Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/evalenti/linux...

[mirror_ubuntu-artful-kernel.git] / fs / btrfs / file.c

/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/mpage.h>
#include <linux/falloc.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/compat.h>
#include <linux/slab.h>
#include <linux/btrfs.h>
#include <linux/uio.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "print-tree.h"
#include "tree-log.h"
#include "locking.h"
#include "volumes.h"
#include "qgroup.h"
#include "compression.h"

static struct kmem_cache *btrfs_inode_defrag_cachep;
/*
 * when auto defrag is enabled we
 * queue up these defrag structs to remember which
 * inodes need defragging passes
 */
struct inode_defrag {
        struct rb_node rb_node;
        /* objectid */
        u64 ino;
        /*
         * transid where the defrag was added, we search for
         * extents newer than this
         */
        u64 transid;

        /* root objectid */
        u64 root;

        /* last offset we were able to defrag */
        u64 last_offset;

        /* if we've wrapped around back to zero once already */
        int cycled;
};

static int __compare_inode_defrag(struct inode_defrag *defrag1,
                                  struct inode_defrag *defrag2)
{
        if (defrag1->root > defrag2->root)
                return 1;
        else if (defrag1->root < defrag2->root)
                return -1;
        else if (defrag1->ino > defrag2->ino)
                return 1;
        else if (defrag1->ino < defrag2->ino)
                return -1;
        else
                return 0;
}

/* pop a record for an inode into the defrag tree.  The lock
 * must be held already
 *
 * If you're inserting a record for an older transid than an
 * existing record, the transid already in the tree is lowered
 *
 * If an existing record is found the defrag item you
 * pass in is freed
 */
static int __btrfs_add_inode_defrag(struct inode *inode,
                                    struct inode_defrag *defrag)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct inode_defrag *entry;
        struct rb_node **p;
        struct rb_node *parent = NULL;
        int ret;

        p = &fs_info->defrag_inodes.rb_node;
        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct inode_defrag, rb_node);

                ret = __compare_inode_defrag(defrag, entry);
                if (ret < 0)
                        p = &parent->rb_left;
                else if (ret > 0)
                        p = &parent->rb_right;
                else {
                        /* if we're reinserting an entry for
                         * an old defrag run, make sure to
                         * lower the transid of our existing record
                         */
                        if (defrag->transid < entry->transid)
                                entry->transid = defrag->transid;
                        if (defrag->last_offset > entry->last_offset)
                                entry->last_offset = defrag->last_offset;
                        return -EEXIST;
                }
        }
        set_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags);
        rb_link_node(&defrag->rb_node, parent, p);
        rb_insert_color(&defrag->rb_node, &fs_info->defrag_inodes);
        return 0;
}

static inline int __need_auto_defrag(struct btrfs_fs_info *fs_info)
{
        if (!btrfs_test_opt(fs_info, AUTO_DEFRAG))
                return 0;

        if (btrfs_fs_closing(fs_info))
                return 0;

        return 1;
}

/*
 * insert a defrag record for this inode if auto defrag is
 * enabled
 */
int btrfs_add_inode_defrag(struct btrfs_trans_handle *trans,
                           struct inode *inode)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct inode_defrag *defrag;
        u64 transid;
        int ret;

        if (!__need_auto_defrag(fs_info))
                return 0;

        if (test_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags))
                return 0;

        if (trans)
                transid = trans->transid;
        else
                transid = BTRFS_I(inode)->root->last_trans;

        defrag = kmem_cache_zalloc(btrfs_inode_defrag_cachep, GFP_NOFS);
        if (!defrag)
                return -ENOMEM;

        defrag->ino = btrfs_ino(inode);
        defrag->transid = transid;
        defrag->root = root->root_key.objectid;

        spin_lock(&fs_info->defrag_inodes_lock);
        if (!test_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags)) {
                /*
                 * If we set IN_DEFRAG flag and evict the inode from memory,
                 * and then re-read this inode, this new inode doesn't have
                 * IN_DEFRAG flag. At the case, we may find the existed defrag.
                 */
                ret = __btrfs_add_inode_defrag(inode, defrag);
                if (ret)
                        kmem_cache_free(btrfs_inode_defrag_cachep, defrag);
        } else {
                kmem_cache_free(btrfs_inode_defrag_cachep, defrag);
        }
        spin_unlock(&fs_info->defrag_inodes_lock);
        return 0;
}

/*
 * Requeue the defrag object. If there is a defrag object that points to
 * the same inode in the tree, we will merge them together (by
 * __btrfs_add_inode_defrag()) and free the one that we want to requeue.
 */
static void btrfs_requeue_inode_defrag(struct inode *inode,
                                       struct inode_defrag *defrag)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        int ret;

        if (!__need_auto_defrag(fs_info))
                goto out;

        /*
         * Here we don't check the IN_DEFRAG flag, because we need merge
         * them together.
         */
        spin_lock(&fs_info->defrag_inodes_lock);
        ret = __btrfs_add_inode_defrag(inode, defrag);
        spin_unlock(&fs_info->defrag_inodes_lock);
        if (ret)
                goto out;
        return;
out:
        kmem_cache_free(btrfs_inode_defrag_cachep, defrag);
}

/*
 * pick the defragable inode that we want, if it doesn't exist, we will get
 * the next one.
 */
static struct inode_defrag *
btrfs_pick_defrag_inode(struct btrfs_fs_info *fs_info, u64 root, u64 ino)
{
        struct inode_defrag *entry = NULL;
        struct inode_defrag tmp;
        struct rb_node *p;
        struct rb_node *parent = NULL;
        int ret;

        tmp.ino = ino;
        tmp.root = root;

        spin_lock(&fs_info->defrag_inodes_lock);
        p = fs_info->defrag_inodes.rb_node;
        while (p) {
                parent = p;
                entry = rb_entry(parent, struct inode_defrag, rb_node);

                ret = __compare_inode_defrag(&tmp, entry);
                if (ret < 0)
                        p = parent->rb_left;
                else if (ret > 0)
                        p = parent->rb_right;
                else
                        goto out;
        }

        if (parent && __compare_inode_defrag(&tmp, entry) > 0) {
                parent = rb_next(parent);
                if (parent)
                        entry = rb_entry(parent, struct inode_defrag, rb_node);
                else
                        entry = NULL;
        }
out:
        if (entry)
                rb_erase(parent, &fs_info->defrag_inodes);
        spin_unlock(&fs_info->defrag_inodes_lock);
        return entry;
}

void btrfs_cleanup_defrag_inodes(struct btrfs_fs_info *fs_info)
{
        struct inode_defrag *defrag;
        struct rb_node *node;

        spin_lock(&fs_info->defrag_inodes_lock);
        node = rb_first(&fs_info->defrag_inodes);
        while (node) {
                rb_erase(node, &fs_info->defrag_inodes);
                defrag = rb_entry(node, struct inode_defrag, rb_node);
                kmem_cache_free(btrfs_inode_defrag_cachep, defrag);

                cond_resched_lock(&fs_info->defrag_inodes_lock);

                node = rb_first(&fs_info->defrag_inodes);
        }
        spin_unlock(&fs_info->defrag_inodes_lock);
}

#define BTRFS_DEFRAG_BATCH      1024

static int __btrfs_run_defrag_inode(struct btrfs_fs_info *fs_info,
                                    struct inode_defrag *defrag)
{
        struct btrfs_root *inode_root;
        struct inode *inode;
        struct btrfs_key key;
        struct btrfs_ioctl_defrag_range_args range;
        int num_defrag;
        int index;
        int ret;

        /* get the inode */
        key.objectid = defrag->root;
        key.type = BTRFS_ROOT_ITEM_KEY;
        key.offset = (u64)-1;

        index = srcu_read_lock(&fs_info->subvol_srcu);

        inode_root = btrfs_read_fs_root_no_name(fs_info, &key);
        if (IS_ERR(inode_root)) {
                ret = PTR_ERR(inode_root);
                goto cleanup;
        }

        key.objectid = defrag->ino;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;
        inode = btrfs_iget(fs_info->sb, &key, inode_root, NULL);
        if (IS_ERR(inode)) {
                ret = PTR_ERR(inode);
                goto cleanup;
        }
        srcu_read_unlock(&fs_info->subvol_srcu, index);

        /* do a chunk of defrag */
        clear_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags);
        memset(&range, 0, sizeof(range));
        range.len = (u64)-1;
        range.start = defrag->last_offset;

        sb_start_write(fs_info->sb);
        num_defrag = btrfs_defrag_file(inode, NULL, &range, defrag->transid,
                                       BTRFS_DEFRAG_BATCH);
        sb_end_write(fs_info->sb);
        /*
         * if we filled the whole defrag batch, there
         * must be more work to do.  Queue this defrag
         * again
         */
        if (num_defrag == BTRFS_DEFRAG_BATCH) {
                defrag->last_offset = range.start;
                btrfs_requeue_inode_defrag(inode, defrag);
        } else if (defrag->last_offset && !defrag->cycled) {
                /*
                 * we didn't fill our defrag batch, but
                 * we didn't start at zero.  Make sure we loop
                 * around to the start of the file.
                 */
                defrag->last_offset = 0;
                defrag->cycled = 1;
                btrfs_requeue_inode_defrag(inode, defrag);
        } else {
                kmem_cache_free(btrfs_inode_defrag_cachep, defrag);
        }

        iput(inode);
        return 0;
cleanup:
        srcu_read_unlock(&fs_info->subvol_srcu, index);
        kmem_cache_free(btrfs_inode_defrag_cachep, defrag);
        return ret;
}

/*
 * run through the list of inodes in the FS that need
 * defragging
 */
int btrfs_run_defrag_inodes(struct btrfs_fs_info *fs_info)
{
        struct inode_defrag *defrag;
        u64 first_ino = 0;
        u64 root_objectid = 0;

        atomic_inc(&fs_info->defrag_running);
        while (1) {
                /* Pause the auto defragger. */
                if (test_bit(BTRFS_FS_STATE_REMOUNTING,
                             &fs_info->fs_state))
                        break;

                if (!__need_auto_defrag(fs_info))
                        break;

                /* find an inode to defrag */
                defrag = btrfs_pick_defrag_inode(fs_info, root_objectid,
                                                 first_ino);
                if (!defrag) {
                        if (root_objectid || first_ino) {
                                root_objectid = 0;
                                first_ino = 0;
                                continue;
                        } else {
                                break;
                        }
                }

                first_ino = defrag->ino + 1;
                root_objectid = defrag->root;

                __btrfs_run_defrag_inode(fs_info, defrag);
        }
        atomic_dec(&fs_info->defrag_running);

        /*
         * during unmount, we use the transaction_wait queue to
         * wait for the defragger to stop
         */
        wake_up(&fs_info->transaction_wait);
        return 0;
}

