// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 */

#include <crypto/hash.h>
#include <linux/kernel.h>
#include <linux/bio.h>
#include <linux/blk-cgroup.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/writeback.h>
#include <linux/compat.h>
#include <linux/xattr.h>
#include <linux/posix_acl.h>
#include <linux/falloc.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include <linux/btrfs.h>
#include <linux/blkdev.h>
#include <linux/posix_acl_xattr.h>
#include <linux/uio.h>
#include <linux/magic.h>
#include <linux/iversion.h>
#include <linux/swap.h>
#include <linux/migrate.h>
#include <linux/sched/mm.h>
#include <linux/iomap.h>
#include <asm/unaligned.h>
#include <linux/fsverity.h>
#include "misc.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 "props.h"
#include "qgroup.h"
#include "delalloc-space.h"
#include "block-group.h"
#include "space-info.h"
#include "zoned.h"
#include "subpage.h"
#include "inode-item.h"

struct btrfs_iget_args {
        u64 ino;
        struct btrfs_root *root;
};

struct btrfs_dio_data {
        ssize_t submitted;
        struct extent_changeset *data_reserved;
};

struct btrfs_rename_ctx {
        /* Output field. Stores the index number of the old directory entry. */
        u64 index;
};

static const struct inode_operations btrfs_dir_inode_operations;
static const struct inode_operations btrfs_symlink_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 file_operations btrfs_dir_file_operations;

static struct kmem_cache *btrfs_inode_cachep;
struct kmem_cache *btrfs_trans_handle_cachep;
struct kmem_cache *btrfs_path_cachep;
struct kmem_cache *btrfs_free_space_cachep;
struct kmem_cache *btrfs_free_space_bitmap_cachep;

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

static void __endio_write_update_ordered(struct btrfs_inode *inode,
                                         const u64 offset, const u64 bytes,
                                         const bool uptodate);

/*
 * btrfs_inode_lock - lock inode i_rwsem based on arguments passed
 *
 * ilock_flags can have the following bit set:
 *
 * BTRFS_ILOCK_SHARED - acquire a shared lock on the inode
 * BTRFS_ILOCK_TRY - try to acquire the lock, if fails on first attempt
 *                   return -EAGAIN
 * BTRFS_ILOCK_MMAP - acquire a write lock on the i_mmap_lock
 */
int btrfs_inode_lock(struct inode *inode, unsigned int ilock_flags)
{
        if (ilock_flags & BTRFS_ILOCK_SHARED) {
                if (ilock_flags & BTRFS_ILOCK_TRY) {
                        if (!inode_trylock_shared(inode))
                                return -EAGAIN;
                        else
                                return 0;
                }
                inode_lock_shared(inode);
        } else {
                if (ilock_flags & BTRFS_ILOCK_TRY) {
                        if (!inode_trylock(inode))
                                return -EAGAIN;
                        else
                                return 0;
                }
                inode_lock(inode);
        }
        if (ilock_flags & BTRFS_ILOCK_MMAP)
                down_write(&BTRFS_I(inode)->i_mmap_lock);
        return 0;
}

/*
 * btrfs_inode_unlock - unock inode i_rwsem
 *
 * ilock_flags should contain the same bits set as passed to btrfs_inode_lock()
 * to decide whether the lock acquired is shared or exclusive.
 */
void btrfs_inode_unlock(struct inode *inode, unsigned int ilock_flags)
{
        if (ilock_flags & BTRFS_ILOCK_MMAP)
                up_write(&BTRFS_I(inode)->i_mmap_lock);
        if (ilock_flags & BTRFS_ILOCK_SHARED)
                inode_unlock_shared(inode);
        else
                inode_unlock(inode);
}

/*
 * Cleanup all submitted ordered extents in specified range to handle errors
 * from the btrfs_run_delalloc_range() callback.
 *
 * NOTE: caller must ensure that when an error happens, it can not call
 * extent_clear_unlock_delalloc() to clear both the bits EXTENT_DO_ACCOUNTING
 * and EXTENT_DELALLOC simultaneously, because that causes the reserved metadata
 * to be released, which we want to happen only when finishing the ordered
 * extent (btrfs_finish_ordered_io()).
 */
static inline void btrfs_cleanup_ordered_extents(struct btrfs_inode *inode,
                                                 struct page *locked_page,
                                                 u64 offset, u64 bytes)
{
        unsigned long index = offset >> PAGE_SHIFT;
        unsigned long end_index = (offset + bytes - 1) >> PAGE_SHIFT;
        u64 page_start = page_offset(locked_page);
        u64 page_end = page_start + PAGE_SIZE - 1;

        struct page *page;

        while (index <= end_index) {
                /*
                 * For locked page, we will call end_extent_writepage() on it
                 * in run_delalloc_range() for the error handling.  That
                 * end_extent_writepage() function will call
                 * btrfs_mark_ordered_io_finished() to clear page Ordered and
                 * run the ordered extent accounting.
                 *
                 * Here we can't just clear the Ordered bit, or
                 * btrfs_mark_ordered_io_finished() would skip the accounting
                 * for the page range, and the ordered extent will never finish.
                 */
                if (index == (page_offset(locked_page) >> PAGE_SHIFT)) {
                        index++;
                        continue;
                }
                page = find_get_page(inode->vfs_inode.i_mapping, index);
                index++;
                if (!page)
                        continue;

                /*
                 * Here we just clear all Ordered bits for every page in the
                 * range, then __endio_write_update_ordered() will handle
                 * the ordered extent accounting for the range.
                 */
                btrfs_page_clamp_clear_ordered(inode->root->fs_info, page,
                                               offset, bytes);
                put_page(page);
        }

        /* The locked page covers the full range, nothing needs to be done */
        if (bytes + offset <= page_offset(locked_page) + PAGE_SIZE)
                return;
        /*
         * In case this page belongs to the delalloc range being instantiated
         * then skip it, since the first page of a range is going to be
         * properly cleaned up by the caller of run_delalloc_range
         */
        if (page_start >= offset && page_end <= (offset + bytes - 1)) {
                bytes = offset + bytes - page_offset(locked_page) - PAGE_SIZE;
                offset = page_offset(locked_page) + PAGE_SIZE;
        }

        return __endio_write_update_ordered(inode, offset, bytes, false);
}

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,
                                struct btrfs_inode *inode, bool extent_inserted,
                                size_t size, size_t compressed_size,
                                int compress_type,
                                struct page **compressed_pages,
                                bool update_i_size)
{
        struct btrfs_root *root = inode->root;
        struct extent_buffer *leaf;
        struct page *page = NULL;
        char *kaddr;
        unsigned long ptr;
        struct btrfs_file_extent_item *ei;
        int ret;
        size_t cur_size = size;
        u64 i_size;

        ASSERT((compressed_size > 0 && compressed_pages) ||
               (compressed_size == 0 && !compressed_pages));

        if (compressed_size && compressed_pages)
                cur_size = compressed_size;

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

                key.objectid = btrfs_ino(inode);
                key.offset = 0;
                key.type = BTRFS_EXTENT_DATA_KEY;

                datasize = btrfs_file_extent_calc_inline_size(cur_size);
                ret = btrfs_insert_empty_item(trans, root, path, &key,
                                              datasize);
                if (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_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->vfs_inode.i_mapping, 0);
                btrfs_set_file_extent_compression(leaf, ei, 0);
                kaddr = kmap_atomic(page);
                write_extent_buffer(leaf, kaddr, ptr, size);
                kunmap_atomic(kaddr);
                put_page(page);
        }
        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        /*
         * We align size to sectorsize for inline extents just for simplicity
         * sake.
         */
        ret = btrfs_inode_set_file_extent_range(inode, 0,
                                        ALIGN(size, root->fs_info->sectorsize));
        if (ret)
                goto fail;

        /*
         * 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 i_size and inode updates before we unlock the pages.
         * Otherwise we could end up racing with unlink.
         */
        i_size = i_size_read(&inode->vfs_inode);
        if (update_i_size && size > i_size) {
                i_size_write(&inode->vfs_inode, size);
                i_size = size;
        }
        inode->disk_i_size = i_size;

fail:
        return ret;
}


/*
 * 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_inode *inode, u64 size,
                                          size_t compressed_size,
                                          int compress_type,
                                          struct page **compressed_pages,
                                          bool update_i_size)
{
        struct btrfs_drop_extents_args drop_args = { 0 };
        struct btrfs_root *root = inode->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_trans_handle *trans;
        u64 data_len = (compressed_size ?: size);
        int ret;
        struct btrfs_path *path;

        /*
         * We can create an inline extent if it ends at or beyond the current
         * i_size, is no larger than a sector (decompressed), and the (possibly
         * compressed) data fits in a leaf and the configured maximum inline
         * size.
         */
        if (size < i_size_read(&inode->vfs_inode) ||
            size > fs_info->sectorsize ||
            data_len > BTRFS_MAX_INLINE_DATA_SIZE(fs_info) ||
            data_len > 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 = &inode->block_rsv;

        drop_args.path = path;
        drop_args.start = 0;
        drop_args.end = fs_info->sectorsize;
        drop_args.drop_cache = true;
        drop_args.replace_extent = true;
        drop_args.extent_item_size = btrfs_file_extent_calc_inline_size(data_len);
        ret = btrfs_drop_extents(trans, root, inode, &drop_args);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

        ret = insert_inline_extent(trans, path, inode, drop_args.extent_inserted,
                                   size, compressed_size, compress_type,
                                   compressed_pages, update_i_size);
        if (ret && ret != -ENOSPC) {
                btrfs_abort_transaction(trans, ret);
                goto out;
        } else if (ret == -ENOSPC) {
                ret = 1;
                goto out;
        }

        btrfs_update_inode_bytes(inode, size, drop_args.bytes_found);
        ret = btrfs_update_inode(trans, root, inode);
        if (ret && ret != -ENOSPC) {
                btrfs_abort_transaction(trans, ret);
                goto out;
        } else if (ret == -ENOSPC) {
                ret = 1;
                goto out;
        }

        btrfs_set_inode_full_sync(inode);
out:
        /*
         * Don't forget to free the reserved space, as for inlined extent
         * it won't count as data extent, free them directly here.
         * And at reserve time, it's always aligned to page size, so
         * just free one page here.
         */
        btrfs_qgroup_free_data(inode, NULL, 0, PAGE_SIZE);
        btrfs_free_path(path);
        btrfs_end_transaction(trans);
        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_chunk {
        struct inode *inode;
        struct page *locked_page;
        u64 start;
        u64 end;
        unsigned int write_flags;
        struct list_head extents;
        struct cgroup_subsys_state *blkcg_css;
        struct btrfs_work work;
        struct async_cow *async_cow;
};

struct async_cow {
        atomic_t num_chunks;
        struct async_chunk chunks[];
};

static noinline int add_async_extent(struct async_chunk *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;
}

