Btrfs: Extent based page cache code. This uses an rbtree of extents and tests

instead of buffer heads.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1656 insertions, 0 deletions

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
new file mode 100644
index 000000000000..d378edf0964e
--- /dev/null
+++ b/fs/btrfs/extent_map.c
@@ -0,0 +1,1656 @@
+#include <linux/bitops.h>
+#include <linux/slab.h>
+#include <linux/bio.h>
+#include <linux/mm.h>
+#include <linux/gfp.h>
+#include <linux/pagemap.h>
+#include <linux/page-flags.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/blkdev.h>
+#include "extent_map.h"
+
+static struct kmem_cache *extent_map_cache;
+static struct kmem_cache *extent_state_cache;
+
+struct tree_entry {
+        u64 start;
+        u64 end;
+        int in_tree;
+        struct rb_node rb_node;
+};
+
+/* bits for the extent state */
+#define EXTENT_DIRTY 1
+#define EXTENT_WRITEBACK (1 << 1)
+#define EXTENT_UPTODATE (1 << 2)
+#define EXTENT_LOCKED (1 << 3)
+#define EXTENT_NEW (1 << 4)
+#define EXTENT_DELALLOC (1 << 5)
+
+#define EXTENT_IOBITS (EXTENT_LOCKED | EXTENT_WRITEBACK)
+
+static LIST_HEAD(all_states);
+spinlock_t state_lock = SPIN_LOCK_UNLOCKED;
+
+void __init extent_map_init(void)
+{
+        extent_map_cache = kmem_cache_create("extent_map",
+                                            sizeof(struct extent_map), 0,
+                                            SLAB_RECLAIM_ACCOUNT |
+                                            SLAB_DESTROY_BY_RCU,
+                                            NULL);
+        extent_state_cache = kmem_cache_create("extent_state",
+                                            sizeof(struct extent_state), 0,
+                                            SLAB_RECLAIM_ACCOUNT |
+                                            SLAB_DESTROY_BY_RCU,
+                                            NULL);
+}
+
+void __exit extent_map_exit(void)
+{
+        while(!list_empty(&all_states)) {
+                struct extent_state *state;
+                struct list_head *cur = all_states.next;
+                state = list_entry(cur, struct extent_state, list);
+                printk("found leaked state %Lu %Lu state %d in_tree %d\n",
+                       state->start, state->end, state->state, state->in_tree);
+                list_del(&state->list);
+                kfree(state);
+        }
+        if (extent_map_cache)
+                kmem_cache_destroy(extent_map_cache);
+        if (extent_state_cache)
+                kmem_cache_destroy(extent_state_cache);
+}
+
+void extent_map_tree_init(struct extent_map_tree *tree,
+                          struct address_space *mapping, gfp_t mask)
+{
+        tree->map.rb_node = NULL;
+        tree->state.rb_node = NULL;
+        rwlock_init(&tree->lock);
+        tree->mapping = mapping;
+}
+EXPORT_SYMBOL(extent_map_tree_init);
+
+struct extent_map *alloc_extent_map(gfp_t mask)
+{
+        struct extent_map *em;
+        em = kmem_cache_alloc(extent_map_cache, mask);
+        if (!em || IS_ERR(em))
+                return em;
+        em->in_tree = 0;
+        atomic_set(&em->refs, 1);
+        return em;
+}
+EXPORT_SYMBOL(alloc_extent_map);
+
+void free_extent_map(struct extent_map *em)
+{
+        if (atomic_dec_and_test(&em->refs)) {
+                WARN_ON(em->in_tree);
+                kmem_cache_free(extent_map_cache, em);
+        }
+}
+EXPORT_SYMBOL(free_extent_map);
+
+
+struct extent_state *alloc_extent_state(gfp_t mask)
+{
+        struct extent_state *state;
+        state = kmem_cache_alloc(extent_state_cache, mask);
+        if (!state || IS_ERR(state))
+                return state;
+        state->state = 0;
+        state->in_tree = 0;
+        atomic_set(&state->refs, 1);
+        init_waitqueue_head(&state->wq);
+        spin_lock_irq(&state_lock);
+        list_add(&state->list, &all_states);
+        spin_unlock_irq(&state_lock);
+        return state;
+}
+EXPORT_SYMBOL(alloc_extent_state);
+
+void free_extent_state(struct extent_state *state)
+{
+        if (atomic_dec_and_test(&state->refs)) {
+                WARN_ON(state->in_tree);
+                spin_lock_irq(&state_lock);
+                list_del_init(&state->list);
+                spin_unlock_irq(&state_lock);
+                kmem_cache_free(extent_state_cache, state);
+        }
+}
+EXPORT_SYMBOL(free_extent_state);
+
+static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
+                                   struct rb_node *node)
+{
+        struct rb_node ** p = &root->rb_node;
+        struct rb_node * parent = NULL;
+        struct tree_entry *entry;
+
+        while(*p) {
+                parent = *p;
+                entry = rb_entry(parent, struct tree_entry, rb_node);
+
+                if (offset < entry->start)
+                        p = &(*p)->rb_left;
+                else if (offset > entry->end)
+                        p = &(*p)->rb_right;
+                else
+                        return parent;
+        }
+
+        entry = rb_entry(node, struct tree_entry, rb_node);
+        entry->in_tree = 1;
+        rb_link_node(node, parent, p);
+        rb_insert_color(node, root);
+        return NULL;
+}
+
+static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
+                                   struct rb_node **prev_ret)
+{
+        struct rb_node * n = root->rb_node;
+        struct rb_node *prev = NULL;
+        struct tree_entry *entry;
+        struct tree_entry *prev_entry = NULL;
+
+        while(n) {
+                entry = rb_entry(n, struct tree_entry, rb_node);
+                prev = n;
+                prev_entry = entry;
+
+                if (offset < entry->start)
+                        n = n->rb_left;
+                else if (offset > entry->end)
+                        n = n->rb_right;
+                else
+                        return n;
+        }
+        if (!prev_ret)
+                return NULL;
+        while(prev && offset > prev_entry->end) {
+                prev = rb_next(prev);
+                prev_entry = rb_entry(prev, struct tree_entry, rb_node);
+        }
+        *prev_ret = prev;
+        return NULL;
+}
+
+static inline struct rb_node *tree_search(struct rb_root *root, u64 offset)
+{
+        struct rb_node *prev;
+        struct rb_node *ret;
+        ret = __tree_search(root, offset, &prev);
+        if (!ret)
+                return prev;
+        return ret;
+}
+
+static int tree_delete(struct rb_root *root, u64 offset)
+{
+        struct rb_node *node;
+        struct tree_entry *entry;
+
+        node = __tree_search(root, offset, NULL);
+        if (!node)
+                return -ENOENT;
+        entry = rb_entry(node, struct tree_entry, rb_node);
+        entry->in_tree = 0;
+        rb_erase(node, root);
+        return 0;
+}
+
+/*
+ * add_extent_mapping tries a simple backward merge with existing
+ * mappings.  The extent_map struct passed in will be inserted into
+ * the tree directly (no copies made, just a reference taken).
