// SPDX-License-Identifier: GPL-2.0

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

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

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

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

static DEFINE_SPINLOCK(leak_lock);

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

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

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

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

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

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

#define btrfs_debug_check_extent_io_range(tree, start, end)             \
        __btrfs_debug_check_extent_io_range(__func__, (tree), (start), (end))
static inline void __btrfs_debug_check_extent_io_range(const char *caller,
                struct extent_io_tree *tree, u64 start, u64 end)
{
        if (tree->ops && tree->ops->check_extent_io_range)
                tree->ops->check_extent_io_range(tree->private_data, caller,
                                                 start, end);
}
#else
#define btrfs_leak_debug_add(new, head) do {} while (0)
#define btrfs_leak_debug_del(entry)     do {} while (0)
#define btrfs_leak_debug_check()        do {} while (0)
#define btrfs_debug_check_extent_io_range(c, s, e)      do {} while (0)
#endif

#define BUFFER_LRU_MAX 64

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

struct extent_page_data {
        struct bio *bio;
        struct extent_io_tree *tree;
        /* 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 REQ_SYNC */
        unsigned int sync_io:1;
};

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

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

static void flush_write_bio(struct extent_page_data *epd);

static inline struct btrfs_fs_info *
tree_fs_info(struct extent_io_tree *tree)
{
        if (tree->ops)
                return tree->ops->tree_fs_info(tree->private_data);
        return NULL;
}

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

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

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

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

        return 0;

free_bioset:
        bioset_free(btrfs_bioset);
        btrfs_bioset = NULL;

free_buffer_cache:
        kmem_cache_destroy(extent_buffer_cache);
        extent_buffer_cache = NULL;

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

void __cold extent_io_exit(void)
{
        btrfs_leak_debug_check();

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

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

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

        /*
         * The given mask might be not appropriate for the slab allocator,
         * drop the unsupported bits
         */
        mask &= ~(__GFP_DMA32|__GFP_HIGHMEM);
        state = kmem_cache_alloc(extent_state_cache, mask);
        if (!state)
                return state;
        state->state = 0;
        state->failrec = NULL;
        RB_CLEAR_NODE(&state->rb_node);
        btrfs_leak_debug_add(&state->leak_list, &states);
        refcount_set(&state->refs, 1);
        init_waitqueue_head(&state->wq);
        trace_alloc_extent_state(state, mask, _RET_IP_);
        return state;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        set_state_bits(tree, state, bits, changeset);

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

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

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

        split_cb(tree, orig, split);

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

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

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

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

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

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

        return prealloc;
}

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

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

        btrfs_debug_check_extent_io_range(tree, start, end);

        if (bits & EXTENT_DELALLOC)
                bits |= EXTENT_NORESERVE;

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

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

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

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

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

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

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

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

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

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

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

                prealloc = NULL;
                goto out;
        }

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

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

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

        return 0;

}

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

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

        btrfs_debug_check_extent_io_range(tree, start, end);

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

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

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

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

                if (start > end)
                        break;

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

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

        set_state_cb(tree, state, bits);
        if ((bits_to_set & EXTENT_DIRTY) && !(state->state & EXTENT_DIRTY)) {
                u64 range = state->end - state->start + 1;
                tree->dirty_bytes += range;
        }
        ret = add_extent_changeset(state, bits_to_set, changeset, 1);
        BUG_ON(ret < 0);
        state->state |= bits_to_set;
}

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

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

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

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

        btrfs_debug_check_extent_io_range(tree, start, end);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        return err;

}

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


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

        btrfs_debug_check_extent_io_range(tree, start, end);

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

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

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

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

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

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

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

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

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

search_again:
        if (start > end)
                goto out;
        spin_unlock(&tree->lock);
        cond_resched();
        first_iteration = false;
        goto again;

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

        return err;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

/*
 * helper function to set both pages and extents in the tree writeback
 */
static void set_range_writeback(struct extent_io_tree *tree, u64 start, u64 end)
{
        tree->ops->set_range_writeback(tree->private_data, start, end);
}

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

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

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

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

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

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

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

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

        spin_lock(&tree->lock);

