(struct extent_io_tree *tree,
                     struct address_space *mapping,
                     struct list_head *pages, unsigned nr_pages,
                     get_extent_t get_extent)
{
        struct bio *bio = NULL;
        unsigned page_idx;
        unsigned long bio_flags = 0;
        struct page *pagepool[16];
        struct page *page;
        struct extent_map *em_cached = NULL;
        int nr = 0;
        u64 prev_em_start = (u64)-1;

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

                prefetchw(&page->flags);
                list_del(&page->lru);
                if (add_to_page_cache_lru(page, mapping,
                                        page->index, GFP_NOFS)) {
                        page_cache_release(page);
                        continue;
                }

                pagepool[nr++] = page;
                if (nr < ARRAY_SIZE(pagepool))
                        continue;
                __extent_readpages(tree, pagepool, nr, get_extent, &em_cached,
                                   &bio, 0, &bio_flags, READ, &prev_em_start);
                nr = 0;
        }
        if (nr)
                __extent_readpages(tree, pagepool, nr, get_extent, &em_cached,
                                   &bio, 0, &bio_flags, READ, &prev_em_start);

        if (em_cached)
                free_extent_map(em_cached);

        BUG_ON(!list_empty(pages));
        if (bio)
                return 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)
{
        struct extent_state *cached_state = NULL;
        u64 start = page_offset(page);
        u64 end = start + PAGE_CACHE_SIZE - 1;
        size_t blocksize = page->mapping->host->i_sb->s_blocksize;

        start += ALIGN(offset, blocksize);
        if (start > end)
                return 0;

        lock_extent_bits(tree, start, end, &cached_state);
        wait_on_page_writeback(page);
        clear_extent_bit(tree, start, end,
                         EXTENT_LOCKED | EXTENT_DIRTY | EXTENT_DELALLOC |
                         EXTENT_DO_ACCOUNTING,
                         1, 1, &cached_state, GFP_NOFS);
        return 0;
}

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

        if (test_range_bit(tree, start, end,
                           EXTENT_IOBITS, 0, NULL))
                ret = 0;
        else {
                if ((mask & GFP_NOFS) == GFP_NOFS)
                        mask = GFP_NOFS;
                /*
                 * at this point we can safely clear everything except the
                 * locked bit and the nodatasum bit
                 */
                ret = clear_extent_bit(tree, start, end,
                                 ~(EXTENT_LOCKED | EXTENT_NODATASUM),
                                 0, 0, NULL, mask);

                /* if clear_extent_bit failed for enomem reasons,
                 * we can't allow the release to continue.
                 */
                if (ret < 0)
                        ret = 0;
                else
                        ret = 1;
        }
        return ret;
}

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

        if (gfpflags_allow_blocking(mask) &&
            page->mapping->host->i_size > SZ_16M) {
                u64 len;
                while (start <= end) {
                        len = end - start + 1;
                        write_lock(&map->lock);
                        em = lookup_extent_mapping(map, start, len);
                        if (!em) {
                                write_unlock(&map->lock);
                                break;
                        }
                        if (test_bit(EXTENT_FLAG_PINNED, &em->flags) ||
                            em->start != start) {
                                write_unlock(&map->lock);
                                free_extent_map(em);
                                break;
                        }
                        if (!test_range_bit(tree, em->start,
                                            extent_map_end(em) - 1,
                                            EXTENT_LOCKED | EXTENT_WRITEBACK,
                                            0, NULL)) {
                                remove_extent_mapping(map, em);
                                /* once for the rb tree */
                                free_extent_map(em);
                        }
                        start = extent_map_end(em);
                        write_unlock(&map->lock);

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

/*
 * helper function for fiemap, which doesn't want to see any holes.
 * This maps until we find something past 'last'
 */
static struct extent_map *get_extent_skip_holes(struct inode *inode,
                                                u64 offset,
                                                u64 last,
                                                get_extent_t *get_extent)
{
        u64 sectorsize = BTRFS_I(inode)->root->sectorsize;
        struct extent_map *em;
        u64 len;

        if (offset >= last)
                return NULL;

        while (1) {
                len = last - offset;
                if (len == 0)
                        break;
                len = ALIGN(len, sectorsize);
                em = get_extent(inode, NULL, 0, offset, len, 0);
                if (IS_ERR_OR_NULL(em))
                        return em;

                /* if this isn't a hole return it */
                if (!test_bit(EXTENT_FLAG_VACANCY, &em->flags) &&
                    em->block_start != EXTENT_MAP_HOLE) {
                        return em;
                }

                /* this is a hole, advance to the next extent */
                offset = extent_map_end(em);
                free_extent_map(em);
                if (offset >= last)
                        break;
        }
        return NULL;
}

int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                __u64 start, __u64 len, get_extent_t *get_extent)
{
        int ret = 0;
        u64 off = start;
        u64 max = start + len;
        u32 flags = 0;
        u32 found_type;
        u64 last;
        u64 last_for_get_extent = 0;
        u64 disko = 0;
        u64 isize = i_size_read(inode);
        struct btrfs_key found_key;
        struct extent_map *em = NULL;
        struct extent_state *cached_state = NULL;
        struct btrfs_path *path;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        int end = 0;
        u64 em_start = 0;
        u64 em_len = 0;
        u64 em_end = 0;

        if (len == 0)
                return -EINVAL;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        path->leave_spinning = 1;

        start = round_down(start, BTRFS_I(inode)->root->sectorsize);
        len = round_up(max, BTRFS_I(inode)->root->sectorsize) - start;

