/*
 * 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/kernel.h>
#include <linux/bio.h>
#include <linux/buffer_head.h>
#include <linux/file.h>
#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/swap.h>
#include <linux/writeback.h>
#include <linux/statfs.h>
#include <linux/compat.h>
#include <linux/aio.h>
#include <linux/bit_spinlock.h>
#include <linux/xattr.h>
#include <linux/posix_acl.h>
#include <linux/falloc.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include <linux/mount.h>
#include <linux/btrfs.h>
#include <linux/blkdev.h>
#include <linux/posix_acl_xattr.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "print-tree.h"
#include "ordered-data.h"
#include "xattr.h"
#include "tree-log.h"
#include "volumes.h"
#include "compression.h"
#include "locking.h"
#include "free-space-cache.h"
#include "inode-map.h"
#include "backref.h"
#include "hash.h"
#include "props.h"

struct btrfs_iget_args {
        struct btrfs_key *location;
        struct btrfs_root *root;
};

static const struct inode_operations btrfs_dir_inode_operations;
static const struct inode_operations btrfs_symlink_inode_operations;
static const struct inode_operations btrfs_dir_ro_inode_operations;
static const struct inode_operations btrfs_special_inode_operations;
static const struct inode_operations btrfs_file_inode_operations;
static const struct address_space_operations btrfs_aops;
static const struct address_space_operations btrfs_symlink_aops;
static const struct file_operations btrfs_dir_file_operations;
static struct extent_io_ops btrfs_extent_io_ops;

static struct kmem_cache *btrfs_inode_cachep;
static struct kmem_cache *btrfs_delalloc_work_cachep;
struct kmem_cache *btrfs_trans_handle_cachep;
struct kmem_cache *btrfs_transaction_cachep;
struct kmem_cache *btrfs_path_cachep;
struct kmem_cache *btrfs_free_space_cachep;

#define S_SHIFT 12
static unsigned char btrfs_type_by_mode[S_IFMT >> S_SHIFT] = {
        [S_IFREG >> S_SHIFT]    = BTRFS_FT_REG_FILE,
        [S_IFDIR >> S_SHIFT]    = BTRFS_FT_DIR,
        [S_IFCHR >> S_SHIFT]    = BTRFS_FT_CHRDEV,
        [S_IFBLK >> S_SHIFT]    = BTRFS_FT_BLKDEV,
        [S_IFIFO >> S_SHIFT]    = BTRFS_FT_FIFO,
        [S_IFSOCK >> S_SHIFT]   = BTRFS_FT_SOCK,
        [S_IFLNK >> S_SHIFT]    = BTRFS_FT_SYMLINK,
};

static int btrfs_setsize(struct inode *inode, struct iattr *attr);
static int btrfs_truncate(struct inode *inode);
static int btrfs_finish_ordered_io(struct btrfs_ordered_extent *ordered_extent);
static noinline int cow_file_range(struct inode *inode,
                                   struct page *locked_page,
                                   u64 start, u64 end, int *page_started,
                                   unsigned long *nr_written, int unlock);
static struct extent_map *create_pinned_em(struct inode *inode, u64 start,
                                           u64 len, u64 orig_start,
                                           u64 block_start, u64 block_len,
                                           u64 orig_block_len, u64 ram_bytes,
                                           int type);

static int btrfs_dirty_inode(struct inode *inode);

static int btrfs_init_inode_security(struct btrfs_trans_handle *trans,
                                     struct inode *inode,  struct inode *dir,
                                     const struct qstr *qstr)
{
        int err;

        err = btrfs_init_acl(trans, inode, dir);
        if (!err)
                err = btrfs_xattr_security_init(trans, inode, dir, qstr);
        return err;
}

/*
 * this does all the hard work for inserting an inline extent into
 * the btree.  The caller should have done a btrfs_drop_extents so that
 * no overlapping inline items exist in the btree
 */
static int insert_inline_extent(struct btrfs_trans_handle *trans,
                                struct btrfs_path *path, int extent_inserted,
                                struct btrfs_root *root, struct inode *inode,
                                u64 start, size_t size, size_t compressed_size,
                                int compress_type,
                                struct page **compressed_pages)
{
        struct extent_buffer *leaf;
        struct page *page = NULL;
        char *kaddr;
        unsigned long ptr;
        struct btrfs_file_extent_item *ei;
        int err = 0;
        int ret;
        size_t cur_size = size;
        unsigned long offset;

        if (compressed_size && compressed_pages)
                cur_size = compressed_size;

        inode_add_bytes(inode, size);

        if (!extent_inserted) {
                struct btrfs_key key;
                size_t datasize;

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

                datasize = btrfs_file_extent_calc_inline_size(cur_size);
                path->leave_spinning = 1;
                ret = btrfs_insert_empty_item(trans, root, path, &key,
                                              datasize);
                if (ret) {
                        err = ret;
                        goto fail;
                }
        }
        leaf = path->nodes[0];
        ei = btrfs_item_ptr(leaf, path->slots[0],
                            struct btrfs_file_extent_item);
        btrfs_set_file_extent_generation(leaf, ei, trans->transid);
        btrfs_set_file_extent_type(leaf, ei, BTRFS_FILE_EXTENT_INLINE);
        btrfs_set_file_extent_encryption(leaf, ei, 0);
        btrfs_set_file_extent_other_encoding(leaf, ei, 0);
        btrfs_set_file_extent_ram_bytes(leaf, ei, size);
        ptr = btrfs_file_extent_inline_start(ei);

        if (compress_type != BTRFS_COMPRESS_NONE) {
                struct page *cpage;
                int i = 0;
                while (compressed_size > 0) {
                        cpage = compressed_pages[i];
                        cur_size = min_t(unsigned long, compressed_size,
                                       PAGE_CACHE_SIZE);

                        kaddr = kmap_atomic(cpage);
                        write_extent_buffer(leaf, kaddr, ptr, cur_size);
                        kunmap_atomic(kaddr);

                        i++;
                        ptr += cur_size;
                        compressed_size -= cur_size;
                }
                btrfs_set_file_extent_compression(leaf, ei,
                                                  compress_type);
        } else {
                page = find_get_page(inode->i_mapping,
                                     start >> PAGE_CACHE_SHIFT);
                btrfs_set_file_extent_compression(leaf, ei, 0);
                kaddr = kmap_atomic(page);
                offset = start & (PAGE_CACHE_SIZE - 1);
                write_extent_buffer(leaf, kaddr + offset, ptr, size);
                kunmap_atomic(kaddr);
                page_cache_release(page);
        }
        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        /*
         * we're an inline extent, so nobody can
         * extend the file past i_size without locking
         * a page we already have locked.
         *
         * We must do any isize and inode updates
         * before we unlock the pages.  Otherwise we
         * could end up racing with unlink.
         */
        BTRFS_I(inode)->disk_i_size = inode->i_size;
        ret = btrfs_update_inode(trans, root, inode);

        return ret;
fail:
        return err;
}


/*
 * conditionally insert an inline extent into the file.  This
 * does the checks required to make sure the data is small enough
 * to fit as an inline extent.
 */
static noinline int cow_file_range_inline(struct btrfs_root *root,
                                          struct inode *inode, u64 start,
                                          u64 end, size_t compressed_size,
                                          int compress_type,
                                          struct page **compressed_pages)
{
        struct btrfs_trans_handle *trans;
        u64 isize = i_size_read(inode);
        u64 actual_end = min(end + 1, isize);
        u64 inline_len = actual_end - start;
        u64 aligned_end = ALIGN(end, root->sectorsize);
        u64 data_len = inline_len;
        int ret;
        struct btrfs_path *path;
        int extent_inserted = 0;
        u32 extent_item_size;

        if (compressed_size)
                data_len = compressed_size;

        if (start > 0 ||
            actual_end > PAGE_CACHE_SIZE ||
            data_len > BTRFS_MAX_INLINE_DATA_SIZE(root) ||
            (!compressed_size &&
            (actual_end & (root->sectorsize - 1)) == 0) ||
            end + 1 < isize ||
            data_len > root->fs_info->max_inline) {
                return 1;
        }

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans)) {
                btrfs_free_path(path);
                return PTR_ERR(trans);
        }
        trans->block_rsv = &root->fs_info->delalloc_block_rsv;

        if (compressed_size && compressed_pages)
                extent_item_size = btrfs_file_extent_calc_inline_size(
                   compressed_size);
        else
                extent_item_size = btrfs_file_extent_calc_inline_size(
                    inline_len);

        ret = __btrfs_drop_extents(trans, root, inode, path,
                                   start, aligned_end, NULL,
                                   1, 1, extent_item_size, &extent_inserted);
        if (ret) {
                btrfs_abort_transaction(trans, root, ret);
                goto out;
        }

        if (isize > actual_end)
                inline_len = min_t(u64, isize, actual_end);
        ret = insert_inline_extent(trans, path, extent_inserted,
                                   root, inode, start,
                                   inline_len, compressed_size,
                                   compress_type, compressed_pages);
        if (ret && ret != -ENOSPC) {
                btrfs_abort_transaction(trans, root, ret);
                goto out;
        } else if (ret == -ENOSPC) {
                ret = 1;
                goto out;
        }

        set_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &BTRFS_I(inode)->runtime_flags);
        btrfs_delalloc_release_metadata(inode, end + 1 - start);
        btrfs_drop_extent_cache(inode, start, aligned_end - 1, 0);
out:
        btrfs_free_path(path);
        btrfs_end_transaction(trans, root);
        return ret;
}

struct async_extent {
        u64 start;
        u64 ram_size;
        u64 compressed_size;
        struct page **pages;
        unsigned long nr_pages;
        int compress_type;
        struct list_head list;
};

struct async_cow {
        struct inode *inode;
        struct btrfs_root *root;
        struct page *locked_page;
        u64 start;
        u64 end;
        struct list_head extents;
        struct btrfs_work work;
};

static noinline int add_async_extent(struct async_cow *cow,
                                     u64 start, u64 ram_size,
                                     u64 compressed_size,
                                     struct page **pages,
                                     unsigned long nr_pages,
                                     int compress_type)
{
        struct async_extent *async_extent;

        async_extent = kmalloc(sizeof(*async_extent), GFP_NOFS);
        BUG_ON(!async_extent); /* -ENOMEM */
        async_extent->start = start;
        async_extent->ram_size = ram_size;
        async_extent->compressed_size = compressed_size;
        async_extent->pages = pages;
        async_extent->nr_pages = nr_pages;
        async_extent->compress_type = compress_type;
        list_add_tail(&async_extent->list, &cow->extents);
        return 0;
}

static inline int inode_need_compress(struct inode *inode)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;

        /* force compress */
        if (btrfs_test_opt(root, FORCE_COMPRESS))
                return 1;
        /* bad compression ratios */
        if (BTRFS_I(inode)->flags & BTRFS_INODE_NOCOMPRESS)
                return 0;
        if (btrfs_test_opt(root, COMPRESS) ||
            BTRFS_I(inode)->flags & BTRFS_INODE_COMPRESS ||
            BTRFS_I(inode)->force_compress)
                return 1;
        return 0;
}

/*
 * we create compressed extents in two phases.  The first
 * phase compresses a range of pages that have already been
 * locked (both pages and state bits are locked).
 *
 * This is done inside an ordered work queue, and the compression
 * is spread across many cpus.  The actual IO submission is step
 * two, and the ordered work queue takes care of making sure that
 * happens in the same order things were put onto the queue by
 * writepages and friends.
 *
 * If this code finds it can't get good compression, it puts an
 * entry onto the work queue to write the uncompressed bytes.  This
 * makes sure that both compressed inodes and uncompressed inodes
 * are written in the same order that the flusher thread sent them
 * down.
 */
static noinline int compress_file_range(struct inode *inode,
                                        struct page *locked_page,
                                        u64 start, u64 end,
                                        struct async_cow *async_cow,
                                        int *num_added)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        u64 num_bytes;
        u64 blocksize = root->sectorsize;
        u64 actual_end;
        u64 isize = i_size_read(inode);
        int ret = 0;
        struct page **pages = NULL;
        unsigned long nr_pages;
        unsigned long nr_pages_ret = 0;
        unsigned long total_compressed = 0;
        unsigned long total_in = 0;
        unsigned long max_compressed = 128 * 1024;
        unsigned long max_uncompressed = 128 * 1024;
        int i;
        int will_compress;
        int compress_type = root->fs_info->compress_type;
        int redirty = 0;