/*
 * Check if the inode needs to be submitted to compression, based on mount
 * options, defragmentation, properties or heuristics.
 */
static inline int inode_need_compress(struct btrfs_inode *inode, u64 start,
                                      u64 end)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;

        if (!btrfs_inode_can_compress(inode)) {
                WARN(IS_ENABLED(CONFIG_BTRFS_DEBUG),
                        KERN_ERR "BTRFS: unexpected compression for ino %llu\n",
                        btrfs_ino(inode));
                return 0;
        }
        /*
         * Special check for subpage.
         *
         * We lock the full page then run each delalloc range in the page, thus
         * for the following case, we will hit some subpage specific corner case:
         *
         * 0            32K             64K
         * |    |///////|       |///////|
         *              \- A            \- B
         *
         * In above case, both range A and range B will try to unlock the full
         * page [0, 64K), causing the one finished later will have page
         * unlocked already, triggering various page lock requirement BUG_ON()s.
         *
         * So here we add an artificial limit that subpage compression can only
         * if the range is fully page aligned.
         *
         * In theory we only need to ensure the first page is fully covered, but
         * the tailing partial page will be locked until the full compression
         * finishes, delaying the write of other range.
         *
         * TODO: Make btrfs_run_delalloc_range() to lock all delalloc range
         * first to prevent any submitted async extent to unlock the full page.
         * By this, we can ensure for subpage case that only the last async_cow
         * will unlock the full page.
         */
        if (fs_info->sectorsize < PAGE_SIZE) {
                if (!IS_ALIGNED(start, PAGE_SIZE) ||
                    !IS_ALIGNED(end + 1, PAGE_SIZE))
                        return 0;
        }

        /* force compress */
        if (btrfs_test_opt(fs_info, FORCE_COMPRESS))
                return 1;
        /* defrag ioctl */
        if (inode->defrag_compress)
                return 1;
        /* bad compression ratios */
        if (inode->flags & BTRFS_INODE_NOCOMPRESS)
                return 0;
        if (btrfs_test_opt(fs_info, COMPRESS) ||
            inode->flags & BTRFS_INODE_COMPRESS ||
            inode->prop_compress)
                return btrfs_compress_heuristic(&inode->vfs_inode, start, end);
        return 0;
}

static inline void inode_should_defrag(struct btrfs_inode *inode,
                u64 start, u64 end, u64 num_bytes, u32 small_write)
{
        /* If this is a small write inside eof, kick off a defrag */
        if (num_bytes < small_write &&
            (start > 0 || end + 1 < inode->disk_i_size))
                btrfs_add_inode_defrag(NULL, inode, small_write);
}

/*
 * 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 async_chunk *async_chunk)
{
        struct inode *inode = async_chunk->inode;
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        u64 blocksize = fs_info->sectorsize;
        u64 start = async_chunk->start;
        u64 end = async_chunk->end;
        u64 actual_end;
        u64 i_size;
        int ret = 0;
        struct page **pages = NULL;
        unsigned long nr_pages;
        unsigned long total_compressed = 0;
        unsigned long total_in = 0;
        int i;
        int will_compress;
        int compress_type = fs_info->compress_type;
        int compressed_extents = 0;
        int redirty = 0;

        inode_should_defrag(BTRFS_I(inode), start, end, end - start + 1,
                        SZ_16K);

        /*
         * We need to save i_size before now because it could change in between
         * us evaluating the size and assigning it.  This is because we lock and
         * unlock the page in truncate and fallocate, and then modify the i_size
         * later on.
         *
         * The barriers are to emulate READ_ONCE, remove that once i_size_read
         * does that for us.
         */
        barrier();
        i_size = i_size_read(inode);
        barrier();
        actual_end = min_t(u64, i_size, end + 1);
again:
        will_compress = 0;
        nr_pages = (end >> PAGE_SHIFT) - (start >> PAGE_SHIFT) + 1;
        nr_pages = min_t(unsigned long, nr_pages,
                        BTRFS_MAX_COMPRESSED / PAGE_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;

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

        /*
         * For subpage case, we require full page alignment for the sector
         * aligned range.
         * Thus we must also check against @actual_end, not just @end.
         */
        if (blocksize < PAGE_SIZE) {
                if (!IS_ALIGNED(start, PAGE_SIZE) ||
                    !IS_ALIGNED(round_up(actual_end, blocksize), PAGE_SIZE))
                        goto cleanup_and_bail_uncompressed;
        }

        total_compressed = min_t(unsigned long, total_compressed,
                        BTRFS_MAX_UNCOMPRESSED);
        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(BTRFS_I(inode), start, end)) {
                WARN_ON(pages);
                pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
                if (!pages) {
                        /* just bail out to the uncompressed code */
                        nr_pages = 0;
                        goto cont;
                }

                if (BTRFS_I(inode)->defrag_compress)
                        compress_type = BTRFS_I(inode)->defrag_compress;
                else if (BTRFS_I(inode)->prop_compress)
                        compress_type = BTRFS_I(inode)->prop_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.
                 *
                 * Note that the remaining part is redirtied, the start pointer
                 * has moved, the end is the original one.
                 */
                if (!redirty) {
                        extent_range_clear_dirty_for_io(inode, start, end);
                        redirty = 1;
                }

                /* Compression level is applied here and only here */
                ret = btrfs_compress_pages(
                        compress_type | (fs_info->compress_level << 4),
                                           inode->i_mapping, start,
                                           pages,
                                           &nr_pages,
                                           &total_in,
                                           &total_compressed);

                if (!ret) {
                        unsigned long offset = offset_in_page(total_compressed);
                        struct page *page = pages[nr_pages - 1];

                        /* zero the tail end of the last page, we might be
                         * sending it down to disk
                         */
                        if (offset)
                                memzero_page(page, offset, PAGE_SIZE - offset);
                        will_compress = 1;
                }
        }
cont:
        /*
         * Check cow_file_range() for why we don't even try to create inline
         * extent for subpage case.
         */
        if (start == 0 && fs_info->sectorsize == PAGE_SIZE) {
                /* lets try to make an inline extent */
                if (ret || total_in < actual_end) {
                        /* we didn't compress the entire range, try
                         * to make an uncompressed inline extent.
                         */
                        ret = cow_file_range_inline(BTRFS_I(inode), actual_end,
                                                    0, BTRFS_COMPRESS_NONE,
                                                    NULL, false);
                } else {
                        /* try making a compressed inline extent */
                        ret = cow_file_range_inline(BTRFS_I(inode), actual_end,
                                                    total_compressed,
                                                    compress_type, pages,
                                                    false);
                }
                if (ret <= 0) {
                        unsigned long clear_flags = EXTENT_DELALLOC |
                                EXTENT_DELALLOC_NEW | EXTENT_DEFRAG |
                                EXTENT_DO_ACCOUNTING;
                        unsigned long page_error_op;

                        page_error_op = ret < 0 ? PAGE_SET_ERROR : 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.
                         *
                         * We use DO_ACCOUNTING here because we need the
                         * delalloc_release_metadata to be done _after_ we drop
                         * our outstanding extent for clearing delalloc for this
                         * range.
                         */
                        extent_clear_unlock_delalloc(BTRFS_I(inode), start, end,
                                                     NULL,
                                                     clear_flags,
                                                     PAGE_UNLOCK |
                                                     PAGE_START_WRITEBACK |
                                                     page_error_op |
                                                     PAGE_END_WRITEBACK);

                        /*
                         * Ensure we only free the compressed pages if we have
                         * them allocated, as we can still reach here with
                         * inode_need_compress() == false.
                         */
                        if (pages) {
                                for (i = 0; i < nr_pages; i++) {
                                        WARN_ON(pages[i]->mapping);
                                        put_page(pages[i]);
                                }
                                kfree(pages);
                        }
                        return 0;
                }
        }

        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,
                 * compression must free at least one sector size
                 */
                total_in = round_up(total_in, fs_info->sectorsize);
                if (total_compressed + blocksize <= total_in) {
                        compressed_extents++;

                        /*
                         * 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_chunk, start, total_in,
                                        total_compressed, pages, nr_pages,
                                        compress_type);

                        if (start + total_in < end) {
                                start += total_in;
                                pages = NULL;
                                cond_resched();
                                goto again;
                        }
                        return compressed_extents;
                }
        }
        if (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; i++) {
                        WARN_ON(pages[i]->mapping);
                        put_page(pages[i]);
                }
                kfree(pages);
                pages = NULL;
                total_compressed = 0;
                nr_pages = 0;

                /* flag the file so we don't compress in the future */
                if (!btrfs_test_opt(fs_info, FORCE_COMPRESS) &&
                    !(BTRFS_I(inode)->prop_compress)) {
                        BTRFS_I(inode)->flags |= BTRFS_INODE_NOCOMPRESS;
                }
        }
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 (async_chunk->locked_page &&
            (page_offset(async_chunk->locked_page) >= start &&
             page_offset(async_chunk->locked_page)) <= end) {
                __set_page_dirty_nobuffers(async_chunk->locked_page);
                /* unlocked later on in the async handlers */
        }

        if (redirty)
                extent_range_redirty_for_io(inode, start, end);
        add_async_extent(async_chunk, start, end - start + 1, 0, NULL, 0,
                         BTRFS_COMPRESS_NONE);
        compressed_extents++;

        return compressed_extents;
}

static void free_async_extent_pages(struct async_extent *async_extent)
{
        int i;

        if (!async_extent->pages)
                return;

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

static int submit_uncompressed_range(struct btrfs_inode *inode,
                                     struct async_extent *async_extent,
                                     struct page *locked_page)
{
        u64 start = async_extent->start;
        u64 end = async_extent->start + async_extent->ram_size - 1;
        unsigned long nr_written = 0;
        int page_started = 0;
        int ret;