/* simple helper to fault in pages and copy.  This should go away
 * and be replaced with calls into generic code.
 */
static noinline int btrfs_copy_from_user(loff_t pos, size_t write_bytes,
                                         struct page **prepared_pages,
                                         struct iov_iter *i)
{
        size_t copied = 0;
        size_t total_copied = 0;
        int pg = 0;
        int offset = pos & (PAGE_SIZE - 1);

        while (write_bytes > 0) {
                size_t count = min_t(size_t,
                                     PAGE_SIZE - offset, write_bytes);
                struct page *page = prepared_pages[pg];
                /*
                 * Copy data from userspace to the current page
                 */
                copied = iov_iter_copy_from_user_atomic(page, i, offset, count);

                /* Flush processor's dcache for this page */
                flush_dcache_page(page);

                /*
                 * if we get a partial write, we can end up with
                 * partially up to date pages.  These add
                 * a lot of complexity, so make sure they don't
                 * happen by forcing this copy to be retried.
                 *
                 * The rest of the btrfs_file_write code will fall
                 * back to page at a time copies after we return 0.
                 */
                if (!PageUptodate(page) && copied < count)
                        copied = 0;

                iov_iter_advance(i, copied);
                write_bytes -= copied;
                total_copied += copied;

                /* Return to btrfs_file_write_iter to fault page */
                if (unlikely(copied == 0))
                        break;

                if (copied < PAGE_SIZE - offset) {
                        offset += copied;
                } else {
                        pg++;
                        offset = 0;
                }
        }
        return total_copied;
}

/*
 * unlocks pages after btrfs_file_write is done with them
 */
static void btrfs_drop_pages(struct page **pages, size_t num_pages)
{
        size_t i;
        for (i = 0; i < num_pages; i++) {
                /* page checked is some magic around finding pages that
                 * have been modified without going through btrfs_set_page_dirty
                 * clear it here. There should be no need to mark the pages
                 * accessed as prepare_pages should have marked them accessed
                 * in prepare_pages via find_or_create_page()
                 */
                ClearPageChecked(pages[i]);
                unlock_page(pages[i]);
                put_page(pages[i]);
        }
}

/*
 * after copy_from_user, pages need to be dirtied and we need to make
 * sure holes are created between the current EOF and the start of
 * any next extents (if required).
 *
 * this also makes the decision about creating an inline extent vs
 * doing real data extents, marking pages dirty and delalloc as required.
 */
int btrfs_dirty_pages(struct inode *inode, struct page **pages,
                      size_t num_pages, loff_t pos, size_t write_bytes,
                      struct extent_state **cached)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        int err = 0;
        int i;
        u64 num_bytes;
        u64 start_pos;
        u64 end_of_last_block;
        u64 end_pos = pos + write_bytes;
        loff_t isize = i_size_read(inode);

        start_pos = pos & ~((u64) fs_info->sectorsize - 1);
        num_bytes = round_up(write_bytes + pos - start_pos,
                             fs_info->sectorsize);

        end_of_last_block = start_pos + num_bytes - 1;
        err = btrfs_set_extent_delalloc(inode, start_pos, end_of_last_block,
                                        cached, 0);
        if (err)
                return err;

        for (i = 0; i < num_pages; i++) {
                struct page *p = pages[i];
                SetPageUptodate(p);
                ClearPageChecked(p);
                set_page_dirty(p);
        }

        /*
         * we've only changed i_size in ram, and we haven't updated
         * the disk i_size.  There is no need to log the inode
         * at this time.
         */
        if (end_pos > isize)
                i_size_write(inode, end_pos);
        return 0;
}

/*
 * this drops all the extents in the cache that intersect the range
 * [start, end].  Existing extents are split as required.
 */
void btrfs_drop_extent_cache(struct inode *inode, u64 start, u64 end,
                             int skip_pinned)
{
        struct extent_map *em;
        struct extent_map *split = NULL;
        struct extent_map *split2 = NULL;
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        u64 len = end - start + 1;
        u64 gen;
        int ret;
        int testend = 1;
        unsigned long flags;
        int compressed = 0;
        bool modified;

        WARN_ON(end < start);
        if (end == (u64)-1) {
                len = (u64)-1;
                testend = 0;
        }
        while (1) {
                int no_splits = 0;

                modified = false;
                if (!split)
                        split = alloc_extent_map();
                if (!split2)
                        split2 = alloc_extent_map();
                if (!split || !split2)
                        no_splits = 1;

                write_lock(&em_tree->lock);
                em = lookup_extent_mapping(em_tree, start, len);
                if (!em) {
                        write_unlock(&em_tree->lock);
                        break;
                }
                flags = em->flags;
                gen = em->generation;
                if (skip_pinned && test_bit(EXTENT_FLAG_PINNED, &em->flags)) {
                        if (testend && em->start + em->len >= start + len) {
                                free_extent_map(em);
                                write_unlock(&em_tree->lock);
                                break;
                        }
                        start = em->start + em->len;
                        if (testend)
                                len = start + len - (em->start + em->len);
                        free_extent_map(em);
                        write_unlock(&em_tree->lock);
                        continue;
                }
                compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
                clear_bit(EXTENT_FLAG_PINNED, &em->flags);
                clear_bit(EXTENT_FLAG_LOGGING, &flags);
                modified = !list_empty(&em->list);
                if (no_splits)
                        goto next;

                if (em->start < start) {
                        split->start = em->start;
                        split->len = start - em->start;

                        if (em->block_start < EXTENT_MAP_LAST_BYTE) {
                                split->orig_start = em->orig_start;
                                split->block_start = em->block_start;

                                if (compressed)
                                        split->block_len = em->block_len;
                                else
                                        split->block_len = split->len;
                                split->orig_block_len = max(split->block_len,
                                                em->orig_block_len);
                                split->ram_bytes = em->ram_bytes;
                        } else {
                                split->orig_start = split->start;
                                split->block_len = 0;
                                split->block_start = em->block_start;
                                split->orig_block_len = 0;
                                split->ram_bytes = split->len;
                        }

                        split->generation = gen;
                        split->bdev = em->bdev;
                        split->flags = flags;
                        split->compress_type = em->compress_type;
                        replace_extent_mapping(em_tree, em, split, modified);
                        free_extent_map(split);
                        split = split2;
                        split2 = NULL;
                }
                if (testend && em->start + em->len > start + len) {
                        u64 diff = start + len - em->start;

                        split->start = start + len;
                        split->len = em->start + em->len - (start + len);
                        split->bdev = em->bdev;
                        split->flags = flags;
                        split->compress_type = em->compress_type;
                        split->generation = gen;

                        if (em->block_start < EXTENT_MAP_LAST_BYTE) {
                                split->orig_block_len = max(em->block_len,
                                                    em->orig_block_len);

                                split->ram_bytes = em->ram_bytes;
                                if (compressed) {
                                        split->block_len = em->block_len;
                                        split->block_start = em->block_start;
                                        split->orig_start = em->orig_start;
                                } else {
                                        split->block_len = split->len;
                                        split->block_start = em->block_start
                                                + diff;
                                        split->orig_start = em->orig_start;
                                }
                        } else {
                                split->ram_bytes = split->len;
                                split->orig_start = split->start;
                                split->block_len = 0;
                                split->block_start = em->block_start;
                                split->orig_block_len = 0;
                        }

                        if (extent_map_in_tree(em)) {
                                replace_extent_mapping(em_tree, em, split,
                                                       modified);
                        } else {
                                ret = add_extent_mapping(em_tree, split,
                                                         modified);
                                ASSERT(ret == 0); /* Logic error */
                        }
                        free_extent_map(split);
                        split = NULL;
                }
next:
                if (extent_map_in_tree(em))
                        remove_extent_mapping(em_tree, em);
                write_unlock(&em_tree->lock);

                /* once for us */
                free_extent_map(em);
                /* once for the tree*/
                free_extent_map(em);
        }
        if (split)
                free_extent_map(split);
        if (split2)
                free_extent_map(split2);
}

/*
 * this is very complex, but the basic idea is to drop all extents
 * in the range start - end.  hint_block is filled in with a block number
 * that would be a good hint to the block allocator for this file.
 *
 * If an extent intersects the range but is not entirely inside the range
 * it is either truncated or split.  Anything entirely inside the range
 * is deleted from the tree.
 */
int __btrfs_drop_extents(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root, struct inode *inode,
                         struct btrfs_path *path, u64 start, u64 end,
                         u64 *drop_end, int drop_cache,
                         int replace_extent,
                         u32 extent_item_size,
                         int *key_inserted)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct extent_buffer *leaf;
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;
        struct btrfs_key new_key;
        u64 ino = btrfs_ino(inode);
        u64 search_start = start;
        u64 disk_bytenr = 0;
        u64 num_bytes = 0;
        u64 extent_offset = 0;
        u64 extent_end = 0;
        u64 last_end = start;
        int del_nr = 0;
        int del_slot = 0;
        int extent_type;
        int recow;
        int ret;
        int modify_tree = -1;
        int update_refs;
        int found = 0;
        int leafs_visited = 0;

        if (drop_cache)
                btrfs_drop_extent_cache(inode, start, end - 1, 0);

        if (start >= BTRFS_I(inode)->disk_i_size && !replace_extent)
                modify_tree = 0;

        update_refs = (test_bit(BTRFS_ROOT_REF_COWS, &root->state) ||
                       root == fs_info->tree_root);
        while (1) {
                recow = 0;
                ret = btrfs_lookup_file_extent(trans, root, path, ino,
                                               search_start, modify_tree);
                if (ret < 0)
                        break;
                if (ret > 0 && path->slots[0] > 0 && search_start == start) {
                        leaf = path->nodes[0];
                        btrfs_item_key_to_cpu(leaf, &key, path->slots[0] - 1);
                        if (key.objectid == ino &&
                            key.type == BTRFS_EXTENT_DATA_KEY)
                                path->slots[0]--;
                }
                ret = 0;
                leafs_visited++;
next_slot:
                leaf = path->nodes[0];
                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        BUG_ON(del_nr > 0);
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                break;
                        if (ret > 0) {
                                ret = 0;
                                break;
                        }
                        leafs_visited++;
                        leaf = path->nodes[0];
                        recow = 1;
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

                if (key.objectid > ino)
                        break;
                if (WARN_ON_ONCE(key.objectid < ino) ||
                    key.type < BTRFS_EXTENT_DATA_KEY) {
                        ASSERT(del_nr == 0);
                        path->slots[0]++;
                        goto next_slot;
                }
                if (key.type > BTRFS_EXTENT_DATA_KEY || key.offset >= end)
                        break;

                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                extent_type = btrfs_file_extent_type(leaf, fi);

                if (extent_type == BTRFS_FILE_EXTENT_REG ||
                    extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
                        disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
                        num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
                        extent_offset = btrfs_file_extent_offset(leaf, fi);
                        extent_end = key.offset +
                                btrfs_file_extent_num_bytes(leaf, fi);
                } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                        extent_end = key.offset +
                                btrfs_file_extent_inline_len(leaf,
                                                     path->slots[0], fi);
                } else {
                        /* can't happen */
                        BUG();
                }