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

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

static int __process_pages_contig(struct address_space *mapping,
                                  struct page *locked_page,
                                  pgoff_t start_index, pgoff_t end_index,
                                  unsigned long page_ops, pgoff_t *index_ret);

static noinline void __unlock_for_delalloc(struct inode *inode,
                                           struct page *locked_page,
                                           u64 start, u64 end)
{
        unsigned long index = start >> PAGE_SHIFT;
        unsigned long end_index = end >> PAGE_SHIFT;

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

        __process_pages_contig(inode->i_mapping, locked_page, index, end_index,
                               PAGE_UNLOCK, NULL);
}

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_SHIFT;
        unsigned long index_ret = index;
        unsigned long end_index = delalloc_end >> PAGE_SHIFT;
        int ret;

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

        ret = __process_pages_contig(inode->i_mapping, locked_page, index,
                                     end_index, PAGE_LOCK, &index_ret);
        if (ret == -EAGAIN)
                __unlock_for_delalloc(inode, locked_page, delalloc_start,
                                      (u64)index_ret << PAGE_SHIFT);
        return ret;
}

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

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

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

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

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

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

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

static int __process_pages_contig(struct address_space *mapping,
                                  struct page *locked_page,
                                  pgoff_t start_index, pgoff_t end_index,
                                  unsigned long page_ops, pgoff_t *index_ret)
{
        unsigned long nr_pages = end_index - start_index + 1;
        unsigned long pages_locked = 0;
        pgoff_t index = start_index;
        struct page *pages[16];
        unsigned ret;
        int err = 0;
        int i;

        if (page_ops & PAGE_LOCK) {
                ASSERT(page_ops == PAGE_LOCK);
                ASSERT(index_ret && *index_ret == start_index);
        }

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

        while (nr_pages > 0) {
                ret = find_get_pages_contig(mapping, index,
                                     min_t(unsigned long,
                                     nr_pages, ARRAY_SIZE(pages)), pages);
                if (ret == 0) {
                        /*
                         * Only if we're going to lock these pages,
                         * can we find nothing at @index.
                         */
                        ASSERT(page_ops & PAGE_LOCK);
                        err = -EAGAIN;
                        goto out;
                }

                for (i = 0; i < ret; i++) {
                        if (page_ops & PAGE_SET_PRIVATE2)
                                SetPagePrivate2(pages[i]);

                        if (pages[i] == locked_page) {
                                put_page(pages[i]);
                                pages_locked++;
                                continue;
                        }
                        if (page_ops & PAGE_CLEAR_DIRTY)
                                clear_page_dirty_for_io(pages[i]);
                        if (page_ops & PAGE_SET_WRITEBACK)
                                set_page_writeback(pages[i]);
                        if (page_ops & PAGE_SET_ERROR)
                                SetPageError(pages[i]);
                        if (page_ops & PAGE_END_WRITEBACK)
                                end_page_writeback(pages[i]);
                        if (page_ops & PAGE_UNLOCK)
                                unlock_page(pages[i]);
                        if (page_ops & PAGE_LOCK) {
                                lock_page(pages[i]);
                                if (!PageDirty(pages[i]) ||
                                    pages[i]->mapping != mapping) {
                                        unlock_page(pages[i]);
                                        put_page(pages[i]);
                                        err = -EAGAIN;
                                        goto out;
                                }
                        }
                        put_page(pages[i]);
                        pages_locked++;
                }
                nr_pages -= ret;
                index += ret;
                cond_resched();
        }
out:
        if (err && index_ret)
                *index_ret = start_index + pages_locked - 1;
        return err;
}

void extent_clear_unlock_delalloc(struct inode *inode, u64 start, u64 end,
                                 u64 delalloc_end, struct page *locked_page,
                                 unsigned clear_bits,
                                 unsigned long page_ops)
{
        clear_extent_bit(&BTRFS_I(inode)->io_tree, start, end, clear_bits, 1, 0,
                         NULL);

        __process_pages_contig(inode->i_mapping, locked_page,
                               start >> PAGE_SHIFT, end >> PAGE_SHIFT,
                               page_ops, NULL);
}