+ */
+int add_extent_mapping(struct extent_map_tree *tree,
+                       struct extent_map *em)
+{
+        int ret = 0;
+        struct extent_map *prev = NULL;
+        struct rb_node *rb;
+
+        write_lock_irq(&tree->lock);
+        rb = tree_insert(&tree->map, em->end, &em->rb_node);
+        if (rb) {
+                prev = rb_entry(rb, struct extent_map, rb_node);
+                printk("found extent map %Lu %Lu on insert of %Lu %Lu\n", prev->start, prev->end, em->start, em->end);
+                ret = -EEXIST;
+                goto out;
+        }
+        atomic_inc(&em->refs);
+        if (em->start != 0) {
+                rb = rb_prev(&em->rb_node);
+                if (rb)
+                        prev = rb_entry(rb, struct extent_map, rb_node);
+                if (prev && prev->end + 1 == em->start &&
+                    ((em->block_start == 0 && prev->block_start == 0) ||
+                             (em->block_start == prev->block_end + 1))) {
+                        em->start = prev->start;
+                        em->block_start = prev->block_start;
+                        rb_erase(&prev->rb_node, &tree->map);
+                        prev->in_tree = 0;
+                        free_extent_map(prev);
+                }
+         }
+out:
+        write_unlock_irq(&tree->lock);
+        return ret;
+}
+EXPORT_SYMBOL(add_extent_mapping);
+
+/*
+ * lookup_extent_mapping returns the first extent_map struct in the
+ * tree that intersects the [start, end] (inclusive) range.  There may
+ * be additional objects in the tree that intersect, so check the object
+ * returned carefully to make sure you don't need additional lookups.
+ */
+struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
+                                         u64 start, u64 end)
+{
+        struct extent_map *em;
+        struct rb_node *rb_node;
+
+        read_lock_irq(&tree->lock);
+        rb_node = tree_search(&tree->map, start);
+        if (!rb_node) {
+                em = NULL;
+                goto out;
+        }
+        if (IS_ERR(rb_node)) {
+                em = ERR_PTR(PTR_ERR(rb_node));
+                goto out;
+        }
+        em = rb_entry(rb_node, struct extent_map, rb_node);
+        if (em->end < start || em->start > end) {
+                em = NULL;
+                goto out;
+        }
+        atomic_inc(&em->refs);
+out:
+        read_unlock_irq(&tree->lock);
+        return em;
+}
+EXPORT_SYMBOL(lookup_extent_mapping);
+
+/*
+ * removes an extent_map struct from the tree.  No reference counts are
+ * dropped, and no checks are done to  see if the range is in use
+ */
+int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
+{
+        int ret;
+
+        write_lock_irq(&tree->lock);
+        ret = tree_delete(&tree->map, em->end);
+        write_unlock_irq(&tree->lock);
+        return ret;
+}
+EXPORT_SYMBOL(remove_extent_mapping);
+
+/*
+ * utility function to look for merge candidates inside a given range.
+ * Any extents with matching state are merged together into a single
+ * extent in the tree.  Extents with EXTENT_IO in their state field
+ * are not merged because the end_io handlers need to be able to do
+ * operations on them without sleeping (or doing allocations/splits).
+ *
+ * This should be called with the tree lock held.
+ */
+static int merge_state(struct extent_map_tree *tree,
+                       struct extent_state *state)
+{
+        struct extent_state *other;
+        struct rb_node *other_node;
+
+        if (state->state & EXTENT_IOBITS)
+                return 0;
+
+        other_node = rb_prev(&state->rb_node);
+        if (other_node) {
+                other = rb_entry(other_node, struct extent_state, rb_node);
+                if (other->end == state->start - 1 &&
+                    other->state == state->state) {
+                        state->start = other->start;
+                        other->in_tree = 0;
+                        rb_erase(&other->rb_node, &tree->state);
+                        free_extent_state(other);
+                }
+        }
+        other_node = rb_next(&state->rb_node);
+        if (other_node) {
+                other = rb_entry(other_node, struct extent_state, rb_node);
+                if (other->start == state->end + 1 &&
+                    other->state == state->state) {
+                        other->start = state->start;
+                        state->in_tree = 0;
+                        rb_erase(&state->rb_node, &tree->state);
+                        free_extent_state(state);
+                }
+        }
+        return 0;
+}
+
+/*
+ * insert an extent_state struct into the tree.  'bits' are set on the
+ * struct before it is inserted.
+ *
+ * This may return -EEXIST if the extent is already there, in which case the
+ * state struct is freed.
+ *
+ * The tree lock is not taken internally.  This is a utility function and
+ * probably isn't what you want to call (see set/clear_extent_bit).
+ */
+static int insert_state(struct extent_map_tree *tree,
+                        struct extent_state *state, u64 start, u64 end,
+                        int bits)
+{
+        struct rb_node *node;
+
+        if (end < start) {
+                printk("end < start %Lu %Lu\n", end, start);
+                WARN_ON(1);
+        }
+        state->state |= bits;
+        state->start = start;
+        state->end = end;
+        if ((end & 4095) == 0) {
+                printk("insert state %Lu %Lu strange end\n", start, end);
+                WARN_ON(1);
+        }
+        node = tree_insert(&tree->state, end, &state->rb_node);
+        if (node) {
+                struct extent_state *found;
+                found = rb_entry(node, struct extent_state, rb_node);
+printk("found node %Lu %Lu on insert of %Lu %Lu\n", found->start, found->end, start, end);
+                free_extent_state(state);
+                return -EEXIST;
+        }
+        merge_state(tree, state);
+        return 0;
+}
+
+/*
+ * split a given extent state struct in two, inserting the preallocated
+ * struct 'prealloc' as the newly created second half.  'split' indicates an
+ * offset inside 'orig' where it should be split.
+ *
+ * Before calling,
+ * the tree has 'orig' at [orig->start, orig->end].  After calling, there
+ * are two extent state structs in the tree:
+ * prealloc: [orig->start, split - 1]
+ * orig: [ split, orig->end ]
+ *
+ * The tree locks are not taken by this function. They need to be held
+ * by the caller.