                /*
                 * Don't skip extent items representing 0 byte lengths. They
                 * used to be created (bug) if while punching holes we hit
                 * -ENOSPC condition. So if we find one here, just ensure we
                 * delete it, otherwise we would insert a new file extent item
                 * with the same key (offset) as that 0 bytes length file
                 * extent item in the call to setup_items_for_insert() later
                 * in this function.
                 */
                if (extent_end == key.offset && extent_end >= search_start) {
                        last_end = extent_end;
                        goto delete_extent_item;
                }

                if (extent_end <= search_start) {
                        path->slots[0]++;
                        goto next_slot;
                }

                found = 1;
                search_start = max(key.offset, start);
                if (recow || !modify_tree) {
                        modify_tree = -1;
                        btrfs_release_path(path);
                        continue;
                }

                /*
                 *     | - range to drop - |
                 *  | -------- extent -------- |
                 */
                if (start > key.offset && end < extent_end) {
                        BUG_ON(del_nr > 0);
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        memcpy(&new_key, &key, sizeof(new_key));
                        new_key.offset = start;
                        ret = btrfs_duplicate_item(trans, root, path,
                                                   &new_key);
                        if (ret == -EAGAIN) {
                                btrfs_release_path(path);
                                continue;
                        }
                        if (ret < 0)
                                break;

                        leaf = path->nodes[0];
                        fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        start - key.offset);

                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);

                        extent_offset += start - key.offset;
                        btrfs_set_file_extent_offset(leaf, fi, extent_offset);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - start);
                        btrfs_mark_buffer_dirty(leaf);

                        if (update_refs && disk_bytenr > 0) {
                                ret = btrfs_inc_extent_ref(trans, fs_info,
                                                disk_bytenr, num_bytes, 0,
                                                root->root_key.objectid,
                                                new_key.objectid,
                                                start - extent_offset);
                                BUG_ON(ret); /* -ENOMEM */
                        }
                        key.offset = start;
                }
                /*
                 * From here on out we will have actually dropped something, so
                 * last_end can be updated.
                 */
                last_end = extent_end;

                /*
                 *  | ---- range to drop ----- |
                 *      | -------- extent -------- |
                 */
                if (start <= key.offset && end < extent_end) {
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        memcpy(&new_key, &key, sizeof(new_key));
                        new_key.offset = end;
                        btrfs_set_item_key_safe(fs_info, path, &new_key);

                        extent_offset += end - key.offset;
                        btrfs_set_file_extent_offset(leaf, fi, extent_offset);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - end);
                        btrfs_mark_buffer_dirty(leaf);
                        if (update_refs && disk_bytenr > 0)
                                inode_sub_bytes(inode, end - key.offset);
                        break;
                }

                search_start = extent_end;
                /*
                 *       | ---- range to drop ----- |
                 *  | -------- extent -------- |
                 */
                if (start > key.offset && end >= extent_end) {
                        BUG_ON(del_nr > 0);
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        start - key.offset);
                        btrfs_mark_buffer_dirty(leaf);
                        if (update_refs && disk_bytenr > 0)
                                inode_sub_bytes(inode, extent_end - start);
                        if (end == extent_end)
                                break;

                        path->slots[0]++;
                        goto next_slot;
                }

                /*
                 *  | ---- range to drop ----- |
                 *    | ------ extent ------ |
                 */
                if (start <= key.offset && end >= extent_end) {
delete_extent_item:
                        if (del_nr == 0) {
                                del_slot = path->slots[0];
                                del_nr = 1;
                        } else {
                                BUG_ON(del_slot + del_nr != path->slots[0]);
                                del_nr++;
                        }

                        if (update_refs &&
                            extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                inode_sub_bytes(inode,
                                                extent_end - key.offset);
                                extent_end = ALIGN(extent_end,
                                                   fs_info->sectorsize);
                        } else if (update_refs && disk_bytenr > 0) {
                                ret = btrfs_free_extent(trans, fs_info,
                                                disk_bytenr, num_bytes, 0,
                                                root->root_key.objectid,
                                                key.objectid, key.offset -
                                                extent_offset);
                                BUG_ON(ret); /* -ENOMEM */
                                inode_sub_bytes(inode,
                                                extent_end - key.offset);
                        }

                        if (end == extent_end)
                                break;

                        if (path->slots[0] + 1 < btrfs_header_nritems(leaf)) {
                                path->slots[0]++;
                                goto next_slot;
                        }

                        ret = btrfs_del_items(trans, root, path, del_slot,
                                              del_nr);
                        if (ret) {
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }

                        del_nr = 0;
                        del_slot = 0;

                        btrfs_release_path(path);
                        continue;
                }

                BUG_ON(1);
        }

        if (!ret && del_nr > 0) {
                /*
                 * Set path->slots[0] to first slot, so that after the delete
                 * if items are move off from our leaf to its immediate left or
                 * right neighbor leafs, we end up with a correct and adjusted
                 * path->slots[0] for our insertion (if replace_extent != 0).
                 */
                path->slots[0] = del_slot;
                ret = btrfs_del_items(trans, root, path, del_slot, del_nr);
                if (ret)
                        btrfs_abort_transaction(trans, ret);
        }

        leaf = path->nodes[0];
        /*
         * If btrfs_del_items() was called, it might have deleted a leaf, in
         * which case it unlocked our path, so check path->locks[0] matches a
         * write lock.
         */
        if (!ret && replace_extent && leafs_visited == 1 &&
            (path->locks[0] == BTRFS_WRITE_LOCK_BLOCKING ||
             path->locks[0] == BTRFS_WRITE_LOCK) &&
            btrfs_leaf_free_space(fs_info, leaf) >=
            sizeof(struct btrfs_item) + extent_item_size) {

                key.objectid = ino;
                key.type = BTRFS_EXTENT_DATA_KEY;
                key.offset = start;
                if (!del_nr && path->slots[0] < btrfs_header_nritems(leaf)) {
                        struct btrfs_key slot_key;

                        btrfs_item_key_to_cpu(leaf, &slot_key, path->slots[0]);
                        if (btrfs_comp_cpu_keys(&key, &slot_key) > 0)
                                path->slots[0]++;
                }
                setup_items_for_insert(root, path, &key,
                                       &extent_item_size,
                                       extent_item_size,
                                       sizeof(struct btrfs_item) +
                                       extent_item_size, 1);
                *key_inserted = 1;
        }

        if (!replace_extent || !(*key_inserted))
                btrfs_release_path(path);
        if (drop_end)
                *drop_end = found ? min(end, last_end) : end;
        return ret;
}

int btrfs_drop_extents(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct inode *inode, u64 start,
                       u64 end, int drop_cache)
{
        struct btrfs_path *path;
        int ret;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        ret = __btrfs_drop_extents(trans, root, inode, path, start, end, NULL,
                                   drop_cache, 0, 0, NULL);
        btrfs_free_path(path);
        return ret;
}

static int extent_mergeable(struct extent_buffer *leaf, int slot,
                            u64 objectid, u64 bytenr, u64 orig_offset,
                            u64 *start, u64 *end)
{
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;
        u64 extent_end;

        if (slot < 0 || slot >= btrfs_header_nritems(leaf))
                return 0;

        btrfs_item_key_to_cpu(leaf, &key, slot);
        if (key.objectid != objectid || key.type != BTRFS_EXTENT_DATA_KEY)
                return 0;

        fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
        if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG ||
            btrfs_file_extent_disk_bytenr(leaf, fi) != bytenr ||
            btrfs_file_extent_offset(leaf, fi) != key.offset - orig_offset ||
            btrfs_file_extent_compression(leaf, fi) ||
            btrfs_file_extent_encryption(leaf, fi) ||
            btrfs_file_extent_other_encoding(leaf, fi))
                return 0;

        extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
        if ((*start && *start != key.offset) || (*end && *end != extent_end))
                return 0;

        *start = key.offset;
        *end = extent_end;
        return 1;
}

/*
 * Mark extent in the range start - end as written.
 *
 * This changes extent type from 'pre-allocated' to 'regular'. If only
 * part of extent is marked as written, the extent will be split into
 * two or three.
 */
int btrfs_mark_extent_written(struct btrfs_trans_handle *trans,
                              struct inode *inode, u64 start, u64 end)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_buffer *leaf;
        struct btrfs_path *path;
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;
        struct btrfs_key new_key;
        u64 bytenr;
        u64 num_bytes;
        u64 extent_end;
        u64 orig_offset;
        u64 other_start;
        u64 other_end;
        u64 split;
        int del_nr = 0;
        int del_slot = 0;
        int recow;
        int ret;
        u64 ino = btrfs_ino(inode);

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
again:
        recow = 0;
        split = start;
        key.objectid = ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = split;

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret < 0)
                goto out;
        if (ret > 0 && path->slots[0] > 0)
                path->slots[0]--;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (key.objectid != ino ||
            key.type != BTRFS_EXTENT_DATA_KEY) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }
        fi = btrfs_item_ptr(leaf, path->slots[0],
                            struct btrfs_file_extent_item);
        if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_PREALLOC) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }
        extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
        if (key.offset > start || extent_end < end) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

        bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
        num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
        orig_offset = key.offset - btrfs_file_extent_offset(leaf, fi);
        memcpy(&new_key, &key, sizeof(new_key));

        if (start == key.offset && end < extent_end) {
                other_start = 0;
                other_end = start;
                if (extent_mergeable(leaf, path->slots[0] - 1,
                                     ino, bytenr, orig_offset,
                                     &other_start, &other_end)) {
                        new_key.offset = end;
                        btrfs_set_item_key_safe(fs_info, path, &new_key);
                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - end);
                        btrfs_set_file_extent_offset(leaf, fi,
                                                     end - orig_offset);
                        fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        end - other_start);
                        btrfs_mark_buffer_dirty(leaf);
                        goto out;
                }
        }

        if (start > key.offset && end == extent_end) {
                other_start = end;
                other_end = 0;
                if (extent_mergeable(leaf, path->slots[0] + 1,
                                     ino, bytenr, orig_offset,
                                     &other_start, &other_end)) {
                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        start - key.offset);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        path->slots[0]++;
                        new_key.offset = start;
                        btrfs_set_item_key_safe(fs_info, path, &new_key);

                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        other_end - start);
                        btrfs_set_file_extent_offset(leaf, fi,
                                                     start - orig_offset);
                        btrfs_mark_buffer_dirty(leaf);
                        goto out;
                }
        }

        while (start > key.offset || end < extent_end) {
                if (key.offset == start)
                        split = end;

                new_key.offset = split;
                ret = btrfs_duplicate_item(trans, root, path, &new_key);
                if (ret == -EAGAIN) {
                        btrfs_release_path(path);
                        goto again;
                }
                if (ret < 0) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                leaf = path->nodes[0];
                fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                    struct btrfs_file_extent_item);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                split - key.offset);

                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);