        /* if this is a small write inside eof, kick off a defrag */
        if ((end - start + 1) < 16 * 1024 &&
            (start > 0 || end + 1 < BTRFS_I(inode)->disk_i_size))
                btrfs_add_inode_defrag(NULL, inode);

        /*
         * skip compression for a small file range(<=blocksize) that
         * isn't an inline extent, since it dosen't save disk space at all.
         */
        if ((end - start + 1) <= blocksize &&
            (start > 0 || end + 1 < BTRFS_I(inode)->disk_i_size))
                goto cleanup_and_bail_uncompressed;

        actual_end = min_t(u64, isize, end + 1);
again:
        will_compress = 0;
        nr_pages = (end >> PAGE_CACHE_SHIFT) - (start >> PAGE_CACHE_SHIFT) + 1;
        nr_pages = min(nr_pages, (128 * 1024UL) / PAGE_CACHE_SIZE);

        /*
         * we don't want to send crud past the end of i_size through
         * compression, that's just a waste of CPU time.  So, if the
         * end of the file is before the start of our current
         * requested range of bytes, we bail out to the uncompressed
         * cleanup code that can deal with all of this.
         *
         * It isn't really the fastest way to fix things, but this is a
         * very uncommon corner.
         */
        if (actual_end <= start)
                goto cleanup_and_bail_uncompressed;

        total_compressed = actual_end - start;

        /* we want to make sure that amount of ram required to uncompress
         * an extent is reasonable, so we limit the total size in ram
         * of a compressed extent to 128k.  This is a crucial number
         * because it also controls how easily we can spread reads across
         * cpus for decompression.
         *
         * We also want to make sure the amount of IO required to do
         * a random read is reasonably small, so we limit the size of
         * a compressed extent to 128k.
         */
        total_compressed = min(total_compressed, max_uncompressed);
        num_bytes = ALIGN(end - start + 1, blocksize);
        num_bytes = max(blocksize,  num_bytes);
        total_in = 0;
        ret = 0;

        /*
         * we do compression for mount -o compress and when the
         * inode has not been flagged as nocompress.  This flag can
         * change at any time if we discover bad compression ratios.
         */
        if (inode_need_compress(inode)) {
                WARN_ON(pages);
                pages = kzalloc(sizeof(struct page *) * nr_pages, GFP_NOFS);
                if (!pages) {
                        /* just bail out to the uncompressed code */
                        goto cont;
                }

                if (BTRFS_I(inode)->force_compress)
                        compress_type = BTRFS_I(inode)->force_compress;

                /*
                 * we need to call clear_page_dirty_for_io on each
                 * page in the range.  Otherwise applications with the file
                 * mmap'd can wander in and change the page contents while
                 * we are compressing them.
                 *
                 * If the compression fails for any reason, we set the pages
                 * dirty again later on.
                 */
                extent_range_clear_dirty_for_io(inode, start, end);
                redirty = 1;
                ret = btrfs_compress_pages(compress_type,
                                           inode->i_mapping, start,
                                           total_compressed, pages,
                                           nr_pages, &nr_pages_ret,
                                           &total_in,
                                           &total_compressed,
                                           max_compressed);

                if (!ret) {
                        unsigned long offset = total_compressed &
                                (PAGE_CACHE_SIZE - 1);
                        struct page *page = pages[nr_pages_ret - 1];
                        char *kaddr;

                        /* zero the tail end of the last page, we might be
                         * sending it down to disk
                         */
                        if (offset) {
                                kaddr = kmap_atomic(page);
                                memset(kaddr + offset, 0,
                                       PAGE_CACHE_SIZE - offset);
                                kunmap_atomic(kaddr);
                        }
                        will_compress = 1;
                }
        }
cont:
        if (start == 0) {
                /* lets try to make an inline extent */
                if (ret || total_in < (actual_end - start)) {
                        /* we didn't compress the entire range, try
                         * to make an uncompressed inline extent.
                         */
                        ret = cow_file_range_inline(root, inode, start, end,
                                                    0, 0, NULL);
                } else {
                        /* try making a compressed inline extent */
                        ret = cow_file_range_inline(root, inode, start, end,
                                                    total_compressed,
                                                    compress_type, pages);
                }
                if (ret <= 0) {
                        unsigned long clear_flags = EXTENT_DELALLOC |
                                EXTENT_DEFRAG;
                        clear_flags |= (ret < 0) ? EXTENT_DO_ACCOUNTING : 0;

                        /*
                         * inline extent creation worked or returned error,
                         * we don't need to create any more async work items.
                         * Unlock and free up our temp pages.
                         */
                        extent_clear_unlock_delalloc(inode, start, end, NULL,
                                                     clear_flags, PAGE_UNLOCK |
                                                     PAGE_CLEAR_DIRTY |
                                                     PAGE_SET_WRITEBACK |
                                                     PAGE_END_WRITEBACK);
                        goto free_pages_out;
                }
        }

        if (will_compress) {
                /*
                 * we aren't doing an inline extent round the compressed size
                 * up to a block size boundary so the allocator does sane
                 * things
                 */
                total_compressed = ALIGN(total_compressed, blocksize);

                /*
                 * one last check to make sure the compression is really a
                 * win, compare the page count read with the blocks on disk
                 */
                total_in = ALIGN(total_in, PAGE_CACHE_SIZE);
                if (total_compressed >= total_in) {
                        will_compress = 0;
                } else {
                        num_bytes = total_in;
                }
        }
        if (!will_compress && pages) {
                /*
                 * the compression code ran but failed to make things smaller,
                 * free any pages it allocated and our page pointer array
                 */
                for (i = 0; i < nr_pages_ret; i++) {
                        WARN_ON(pages[i]->mapping);
                        page_cache_release(pages[i]);
                }
                kfree(pages);
                pages = NULL;
                total_compressed = 0;
                nr_pages_ret = 0;

                /* flag the file so we don't compress in the future */
                if (!btrfs_test_opt(root, FORCE_COMPRESS) &&
                    !(BTRFS_I(inode)->force_compress)) {
                        BTRFS_I(inode)->flags |= BTRFS_INODE_NOCOMPRESS;
                }
        }
        if (will_compress) {
                *num_added += 1;

                /* the async work queues will take care of doing actual
                 * allocation on disk for these compressed pages,
                 * and will submit them to the elevator.
                 */
                add_async_extent(async_cow, start, num_bytes,
                                 total_compressed, pages, nr_pages_ret,
                                 compress_type);

                if (start + num_bytes < end) {
                        start += num_bytes;
                        pages = NULL;
                        cond_resched();
                        goto again;
                }
        } else {
cleanup_and_bail_uncompressed:
                /*
                 * No compression, but we still need to write the pages in
                 * the file we've been given so far.  redirty the locked
                 * page if it corresponds to our extent and set things up
                 * for the async work queue to run cow_file_range to do
                 * the normal delalloc dance
                 */
                if (page_offset(locked_page) >= start &&
                    page_offset(locked_page) <= end) {
                        __set_page_dirty_nobuffers(locked_page);
                        /* unlocked later on in the async handlers */
                }
                if (redirty)
                        extent_range_redirty_for_io(inode, start, end);
                add_async_extent(async_cow, start, end - start + 1,
                                 0, NULL, 0, BTRFS_COMPRESS_NONE);
                *num_added += 1;
        }

out:
        return ret;

free_pages_out:
        for (i = 0; i < nr_pages_ret; i++) {
                WARN_ON(pages[i]->mapping);
                page_cache_release(pages[i]);
        }
        kfree(pages);

        goto out;
}

/*
 * phase two of compressed writeback.  This is the ordered portion
 * of the code, which only gets called in the order the work was
 * queued.  We walk all the async extents created by compress_file_range
 * and send them down to the disk.
 */
static noinline int submit_compressed_extents(struct inode *inode,
                                              struct async_cow *async_cow)
{
        struct async_extent *async_extent;
        u64 alloc_hint = 0;
        struct btrfs_key ins;
        struct extent_map *em;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        struct extent_io_tree *io_tree;
        int ret = 0;

        if (list_empty(&async_cow->extents))
                return 0;

again:
        while (!list_empty(&async_cow->extents)) {
                async_extent = list_entry(async_cow->extents.next,
                                          struct async_extent, list);
                list_del(&async_extent->list);

                io_tree = &BTRFS_I(inode)->io_tree;

retry:
                /* did the compression code fall back to uncompressed IO? */
                if (!async_extent->pages) {
                        int page_started = 0;
                        unsigned long nr_written = 0;

                        lock_extent(io_tree, async_extent->start,
                                         async_extent->start +
                                         async_extent->ram_size - 1);

                        /* allocate blocks */
                        ret = cow_file_range(inode, async_cow->locked_page,
                                             async_extent->start,
                                             async_extent->start +
                                             async_extent->ram_size - 1,
                                             &page_started, &nr_written, 0);

                        /* JDM XXX */

                        /*
                         * if page_started, cow_file_range inserted an
                         * inline extent and took care of all the unlocking
                         * and IO for us.  Otherwise, we need to submit
                         * all those pages down to the drive.
                         */
                        if (!page_started && !ret)
                                extent_write_locked_range(io_tree,
                                                  inode, async_extent->start,
                                                  async_extent->start +
                                                  async_extent->ram_size - 1,
                                                  btrfs_get_extent,
                                                  WB_SYNC_ALL);
                        else if (ret)
                                unlock_page(async_cow->locked_page);
                        kfree(async_extent);
                        cond_resched();
                        continue;
                }

                lock_extent(io_tree, async_extent->start,
                            async_extent->start + async_extent->ram_size - 1);

                ret = btrfs_reserve_extent(root,
                                           async_extent->compressed_size,
                                           async_extent->compressed_size,
                                           0, alloc_hint, &ins, 1, 1);
                if (ret) {
                        int i;

                        for (i = 0; i < async_extent->nr_pages; i++) {
                                WARN_ON(async_extent->pages[i]->mapping);
                                page_cache_release(async_extent->pages[i]);
                        }
                        kfree(async_extent->pages);
                        async_extent->nr_pages = 0;
                        async_extent->pages = NULL;

                        if (ret == -ENOSPC) {
                                unlock_extent(io_tree, async_extent->start,
                                              async_extent->start +
                                              async_extent->ram_size - 1);

                                /*
                                 * we need to redirty the pages if we decide to
                                 * fallback to uncompressed IO, otherwise we
                                 * will not submit these pages down to lower
                                 * layers.
                                 */
                                extent_range_redirty_for_io(inode,
                                                async_extent->start,
                                                async_extent->start +
                                                async_extent->ram_size - 1);

                                goto retry;
                        }
                        goto out_free;
                }