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

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

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

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

/*
 * set the private field for a given byte offset in the tree.  If there isn't
 * an extent_state there already, this does nothing.
 */
static noinline int set_state_failrec(struct extent_io_tree *tree, u64 start,
                struct io_failure_record *failrec)
{
        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->failrec = failrec;
out:
        spin_unlock(&tree->lock);
        return ret;
}

static noinline int get_state_failrec(struct extent_io_tree *tree, u64 start,
                struct io_failure_record **failrec)
{
        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;
        }
        *failrec = state->failrec;
out:
        spin_unlock(&tree->lock);
        return ret;
}

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

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

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

                if (state->start > end)
                        break;

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

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

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

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

int free_io_failure(struct extent_io_tree *failure_tree,
                    struct extent_io_tree *io_tree,
                    struct io_failure_record *rec)
{
        int ret;
        int err = 0;

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

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

        kfree(rec);
        return err;
}

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

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

        bio = btrfs_io_bio_alloc(1);
        bio->bi_iter.bi_size = 0;
        map_length = length;

        /*
         * Avoid races with device replace and make sure our bbio has devices
         * associated to its stripes that don't go away while we are doing the

         * read repair operation.
         */
        btrfs_bio_counter_inc_blocked(fs_info);
        if (btrfs_is_parity_mirror(fs_info, logical, length)) {
                /*
                 * Note that we don't use BTRFS_MAP_WRITE because it's supposed
                 * to update all raid stripes, but here we just want to correct
                 * bad stripe, thus BTRFS_MAP_READ is abused to only get the bad
                 * stripe's dev and sector.
                 */
                ret = btrfs_map_block(fs_info, BTRFS_MAP_READ, logical,
                                      &map_length, &bbio, 0);
                if (ret) {
                        btrfs_bio_counter_dec(fs_info);
                        bio_put(bio);
                        return -EIO;
                }
                ASSERT(bbio->mirror_num == 1);
        } else {
                ret = btrfs_map_block(fs_info, BTRFS_MAP_WRITE, logical,
                                      &map_length, &bbio, mirror_num);
                if (ret) {
                        btrfs_bio_counter_dec(fs_info);
                        bio_put(bio);
                        return -EIO;
                }
                BUG_ON(mirror_num != bbio->mirror_num);
        }

        sector = bbio->stripes[bbio->mirror_num - 1].physical >> 9;
        bio->bi_iter.bi_sector = sector;
        dev = bbio->stripes[bbio->mirror_num - 1].dev;
        btrfs_put_bbio(bbio);
        if (!dev || !dev->bdev ||
            !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state)) {
                btrfs_bio_counter_dec(fs_info);
                bio_put(bio);
                return -EIO;
        }
        bio_set_dev(bio, dev->bdev);
        bio->bi_opf = REQ_OP_WRITE | REQ_SYNC;
        bio_add_page(bio, page, length, pg_offset);

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

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

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

        if (sb_rdonly(fs_info->sb))
                return -EROFS;

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

                ret = repair_io_failure(fs_info, 0, start, PAGE_SIZE, start, p,
                                        start - page_offset(p), mirror_num);
                if (ret)
                        break;
                start += PAGE_SIZE;
        }

        return ret;
}

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

        private = 0;
        ret = count_range_bits(failure_tree, &private, (u64)-1, 1,
                               EXTENT_DIRTY, 0);
        if (!ret)
                return 0;

        ret = get_state_failrec(failure_tree, start, &failrec);
        if (ret)
                return 0;

        BUG_ON(!failrec->this_mirror);

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

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

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

out:
        free_io_failure(failure_tree, io_tree, failrec);

        return 0;
}

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

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

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

                ASSERT(state->end <= end);

                next = next_state(state);

                failrec = state->failrec;
                free_extent_state(state);
                kfree(failrec);

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

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

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

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

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

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

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

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

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

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

        *failrec_ret = failrec;

        return 0;
}

bool btrfs_check_repairable(struct inode *inode, unsigned failed_bio_pages,
                           struct io_failure_record *failrec, int failed_mirror)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        int num_copies;