                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_offset(leaf, fi, split - orig_offset);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                extent_end - split);
                btrfs_mark_buffer_dirty(leaf);

                ret = btrfs_inc_extent_ref(trans, fs_info, bytenr, num_bytes,
                                           0, root->root_key.objectid,
                                           ino, orig_offset);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                if (split == start) {
                        key.offset = start;
                } else {
                        if (start != key.offset) {
                                ret = -EINVAL;
                                btrfs_abort_transaction(trans, ret);
                                goto out;
                        }
                        path->slots[0]--;
                        extent_end = end;
                }
                recow = 1;
        }

        other_start = end;
        other_end = 0;
        if (extent_mergeable(leaf, path->slots[0] + 1,
                             ino, bytenr, orig_offset,
                             &other_start, &other_end)) {
                if (recow) {
                        btrfs_release_path(path);
                        goto again;
                }
                extent_end = other_end;
                del_slot = path->slots[0] + 1;
                del_nr++;
                ret = btrfs_free_extent(trans, fs_info, bytenr, num_bytes,
                                        0, root->root_key.objectid,
                                        ino, orig_offset);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        }
        other_start = 0;
        other_end = start;
        if (extent_mergeable(leaf, path->slots[0] - 1,
                             ino, bytenr, orig_offset,
                             &other_start, &other_end)) {
                if (recow) {
                        btrfs_release_path(path);
                        goto again;
                }
                key.offset = other_start;
                del_slot = path->slots[0];
                del_nr++;
                ret = btrfs_free_extent(trans, fs_info, bytenr, num_bytes,
                                        0, root->root_key.objectid,
                                        ino, orig_offset);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        }
        if (del_nr == 0) {
                fi = btrfs_item_ptr(leaf, path->slots[0],
                           struct btrfs_file_extent_item);
                btrfs_set_file_extent_type(leaf, fi,
                                           BTRFS_FILE_EXTENT_REG);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_mark_buffer_dirty(leaf);
        } else {
                fi = btrfs_item_ptr(leaf, del_slot - 1,
                           struct btrfs_file_extent_item);
                btrfs_set_file_extent_type(leaf, fi,
                                           BTRFS_FILE_EXTENT_REG);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                extent_end - key.offset);
                btrfs_mark_buffer_dirty(leaf);

                ret = btrfs_del_items(trans, root, path, del_slot, del_nr);
                if (ret < 0) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        }
out:
        btrfs_free_path(path);
        return 0;
}

/*
 * on error we return an unlocked page and the error value
 * on success we return a locked page and 0
 */
static int prepare_uptodate_page(struct inode *inode,
                                 struct page *page, u64 pos,
                                 bool force_uptodate)
{
        int ret = 0;

        if (((pos & (PAGE_SIZE - 1)) || force_uptodate) &&
            !PageUptodate(page)) {
                ret = btrfs_readpage(NULL, page);
                if (ret)
                        return ret;
                lock_page(page);
                if (!PageUptodate(page)) {
                        unlock_page(page);
                        return -EIO;
                }
                if (page->mapping != inode->i_mapping) {
                        unlock_page(page);
                        return -EAGAIN;
                }
        }
        return 0;
}

/*
 * this just gets pages into the page cache and locks them down.
 */
static noinline int prepare_pages(struct inode *inode, struct page **pages,
                                  size_t num_pages, loff_t pos,
                                  size_t write_bytes, bool force_uptodate)
{
        int i;
        unsigned long index = pos >> PAGE_SHIFT;
        gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
        int err = 0;
        int faili;

        for (i = 0; i < num_pages; i++) {
again:
                pages[i] = find_or_create_page(inode->i_mapping, index + i,
                                               mask | __GFP_WRITE);
                if (!pages[i]) {
                        faili = i - 1;
                        err = -ENOMEM;
                        goto fail;
                }

                if (i == 0)
                        err = prepare_uptodate_page(inode, pages[i], pos,
                                                    force_uptodate);
                if (!err && i == num_pages - 1)
                        err = prepare_uptodate_page(inode, pages[i],
                                                    pos + write_bytes, false);
                if (err) {
                        put_page(pages[i]);
                        if (err == -EAGAIN) {
                                err = 0;
                                goto again;
                        }
                        faili = i - 1;
                        goto fail;
                }
                wait_on_page_writeback(pages[i]);
        }

        return 0;
fail:
        while (faili >= 0) {
                unlock_page(pages[faili]);
                put_page(pages[faili]);
                faili--;
        }
        return err;

}

/*
 * This function locks the extent and properly waits for data=ordered extents
 * to finish before allowing the pages to be modified if need.
 *
 * The return value:
 * 1 - the extent is locked
 * 0 - the extent is not locked, and everything is OK
 * -EAGAIN - need re-prepare the pages
 * the other < 0 number - Something wrong happens
 */
static noinline int
lock_and_cleanup_extent_if_need(struct inode *inode, struct page **pages,
                                size_t num_pages, loff_t pos,
                                size_t write_bytes,
                                u64 *lockstart, u64 *lockend,
                                struct extent_state **cached_state)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        u64 start_pos;
        u64 last_pos;
        int i;
        int ret = 0;

        start_pos = round_down(pos, fs_info->sectorsize);
        last_pos = start_pos
                + round_up(pos + write_bytes - start_pos,
                           fs_info->sectorsize) - 1;

        if (start_pos < inode->i_size) {
                struct btrfs_ordered_extent *ordered;
                lock_extent_bits(&BTRFS_I(inode)->io_tree,
                                 start_pos, last_pos, cached_state);
                ordered = btrfs_lookup_ordered_range(inode, start_pos,
                                                     last_pos - start_pos + 1);
                if (ordered &&
                    ordered->file_offset + ordered->len > start_pos &&
                    ordered->file_offset <= last_pos) {
                        unlock_extent_cached(&BTRFS_I(inode)->io_tree,
                                             start_pos, last_pos,
                                             cached_state, GFP_NOFS);
                        for (i = 0; i < num_pages; i++) {
                                unlock_page(pages[i]);
                                put_page(pages[i]);
                        }
                        btrfs_start_ordered_extent(inode, ordered, 1);
                        btrfs_put_ordered_extent(ordered);
                        return -EAGAIN;
                }
                if (ordered)
                        btrfs_put_ordered_extent(ordered);

                clear_extent_bit(&BTRFS_I(inode)->io_tree, start_pos,
                                  last_pos, EXTENT_DIRTY | EXTENT_DELALLOC |
                                  EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG,
                                  0, 0, cached_state, GFP_NOFS);
                *lockstart = start_pos;
                *lockend = last_pos;
                ret = 1;
        }

        for (i = 0; i < num_pages; i++) {
                if (clear_page_dirty_for_io(pages[i]))
                        account_page_redirty(pages[i]);
                set_page_extent_mapped(pages[i]);
                WARN_ON(!PageLocked(pages[i]));
        }

        return ret;
}

static noinline int check_can_nocow(struct inode *inode, loff_t pos,
                                    size_t *write_bytes)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_ordered_extent *ordered;
        u64 lockstart, lockend;
        u64 num_bytes;
        int ret;

        ret = btrfs_start_write_no_snapshoting(root);
        if (!ret)
                return -ENOSPC;

        lockstart = round_down(pos, fs_info->sectorsize);
        lockend = round_up(pos + *write_bytes,
                           fs_info->sectorsize) - 1;

        while (1) {
                lock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend);
                ordered = btrfs_lookup_ordered_range(inode, lockstart,
                                                     lockend - lockstart + 1);
                if (!ordered) {
                        break;
                }
                unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend);
                btrfs_start_ordered_extent(inode, ordered, 1);
                btrfs_put_ordered_extent(ordered);
        }

        num_bytes = lockend - lockstart + 1;
        ret = can_nocow_extent(inode, lockstart, &num_bytes, NULL, NULL, NULL);
        if (ret <= 0) {
                ret = 0;
                btrfs_end_write_no_snapshoting(root);
        } else {
                *write_bytes = min_t(size_t, *write_bytes ,
                                     num_bytes - pos + lockstart);
        }

        unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend);

        return ret;
}

static noinline ssize_t __btrfs_buffered_write(struct file *file,
                                               struct iov_iter *i,
                                               loff_t pos)
{
        struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct page **pages = NULL;
        struct extent_state *cached_state = NULL;
        u64 release_bytes = 0;
        u64 lockstart;
        u64 lockend;
        size_t num_written = 0;
        int nrptrs;
        int ret = 0;
        bool only_release_metadata = false;
        bool force_page_uptodate = false;
        bool need_unlock;

        nrptrs = min(DIV_ROUND_UP(iov_iter_count(i), PAGE_SIZE),
                        PAGE_SIZE / (sizeof(struct page *)));
        nrptrs = min(nrptrs, current->nr_dirtied_pause - current->nr_dirtied);
        nrptrs = max(nrptrs, 8);
        pages = kmalloc_array(nrptrs, sizeof(struct page *), GFP_KERNEL);
        if (!pages)
                return -ENOMEM;

        while (iov_iter_count(i) > 0) {
                size_t offset = pos & (PAGE_SIZE - 1);
                size_t sector_offset;
                size_t write_bytes = min(iov_iter_count(i),
                                         nrptrs * (size_t)PAGE_SIZE -
                                         offset);
                size_t num_pages = DIV_ROUND_UP(write_bytes + offset,
                                                PAGE_SIZE);
                size_t reserve_bytes;
                size_t dirty_pages;
                size_t copied;
                size_t dirty_sectors;
                size_t num_sectors;

                WARN_ON(num_pages > nrptrs);

                /*
                 * Fault pages before locking them in prepare_pages
                 * to avoid recursive lock
                 */
                if (unlikely(iov_iter_fault_in_readable(i, write_bytes))) {
                        ret = -EFAULT;
                        break;
                }

                sector_offset = pos & (fs_info->sectorsize - 1);
                reserve_bytes = round_up(write_bytes + sector_offset,
                                fs_info->sectorsize);

                ret = btrfs_check_data_free_space(inode, pos, write_bytes);
                if (ret < 0) {
                        if ((BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW |
                                                      BTRFS_INODE_PREALLOC)) &&
                            check_can_nocow(inode, pos, &write_bytes) > 0) {
                                /*
                                 * For nodata cow case, no need to reserve
                                 * data space.
                                 */
                                only_release_metadata = true;
                                /*
                                 * our prealloc extent may be smaller than
                                 * write_bytes, so scale down.
                                 */
                                num_pages = DIV_ROUND_UP(write_bytes + offset,
                                                         PAGE_SIZE);
                                reserve_bytes = round_up(write_bytes +
                                                         sector_offset,
                                                         fs_info->sectorsize);
                        } else {
                                break;
                        }
                }

                ret = btrfs_delalloc_reserve_metadata(inode, reserve_bytes);
                if (ret) {
                        if (!only_release_metadata)
                                btrfs_free_reserved_data_space(inode, pos,
                                                               write_bytes);
                        else
                                btrfs_end_write_no_snapshoting(root);
                        break;
                }

                release_bytes = reserve_bytes;
                need_unlock = false;
again:
                /*
                 * This is going to setup the pages array with the number of
                 * pages we want, so we don't really need to worry about the
                 * contents of pages from loop to loop
                 */
                ret = prepare_pages(inode, pages, num_pages,
                                    pos, write_bytes,
                                    force_page_uptodate);
                if (ret)
                        break;

                ret = lock_and_cleanup_extent_if_need(inode, pages, num_pages,
                                                pos, write_bytes, &lockstart,
                                                &lockend, &cached_state);
                if (ret < 0) {
                        if (ret == -EAGAIN)
                                goto again;
                        break;
                } else if (ret > 0) {
                        need_unlock = true;
                        ret = 0;
                }

                copied = btrfs_copy_from_user(pos, write_bytes, pages, i);

                num_sectors = BTRFS_BYTES_TO_BLKS(fs_info, reserve_bytes);
                dirty_sectors = round_up(copied + sector_offset,
                                        fs_info->sectorsize);
                dirty_sectors = BTRFS_BYTES_TO_BLKS(fs_info, dirty_sectors);