+ */
+static int split_state(struct extent_map_tree *tree, struct extent_state *orig,
+                       struct extent_state *prealloc, u64 split)
+{
+        struct rb_node *node;
+        prealloc->start = orig->start;
+        prealloc->end = split - 1;
+        prealloc->state = orig->state;
+        orig->start = split;
+        if ((prealloc->end & 4095) == 0) {
+                printk("insert state %Lu %Lu strange end\n", prealloc->start,
+                       prealloc->end);
+                WARN_ON(1);
+        }
+        node = tree_insert(&tree->state, prealloc->end, &prealloc->rb_node);
+        if (node) {
+                struct extent_state *found;
+                found = rb_entry(node, struct extent_state, rb_node);
+printk("found node %Lu %Lu on insert of %Lu %Lu\n", found->start, found->end, prealloc->start, prealloc->end);
+                free_extent_state(prealloc);
+                return -EEXIST;
+        }
+        return 0;
+}
+
+/*
+ * utility function to clear some bits in an extent state struct.
+ * it will optionally wake up any one waiting on this state (wake == 1), or
+ * forcibly remove the state from the tree (delete == 1).
+ *
+ * If no bits are set on the state struct after clearing things, the
+ * struct is freed and removed from the tree
+ */
+static int clear_state_bit(struct extent_map_tree *tree,
+                            struct extent_state *state, int bits, int wake,
+                            int delete)
+{
+        int ret = state->state & bits;
+        state->state &= ~bits;
+        if (wake)
+                wake_up(&state->wq);
+        if (delete || state->state == 0) {
+                if (state->in_tree) {
+                        rb_erase(&state->rb_node, &tree->state);
+                        state->in_tree = 0;
+                        free_extent_state(state);
+                } else {
+                        WARN_ON(1);
+                }
+        } else {
+                merge_state(tree, state);
+        }
+        return ret;
+}
+
+/*
+ * clear some bits on a range in the tree.  This may require splitting
+ * or inserting elements in the tree, so the gfp mask is used to
+ * indicate which allocations or sleeping are allowed.
+ *
+ * pass 'wake' == 1 to kick any sleepers, and 'delete' == 1 to remove
+ * the given range from the tree regardless of state (ie for truncate).
+ *
+ * the range [start, end] is inclusive.
+ *
+ * This takes the tree lock, and returns < 0 on error, > 0 if any of the
+ * bits were already set, or zero if none of the bits were already set.
+ */
+int clear_extent_bit(struct extent_map_tree *tree, u64 start, u64 end,
+                     int bits, int wake, int delete, gfp_t mask)
+{
+        struct extent_state *state;
+        struct extent_state *prealloc = NULL;
+        struct rb_node *node;
+        int err;
+        int set = 0;
+
+again:
+        if (!prealloc && (mask & __GFP_WAIT)) {
+                prealloc = alloc_extent_state(mask);
+                if (!prealloc)
+                        return -ENOMEM;
+        }
+
+        write_lock_irq(&tree->lock);
+        /*
+         * this search will find the extents that end after
+         * our range starts
+         */
+        node = tree_search(&tree->state, start);
+        if (!node)
+                goto out;
+        state = rb_entry(node, struct extent_state, rb_node);
+        if (state->start > end)
+                goto out;
+        WARN_ON(state->end < start);
+
+        /*
+         *     | ---- desired range ---- |
+         *  | state | or
+         *  | ------------- state -------------- |
+         *
+         * We need to split the extent we found, and may flip
+         * bits on second half.
+         *
+         * If the extent we found extends past our range, we
+         * just split and search again.  It'll get split again
+         * the next time though.
+         *
+         * If the extent we found is inside our range, we clear
+         * the desired bit on it.
+         */
+
+        if (state->start < start) {
+                err = split_state(tree, state, prealloc, start);
+                BUG_ON(err == -EEXIST);
+                prealloc = NULL;
+                if (err)
+                        goto out;
+                if (state->end <= end) {
+                        start = state->end + 1;
+                        set |= clear_state_bit(tree, state, bits,
+                                        wake, delete);
+                } else {
+                        start = state->start;
+                }
+                goto search_again;
+        }
+        /*
+         * | ---- desired range ---- |
+         *                        | state |
+         * We need to split the extent, and clear the bit
+         * on the first half
+         */
+        if (state->start <= end && state->end > end) {
+                err = split_state(tree, state, prealloc, end + 1);
+                BUG_ON(err == -EEXIST);
+
+                if (wake)
+                        wake_up(&state->wq);
+                set |= clear_state_bit(tree, prealloc, bits,
+                                       wake, delete);
+                prealloc = NULL;
+                goto out;
+        }
+
+        start = state->end + 1;
+        set |= clear_state_bit(tree, state, bits, wake, delete);
+        goto search_again;
+
+out:
+        write_unlock_irq(&tree->lock);
+        if (prealloc)
+                free_extent_state(prealloc);
+
+        return set;
+
+search_again:
+        if (start >= end)
+                goto out;
+        write_unlock_irq(&tree->lock);
+        if (mask & __GFP_WAIT)
+                cond_resched();
+        goto again;
+}
+EXPORT_SYMBOL(clear_extent_bit);
+
+static int wait_on_state(struct extent_map_tree *tree,
+                         struct extent_state *state)
+{
+        DEFINE_WAIT(wait);
+        prepare_to_wait(&state->wq, &wait, TASK_UNINTERRUPTIBLE);
+        read_unlock_irq(&tree->lock);
+        schedule();
+        read_lock_irq(&tree->lock);
+        finish_wait(&state->wq, &wait);
+        return 0;
+}
+
+/*
+ * waits for one or more bits to clear on a range in the state tree.
+ * The range [start, end] is inclusive.
+ * The tree lock is taken by this function
+ */
+int wait_extent_bit(struct extent_map_tree *tree, u64 start, u64 end, int bits)
+{
+        struct extent_state *state;
+        struct rb_node *node;
+
+        read_lock_irq(&tree->lock);
+again:
+        while (1) {
+                /*
+                 * this search will find all the extents that end after
+                 * our range starts
+                 */
+                node = tree_search(&tree->state, start);
+                if (!node)
+                        break;
+
+                state = rb_entry(node, struct extent_state, rb_node);
+
+                if (state->start > end)
+                        goto out;
+
+                if (state->state & bits) {
+                        start = state->start;
+                        atomic_inc(&state->refs);
+                        wait_on_state(tree, state);
+                        free_extent_state(state);
+                        goto again;
+                }
+                start = state->end + 1;
+
+                if (start > end)
+                        break;
+
+                if (need_resched()) {
+                        read_unlock_irq(&tree->lock);
+                        cond_resched();
+                        read_lock_irq(&tree->lock);
+                }
+        }
+out:
+        read_unlock_irq(&tree->lock);
+        return 0;
+}
+EXPORT_SYMBOL(wait_extent_bit);
+
+/*
+ * set some bits on a range in the tree.  This may require allocations
+ * or sleeping, so the gfp mask is used to indicate what is allowed.
+ *
+ * If 'exclusive' == 1, this will fail with -EEXIST if some part of the
+ * range already has the desired bits set.  The start of the existing
+ * range is returned in failed_start in this case.