        /*
         * Call cow_file_range() to run the delalloc range directly, since we
         * won't go to NOCOW or async path again.
         *
         * Also we call cow_file_range() with @unlock_page == 0, so that we
         * can directly submit them without interruption.
         */
        ret = cow_file_range(inode, locked_page, start, end, &page_started,
                             &nr_written, 0);
        /* Inline extent inserted, page gets unlocked and everything is done */
        if (page_started) {
                ret = 0;
                goto out;
        }
        if (ret < 0) {
                if (locked_page)
                        unlock_page(locked_page);
                goto out;
        }

        ret = extent_write_locked_range(&inode->vfs_inode, start, end);
        /* All pages will be unlocked, including @locked_page */
out:
        kfree(async_extent);
        return ret;
}

static int submit_one_async_extent(struct btrfs_inode *inode,
                                   struct async_chunk *async_chunk,
                                   struct async_extent *async_extent,
                                   u64 *alloc_hint)
{
        struct extent_io_tree *io_tree = &inode->io_tree;
        struct btrfs_root *root = inode->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_key ins;
        struct page *locked_page = NULL;
        struct extent_map *em;
        int ret = 0;
        u64 start = async_extent->start;
        u64 end = async_extent->start + async_extent->ram_size - 1;

        /*
         * If async_chunk->locked_page is in the async_extent range, we need to
         * handle it.
         */
        if (async_chunk->locked_page) {
                u64 locked_page_start = page_offset(async_chunk->locked_page);
                u64 locked_page_end = locked_page_start + PAGE_SIZE - 1;

                if (!(start >= locked_page_end || end <= locked_page_start))
                        locked_page = async_chunk->locked_page;
        }
        lock_extent(io_tree, start, end);

        /* We have fall back to uncompressed write */
        if (!async_extent->pages)
                return submit_uncompressed_range(inode, async_extent, locked_page);

        ret = btrfs_reserve_extent(root, async_extent->ram_size,
                                   async_extent->compressed_size,
                                   async_extent->compressed_size,
                                   0, *alloc_hint, &ins, 1, 1);
        if (ret) {
                free_async_extent_pages(async_extent);
                /*
                 * Here we used to try again by going back to non-compressed
                 * path for ENOSPC.  But we can't reserve space even for
                 * compressed size, how could it work for uncompressed size
                 * which requires larger size?  So here we directly go error
                 * path.
                 */
                goto out_free;
        }

        /* Here we're doing allocation and writeback of the compressed pages */
        em = create_io_em(inode, start,
                          async_extent->ram_size,       /* len */
                          start,                        /* orig_start */
                          ins.objectid,                 /* block_start */
                          ins.offset,                   /* block_len */
                          ins.offset,                   /* orig_block_len */
                          async_extent->ram_size,       /* ram_bytes */
                          async_extent->compress_type,
                          BTRFS_ORDERED_COMPRESSED);
        if (IS_ERR(em)) {
                ret = PTR_ERR(em);
                goto out_free_reserve;
        }
        free_extent_map(em);

        ret = btrfs_add_ordered_extent(inode, start,            /* file_offset */
                                       async_extent->ram_size,  /* num_bytes */
                                       async_extent->ram_size,  /* ram_bytes */
                                       ins.objectid,            /* disk_bytenr */
                                       ins.offset,              /* disk_num_bytes */
                                       0,                       /* offset */
                                       1 << BTRFS_ORDERED_COMPRESSED,
                                       async_extent->compress_type);
        if (ret) {
                btrfs_drop_extent_cache(inode, start, end, 0);
                goto out_free_reserve;
        }
        btrfs_dec_block_group_reservations(fs_info, ins.objectid);

        /* Clear dirty, set writeback and unlock the pages. */
        extent_clear_unlock_delalloc(inode, start, end,
                        NULL, EXTENT_LOCKED | EXTENT_DELALLOC,
                        PAGE_UNLOCK | PAGE_START_WRITEBACK);
        if (btrfs_submit_compressed_write(inode, start, /* file_offset */
                            async_extent->ram_size,     /* num_bytes */
                            ins.objectid,               /* disk_bytenr */
                            ins.offset,                 /* compressed_len */
                            async_extent->pages,        /* compressed_pages */
                            async_extent->nr_pages,
                            async_chunk->write_flags,
                            async_chunk->blkcg_css, true)) {
                const u64 start = async_extent->start;
                const u64 end = start + async_extent->ram_size - 1;

                btrfs_writepage_endio_finish_ordered(inode, NULL, start, end, 0);

                extent_clear_unlock_delalloc(inode, start, end, NULL, 0,
                                             PAGE_END_WRITEBACK | PAGE_SET_ERROR);

                free_async_extent_pages(async_extent);
        }
        *alloc_hint = ins.objectid + ins.offset;
        kfree(async_extent);
        return ret;

out_free_reserve:
        btrfs_dec_block_group_reservations(fs_info, ins.objectid);
        btrfs_free_reserved_extent(fs_info, ins.objectid, ins.offset, 1);
out_free:
        extent_clear_unlock_delalloc(inode, start, end,
                                     NULL, EXTENT_LOCKED | EXTENT_DELALLOC |
                                     EXTENT_DELALLOC_NEW |
                                     EXTENT_DEFRAG | EXTENT_DO_ACCOUNTING,
                                     PAGE_UNLOCK | PAGE_START_WRITEBACK |
                                     PAGE_END_WRITEBACK | PAGE_SET_ERROR);
        free_async_extent_pages(async_extent);
        kfree(async_extent);
        return ret;
}

/*
 * 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 void submit_compressed_extents(struct async_chunk *async_chunk)
{
        struct btrfs_inode *inode = BTRFS_I(async_chunk->inode);
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct async_extent *async_extent;
        u64 alloc_hint = 0;
        int ret = 0;

        while (!list_empty(&async_chunk->extents)) {
                u64 extent_start;
                u64 ram_size;

                async_extent = list_entry(async_chunk->extents.next,
                                          struct async_extent, list);
                list_del(&async_extent->list);
                extent_start = async_extent->start;
                ram_size = async_extent->ram_size;

                ret = submit_one_async_extent(inode, async_chunk, async_extent,
                                              &alloc_hint);
                btrfs_debug(fs_info,
"async extent submission failed root=%lld inode=%llu start=%llu len=%llu ret=%d",
                            inode->root->root_key.objectid,
                            btrfs_ino(inode), extent_start, ram_size, ret);
        }
}

static u64 get_extent_allocation_hint(struct btrfs_inode *inode, u64 start,
                                      u64 num_bytes)
{
        struct extent_map_tree *em_tree = &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 btrfs_inode *inode,
                                   struct page *locked_page,
                                   u64 start, u64 end, int *page_started,
                                   unsigned long *nr_written, int unlock)
{
        struct btrfs_root *root = inode->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 alloc_hint = 0;
        u64 num_bytes;
        unsigned long ram_size;
        u64 cur_alloc_size = 0;
        u64 min_alloc_size;
        u64 blocksize = fs_info->sectorsize;
        struct btrfs_key ins;
        struct extent_map *em;
        unsigned clear_bits;
        unsigned long page_ops;
        bool extent_reserved = false;
        int ret = 0;

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

        num_bytes = ALIGN(end - start + 1, blocksize);
        num_bytes = max(blocksize,  num_bytes);
        ASSERT(num_bytes <= btrfs_super_total_bytes(fs_info->super_copy));

        inode_should_defrag(inode, start, end, num_bytes, SZ_64K);

        /*
         * Due to the page size limit, for subpage we can only trigger the
         * writeback for the dirty sectors of page, that means data writeback
         * is doing more writeback than what we want.
         *
         * This is especially unexpected for some call sites like fallocate,
         * where we only increase i_size after everything is done.
         * This means we can trigger inline extent even if we didn't want to.
         * So here we skip inline extent creation completely.
         */
        if (start == 0 && fs_info->sectorsize == PAGE_SIZE) {
                u64 actual_end = min_t(u64, i_size_read(&inode->vfs_inode),
                                       end + 1);

                /* lets try to make an inline extent */
                ret = cow_file_range_inline(inode, actual_end, 0,
                                            BTRFS_COMPRESS_NONE, NULL, false);
                if (ret == 0) {
                        /*
                         * We use DO_ACCOUNTING here because we need the
                         * delalloc_release_metadata to be run _after_ we drop
                         * our outstanding extent for clearing delalloc for this
                         * range.
                         */
                        extent_clear_unlock_delalloc(inode, start, end,
                                     locked_page,
                                     EXTENT_LOCKED | EXTENT_DELALLOC |
                                     EXTENT_DELALLOC_NEW | EXTENT_DEFRAG |
                                     EXTENT_DO_ACCOUNTING, PAGE_UNLOCK |
                                     PAGE_START_WRITEBACK | PAGE_END_WRITEBACK);
                        *nr_written = *nr_written +
                             (end - start + PAGE_SIZE) / PAGE_SIZE;
                        *page_started = 1;
                        /*
                         * locked_page is locked by the caller of
                         * writepage_delalloc(), not locked by
                         * __process_pages_contig().
                         *
                         * We can't let __process_pages_contig() to unlock it,
                         * as it doesn't have any subpage::writers recorded.
                         *
                         * Here we manually unlock the page, since the caller
                         * can't use page_started to determine if it's an
                         * inline extent or a compressed extent.
                         */
                        unlock_page(locked_page);
                        goto out;
                } else if (ret < 0) {
                        goto out_unlock;
                }
        }

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

        /*
         * Relocation relies on the relocated extents to have exactly the same
         * size as the original extents. Normally writeback for relocation data
         * extents follows a NOCOW path because relocation preallocates the
         * extents. However, due to an operation such as scrub turning a block
         * group to RO mode, it may fallback to COW mode, so we must make sure
         * an extent allocated during COW has exactly the requested size and can
         * not be split into smaller extents, otherwise relocation breaks and
         * fails during the stage where it updates the bytenr of file extent
         * items.
         */
        if (btrfs_is_data_reloc_root(root))
                min_alloc_size = num_bytes;
        else
                min_alloc_size = fs_info->sectorsize;

        while (num_bytes > 0) {
                cur_alloc_size = num_bytes;
                ret = btrfs_reserve_extent(root, cur_alloc_size, cur_alloc_size,
                                           min_alloc_size, 0, alloc_hint,
                                           &ins, 1, 1);
                if (ret < 0)
                        goto out_unlock;
                cur_alloc_size = ins.offset;
                extent_reserved = true;

                ram_size = ins.offset;
                em = create_io_em(inode, start, ins.offset, /* len */
                                  start, /* orig_start */
                                  ins.objectid, /* block_start */
                                  ins.offset, /* block_len */
                                  ins.offset, /* orig_block_len */
                                  ram_size, /* ram_bytes */
                                  BTRFS_COMPRESS_NONE, /* compress_type */
                                  BTRFS_ORDERED_REGULAR /* type */);
                if (IS_ERR(em)) {
                        ret = PTR_ERR(em);
                        goto out_reserve;
                }
                free_extent_map(em);

                ret = btrfs_add_ordered_extent(inode, start, ram_size, ram_size,
                                               ins.objectid, cur_alloc_size, 0,
                                               1 << BTRFS_ORDERED_REGULAR,
                                               BTRFS_COMPRESS_NONE);
                if (ret)
                        goto out_drop_extent_cache;

                if (btrfs_is_data_reloc_root(root)) {
                        ret = btrfs_reloc_clone_csums(inode, start,
                                                      cur_alloc_size);
                        /*
                         * Only drop cache here, and process as normal.
                         *
                         * We must not allow extent_clear_unlock_delalloc()
                         * at out_unlock label to free meta of this ordered
                         * extent, as its meta should be freed by
                         * btrfs_finish_ordered_io().
                         *
                         * So we must continue until @start is increased to
                         * skip current ordered extent.
                         */
                        if (ret)
                                btrfs_drop_extent_cache(inode, start,
                                                start + ram_size - 1, 0);
                }

                btrfs_dec_block_group_reservations(fs_info, ins.objectid);