                /*
                 * here we're doing allocation and writeback of the
                 * compressed pages
                 */
                btrfs_drop_extent_cache(inode, async_extent->start,
                                        async_extent->start +
                                        async_extent->ram_size - 1, 0);

                em = alloc_extent_map();
                if (!em) {
                        ret = -ENOMEM;
                        goto out_free_reserve;
                }
                em->start = async_extent->start;
                em->len = async_extent->ram_size;
                em->orig_start = em->start;
                em->mod_start = em->start;
                em->mod_len = em->len;

                em->block_start = ins.objectid;
                em->block_len = ins.offset;
                em->orig_block_len = ins.offset;
                em->ram_bytes = async_extent->ram_size;
                em->bdev = root->fs_info->fs_devices->latest_bdev;
                em->compress_type = async_extent->compress_type;
                set_bit(EXTENT_FLAG_PINNED, &em->flags);
                set_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
                em->generation = -1;

                while (1) {
                        write_lock(&em_tree->lock);
                        ret = add_extent_mapping(em_tree, em, 1);
                        write_unlock(&em_tree->lock);
                        if (ret != -EEXIST) {
                                free_extent_map(em);
                                break;
                        }
                        btrfs_drop_extent_cache(inode, async_extent->start,
                                                async_extent->start +
                                                async_extent->ram_size - 1, 0);
                }

                if (ret)
                        goto out_free_reserve;

                ret = btrfs_add_ordered_extent_compress(inode,
                                                async_extent->start,
                                                ins.objectid,
                                                async_extent->ram_size,
                                                ins.offset,
                                                BTRFS_ORDERED_COMPRESSED,
                                                async_extent->compress_type);
                if (ret) {
                        btrfs_drop_extent_cache(inode, async_extent->start,
                                                async_extent->start +
                                                async_extent->ram_size - 1, 0);
                        goto out_free_reserve;
                }

                /*
                 * clear dirty, set writeback and unlock the pages.
                 */
                extent_clear_unlock_delalloc(inode, async_extent->start,
                                async_extent->start +
                                async_extent->ram_size - 1,
                                NULL, EXTENT_LOCKED | EXTENT_DELALLOC,
                                PAGE_UNLOCK | PAGE_CLEAR_DIRTY |
                                PAGE_SET_WRITEBACK);
                ret = btrfs_submit_compressed_write(inode,
                                    async_extent->start,
                                    async_extent->ram_size,
                                    ins.objectid,
                                    ins.offset, async_extent->pages,
                                    async_extent->nr_pages);
                alloc_hint = ins.objectid + ins.offset;
                kfree(async_extent);
                if (ret)
                        goto out;
                cond_resched();
        }
        ret = 0;
out:
        return ret;
out_free_reserve:
        btrfs_free_reserved_extent(root, ins.objectid, ins.offset, 1);
out_free:
        extent_clear_unlock_delalloc(inode, async_extent->start,
                                     async_extent->start +
                                     async_extent->ram_size - 1,
                                     NULL, EXTENT_LOCKED | EXTENT_DELALLOC |
                                     EXTENT_DEFRAG | EXTENT_DO_ACCOUNTING,
                                     PAGE_UNLOCK | PAGE_CLEAR_DIRTY |
                                     PAGE_SET_WRITEBACK | PAGE_END_WRITEBACK);
        kfree(async_extent);
        goto again;
}

static u64 get_extent_allocation_hint(struct inode *inode, u64 start,
                                      u64 num_bytes)
{
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        struct extent_map *em;
        u64 alloc_hint = 0;

        read_lock(&em_tree->lock);
        em = search_extent_mapping(em_tree, start, num_bytes);
        if (em) {
                /*
                 * if block start isn't an actual block number then find the
                 * first block in this inode and use that as a hint.  If that
                 * block is also bogus then just don't worry about it.
                 */
                if (em->block_start >= EXTENT_MAP_LAST_BYTE) {
                        free_extent_map(em);
                        em = search_extent_mapping(em_tree, 0, 0);
                        if (em && em->block_start < EXTENT_MAP_LAST_BYTE)
                                alloc_hint = em->block_start;
                        if (em)
                                free_extent_map(em);
                } else {
                        alloc_hint = em->block_start;
                        free_extent_map(em);
                }
        }
        read_unlock(&em_tree->lock);

        return alloc_hint;
}

/*
 * when extent_io.c finds a delayed allocation range in the file,
 * the call backs end up in this code.  The basic idea is to
 * allocate extents on disk for the range, and create ordered data structs
 * in ram to track those extents.
 *
 * locked_page is the page that writepage had locked already.  We use
 * it to make sure we don't do extra locks or unlocks.
 *
 * *page_started is set to one if we unlock locked_page and do everything
 * required to start IO on it.  It may be clean and already done with
 * IO when we return.
 */
static noinline int cow_file_range(struct inode *inode,
                                   struct page *locked_page,
                                   u64 start, u64 end, int *page_started,
                                   unsigned long *nr_written,
                                   int unlock)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        u64 alloc_hint = 0;
        u64 num_bytes;
        unsigned long ram_size;
        u64 disk_num_bytes;
        u64 cur_alloc_size;
        u64 blocksize = root->sectorsize;
        struct btrfs_key ins;
        struct extent_map *em;
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        int ret = 0;

        if (btrfs_is_free_space_inode(inode)) {
                WARN_ON_ONCE(1);
                ret = -EINVAL;
                goto out_unlock;
        }

        num_bytes = ALIGN(end - start + 1, blocksize);
        num_bytes = max(blocksize,  num_bytes);
        disk_num_bytes = num_bytes;

        /* if this is a small write inside eof, kick off defrag */
        if (num_bytes < 64 * 1024 &&
            (start > 0 || end + 1 < BTRFS_I(inode)->disk_i_size))
                btrfs_add_inode_defrag(NULL, inode);

        if (start == 0) {
                /* lets try to make an inline extent */
                ret = cow_file_range_inline(root, inode, start, end, 0, 0,
                                            NULL);
                if (ret == 0) {
                        extent_clear_unlock_delalloc(inode, start, end, NULL,
                                     EXTENT_LOCKED | EXTENT_DELALLOC |
                                     EXTENT_DEFRAG, PAGE_UNLOCK |
                                     PAGE_CLEAR_DIRTY | PAGE_SET_WRITEBACK |
                                     PAGE_END_WRITEBACK);

                        *nr_written = *nr_written +
                             (end - start + PAGE_CACHE_SIZE) / PAGE_CACHE_SIZE;
                        *page_started = 1;
                        goto out;
                } else if (ret < 0) {
                        goto out_unlock;
                }
        }

        BUG_ON(disk_num_bytes >
               btrfs_super_total_bytes(root->fs_info->super_copy));

        alloc_hint = get_extent_allocation_hint(inode, start, num_bytes);
        btrfs_drop_extent_cache(inode, start, start + num_bytes - 1, 0);

        while (disk_num_bytes > 0) {
                unsigned long op;

                cur_alloc_size = disk_num_bytes;
                ret = btrfs_reserve_extent(root, cur_alloc_size,
                                           root->sectorsize, 0, alloc_hint,
                                           &ins, 1, 1);
                if (ret < 0)
                        goto out_unlock;

                em = alloc_extent_map();
                if (!em) {
                        ret = -ENOMEM;
                        goto out_reserve;
                }
                em->start = start;
                em->orig_start = em->start;
                ram_size = ins.offset;
                em->len = ins.offset;
                em->mod_start = em->start;
                em->mod_len = em->len;

                em->block_start = ins.objectid;
                em->block_len = ins.offset;
                em->orig_block_len = ins.offset;
                em->ram_bytes = ram_size;
                em->bdev = root->fs_info->fs_devices->latest_bdev;
                set_bit(EXTENT_FLAG_PINNED, &em->flags);
                em->generation = -1;

                while (1) {
                        write_lock(&em_tree->lock);
                        ret = add_extent_mapping(em_tree, em, 1);
                        write_unlock(&em_tree->lock);
                        if (ret != -EEXIST) {
                                free_extent_map(em);
                                break;
                        }
                        btrfs_drop_extent_cache(inode, start,
                                                start + ram_size - 1, 0);
                }
                if (ret)
                        goto out_reserve;

                cur_alloc_size = ins.offset;
                ret = btrfs_add_ordered_extent(inode, start, ins.objectid,
                                               ram_size, cur_alloc_size, 0);
                if (ret)
                        goto out_drop_extent_cache;

                if (root->root_key.objectid ==
                    BTRFS_DATA_RELOC_TREE_OBJECTID) {
                        ret = btrfs_reloc_clone_csums(inode, start,
                                                      cur_alloc_size);
                        if (ret)
                                goto out_drop_extent_cache;
                }

                if (disk_num_bytes < cur_alloc_size)
                        break;

                /* we're not doing compressed IO, don't unlock the first
                 * page (which the caller expects to stay locked), don't
                 * clear any dirty bits and don't set any writeback bits
                 *
                 * Do set the Private2 bit so we know this page was properly
                 * setup for writepage
                 */
                op = unlock ? PAGE_UNLOCK : 0;
                op |= PAGE_SET_PRIVATE2;

                extent_clear_unlock_delalloc(inode, start,
                                             start + ram_size - 1, locked_page,
                                             EXTENT_LOCKED | EXTENT_DELALLOC,
                                             op);
                disk_num_bytes -= cur_alloc_size;
                num_bytes -= cur_alloc_size;
                alloc_hint = ins.objectid + ins.offset;
                start += cur_alloc_size;
        }
out:
        return ret;

out_drop_extent_cache:
        btrfs_drop_extent_cache(inode, start, start + ram_size - 1, 0);
out_reserve:
        btrfs_free_reserved_extent(root, ins.objectid, ins.offset, 1);
out_unlock:
        extent_clear_unlock_delalloc(inode, start, end, locked_page,
                                     EXTENT_LOCKED | EXTENT_DO_ACCOUNTING |
                                     EXTENT_DELALLOC | EXTENT_DEFRAG,
                                     PAGE_UNLOCK | PAGE_CLEAR_DIRTY |
                                     PAGE_SET_WRITEBACK | PAGE_END_WRITEBACK);
        goto out;
}

/*
 * work queue call back to started compression on a file and pages
 */
static noinline void async_cow_start(struct btrfs_work *work)
{
        struct async_cow *async_cow;
        int num_added = 0;
        async_cow = container_of(work, struct async_cow, work);

        compress_file_range(async_cow->inode, async_cow->locked_page,
                            async_cow->start, async_cow->end, async_cow,
                            &num_added);
        if (num_added == 0) {
                btrfs_add_delayed_iput(async_cow->inode);
                async_cow->inode = NULL;
        }
}

/*
 * work queue call back to submit previously compressed pages
 */
static noinline void async_cow_submit(struct btrfs_work *work)
{
        struct async_cow *async_cow;
        struct btrfs_root *root;
        unsigned long nr_pages;

        async_cow = container_of(work, struct async_cow, work);

        root = async_cow->root;
        nr_pages = (async_cow->end - async_cow->start + PAGE_CACHE_SIZE) >>
                PAGE_CACHE_SHIFT;

        if (atomic_sub_return(nr_pages, &root->fs_info->async_delalloc_pages) <
            5 * 1024 * 1024 &&
            waitqueue_active(&root->fs_info->async_submit_wait))
                wake_up(&root->fs_info->async_submit_wait);

        if (async_cow->inode)
                submit_compressed_extents(async_cow->inode, async_cow);
}

static noinline void async_cow_free(struct btrfs_work *work)
{
        struct async_cow *async_cow;
        async_cow = container_of(work, struct async_cow, work);
        if (async_cow->inode)
                btrfs_add_delayed_iput(async_cow->inode);
        kfree(async_cow);
}

static int cow_file_range_async(struct inode *inode, struct page *locked_page,
                                u64 start, u64 end, int *page_started,
                                unsigned long *nr_written)
{
        struct async_cow *async_cow;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        unsigned long nr_pages;
        u64 cur_end;
        int limit = 10 * 1024 * 1024;

        clear_extent_bit(&BTRFS_I(inode)->io_tree, start, end, EXTENT_LOCKED,
                         1, 0, NULL, GFP_NOFS);
        while (start < end) {
                async_cow = kmalloc(sizeof(*async_cow), GFP_NOFS);
                BUG_ON(!async_cow); /* -ENOMEM */
                async_cow->inode = igrab(inode);
                async_cow->root = root;
                async_cow->locked_page = locked_page;
                async_cow->start = start;

                if (BTRFS_I(inode)->flags & BTRFS_INODE_NOCOMPRESS &&
                    !btrfs_test_opt(root, FORCE_COMPRESS))
                        cur_end = end;
                else
                        cur_end = min(end, start + 512 * 1024 - 1);

                async_cow->end = cur_end;
                INIT_LIST_HEAD(&async_cow->extents);

                btrfs_init_work(&async_cow->work,
                                btrfs_delalloc_helper,
                                async_cow_start, async_cow_submit,
                                async_cow_free);

                nr_pages = (cur_end - start + PAGE_CACHE_SIZE) >>
                        PAGE_CACHE_SHIFT;
                atomic_add(nr_pages, &root->fs_info->async_delalloc_pages);

                btrfs_queue_work(root->fs_info->delalloc_workers,
                                 &async_cow->work);

                if (atomic_read(&root->fs_info->async_delalloc_pages) > limit) {
                        wait_event(root->fs_info->async_submit_wait,
                           (atomic_read(&root->fs_info->async_delalloc_pages) <
                            limit));
                }

                while (atomic_read(&root->fs_info->async_submit_draining) &&
                      atomic_read(&root->fs_info->async_delalloc_pages)) {
                        wait_event(root->fs_info->async_submit_wait,
                          (atomic_read(&root->fs_info->async_delalloc_pages) ==
                           0));
                }

