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extent_io.c

#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/bio.h>
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/pagemap.h>
#include <linux/page-flags.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/blkdev.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include "extent_io.h"
#include "extent_map.h"
#include "compat.h"
#include "ctree.h"
#include "btrfs_inode.h"

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

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

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

#define BUFFER_LRU_MAX 64

00033 struct tree_entry {
      u64 start;
      u64 end;
      struct rb_node rb_node;
};

00039 struct extent_page_data {
      struct bio *bio;
      struct extent_io_tree *tree;
      get_extent_t *get_extent;

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

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

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

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

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

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

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

      }

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

      if (end < start) {
            printk(KERN_ERR "btrfs end < start %llu %llu\n",
                   (unsigned long long)end,
                   (unsigned long long)start);
            WARN_ON(1);
      }
      if (bits & EXTENT_DIRTY)
            tree->dirty_bytes += end - start + 1;
      set_state_cb(tree, state, bits);
      state->state |= bits;
      state->start = start;
      state->end = end;
      node = tree_insert(&tree->state, end, &state->rb_node);
      if (node) {
            struct extent_state *found;
            found = rb_entry(node, struct extent_state, rb_node);
            printk(KERN_ERR "btrfs found node %llu %llu on insert of "
                   "%llu %llu\n", (unsigned long long)found->start,
                   (unsigned long long)found->end,
                   (unsigned long long)start, (unsigned long long)end);
            free_extent_state(state);
            return -EEXIST;
      }
      state->tree = tree;
      merge_state(tree, state);
      return 0;
}

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

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

/*
 * utility function to clear some bits in an extent state struct.
 * it will optionally wake up any one waiting on this state (wake == 1), or
 * forcibly remove the state from the tree (delete == 1).
 *
 * If no bits are set on the state struct after clearing things, the
 * struct is freed and removed from the tree
 */
static int clear_state_bit(struct extent_io_tree *tree,
                      struct extent_state *state, int bits, int wake,
                      int delete)
{
      int ret = state->state & bits;

      if ((bits & EXTENT_DIRTY) && (state->state & EXTENT_DIRTY)) {
            u64 range = state->end - state->start + 1;
            WARN_ON(range > tree->dirty_bytes);
            tree->dirty_bytes -= range;
      }
      clear_state_cb(tree, state, bits);
      state->state &= ~bits;
      if (wake)
            wake_up(&state->wq);
      if (delete || state->state == 0) {
            if (state->tree) {
                  clear_state_cb(tree, state, state->state);
                  rb_erase(&state->rb_node, &tree->state);
                  state->tree = NULL;
                  free_extent_state(state);
            } else {
                  WARN_ON(1);
            }
      } else {
            merge_state(tree, state);
      }
      return ret;
}

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

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

      spin_lock(&tree->lock);
      /*
       * 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);
      if (state->start > end)
            goto out;
      WARN_ON(state->end < start);
      last_end = state->end;

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

      if (state->start < start) {
            if (!prealloc)
                  prealloc = alloc_extent_state(GFP_ATOMIC);
            err = split_state(tree, state, prealloc, start);
            BUG_ON(err == -EEXIST);
            prealloc = NULL;
            if (err)
                  goto out;
            if (state->end <= end) {
                  set |= clear_state_bit(tree, state, bits,
                              wake, delete);
                  if (last_end == (u64)-1)
                        goto out;
                  start = last_end + 1;
            } else {
                  start = state->start;
            }
            goto search_again;
      }
      /*
       * | ---- desired range ---- |
       *                        | state |
       * We need to split the extent, and clear the bit
       * on the first half
       */
      if (state->start <= end && state->end > end) {
            if (!prealloc)
                  prealloc = alloc_extent_state(GFP_ATOMIC);
            err = split_state(tree, state, prealloc, end + 1);
            BUG_ON(err == -EEXIST);

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

      set |= clear_state_bit(tree, state, bits, wake, delete);
      if (last_end == (u64)-1)
            goto out;
      start = last_end + 1;
      goto search_again;