                /*
                 * 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 Ordered (Private2) bit so we know this page was
                 * properly setup for writepage.
                 */
                page_ops = unlock ? PAGE_UNLOCK : 0;
                page_ops |= PAGE_SET_ORDERED;

                extent_clear_unlock_delalloc(inode, start, start + ram_size - 1,
                                             locked_page,
                                             EXTENT_LOCKED | EXTENT_DELALLOC,
                                             page_ops);
                if (num_bytes < cur_alloc_size)
                        num_bytes = 0;
                else
                        num_bytes -= cur_alloc_size;
                alloc_hint = ins.objectid + ins.offset;
                start += cur_alloc_size;
                extent_reserved = false;

                /*
                 * btrfs_reloc_clone_csums() error, since start is increased
                 * extent_clear_unlock_delalloc() at out_unlock label won't
                 * free metadata of current ordered extent, we're OK to exit.
                 */
                if (ret)
                        goto out_unlock;
        }
out:
        return ret;

out_drop_extent_cache:
        btrfs_drop_extent_cache(inode, start, start + ram_size - 1, 0);
out_reserve:
        btrfs_dec_block_group_reservations(fs_info, ins.objectid);
        btrfs_free_reserved_extent(fs_info, ins.objectid, ins.offset, 1);
out_unlock:
        clear_bits = EXTENT_LOCKED | EXTENT_DELALLOC | EXTENT_DELALLOC_NEW |
                EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV;
        page_ops = PAGE_UNLOCK | PAGE_START_WRITEBACK | PAGE_END_WRITEBACK;
        /*
         * If we reserved an extent for our delalloc range (or a subrange) and
         * failed to create the respective ordered extent, then it means that
         * when we reserved the extent we decremented the extent's size from
         * the data space_info's bytes_may_use counter and incremented the
         * space_info's bytes_reserved counter by the same amount. We must make
         * sure extent_clear_unlock_delalloc() does not try to decrement again
         * the data space_info's bytes_may_use counter, therefore we do not pass
         * it the flag EXTENT_CLEAR_DATA_RESV.
         */
        if (extent_reserved) {
                extent_clear_unlock_delalloc(inode, start,
                                             start + cur_alloc_size - 1,
                                             locked_page,
                                             clear_bits,
                                             page_ops);
                start += cur_alloc_size;
                if (start >= end)
                        goto out;
        }
        extent_clear_unlock_delalloc(inode, start, end, locked_page,
                                     clear_bits | EXTENT_CLEAR_DATA_RESV,
                                     page_ops);
        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_chunk *async_chunk;
        int compressed_extents;

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

        compressed_extents = compress_file_range(async_chunk);
        if (compressed_extents == 0) {
                btrfs_add_delayed_iput(async_chunk->inode);
                async_chunk->inode = NULL;
        }
}

/*
 * work queue call back to submit previously compressed pages
 */
static noinline void async_cow_submit(struct btrfs_work *work)
{
        struct async_chunk *async_chunk = container_of(work, struct async_chunk,
                                                     work);
        struct btrfs_fs_info *fs_info = btrfs_work_owner(work);
        unsigned long nr_pages;

        nr_pages = (async_chunk->end - async_chunk->start + PAGE_SIZE) >>
                PAGE_SHIFT;

        /*
         * ->inode could be NULL if async_chunk_start has failed to compress,
         * in which case we don't have anything to submit, yet we need to
         * always adjust ->async_delalloc_pages as its paired with the init
         * happening in cow_file_range_async
         */
        if (async_chunk->inode)
                submit_compressed_extents(async_chunk);

        /* atomic_sub_return implies a barrier */
        if (atomic_sub_return(nr_pages, &fs_info->async_delalloc_pages) <
            5 * SZ_1M)
                cond_wake_up_nomb(&fs_info->async_submit_wait);
}

static noinline void async_cow_free(struct btrfs_work *work)
{
        struct async_chunk *async_chunk;
        struct async_cow *async_cow;

        async_chunk = container_of(work, struct async_chunk, work);
        if (async_chunk->inode)
                btrfs_add_delayed_iput(async_chunk->inode);
        if (async_chunk->blkcg_css)
                css_put(async_chunk->blkcg_css);

        async_cow = async_chunk->async_cow;
        if (atomic_dec_and_test(&async_cow->num_chunks))
                kvfree(async_cow);
}

static int cow_file_range_async(struct btrfs_inode *inode,
                                struct writeback_control *wbc,
                                struct page *locked_page,
                                u64 start, u64 end, int *page_started,
                                unsigned long *nr_written)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct cgroup_subsys_state *blkcg_css = wbc_blkcg_css(wbc);
        struct async_cow *ctx;
        struct async_chunk *async_chunk;
        unsigned long nr_pages;
        u64 cur_end;
        u64 num_chunks = DIV_ROUND_UP(end - start, SZ_512K);
        int i;
        bool should_compress;
        unsigned nofs_flag;
        const unsigned int write_flags = wbc_to_write_flags(wbc);

        unlock_extent(&inode->io_tree, start, end);

        if (inode->flags & BTRFS_INODE_NOCOMPRESS &&
            !btrfs_test_opt(fs_info, FORCE_COMPRESS)) {
                num_chunks = 1;
                should_compress = false;
        } else {
                should_compress = true;
        }

        nofs_flag = memalloc_nofs_save();
        ctx = kvmalloc(struct_size(ctx, chunks, num_chunks), GFP_KERNEL);
        memalloc_nofs_restore(nofs_flag);

        if (!ctx) {
                unsigned clear_bits = EXTENT_LOCKED | EXTENT_DELALLOC |
                        EXTENT_DELALLOC_NEW | EXTENT_DEFRAG |
                        EXTENT_DO_ACCOUNTING;
                unsigned long page_ops = PAGE_UNLOCK | PAGE_START_WRITEBACK |
                                         PAGE_END_WRITEBACK | PAGE_SET_ERROR;

                extent_clear_unlock_delalloc(inode, start, end, locked_page,
                                             clear_bits, page_ops);
                return -ENOMEM;
        }

        async_chunk = ctx->chunks;
        atomic_set(&ctx->num_chunks, num_chunks);

        for (i = 0; i < num_chunks; i++) {
                if (should_compress)
                        cur_end = min(end, start + SZ_512K - 1);
                else
                        cur_end = end;

                /*
                 * igrab is called higher up in the call chain, take only the
                 * lightweight reference for the callback lifetime
                 */
                ihold(&inode->vfs_inode);
                async_chunk[i].async_cow = ctx;
                async_chunk[i].inode = &inode->vfs_inode;
                async_chunk[i].start = start;
                async_chunk[i].end = cur_end;
                async_chunk[i].write_flags = write_flags;
                INIT_LIST_HEAD(&async_chunk[i].extents);

                /*
                 * The locked_page comes all the way from writepage and its
                 * the original page we were actually given.  As we spread
                 * this large delalloc region across multiple async_chunk
                 * structs, only the first struct needs a pointer to locked_page
                 *
                 * This way we don't need racey decisions about who is supposed
                 * to unlock it.
                 */
                if (locked_page) {
                        /*
                         * Depending on the compressibility, the pages might or
                         * might not go through async.  We want all of them to
                         * be accounted against wbc once.  Let's do it here
                         * before the paths diverge.  wbc accounting is used
                         * only for foreign writeback detection and doesn't
                         * need full accuracy.  Just account the whole thing
                         * against the first page.
                         */
                        wbc_account_cgroup_owner(wbc, locked_page,
                                                 cur_end - start);
                        async_chunk[i].locked_page = locked_page;
                        locked_page = NULL;
                } else {
                        async_chunk[i].locked_page = NULL;
                }

                if (blkcg_css != blkcg_root_css) {
                        css_get(blkcg_css);
                        async_chunk[i].blkcg_css = blkcg_css;
                } else {
                        async_chunk[i].blkcg_css = NULL;
                }

                btrfs_init_work(&async_chunk[i].work, async_cow_start,
                                async_cow_submit, async_cow_free);

                nr_pages = DIV_ROUND_UP(cur_end - start, PAGE_SIZE);
                atomic_add(nr_pages, &fs_info->async_delalloc_pages);

                btrfs_queue_work(fs_info->delalloc_workers, &async_chunk[i].work);

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

static noinline int run_delalloc_zoned(struct btrfs_inode *inode,
                                       struct page *locked_page, u64 start,
                                       u64 end, int *page_started,
                                       unsigned long *nr_written)
{
        int ret;

        ret = cow_file_range(inode, locked_page, start, end, page_started,
                             nr_written, 0);
        if (ret)
                return ret;

        if (*page_started)
                return 0;

        __set_page_dirty_nobuffers(locked_page);
        account_page_redirty(locked_page);
        extent_write_locked_range(&inode->vfs_inode, start, end);
        *page_started = 1;

        return 0;
}

static noinline int csum_exist_in_range(struct btrfs_fs_info *fs_info,
                                        u64 bytenr, u64 num_bytes)
{
        struct btrfs_root *csum_root = btrfs_csum_root(fs_info, bytenr);
        struct btrfs_ordered_sum *sums;
        int ret;
        LIST_HEAD(list);

        ret = btrfs_lookup_csums_range(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);
        }
        if (ret < 0)
                return ret;
        return 1;
}

static int fallback_to_cow(struct btrfs_inode *inode, struct page *locked_page,
                           const u64 start, const u64 end,
                           int *page_started, unsigned long *nr_written)
{
        const bool is_space_ino = btrfs_is_free_space_inode(inode);
        const bool is_reloc_ino = btrfs_is_data_reloc_root(inode->root);
        const u64 range_bytes = end + 1 - start;
        struct extent_io_tree *io_tree = &inode->io_tree;
        u64 range_start = start;
        u64 count;