        /*
         * lookup the last file extent.  We're not using i_size here
         * because there might be preallocation past i_size
         */
        ret = btrfs_lookup_file_extent(NULL, root, path, btrfs_ino(inode), -1,
                                       0);
        if (ret < 0) {
                btrfs_free_path(path);
                return ret;
        }
        WARN_ON(!ret);
        path->slots[0]--;
        btrfs_item_key_to_cpu(path->nodes[0], &found_key, path->slots[0]);
        found_type = found_key.type;

        /* No extents, but there might be delalloc bits */
        if (found_key.objectid != btrfs_ino(inode) ||
            found_type != BTRFS_EXTENT_DATA_KEY) {
                /* have to trust i_size as the end */
                last = (u64)-1;
                last_for_get_extent = isize;
        } else {
                /*
                 * remember the start of the last extent.  There are a
                 * bunch of different factors that go into the length of the
                 * extent, so its much less complex to remember where it started
                 */
                last = found_key.offset;
                last_for_get_extent = last + 1;
        }
        btrfs_release_path(path);

        /*
         * we might have some extents allocated but more delalloc past those
         * extents.  so, we trust isize unless the start of the last extent is
         * beyond isize
         */
        if (last < isize) {
                last = (u64)-1;
                last_for_get_extent = isize;
        }

        lock_extent_bits(&BTRFS_I(inode)->io_tree, start, start + len - 1,
                         &cached_state);

        em = get_extent_skip_holes(inode, start, last_for_get_extent,
                                   get_extent);
        if (!em)
                goto out;
        if (IS_ERR(em)) {
                ret = PTR_ERR(em);
                goto out;
        }

        while (!end) {
                u64 offset_in_extent = 0;

                /* break if the extent we found is outside the range */
                if (em->start >= max || extent_map_end(em) < off)
                        break;

                /*
                 * get_extent may return an extent that starts before our
                 * requested range.  We have to make sure the ranges
                 * we return to fiemap always move forward and don't
                 * overlap, so adjust the offsets here
                 */
                em_start = max(em->start, off);

                /*
                 * record the offset from the start of the extent
                 * for adjusting the disk offset below.  Only do this if the
                 * extent isn't compressed since our in ram offset may be past
                 * what we have actually allocated on disk.
                 */
                if (!test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
                        offset_in_extent = em_start - em->start;
                em_end = extent_map_end(em);
                em_len = em_end - em_start;
                disko = 0;
                flags = 0;

                /*
                 * bump off for our next call to get_extent
                 */
                off = extent_map_end(em);
                if (off >= max)
                        end = 1;

                if (em->block_start == EXTENT_MAP_LAST_BYTE) {
                        end = 1;
                        flags |= FIEMAP_EXTENT_LAST;
                } else if (em->block_start == EXTENT_MAP_INLINE) {
                        flags |= (FIEMAP_EXTENT_DATA_INLINE |
                                  FIEMAP_EXTENT_NOT_ALIGNED);
                } else if (em->block_start == EXTENT_MAP_DELALLOC) {
                        flags |= (FIEMAP_EXTENT_DELALLOC |
                                  FIEMAP_EXTENT_UNKNOWN);
                } else if (fieinfo->fi_extents_max) {
                        u64 bytenr = em->block_start -
                                (em->start - em->orig_start);

                        disko = em->block_start + offset_in_extent;

                        /*
                         * As btrfs supports shared space, this information
                         * can be exported to userspace tools via
                         * flag FIEMAP_EXTENT_SHARED.  If fi_extents_max == 0
                         * then we're just getting a count and we can skip the
                         * lookup stuff.
                         */
                        ret = btrfs_check_shared(NULL, root->fs_info,
                                                 root->objectid,
                                                 btrfs_ino(inode), bytenr);
                        if (ret < 0)
                                goto out_free;
                        if (ret)
                                flags |= FIEMAP_EXTENT_SHARED;
                        ret = 0;
                }
                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
                        flags |= FIEMAP_EXTENT_ENCODED;
                if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
                        flags |= FIEMAP_EXTENT_UNWRITTEN;

                free_extent_map(em);
                em = NULL;
                if ((em_start >= last) || em_len == (u64)-1 ||
                   (last == (u64)-1 && isize <= em_end)) {
                        flags |= FIEMAP_EXTENT_LAST;
                        end = 1;
                }