                *nr_written += nr_pages;
                start = cur_end + 1;
        }
        *page_started = 1;
        return 0;
}

static noinline int csum_exist_in_range(struct btrfs_root *root,
                                        u64 bytenr, u64 num_bytes)
{
        int ret;
        struct btrfs_ordered_sum *sums;
        LIST_HEAD(list);

        ret = btrfs_lookup_csums_range(root->fs_info->csum_root, bytenr,
                                       bytenr + num_bytes - 1, &list, 0);
        if (ret == 0 && list_empty(&list))
                return 0;

        while (!list_empty(&list)) {
                sums = list_entry(list.next, struct btrfs_ordered_sum, list);
                list_del(&sums->list);
                kfree(sums);
        }
        return 1;
}

/*
 * when nowcow writeback call back.  This checks for snapshots or COW copies
 * of the extents that exist in the file, and COWs the file as required.
 *
 * If no cow copies or snapshots exist, we write directly to the existing
 * blocks on disk
 */
static noinline int run_delalloc_nocow(struct inode *inode,
                                       struct page *locked_page,
                              u64 start, u64 end, int *page_started, int force,
                              unsigned long *nr_written)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_trans_handle *trans;
        struct extent_buffer *leaf;
        struct btrfs_path *path;
        struct btrfs_file_extent_item *fi;
        struct btrfs_key found_key;
        u64 cow_start;
        u64 cur_offset;
        u64 extent_end;
        u64 extent_offset;
        u64 disk_bytenr;
        u64 num_bytes;
        u64 disk_num_bytes;
        u64 ram_bytes;
        int extent_type;
        int ret, err;
        int type;
        int nocow;
        int check_prev = 1;
        bool nolock;
        u64 ino = btrfs_ino(inode);

        path = btrfs_alloc_path();
        if (!path) {
                extent_clear_unlock_delalloc(inode, start, end, locked_page,
                                             EXTENT_LOCKED | EXTENT_DELALLOC |
                                             EXTENT_DO_ACCOUNTING |
                                             EXTENT_DEFRAG, PAGE_UNLOCK |
                                             PAGE_CLEAR_DIRTY |
                                             PAGE_SET_WRITEBACK |
                                             PAGE_END_WRITEBACK);
                return -ENOMEM;
        }

        nolock = btrfs_is_free_space_inode(inode);

        if (nolock)
                trans = btrfs_join_transaction_nolock(root);
        else
                trans = btrfs_join_transaction(root);

        if (IS_ERR(trans)) {
                extent_clear_unlock_delalloc(inode, start, end, locked_page,
                                             EXTENT_LOCKED | EXTENT_DELALLOC |
                                             EXTENT_DO_ACCOUNTING |
                                             EXTENT_DEFRAG, PAGE_UNLOCK |
                                             PAGE_CLEAR_DIRTY |
                                             PAGE_SET_WRITEBACK |
                                             PAGE_END_WRITEBACK);
                btrfs_free_path(path);
                return PTR_ERR(trans);
        }

        trans->block_rsv = &root->fs_info->delalloc_block_rsv;

        cow_start = (u64)-1;
        cur_offset = start;
        while (1) {
                ret = btrfs_lookup_file_extent(trans, root, path, ino,
                                               cur_offset, 0);
                if (ret < 0)
                        goto error;
                if (ret > 0 && path->slots[0] > 0 && check_prev) {
                        leaf = path->nodes[0];
                        btrfs_item_key_to_cpu(leaf, &found_key,
                                              path->slots[0] - 1);
                        if (found_key.objectid == ino &&
                            found_key.type == BTRFS_EXTENT_DATA_KEY)
                                path->slots[0]--;
                }
                check_prev = 0;
next_slot:
                leaf = path->nodes[0];
                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                goto error;
                        if (ret > 0)
                                break;
                        leaf = path->nodes[0];
                }

                nocow = 0;
                disk_bytenr = 0;
                num_bytes = 0;
                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);

                if (found_key.objectid > ino ||
                    found_key.type > BTRFS_EXTENT_DATA_KEY ||
                    found_key.offset > end)
                        break;

                if (found_key.offset > cur_offset) {
                        extent_end = found_key.offset;
                        extent_type = 0;
                        goto out_check;
                }

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

                ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi);
                if (extent_type == BTRFS_FILE_EXTENT_REG ||
                    extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
                        disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
                        extent_offset = btrfs_file_extent_offset(leaf, fi);
                        extent_end = found_key.offset +
                                btrfs_file_extent_num_bytes(leaf, fi);
                        disk_num_bytes =
                                btrfs_file_extent_disk_num_bytes(leaf, fi);
                        if (extent_end <= start) {
                                path->slots[0]++;
                                goto next_slot;
                        }
                        if (disk_bytenr == 0)
                                goto out_check;
                        if (btrfs_file_extent_compression(leaf, fi) ||
                            btrfs_file_extent_encryption(leaf, fi) ||
                            btrfs_file_extent_other_encoding(leaf, fi))
                                goto out_check;
                        if (extent_type == BTRFS_FILE_EXTENT_REG && !force)
                                goto out_check;
                        if (btrfs_extent_readonly(root, disk_bytenr))
                                goto out_check;
                        if (btrfs_cross_ref_exist(trans, root, ino,
                                                  found_key.offset -
                                                  extent_offset, disk_bytenr))
                                goto out_check;
                        disk_bytenr += extent_offset;
                        disk_bytenr += cur_offset - found_key.offset;
                        num_bytes = min(end + 1, extent_end) - cur_offset;
                        /*
                         * if there are pending snapshots for this root,
                         * we fall into common COW way.
                         */
                        if (!nolock) {
                                err = btrfs_start_nocow_write(root);
                                if (!err)
                                        goto out_check;
                        }
                        /*
                         * force cow if csum exists in the range.
                         * this ensure that csum for a given extent are
                         * either valid or do not exist.
                         */
                        if (csum_exist_in_range(root, disk_bytenr, num_bytes))
                                goto out_check;
                        nocow = 1;
                } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                        extent_end = found_key.offset +
                                btrfs_file_extent_inline_len(leaf,
                                                     path->slots[0], fi);
                        extent_end = ALIGN(extent_end, root->sectorsize);
                } else {
                        BUG_ON(1);
                }
out_check:
                if (extent_end <= start) {
                        path->slots[0]++;
                        if (!nolock && nocow)
                                btrfs_end_nocow_write(root);
                        goto next_slot;
                }
                if (!nocow) {
                        if (cow_start == (u64)-1)
                                cow_start = cur_offset;
                        cur_offset = extent_end;
                        if (cur_offset > end)
                                break;
                        path->slots[0]++;
                        goto next_slot;
                }

                btrfs_release_path(path);
                if (cow_start != (u64)-1) {
                        ret = cow_file_range(inode, locked_page,
                                             cow_start, found_key.offset - 1,
                                             page_started, nr_written, 1);
                        if (ret) {
                                if (!nolock && nocow)
                                        btrfs_end_nocow_write(root);
                                goto error;
                        }
                        cow_start = (u64)-1;
                }

                if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
                        struct extent_map *em;
                        struct extent_map_tree *em_tree;
                        em_tree = &BTRFS_I(inode)->extent_tree;
                        em = alloc_extent_map();
                        BUG_ON(!em); /* -ENOMEM */
                        em->start = cur_offset;
                        em->orig_start = found_key.offset - extent_offset;
                        em->len = num_bytes;
                        em->block_len = num_bytes;
                        em->block_start = disk_bytenr;
                        em->orig_block_len = disk_num_bytes;
                        em->ram_bytes = ram_bytes;
                        em->bdev = root->fs_info->fs_devices->latest_bdev;
                        em->mod_start = em->start;
                        em->mod_len = em->len;
                        set_bit(EXTENT_FLAG_PINNED, &em->flags);
                        set_bit(EXTENT_FLAG_FILLING, &em->flags);
                        em->generation = -1;
                        while (1) {
                                write_lock(&em_tree->lock);
                                ret = add_extent_mapping(em_tree, em, 1);
                                write_unlock(&em_tree->lock);
                                if (ret != -EEXIST) {
                                        free_extent_map(em);
                                        break;
                                }
                                btrfs_drop_extent_cache(inode, em->start,
                                                em->start + em->len - 1, 0);
                        }
                        type = BTRFS_ORDERED_PREALLOC;
                } else {
                        type = BTRFS_ORDERED_NOCOW;
                }

                ret = btrfs_add_ordered_extent(inode, cur_offset, disk_bytenr,
                                               num_bytes, num_bytes, type);
                BUG_ON(ret); /* -ENOMEM */

                if (root->root_key.objectid ==
                    BTRFS_DATA_RELOC_TREE_OBJECTID) {
                        ret = btrfs_reloc_clone_csums(inode, cur_offset,
                                                      num_bytes);
                        if (ret) {
                                if (!nolock && nocow)
                                        btrfs_end_nocow_write(root);
                                goto error;
                        }
                }

                extent_clear_unlock_delalloc(inode, cur_offset,
                                             cur_offset + num_bytes - 1,
                                             locked_page, EXTENT_LOCKED |
                                             EXTENT_DELALLOC, PAGE_UNLOCK |
                                             PAGE_SET_PRIVATE2);
                if (!nolock && nocow)
                        btrfs_end_nocow_write(root);
                cur_offset = extent_end;
                if (cur_offset > end)
                        break;
        }
        btrfs_release_path(path);

        if (cur_offset <= end && cow_start == (u64)-1) {
                cow_start = cur_offset;
                cur_offset = end;
        }

        if (cow_start != (u64)-1) {
                ret = cow_file_range(inode, locked_page, cow_start, end,
                                     page_started, nr_written, 1);
                if (ret)
                        goto error;
        }

error:
        err = btrfs_end_transaction(trans, root);
        if (!ret)
                ret = err;

        if (ret && cur_offset < end)
                extent_clear_unlock_delalloc(inode, cur_offset, end,
                                             locked_page, EXTENT_LOCKED |
                                             EXTENT_DELALLOC | EXTENT_DEFRAG |
                                             EXTENT_DO_ACCOUNTING, PAGE_UNLOCK |
                                             PAGE_CLEAR_DIRTY |
                                             PAGE_SET_WRITEBACK |
                                             PAGE_END_WRITEBACK);
        btrfs_free_path(path);
        return ret;
}

static inline int need_force_cow(struct inode *inode, u64 start, u64 end)
{

        if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW) &&
            !(BTRFS_I(inode)->flags & BTRFS_INODE_PREALLOC))
                return 0;