        /*
         * If EXTENT_NORESERVE is set it means that when the buffered write was
         * made we had not enough available data space and therefore we did not
         * reserve data space for it, since we though we could do NOCOW for the
         * respective file range (either there is prealloc extent or the inode
         * has the NOCOW bit set).
         *
         * However when we need to fallback to COW mode (because for example the
         * block group for the corresponding extent was turned to RO mode by a
         * scrub or relocation) we need to do the following:
         *
         * 1) We increment the bytes_may_use counter of the data space info.
         *    If COW succeeds, it allocates a new data extent and after doing
         *    that it decrements the space info's bytes_may_use counter and
         *    increments its bytes_reserved counter by the same amount (we do
         *    this at btrfs_add_reserved_bytes()). So we need to increment the
         *    bytes_may_use counter to compensate (when space is reserved at
         *    buffered write time, the bytes_may_use counter is incremented);
         *
         * 2) We clear the EXTENT_NORESERVE bit from the range. We do this so
         *    that if the COW path fails for any reason, it decrements (through
         *    extent_clear_unlock_delalloc()) the bytes_may_use counter of the
         *    data space info, which we incremented in the step above.
         *
         * If we need to fallback to cow and the inode corresponds to a free
         * space cache inode or an inode of the data relocation tree, we must
         * also increment bytes_may_use of the data space_info for the same
         * reason. Space caches and relocated data extents always get a prealloc
         * extent for them, however scrub or balance may have set the block
         * group that contains that extent to RO mode and therefore force COW
         * when starting writeback.
         */
        count = count_range_bits(io_tree, &range_start, end, range_bytes,
                                 EXTENT_NORESERVE, 0);
        if (count > 0 || is_space_ino || is_reloc_ino) {
                u64 bytes = count;
                struct btrfs_fs_info *fs_info = inode->root->fs_info;
                struct btrfs_space_info *sinfo = fs_info->data_sinfo;

                if (is_space_ino || is_reloc_ino)
                        bytes = range_bytes;

                spin_lock(&sinfo->lock);
                btrfs_space_info_update_bytes_may_use(fs_info, sinfo, bytes);
                spin_unlock(&sinfo->lock);

                if (count > 0)
                        clear_extent_bit(io_tree, start, end, EXTENT_NORESERVE,
                                         0, 0, NULL);
        }

        return cow_file_range(inode, locked_page, start, end, page_started,
                              nr_written, 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 btrfs_inode *inode,
                                       struct page *locked_page,
                                       const u64 start, const u64 end,
                                       int *page_started,
                                       unsigned long *nr_written)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct btrfs_root *root = inode->root;
        struct btrfs_path *path;
        u64 cow_start = (u64)-1;
        u64 cur_offset = start;
        int ret;
        bool check_prev = true;
        const bool freespace_inode = btrfs_is_free_space_inode(inode);
        u64 ino = btrfs_ino(inode);
        bool nocow = false;
        u64 disk_bytenr = 0;
        const bool force = inode->flags & BTRFS_INODE_NODATACOW;

        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_START_WRITEBACK |
                                             PAGE_END_WRITEBACK);
                return -ENOMEM;
        }

        while (1) {
                struct btrfs_key found_key;
                struct btrfs_file_extent_item *fi;
                struct extent_buffer *leaf;
                u64 extent_end;
                u64 extent_offset;
                u64 num_bytes = 0;
                u64 disk_num_bytes;
                u64 ram_bytes;
                int extent_type;

                nocow = false;

                ret = btrfs_lookup_file_extent(NULL, root, path, ino,
                                               cur_offset, 0);
                if (ret < 0)
                        goto error;

                /*
                 * If there is no extent for our range when doing the initial
                 * search, then go back to the previous slot as it will be the
                 * one containing the search offset
                 */
                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 = false;
next_slot:
                /* Go to next leaf if we have exhausted the current one */
                leaf = path->nodes[0];
                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0) {
                                if (cow_start != (u64)-1)
                                        cur_offset = cow_start;
                                goto error;
                        }
                        if (ret > 0)
                                break;
                        leaf = path->nodes[0];
                }

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

                /* Didn't find anything for our INO */
                if (found_key.objectid > ino)
                        break;
                /*
                 * Keep searching until we find an EXTENT_ITEM or there are no
                 * more extents for this inode
                 */
                if (WARN_ON_ONCE(found_key.objectid < ino) ||
                    found_key.type < BTRFS_EXTENT_DATA_KEY) {
                        path->slots[0]++;
                        goto next_slot;
                }

                /* Found key is not EXTENT_DATA_KEY or starts after req range */
                if (found_key.type > BTRFS_EXTENT_DATA_KEY ||
                    found_key.offset > end)
                        break;

                /*
                 * If the found extent starts after requested offset, then
                 * adjust extent_end to be right before this extent begins
                 */
                if (found_key.offset > cur_offset) {
                        extent_end = found_key.offset;
                        extent_type = 0;
                        goto out_check;
                }

                /*
                 * Found extent which begins before our range and potentially
                 * intersect it
                 */
                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 the extent we got ends before our current offset,
                         * skip to the next extent.
                         */
                        if (extent_end <= cur_offset) {
                                path->slots[0]++;
                                goto next_slot;
                        }
                        /* Skip holes */
                        if (disk_bytenr == 0)
                                goto out_check;
                        /* Skip compressed/encrypted/encoded extents */
                        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 is created before the last volume's snapshot
                         * this implies the extent is shared, hence we can't do
                         * nocow. This is the same check as in
                         * btrfs_cross_ref_exist but without calling
                         * btrfs_search_slot.
                         */
                        if (!freespace_inode &&
                            btrfs_file_extent_generation(leaf, fi) <=
                            btrfs_root_last_snapshot(&root->root_item))
                                goto out_check;
                        if (extent_type == BTRFS_FILE_EXTENT_REG && !force)
                                goto out_check;

                        /*
                         * The following checks can be expensive, as they need to
                         * take other locks and do btree or rbtree searches, so
                         * release the path to avoid blocking other tasks for too
                         * long.
                         */
                        btrfs_release_path(path);

                        ret = btrfs_cross_ref_exist(root, ino,
                                                    found_key.offset -
                                                    extent_offset, disk_bytenr, false);
                        if (ret) {
                                /*
                                 * ret could be -EIO if the above fails to read
                                 * metadata.
                                 */
                                if (ret < 0) {
                                        if (cow_start != (u64)-1)
                                                cur_offset = cow_start;
                                        goto error;
                                }

                                WARN_ON_ONCE(freespace_inode);
                                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 (!freespace_inode && atomic_read(&root->snapshot_force_cow))
                                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.
                         */
                        ret = csum_exist_in_range(fs_info, disk_bytenr,
                                                  num_bytes);
                        if (ret) {
                                /*
                                 * ret could be -EIO if the above fails to read
                                 * metadata.
                                 */
                                if (ret < 0) {
                                        if (cow_start != (u64)-1)
                                                cur_offset = cow_start;
                                        goto error;
                                }
                                WARN_ON_ONCE(freespace_inode);
                                goto out_check;
                        }
                        /* If the extent's block group is RO, we must COW */
                        if (!btrfs_inc_nocow_writers(fs_info, disk_bytenr))
                                goto out_check;
                        nocow = true;
                } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                        extent_end = found_key.offset + ram_bytes;
                        extent_end = ALIGN(extent_end, fs_info->sectorsize);
                        /* Skip extents outside of our requested range */
                        if (extent_end <= start) {
                                path->slots[0]++;
                                goto next_slot;
                        }
                } else {
                        /* If this triggers then we have a memory corruption */
                        BUG();
                }
out_check:
                /*
                 * If nocow is false then record the beginning of the range
                 * that needs to be COWed
                 */
                if (!nocow) {
                        if (cow_start == (u64)-1)
                                cow_start = cur_offset;
                        cur_offset = extent_end;
                        if (cur_offset > end)
                                break;
                        if (!path->nodes[0])
                                continue;
                        path->slots[0]++;
                        goto next_slot;
                }

                /*
                 * COW range from cow_start to found_key.offset - 1. As the key
                 * will contain the beginning of the first extent that can be
                 * NOCOW, following one which needs to be COW'ed
                 */
                if (cow_start != (u64)-1) {
                        ret = fallback_to_cow(inode, locked_page,
                                              cow_start, found_key.offset - 1,
                                              page_started, nr_written);
                        if (ret)
                                goto error;
                        cow_start = (u64)-1;
                }

                if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
                        u64 orig_start = found_key.offset - extent_offset;
                        struct extent_map *em;

                        em = create_io_em(inode, cur_offset, num_bytes,
                                          orig_start,
                                          disk_bytenr, /* block_start */
                                          num_bytes, /* block_len */
                                          disk_num_bytes, /* orig_block_len */
                                          ram_bytes, BTRFS_COMPRESS_NONE,
                                          BTRFS_ORDERED_PREALLOC);
                        if (IS_ERR(em)) {
                                ret = PTR_ERR(em);
                                goto error;
                        }
                        free_extent_map(em);
                        ret = btrfs_add_ordered_extent(inode,
                                        cur_offset, num_bytes, num_bytes,
                                        disk_bytenr, num_bytes, 0,
                                        1 << BTRFS_ORDERED_PREALLOC,
                                        BTRFS_COMPRESS_NONE);
                        if (ret) {
                                btrfs_drop_extent_cache(inode, cur_offset,
                                                        cur_offset + num_bytes - 1,
                                                        0);
                                goto error;
                        }
                } else {
                        ret = btrfs_add_ordered_extent(inode, cur_offset,
                                                       num_bytes, num_bytes,
                                                       disk_bytenr, num_bytes,
                                                       0,
                                                       1 << BTRFS_ORDERED_NOCOW,
                                                       BTRFS_COMPRESS_NONE);
                        if (ret)
                                goto error;
                }

                if (nocow)
                        btrfs_dec_nocow_writers(fs_info, disk_bytenr);
                nocow = false;

                if (btrfs_is_data_reloc_root(root))
                        /*
                         * Error handled later, as we must prevent
                         * extent_clear_unlock_delalloc() in error handler
                         * from freeing metadata of created ordered extent.
                         */
                        ret = btrfs_reloc_clone_csums(inode, cur_offset,
                                                      num_bytes);

                extent_clear_unlock_delalloc(inode, cur_offset,
                                             cur_offset + num_bytes - 1,
                                             locked_page, EXTENT_LOCKED |
                                             EXTENT_DELALLOC |
                                             EXTENT_CLEAR_DATA_RESV,
                                             PAGE_UNLOCK | PAGE_SET_ORDERED);

                cur_offset = extent_end;