                /* now scan forward to see if this is really the last extent. */
                em = get_extent_skip_holes(inode, off, last_for_get_extent,
                                           get_extent);
                if (IS_ERR(em)) {
                        ret = PTR_ERR(em);
                        goto out;
                }
                if (!em) {
                        flags |= FIEMAP_EXTENT_LAST;
                        end = 1;
                }
                ret = fiemap_fill_next_extent(fieinfo, em_start, disko,
                                              em_len, flags);
                if (ret) {
                        if (ret == 1)
                                ret = 0;
                        goto out_free;
                }
        }
out_free:
        free_extent_map(em);
out:
        btrfs_free_path(path);
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, start + len - 1,
                             &cached_state, GFP_NOFS);
        return ret;
}

static void __free_extent_buffer(struct extent_buffer *eb)
{
        btrfs_leak_debug_del(&eb->leak_list);
        kmem_cache_free(extent_buffer_cache, eb);
}

int extent_buffer_under_io(struct extent_buffer *eb)
{
        return (atomic_read(&eb->io_pages) ||
                test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
                test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
}

/*
 * Helper for releasing extent buffer page.
 */
static void btrfs_release_extent_buffer_page(struct extent_buffer *eb)
{
        unsigned long index;
        struct page *page;
        int mapped = !test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);

        BUG_ON(extent_buffer_under_io(eb));

        index = num_extent_pages(eb->start, eb->len);
        if (index == 0)
                return;

        do {
                index--;
                page = eb->pages[index];
                if (!page)
                        continue;
                if (mapped)
                        spin_lock(&page->mapping->private_lock);
                /*
                 * We do this since we'll remove the pages after we've
                 * removed the eb from the radix tree, so we could race
                 * and have this page now attached to the new eb.  So
                 * only clear page_private if it's still connected to
                 * this eb.
                 */
                if (PagePrivate(page) &&
                    page->private == (unsigned long)eb) {
                        BUG_ON(test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
                        BUG_ON(PageDirty(page));
                        BUG_ON(PageWriteback(page));
                        /*
                         * We need to make sure we haven't be attached
                         * to a new eb.
                         */
                        ClearPagePrivate(page);
                        set_page_private(page, 0);
                        /* One for the page private */
                        page_cache_release(page);
                }

                if (mapped)
                        spin_unlock(&page->mapping->private_lock);

                /* One for when we alloced the page */
                page_cache_release(page);
        } while (index != 0);
}

/*
 * Helper for releasing the extent buffer.
 */
static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
{
        btrfs_release_extent_buffer_page(eb);
        __free_extent_buffer(eb);
}

static struct extent_buffer *
__alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
                      unsigned long len)
{
        struct extent_buffer *eb = NULL;

        eb = kmem_cache_zalloc(extent_buffer_cache, GFP_NOFS|__GFP_NOFAIL);
        eb->start = start;
        eb->len = len;
        eb->fs_info = fs_info;
        eb->bflags = 0;
        rwlock_init(&eb->lock);
        atomic_set(&eb->write_locks, 0);
        atomic_set(&eb->read_locks, 0);
        atomic_set(&eb->blocking_readers, 0);
        atomic_set(&eb->blocking_writers, 0);
        atomic_set(&eb->spinning_readers, 0);
        atomic_set(&eb->spinning_writers, 0);
        eb->lock_nested = 0;
        init_waitqueue_head(&eb->write_lock_wq);
        init_waitqueue_head(&eb->read_lock_wq);

        btrfs_leak_debug_add(&eb->leak_list, &buffers);

        spin_lock_init(&eb->refs_lock);
        atomic_set(&eb->refs, 1);
        atomic_set(&eb->io_pages, 0);

        /*
         * Sanity checks, currently the maximum is 64k covered by 16x 4k pages
         */
        BUILD_BUG_ON(BTRFS_MAX_METADATA_BLOCKSIZE
                > MAX_INLINE_EXTENT_BUFFER_SIZE);
        BUG_ON(len > MAX_INLINE_EXTENT_BUFFER_SIZE);

        return eb;
}

struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src)
{
        unsigned long i;
        struct page *p;
        struct extent_buffer *new;
        unsigned long num_pages = num_extent_pages(src->start, src->len);

        new = __alloc_extent_buffer(src->fs_info, src->start, src->len);
        if (new == NULL)
                return NULL;

        for (i = 0; i < num_pages; i++) {
                p = alloc_page(GFP_NOFS);
                if (!p) {
                        btrfs_release_extent_buffer(new);
                        return NULL;
                }
                attach_extent_buffer_page(new, p);
                WARN_ON(PageDirty(p));
                SetPageUptodate(p);
                new->pages[i] = p;
        }

        copy_extent_buffer(new, src, 0, 0, src->len);
        set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags);
        set_bit(EXTENT_BUFFER_DUMMY, &new->bflags);

        return new;
}

struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
                                                  u64 start, unsigned long len)
{
        struct extent_buffer *eb;
        unsigned long num_pages;
        unsigned long i;

        num_pages = num_extent_pages(start, len);