        /*
         * @defrag_bytes is a hint value, no spinlock held here,
         * if is not zero, it means the file is defragging.
         * Force cow if given extent needs to be defragged.
         */
        if (BTRFS_I(inode)->defrag_bytes &&
            test_range_bit(&BTRFS_I(inode)->io_tree, start, end,
                           EXTENT_DEFRAG, 0, NULL))
                return 1;

        return 0;
}

/*
 * extent_io.c call back to do delayed allocation processing
 */
static int run_delalloc_range(struct inode *inode, struct page *locked_page,
                              u64 start, u64 end, int *page_started,
                              unsigned long *nr_written)
{
        int ret;
        int force_cow = need_force_cow(inode, start, end);

        if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW && !force_cow) {
                ret = run_delalloc_nocow(inode, locked_page, start, end,
                                         page_started, 1, nr_written);
        } else if (BTRFS_I(inode)->flags & BTRFS_INODE_PREALLOC && !force_cow) {
                ret = run_delalloc_nocow(inode, locked_page, start, end,
                                         page_started, 0, nr_written);
        } else if (!inode_need_compress(inode)) {
                ret = cow_file_range(inode, locked_page, start, end,
                                      page_started, nr_written, 1);
        } else {
                set_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
                        &BTRFS_I(inode)->runtime_flags);
                ret = cow_file_range_async(inode, locked_page, start, end,
                                           page_started, nr_written);
        }
        return ret;
}

static void btrfs_split_extent_hook(struct inode *inode,
                                    struct extent_state *orig, u64 split)
{
        /* not delalloc, ignore it */
        if (!(orig->state & EXTENT_DELALLOC))
                return;

        spin_lock(&BTRFS_I(inode)->lock);
        BTRFS_I(inode)->outstanding_extents++;
        spin_unlock(&BTRFS_I(inode)->lock);
}

/*
 * extent_io.c merge_extent_hook, used to track merged delayed allocation
 * extents so we can keep track of new extents that are just merged onto old
 * extents, such as when we are doing sequential writes, so we can properly
 * account for the metadata space we'll need.
 */
static void btrfs_merge_extent_hook(struct inode *inode,
                                    struct extent_state *new,
                                    struct extent_state *other)
{
        /* not delalloc, ignore it */
        if (!(other->state & EXTENT_DELALLOC))
                return;

        spin_lock(&BTRFS_I(inode)->lock);
        BTRFS_I(inode)->outstanding_extents--;
        spin_unlock(&BTRFS_I(inode)->lock);
}

static void btrfs_add_delalloc_inodes(struct btrfs_root *root,
                                      struct inode *inode)
{
        spin_lock(&root->delalloc_lock);
        if (list_empty(&BTRFS_I(inode)->delalloc_inodes)) {
                list_add_tail(&BTRFS_I(inode)->delalloc_inodes,
                              &root->delalloc_inodes);
                set_bit(BTRFS_INODE_IN_DELALLOC_LIST,
                        &BTRFS_I(inode)->runtime_flags);
                root->nr_delalloc_inodes++;
                if (root->nr_delalloc_inodes == 1) {
                        spin_lock(&root->fs_info->delalloc_root_lock);
                        BUG_ON(!list_empty(&root->delalloc_root));
                        list_add_tail(&root->delalloc_root,
                                      &root->fs_info->delalloc_roots);
                        spin_unlock(&root->fs_info->delalloc_root_lock);
                }
        }
        spin_unlock(&root->delalloc_lock);
}

static void btrfs_del_delalloc_inode(struct btrfs_root *root,
                                     struct inode *inode)
{
        spin_lock(&root->delalloc_lock);
        if (!list_empty(&BTRFS_I(inode)->delalloc_inodes)) {
                list_del_init(&BTRFS_I(inode)->delalloc_inodes);
                clear_bit(BTRFS_INODE_IN_DELALLOC_LIST,
                          &BTRFS_I(inode)->runtime_flags);
                root->nr_delalloc_inodes--;
                if (!root->nr_delalloc_inodes) {
                        spin_lock(&root->fs_info->delalloc_root_lock);
                        BUG_ON(list_empty(&root->delalloc_root));
                        list_del_init(&root->delalloc_root);
                        spin_unlock(&root->fs_info->delalloc_root_lock);
                }
        }
        spin_unlock(&root->delalloc_lock);
}

/*
 * extent_io.c set_bit_hook, used to track delayed allocation
 * bytes in this file, and to maintain the list of inodes that
 * have pending delalloc work to be done.
 */
static void btrfs_set_bit_hook(struct inode *inode,
                               struct extent_state *state, unsigned long *bits)
{

        if ((*bits & EXTENT_DEFRAG) && !(*bits & EXTENT_DELALLOC))
                WARN_ON(1);
        /*
         * set_bit and clear bit hooks normally require _irqsave/restore
         * but in this case, we are only testing for the DELALLOC
         * bit, which is only set or cleared with irqs on
         */
        if (!(state->state & EXTENT_DELALLOC) && (*bits & EXTENT_DELALLOC)) {
                struct btrfs_root *root = BTRFS_I(inode)->root;
                u64 len = state->end + 1 - state->start;
                bool do_list = !btrfs_is_free_space_inode(inode);

                if (*bits & EXTENT_FIRST_DELALLOC) {
                        *bits &= ~EXTENT_FIRST_DELALLOC;
                } else {
                        spin_lock(&BTRFS_I(inode)->lock);
                        BTRFS_I(inode)->outstanding_extents++;
                        spin_unlock(&BTRFS_I(inode)->lock);
                }

                __percpu_counter_add(&root->fs_info->delalloc_bytes, len,
                                     root->fs_info->delalloc_batch);
                spin_lock(&BTRFS_I(inode)->lock);
                BTRFS_I(inode)->delalloc_bytes += len;
                if (*bits & EXTENT_DEFRAG)
                        BTRFS_I(inode)->defrag_bytes += len;
                if (do_list && !test_bit(BTRFS_INODE_IN_DELALLOC_LIST,
                                         &BTRFS_I(inode)->runtime_flags))
                        btrfs_add_delalloc_inodes(root, inode);
                spin_unlock(&BTRFS_I(inode)->lock);
        }
}

/*
 * extent_io.c clear_bit_hook, see set_bit_hook for why
 */
static void btrfs_clear_bit_hook(struct inode *inode,
                                 struct extent_state *state,
                                 unsigned long *bits)
{
        u64 len = state->end + 1 - state->start;

        spin_lock(&BTRFS_I(inode)->lock);
        if ((state->state & EXTENT_DEFRAG) && (*bits & EXTENT_DEFRAG))
                BTRFS_I(inode)->defrag_bytes -= len;
        spin_unlock(&BTRFS_I(inode)->lock);

        /*
         * set_bit and clear bit hooks normally require _irqsave/restore
         * but in this case, we are only testing for the DELALLOC
         * bit, which is only set or cleared with irqs on
         */
        if ((state->state & EXTENT_DELALLOC) && (*bits & EXTENT_DELALLOC)) {
                struct btrfs_root *root = BTRFS_I(inode)->root;
                bool do_list = !btrfs_is_free_space_inode(inode);

                if (*bits & EXTENT_FIRST_DELALLOC) {
                        *bits &= ~EXTENT_FIRST_DELALLOC;
                } else if (!(*bits & EXTENT_DO_ACCOUNTING)) {
                        spin_lock(&BTRFS_I(inode)->lock);
                        BTRFS_I(inode)->outstanding_extents--;
                        spin_unlock(&BTRFS_I(inode)->lock);
                }

                /*
                 * We don't reserve metadata space for space cache inodes so we
                 * don't need to call dellalloc_release_metadata if there is an
                 * error.
                 */
                if (*bits & EXTENT_DO_ACCOUNTING &&
                    root != root->fs_info->tree_root)
                        btrfs_delalloc_release_metadata(inode, len);

                if (root->root_key.objectid != BTRFS_DATA_RELOC_TREE_OBJECTID
                    && do_list && !(state->state & EXTENT_NORESERVE))
                        btrfs_free_reserved_data_space(inode, len);

                __percpu_counter_add(&root->fs_info->delalloc_bytes, -len,
                                     root->fs_info->delalloc_batch);
                spin_lock(&BTRFS_I(inode)->lock);
                BTRFS_I(inode)->delalloc_bytes -= len;
                if (do_list && BTRFS_I(inode)->delalloc_bytes == 0 &&
                    test_bit(BTRFS_INODE_IN_DELALLOC_LIST,
                             &BTRFS_I(inode)->runtime_flags))
                        btrfs_del_delalloc_inode(root, inode);
                spin_unlock(&BTRFS_I(inode)->lock);
        }
}

/*
 * extent_io.c merge_bio_hook, this must check the chunk tree to make sure
 * we don't create bios that span stripes or chunks
 */
int btrfs_merge_bio_hook(int rw, struct page *page, unsigned long offset,
                         size_t size, struct bio *bio,
                         unsigned long bio_flags)
{
        struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
        u64 logical = (u64)bio->bi_iter.bi_sector << 9;
        u64 length = 0;
        u64 map_length;
        int ret;

        if (bio_flags & EXTENT_BIO_COMPRESSED)
                return 0;

        length = bio->bi_iter.bi_size;
        map_length = length;
        ret = btrfs_map_block(root->fs_info, rw, logical,
                              &map_length, NULL, 0);
        /* Will always return 0 with map_multi == NULL */
        BUG_ON(ret < 0);
        if (map_length < length + size)
                return 1;
        return 0;
}

/*
 * in order to insert checksums into the metadata in large chunks,
 * we wait until bio submission time.   All the pages in the bio are
 * checksummed and sums are attached onto the ordered extent record.
 *
 * At IO completion time the cums attached on the ordered extent record
 * are inserted into the btree
 */
static int __btrfs_submit_bio_start(struct inode *inode, int rw,
                                    struct bio *bio, int mirror_num,
                                    unsigned long bio_flags,
                                    u64 bio_offset)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        int ret = 0;

        ret = btrfs_csum_one_bio(root, inode, bio, 0, 0);
        BUG_ON(ret); /* -ENOMEM */
        return 0;
}

/*
 * in order to insert checksums into the metadata in large chunks,
 * we wait until bio submission time.   All the pages in the bio are
 * checksummed and sums are attached onto the ordered extent record.
 *
 * At IO completion time the cums attached on the ordered extent record
 * are inserted into the btree
 */
static int __btrfs_submit_bio_done(struct inode *inode, int rw, struct bio *bio,
                          int mirror_num, unsigned long bio_flags,
                          u64 bio_offset)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        int ret;

        ret = btrfs_map_bio(root, rw, bio, mirror_num, 1);
        if (ret)
                bio_endio(bio, ret);
        return ret;
}

/*
 * extent_io.c submission hook. This does the right thing for csum calculation
 * on write, or reading the csums from the tree before a read
 */
static int btrfs_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
                          int mirror_num, unsigned long bio_flags,
                          u64 bio_offset)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        int ret = 0;
        int skip_sum;
        int metadata = 0;
        int async = !atomic_read(&BTRFS_I(inode)->sync_writers);

        skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;

        if (btrfs_is_free_space_inode(inode))
                metadata = 2;

        if (!(rw & REQ_WRITE)) {
                ret = btrfs_bio_wq_end_io(root->fs_info, bio, metadata);
                if (ret)
                        goto out;

                if (bio_flags & EXTENT_BIO_COMPRESSED) {
                        ret = btrfs_submit_compressed_read(inode, bio,
                                                           mirror_num,
                                                           bio_flags);
                        goto out;
                } else if (!skip_sum) {
                        ret = btrfs_lookup_bio_sums(root, inode, bio, NULL);
                        if (ret)
                                goto out;
                }
                goto mapit;
        } else if (async && !skip_sum) {
                /* csum items have already been cloned */
                if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID)
                        goto mapit;
                /* we're doing a write, do the async checksumming */
                ret = btrfs_wq_submit_bio(BTRFS_I(inode)->root->fs_info,
                                   inode, rw, bio, mirror_num,
                                   bio_flags, bio_offset,
                                   __btrfs_submit_bio_start,
                                   __btrfs_submit_bio_done);
                goto out;
        } else if (!skip_sum) {
                ret = btrfs_csum_one_bio(root, inode, bio, 0, 0);
                if (ret)
                        goto out;
        }

mapit:
        ret = btrfs_map_bio(root, rw, bio, mirror_num, 0);

out:
        if (ret < 0)
                bio_endio(bio, ret);
        return ret;
}