+ *
+ * [start, end] is inclusive
+ * This takes the tree lock.
+ */
+int set_extent_bit(struct extent_map_tree *tree, u64 start, u64 end, int bits,
+                   int exclusive, u64 *failed_start, gfp_t mask)
+{
+        struct extent_state *state;
+        struct extent_state *prealloc = NULL;
+        struct rb_node *node;
+        int err = 0;
+        int set;
+        u64 last_start;
+        u64 last_end;
+again:
+        if (!prealloc && (mask & __GFP_WAIT)) {
+                prealloc = alloc_extent_state(mask);
+                if (!prealloc)
+                        return -ENOMEM;
+        }
+
+        write_lock_irq(&tree->lock);
+        /*
+         * this search will find all the extents that end after
+         * our range starts.
+         */
+        node = tree_search(&tree->state, start);
+        if (!node) {
+                err = insert_state(tree, prealloc, start, end, bits);
+                prealloc = NULL;
+                BUG_ON(err == -EEXIST);
+                goto out;
+        }
+
+        state = rb_entry(node, struct extent_state, rb_node);
+        last_start = state->start;
+        last_end = state->end;
+
+        /*
+         * | ---- desired range ---- |
+         * | state |
+         *
+         * Just lock what we found and keep going
+         */
+        if (state->start == start && state->end <= end) {
+                set = state->state & bits;
+                if (set && exclusive) {
+                        *failed_start = state->start;
+                        err = -EEXIST;
+                        goto out;
+                }
+                state->state |= bits;
+                start = state->end + 1;
+                merge_state(tree, state);
+                goto search_again;
+        }
+
+        /*
+         *     | ---- desired range ---- |
+         * | state |
+         *   or
+         * | ------------- state -------------- |
+         *
+         * We need to split the extent we found, and may flip bits on
+         * second half.
+         *
+         * If the extent we found extends past our
+         * range, we just split and search again.  It'll get split
+         * again the next time though.
+         *
+         * If the extent we found is inside our range, we set the
+         * desired bit on it.
+         */
+        if (state->start < start) {
+                set = state->state & bits;
+                if (exclusive && set) {
+                        *failed_start = start;
+                        err = -EEXIST;
+                        goto out;
+                }
+                err = split_state(tree, state, prealloc, start);
+                BUG_ON(err == -EEXIST);
+                prealloc = NULL;
+                if (err)
+                        goto out;
+                if (state->end <= end) {
+                        state->state |= bits;
+                        start = state->end + 1;
+                        merge_state(tree, state);
+                } else {
+                        start = state->start;
+                }
+                goto search_again;
+        }
+        /*
+         * | ---- desired range ---- |
+         *                        | state |
+         * We need to split the extent, and set the bit
+         * on the first half
+         */
+        if (state->start <= end && state->end > end) {
+                set = state->state & bits;
+                if (exclusive && set) {
+                        *failed_start = start;
+                        err = -EEXIST;
+                        goto out;
+                }
+                err = split_state(tree, state, prealloc, end + 1);
+                BUG_ON(err == -EEXIST);
+
+                prealloc->state |= bits;
+                merge_state(tree, prealloc);
+                prealloc = NULL;
+                goto out;
+        }
+
+        /*
+         * | ---- 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;
+        }
+        goto search_again;
+
+out:
+        write_unlock_irq(&tree->lock);
+        if (prealloc)
+                free_extent_state(prealloc);
+
+        return err;
+
+search_again:
+        if (start > end)
+                goto out;
+        write_unlock_irq(&tree->lock);
+        if (mask & __GFP_WAIT)
+                cond_resched();
+        goto again;
+}
+EXPORT_SYMBOL(set_extent_bit);
+
+/* wrappers around set/clear extent bit */
+int set_extent_dirty(struct extent_map_tree *tree, u64 start, u64 end,
+                     gfp_t mask)
+{
+        return set_extent_bit(tree, start, end, EXTENT_DIRTY, 0, NULL,
+                              mask);
+}
+EXPORT_SYMBOL(set_extent_dirty);
+
+int clear_extent_dirty(struct extent_map_tree *tree, u64 start, u64 end,
+                       gfp_t mask)
+{
+        return clear_extent_bit(tree, start, end, EXTENT_DIRTY, 0, 0, mask);
+}
+EXPORT_SYMBOL(clear_extent_dirty);
+
+int set_extent_new(struct extent_map_tree *tree, u64 start, u64 end,
+                     gfp_t mask)
+{
+        return set_extent_bit(tree, start, end, EXTENT_NEW, 0, NULL,
+                              mask);
+}
+EXPORT_SYMBOL(set_extent_new);
+
+int clear_extent_new(struct extent_map_tree *tree, u64 start, u64 end,
+                       gfp_t mask)
+{
+        return clear_extent_bit(tree, start, end, EXTENT_NEW, 0, 0, mask);
+}
+EXPORT_SYMBOL(clear_extent_new);
+
+int set_extent_uptodate(struct extent_map_tree *tree, u64 start, u64 end,
+                        gfp_t mask)
+{
+        return set_extent_bit(tree, start, end, EXTENT_UPTODATE, 0, NULL,
+                              mask);
+}
+EXPORT_SYMBOL(set_extent_uptodate);
+
+int clear_extent_uptodate(struct extent_map_tree *tree, u64 start, u64 end,
+                          gfp_t mask)
+{
+        return clear_extent_bit(tree, start, end, EXTENT_UPTODATE, 0, 0, mask);
+}
+EXPORT_SYMBOL(clear_extent_uptodate);
+
+int set_extent_writeback(struct extent_map_tree *tree, u64 start, u64 end,
+                         gfp_t mask)
+{
+        return set_extent_bit(tree, start, end, EXTENT_WRITEBACK,
+                              0, NULL, mask);
+}
+EXPORT_SYMBOL(set_extent_writeback);
+
+int clear_extent_writeback(struct extent_map_tree *tree, u64 start, u64 end,
+                           gfp_t mask)
+{
+        return clear_extent_bit(tree, start, end, EXTENT_WRITEBACK, 1, 0, mask);
+}
+EXPORT_SYMBOL(clear_extent_writeback);
+
+int wait_on_extent_writeback(struct extent_map_tree *tree, u64 start, u64 end)
+{
+        return wait_extent_bit(tree, start, end, EXTENT_WRITEBACK);
+}
+EXPORT_SYMBOL(wait_on_extent_writeback);
+
+/*
+ * locks a range in ascending order, waiting for any locked regions
+ * it hits on the way.  [start,end] are inclusive, and this will sleep.