                /*
                 * btrfs_reloc_clone_csums() error, now we're OK to call error
                 * handler, as metadata for created ordered extent will only
                 * be freed by btrfs_finish_ordered_io().
                 */
                if (ret)
                        goto error;
                if (cur_offset > end)
                        break;
        }
        btrfs_release_path(path);

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

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

error:
        if (nocow)
                btrfs_dec_nocow_writers(fs_info, disk_bytenr);

        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_START_WRITEBACK |
                                             PAGE_END_WRITEBACK);
        btrfs_free_path(path);
        return ret;
}

static bool should_nocow(struct btrfs_inode *inode, u64 start, u64 end)
{
        if (inode->flags & (BTRFS_INODE_NODATACOW | BTRFS_INODE_PREALLOC)) {
                if (inode->defrag_bytes &&
                    test_range_bit(&inode->io_tree, start, end, EXTENT_DEFRAG,
                                   0, NULL))
                        return false;
                return true;
        }
        return false;
}

/*
 * Function to process delayed allocation (create CoW) for ranges which are
 * being touched for the first time.
 */
int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct page *locked_page,
                u64 start, u64 end, int *page_started, unsigned long *nr_written,
                struct writeback_control *wbc)
{
        int ret;
        const bool zoned = btrfs_is_zoned(inode->root->fs_info);

        /*
         * The range must cover part of the @locked_page, or the returned
         * @page_started can confuse the caller.
         */
        ASSERT(!(end <= page_offset(locked_page) ||
                 start >= page_offset(locked_page) + PAGE_SIZE));

        if (should_nocow(inode, start, end)) {

                /*
                 * Normally on a zoned device we're only doing COW writes, but
                 * in case of relocation on a zoned filesystem we have taken
                 * precaution, that we're only writing sequentially. It's safe
                 * to use run_delalloc_nocow() here, like for  regular
                 * preallocated inodes.
                 */
                ASSERT(!zoned || btrfs_is_data_reloc_root(inode->root));
                ret = run_delalloc_nocow(inode, locked_page, start, end,
                                         page_started, nr_written);
        } else if (!btrfs_inode_can_compress(inode) ||
                   !inode_need_compress(inode, start, end)) {
                if (zoned)
                        ret = run_delalloc_zoned(inode, locked_page, start, end,
                                                 page_started, nr_written);
                else
                        ret = cow_file_range(inode, locked_page, start, end,
                                             page_started, nr_written, 1);
        } else {
                set_bit(BTRFS_INODE_HAS_ASYNC_EXTENT, &inode->runtime_flags);
                ret = cow_file_range_async(inode, wbc, locked_page, start, end,
                                           page_started, nr_written);
        }
        ASSERT(ret <= 0);
        if (ret)
                btrfs_cleanup_ordered_extents(inode, locked_page, start,
                                              end - start + 1);
        return ret;
}

void btrfs_split_delalloc_extent(struct inode *inode,
                                 struct extent_state *orig, u64 split)
{
        u64 size;

        /* not delalloc, ignore it */
        if (!(orig->state & EXTENT_DELALLOC))
                return;

        size = orig->end - orig->start + 1;
        if (size > BTRFS_MAX_EXTENT_SIZE) {
                u32 num_extents;
                u64 new_size;

                /*
                 * See the explanation in btrfs_merge_delalloc_extent, the same
                 * applies here, just in reverse.
                 */
                new_size = orig->end - split + 1;
                num_extents = count_max_extents(new_size);
                new_size = split - orig->start;
                num_extents += count_max_extents(new_size);
                if (count_max_extents(size) >= num_extents)
                        return;
        }

        spin_lock(&BTRFS_I(inode)->lock);
        btrfs_mod_outstanding_extents(BTRFS_I(inode), 1);
        spin_unlock(&BTRFS_I(inode)->lock);
}

/*
 * Handle 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.
 */
void btrfs_merge_delalloc_extent(struct inode *inode, struct extent_state *new,
                                 struct extent_state *other)
{
        u64 new_size, old_size;
        u32 num_extents;

        /* not delalloc, ignore it */
        if (!(other->state & EXTENT_DELALLOC))
                return;

        if (new->start > other->start)
                new_size = new->end - other->start + 1;
        else
                new_size = other->end - new->start + 1;

        /* we're not bigger than the max, unreserve the space and go */
        if (new_size <= BTRFS_MAX_EXTENT_SIZE) {
                spin_lock(&BTRFS_I(inode)->lock);
                btrfs_mod_outstanding_extents(BTRFS_I(inode), -1);
                spin_unlock(&BTRFS_I(inode)->lock);
                return;
        }

        /*
         * We have to add up either side to figure out how many extents were
         * accounted for before we merged into one big extent.  If the number of
         * extents we accounted for is <= the amount we need for the new range
         * then we can return, otherwise drop.  Think of it like this
         *
         * [ 4k][MAX_SIZE]
         *
         * So we've grown the extent by a MAX_SIZE extent, this would mean we
         * need 2 outstanding extents, on one side we have 1 and the other side
         * we have 1 so they are == and we can return.  But in this case
         *
         * [MAX_SIZE+4k][MAX_SIZE+4k]
         *
         * Each range on their own accounts for 2 extents, but merged together
         * they are only 3 extents worth of accounting, so we need to drop in
         * this case.
         */
        old_size = other->end - other->start + 1;
        num_extents = count_max_extents(old_size);
        old_size = new->end - new->start + 1;
        num_extents += count_max_extents(old_size);
        if (count_max_extents(new_size) >= num_extents)
                return;

        spin_lock(&BTRFS_I(inode)->lock);
        btrfs_mod_outstanding_extents(BTRFS_I(inode), -1);
        spin_unlock(&BTRFS_I(inode)->lock);
}

static void btrfs_add_delalloc_inodes(struct btrfs_root *root,
                                      struct inode *inode)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);

        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(&fs_info->delalloc_root_lock);
                        BUG_ON(!list_empty(&root->delalloc_root));
                        list_add_tail(&root->delalloc_root,
                                      &fs_info->delalloc_roots);
                        spin_unlock(&fs_info->delalloc_root_lock);
                }
        }
        spin_unlock(&root->delalloc_lock);
}


void __btrfs_del_delalloc_inode(struct btrfs_root *root,
                                struct btrfs_inode *inode)
{
        struct btrfs_fs_info *fs_info = root->fs_info;

        if (!list_empty(&inode->delalloc_inodes)) {
                list_del_init(&inode->delalloc_inodes);
                clear_bit(BTRFS_INODE_IN_DELALLOC_LIST,
                          &inode->runtime_flags);
                root->nr_delalloc_inodes--;
                if (!root->nr_delalloc_inodes) {
                        ASSERT(list_empty(&root->delalloc_inodes));
                        spin_lock(&fs_info->delalloc_root_lock);
                        BUG_ON(list_empty(&root->delalloc_root));
                        list_del_init(&root->delalloc_root);
                        spin_unlock(&fs_info->delalloc_root_lock);
                }
        }
}

static void btrfs_del_delalloc_inode(struct btrfs_root *root,
                                     struct btrfs_inode *inode)
{
        spin_lock(&root->delalloc_lock);
        __btrfs_del_delalloc_inode(root, inode);
        spin_unlock(&root->delalloc_lock);
}

/*
 * Properly track delayed allocation bytes in the inode and to maintain the
 * list of inodes that have pending delalloc work to be done.
 */
void btrfs_set_delalloc_extent(struct inode *inode, struct extent_state *state,
                               unsigned *bits)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);

        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;
                u32 num_extents = count_max_extents(len);
                bool do_list = !btrfs_is_free_space_inode(BTRFS_I(inode));

                spin_lock(&BTRFS_I(inode)->lock);
                btrfs_mod_outstanding_extents(BTRFS_I(inode), num_extents);
                spin_unlock(&BTRFS_I(inode)->lock);

                /* For sanity tests */
                if (btrfs_is_testing(fs_info))
                        return;

                percpu_counter_add_batch(&fs_info->delalloc_bytes, len,
                                         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);
        }

        if (!(state->state & EXTENT_DELALLOC_NEW) &&
            (*bits & EXTENT_DELALLOC_NEW)) {
                spin_lock(&BTRFS_I(inode)->lock);
                BTRFS_I(inode)->new_delalloc_bytes += state->end + 1 -
                        state->start;
                spin_unlock(&BTRFS_I(inode)->lock);
        }
}

/*
 * Once a range is no longer delalloc this function ensures that proper
 * accounting happens.
 */
void btrfs_clear_delalloc_extent(struct inode *vfs_inode,
                                 struct extent_state *state, unsigned *bits)
{
        struct btrfs_inode *inode = BTRFS_I(vfs_inode);
        struct btrfs_fs_info *fs_info = btrfs_sb(vfs_inode->i_sb);
        u64 len = state->end + 1 - state->start;
        u32 num_extents = count_max_extents(len);

        if ((state->state & EXTENT_DEFRAG) && (*bits & EXTENT_DEFRAG)) {
                spin_lock(&inode->lock);
                inode->defrag_bytes -= len;
                spin_unlock(&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 = inode->root;
                bool do_list = !btrfs_is_free_space_inode(inode);

                spin_lock(&inode->lock);
                btrfs_mod_outstanding_extents(inode, -num_extents);
                spin_unlock(&inode->lock);

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

                /* For sanity tests. */
                if (btrfs_is_testing(fs_info))
                        return;

                if (!btrfs_is_data_reloc_root(root) &&
                    do_list && !(state->state & EXTENT_NORESERVE) &&
                    (*bits & EXTENT_CLEAR_DATA_RESV))
                        btrfs_free_reserved_data_space_noquota(fs_info, len);