/*
 * given a list of ordered sums record them in the inode.  This happens
 * at IO completion time based on sums calculated at bio submission time.
 */
static noinline int add_pending_csums(struct btrfs_trans_handle *trans,
                             struct inode *inode, u64 file_offset,
                             struct list_head *list)
{
        struct btrfs_ordered_sum *sum;

        list_for_each_entry(sum, list, list) {
                trans->adding_csums = 1;
                btrfs_csum_file_blocks(trans,
                       BTRFS_I(inode)->root->fs_info->csum_root, sum);
                trans->adding_csums = 0;
        }
        return 0;
}

int btrfs_set_extent_delalloc(struct inode *inode, u64 start, u64 end,
                              struct extent_state **cached_state)
{
        WARN_ON((end & (PAGE_CACHE_SIZE - 1)) == 0);
        return set_extent_delalloc(&BTRFS_I(inode)->io_tree, start, end,
                                   cached_state, GFP_NOFS);
}

/* see btrfs_writepage_start_hook for details on why this is required */
struct btrfs_writepage_fixup {
        struct page *page;
        struct btrfs_work work;
};

static void btrfs_writepage_fixup_worker(struct btrfs_work *work)
{
        struct btrfs_writepage_fixup *fixup;
        struct btrfs_ordered_extent *ordered;
        struct extent_state *cached_state = NULL;
        struct page *page;
        struct inode *inode;
        u64 page_start;
        u64 page_end;
        int ret;

        fixup = container_of(work, struct btrfs_writepage_fixup, work);
        page = fixup->page;
again:
        lock_page(page);
        if (!page->mapping || !PageDirty(page) || !PageChecked(page)) {
                ClearPageChecked(page);
                goto out_page;
        }

        inode = page->mapping->host;
        page_start = page_offset(page);
        page_end = page_offset(page) + PAGE_CACHE_SIZE - 1;

        lock_extent_bits(&BTRFS_I(inode)->io_tree, page_start, page_end, 0,
                         &cached_state);

        /* already ordered? We're done */
        if (PagePrivate2(page))
                goto out;

        ordered = btrfs_lookup_ordered_extent(inode, page_start);
        if (ordered) {
                unlock_extent_cached(&BTRFS_I(inode)->io_tree, page_start,
                                     page_end, &cached_state, GFP_NOFS);
                unlock_page(page);
                btrfs_start_ordered_extent(inode, ordered, 1);
                btrfs_put_ordered_extent(ordered);
                goto again;
        }

        ret = btrfs_delalloc_reserve_space(inode, PAGE_CACHE_SIZE);
        if (ret) {
                mapping_set_error(page->mapping, ret);
                end_extent_writepage(page, ret, page_start, page_end);
                ClearPageChecked(page);
                goto out;
         }

        btrfs_set_extent_delalloc(inode, page_start, page_end, &cached_state);
        ClearPageChecked(page);
        set_page_dirty(page);
out:
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, page_start, page_end,
                             &cached_state, GFP_NOFS);
out_page:
        unlock_page(page);
        page_cache_release(page);
        kfree(fixup);
}

/*
 * There are a few paths in the higher layers of the kernel that directly
 * set the page dirty bit without asking the filesystem if it is a
 * good idea.  This causes problems because we want to make sure COW
 * properly happens and the data=ordered rules are followed.
 *
 * In our case any range that doesn't have the ORDERED bit set
 * hasn't been properly setup for IO.  We kick off an async process
 * to fix it up.  The async helper will wait for ordered extents, set
 * the delalloc bit and make it safe to write the page.
 */
static int btrfs_writepage_start_hook(struct page *page, u64 start, u64 end)
{
        struct inode *inode = page->mapping->host;
        struct btrfs_writepage_fixup *fixup;
        struct btrfs_root *root = BTRFS_I(inode)->root;

        /* this page is properly in the ordered list */
        if (TestClearPagePrivate2(page))
                return 0;

        if (PageChecked(page))
                return -EAGAIN;

        fixup = kzalloc(sizeof(*fixup), GFP_NOFS);
        if (!fixup)
                return -EAGAIN;

        SetPageChecked(page);
        page_cache_get(page);
        btrfs_init_work(&fixup->work, btrfs_fixup_helper,
                        btrfs_writepage_fixup_worker, NULL, NULL);
        fixup->page = page;
        btrfs_queue_work(root->fs_info->fixup_workers, &fixup->work);
        return -EBUSY;
}

static int insert_reserved_file_extent(struct btrfs_trans_handle *trans,
                                       struct inode *inode, u64 file_pos,
                                       u64 disk_bytenr, u64 disk_num_bytes,
                                       u64 num_bytes, u64 ram_bytes,
                                       u8 compression, u8 encryption,
                                       u16 other_encoding, int extent_type)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_file_extent_item *fi;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_key ins;
        int extent_inserted = 0;
        int ret;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /*
         * we may be replacing one extent in the tree with another.
         * The new extent is pinned in the extent map, and we don't want
         * to drop it from the cache until it is completely in the btree.
         *
         * So, tell btrfs_drop_extents to leave this extent in the cache.
         * the caller is expected to unpin it and allow it to be merged
         * with the others.
         */
        ret = __btrfs_drop_extents(trans, root, inode, path, file_pos,
                                   file_pos + num_bytes, NULL, 0,
                                   1, sizeof(*fi), &extent_inserted);
        if (ret)
                goto out;

        if (!extent_inserted) {
                ins.objectid = btrfs_ino(inode);
                ins.offset = file_pos;
                ins.type = BTRFS_EXTENT_DATA_KEY;

                path->leave_spinning = 1;
                ret = btrfs_insert_empty_item(trans, root, path, &ins,
                                              sizeof(*fi));
                if (ret)
                        goto out;
        }
        leaf = path->nodes[0];
        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_type(leaf, fi, extent_type);
        btrfs_set_file_extent_disk_bytenr(leaf, fi, disk_bytenr);
        btrfs_set_file_extent_disk_num_bytes(leaf, fi, disk_num_bytes);
        btrfs_set_file_extent_offset(leaf, fi, 0);
        btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
        btrfs_set_file_extent_ram_bytes(leaf, fi, ram_bytes);
        btrfs_set_file_extent_compression(leaf, fi, compression);
        btrfs_set_file_extent_encryption(leaf, fi, encryption);
        btrfs_set_file_extent_other_encoding(leaf, fi, other_encoding);

        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        inode_add_bytes(inode, num_bytes);

        ins.objectid = disk_bytenr;
        ins.offset = disk_num_bytes;
        ins.type = BTRFS_EXTENT_ITEM_KEY;
        ret = btrfs_alloc_reserved_file_extent(trans, root,
                                        root->root_key.objectid,
                                        btrfs_ino(inode), file_pos, &ins);
out:
        btrfs_free_path(path);

        return ret;
}

/* snapshot-aware defrag */
struct sa_defrag_extent_backref {
        struct rb_node node;
        struct old_sa_defrag_extent *old;
        u64 root_id;
        u64 inum;
        u64 file_pos;
        u64 extent_offset;
        u64 num_bytes;
        u64 generation;
};

struct old_sa_defrag_extent {
        struct list_head list;
        struct new_sa_defrag_extent *new;

        u64 extent_offset;
        u64 bytenr;
        u64 offset;
        u64 len;
        int count;
};

struct new_sa_defrag_extent {
        struct rb_root root;
        struct list_head head;
        struct btrfs_path *path;
        struct inode *inode;
        u64 file_pos;
        u64 len;
        u64 bytenr;
        u64 disk_len;
        u8 compress_type;
};

static int backref_comp(struct sa_defrag_extent_backref *b1,
                        struct sa_defrag_extent_backref *b2)
{
        if (b1->root_id < b2->root_id)
                return -1;
        else if (b1->root_id > b2->root_id)
                return 1;

        if (b1->inum < b2->inum)
                return -1;
        else if (b1->inum > b2->inum)
                return 1;

        if (b1->file_pos < b2->file_pos)
                return -1;
        else if (b1->file_pos > b2->file_pos)
                return 1;

        /*
         * [------------------------------] ===> (a range of space)
         *     |<--->|   |<---->| =============> (fs/file tree A)
         * |<---------------------------->| ===> (fs/file tree B)
         *
         * A range of space can refer to two file extents in one tree while
         * refer to only one file extent in another tree.
         *
         * So we may process a disk offset more than one time(two extents in A)
         * and locate at the same extent(one extent in B), then insert two same
         * backrefs(both refer to the extent in B).
         */
        return 0;
}

static void backref_insert(struct rb_root *root,
                           struct sa_defrag_extent_backref *backref)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct sa_defrag_extent_backref *entry;
        int ret;

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct sa_defrag_extent_backref, node);

                ret = backref_comp(backref, entry);
                if (ret < 0)
                        p = &(*p)->rb_left;
                else
                        p = &(*p)->rb_right;
        }

        rb_link_node(&backref->node, parent, p);
        rb_insert_color(&backref->node, root);
}

/*
 * Note the backref might has changed, and in this case we just return 0.
 */
static noinline int record_one_backref(u64 inum, u64 offset, u64 root_id,
                                       void *ctx)
{
        struct btrfs_file_extent_item *extent;
        struct btrfs_fs_info *fs_info;
        struct old_sa_defrag_extent *old = ctx;
        struct new_sa_defrag_extent *new = old->new;
        struct btrfs_path *path = new->path;
        struct btrfs_key key;
        struct btrfs_root *root;
        struct sa_defrag_extent_backref *backref;
        struct extent_buffer *leaf;
        struct inode *inode = new->inode;
        int slot;
        int ret;
        u64 extent_offset;
        u64 num_bytes;

        if (BTRFS_I(inode)->root->root_key.objectid == root_id &&
            inum == btrfs_ino(inode))
                return 0;

        key.objectid = root_id;
        key.type = BTRFS_ROOT_ITEM_KEY;
        key.offset = (u64)-1;

        fs_info = BTRFS_I(inode)->root->fs_info;
        root = btrfs_read_fs_root_no_name(fs_info, &key);
        if (IS_ERR(root)) {
                if (PTR_ERR(root) == -ENOENT)
                        return 0;
                WARN_ON(1);
                pr_debug("inum=%llu, offset=%llu, root_id=%llu\n",
                         inum, offset, root_id);
                return PTR_ERR(root);
        }

        key.objectid = inum;
        key.type = BTRFS_EXTENT_DATA_KEY;
        if (offset > (u64)-1 << 32)
                key.offset = 0;
        else
                key.offset = offset;

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (WARN_ON(ret < 0))
                return ret;
        ret = 0;

        while (1) {
                cond_resched();

                leaf = path->nodes[0];
                slot = path->slots[0];

                if (slot >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0) {
                                goto out;
                        } else if (ret > 0) {
                                ret = 0;
                                goto out;
                        }
                        continue;
                }

                path->slots[0]++;

                btrfs_item_key_to_cpu(leaf, &key, slot);

                if (key.objectid > inum)
                        goto out;

                if (key.objectid < inum || key.type != BTRFS_EXTENT_DATA_KEY)
                        continue;

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

                if (btrfs_file_extent_disk_bytenr(leaf, extent) != old->bytenr)
                        continue;