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

        for (i = 0; i < num_pages; i++) {
                eb->pages[i] = alloc_page(GFP_NOFS);
                if (!eb->pages[i])
                        goto err;
        }
        set_extent_buffer_uptodate(eb);
        btrfs_set_header_nritems(eb, 0);
        set_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);

        return eb;
err:
        for (; i > 0; i--)
                __free_page(eb->pages[i - 1]);
        __free_extent_buffer(eb);
        return NULL;
}

struct extent_buffer *alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
                                                u64 start)
{
        unsigned long len;

        if (!fs_info) {
                /*
                 * Called only from tests that don't always have a fs_info
                 * available, but we know that nodesize is 4096
                 */
                len = 4096;
        } else {
                len = fs_info->tree_root->nodesize;
        }

        return __alloc_dummy_extent_buffer(fs_info, start, len);
}

static void check_buffer_tree_ref(struct extent_buffer *eb)
{
        int refs;
        /* the ref bit is tricky.  We have to make sure it is set
         * if we have the buffer dirty.   Otherwise the
         * code to free a buffer can end up dropping a dirty
         * page
         *
         * Once the ref bit is set, it won't go away while the
         * buffer is dirty or in writeback, and it also won't
         * go away while we have the reference count on the
         * eb bumped.
         *
         * We can't just set the ref bit without bumping the
         * ref on the eb because free_extent_buffer might
         * see the ref bit and try to clear it.  If this happens
         * free_extent_buffer might end up dropping our original
         * ref by mistake and freeing the page before we are able
         * to add one more ref.
         *
         * So bump the ref count first, then set the bit.  If someone
         * beat us to it, drop the ref we added.
         */
        refs = atomic_read(&eb->refs);
        if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                return;

        spin_lock(&eb->refs_lock);
        if (!test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                atomic_inc(&eb->refs);
        spin_unlock(&eb->refs_lock);
}

static void mark_extent_buffer_accessed(struct extent_buffer *eb,
                struct page *accessed)
{
        unsigned long num_pages, i;

        check_buffer_tree_ref(eb);

        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++) {
                struct page *p = eb->pages[i];

                if (p != accessed)
                        mark_page_accessed(p);
        }
}

struct extent_buffer *find_extent_buffer(struct btrfs_fs_info *fs_info,
                                         u64 start)
{
        struct extent_buffer *eb;

        rcu_read_lock();
        eb = radix_tree_lookup(&fs_info->buffer_radix,
                               start >> PAGE_CACHE_SHIFT);
        if (eb && atomic_inc_not_zero(&eb->refs)) {
                rcu_read_unlock();
                /*
                 * Lock our eb's refs_lock to avoid races with
                 * free_extent_buffer. When we get our eb it might be flagged
                 * with EXTENT_BUFFER_STALE and another task running
                 * free_extent_buffer might have seen that flag set,
                 * eb->refs == 2, that the buffer isn't under IO (dirty and
                 * writeback flags not set) and it's still in the tree (flag
                 * EXTENT_BUFFER_TREE_REF set), therefore being in the process
                 * of decrementing the extent buffer's reference count twice.
                 * So here we could race and increment the eb's reference count,
                 * clear its stale flag, mark it as dirty and drop our reference
                 * before the other task finishes executing free_extent_buffer,
                 * which would later result in an attempt to free an extent
                 * buffer that is dirty.
                 */
                if (test_bit(EXTENT_BUFFER_STALE, &eb->bflags)) {
                        spin_lock(&eb->refs_lock);
                        spin_unlock(&eb->refs_lock);
                }
                mark_extent_buffer_accessed(eb, NULL);
                return eb;
        }
        rcu_read_unlock();

        return NULL;
}

#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
                                               u64 start)
{
        struct extent_buffer *eb, *exists = NULL;
        int ret;

        eb = find_extent_buffer(fs_info, start);
        if (eb)
                return eb;
        eb = alloc_dummy_extent_buffer(fs_info, start);
        if (!eb)
                return NULL;
        eb->fs_info = fs_info;
again:
        ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
        if (ret)
                goto free_eb;
        spin_lock(&fs_info->buffer_lock);
        ret = radix_tree_insert(&fs_info->buffer_radix,
                                start >> PAGE_CACHE_SHIFT, eb);
        spin_unlock(&fs_info->buffer_lock);
        radix_tree_preload_end();
        if (ret == -EEXIST) {
                exists = find_extent_buffer(fs_info, start);
                if (exists)
                        goto free_eb;
                else
                        goto again;
        }
        check_buffer_tree_ref(eb);
        set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);

        /*
         * We will free dummy extent buffer's if they come into
         * free_extent_buffer with a ref count of 2, but if we are using this we
         * want the buffers to stay in memory until we're done with them, so
         * bump the ref count again.
         */
        atomic_inc(&eb->refs);
        return eb;
free_eb:
        btrfs_release_extent_buffer(eb);
        return exists;
}
#endif

struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
                                          u64 start)
{
        unsigned long len = fs_info->tree_root->nodesize;
        unsigned long num_pages = num_extent_pages(start, len);
        unsigned long i;
        unsigned long index = start >> PAGE_CACHE_SHIFT;
        struct extent_buffer *eb;
        struct extent_buffer *exists = NULL;
        struct page *p;
        struct address_space *mapping = fs_info->btree_inode->i_mapping;
        int uptodate = 1;
        int ret;

        eb = find_extent_buffer(fs_info, start);
        if (eb)
                return eb;