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

      return set;

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

static int wait_on_state(struct extent_io_tree *tree,
                   struct extent_state *state)
            __releases(tree->lock)
            __acquires(tree->lock)
{
      DEFINE_WAIT(wait);
      prepare_to_wait(&state->wq, &wait, TASK_UNINTERRUPTIBLE);
      spin_unlock(&tree->lock);
      schedule();
      spin_lock(&tree->lock);
      finish_wait(&state->wq, &wait);
      return 0;
}

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

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

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

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

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

            if (start > end)
                  break;

            if (need_resched()) {
                  spin_unlock(&tree->lock);
                  cond_resched();
                  spin_lock(&tree->lock);
            }
      }
out:
      spin_unlock(&tree->lock);
      return 0;
}

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

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

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

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

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

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

            set_state_bits(tree, prealloc, bits);
            merge_state(tree, prealloc);
            prealloc = NULL;
            goto out;
      }

      goto search_again;

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

      return err;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

/*
 * either insert or lock state struct between start and end use mask to tell
 * us if waiting is desired.
 */
int lock_extent(struct extent_io_tree *tree, u64 start, u64 end, gfp_t mask)
{
      int err;
      u64 failed_start;
      while (1) {
            err = set_extent_bit(tree, start, end, EXTENT_LOCKED, 1,
                             &failed_start, mask);
            if (err == -EEXIST && (mask & __GFP_WAIT)) {
                  wait_extent_bit(tree, failed_start, end, EXTENT_LOCKED);
                  start = failed_start;
            } else {
                  break;
            }
            WARN_ON(start > end);
      }
      return err;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

      spin_lock(&tree->lock);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

      if (clear_delalloc)
            clear_bits |= EXTENT_DELALLOC;

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

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

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

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

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

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

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

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

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

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

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

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

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

            if (state->start > end)
                  break;

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

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

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

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

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

/*
 * after a writepage IO is done, we need to:
 * clear the uptodate bits on error
 * clear the writeback bits in the extent tree for this IO
 * end_page_writeback if the page has no more pending IO
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bio_extent_writepage(struct bio *bio, int err)
{
      int uptodate = err == 0;
      struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
      struct extent_io_tree *tree;
      u64 start;
      u64 end;
      int whole_page;
      int ret;

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

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

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

            if (--bvec >= bio->bi_io_vec)
                  prefetchw(&bvec->bv_page->flags);
            if (tree->ops && tree->ops->writepage_end_io_hook) {
                  ret = tree->ops->writepage_end_io_hook(page, start,
                                           end, NULL, uptodate);
                  if (ret)
                        uptodate = 0;
            }

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

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

            clear_extent_writeback(tree, start, end, GFP_ATOMIC);

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

      bio_put(bio);
}

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

      if (err)
            uptodate = 0;

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

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

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

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

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

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

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

      bio_put(bio);
}

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

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

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

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

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

            unlock_extent(tree, start, end, GFP_ATOMIC);

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

      bio_put(bio);
}

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

      bio = bio_alloc(gfp_flags, nr_vecs);

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

      if (bio) {
            bio->bi_size = 0;
            bio->bi_bdev = bdev;
            bio->bi_sector = first_sector;
      }
      return bio;
}

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

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

      bio->bi_private = NULL;

      bio_get(bio);

      if (tree->ops && tree->ops->submit_bio_hook)
            tree->ops->submit_bio_hook(page->mapping->host, rw, bio,
                                 mirror_num, bio_flags);
      else
            submit_bio(rw, bio);
      if (bio_flagged(bio, BIO_EOPNOTSUPP))
            ret = -EOPNOTSUPP;
      bio_put(bio);
      return ret;
}

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

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

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

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

      bio_add_page(bio, page, page_size, offset);
      bio->bi_end_io = end_io_func;
      bio->bi_private = tree;