                /*
                 * 'offset' refers to the exact key.offset,
                 * NOT the 'offset' field in btrfs_extent_data_ref, ie.
                 * (key.offset - extent_offset).
                 */
                if (key.offset != offset)
                        continue;

                extent_offset = btrfs_file_extent_offset(leaf, extent);
                num_bytes = btrfs_file_extent_num_bytes(leaf, extent);

                if (extent_offset >= old->extent_offset + old->offset +
                    old->len || extent_offset + num_bytes <=
                    old->extent_offset + old->offset)
                        continue;
                break;
        }

        backref = kmalloc(sizeof(*backref), GFP_NOFS);
        if (!backref) {
                ret = -ENOENT;
                goto out;
        }

        backref->root_id = root_id;
        backref->inum = inum;
        backref->file_pos = offset;
        backref->num_bytes = num_bytes;
        backref->extent_offset = extent_offset;
        backref->generation = btrfs_file_extent_generation(leaf, extent);
        backref->old = old;
        backref_insert(&new->root, backref);
        old->count++;
out:
        btrfs_release_path(path);
        WARN_ON(ret);
        return ret;
}

static noinline bool record_extent_backrefs(struct btrfs_path *path,
                                   struct new_sa_defrag_extent *new)
{
        struct btrfs_fs_info *fs_info = BTRFS_I(new->inode)->root->fs_info;
        struct old_sa_defrag_extent *old, *tmp;
        int ret;

        new->path = path;

        list_for_each_entry_safe(old, tmp, &new->head, list) {
                ret = iterate_inodes_from_logical(old->bytenr +
                                                  old->extent_offset, fs_info,
                                                  path, record_one_backref,
                                                  old);
                if (ret < 0 && ret != -ENOENT)
                        return false;

                /* no backref to be processed for this extent */
                if (!old->count) {
                        list_del(&old->list);
                        kfree(old);
                }
        }

        if (list_empty(&new->head))
                return false;

        return true;
}

static int relink_is_mergable(struct extent_buffer *leaf,
                              struct btrfs_file_extent_item *fi,
                              struct new_sa_defrag_extent *new)
{
        if (btrfs_file_extent_disk_bytenr(leaf, fi) != new->bytenr)
                return 0;

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

        if (btrfs_file_extent_compression(leaf, fi) != new->compress_type)
                return 0;

        if (btrfs_file_extent_encryption(leaf, fi) ||
            btrfs_file_extent_other_encoding(leaf, fi))
                return 0;

        return 1;
}

/*
 * Note the backref might has changed, and in this case we just return 0.
 */
static noinline int relink_extent_backref(struct btrfs_path *path,
                                 struct sa_defrag_extent_backref *prev,
                                 struct sa_defrag_extent_backref *backref)
{
        struct btrfs_file_extent_item *extent;
        struct btrfs_file_extent_item *item;
        struct btrfs_ordered_extent *ordered;
        struct btrfs_trans_handle *trans;
        struct btrfs_fs_info *fs_info;
        struct btrfs_root *root;
        struct btrfs_key key;
        struct extent_buffer *leaf;
        struct old_sa_defrag_extent *old = backref->old;
        struct new_sa_defrag_extent *new = old->new;
        struct inode *src_inode = new->inode;
        struct inode *inode;
        struct extent_state *cached = NULL;
        int ret = 0;
        u64 start;
        u64 len;
        u64 lock_start;
        u64 lock_end;
        bool merge = false;
        int index;

        if (prev && prev->root_id == backref->root_id &&
            prev->inum == backref->inum &&
            prev->file_pos + prev->num_bytes == backref->file_pos)
                merge = true;

        /* step 1: get root */
        key.objectid = backref->root_id;
        key.type = BTRFS_ROOT_ITEM_KEY;
        key.offset = (u64)-1;

        fs_info = BTRFS_I(src_inode)->root->fs_info;
        index = srcu_read_lock(&fs_info->subvol_srcu);

        root = btrfs_read_fs_root_no_name(fs_info, &key);
        if (IS_ERR(root)) {
                srcu_read_unlock(&fs_info->subvol_srcu, index);
                if (PTR_ERR(root) == -ENOENT)
                        return 0;
                return PTR_ERR(root);
        }

        if (btrfs_root_readonly(root)) {
                srcu_read_unlock(&fs_info->subvol_srcu, index);
                return 0;
        }

        /* step 2: get inode */
        key.objectid = backref->inum;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;

        inode = btrfs_iget(fs_info->sb, &key, root, NULL);
        if (IS_ERR(inode)) {
                srcu_read_unlock(&fs_info->subvol_srcu, index);
                return 0;
        }

        srcu_read_unlock(&fs_info->subvol_srcu, index);

        /* step 3: relink backref */
        lock_start = backref->file_pos;
        lock_end = backref->file_pos + backref->num_bytes - 1;
        lock_extent_bits(&BTRFS_I(inode)->io_tree, lock_start, lock_end,
                         0, &cached);

        ordered = btrfs_lookup_first_ordered_extent(inode, lock_end);
        if (ordered) {
                btrfs_put_ordered_extent(ordered);
                goto out_unlock;
        }

        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                goto out_unlock;
        }

        key.objectid = backref->inum;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = backref->file_pos;

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0) {
                goto out_free_path;
        } else if (ret > 0) {
                ret = 0;
                goto out_free_path;
        }

        extent = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                struct btrfs_file_extent_item);

        if (btrfs_file_extent_generation(path->nodes[0], extent) !=
            backref->generation)
                goto out_free_path;

        btrfs_release_path(path);

        start = backref->file_pos;
        if (backref->extent_offset < old->extent_offset + old->offset)
                start += old->extent_offset + old->offset -
                         backref->extent_offset;

        len = min(backref->extent_offset + backref->num_bytes,
                  old->extent_offset + old->offset + old->len);
        len -= max(backref->extent_offset, old->extent_offset + old->offset);

        ret = btrfs_drop_extents(trans, root, inode, start,
                                 start + len, 1);
        if (ret)
                goto out_free_path;
again:
        key.objectid = btrfs_ino(inode);
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = start;

        path->leave_spinning = 1;
        if (merge) {
                struct btrfs_file_extent_item *fi;
                u64 extent_len;
                struct btrfs_key found_key;

                ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
                if (ret < 0)
                        goto out_free_path;

                path->slots[0]--;
                leaf = path->nodes[0];
                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);

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

                if (extent_len + found_key.offset == start &&
                    relink_is_mergable(leaf, fi, new)) {
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_len + len);
                        btrfs_mark_buffer_dirty(leaf);
                        inode_add_bytes(inode, len);

                        ret = 1;
                        goto out_free_path;
                } else {
                        merge = false;
                        btrfs_release_path(path);
                        goto again;
                }
        }

        ret = btrfs_insert_empty_item(trans, root, path, &key,
                                        sizeof(*extent));
        if (ret) {
                btrfs_abort_transaction(trans, root, ret);
                goto out_free_path;
        }

        leaf = path->nodes[0];
        item = btrfs_item_ptr(leaf, path->slots[0],
                                struct btrfs_file_extent_item);
        btrfs_set_file_extent_disk_bytenr(leaf, item, new->bytenr);
        btrfs_set_file_extent_disk_num_bytes(leaf, item, new->disk_len);
        btrfs_set_file_extent_offset(leaf, item, start - new->file_pos);
        btrfs_set_file_extent_num_bytes(leaf, item, len);
        btrfs_set_file_extent_ram_bytes(leaf, item, new->len);
        btrfs_set_file_extent_generation(leaf, item, trans->transid);
        btrfs_set_file_extent_type(leaf, item, BTRFS_FILE_EXTENT_REG);
        btrfs_set_file_extent_compression(leaf, item, new->compress_type);
        btrfs_set_file_extent_encryption(leaf, item, 0);
        btrfs_set_file_extent_other_encoding(leaf, item, 0);

        btrfs_mark_buffer_dirty(leaf);
        inode_add_bytes(inode, len);
        btrfs_release_path(path);

        ret = btrfs_inc_extent_ref(trans, root, new->bytenr,
                        new->disk_len, 0,
                        backref->root_id, backref->inum,
                        new->file_pos, 0);      /* start - extent_offset */
        if (ret) {
                btrfs_abort_transaction(trans, root, ret);
                goto out_free_path;
        }

        ret = 1;
out_free_path:
        btrfs_release_path(path);
        path->leave_spinning = 0;
        btrfs_end_transaction(trans, root);
out_unlock:
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, lock_start, lock_end,
                             &cached, GFP_NOFS);
        iput(inode);
        return ret;
}

static void free_sa_defrag_extent(struct new_sa_defrag_extent *new)
{
        struct old_sa_defrag_extent *old, *tmp;

        if (!new)
                return;

        list_for_each_entry_safe(old, tmp, &new->head, list) {
                list_del(&old->list);
                kfree(old);
        }
        kfree(new);
}

static void relink_file_extents(struct new_sa_defrag_extent *new)
{
        struct btrfs_path *path;
        struct sa_defrag_extent_backref *backref;
        struct sa_defrag_extent_backref *prev = NULL;
        struct inode *inode;
        struct btrfs_root *root;
        struct rb_node *node;
        int ret;

        inode = new->inode;
        root = BTRFS_I(inode)->root;

        path = btrfs_alloc_path();
        if (!path)
                return;

        if (!record_extent_backrefs(path, new)) {
                btrfs_free_path(path);
                goto out;
        }
        btrfs_release_path(path);

        while (1) {
                node = rb_first(&new->root);
                if (!node)
                        break;
                rb_erase(node, &new->root);

                backref = rb_entry(node, struct sa_defrag_extent_backref, node);

                ret = relink_extent_backref(path, prev, backref);
                WARN_ON(ret < 0);

                kfree(prev);

                if (ret == 1)
                        prev = backref;
                else
                        prev = NULL;
                cond_resched();
        }
        kfree(prev);

        btrfs_free_path(path);
out:
        free_sa_defrag_extent(new);

        atomic_dec(&root->fs_info->defrag_running);
        wake_up(&root->fs_info->transaction_wait);
}

static struct new_sa_defrag_extent *
record_old_file_extents(struct inode *inode,
                        struct btrfs_ordered_extent *ordered)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct old_sa_defrag_extent *old;
        struct new_sa_defrag_extent *new;
        int ret;

        new = kmalloc(sizeof(*new), GFP_NOFS);
        if (!new)
                return NULL;

        new->inode = inode;
        new->file_pos = ordered->file_offset;
        new->len = ordered->len;
        new->bytenr = ordered->start;
        new->disk_len = ordered->disk_len;
        new->compress_type = ordered->compress_type;
        new->root = RB_ROOT;
        INIT_LIST_HEAD(&new->head);

        path = btrfs_alloc_path();
        if (!path)
                goto out_kfree;

        key.objectid = btrfs_ino(inode);
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = new->file_pos;