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

        if ((state->state & EXTENT_DELALLOC_NEW) &&
            (*bits & EXTENT_DELALLOC_NEW)) {
                spin_lock(&inode->lock);
                ASSERT(inode->new_delalloc_bytes >= len);
                inode->new_delalloc_bytes -= len;
                if (*bits & EXTENT_ADD_INODE_BYTES)
                        inode_add_bytes(&inode->vfs_inode, len);
                spin_unlock(&inode->lock);
        }
}

/*
 * 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 blk_status_t btrfs_submit_bio_start(struct inode *inode, struct bio *bio,
                                           u64 dio_file_offset)
{
        return btrfs_csum_one_bio(BTRFS_I(inode), bio, (u64)-1, false);
}

/*
 * Split an extent_map at [start, start + len]
 *
 * This function is intended to be used only for extract_ordered_extent().
 */
static int split_zoned_em(struct btrfs_inode *inode, u64 start, u64 len,
                          u64 pre, u64 post)
{
        struct extent_map_tree *em_tree = &inode->extent_tree;
        struct extent_map *em;
        struct extent_map *split_pre = NULL;
        struct extent_map *split_mid = NULL;
        struct extent_map *split_post = NULL;
        int ret = 0;
        unsigned long flags;

        /* Sanity check */
        if (pre == 0 && post == 0)
                return 0;

        split_pre = alloc_extent_map();
        if (pre)
                split_mid = alloc_extent_map();
        if (post)
                split_post = alloc_extent_map();
        if (!split_pre || (pre && !split_mid) || (post && !split_post)) {
                ret = -ENOMEM;
                goto out;
        }

        ASSERT(pre + post < len);

        lock_extent(&inode->io_tree, start, start + len - 1);
        write_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, start, len);
        if (!em) {
                ret = -EIO;
                goto out_unlock;
        }

        ASSERT(em->len == len);
        ASSERT(!test_bit(EXTENT_FLAG_COMPRESSED, &em->flags));
        ASSERT(em->block_start < EXTENT_MAP_LAST_BYTE);
        ASSERT(test_bit(EXTENT_FLAG_PINNED, &em->flags));
        ASSERT(!test_bit(EXTENT_FLAG_LOGGING, &em->flags));
        ASSERT(!list_empty(&em->list));

        flags = em->flags;
        clear_bit(EXTENT_FLAG_PINNED, &em->flags);

        /* First, replace the em with a new extent_map starting from * em->start */
        split_pre->start = em->start;
        split_pre->len = (pre ? pre : em->len - post);
        split_pre->orig_start = split_pre->start;
        split_pre->block_start = em->block_start;
        split_pre->block_len = split_pre->len;
        split_pre->orig_block_len = split_pre->block_len;
        split_pre->ram_bytes = split_pre->len;
        split_pre->flags = flags;
        split_pre->compress_type = em->compress_type;
        split_pre->generation = em->generation;

        replace_extent_mapping(em_tree, em, split_pre, 1);

        /*
         * Now we only have an extent_map at:
         *     [em->start, em->start + pre] if pre != 0
         *     [em->start, em->start + em->len - post] if pre == 0
         */

        if (pre) {
                /* Insert the middle extent_map */
                split_mid->start = em->start + pre;
                split_mid->len = em->len - pre - post;
                split_mid->orig_start = split_mid->start;
                split_mid->block_start = em->block_start + pre;
                split_mid->block_len = split_mid->len;
                split_mid->orig_block_len = split_mid->block_len;
                split_mid->ram_bytes = split_mid->len;
                split_mid->flags = flags;
                split_mid->compress_type = em->compress_type;
                split_mid->generation = em->generation;
                add_extent_mapping(em_tree, split_mid, 1);
        }

        if (post) {
                split_post->start = em->start + em->len - post;
                split_post->len = post;
                split_post->orig_start = split_post->start;
                split_post->block_start = em->block_start + em->len - post;
                split_post->block_len = split_post->len;
                split_post->orig_block_len = split_post->block_len;
                split_post->ram_bytes = split_post->len;
                split_post->flags = flags;
                split_post->compress_type = em->compress_type;
                split_post->generation = em->generation;
                add_extent_mapping(em_tree, split_post, 1);
        }

        /* Once for us */
        free_extent_map(em);
        /* Once for the tree */
        free_extent_map(em);

out_unlock:
        write_unlock(&em_tree->lock);
        unlock_extent(&inode->io_tree, start, start + len - 1);
out:
        free_extent_map(split_pre);
        free_extent_map(split_mid);
        free_extent_map(split_post);

        return ret;
}

static blk_status_t extract_ordered_extent(struct btrfs_inode *inode,
                                           struct bio *bio, loff_t file_offset)
{
        struct btrfs_ordered_extent *ordered;
        u64 start = (u64)bio->bi_iter.bi_sector << SECTOR_SHIFT;
        u64 file_len;
        u64 len = bio->bi_iter.bi_size;
        u64 end = start + len;
        u64 ordered_end;
        u64 pre, post;
        int ret = 0;

        ordered = btrfs_lookup_ordered_extent(inode, file_offset);
        if (WARN_ON_ONCE(!ordered))
                return BLK_STS_IOERR;

        /* No need to split */
        if (ordered->disk_num_bytes == len)
                goto out;

        /* We cannot split once end_bio'd ordered extent */
        if (WARN_ON_ONCE(ordered->bytes_left != ordered->disk_num_bytes)) {
                ret = -EINVAL;
                goto out;
        }

        /* We cannot split a compressed ordered extent */
        if (WARN_ON_ONCE(ordered->disk_num_bytes != ordered->num_bytes)) {
                ret = -EINVAL;
                goto out;
        }

        ordered_end = ordered->disk_bytenr + ordered->disk_num_bytes;
        /* bio must be in one ordered extent */
        if (WARN_ON_ONCE(start < ordered->disk_bytenr || end > ordered_end)) {
                ret = -EINVAL;
                goto out;
        }

        /* Checksum list should be empty */
        if (WARN_ON_ONCE(!list_empty(&ordered->list))) {
                ret = -EINVAL;
                goto out;
        }

        file_len = ordered->num_bytes;
        pre = start - ordered->disk_bytenr;
        post = ordered_end - end;

        ret = btrfs_split_ordered_extent(ordered, pre, post);
        if (ret)
                goto out;
        ret = split_zoned_em(inode, file_offset, file_len, pre, post);

out:
        btrfs_put_ordered_extent(ordered);

        return errno_to_blk_status(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.
 *
 * Rules about async/sync submit,
 * a) read:                             sync submit
 *
 * b) write without checksum:           sync submit
 *
 * c) write with checksum:
 *    c-1) if bio is issued by fsync:   sync submit
 *         (sync_writers != 0)
 *
 *    c-2) if root is reloc root:       sync submit
 *         (only in case of buffered IO)
 *
 *    c-3) otherwise:                   async submit
 */
blk_status_t btrfs_submit_data_bio(struct inode *inode, struct bio *bio,
                                   int mirror_num, unsigned long bio_flags)

{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        enum btrfs_wq_endio_type metadata = BTRFS_WQ_ENDIO_DATA;
        blk_status_t ret = 0;
        int skip_sum;
        int async = !atomic_read(&BTRFS_I(inode)->sync_writers);

        skip_sum = (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM) ||
                test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state);

        if (btrfs_is_free_space_inode(BTRFS_I(inode)))
                metadata = BTRFS_WQ_ENDIO_FREE_SPACE;

        if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
                struct page *page = bio_first_bvec_all(bio)->bv_page;
                loff_t file_offset = page_offset(page);

                ret = extract_ordered_extent(BTRFS_I(inode), bio, file_offset);
                if (ret)
                        goto out;
        }

        if (btrfs_op(bio) != BTRFS_MAP_WRITE) {
                ret = btrfs_bio_wq_end_io(fs_info, bio, metadata);
                if (ret)
                        goto out;

                if (bio_flags & EXTENT_BIO_COMPRESSED) {
                        /*
                         * btrfs_submit_compressed_read will handle completing
                         * the bio if there were any errors, so just return
                         * here.
                         */
                        ret = btrfs_submit_compressed_read(inode, bio,
                                                           mirror_num,
                                                           bio_flags);
                        goto out_no_endio;
                } else {
                        /*
                         * Lookup bio sums does extra checks around whether we
                         * need to csum or not, which is why we ignore skip_sum
                         * here.
                         */
                        ret = btrfs_lookup_bio_sums(inode, bio, NULL);
                        if (ret)
                                goto out;
                }
                goto mapit;
        } else if (async && !skip_sum) {
                /* csum items have already been cloned */
                if (btrfs_is_data_reloc_root(root))
                        goto mapit;
                /* we're doing a write, do the async checksumming */
                ret = btrfs_wq_submit_bio(inode, bio, mirror_num, bio_flags,
                                          0, btrfs_submit_bio_start);
                goto out;
        } else if (!skip_sum) {
                ret = btrfs_csum_one_bio(BTRFS_I(inode), bio, (u64)-1, false);
                if (ret)
                        goto out;
        }

mapit:
        ret = btrfs_map_bio(fs_info, bio, mirror_num);

out:
        if (ret) {
                bio->bi_status = ret;
                bio_endio(bio);
        }
out_no_endio:
        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 int add_pending_csums(struct btrfs_trans_handle *trans,
                             struct list_head *list)
{
        struct btrfs_ordered_sum *sum;
        struct btrfs_root *csum_root = NULL;
        int ret;

        list_for_each_entry(sum, list, list) {
                trans->adding_csums = true;
                if (!csum_root)
                        csum_root = btrfs_csum_root(trans->fs_info,
                                                    sum->bytenr);
                ret = btrfs_csum_file_blocks(trans, csum_root, sum);
                trans->adding_csums = false;
                if (ret)
                        return ret;
        }
        return 0;
}

static int btrfs_find_new_delalloc_bytes(struct btrfs_inode *inode,
                                         const u64 start,
                                         const u64 len,
                                         struct extent_state **cached_state)
{
        u64 search_start = start;
        const u64 end = start + len - 1;

        while (search_start < end) {
                const u64 search_len = end - search_start + 1;
                struct extent_map *em;
                u64 em_len;
                int ret = 0;

                em = btrfs_get_extent(inode, NULL, 0, search_start, search_len);
                if (IS_ERR(em))
                        return PTR_ERR(em);

                if (em->block_start != EXTENT_MAP_HOLE)
                        goto next;

                em_len = em->len;
                if (em->start < search_start)
                        em_len -= search_start - em->start;
                if (em_len > search_len)
                        em_len = search_len;

                ret = set_extent_bit(&inode->io_tree, search_start,
                                     search_start + em_len - 1,
                                     EXTENT_DELALLOC_NEW, 0, NULL, cached_state,
                                     GFP_NOFS, NULL);
next:
                search_start = extent_map_end(em);
                free_extent_map(em);
                if (ret)
                        return ret;
        }
        return 0;
}

int btrfs_set_extent_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
                              unsigned int extra_bits,
                              struct extent_state **cached_state)
{
        WARN_ON(PAGE_ALIGNED(end));

        if (start >= i_size_read(&inode->vfs_inode) &&
            !(inode->flags & BTRFS_INODE_PREALLOC)) {
                /*
                 * There can't be any extents following eof in this case so just
                 * set the delalloc new bit for the range directly.
                 */
                extra_bits |= EXTENT_DELALLOC_NEW;
        } else {
                int ret;

                ret = btrfs_find_new_delalloc_bytes(inode, start,
                                                    end + 1 - start,
                                                    cached_state);
                if (ret)
                        return ret;
        }

        return set_extent_delalloc(&inode->io_tree, start, end, extra_bits,
                                   cached_state);
}