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

      return ret;
}

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

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

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

      set_page_extent_mapped(page);

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

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

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

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

            iosize = min(extent_map_end(em) - cur, end - cur + 1);
            cur_end = min(extent_map_end(em) - 1, end);
            iosize = (iosize + blocksize - 1) & ~((u64)blocksize - 1);
            if (this_bio_flag & EXTENT_BIO_COMPRESSED) {
                  disk_io_size = em->block_len;
                  sector = em->block_start >> 9;
            } else {
                  sector = (em->block_start + extent_offset) >> 9;
                  disk_io_size = iosize;
            }
            bdev = em->bdev;
            block_start = em->block_start;
            if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
                  block_start = EXTENT_MAP_HOLE;
            free_extent_map(em);
            em = NULL;

            /* we've found a hole, just zero and go on */
            if (block_start == EXTENT_MAP_HOLE) {
                  char *userpage;
                  userpage = kmap_atomic(page, KM_USER0);
                  memset(userpage + page_offset, 0, iosize);
                  flush_dcache_page(page);
                  kunmap_atomic(userpage, KM_USER0);

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

            ret = 0;
            if (tree->ops && tree->ops->readpage_io_hook) {
                  ret = tree->ops->readpage_io_hook(page, cur,
                                            cur + iosize - 1);
            }
            if (!ret) {
                  unsigned long pnr = (last_byte >> PAGE_CACHE_SHIFT) + 1;
                  pnr -= page->index;
                  ret = submit_extent_page(READ, tree, page,
                               sector, disk_io_size, page_offset,
                               bdev, bio, pnr,
                               end_bio_extent_readpage, mirror_num,
                               *bio_flags,
                               this_bio_flag);
                  nr++;
                  *bio_flags = this_bio_flag;
            }
            if (ret)
                  SetPageError(page);
            cur = cur + iosize;
            page_offset += iosize;
      }
      if (!nr) {
            if (!PageError(page))
                  SetPageUptodate(page);
            unlock_page(page);
      }
      return 0;
}

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

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

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

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

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

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

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

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

      set_page_extent_mapped(page);

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

            while (delalloc_end < page_end) {
                  nr_delalloc = find_lock_delalloc_range(inode, tree,
                                           page,
                                           &delalloc_start,
                                           &delalloc_end,
                                           128 * 1024 * 1024);
                  if (nr_delalloc == 0) {
                        delalloc_start = delalloc_end + 1;
                        continue;
                  }
                  tree->ops->fill_delalloc(inode, page, delalloc_start,
                                     delalloc_end, &page_started,
                                     &nr_written);
                  delalloc_start = delalloc_end + 1;
            }

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

      unlock_start = start;

      if (tree->ops && tree->ops->writepage_start_hook) {
            ret = tree->ops->writepage_start_hook(page, start,
                                          page_end);
            if (ret == -EAGAIN) {
                  unlock_extent(tree, start, page_end, GFP_NOFS);
                  redirty_page_for_writepage(wbc, page);
                  update_nr_written(page, wbc, nr_written);
                  unlock_page(page);
                  ret = 0;
                  goto done_unlocked;
            }
      }

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

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

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

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

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

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

            /*
             * compressed and inline extents are written through other
             * paths in the FS
             */
            if (compressed || block_start == EXTENT_MAP_HOLE ||
                block_start == EXTENT_MAP_INLINE) {
                  clear_extent_dirty(tree, cur,
                                 cur + iosize - 1, GFP_NOFS);

                  unlock_extent(tree, unlock_start, cur + iosize - 1,
                              GFP_NOFS);