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

        /* find out all the old extents for the file range */
        while (1) {
                struct btrfs_file_extent_item *extent;
                struct extent_buffer *l;
                int slot;
                u64 num_bytes;
                u64 offset;
                u64 end;
                u64 disk_bytenr;
                u64 extent_offset;

                l = path->nodes[0];
                slot = path->slots[0];

                if (slot >= btrfs_header_nritems(l)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                goto out_free_path;
                        else if (ret > 0)
                                break;
                        continue;
                }

                btrfs_item_key_to_cpu(l, &key, slot);

                if (key.objectid != btrfs_ino(inode))
                        break;
                if (key.type != BTRFS_EXTENT_DATA_KEY)
                        break;
                if (key.offset >= new->file_pos + new->len)
                        break;

                extent = btrfs_item_ptr(l, slot, struct btrfs_file_extent_item);

                num_bytes = btrfs_file_extent_num_bytes(l, extent);
                if (key.offset + num_bytes < new->file_pos)
                        goto next;

                disk_bytenr = btrfs_file_extent_disk_bytenr(l, extent);
                if (!disk_bytenr)
                        goto next;

                extent_offset = btrfs_file_extent_offset(l, extent);

                old = kmalloc(sizeof(*old), GFP_NOFS);
                if (!old)
                        goto out_free_path;

                offset = max(new->file_pos, key.offset);
                end = min(new->file_pos + new->len, key.offset + num_bytes);

                old->bytenr = disk_bytenr;
                old->extent_offset = extent_offset;
                old->offset = offset - key.offset;
                old->len = end - offset;
                old->new = new;
                old->count = 0;
                list_add_tail(&old->list, &new->head);
next:
                path->slots[0]++;
                cond_resched();
        }

        btrfs_free_path(path);
        atomic_inc(&root->fs_info->defrag_running);

        return new;

out_free_path:
        btrfs_free_path(path);
out_kfree:
        free_sa_defrag_extent(new);
        return NULL;
}

static void btrfs_release_delalloc_bytes(struct btrfs_root *root,
                                         u64 start, u64 len)
{
        struct btrfs_block_group_cache *cache;

        cache = btrfs_lookup_block_group(root->fs_info, start);
        ASSERT(cache);

        spin_lock(&cache->lock);
        cache->delalloc_bytes -= len;
        spin_unlock(&cache->lock);

        btrfs_put_block_group(cache);
}

/* as ordered data IO finishes, this gets called so we can finish
 * an ordered extent if the range of bytes in the file it covers are
 * fully written.
 */
static int btrfs_finish_ordered_io(struct btrfs_ordered_extent *ordered_extent)
{
        struct inode *inode = ordered_extent->inode;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_trans_handle *trans = NULL;
        struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
        struct extent_state *cached_state = NULL;
        struct new_sa_defrag_extent *new = NULL;
        int compress_type = 0;
        int ret = 0;
        u64 logical_len = ordered_extent->len;
        bool nolock;
        bool truncated = false;

        nolock = btrfs_is_free_space_inode(inode);

        if (test_bit(BTRFS_ORDERED_IOERR, &ordered_extent->flags)) {
                ret = -EIO;
                goto out;
        }

        btrfs_free_io_failure_record(inode, ordered_extent->file_offset,
                                     ordered_extent->file_offset +
                                     ordered_extent->len - 1);

        if (test_bit(BTRFS_ORDERED_TRUNCATED, &ordered_extent->flags)) {
                truncated = true;
                logical_len = ordered_extent->truncated_len;
                /* Truncated the entire extent, don't bother adding */
                if (!logical_len)
                        goto out;
        }

        if (test_bit(BTRFS_ORDERED_NOCOW, &ordered_extent->flags)) {
                BUG_ON(!list_empty(&ordered_extent->list)); /* Logic error */
                btrfs_ordered_update_i_size(inode, 0, ordered_extent);
                if (nolock)
                        trans = btrfs_join_transaction_nolock(root);
                else
                        trans = btrfs_join_transaction(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        trans = NULL;
                        goto out;
                }
                trans->block_rsv = &root->fs_info->delalloc_block_rsv;
                ret = btrfs_update_inode_fallback(trans, root, inode);
                if (ret) /* -ENOMEM or corruption */
                        btrfs_abort_transaction(trans, root, ret);
                goto out;
        }

        lock_extent_bits(io_tree, ordered_extent->file_offset,
                         ordered_extent->file_offset + ordered_extent->len - 1,
                         0, &cached_state);

        ret = test_range_bit(io_tree, ordered_extent->file_offset,
                        ordered_extent->file_offset + ordered_extent->len - 1,
                        EXTENT_DEFRAG, 1, cached_state);
        if (ret) {
                u64 last_snapshot = btrfs_root_last_snapshot(&root->root_item);
                if (0 && last_snapshot >= BTRFS_I(inode)->generation)
                        /* the inode is shared */
                        new = record_old_file_extents(inode, ordered_extent);

                clear_extent_bit(io_tree, ordered_extent->file_offset,
                        ordered_extent->file_offset + ordered_extent->len - 1,
                        EXTENT_DEFRAG, 0, 0, &cached_state, GFP_NOFS);
        }

        if (nolock)
                trans = btrfs_join_transaction_nolock(root);
        else
                trans = btrfs_join_transaction(root);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                trans = NULL;
                goto out_unlock;
        }

        trans->block_rsv = &root->fs_info->delalloc_block_rsv;

        if (test_bit(BTRFS_ORDERED_COMPRESSED, &ordered_extent->flags))
                compress_type = ordered_extent->compress_type;
        if (test_bit(BTRFS_ORDERED_PREALLOC, &ordered_extent->flags)) {
                BUG_ON(compress_type);
                ret = btrfs_mark_extent_written(trans, inode,
                                                ordered_extent->file_offset,
                                                ordered_extent->file_offset +
                                                logical_len);
        } else {
                BUG_ON(root == root->fs_info->tree_root);
                ret = insert_reserved_file_extent(trans, inode,
                                                ordered_extent->file_offset,
                                                ordered_extent->start,
                                                ordered_extent->disk_len,
                                                logical_len, logical_len,
                                                compress_type, 0, 0,
                                                BTRFS_FILE_EXTENT_REG);
                if (!ret)
                        btrfs_release_delalloc_bytes(root,
                                                     ordered_extent->start,
                                                     ordered_extent->disk_len);
        }
        unpin_extent_cache(&BTRFS_I(inode)->extent_tree,
                           ordered_extent->file_offset, ordered_extent->len,
                           trans->transid);
        if (ret < 0) {
                btrfs_abort_transaction(trans, root, ret);
                goto out_unlock;
        }

        add_pending_csums(trans, inode, ordered_extent->file_offset,
                          &ordered_extent->list);

        btrfs_ordered_update_i_size(inode, 0, ordered_extent);
        ret = btrfs_update_inode_fallback(trans, root, inode);
        if (ret) { /* -ENOMEM or corruption */
                btrfs_abort_transaction(trans, root, ret);
                goto out_unlock;
        }
        ret = 0;
out_unlock:
        unlock_extent_cached(io_tree, ordered_extent->file_offset,
                             ordered_extent->file_offset +
                             ordered_extent->len - 1, &cached_state, GFP_NOFS);
out:
        if (root != root->fs_info->tree_root)
                btrfs_delalloc_release_metadata(inode, ordered_extent->len);
        if (trans)
                btrfs_end_transaction(trans, root);

        if (ret || truncated) {
                u64 start, end;

                if (truncated)
                        start = ordered_extent->file_offset + logical_len;
                else
                        start = ordered_extent->file_offset;
                end = ordered_extent->file_offset + ordered_extent->len - 1;
                clear_extent_uptodate(io_tree, start, end, NULL, GFP_NOFS);

                /* Drop the cache for the part of the extent we didn't write. */
                btrfs_drop_extent_cache(inode, start, end, 0);

                /*
                 * If the ordered extent had an IOERR or something else went
                 * wrong we need to return the space for this ordered extent
                 * back to the allocator.  We only free the extent in the
                 * truncated case if we didn't write out the extent at all.
                 */
                if ((ret || !logical_len) &&
                    !test_bit(BTRFS_ORDERED_NOCOW, &ordered_extent->flags) &&
                    !test_bit(BTRFS_ORDERED_PREALLOC, &ordered_extent->flags))
                        btrfs_free_reserved_extent(root, ordered_extent->start,
                                                   ordered_extent->disk_len, 1);
        }


        /*
         * This needs to be done to make sure anybody waiting knows we are done
         * updating everything for this ordered extent.
         */
        btrfs_remove_ordered_extent(inode, ordered_extent);

        /* for snapshot-aware defrag */
        if (new) {
                if (ret) {
                        free_sa_defrag_extent(new);
                        atomic_dec(&root->fs_info->defrag_running);
                } else {
                        relink_file_extents(new);
                }
        }

        /* once for us */
        btrfs_put_ordered_extent(ordered_extent);
        /* once for the tree */
        btrfs_put_ordered_extent(ordered_extent);

        return ret;
}

static void finish_ordered_fn(struct btrfs_work *work)
{
        struct btrfs_ordered_extent *ordered_extent;
        ordered_extent = container_of(work, struct btrfs_ordered_extent, work);
        btrfs_finish_ordered_io(ordered_extent);
}

static int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
                                struct extent_state *state, int uptodate)
{
        struct inode *inode = page->mapping->host;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_ordered_extent *ordered_extent = NULL;
        struct btrfs_workqueue *wq;
        btrfs_work_func_t func;

        trace_btrfs_writepage_end_io_hook(page, start, end, uptodate);

        ClearPagePrivate2(page);
        if (!btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
                                            end - start + 1, uptodate))
                return 0;

        if (btrfs_is_free_space_inode(inode)) {
                wq = root->fs_info->endio_freespace_worker;
                func = btrfs_freespace_write_helper;
        } else {
                wq = root->fs_info->endio_write_workers;
                func = btrfs_endio_write_helper;
        }

        btrfs_init_work(&ordered_extent->work, func, finish_ordered_fn, NULL,
                        NULL);
        btrfs_queue_work(wq, &ordered_extent->work);

        return 0;
}

static int __readpage_endio_check(struct inode *inode,
                                  struct btrfs_io_bio *io_bio,
                                  int icsum, struct page *page,
                                  int pgoff, u64 start, size_t len)
{
        char *kaddr;
        u32 csum_expected;
        u32 csum = ~(u32)0;
        static DEFINE_RATELIMIT_STATE(_rs, DEFAULT_RATELIMIT_INTERVAL,
                                      DEFAULT_RATELIMIT_BURST);

        csum_expected = *(((u32 *)io_bio->csum) + icsum);

        kaddr = kmap_atomic(page);
        csum = btrfs_csum_data(kaddr + pgoff, csum,  len);
        btrfs_csum_final(csum, (char *)&csum);
        if (csum != csum_expected)
                goto zeroit;

        kunmap_atomic(kaddr);
        return 0;
zeroit:
        if (__ratelimit(&_rs))
                btrfs_info(BTRFS_I(inode)->root->fs_info,
                           "csum failed ino %llu off %llu csum %u expected csum %u",
                           btrfs_ino(inode), start, csum, csum_expected);
        memset(kaddr + pgoff, 1, len);
        flush_dcache_page(page);
        kunmap_atomic(kaddr);
        if (csum_expected == 0)
                return 0;
        return -EIO;
}

/*
 * when reads are done, we need to check csums to verify the data is correct
 * if there's a match, we allow the bio to finish.  If not, the code in
 * extent_io.c will try to find good copies for us.
 */
static int btrfs_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
                                      u64 phy_offset, struct page *page,
                                      u64 start, u64 end, int mirror)
{
        size_t offset = start - page_offset(page);
        struct inode *inode = page->mapping->host;
        struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
        struct btrfs_root *root = BTRFS_I(inode)->root;

        if (PageChecked(page)) {
                ClearPageChecked(page);
                return 0;
        }

        if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
                return 0;

        if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID &&
            test_range_bit(io_tree, start, end, EXTENT_NODATASUM, 1, NULL)) {
                clear_extent_bits(io_tree, start, end, EXTENT_NODATASUM,
                                  GFP_NOFS);
                return 0;
        }

        phy_offset >>= inode->i_sb->s_blocksize_bits;
        return __readpage_endio_check(inode, io_bio, phy_offset, page, offset,
                                      start, (size_t)(end - start + 1));
}

struct delayed_iput {
        struct list_head list;
        struct inode *inode;
};

/* JDM: If this is fs-wide, why can't we add a pointer to
 * btrfs_inode instead and avoid the allocation? */
void btrfs_add_delayed_iput(struct inode *inode)
{
        struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
        struct delayed_iput *delayed;

        if (atomic_add_unless(&inode->i_count, -1, 1))
                return;

        delayed = kmalloc(sizeof(*delayed), GFP_NOFS | __GFP_NOFAIL);
        delayed->inode = inode;

        spin_lock(&fs_info->delayed_iput_lock);
        list_add_tail(&delayed->list, &fs_info->delayed_iputs);
        spin_unlock(&fs_info->delayed_iput_lock);
}

void btrfs_run_delayed_iputs(struct btrfs_root *root)
{
        LIST_HEAD(list);
        struct btrfs_fs_info *fs_info = root->fs_info;