                /*
                 * if we have trouble faulting in the pages, fall
                 * back to one page at a time
                 */
                if (copied < write_bytes)
                        nrptrs = 1;

                if (copied == 0) {
                        force_page_uptodate = true;
                        dirty_sectors = 0;
                        dirty_pages = 0;
                } else {
                        force_page_uptodate = false;
                        dirty_pages = DIV_ROUND_UP(copied + offset,
                                                   PAGE_SIZE);
                }

                /*
                 * If we had a short copy we need to release the excess delaloc
                 * bytes we reserved.  We need to increment outstanding_extents
                 * because btrfs_delalloc_release_space and
                 * btrfs_delalloc_release_metadata will decrement it, but
                 * we still have an outstanding extent for the chunk we actually
                 * managed to copy.
                 */
                if (num_sectors > dirty_sectors) {
                        /* release everything except the sectors we dirtied */
                        release_bytes -= dirty_sectors <<
                                                fs_info->sb->s_blocksize_bits;
                        if (copied > 0) {
                                spin_lock(&BTRFS_I(inode)->lock);
                                BTRFS_I(inode)->outstanding_extents++;
                                spin_unlock(&BTRFS_I(inode)->lock);
                        }
                        if (only_release_metadata) {
                                btrfs_delalloc_release_metadata(inode,
                                                                release_bytes);
                        } else {
                                u64 __pos;

                                __pos = round_down(pos,
                                                   fs_info->sectorsize) +
                                        (dirty_pages << PAGE_SHIFT);
                                btrfs_delalloc_release_space(inode, __pos,
                                                             release_bytes);
                        }
                }

                release_bytes = round_up(copied + sector_offset,
                                        fs_info->sectorsize);

                if (copied > 0)
                        ret = btrfs_dirty_pages(inode, pages, dirty_pages,
                                                pos, copied, NULL);
                if (need_unlock)
                        unlock_extent_cached(&BTRFS_I(inode)->io_tree,
                                             lockstart, lockend, &cached_state,
                                             GFP_NOFS);
                if (ret) {
                        btrfs_drop_pages(pages, num_pages);
                        break;
                }

                release_bytes = 0;
                if (only_release_metadata)
                        btrfs_end_write_no_snapshoting(root);

                if (only_release_metadata && copied > 0) {
                        lockstart = round_down(pos,
                                               fs_info->sectorsize);
                        lockend = round_up(pos + copied,
                                           fs_info->sectorsize) - 1;

                        set_extent_bit(&BTRFS_I(inode)->io_tree, lockstart,
                                       lockend, EXTENT_NORESERVE, NULL,
                                       NULL, GFP_NOFS);
                        only_release_metadata = false;
                }

                btrfs_drop_pages(pages, num_pages);

                cond_resched();

                balance_dirty_pages_ratelimited(inode->i_mapping);
                if (dirty_pages < (fs_info->nodesize >> PAGE_SHIFT) + 1)
                        btrfs_btree_balance_dirty(fs_info);

                pos += copied;
                num_written += copied;
        }

        kfree(pages);

        if (release_bytes) {
                if (only_release_metadata) {
                        btrfs_end_write_no_snapshoting(root);
                        btrfs_delalloc_release_metadata(inode, release_bytes);
                } else {
                        btrfs_delalloc_release_space(inode,
                                                round_down(pos, fs_info->sectorsize),
                                                release_bytes);
                }
        }

        return num_written ? num_written : ret;
}

static ssize_t __btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        loff_t pos = iocb->ki_pos;
        ssize_t written;
        ssize_t written_buffered;
        loff_t endbyte;
        int err;

        written = generic_file_direct_write(iocb, from);

        if (written < 0 || !iov_iter_count(from))
                return written;

        pos += written;
        written_buffered = __btrfs_buffered_write(file, from, pos);
        if (written_buffered < 0) {
                err = written_buffered;
                goto out;
        }
        /*
         * Ensure all data is persisted. We want the next direct IO read to be
         * able to read what was just written.
         */
        endbyte = pos + written_buffered - 1;
        err = btrfs_fdatawrite_range(inode, pos, endbyte);
        if (err)
                goto out;
        err = filemap_fdatawait_range(inode->i_mapping, pos, endbyte);
        if (err)
                goto out;
        written += written_buffered;
        iocb->ki_pos = pos + written_buffered;
        invalidate_mapping_pages(file->f_mapping, pos >> PAGE_SHIFT,
                                 endbyte >> PAGE_SHIFT);
out:
        return written ? written : err;
}

static void update_time_for_write(struct inode *inode)
{
        struct timespec now;

        if (IS_NOCMTIME(inode))
                return;

        now = current_time(inode);
        if (!timespec_equal(&inode->i_mtime, &now))
                inode->i_mtime = now;

        if (!timespec_equal(&inode->i_ctime, &now))
                inode->i_ctime = now;

        if (IS_I_VERSION(inode))
                inode_inc_iversion(inode);
}

static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
                                    struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        u64 start_pos;
        u64 end_pos;
        ssize_t num_written = 0;
        bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
        ssize_t err;
        loff_t pos;
        size_t count;
        loff_t oldsize;
        int clean_page = 0;

        inode_lock(inode);
        err = generic_write_checks(iocb, from);
        if (err <= 0) {
                inode_unlock(inode);
                return err;
        }

        current->backing_dev_info = inode_to_bdi(inode);
        err = file_remove_privs(file);
        if (err) {
                inode_unlock(inode);
                goto out;
        }

        /*
         * If BTRFS flips readonly due to some impossible error
         * (fs_info->fs_state now has BTRFS_SUPER_FLAG_ERROR),
         * although we have opened a file as writable, we have
         * to stop this write operation to ensure FS consistency.
         */
        if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
                inode_unlock(inode);
                err = -EROFS;
                goto out;
        }

        /*
         * We reserve space for updating the inode when we reserve space for the
         * extent we are going to write, so we will enospc out there.  We don't
         * need to start yet another transaction to update the inode as we will
         * update the inode when we finish writing whatever data we write.
         */
        update_time_for_write(inode);

        pos = iocb->ki_pos;
        count = iov_iter_count(from);
        start_pos = round_down(pos, fs_info->sectorsize);
        oldsize = i_size_read(inode);
        if (start_pos > oldsize) {
                /* Expand hole size to cover write data, preventing empty gap */
                end_pos = round_up(pos + count,
                                   fs_info->sectorsize);
                err = btrfs_cont_expand(inode, oldsize, end_pos);
                if (err) {
                        inode_unlock(inode);
                        goto out;
                }
                if (start_pos > round_up(oldsize, fs_info->sectorsize))
                        clean_page = 1;
        }

        if (sync)
                atomic_inc(&BTRFS_I(inode)->sync_writers);

        if (iocb->ki_flags & IOCB_DIRECT) {
                num_written = __btrfs_direct_write(iocb, from);
        } else {
                num_written = __btrfs_buffered_write(file, from, pos);
                if (num_written > 0)
                        iocb->ki_pos = pos + num_written;
                if (clean_page)
                        pagecache_isize_extended(inode, oldsize,
                                                i_size_read(inode));
        }

        inode_unlock(inode);

        /*
         * We also have to set last_sub_trans to the current log transid,
         * otherwise subsequent syncs to a file that's been synced in this
         * transaction will appear to have already occurred.
         */
        spin_lock(&BTRFS_I(inode)->lock);
        BTRFS_I(inode)->last_sub_trans = root->log_transid;
        spin_unlock(&BTRFS_I(inode)->lock);
        if (num_written > 0)
                num_written = generic_write_sync(iocb, num_written);

        if (sync)
                atomic_dec(&BTRFS_I(inode)->sync_writers);
out:
        current->backing_dev_info = NULL;
        return num_written ? num_written : err;
}

int btrfs_release_file(struct inode *inode, struct file *filp)
{
        if (filp->private_data)
                btrfs_ioctl_trans_end(filp);
        /*
         * ordered_data_close is set by settattr when we are about to truncate
         * a file from a non-zero size to a zero size.  This tries to
         * flush down new bytes that may have been written if the
         * application were using truncate to replace a file in place.
         */
        if (test_and_clear_bit(BTRFS_INODE_ORDERED_DATA_CLOSE,
                               &BTRFS_I(inode)->runtime_flags))
                        filemap_flush(inode->i_mapping);
        return 0;
}

static int start_ordered_ops(struct inode *inode, loff_t start, loff_t end)
{
        int ret;

        atomic_inc(&BTRFS_I(inode)->sync_writers);
        ret = btrfs_fdatawrite_range(inode, start, end);
        atomic_dec(&BTRFS_I(inode)->sync_writers);

        return ret;
}

/*
 * fsync call for both files and directories.  This logs the inode into
 * the tree log instead of forcing full commits whenever possible.
 *
 * It needs to call filemap_fdatawait so that all ordered extent updates are
 * in the metadata btree are up to date for copying to the log.
 *
 * It drops the inode mutex before doing the tree log commit.  This is an
 * important optimization for directories because holding the mutex prevents
 * new operations on the dir while we write to disk.
 */
int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
{
        struct dentry *dentry = file_dentry(file);
        struct inode *inode = d_inode(dentry);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_trans_handle *trans;
        struct btrfs_log_ctx ctx;
        int ret = 0;
        bool full_sync = 0;
        u64 len;

        /*
         * The range length can be represented by u64, we have to do the typecasts
         * to avoid signed overflow if it's [0, LLONG_MAX] eg. from fsync()
         */
        len = (u64)end - (u64)start + 1;
        trace_btrfs_sync_file(file, datasync);