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

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

        if (failrec->this_mirror > num_copies) {
                btrfs_debug(fs_info,
                        "Check Repairable: (fail) num_copies=%d, next_mirror %d, failed_mirror %d",
                        num_copies, failrec->this_mirror, failed_mirror);
                return false;
        }

        return true;
}


struct bio *btrfs_create_repair_bio(struct inode *inode, struct bio *failed_bio,
                                    struct io_failure_record *failrec,
                                    struct page *page, int pg_offset, int icsum,
                                    bio_end_io_t *endio_func, void *data)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct bio *bio;
        struct btrfs_io_bio *btrfs_failed_bio;
        struct btrfs_io_bio *btrfs_bio;

        bio = btrfs_io_bio_alloc(1);
        bio->bi_end_io = endio_func;
        bio->bi_iter.bi_sector = failrec->logical >> 9;
        bio_set_dev(bio, fs_info->fs_devices->latest_bdev);
        bio->bi_iter.bi_size = 0;
        bio->bi_private = data;

        btrfs_failed_bio = btrfs_io_bio(failed_bio);
        if (btrfs_failed_bio->csum) {
                u16 csum_size = btrfs_super_csum_size(fs_info->super_copy);

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

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

        return bio;
}

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

static int bio_readpage_error(struct bio *failed_bio, u64 phy_offset,
                              struct page *page, u64 start, u64 end,
                              int failed_mirror)
{
        struct io_failure_record *failrec;
        struct inode *inode = page->mapping->host;
        struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
        struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
        struct bio *bio;
        int read_mode = 0;
        blk_status_t status;
        int ret;
        unsigned failed_bio_pages = bio_pages_all(failed_bio);

        BUG_ON(bio_op(failed_bio) == REQ_OP_WRITE);

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

        if (!btrfs_check_repairable(inode, failed_bio_pages, failrec,
                                    failed_mirror)) {
                free_io_failure(failure_tree, tree, failrec);
                return -EIO;
        }

        if (failed_bio_pages > 1)
                read_mode |= REQ_FAILFAST_DEV;

        phy_offset >>= inode->i_sb->s_blocksize_bits;
        bio = btrfs_create_repair_bio(inode, failed_bio, failrec, page,
                                      start - page_offset(page),
                                      (int)phy_offset, failed_bio->bi_end_io,
                                      NULL);
        bio_set_op_attrs(bio, REQ_OP_READ, read_mode);

        btrfs_debug(btrfs_sb(inode->i_sb),
                "Repair Read Error: submitting new read[%#x] to this_mirror=%d, in_validation=%d",
                read_mode, failrec->this_mirror, failrec->in_validation);

        status = tree->ops->submit_bio_hook(tree->private_data, bio, failrec->this_mirror,
                                         failrec->bio_flags, 0);
        if (status) {
                free_io_failure(failure_tree, tree, failrec);
                bio_put(bio);
                ret = blk_status_to_errno(status);
        }

        return ret;
}

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

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

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

        if (tree->ops && tree->ops->writepage_end_io_hook)
                tree->ops->writepage_end_io_hook(page, start, end, NULL,
                                uptodate);

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

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

        ASSERT(!bio_flagged(bio, BIO_CLONED));
        bio_for_each_segment_all(bvec, bio, i) {
                struct page *page = bvec->bv_page;
                struct inode *inode = page->mapping->host;
                struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);

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

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

                end_extent_writepage(page, error, start, end);
                end_page_writeback(page);
        }

        bio_put(bio);
}

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

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

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

        ASSERT(!bio_flagged(bio, BIO_CLONED));
        bio_for_each_segment_all(bvec, bio, i) {
                struct page *page = bvec->bv_page;
                struct inode *inode = page->mapping->host;
                struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);

                btrfs_debug(fs_info,
                        "end_bio_extent_readpage: bi_sector=%llu, err=%d, mirror=%u",
                        (u64)bio->bi_iter.bi_sector, bio->bi_status,
                        io_bio->mirror_num);
                tree = &BTRFS_I(inode)->io_tree;
                failure_tree = &BTRFS_I(inode)->io_failure_tree;

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

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

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

                if (likely(uptodate))
                        goto readpage_ok;

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

                        /*
                         * metadata's readpage_io_failed_hook() always returns
                         * -EIO and fixes nothing.  -EIO is also returned if
                         * data inode error could not be fixed.
                         */
                        ASSERT(ret == -EIO);
                }
readpage_ok:
                if (likely(uptodate)) {
                        loff_t i_size = i_size_read(inode);
                        pgoff_t end_index = i_size >> PAGE_SHIFT;
                        unsigned off;