                  /*
                   * end_io notification does not happen here for
                   * compressed extents
                   */
                  if (!compressed && tree->ops &&
                      tree->ops->writepage_end_io_hook)
                        tree->ops->writepage_end_io_hook(page, cur,
                                           cur + iosize - 1,
                                           NULL, 1);
                  else if (compressed) {
                        /* we don't want to end_page_writeback on
                         * a compressed extent.  this happens
                         * elsewhere
                         */
                        nr++;
                  }

                  cur += iosize;
                  pg_offset += iosize;
                  unlock_start = cur;
                  continue;
            }
            /* leave this out until we have a page_mkwrite call */
            if (0 && !test_range_bit(tree, cur, cur + iosize - 1,
                           EXTENT_DIRTY, 0)) {
                  cur = cur + iosize;
                  pg_offset += iosize;
                  continue;
            }

            clear_extent_dirty(tree, cur, cur + iosize - 1, GFP_NOFS);
            if (tree->ops && tree->ops->writepage_io_hook) {
                  ret = tree->ops->writepage_io_hook(page, cur,
                                    cur + iosize - 1);
            } else {
                  ret = 0;
            }
            if (ret) {
                  SetPageError(page);
            } else {
                  unsigned long max_nr = end_index + 1;

                  set_range_writeback(tree, cur, cur + iosize - 1);
                  if (!PageWriteback(page)) {
                        printk(KERN_ERR "btrfs warning page %lu not "
                               "writeback, cur %llu end %llu\n",
                               page->index, (unsigned long long)cur,
                               (unsigned long long)end);
                  }

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

done_unlocked:

      return 0;
}

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

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

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

                  /*
                   * At this point we hold neither mapping->tree_lock nor
                   * lock on the page itself: the page may be truncated or
                   * invalidated (changing page->mapping to NULL), or even
                   * swizzled back from swapper_space to tmpfs file
                   * mapping
                   */
                  if (tree->ops && tree->ops->write_cache_pages_lock_hook)
                        tree->ops->write_cache_pages_lock_hook(page);
                  else
                        lock_page(page);

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

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

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

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

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

                  if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
                        unlock_page(page);
                        ret = 0;
                  }
                  if (ret || wbc->nr_to_write <= 0)
                        done = 1;
                  if (wbc->nonblocking && bdi_write_congested(bdi)) {
                        wbc->encountered_congestion = 1;
                        done = 1;
                  }
            }
            pagevec_release(&pvec);
            cond_resched();
      }
      if (!scanned && !done) {
            /*
             * We hit the last page and there is more work to be done: wrap
             * back to the start of the file
             */
            scanned = 1;
            index = 0;
            goto retry;
      }
      return ret;
}

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

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

int extent_write_full_page(struct extent_io_tree *tree, struct page *page,
                    get_extent_t *get_extent,
                    struct writeback_control *wbc)
{
      int ret;
      struct address_space *mapping = page->mapping;
      struct extent_page_data epd = {
            .bio = NULL,
            .tree = tree,
            .get_extent = get_extent,
            .extent_locked = 0,
            .sync_io = wbc->sync_mode == WB_SYNC_ALL,
      };
      struct writeback_control wbc_writepages = {
            .bdi        = wbc->bdi,
            .sync_mode  = wbc->sync_mode,
            .older_than_this = NULL,
            .nr_to_write      = 64,
            .range_start      = page_offset(page) + PAGE_CACHE_SIZE,
            .range_end  = (loff_t)-1,
      };

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

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

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

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

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

      flush_epd_write_bio(&epd);
      return ret;
}

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

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

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

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

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

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

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

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

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

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

      set_page_extent_mapped(page);
      set_page_dirty(page);

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

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

      set_page_extent_mapped(page);

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

      lock_extent(tree, page_start, page_end, GFP_NOFS);
      while (block_start <= block_end) {
            em = get_extent(inode, page, page_offset, block_start,
                        block_end - block_start + 1, 1);
            if (IS_ERR(em) || !em)
                  goto err;

            cur_end = min(block_end, extent_map_end(em) - 1);
            block_off_start = block_start & (PAGE_CACHE_SIZE - 1);
            block_off_end = block_off_start + blocksize;
            isnew = clear_extent_new(tree, block_start, cur_end, GFP_NOFS);