+ */
+int lock_extent(struct extent_map_tree *tree, u64 start, u64 end, gfp_t mask)
+{
+        int err;
+        u64 failed_start;
+        while (1) {
+                err = set_extent_bit(tree, start, end, EXTENT_LOCKED, 1,
+                                     &failed_start, mask);
+                if (err == -EEXIST && (mask & __GFP_WAIT)) {
+                        wait_extent_bit(tree, failed_start, end, EXTENT_LOCKED);
+                        start = failed_start;
+                } else {
+                        break;
+                }
+                WARN_ON(start > end);
+        }
+        return err;
+}
+EXPORT_SYMBOL(lock_extent);
+
+int unlock_extent(struct extent_map_tree *tree, u64 start, u64 end,
+                  gfp_t mask)
+{
+        return clear_extent_bit(tree, start, end, EXTENT_LOCKED, 1, 0, mask);
+}
+EXPORT_SYMBOL(unlock_extent);
+
+/*
+ * helper function to set pages and extents in the tree dirty
+ */
+int set_range_dirty(struct extent_map_tree *tree, u64 start, u64 end)
+{
+        unsigned long index = start >> PAGE_CACHE_SHIFT;
+        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
+        struct page *page;
+
+        while (index <= end_index) {
+                page = find_get_page(tree->mapping, index);
+                BUG_ON(!page);
+                __set_page_dirty_nobuffers(page);
+                page_cache_release(page);
+                index++;
+        }
+        set_extent_dirty(tree, start, end, GFP_NOFS);
+        return 0;
+}
+EXPORT_SYMBOL(set_range_dirty);
+
+/*
+ * helper function to set both pages and extents in the tree writeback
+ */
+int set_range_writeback(struct extent_map_tree *tree, u64 start, u64 end)
+{
+        unsigned long index = start >> PAGE_CACHE_SHIFT;
+        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
+        struct page *page;
+
+        while (index <= end_index) {
+                page = find_get_page(tree->mapping, index);
+                BUG_ON(!page);
+                set_page_writeback(page);
+                page_cache_release(page);
+                index++;
+        }
+        set_extent_writeback(tree, start, end, GFP_NOFS);
+        return 0;
+}
+EXPORT_SYMBOL(set_range_writeback);
+
+/*
+ * helper function to lock both pages and extents in the tree.
+ * pages must be locked first.
+ */
+int lock_range(struct extent_map_tree *tree, u64 start, u64 end)
+{
+        unsigned long index = start >> PAGE_CACHE_SHIFT;
+        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
+        struct page *page;
+        int err;
+
+        while (index <= end_index) {
+                page = grab_cache_page(tree->mapping, index);
+                if (!page) {
+                        err = -ENOMEM;
+                        goto failed;
+                }
+                if (IS_ERR(page)) {
+                        err = PTR_ERR(page);
+                        goto failed;
+                }
+                index++;
+        }
+        lock_extent(tree, start, end, GFP_NOFS);
+        return 0;
+
+failed:
+        /*
+         * we failed above in getting the page at 'index', so we undo here
+         * up to but not including the page at 'index'
+         */
+        end_index = index;
+        index = start >> PAGE_CACHE_SHIFT;
+        while (index < end_index) {
+                page = find_get_page(tree->mapping, index);
+                unlock_page(page);
+                page_cache_release(page);
+                index++;
+        }
+        return err;
+}
+EXPORT_SYMBOL(lock_range);
+
+/*
+ * helper function to unlock both pages and extents in the tree.
+ */
+int unlock_range(struct extent_map_tree *tree, u64 start, u64 end)
+{
+        unsigned long index = start >> PAGE_CACHE_SHIFT;
+        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
+        struct page *page;
+
+        while (index <= end_index) {
+                page = find_get_page(tree->mapping, index);
+                unlock_page(page);
+                page_cache_release(page);
+                index++;
+        }
+        unlock_extent(tree, start, end, GFP_NOFS);
+        return 0;
+}
+EXPORT_SYMBOL(unlock_range);
+
+/*
+ * searches a range in the state tree for a given mask.
+ * If 'filled' == 1, this returns 1 only if ever extent in the tree
+ * has the bits set.  Otherwise, 1 is returned if any bit in the
+ * range is found set.
+ */
+static int test_range_bit(struct extent_map_tree *tree, u64 start, u64 end,
+                          int bits, int filled)
+{
+        struct extent_state *state = NULL;
+        struct rb_node *node;
+        int bitset = 0;
+
+        read_lock_irq(&tree->lock);
+        node = tree_search(&tree->state, start);
+        while (node && start <= end) {
+                state = rb_entry(node, struct extent_state, rb_node);
+                if (state->start > end)
+                        break;
+
+                if (filled && state->start > start) {
+                        bitset = 0;
+                        break;
+                }
+                if (state->state & bits) {
+                        bitset = 1;
+                        if (!filled)
+                                break;
+                } else if (filled) {
+                        bitset = 0;
+                        break;
+                }
+                start = state->end + 1;
+                if (start > end)
+                        break;
+                node = rb_next(node);
+        }
+        read_unlock_irq(&tree->lock);
+        return bitset;
+}
+
+/*
+ * helper function to set a given page up to date if all the
+ * extents in the tree for that page are up to date
+ */
+static int check_page_uptodate(struct extent_map_tree *tree,
+                               struct page *page)
+{
+        u64 start = page->index << PAGE_CACHE_SHIFT;
+        u64 end = start + PAGE_CACHE_SIZE - 1;
+        if (test_range_bit(tree, start, end, EXTENT_UPTODATE, 1))
+                SetPageUptodate(page);
+        return 0;
+}
+
+/*
+ * helper function to unlock a page if all the extents in the tree
+ * for that page are unlocked
+ */
+static int check_page_locked(struct extent_map_tree *tree,
+                             struct page *page)
+{
+        u64 start = page->index << PAGE_CACHE_SHIFT;
+        u64 end = start + PAGE_CACHE_SIZE - 1;
+        if (!test_range_bit(tree, start, end, EXTENT_LOCKED, 0))
+                unlock_page(page);
+        return 0;
+}
+
+/*
+ * helper function to end page writeback if all the extents
+ * in the tree for that page are done with writeback
+ */
+static int check_page_writeback(struct extent_map_tree *tree,
+                             struct page *page)
+{
+        u64 start = page->index << PAGE_CACHE_SHIFT;
+        u64 end = start + PAGE_CACHE_SIZE - 1;
+        if (!test_range_bit(tree, start, end, EXTENT_WRITEBACK, 0))
+                end_page_writeback(page);
+        return 0;
+}
+
+/* lots and lots of room for performance fixes in the end_bio funcs */
+
+/*
+ * after a writepage IO is done, we need to:
+ * clear the uptodate bits on error
+ * clear the writeback bits in the extent tree for this IO
+ * end_page_writeback if the page has no more pending IO
+ *
+ * Scheduling is not allowed, so the extent state tree is expected
+ * to have one and only one object corresponding to this IO.