        /*
         * We write the dirty pages in the range and wait until they complete
         * out of the ->i_mutex. If so, we can flush the dirty pages by
         * multi-task, and make the performance up.  See
         * btrfs_wait_ordered_range for an explanation of the ASYNC check.
         */
        ret = start_ordered_ops(inode, start, end);
        if (ret)
                return ret;

        inode_lock(inode);
        atomic_inc(&root->log_batch);
        full_sync = test_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
                             &BTRFS_I(inode)->runtime_flags);
        /*
         * We might have have had more pages made dirty after calling
         * start_ordered_ops and before acquiring the inode's i_mutex.
         */
        if (full_sync) {
                /*
                 * For a full sync, we need to make sure any ordered operations
                 * start and finish before we start logging the inode, so that
                 * all extents are persisted and the respective file extent
                 * items are in the fs/subvol btree.
                 */
                ret = btrfs_wait_ordered_range(inode, start, len);
        } else {
                /*
                 * Start any new ordered operations before starting to log the
                 * inode. We will wait for them to finish in btrfs_sync_log().
                 *
                 * Right before acquiring the inode's mutex, we might have new
                 * writes dirtying pages, which won't immediately start the
                 * respective ordered operations - that is done through the
                 * fill_delalloc callbacks invoked from the writepage and
                 * writepages address space operations. So make sure we start
                 * all ordered operations before starting to log our inode. Not
                 * doing this means that while logging the inode, writeback
                 * could start and invoke writepage/writepages, which would call
                 * the fill_delalloc callbacks (cow_file_range,
                 * submit_compressed_extents). These callbacks add first an
                 * extent map to the modified list of extents and then create
                 * the respective ordered operation, which means in
                 * tree-log.c:btrfs_log_inode() we might capture all existing
                 * ordered operations (with btrfs_get_logged_extents()) before
                 * the fill_delalloc callback adds its ordered operation, and by
                 * the time we visit the modified list of extent maps (with
                 * btrfs_log_changed_extents()), we see and process the extent
                 * map they created. We then use the extent map to construct a
                 * file extent item for logging without waiting for the
                 * respective ordered operation to finish - this file extent
                 * item points to a disk location that might not have yet been
                 * written to, containing random data - so after a crash a log
                 * replay will make our inode have file extent items that point
                 * to disk locations containing invalid data, as we returned
                 * success to userspace without waiting for the respective
                 * ordered operation to finish, because it wasn't captured by
                 * btrfs_get_logged_extents().
                 */
                ret = start_ordered_ops(inode, start, end);
        }
        if (ret) {
                inode_unlock(inode);
                goto out;
        }
        atomic_inc(&root->log_batch);

        /*
         * If the last transaction that changed this file was before the current
         * transaction and we have the full sync flag set in our inode, we can
         * bail out now without any syncing.
         *
         * Note that we can't bail out if the full sync flag isn't set. This is
         * because when the full sync flag is set we start all ordered extents
         * and wait for them to fully complete - when they complete they update
         * the inode's last_trans field through:
         *
         *     btrfs_finish_ordered_io() ->
         *         btrfs_update_inode_fallback() ->
         *             btrfs_update_inode() ->
         *                 btrfs_set_inode_last_trans()
         *
         * So we are sure that last_trans is up to date and can do this check to
         * bail out safely. For the fast path, when the full sync flag is not
         * set in our inode, we can not do it because we start only our ordered
         * extents and don't wait for them to complete (that is when
         * btrfs_finish_ordered_io runs), so here at this point their last_trans
         * value might be less than or equals to fs_info->last_trans_committed,
         * and setting a speculative last_trans for an inode when a buffered
         * write is made (such as fs_info->generation + 1 for example) would not
         * be reliable since after setting the value and before fsync is called
         * any number of transactions can start and commit (transaction kthread
         * commits the current transaction periodically), and a transaction
         * commit does not start nor waits for ordered extents to complete.
         */
        smp_mb();
        if (btrfs_inode_in_log(inode, fs_info->generation) ||
            (full_sync && BTRFS_I(inode)->last_trans <=
             fs_info->last_trans_committed) ||
            (!btrfs_have_ordered_extents_in_range(inode, start, len) &&
             BTRFS_I(inode)->last_trans
             <= fs_info->last_trans_committed)) {
                /*
                 * We've had everything committed since the last time we were
                 * modified so clear this flag in case it was set for whatever
                 * reason, it's no longer relevant.
                 */
                clear_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
                          &BTRFS_I(inode)->runtime_flags);
                /*
                 * An ordered extent might have started before and completed
                 * already with io errors, in which case the inode was not
                 * updated and we end up here. So check the inode's mapping
                 * flags for any errors that might have happened while doing
                 * writeback of file data.
                 */
                ret = filemap_check_errors(inode->i_mapping);
                inode_unlock(inode);
                goto out;
        }

        /*
         * ok we haven't committed the transaction yet, lets do a commit
         */
        if (file->private_data)
                btrfs_ioctl_trans_end(file);

        /*
         * We use start here because we will need to wait on the IO to complete
         * in btrfs_sync_log, which could require joining a transaction (for
         * example checking cross references in the nocow path).  If we use join
         * here we could get into a situation where we're waiting on IO to
         * happen that is blocked on a transaction trying to commit.  With start
         * we inc the extwriter counter, so we wait for all extwriters to exit
         * before we start blocking join'ers.  This comment is to keep somebody
         * from thinking they are super smart and changing this to
         * btrfs_join_transaction *cough*Josef*cough*.
         */
        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                inode_unlock(inode);
                goto out;
        }
        trans->sync = true;

        btrfs_init_log_ctx(&ctx, inode);

        ret = btrfs_log_dentry_safe(trans, root, dentry, start, end, &ctx);
        if (ret < 0) {
                /* Fallthrough and commit/free transaction. */
                ret = 1;
        }

        /* we've logged all the items and now have a consistent
         * version of the file in the log.  It is possible that
         * someone will come in and modify the file, but that's
         * fine because the log is consistent on disk, and we
         * have references to all of the file's extents
         *
         * It is possible that someone will come in and log the
         * file again, but that will end up using the synchronization
         * inside btrfs_sync_log to keep things safe.
         */
        inode_unlock(inode);

        /*
         * If any of the ordered extents had an error, just return it to user
         * space, so that the application knows some writes didn't succeed and
         * can take proper action (retry for e.g.). Blindly committing the
         * transaction in this case, would fool userspace that everything was
         * successful. And we also want to make sure our log doesn't contain
         * file extent items pointing to extents that weren't fully written to -
         * just like in the non fast fsync path, where we check for the ordered
         * operation's error flag before writing to the log tree and return -EIO
         * if any of them had this flag set (btrfs_wait_ordered_range) -
         * therefore we need to check for errors in the ordered operations,
         * which are indicated by ctx.io_err.
         */
        if (ctx.io_err) {
                btrfs_end_transaction(trans);
                ret = ctx.io_err;
                goto out;
        }

        if (ret != BTRFS_NO_LOG_SYNC) {
                if (!ret) {
                        ret = btrfs_sync_log(trans, root, &ctx);
                        if (!ret) {
                                ret = btrfs_end_transaction(trans);
                                goto out;
                        }
                }
                if (!full_sync) {
                        ret = btrfs_wait_ordered_range(inode, start, len);
                        if (ret) {
                                btrfs_end_transaction(trans);
                                goto out;
                        }
                }
                ret = btrfs_commit_transaction(trans);
        } else {
                ret = btrfs_end_transaction(trans);
        }
out:
        return ret > 0 ? -EIO : ret;
}

static const struct vm_operations_struct btrfs_file_vm_ops = {
        .fault          = filemap_fault,
        .map_pages      = filemap_map_pages,
        .page_mkwrite   = btrfs_page_mkwrite,
};

static int btrfs_file_mmap(struct file  *filp, struct vm_area_struct *vma)
{
        struct address_space *mapping = filp->f_mapping;

        if (!mapping->a_ops->readpage)
                return -ENOEXEC;

        file_accessed(filp);
        vma->vm_ops = &btrfs_file_vm_ops;

        return 0;
}

static int hole_mergeable(struct inode *inode, struct extent_buffer *leaf,
                          int slot, u64 start, u64 end)
{
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;

        if (slot < 0 || slot >= btrfs_header_nritems(leaf))
                return 0;

        btrfs_item_key_to_cpu(leaf, &key, slot);
        if (key.objectid != btrfs_ino(inode) ||
            key.type != BTRFS_EXTENT_DATA_KEY)
                return 0;

        fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);

        if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG)
                return 0;

        if (btrfs_file_extent_disk_bytenr(leaf, fi))
                return 0;

        if (key.offset == end)
                return 1;
        if (key.offset + btrfs_file_extent_num_bytes(leaf, fi) == start)
                return 1;
        return 0;
}

static int fill_holes(struct btrfs_trans_handle *trans, struct inode *inode,
                      struct btrfs_path *path, u64 offset, u64 end)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_buffer *leaf;
        struct btrfs_file_extent_item *fi;
        struct extent_map *hole_em;
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        struct btrfs_key key;
        int ret;

        if (btrfs_fs_incompat(fs_info, NO_HOLES))
                goto out;

        key.objectid = btrfs_ino(inode);
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = offset;

        ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
        if (ret <= 0) {
                /*
                 * We should have dropped this offset, so if we find it then
                 * something has gone horribly wrong.
                 */
                if (ret == 0)
                        ret = -EINVAL;
                return ret;
        }

        leaf = path->nodes[0];
        if (hole_mergeable(inode, leaf, path->slots[0]-1, offset, end)) {
                u64 num_bytes;

                path->slots[0]--;
                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                num_bytes = btrfs_file_extent_num_bytes(leaf, fi) +
                        end - offset;
                btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_offset(leaf, fi, 0);
                btrfs_mark_buffer_dirty(leaf);
                goto out;
        }

        if (hole_mergeable(inode, leaf, path->slots[0], offset, end)) {
                u64 num_bytes;

                key.offset = offset;
                btrfs_set_item_key_safe(fs_info, path, &key);
                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                num_bytes = btrfs_file_extent_num_bytes(leaf, fi) + end -
                        offset;
                btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_offset(leaf, fi, 0);
                btrfs_mark_buffer_dirty(leaf);
                goto out;
        }
        btrfs_release_path(path);

        ret = btrfs_insert_file_extent(trans, root, btrfs_ino(inode), offset,
                                       0, 0, end - offset, 0, end - offset,
                                       0, 0, 0);
        if (ret)
                return ret;

out:
        btrfs_release_path(path);

        hole_em = alloc_extent_map();
        if (!hole_em) {
                btrfs_drop_extent_cache(inode, offset, end - 1, 0);
                set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
                        &BTRFS_I(inode)->runtime_flags);
        } else {
                hole_em->start = offset;
                hole_em->len = end - offset;
                hole_em->ram_bytes = hole_em->len;
                hole_em->orig_start = offset;

                hole_em->block_start = EXTENT_MAP_HOLE;
                hole_em->block_len = 0;
                hole_em->orig_block_len = 0;
                hole_em->bdev = fs_info->fs_devices->latest_bdev;
                hole_em->compress_type = BTRFS_COMPRESS_NONE;
                hole_em->generation = trans->transid;

                do {
                        btrfs_drop_extent_cache(inode, offset, end - 1, 0);
                        write_lock(&em_tree->lock);
                        ret = add_extent_mapping(em_tree, hole_em, 1);
                        write_unlock(&em_tree->lock);
                } while (ret == -EEXIST);
                free_extent_map(hole_em);
                if (ret)
                        set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
                                &BTRFS_I(inode)->runtime_flags);
        }

        return 0;
}

/*
 * Find a hole extent on given inode and change start/len to the end of hole
 * extent.(hole/vacuum extent whose em->start <= start &&
 *         em->start + em->len > start)
 * When a hole extent is found, return 1 and modify start/len.
 */
static int find_first_non_hole(struct inode *inode, u64 *start, u64 *len)
{
        struct extent_map *em;
        int ret = 0;

        em = btrfs_get_extent(inode, NULL, 0, *start, *len, 0);
        if (IS_ERR_OR_NULL(em)) {
                if (!em)
                        ret = -ENOMEM;
                else
                        ret = PTR_ERR(em);
                return ret;
        }