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

        for (i = 0; i < num_pages; i++, index++) {
                p = find_or_create_page(mapping, index, GFP_NOFS|__GFP_NOFAIL);
                if (!p)
                        goto free_eb;

                spin_lock(&mapping->private_lock);
                if (PagePrivate(p)) {
                        /*
                         * We could have already allocated an eb for this page
                         * and attached one so lets see if we can get a ref on
                         * the existing eb, and if we can we know it's good and
                         * we can just return that one, else we know we can just
                         * overwrite page->private.
                         */
                        exists = (struct extent_buffer *)p->private;
                        if (atomic_inc_not_zero(&exists->refs)) {
                                spin_unlock(&mapping->private_lock);
                                unlock_page(p);
                                page_cache_release(p);
                                mark_extent_buffer_accessed(exists, p);
                                goto free_eb;
                        }
                        exists = NULL;

                        /*
                         * Do this so attach doesn't complain and we need to
                         * drop the ref the old guy had.
                         */
                        ClearPagePrivate(p);
                        WARN_ON(PageDirty(p));
                        page_cache_release(p);
                }
                attach_extent_buffer_page(eb, p);
                spin_unlock(&mapping->private_lock);
                WARN_ON(PageDirty(p));
                eb->pages[i] = p;
                if (!PageUptodate(p))
                        uptodate = 0;

                /*
                 * see below about how we avoid a nasty race with release page
                 * and why we unlock later
                 */
        }
        if (uptodate)
                set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
again:
        ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
        if (ret)
                goto free_eb;

        spin_lock(&fs_info->buffer_lock);
        ret = radix_tree_insert(&fs_info->buffer_radix,
                                start >> PAGE_CACHE_SHIFT, eb);
        spin_unlock(&fs_info->buffer_lock);
        radix_tree_preload_end();
        if (ret == -EEXIST) {
                exists = find_extent_buffer(fs_info, start);
                if (exists)
                        goto free_eb;
                else
                        goto again;
        }
        /* add one reference for the tree */
        check_buffer_tree_ref(eb);
        set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);

        /*
         * there is a race where release page may have
         * tried to find this extent buffer in the radix
         * but failed.  It will tell the VM it is safe to
         * reclaim the, and it will clear the page private bit.
         * We must make sure to set the page private bit properly
         * after the extent buffer is in the radix tree so
         * it doesn't get lost
         */
        SetPageChecked(eb->pages[0]);
        for (i = 1; i < num_pages; i++) {
                p = eb->pages[i];
                ClearPageChecked(p);
                unlock_page(p);
        }
        unlock_page(eb->pages[0]);
        return eb;

free_eb:
        WARN_ON(!atomic_dec_and_test(&eb->refs));
        for (i = 0; i < num_pages; i++) {
                if (eb->pages[i])
                        unlock_page(eb->pages[i]);
        }

        btrfs_release_extent_buffer(eb);
        return exists;
}

static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
{
        struct extent_buffer *eb =
                        container_of(head, struct extent_buffer, rcu_head);

        __free_extent_buffer(eb);
}

/* Expects to have eb->eb_lock already held */
static int release_extent_buffer(struct extent_buffer *eb)
{
        WARN_ON(atomic_read(&eb->refs) == 0);
        if (atomic_dec_and_test(&eb->refs)) {
                if (test_and_clear_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags)) {
                        struct btrfs_fs_info *fs_info = eb->fs_info;

                        spin_unlock(&eb->refs_lock);

                        spin_lock(&fs_info->buffer_lock);
                        radix_tree_delete(&fs_info->buffer_radix,
                                          eb->start >> PAGE_CACHE_SHIFT);
                        spin_unlock(&fs_info->buffer_lock);
                } else {
                        spin_unlock(&eb->refs_lock);
                }

                /* Should be safe to release our pages at this point */
                btrfs_release_extent_buffer_page(eb);
#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
                if (unlikely(test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags))) {
                        __free_extent_buffer(eb);
                        return 1;
                }
#endif
                call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
                return 1;
        }
        spin_unlock(&eb->refs_lock);

        return 0;
}

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

        while (1) {
                refs = atomic_read(&eb->refs);
                if (refs <= 3)
                        break;
                old = atomic_cmpxchg(&eb->refs, refs, refs - 1);
                if (old == refs)
                        return;
        }

        spin_lock(&eb->refs_lock);
        if (atomic_read(&eb->refs) == 2 &&
            test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags))
                atomic_dec(&eb->refs);

        if (atomic_read(&eb->refs) == 2 &&
            test_bit(EXTENT_BUFFER_STALE, &eb->bflags) &&
            !extent_buffer_under_io(eb) &&
            test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                atomic_dec(&eb->refs);

        /*
         * I know this is terrible, but it's temporary until we stop tracking
         * the uptodate bits and such for the extent buffers.
         */
        release_extent_buffer(eb);
}

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

        spin_lock(&eb->refs_lock);
        set_bit(EXTENT_BUFFER_STALE, &eb->bflags);

        if (atomic_read(&eb->refs) == 2 && !extent_buffer_under_io(eb) &&
            test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                atomic_dec(&eb->refs);
        release_extent_buffer(eb);
}