+ */
+static int end_bio_extent_writepage(struct bio *bio,
+                                   unsigned int bytes_done, int err)
+{
+        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
+        struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
+        struct extent_map_tree *tree = bio->bi_private;
+        u64 start;
+        u64 end;
+        int whole_page;
+
+        if (bio->bi_size)
+                return 1;
+
+        do {
+                struct page *page = bvec->bv_page;
+                start = (page->index << PAGE_CACHE_SHIFT) + bvec->bv_offset;
+                end = start + bvec->bv_len - 1;
+
+                if (bvec->bv_offset == 0 && bvec->bv_len == PAGE_CACHE_SIZE)
+                        whole_page = 1;
+                else
+                        whole_page = 0;
+
+                if (--bvec >= bio->bi_io_vec)
+                        prefetchw(&bvec->bv_page->flags);
+
+                if (!uptodate) {
+                        clear_extent_uptodate(tree, start, end, GFP_ATOMIC);
+                        ClearPageUptodate(page);
+                        SetPageError(page);
+                }
+                clear_extent_writeback(tree, start, end, GFP_ATOMIC);
+
+                if (whole_page)
+                        end_page_writeback(page);
+                else
+                        check_page_writeback(tree, page);
+        } while (bvec >= bio->bi_io_vec);
+
+        bio_put(bio);
+        return 0;
+}
+
+/*
+ * after a readpage IO is done, we need to:
+ * clear the uptodate bits on error
+ * set the uptodate bits if things worked
+ * set the page up to date if all extents in the tree are uptodate
+ * clear the lock bit in the extent tree
+ * unlock the page if there are no other extents locked for it
+ *
+ * Scheduling is not allowed, so the extent state tree is expected
+ * to have one and only one object corresponding to this IO.
+ */
+static int end_bio_extent_readpage(struct bio *bio,
+                                   unsigned int bytes_done, int err)
+{
+        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
+        struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
+        struct extent_map_tree *tree = bio->bi_private;
+        u64 start;
+        u64 end;
+        int whole_page;
+
+        if (bio->bi_size)
+                return 1;
+
+        do {
+                struct page *page = bvec->bv_page;
+                start = (page->index << PAGE_CACHE_SHIFT) + bvec->bv_offset;
+                end = start + bvec->bv_len - 1;
+
+                if (bvec->bv_offset == 0 && bvec->bv_len == PAGE_CACHE_SIZE)
+                        whole_page = 1;
+                else
+                        whole_page = 0;
+
+                if (--bvec >= bio->bi_io_vec)
+                        prefetchw(&bvec->bv_page->flags);
+
+                if (uptodate) {
+                        set_extent_uptodate(tree, start, end, GFP_ATOMIC);
+                        if (whole_page)
+                                SetPageUptodate(page);
+                        else
+                                check_page_uptodate(tree, page);
+                } else {
+                        ClearPageUptodate(page);
+                        SetPageError(page);
+                }
+
+                unlock_extent(tree, start, end, GFP_ATOMIC);
+
+                if (whole_page)
+                        unlock_page(page);
+                else
+                        check_page_locked(tree, page);
+        } while (bvec >= bio->bi_io_vec);
+
+        bio_put(bio);
+        return 0;
+}
+
+/*
+ * IO done from prepare_write is pretty simple, we just unlock
+ * the structs in the extent tree when done, and set the uptodate bits
+ * as appropriate.
+ */
+static int end_bio_extent_preparewrite(struct bio *bio,
+                                       unsigned int bytes_done, int err)
+{
+        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
+        struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
+        struct extent_map_tree *tree = bio->bi_private;
+        u64 start;
+        u64 end;
+
+        if (bio->bi_size)
+                return 1;
+
+        do {
+                struct page *page = bvec->bv_page;
+                start = (page->index << PAGE_CACHE_SHIFT) + bvec->bv_offset;
+                end = start + bvec->bv_len - 1;
+
+                if (--bvec >= bio->bi_io_vec)
+                        prefetchw(&bvec->bv_page->flags);
+
+                if (uptodate) {
+                        set_extent_uptodate(tree, start, end, GFP_ATOMIC);
+                } else {
+                        ClearPageUptodate(page);
+                        SetPageError(page);
+                }
+
+                unlock_extent(tree, start, end, GFP_ATOMIC);
+
+        } while (bvec >= bio->bi_io_vec);
+
+        bio_put(bio);
+        return 0;
+}
+
+static int submit_extent_page(int rw, struct extent_map_tree *tree,
+                              struct page *page, sector_t sector,
+                              size_t size, unsigned long offset,
+                              struct block_device *bdev,
+                              bio_end_io_t end_io_func)
+{
+        struct bio *bio;
+        int ret = 0;
+
+        bio = bio_alloc(GFP_NOIO, 1);
+
+        bio->bi_sector = sector;
+        bio->bi_bdev = bdev;
+        bio->bi_io_vec[0].bv_page = page;
+        bio->bi_io_vec[0].bv_len = size;
+        bio->bi_io_vec[0].bv_offset = offset;
+
+        bio->bi_vcnt = 1;
+        bio->bi_idx = 0;
+        bio->bi_size = size;
+
+        bio->bi_end_io = end_io_func;
+        bio->bi_private = tree;
+
+        bio_get(bio);
+        submit_bio(rw, bio);
+
+        if (bio_flagged(bio, BIO_EOPNOTSUPP))
+                ret = -EOPNOTSUPP;
+
+        bio_put(bio);
+        return ret;
+}
+
+/*
+ * basic readpage implementation.  Locked extent state structs are inserted
+ * into the tree that are removed when the IO is done (by the end_io
+ * handlers)
+ */
+int extent_read_full_page(struct extent_map_tree *tree, struct page *page,
+                          get_extent_t *get_extent)
+{
+        struct inode *inode = page->mapping->host;
+        u64 start = page->index << PAGE_CACHE_SHIFT;
+        u64 page_end = start + PAGE_CACHE_SIZE - 1;
+        u64 end;
+        u64 cur = start;
+        u64 extent_offset;
+        u64 last_byte = i_size_read(inode);
+        u64 block_start;
+        u64 cur_end;
+        sector_t sector;
+        struct extent_map *em;
+        struct block_device *bdev;
+        int ret;
+        int nr = 0;
+        size_t page_offset = 0;
+        size_t iosize;
+        size_t blocksize = inode->i_sb->s_blocksize;
+
+        if (!PagePrivate(page)) {
+                SetPagePrivate(page);
+                set_page_private(page, 1);
+                page_cache_get(page);
+        }
+
+        end = page_end;
+        lock_extent(tree, start, end, GFP_NOFS);
+
+        while (cur <= end) {
+                if (cur >= last_byte) {
+                        iosize = PAGE_CACHE_SIZE - page_offset;
+                        zero_user_page(page, page_offset, iosize, KM_USER0);