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

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

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

/*
 * Initialize the members up to but not including 'bio'. Use after allocating a
 * new bio by bio_alloc_bioset as it does not initialize the bytes outside of
 * 'bio' because use of __GFP_ZERO is not supported.
 */
static inline void btrfs_io_bio_init(struct btrfs_io_bio *btrfs_bio)
{
        memset(btrfs_bio, 0, offsetof(struct btrfs_io_bio, bio));
}

/*
 * The following helpers allocate a bio. As it's backed by a bioset, it'll
 * never fail.  We're returning a bio right now but you can call btrfs_io_bio
 * for the appropriate container_of magic
 */
struct bio *btrfs_bio_alloc(struct block_device *bdev, u64 first_byte)
{
        struct bio *bio;

        bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, btrfs_bioset);
        bio_set_dev(bio, bdev);
        bio->bi_iter.bi_sector = first_byte >> 9;
        btrfs_io_bio_init(btrfs_io_bio(bio));
        return bio;
}

struct bio *btrfs_bio_clone(struct bio *bio)
{
        struct btrfs_io_bio *btrfs_bio;
        struct bio *new;

        /* Bio allocation backed by a bioset does not fail */
        new = bio_clone_fast(bio, GFP_NOFS, btrfs_bioset);
        btrfs_bio = btrfs_io_bio(new);
        btrfs_io_bio_init(btrfs_bio);
        btrfs_bio->iter = bio->bi_iter;
        return new;
}

struct bio *btrfs_io_bio_alloc(unsigned int nr_iovecs)
{
        struct bio *bio;

        /* Bio allocation backed by a bioset does not fail */
        bio = bio_alloc_bioset(GFP_NOFS, nr_iovecs, btrfs_bioset);
        btrfs_io_bio_init(btrfs_io_bio(bio));
        return bio;
}

struct bio *btrfs_bio_clone_partial(struct bio *orig, int offset, int size)
{
        struct bio *bio;
        struct btrfs_io_bio *btrfs_bio;

        /* this will never fail when it's backed by a bioset */
        bio = bio_clone_fast(orig, GFP_NOFS, btrfs_bioset);
        ASSERT(bio);

        btrfs_bio = btrfs_io_bio(bio);
        btrfs_io_bio_init(btrfs_bio);

        bio_trim(bio, offset >> 9, size >> 9);
        btrfs_bio->iter = bio->bi_iter;
        return bio;
}

static int __must_check submit_one_bio(struct bio *bio, int mirror_num,
                                       unsigned long bio_flags)
{
        blk_status_t ret = 0;
        struct bio_vec *bvec = bio_last_bvec_all(bio);
        struct page *page = bvec->bv_page;
        struct extent_io_tree *tree = bio->bi_private;
        u64 start;

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

        bio->bi_private = NULL;

        if (tree->ops)
                ret = tree->ops->submit_bio_hook(tree->private_data, bio,
                                           mirror_num, bio_flags, start);
        else
                btrfsic_submit_bio(bio);

        return blk_status_to_errno(ret);
}

/*
 * @opf:        bio REQ_OP_* and REQ_* flags as one value
 * @tree:       tree so we can call our merge_bio hook
 * @wbc:        optional writeback control for io accounting
 * @page:       page to add to the bio
 * @pg_offset:  offset of the new bio or to check whether we are adding
 *              a contiguous page to the previous one
 * @size:       portion of page that we want to write
 * @offset:     starting offset in the page
 * @bdev:       attach newly created bios to this bdev
 * @bio_ret:    must be valid pointer, newly allocated bio will be stored there
 * @end_io_func:     end_io callback for new bio
 * @mirror_num:      desired mirror to read/write
 * @prev_bio_flags:  flags of previous bio to see if we can merge the current one
 * @bio_flags:  flags of the current bio to see if we can merge them
 */
static int submit_extent_page(unsigned int opf, struct extent_io_tree *tree,
                              struct writeback_control *wbc,
                              struct page *page, u64 offset,
                              size_t size, unsigned long pg_offset,
                              struct block_device *bdev,
                              struct bio **bio_ret,
                              bio_end_io_t end_io_func,
                              int mirror_num,
                              unsigned long prev_bio_flags,
                              unsigned long bio_flags,
                              bool force_bio_submit)
{
        int ret = 0;
        struct bio *bio;
        size_t page_size = min_t(size_t, size, PAGE_SIZE);
        sector_t sector = offset >> 9;