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

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

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

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

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

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

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

sector_t extent_bmap(struct address_space *mapping, sector_t iblock,
            get_extent_t *get_extent)
{
      struct inode *inode = mapping->host;
      u64 start = iblock << inode->i_blkbits;
      sector_t sector = 0;
      size_t blksize = (1 << inode->i_blkbits);
      struct extent_map *em;

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

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

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

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

      if (len == 0)
            return -EINVAL;

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

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

            disko = 0;
            flags = 0;

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

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

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

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

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

      if (i == 0)
            return eb->first_page;
      i += eb->start >> PAGE_CACHE_SHIFT;
      mapping = eb->first_page->mapping;
      if (!mapping)
            return NULL;

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

      return p;
}

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

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

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

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

      return eb;
}

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

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

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

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

      if (page0) {
            eb->first_page = page0;
            i = 1;
            index++;
            page_cache_get(page0);
            mark_page_accessed(page0);
            set_page_extent_mapped(page0);
            set_page_extent_head(page0, len);
            uptodate = PageUptodate(page0);
      } else {
            i = 0;
      }
      for (; i < num_pages; i++, index++) {
            p = find_or_create_page(mapping, index, mask | __GFP_HIGHMEM);
            if (!p) {
                  WARN_ON(1);
                  goto free_eb;
            }
            set_page_extent_mapped(p);
            mark_page_accessed(p);
            if (i == 0) {
                  eb->first_page = p;
                  set_page_extent_head(p, len);
            } else {
                  set_page_private(p, EXTENT_PAGE_PRIVATE);
            }
            if (!PageUptodate(p))
                  uptodate = 0;
            unlock_page(p);
      }
      if (uptodate)
            set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);

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

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

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

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

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

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

      return eb;
}

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

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

      WARN_ON(1);
}

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

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

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

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

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

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

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

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

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

      num_pages = num_extent_pages(eb->start, eb->len);
      clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);

      clear_extent_uptodate(tree, eb->start, eb->start + eb->len - 1,
                        GFP_NOFS);
      for (i = 0; i < num_pages; i++) {
            page = extent_buffer_page(eb, i);
            if (page)
                  ClearPageUptodate(page);
      }
      return 0;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

      num_pages = num_extent_pages(eb->start, eb->len);
      for (i = start_i; i < num_pages; i++) {
            page = extent_buffer_page(eb, i);
            if (!wait) {
                  if (!trylock_page(page))
                        goto unlock_exit;
            } else {
                  lock_page(page);
            }
            locked_pages++;
            if (!PageUptodate(page))
                  all_uptodate = 0;
      }
      if (all_uptodate) {
            if (start_i == 0)
                  set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
            goto unlock_exit;
      }

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

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

      if (ret || !wait)
            return ret;

      for (i = start_i; i < num_pages; i++) {
            page = extent_buffer_page(eb, i);
            wait_on_page_locked(page);
            if (!PageUptodate(page))
                  ret = -EIO;
      }

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

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

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

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

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

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

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

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

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

      if (i != end_i)
            return -EINVAL;

      if (i == 0) {
            offset = start_offset;
            *map_start = 0;
      } else {
            offset = 0;
            *map_start = ((u64)i << PAGE_CACHE_SHIFT) - start_offset;
      }

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

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

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

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

int memcmp_extent_buffer(struct extent_buffer *eb, const void *ptrv,
                    unsigned long start,
                    unsigned long len)
{
      size_t cur;
      size_t offset;
      struct page *page;
      char *kaddr;
      char *ptr = (char *)ptrv;
      size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
      unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
      int ret = 0;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

      WARN_ON(src->len != dst_len);

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

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

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

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

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

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

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

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

static void copy_pages(struct page *dst_page, struct page *src_page,
                   unsigned long dst_off, unsigned long src_off,
                   unsigned long len)
{
      char *dst_kaddr = kmap_atomic(dst_page, KM_USER0);
      char *src_kaddr;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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