        /* Hole or vacuum extent(only exists in no-hole mode) */
        if (em->block_start == EXTENT_MAP_HOLE) {
                ret = 1;
                *len = em->start + em->len > *start + *len ?
                       0 : *start + *len - em->start - em->len;
                *start = em->start + em->len;
        }
        free_extent_map(em);
        return ret;
}

static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_state *cached_state = NULL;
        struct btrfs_path *path;
        struct btrfs_block_rsv *rsv;
        struct btrfs_trans_handle *trans;
        u64 lockstart;
        u64 lockend;
        u64 tail_start;
        u64 tail_len;
        u64 orig_start = offset;
        u64 cur_offset;
        u64 min_size = btrfs_calc_trans_metadata_size(fs_info, 1);
        u64 drop_end;
        int ret = 0;
        int err = 0;
        unsigned int rsv_count;
        bool same_block;
        bool no_holes = btrfs_fs_incompat(fs_info, NO_HOLES);
        u64 ino_size;
        bool truncated_block = false;
        bool updated_inode = false;

        ret = btrfs_wait_ordered_range(inode, offset, len);
        if (ret)
                return ret;

        inode_lock(inode);
        ino_size = round_up(inode->i_size, fs_info->sectorsize);
        ret = find_first_non_hole(inode, &offset, &len);
        if (ret < 0)
                goto out_only_mutex;
        if (ret && !len) {
                /* Already in a large hole */
                ret = 0;
                goto out_only_mutex;
        }

        lockstart = round_up(offset, btrfs_inode_sectorsize(inode));
        lockend = round_down(offset + len,
                             btrfs_inode_sectorsize(inode)) - 1;
        same_block = (BTRFS_BYTES_TO_BLKS(fs_info, offset))
                == (BTRFS_BYTES_TO_BLKS(fs_info, offset + len - 1));
        /*
         * We needn't truncate any block which is beyond the end of the file
         * because we are sure there is no data there.
         */
        /*
         * Only do this if we are in the same block and we aren't doing the
         * entire block.
         */
        if (same_block && len < fs_info->sectorsize) {
                if (offset < ino_size) {
                        truncated_block = true;
                        ret = btrfs_truncate_block(inode, offset, len, 0);
                } else {
                        ret = 0;
                }
                goto out_only_mutex;
        }

        /* zero back part of the first block */
        if (offset < ino_size) {
                truncated_block = true;
                ret = btrfs_truncate_block(inode, offset, 0, 0);
                if (ret) {
                        inode_unlock(inode);
                        return ret;
                }
        }

        /* Check the aligned pages after the first unaligned page,
         * if offset != orig_start, which means the first unaligned page
         * including several following pages are already in holes,
         * the extra check can be skipped */
        if (offset == orig_start) {
                /* after truncate page, check hole again */
                len = offset + len - lockstart;
                offset = lockstart;
                ret = find_first_non_hole(inode, &offset, &len);
                if (ret < 0)
                        goto out_only_mutex;
                if (ret && !len) {
                        ret = 0;
                        goto out_only_mutex;
                }
                lockstart = offset;
        }

        /* Check the tail unaligned part is in a hole */
        tail_start = lockend + 1;
        tail_len = offset + len - tail_start;
        if (tail_len) {
                ret = find_first_non_hole(inode, &tail_start, &tail_len);
                if (unlikely(ret < 0))
                        goto out_only_mutex;
                if (!ret) {
                        /* zero the front end of the last page */
                        if (tail_start + tail_len < ino_size) {
                                truncated_block = true;
                                ret = btrfs_truncate_block(inode,
                                                        tail_start + tail_len,
                                                        0, 1);
                                if (ret)
                                        goto out_only_mutex;
                        }
                }
        }

        if (lockend < lockstart) {
                ret = 0;
                goto out_only_mutex;
        }

        while (1) {
                struct btrfs_ordered_extent *ordered;

                truncate_pagecache_range(inode, lockstart, lockend);

                lock_extent_bits(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                                 &cached_state);
                ordered = btrfs_lookup_first_ordered_extent(inode, lockend);

                /*
                 * We need to make sure we have no ordered extents in this range
                 * and nobody raced in and read a page in this range, if we did
                 * we need to try again.
                 */
                if ((!ordered ||
                    (ordered->file_offset + ordered->len <= lockstart ||
                     ordered->file_offset > lockend)) &&
                     !btrfs_page_exists_in_range(inode, lockstart, lockend)) {
                        if (ordered)
                                btrfs_put_ordered_extent(ordered);
                        break;
                }
                if (ordered)
                        btrfs_put_ordered_extent(ordered);
                unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart,
                                     lockend, &cached_state, GFP_NOFS);
                ret = btrfs_wait_ordered_range(inode, lockstart,
                                               lockend - lockstart + 1);
                if (ret) {
                        inode_unlock(inode);
                        return ret;
                }
        }

        path = btrfs_alloc_path();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        rsv = btrfs_alloc_block_rsv(fs_info, BTRFS_BLOCK_RSV_TEMP);
        if (!rsv) {
                ret = -ENOMEM;
                goto out_free;
        }
        rsv->size = btrfs_calc_trans_metadata_size(fs_info, 1);
        rsv->failfast = 1;

        /*
         * 1 - update the inode
         * 1 - removing the extents in the range
         * 1 - adding the hole extent if no_holes isn't set
         */
        rsv_count = no_holes ? 2 : 3;
        trans = btrfs_start_transaction(root, rsv_count);
        if (IS_ERR(trans)) {
                err = PTR_ERR(trans);
                goto out_free;
        }

        ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, rsv,
                                      min_size, 0);
        BUG_ON(ret);
        trans->block_rsv = rsv;

        cur_offset = lockstart;
        len = lockend - cur_offset;
        while (cur_offset < lockend) {
                ret = __btrfs_drop_extents(trans, root, inode, path,
                                           cur_offset, lockend + 1,
                                           &drop_end, 1, 0, 0, NULL);
                if (ret != -ENOSPC)
                        break;

                trans->block_rsv = &fs_info->trans_block_rsv;

                if (cur_offset < drop_end && cur_offset < ino_size) {
                        ret = fill_holes(trans, inode, path, cur_offset,
                                         drop_end);
                        if (ret) {
                                /*
                                 * If we failed then we didn't insert our hole
                                 * entries for the area we dropped, so now the
                                 * fs is corrupted, so we must abort the
                                 * transaction.
                                 */
                                btrfs_abort_transaction(trans, ret);
                                err = ret;
                                break;
                        }
                }

                cur_offset = drop_end;

                ret = btrfs_update_inode(trans, root, inode);
                if (ret) {
                        err = ret;
                        break;
                }

                btrfs_end_transaction(trans);
                btrfs_btree_balance_dirty(fs_info);

                trans = btrfs_start_transaction(root, rsv_count);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        trans = NULL;
                        break;
                }

                ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
                                              rsv, min_size, 0);
                BUG_ON(ret);    /* shouldn't happen */
                trans->block_rsv = rsv;

                ret = find_first_non_hole(inode, &cur_offset, &len);
                if (unlikely(ret < 0))
                        break;
                if (ret && !len) {
                        ret = 0;
                        break;
                }
        }

        if (ret) {
                err = ret;
                goto out_trans;
        }

        trans->block_rsv = &fs_info->trans_block_rsv;
        /*
         * If we are using the NO_HOLES feature we might have had already an
         * hole that overlaps a part of the region [lockstart, lockend] and
         * ends at (or beyond) lockend. Since we have no file extent items to
         * represent holes, drop_end can be less than lockend and so we must
         * make sure we have an extent map representing the existing hole (the
         * call to __btrfs_drop_extents() might have dropped the existing extent
         * map representing the existing hole), otherwise the fast fsync path
         * will not record the existence of the hole region
         * [existing_hole_start, lockend].
         */
        if (drop_end <= lockend)
                drop_end = lockend + 1;
        /*
         * Don't insert file hole extent item if it's for a range beyond eof
         * (because it's useless) or if it represents a 0 bytes range (when
         * cur_offset == drop_end).
         */
        if (cur_offset < ino_size && cur_offset < drop_end) {
                ret = fill_holes(trans, inode, path, cur_offset, drop_end);
                if (ret) {
                        /* Same comment as above. */
                        btrfs_abort_transaction(trans, ret);
                        err = ret;
                        goto out_trans;
                }
        }

out_trans:
        if (!trans)
                goto out_free;

        inode_inc_iversion(inode);
        inode->i_mtime = inode->i_ctime = current_time(inode);

        trans->block_rsv = &fs_info->trans_block_rsv;
        ret = btrfs_update_inode(trans, root, inode);
        updated_inode = true;
        btrfs_end_transaction(trans);
        btrfs_btree_balance_dirty(fs_info);
out_free:
        btrfs_free_path(path);
        btrfs_free_block_rsv(fs_info, rsv);
out:
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                             &cached_state, GFP_NOFS);
out_only_mutex:
        if (!updated_inode && truncated_block && !ret && !err) {
                /*
                 * If we only end up zeroing part of a page, we still need to
                 * update the inode item, so that all the time fields are
                 * updated as well as the necessary btrfs inode in memory fields
                 * for detecting, at fsync time, if the inode isn't yet in the
                 * log tree or it's there but not up to date.
                 */
                trans = btrfs_start_transaction(root, 1);
                if (IS_ERR(trans)) {
                        err = PTR_ERR(trans);
                } else {
                        err = btrfs_update_inode(trans, root, inode);
                        ret = btrfs_end_transaction(trans);
                }
        }
        inode_unlock(inode);
        if (ret && !err)
                err = ret;
        return err;
}

/* Helper structure to record which range is already reserved */
struct falloc_range {
        struct list_head list;
        u64 start;
        u64 len;
};

/*
 * Helper function to add falloc range
 *
 * Caller should have locked the larger range of extent containing
 * [start, len)
 */
static int add_falloc_range(struct list_head *head, u64 start, u64 len)
{
        struct falloc_range *prev = NULL;
        struct falloc_range *range = NULL;

        if (list_empty(head))
                goto insert;

        /*
         * As fallocate iterate by bytenr order, we only need to check
         * the last range.
         */
        prev = list_entry(head->prev, struct falloc_range, list);
        if (prev->start + prev->len == start) {
                prev->len += len;
                return 0;
        }
insert:
        range = kmalloc(sizeof(*range), GFP_KERNEL);
        if (!range)
                return -ENOMEM;
        range->start = start;
        range->len = len;
        list_add_tail(&range->list, head);
        return 0;
}

static long btrfs_fallocate(struct file *file, int mode,
                            loff_t offset, loff_t len)
{
        struct inode *inode = file_inode(file);
        struct extent_state *cached_state = NULL;
        struct falloc_range *range;
        struct falloc_range *tmp;
        struct list_head reserve_list;
        u64 cur_offset;
        u64 last_byte;
        u64 alloc_start;
        u64 alloc_end;
        u64 alloc_hint = 0;
        u64 locked_end;
        u64 actual_end = 0;
        struct extent_map *em;
        int blocksize = btrfs_inode_sectorsize(inode);
        int ret;

        alloc_start = round_down(offset, blocksize);
        alloc_end = round_up(offset + len, blocksize);
        cur_offset = alloc_start;