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

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

        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];
                if (!PageDirty(page))
                        continue;

                lock_page(page);
                WARN_ON(!PagePrivate(page));

                clear_page_dirty_for_io(page);
                spin_lock_irq(&page->mapping->tree_lock);
                if (!PageDirty(page)) {
                        radix_tree_tag_clear(&page->mapping->page_tree,
                                                page_index(page),
                                                PAGECACHE_TAG_DIRTY);
                }
                spin_unlock_irq(&page->mapping->tree_lock);
                ClearPageError(page);
                unlock_page(page);
        }
        WARN_ON(atomic_read(&eb->refs) == 0);
}

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

        check_buffer_tree_ref(eb);

        was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);

        num_pages = num_extent_pages(eb->start, eb->len);
        WARN_ON(atomic_read(&eb->refs) == 0);
        WARN_ON(!test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags));

        for (i = 0; i < num_pages; i++)
                set_page_dirty(eb->pages[i]);
        return was_dirty;
}

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

        clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];
                if (page)
                        ClearPageUptodate(page);
        }
}

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

        set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];
                SetPageUptodate(page);
        }
}

int extent_buffer_uptodate(struct extent_buffer *eb)
{
        return test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
}

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

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

        if (start) {
                WARN_ON(start < eb->start);
                start_i = (start >> PAGE_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 = eb->pages[i];
                if (wait == WAIT_NONE) {
                        if (!trylock_page(page))
                                goto unlock_exit;
                } else {
                        lock_page(page);
                }
                locked_pages++;
                if (!PageUptodate(page)) {
                        num_reads++;
                        all_uptodate = 0;
                }
        }
        if (all_uptodate) {
                if (start_i == 0)
                        set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
                goto unlock_exit;
        }

        clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
        eb->read_mirror = 0;
        atomic_set(&eb->io_pages, num_reads);
        for (i = start_i; i < num_pages; i++) {
                page = eb->pages[i];
                if (!PageUptodate(page)) {
                        ClearPageError(page);
                        err = __extent_read_full_page(tree, page,
                                                      get_extent, &bio,
                                                      mirror_num, &bio_flags,
                                                      READ | REQ_META);
                        if (err)
                                ret = err;
                } else {
                        unlock_page(page);
                }
        }

        if (bio) {
                err = submit_one_bio(READ | REQ_META, bio, mirror_num,
                                     bio_flags);
                if (err)
                        return err;
        }

        if (ret || wait != WAIT_COMPLETE)
                return ret;

        for (i = start_i; i < num_pages; i++) {
                page = eb->pages[i];
                wait_on_page_locked(page);
                if (!PageUptodate(page))
                        ret = -EIO;
        }

        return ret;

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

void read_extent_buffer(struct extent_buffer *eb, void *dstv,
                        unsigned long start,
                        unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char *dst = (char *)dstv;
        size_t start_offset = eb->start & ((u64)PAGE_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) & (PAGE_CACHE_SIZE - 1);

        while (len > 0) {
                page = eb->pages[i];

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

                dst += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

int read_extent_buffer_to_user(struct extent_buffer *eb, void __user *dstv,
                        unsigned long start,
                        unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char __user *dst = (char __user *)dstv;
        size_t start_offset = eb->start & ((u64)PAGE_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) & (PAGE_CACHE_SIZE - 1);

        while (len > 0) {
                page = eb->pages[i];

                cur = min(len, (PAGE_CACHE_SIZE - offset));
                kaddr = page_address(page);
                if (copy_to_user(dst, kaddr + offset, cur)) {
                        ret = -EFAULT;
                        break;
                }

                dst += cur;
                len -= cur;
                offset = 0;
                i++;
        }

        return ret;
}

int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
                               unsigned long min_len, char **map,
                               unsigned long *map_start,
                               unsigned long *map_len)
{
        size_t offset = start & (PAGE_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) {
                WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, "
                       "wanted %lu %lu\n",
                       eb->start, eb->len, start, min_len);
                return -EINVAL;
        }

        p = eb->pages[i];
        kaddr = page_address(p);
        *map = kaddr + offset;
        *map_len = PAGE_CACHE_SIZE - offset;
        return 0;
}

int memcmp_extent_buffer(struct extent_buffer *eb, const void *ptrv,
                          unsigned long start,
                          unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char *ptr = (char *)ptrv;
        size_t start_offset = eb->start & ((u64)PAGE_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) & (PAGE_CACHE_SIZE - 1);

        while (len > 0) {
                page = eb->pages[i];

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

                kaddr = page_address(page);
                ret = memcmp(ptr, kaddr + offset, cur);
                if (ret)
                        break;

                ptr += cur;
                len -= cur;
                offset = 0;
                i++;
        }
        return ret;
}

void write_extent_buffer(struct extent_buffer *eb, const void *srcv,
                         unsigned long start, unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char *src = (char *)srcv;
        size_t start_offset = eb->start & ((u64)PAGE_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) & (PAGE_CACHE_SIZE - 1);

        while (len > 0) {
                page = eb->pages[i];
                WARN_ON(!PageUptodate(page));