+                        set_extent_uptodate(tree, cur, cur + iosize - 1,
+                                            GFP_NOFS);
+                        unlock_extent(tree, cur, cur + iosize - 1, GFP_NOFS);
+                        break;
+                }
+                em = get_extent(inode, page, page_offset, cur, end, 0);
+                if (IS_ERR(em) || !em) {
+                        SetPageError(page);
+                        unlock_extent(tree, cur, end, GFP_NOFS);
+                        break;
+                }
+
+                extent_offset = cur - em->start;
+                BUG_ON(em->end < cur);
+                BUG_ON(end < cur);
+
+                iosize = min(em->end - cur, end - cur) + 1;
+                cur_end = min(em->end, end);
+                iosize = (iosize + blocksize - 1) & ~((u64)blocksize - 1);
+                sector = (em->block_start + extent_offset) >> 9;
+                bdev = em->bdev;
+                block_start = em->block_start;
+                free_extent_map(em);
+                em = NULL;
+
+                /* we've found a hole, just zero and go on */
+                if (block_start == 0) {
+                        zero_user_page(page, page_offset, iosize, KM_USER0);
+                        set_extent_uptodate(tree, cur, cur + iosize - 1,
+                                            GFP_NOFS);
+                        unlock_extent(tree, cur, cur + iosize - 1, GFP_NOFS);
+                        cur = cur + iosize;
+                        page_offset += iosize;
+                        continue;
+                }
+                /* the get_extent function already copied into the page */
+                if (test_range_bit(tree, cur, cur_end, EXTENT_UPTODATE, 1)) {
+                        unlock_extent(tree, cur, cur + iosize - 1, GFP_NOFS);
+                        cur = cur + iosize;
+                        page_offset += iosize;
+                        continue;
+                }
+
+                ret = submit_extent_page(READ, tree, page,
+                                         sector, iosize, page_offset, bdev,
+                                         end_bio_extent_readpage);
+                if (ret)
+                        SetPageError(page);
+                cur = cur + iosize;
+                page_offset += iosize;
+                nr++;
+        }
+        if (!nr) {
+                if (!PageError(page))
+                        SetPageUptodate(page);
+                unlock_page(page);
+        }
+        return 0;
+}
+EXPORT_SYMBOL(extent_read_full_page);
+
+/*
+ * the writepage semantics are similar to regular writepage.  extent
+ * records are inserted to lock ranges in the tree, and as dirty areas
+ * are found, they are marked writeback.  Then the lock bits are removed
+ * and the end_io handler clears the writeback ranges
+ */
+int extent_write_full_page(struct extent_map_tree *tree, struct page *page,
+                          get_extent_t *get_extent,
+                          struct writeback_control *wbc)
+{
+        struct inode *inode = page->mapping->host;
+        u64 start = page->index << PAGE_CACHE_SHIFT;
+        u64 page_end = start + PAGE_CACHE_SIZE - 1;
+        u64 end;
+        u64 cur = start;
+        u64 extent_offset;
+        u64 last_byte = i_size_read(inode);
+        u64 block_start;
+        sector_t sector;
+        struct extent_map *em;
+        struct block_device *bdev;
+        int ret;
+        int nr = 0;
+        size_t page_offset = 0;
+        size_t iosize;
+        size_t blocksize;
+        loff_t i_size = i_size_read(inode);
+        unsigned long end_index = i_size >> PAGE_CACHE_SHIFT;
+
+        if (page->index > end_index) {
+                clear_extent_dirty(tree, start, page_end, GFP_NOFS);
+                unlock_page(page);
+                return 0;
+        }
+
+        if (page->index == end_index) {
+                size_t offset = i_size & (PAGE_CACHE_SIZE - 1);
+                zero_user_page(page, offset,
+                               PAGE_CACHE_SIZE - offset, KM_USER0);
+        }
+
+        if (!PagePrivate(page)) {
+                SetPagePrivate(page);
+                set_page_private(page, 1);
+                page_cache_get(page);
+        }
+
+        end = page_end;
+        lock_extent(tree, start, page_end, GFP_NOFS);
+
+        if (last_byte <= start) {
+                clear_extent_dirty(tree, start, page_end, GFP_NOFS);
+                goto done;
+        }
+
+        set_extent_uptodate(tree, start, page_end, GFP_NOFS);
+        blocksize = inode->i_sb->s_blocksize;
+
+        while (cur <= end) {
+                if (cur >= last_byte) {
+                        clear_extent_dirty(tree, cur, page_end, GFP_NOFS);
+                        break;
+                }
+                em = get_extent(inode, page, page_offset, cur, end, 1);
+                if (IS_ERR(em) || !em) {
+                        SetPageError(page);
+                        break;
+                }
+
+                extent_offset = cur - em->start;
+                BUG_ON(em->end < cur);
+                BUG_ON(end < cur);
+                iosize = min(em->end - cur, end - cur) + 1;
+                iosize = (iosize + blocksize - 1) & ~((u64)blocksize - 1);
+                sector = (em->block_start + extent_offset) >> 9;
+                bdev = em->bdev;
+                block_start = em->block_start;
+                free_extent_map(em);
+                em = NULL;
+
+                if (block_start == 0 || block_start == EXTENT_MAP_INLINE) {
+                        clear_extent_dirty(tree, cur,
+                                           cur + iosize - 1, GFP_NOFS);
+                        cur = cur + iosize;
+                        page_offset += iosize;
+                        continue;
+                }
+
+                /* leave this out until we have a page_mkwrite call */
+                if (0 && !test_range_bit(tree, cur, cur + iosize - 1,
+                                   EXTENT_DIRTY, 0)) {
+                        cur = cur + iosize;
+                        page_offset += iosize;
+                        continue;
+                }
+                clear_extent_dirty(tree, cur, cur + iosize - 1, GFP_NOFS);
+                set_range_writeback(tree, cur, cur + iosize - 1);
+                ret = submit_extent_page(WRITE, tree, page,
+                                         sector, iosize, page_offset, bdev,
+                                         end_bio_extent_writepage);
+                if (ret)
+                        SetPageError(page);
+                cur = cur + iosize;
+                page_offset += iosize;
+                nr++;
+        }
+done:
+        WARN_ON(test_range_bit(tree, start, page_end, EXTENT_DIRTY, 0));
+        unlock_extent(tree, start, page_end, GFP_NOFS);
+        unlock_page(page);
+        return 0;
+}
+EXPORT_SYMBOL(extent_write_full_page);
+
+/*
+ * basic invalidatepage code, this waits on any locked or writeback
+ * ranges corresponding to the page, and then deletes any extent state
+ * records from the tree
+ */
+int extent_invalidatepage(struct extent_map_tree *tree,
+                          struct page *page, unsigned long offset)