        /* Make sure we aren't being give some crap mode */
        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
                return -EOPNOTSUPP;

        if (mode & FALLOC_FL_PUNCH_HOLE)
                return btrfs_punch_hole(inode, offset, len);

        /*
         * Only trigger disk allocation, don't trigger qgroup reserve
         *
         * For qgroup space, it will be checked later.
         */
        ret = btrfs_alloc_data_chunk_ondemand(inode, alloc_end - alloc_start);
        if (ret < 0)
                return ret;

        inode_lock(inode);

        if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size) {
                ret = inode_newsize_ok(inode, offset + len);
                if (ret)
                        goto out;
        }

        /*
         * TODO: Move these two operations after we have checked
         * accurate reserved space, or fallocate can still fail but
         * with page truncated or size expanded.
         *
         * But that's a minor problem and won't do much harm BTW.
         */
        if (alloc_start > inode->i_size) {
                ret = btrfs_cont_expand(inode, i_size_read(inode),
                                        alloc_start);
                if (ret)
                        goto out;
        } else if (offset + len > inode->i_size) {
                /*
                 * If we are fallocating from the end of the file onward we
                 * need to zero out the end of the block if i_size lands in the
                 * middle of a block.
                 */
                ret = btrfs_truncate_block(inode, inode->i_size, 0, 0);
                if (ret)
                        goto out;
        }

        /*
         * wait for ordered IO before we have any locks.  We'll loop again
         * below with the locks held.
         */
        ret = btrfs_wait_ordered_range(inode, alloc_start,
                                       alloc_end - alloc_start);
        if (ret)
                goto out;

        locked_end = alloc_end - 1;
        while (1) {
                struct btrfs_ordered_extent *ordered;

                /* the extent lock is ordered inside the running
                 * transaction
                 */
                lock_extent_bits(&BTRFS_I(inode)->io_tree, alloc_start,
                                 locked_end, &cached_state);
                ordered = btrfs_lookup_first_ordered_extent(inode,
                                                            alloc_end - 1);
                if (ordered &&
                    ordered->file_offset + ordered->len > alloc_start &&
                    ordered->file_offset < alloc_end) {
                        btrfs_put_ordered_extent(ordered);
                        unlock_extent_cached(&BTRFS_I(inode)->io_tree,
                                             alloc_start, locked_end,
                                             &cached_state, GFP_KERNEL);
                        /*
                         * we can't wait on the range with the transaction
                         * running or with the extent lock held
                         */
                        ret = btrfs_wait_ordered_range(inode, alloc_start,
                                                       alloc_end - alloc_start);
                        if (ret)
                                goto out;
                } else {
                        if (ordered)
                                btrfs_put_ordered_extent(ordered);
                        break;
                }
        }

        /* First, check if we exceed the qgroup limit */
        INIT_LIST_HEAD(&reserve_list);
        while (1) {
                em = btrfs_get_extent(inode, NULL, 0, cur_offset,
                                      alloc_end - cur_offset, 0);
                if (IS_ERR_OR_NULL(em)) {
                        if (!em)
                                ret = -ENOMEM;
                        else
                                ret = PTR_ERR(em);
                        break;
                }
                last_byte = min(extent_map_end(em), alloc_end);
                actual_end = min_t(u64, extent_map_end(em), offset + len);
                last_byte = ALIGN(last_byte, blocksize);
                if (em->block_start == EXTENT_MAP_HOLE ||
                    (cur_offset >= inode->i_size &&
                     !test_bit(EXTENT_FLAG_PREALLOC, &em->flags))) {
                        ret = add_falloc_range(&reserve_list, cur_offset,
                                               last_byte - cur_offset);
                        if (ret < 0) {
                                free_extent_map(em);
                                break;
                        }
                        ret = btrfs_qgroup_reserve_data(inode, cur_offset,
                                        last_byte - cur_offset);
                        if (ret < 0)
                                break;
                } else {
                        /*
                         * Do not need to reserve unwritten extent for this
                         * range, free reserved data space first, otherwise
                         * it'll result in false ENOSPC error.
                         */
                        btrfs_free_reserved_data_space(inode, cur_offset,
                                last_byte - cur_offset);
                }
                free_extent_map(em);
                cur_offset = last_byte;
                if (cur_offset >= alloc_end)
                        break;
        }

        /*
         * If ret is still 0, means we're OK to fallocate.
         * Or just cleanup the list and exit.
         */
        list_for_each_entry_safe(range, tmp, &reserve_list, list) {
                if (!ret)
                        ret = btrfs_prealloc_file_range(inode, mode,
                                        range->start,
                                        range->len, 1 << inode->i_blkbits,
                                        offset + len, &alloc_hint);
                else
                        btrfs_free_reserved_data_space(inode, range->start,
                                                       range->len);
                list_del(&range->list);
                kfree(range);
        }
        if (ret < 0)
                goto out_unlock;

        if (actual_end > inode->i_size &&
            !(mode & FALLOC_FL_KEEP_SIZE)) {
                struct btrfs_trans_handle *trans;
                struct btrfs_root *root = BTRFS_I(inode)->root;

                /*
                 * We didn't need to allocate any more space, but we
                 * still extended the size of the file so we need to
                 * update i_size and the inode item.
                 */
                trans = btrfs_start_transaction(root, 1);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                } else {
                        inode->i_ctime = current_time(inode);
                        i_size_write(inode, actual_end);
                        btrfs_ordered_update_i_size(inode, actual_end, NULL);
                        ret = btrfs_update_inode(trans, root, inode);
                        if (ret)
                                btrfs_end_transaction(trans);
                        else
                                ret = btrfs_end_transaction(trans);
                }
        }
out_unlock:
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
                             &cached_state, GFP_KERNEL);
out:
        inode_unlock(inode);
        /* Let go of our reservation. */
        if (ret != 0)
                btrfs_free_reserved_data_space(inode, alloc_start,
                                       alloc_end - cur_offset);
        return ret;
}

static int find_desired_extent(struct inode *inode, loff_t *offset, int whence)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct extent_map *em = NULL;
        struct extent_state *cached_state = NULL;
        u64 lockstart;
        u64 lockend;
        u64 start;
        u64 len;
        int ret = 0;

        if (inode->i_size == 0)
                return -ENXIO;

        /*
         * *offset can be negative, in this case we start finding DATA/HOLE from
         * the very start of the file.
         */
        start = max_t(loff_t, 0, *offset);

        lockstart = round_down(start, fs_info->sectorsize);
        lockend = round_up(i_size_read(inode),
                           fs_info->sectorsize);
        if (lockend <= lockstart)
                lockend = lockstart + fs_info->sectorsize;
        lockend--;
        len = lockend - lockstart + 1;

        lock_extent_bits(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                         &cached_state);

        while (start < inode->i_size) {
                em = btrfs_get_extent_fiemap(inode, NULL, 0, start, len, 0);
                if (IS_ERR(em)) {
                        ret = PTR_ERR(em);
                        em = NULL;
                        break;
                }

                if (whence == SEEK_HOLE &&
                    (em->block_start == EXTENT_MAP_HOLE ||
                     test_bit(EXTENT_FLAG_PREALLOC, &em->flags)))
                        break;
                else if (whence == SEEK_DATA &&
                           (em->block_start != EXTENT_MAP_HOLE &&
                            !test_bit(EXTENT_FLAG_PREALLOC, &em->flags)))
                        break;

                start = em->start + em->len;
                free_extent_map(em);
                em = NULL;
                cond_resched();
        }
        free_extent_map(em);
        if (!ret) {
                if (whence == SEEK_DATA && start >= inode->i_size)
                        ret = -ENXIO;
                else
                        *offset = min_t(loff_t, start, inode->i_size);
        }
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                             &cached_state, GFP_NOFS);
        return ret;
}

static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file->f_mapping->host;
        int ret;

        inode_lock(inode);
        switch (whence) {
        case SEEK_END:
        case SEEK_CUR:
                offset = generic_file_llseek(file, offset, whence);
                goto out;
        case SEEK_DATA:
        case SEEK_HOLE:
                if (offset >= i_size_read(inode)) {
                        inode_unlock(inode);
                        return -ENXIO;
                }

                ret = find_desired_extent(inode, &offset, whence);
                if (ret) {
                        inode_unlock(inode);
                        return ret;
                }
        }

        offset = vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
out:
        inode_unlock(inode);
        return offset;
}

const struct file_operations btrfs_file_operations = {
        .llseek         = btrfs_file_llseek,
        .read_iter      = generic_file_read_iter,
        .splice_read    = generic_file_splice_read,
        .write_iter     = btrfs_file_write_iter,
        .mmap           = btrfs_file_mmap,
        .open           = generic_file_open,
        .release        = btrfs_release_file,
        .fsync          = btrfs_sync_file,
        .fallocate      = btrfs_fallocate,
        .unlocked_ioctl = btrfs_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = btrfs_compat_ioctl,
#endif
        .clone_file_range = btrfs_clone_file_range,
        .dedupe_file_range = btrfs_dedupe_file_range,
};

void btrfs_auto_defrag_exit(void)
{
        kmem_cache_destroy(btrfs_inode_defrag_cachep);
}

int btrfs_auto_defrag_init(void)
{
        btrfs_inode_defrag_cachep = kmem_cache_create("btrfs_inode_defrag",
                                        sizeof(struct inode_defrag), 0,
                                        SLAB_MEM_SPREAD,
                                        NULL);
        if (!btrfs_inode_defrag_cachep)
                return -ENOMEM;

        return 0;
}

int btrfs_fdatawrite_range(struct inode *inode, loff_t start, loff_t end)
{
        int ret;

        /*
         * So with compression we will find and lock a dirty page and clear the
         * first one as dirty, setup an async extent, and immediately return
         * with the entire range locked but with nobody actually marked with
         * writeback.  So we can't just filemap_write_and_wait_range() and
         * expect it to work since it will just kick off a thread to do the
         * actual work.  So we need to call filemap_fdatawrite_range _again_
         * since it will wait on the page lock, which won't be unlocked until
         * after the pages have been marked as writeback and so we're good to go
         * from there.  We have to do this otherwise we'll miss the ordered
         * extents and that results in badness.  Please Josef, do not think you
         * know better and pull this out at some point in the future, it is
         * right and you are wrong.
         */
        ret = filemap_fdatawrite_range(inode->i_mapping, start, end);
        if (!ret && test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
                             &BTRFS_I(inode)->runtime_flags))
                ret = filemap_fdatawrite_range(inode->i_mapping, start, end);

        return ret;
}