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

                src += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

void memset_extent_buffer(struct extent_buffer *eb, char c,
                          unsigned long start, unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        size_t start_offset = eb->start & ((u64)PAGE_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) & (PAGE_CACHE_SIZE - 1);

        while (len > 0) {
                page = eb->pages[i];
                WARN_ON(!PageUptodate(page));

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

                len -= cur;
                offset = 0;
                i++;
        }
}

void copy_extent_buffer(struct extent_buffer *dst, struct extent_buffer *src,
                        unsigned long dst_offset, unsigned long src_offset,
                        unsigned long len)
{
        u64 dst_len = dst->len;
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE - 1);
        unsigned long i = (start_offset + dst_offset) >> PAGE_CACHE_SHIFT;

        WARN_ON(src->len != dst_len);

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

        while (len > 0) {
                page = dst->pages[i];
                WARN_ON(!PageUptodate(page));

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

                kaddr = page_address(page);
                read_extent_buffer(src, kaddr + offset, src_offset, cur);

                src_offset += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

/*
 * The extent buffer bitmap operations are done with byte granularity because
 * bitmap items are not guaranteed to be aligned to a word and therefore a
 * single word in a bitmap may straddle two pages in the extent buffer.
 */
#define BIT_BYTE(nr) ((nr) / BITS_PER_BYTE)
#define BYTE_MASK ((1 << BITS_PER_BYTE) - 1)
#define BITMAP_FIRST_BYTE_MASK(start) \
        ((BYTE_MASK << ((start) & (BITS_PER_BYTE - 1))) & BYTE_MASK)
#define BITMAP_LAST_BYTE_MASK(nbits) \
        (BYTE_MASK >> (-(nbits) & (BITS_PER_BYTE - 1)))

/*
 * eb_bitmap_offset() - calculate the page and offset of the byte containing the
 * given bit number
 * @eb: the extent buffer
 * @start: offset of the bitmap item in the extent buffer
 * @nr: bit number
 * @page_index: return index of the page in the extent buffer that contains the
 * given bit number
 * @page_offset: return offset into the page given by page_index
 *
 * This helper hides the ugliness of finding the byte in an extent buffer which
 * contains a given bit.
 */
static inline void eb_bitmap_offset(struct extent_buffer *eb,
                                    unsigned long start, unsigned long nr,
                                    unsigned long *page_index,
                                    size_t *page_offset)
{
        size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
        size_t byte_offset = BIT_BYTE(nr);
        size_t offset;

        /*
         * The byte we want is the offset of the extent buffer + the offset of
         * the bitmap item in the extent buffer + the offset of the byte in the
         * bitmap item.
         */
        offset = start_offset + start + byte_offset;

        *page_index = offset >> PAGE_CACHE_SHIFT;
        *page_offset = offset & (PAGE_CACHE_SIZE - 1);
}

/**
 * extent_buffer_test_bit - determine whether a bit in a bitmap item is set
 * @eb: the extent buffer
 * @start: offset of the bitmap item in the extent buffer
 * @nr: bit number to test
 */
int extent_buffer_test_bit(struct extent_buffer *eb, unsigned long start,
                           unsigned long nr)
{
        char *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;

        eb_bitmap_offset(eb, start, nr, &i, &offset);
        page = eb->pages[i];
        WARN_ON(!PageUptodate(page));
        kaddr = page_address(page);
        return 1U & (kaddr[offset] >> (nr & (BITS_PER_BYTE - 1)));
}

/**
 * extent_buffer_bitmap_set - set an area of a bitmap
 * @eb: the extent buffer
 * @start: offset of the bitmap item in the extent buffer
 * @pos: bit number of the first bit
 * @len: number of bits to set
 */
void extent_buffer_bitmap_set(struct extent_buffer *eb, unsigned long start,
                              unsigned long pos, unsigned long len)
{
        char *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;
        const unsigned int size = pos + len;
        int bits_to_set = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
        unsigned int mask_to_set = BITMAP_FIRST_BYTE_MASK(pos);

        eb_bitmap_offset(eb, start, pos, &i, &offset);
        page = eb->pages[i];
        WARN_ON(!PageUptodate(page));
        kaddr = page_address(page);

        while (len >= bits_to_set) {
                kaddr[offset] |= mask_to_set;
                len -= bits_to_set;
                bits_to_set = BITS_PER_BYTE;
                mask_to_set = ~0U;
                if (++offset >= PAGE_CACHE_SIZE && len > 0) {
                        offset = 0;
                        page = eb->pages[++i];
                        WARN_ON(!PageUptodate(page));
                        kaddr = page_address(page);
                }
        }
        if (len) {
                mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
                kaddr[offset] |= mask_to_set;
        }
}