+{
+        u64 start = (page->index << PAGE_CACHE_SHIFT);
+        u64 end = start + PAGE_CACHE_SIZE - 1;
+        size_t blocksize = page->mapping->host->i_sb->s_blocksize;
+
+        start += (offset + blocksize -1) & ~(blocksize - 1);
+        if (start > end)
+                return 0;
+
+        lock_extent(tree, start, end, GFP_NOFS);
+        wait_on_extent_writeback(tree, start, end);
+        clear_extent_bit(tree, start, end, EXTENT_LOCKED | EXTENT_DIRTY,
+                         1, 1, GFP_NOFS);
+        return 0;
+}
+EXPORT_SYMBOL(extent_invalidatepage);
+
+/*
+ * simple commit_write call, set_range_dirty is used to mark both
+ * the pages and the extent records as dirty
+ */
+int extent_commit_write(struct extent_map_tree *tree,
+                        struct inode *inode, struct page *page,
+                        unsigned from, unsigned to)
+{
+        loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+
+        if (!PagePrivate(page)) {
+                SetPagePrivate(page);
+                set_page_private(page, 1);
+                page_cache_get(page);
+        }
+
+        set_page_dirty(page);
+
+        if (pos > inode->i_size) {
+                i_size_write(inode, pos);
+                mark_inode_dirty(inode);
+        }
+        return 0;
+}
+EXPORT_SYMBOL(extent_commit_write);
+
+int extent_prepare_write(struct extent_map_tree *tree,
+                         struct inode *inode, struct page *page,
+                         unsigned from, unsigned to, get_extent_t *get_extent)
+{
+        u64 page_start = page->index << PAGE_CACHE_SHIFT;
+        u64 page_end = page_start + PAGE_CACHE_SIZE - 1;
+        u64 block_start;
+        u64 orig_block_start;
+        u64 block_end;
+        u64 cur_end;
+        struct extent_map *em;
+        unsigned blocksize = 1 << inode->i_blkbits;
+        size_t page_offset = 0;
+        size_t block_off_start;
+        size_t block_off_end;
+        int err = 0;
+        int iocount = 0;
+        int ret = 0;
+        int isnew;
+
+        if (!PagePrivate(page)) {
+                SetPagePrivate(page);
+                set_page_private(page, 1);
+                page_cache_get(page);
+        }
+        block_start = (page_start + from) & ~((u64)blocksize - 1);
+        block_end = (page_start + to - 1) | (blocksize - 1);
+        orig_block_start = block_start;
+
+        lock_extent(tree, page_start, page_end, GFP_NOFS);
+        while(block_start <= block_end) {
+                em = get_extent(inode, page, page_offset, block_start,
+                                block_end, 1);
+                if (IS_ERR(em) || !em) {
+                        goto err;
+                }
+                cur_end = min(block_end, em->end);
+                block_off_start = block_start & (PAGE_CACHE_SIZE - 1);
+                block_off_end = block_off_start + blocksize;
+                isnew = clear_extent_new(tree, block_start, cur_end, GFP_NOFS);
+
+                if (!PageUptodate(page) && isnew &&
+                    (block_off_end > to || block_off_start < from)) {
+                        void *kaddr;
+
+                        kaddr = kmap_atomic(page, KM_USER0);
+                        if (block_off_end > to)
+                                memset(kaddr + to, 0, block_off_end - to);
+                        if (block_off_start < from)
+                                memset(kaddr + block_off_start, 0,
+                                       from - block_off_start);
+                        flush_dcache_page(page);
+                        kunmap_atomic(kaddr, KM_USER0);
+                }
+                if (!isnew && !PageUptodate(page) &&
+                    (block_off_end > to || block_off_start < from) &&
+                    !test_range_bit(tree, block_start, cur_end,
+                                    EXTENT_UPTODATE, 1)) {
+                        u64 sector;
+                        u64 extent_offset = block_start - em->start;
+                        size_t iosize;
+                        sector = (em->block_start + extent_offset) >> 9;
+                        iosize = (cur_end - block_start + blocksize - 1) &
+                                ~((u64)blocksize - 1);
+                        /*
+                         * we've already got the extent locked, but we
+                         * need to split the state such that our end_bio
+                         * handler can clear the lock.
+                         */
+                        set_extent_bit(tree, block_start,
+                                       block_start + iosize - 1,
+                                       EXTENT_LOCKED, 0, NULL, GFP_NOFS);
+                        ret = submit_extent_page(READ, tree, page,
+                                         sector, iosize, page_offset, em->bdev,
+                                         end_bio_extent_preparewrite);
+                        iocount++;
+                        block_start = block_start + iosize;
+                } else {
+                        set_extent_uptodate(tree, block_start, cur_end,
+                                            GFP_NOFS);
+                        unlock_extent(tree, block_start, cur_end, GFP_NOFS);
+                        block_start = cur_end + 1;
+                }
+                page_offset = block_start & (PAGE_CACHE_SIZE - 1);
+                free_extent_map(em);
+        }
+        if (iocount) {
+                wait_extent_bit(tree, orig_block_start,
+                                block_end, EXTENT_LOCKED);
+        }
+        check_page_uptodate(tree, page);
+err:
+        /* FIXME, zero out newly allocated blocks on error */
+        return err;
+}
+EXPORT_SYMBOL(extent_prepare_write);
+
+/*
+ * a helper for releasepage.  As long as there are no locked extents
+ * in the range corresponding to the page, both state records and extent
+ * map records are removed
+ */
+int try_release_extent_mapping(struct extent_map_tree *tree, struct page *page)
+{
+        struct extent_map *em;
+        u64 start = page->index << PAGE_CACHE_SHIFT;
+        u64 end = start + PAGE_CACHE_SIZE - 1;
+        u64 orig_start = start;
+
+        while (start <= end) {
+                em = lookup_extent_mapping(tree, start, end);
+                if (!em || IS_ERR(em))
+                        break;
+                if (test_range_bit(tree, em->start, em->end,
+                                   EXTENT_LOCKED, 0)) {
+                        free_extent_map(em);
+                        start = em->end + 1;
+printk("range still locked %Lu %Lu\n", em->start, em->end);
+                        break;
+                }
+                remove_extent_mapping(tree, em);
+                start = em->end + 1;
+                /* once for the rb tree */
+                free_extent_map(em);
+                /* once for us */
+                free_extent_map(em);
+        }
+        WARN_ON(test_range_bit(tree, orig_start, end, EXTENT_WRITEBACK, 0));
+        clear_extent_bit(tree, orig_start, end, EXTENT_UPTODATE,
+                         1, 1, GFP_NOFS);
+        return 1;
+}
+EXPORT_SYMBOL(try_release_extent_mapping);
+