        ASSERT(bio_ret);

        if (*bio_ret) {
                bool contig;
                bool can_merge = true;

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

                if (tree->ops && tree->ops->merge_bio_hook(page, offset,
                                        page_size, bio, bio_flags))
                        can_merge = false;

                if (prev_bio_flags != bio_flags || !contig || !can_merge ||
                    force_bio_submit ||
                    bio_add_page(bio, page, page_size, pg_offset) < page_size) {
                        ret = submit_one_bio(bio, mirror_num, prev_bio_flags);
                        if (ret < 0) {
                                *bio_ret = NULL;
                                return ret;
                        }
                        bio = NULL;
                } else {
                        if (wbc)
                                wbc_account_io(wbc, page, page_size);
                        return 0;
                }
        }

        bio = btrfs_bio_alloc(bdev, offset);
        bio_add_page(bio, page, page_size, pg_offset);
        bio->bi_end_io = end_io_func;
        bio->bi_private = tree;
        bio->bi_write_hint = page->mapping->host->i_write_hint;
        bio->bi_opf = opf;
        if (wbc) {
                wbc_init_bio(wbc, bio);
                wbc_account_io(wbc, page, page_size);
        }

        *bio_ret = bio;

        return ret;
}

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

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

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

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

                free_extent_map(em);
                *em_cached = NULL;
        }

        em = get_extent(BTRFS_I(inode), page, pg_offset, start, len, 0);
        if (em_cached && !IS_ERR_OR_NULL(em)) {
                BUG_ON(*em_cached);
                refcount_inc(&em->refs);
                *em_cached = em;
        }
        return em;
}
/*
 * basic readpage implementation.  Locked extent state structs are inserted
 * into the tree that are removed when the IO is done (by the end_io
 * handlers)
 * XXX JDM: This needs looking at to ensure proper page locking
 * return 0 on success, otherwise return error
 */
static int __do_readpage(struct extent_io_tree *tree,
                         struct page *page,
                         get_extent_t *get_extent,
                         struct extent_map **em_cached,
                         struct bio **bio, int mirror_num,
                         unsigned long *bio_flags, unsigned int read_flags,
                         u64 *prev_em_start)
{
        struct inode *inode = page->mapping->host;
        u64 start = page_offset(page);
        const u64 end = start + PAGE_SIZE - 1;
        u64 cur = start;
        u64 extent_offset;
        u64 last_byte = i_size_read(inode);
        u64 block_start;
        u64 cur_end;
        struct extent_map *em;
        struct block_device *bdev;
        int ret = 0;
        int nr = 0;
        size_t pg_offset = 0;
        size_t iosize;
        size_t disk_io_size;
        size_t blocksize = inode->i_sb->s_blocksize;
        unsigned long this_bio_flag = 0;

        set_page_extent_mapped(page);

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

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

                if (zero_offset) {
                        iosize = PAGE_SIZE - zero_offset;
                        userpage = kmap_atomic(page);
                        memset(userpage + zero_offset, 0, iosize);
                        flush_dcache_page(page);
                        kunmap_atomic(userpage);
                }
        }
        while (cur <= end) {
                bool force_bio_submit = false;
                u64 offset;

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

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

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

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

                /*
                 * If we have a file range that points to a compressed extent
                 * and it's followed by a consecutive file range that points to
                 * to the same compressed extent (possibly with a different
                 * offset and/or length, so it either points to the whole extent
                 * or only part of it), we must make sure we do not submit a
                 * single bio to populate the pages for the 2 ranges because
                 * this makes the compressed extent read zero out the pages
                 * belonging to the 2nd range. Imagine the following scenario:
                 *
                 *  File layout
                 *  [0 - 8K]                     [8K - 24K]
                 *    |                               |
                 *    |                               |
                 * points to extent X,         points to extent X,