/**
 * extent_buffer_bitmap_clear - clear an area of a bitmap
 * @eb: the extent buffer
 * @start: offset of the bitmap item in the extent buffer
 * @pos: bit number of the first bit
 * @len: number of bits to clear
 */
void extent_buffer_bitmap_clear(struct extent_buffer *eb, unsigned long start,
                                unsigned long pos, unsigned long len)
{
        char *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;
        const unsigned int size = pos + len;
        int bits_to_clear = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
        unsigned int mask_to_clear = BITMAP_FIRST_BYTE_MASK(pos);

        eb_bitmap_offset(eb, start, pos, &i, &offset);
        page = eb->pages[i];
        WARN_ON(!PageUptodate(page));
        kaddr = page_address(page);

        while (len >= bits_to_clear) {
                kaddr[offset] &= ~mask_to_clear;
                len -= bits_to_clear;
                bits_to_clear = BITS_PER_BYTE;
                mask_to_clear = ~0U;
                if (++offset >= PAGE_CACHE_SIZE && len > 0) {
                        offset = 0;
                        page = eb->pages[++i];
                        WARN_ON(!PageUptodate(page));
                        kaddr = page_address(page);
                }
        }
        if (len) {
                mask_to_clear &= BITMAP_LAST_BYTE_MASK(size);
                kaddr[offset] &= ~mask_to_clear;
        }
}

static inline bool areas_overlap(unsigned long src, unsigned long dst, unsigned long len)
{
        unsigned long distance = (src > dst) ? src - dst : dst - src;
        return distance < len;
}

static void copy_pages(struct page *dst_page, struct page *src_page,
                       unsigned long dst_off, unsigned long src_off,
                       unsigned long len)
{
        char *dst_kaddr = page_address(dst_page);
        char *src_kaddr;
        int must_memmove = 0;

        if (dst_page != src_page) {
                src_kaddr = page_address(src_page);
        } else {
                src_kaddr = dst_kaddr;
                if (areas_overlap(src_off, dst_off, len))
                        must_memmove = 1;
        }

        if (must_memmove)
                memmove(dst_kaddr + dst_off, src_kaddr + src_off, len);
        else
                memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
}

void memcpy_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
                           unsigned long src_offset, unsigned long len)
{
        size_t cur;
        size_t dst_off_in_page;
        size_t src_off_in_page;
        size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE - 1);
        unsigned long dst_i;
        unsigned long src_i;

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

        while (len > 0) {
                dst_off_in_page = (start_offset + dst_offset) &
                        (PAGE_CACHE_SIZE - 1);
                src_off_in_page = (start_offset + src_offset) &
                        (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(dst->pages[dst_i], dst->pages[src_i],
                           dst_off_in_page, src_off_in_page, cur);

                src_offset += cur;
                dst_offset += cur;
                len -= cur;
        }
}

void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
                           unsigned long src_offset, unsigned long len)
{
        size_t cur;
        size_t dst_off_in_page;
        size_t src_off_in_page;
        unsigned long dst_end = dst_offset + len - 1;
        unsigned long src_end = src_offset + len - 1;
        size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE - 1);
        unsigned long dst_i;
        unsigned long src_i;

        if (src_offset + len > dst->len) {
                btrfs_err(dst->fs_info, "memmove bogus src_offset %lu move "
                       "len %lu len %lu", src_offset, len, dst->len);
                BUG_ON(1);
        }
        if (dst_offset + len > dst->len) {
                btrfs_err(dst->fs_info, "memmove bogus dst_offset %lu move "
                       "len %lu len %lu", dst_offset, len, dst->len);
                BUG_ON(1);
        }
        if (dst_offset < src_offset) {
                memcpy_extent_buffer(dst, dst_offset, src_offset, len);
                return;
        }
        while (len > 0) {
                dst_i = (start_offset + dst_end) >> PAGE_CACHE_SHIFT;
                src_i = (start_offset + src_end) >> PAGE_CACHE_SHIFT;

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

                cur = min_t(unsigned long, len, src_off_in_page + 1);
                cur = min(cur, dst_off_in_page + 1);
                copy_pages(dst->pages[dst_i], dst->pages[src_i],
                           dst_off_in_page - cur + 1,
                           src_off_in_page - cur + 1, cur);

                dst_end -= cur;
                src_end -= cur;
                len -= cur;
        }
}

int try_release_extent_buffer(struct page *page)
{
        struct extent_buffer *eb;

        /*
         * We need to make sure noboody is attaching this page to an eb right
         * now.
         */
        spin_lock(&page->mapping->private_lock);
        if (!PagePrivate(page)) {
                spin_unlock(&page->mapping->private_lock);
                return 1;
        }

        eb = (struct extent_buffer *)page->private;
        BUG_ON(!eb);

        /*
         * This is a little awful but should be ok, we need to make sure that
         * the eb doesn't disappear out from under us while we're looking at
         * this page.
         */
        spin_lock(&eb->refs_lock);
        if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
                spin_unlock(&eb->refs_lock);
                spin_unlock(&page->mapping->private_lock);
                return 0;
        }
        spin_unlock(&page->mapping->private_lock);

        /*
         * If tree ref isn't set then we know the ref on this eb is a real ref,
         * so just return, this page will likely be freed soon anyway.
         */
        if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
                spin_unlock(&eb->refs_lock);
                return 0;
        }

        return release_extent_buffer(eb);
}