/* see btrfs_writepage_start_hook for details on why this is required */
struct btrfs_writepage_fixup {
        struct page *page;
        struct inode *inode;
        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 extent_changeset *data_reserved = NULL;
        struct page *page;
        struct btrfs_inode *inode;
        u64 page_start;
        u64 page_end;
        int ret = 0;
        bool free_delalloc_space = true;

        fixup = container_of(work, struct btrfs_writepage_fixup, work);
        page = fixup->page;
        inode = BTRFS_I(fixup->inode);
        page_start = page_offset(page);
        page_end = page_offset(page) + PAGE_SIZE - 1;

        /*
         * This is similar to page_mkwrite, we need to reserve the space before
         * we take the page lock.
         */
        ret = btrfs_delalloc_reserve_space(inode, &data_reserved, page_start,
                                           PAGE_SIZE);
again:
        lock_page(page);

        /*
         * Before we queued this fixup, we took a reference on the page.
         * page->mapping may go NULL, but it shouldn't be moved to a different
         * address space.
         */
        if (!page->mapping || !PageDirty(page) || !PageChecked(page)) {
                /*
                 * Unfortunately this is a little tricky, either
                 *
                 * 1) We got here and our page had already been dealt with and
                 *    we reserved our space, thus ret == 0, so we need to just
                 *    drop our space reservation and bail.  This can happen the
                 *    first time we come into the fixup worker, or could happen
                 *    while waiting for the ordered extent.
                 * 2) Our page was already dealt with, but we happened to get an
                 *    ENOSPC above from the btrfs_delalloc_reserve_space.  In
                 *    this case we obviously don't have anything to release, but
                 *    because the page was already dealt with we don't want to
                 *    mark the page with an error, so make sure we're resetting
                 *    ret to 0.  This is why we have this check _before_ the ret
                 *    check, because we do not want to have a surprise ENOSPC
                 *    when the page was already properly dealt with.
                 */
                if (!ret) {
                        btrfs_delalloc_release_extents(inode, PAGE_SIZE);
                        btrfs_delalloc_release_space(inode, data_reserved,
                                                     page_start, PAGE_SIZE,
                                                     true);
                }
                ret = 0;
                goto out_page;
        }

        /*
         * We can't mess with the page state unless it is locked, so now that
         * it is locked bail if we failed to make our space reservation.
         */
        if (ret)
                goto out_page;

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

        /* already ordered? We're done */
        if (PageOrdered(page))
                goto out_reserved;

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

        ret = btrfs_set_extent_delalloc(inode, page_start, page_end, 0,
                                        &cached_state);
        if (ret)
                goto out_reserved;

        /*
         * Everything went as planned, we're now the owner of a dirty page with
         * delayed allocation bits set and space reserved for our COW
         * destination.
         *
         * The page was dirty when we started, nothing should have cleaned it.
         */
        BUG_ON(!PageDirty(page));
        free_delalloc_space = false;
out_reserved:
        btrfs_delalloc_release_extents(inode, PAGE_SIZE);
        if (free_delalloc_space)
                btrfs_delalloc_release_space(inode, data_reserved, page_start,
                                             PAGE_SIZE, true);
        unlock_extent_cached(&inode->io_tree, page_start, page_end,
                             &cached_state);
out_page:
        if (ret) {
                /*
                 * We hit ENOSPC or other errors.  Update the mapping and page
                 * to reflect the errors and clean the page.
                 */
                mapping_set_error(page->mapping, ret);
                end_extent_writepage(page, ret, page_start, page_end);
                clear_page_dirty_for_io(page);
                SetPageError(page);
        }
        btrfs_page_clear_checked(inode->root->fs_info, page, page_start, PAGE_SIZE);
        unlock_page(page);
        put_page(page);
        kfree(fixup);
        extent_changeset_free(data_reserved);
        /*
         * As a precaution, do a delayed iput in case it would be the last iput
         * that could need flushing space. Recursing back to fixup worker would
         * deadlock.
         */
        btrfs_add_delayed_iput(&inode->vfs_inode);
}

/*
 * 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.
 */
int btrfs_writepage_cow_fixup(struct page *page)
{
        struct inode *inode = page->mapping->host;
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_writepage_fixup *fixup;

        /* This page has ordered extent covering it already */
        if (PageOrdered(page))
                return 0;

        /*
         * PageChecked is set below when we create a fixup worker for this page,
         * don't try to create another one if we're already PageChecked()
         *
         * The extent_io writepage code will redirty the page if we send back
         * EAGAIN.
         */
        if (PageChecked(page))
                return -EAGAIN;

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

        /*
         * We are already holding a reference to this inode from
         * write_cache_pages.  We need to hold it because the space reservation
         * takes place outside of the page lock, and we can't trust
         * page->mapping outside of the page lock.
         */
        ihold(inode);
        btrfs_page_set_checked(fs_info, page, page_offset(page), PAGE_SIZE);
        get_page(page);
        btrfs_init_work(&fixup->work, btrfs_writepage_fixup_worker, NULL, NULL);
        fixup->page = page;
        fixup->inode = inode;
        btrfs_queue_work(fs_info->fixup_workers, &fixup->work);

        return -EAGAIN;
}

static int insert_reserved_file_extent(struct btrfs_trans_handle *trans,
                                       struct btrfs_inode *inode, u64 file_pos,
                                       struct btrfs_file_extent_item *stack_fi,
                                       const bool update_inode_bytes,
                                       u64 qgroup_reserved)
{
        struct btrfs_root *root = inode->root;
        const u64 sectorsize = root->fs_info->sectorsize;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_key ins;
        u64 disk_num_bytes = btrfs_stack_file_extent_disk_num_bytes(stack_fi);
        u64 disk_bytenr = btrfs_stack_file_extent_disk_bytenr(stack_fi);
        u64 offset = btrfs_stack_file_extent_offset(stack_fi);
        u64 num_bytes = btrfs_stack_file_extent_num_bytes(stack_fi);
        u64 ram_bytes = btrfs_stack_file_extent_ram_bytes(stack_fi);
        struct btrfs_drop_extents_args drop_args = { 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.
         */
        drop_args.path = path;
        drop_args.start = file_pos;
        drop_args.end = file_pos + num_bytes;
        drop_args.replace_extent = true;
        drop_args.extent_item_size = sizeof(*stack_fi);
        ret = btrfs_drop_extents(trans, root, inode, &drop_args);
        if (ret)
                goto out;

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

                ret = btrfs_insert_empty_item(trans, root, path, &ins,
                                              sizeof(*stack_fi));
                if (ret)
                        goto out;
        }
        leaf = path->nodes[0];
        btrfs_set_stack_file_extent_generation(stack_fi, trans->transid);
        write_extent_buffer(leaf, stack_fi,
                        btrfs_item_ptr_offset(leaf, path->slots[0]),
                        sizeof(struct btrfs_file_extent_item));

        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        /*
         * If we dropped an inline extent here, we know the range where it is
         * was not marked with the EXTENT_DELALLOC_NEW bit, so we update the
         * number of bytes only for that range containing the inline extent.
         * The remaining of the range will be processed when clearning the
         * EXTENT_DELALLOC_BIT bit through the ordered extent completion.
         */
        if (file_pos == 0 && !IS_ALIGNED(drop_args.bytes_found, sectorsize)) {
                u64 inline_size = round_down(drop_args.bytes_found, sectorsize);

                inline_size = drop_args.bytes_found - inline_size;
                btrfs_update_inode_bytes(inode, sectorsize, inline_size);
                drop_args.bytes_found -= inline_size;
                num_bytes -= sectorsize;
        }

        if (update_inode_bytes)
                btrfs_update_inode_bytes(inode, num_bytes, drop_args.bytes_found);

        ins.objectid = disk_bytenr;
        ins.offset = disk_num_bytes;
        ins.type = BTRFS_EXTENT_ITEM_KEY;

        ret = btrfs_inode_set_file_extent_range(inode, file_pos, ram_bytes);
        if (ret)
                goto out;

        ret = btrfs_alloc_reserved_file_extent(trans, root, btrfs_ino(inode),
                                               file_pos - offset,
                                               qgroup_reserved, &ins);
out:
        btrfs_free_path(path);

        return ret;
}

static void btrfs_release_delalloc_bytes(struct btrfs_fs_info *fs_info,
                                         u64 start, u64 len)
{
        struct btrfs_block_group *cache;

        cache = btrfs_lookup_block_group(fs_info, start);
        ASSERT(cache);

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

        btrfs_put_block_group(cache);
}

static int insert_ordered_extent_file_extent(struct btrfs_trans_handle *trans,
                                             struct btrfs_ordered_extent *oe)
{
        struct btrfs_file_extent_item stack_fi;
        bool update_inode_bytes;
        u64 num_bytes = oe->num_bytes;
        u64 ram_bytes = oe->ram_bytes;

        memset(&stack_fi, 0, sizeof(stack_fi));
        btrfs_set_stack_file_extent_type(&stack_fi, BTRFS_FILE_EXTENT_REG);
        btrfs_set_stack_file_extent_disk_bytenr(&stack_fi, oe->disk_bytenr);
        btrfs_set_stack_file_extent_disk_num_bytes(&stack_fi,
                                                   oe->disk_num_bytes);
        btrfs_set_stack_file_extent_offset(&stack_fi, oe->offset);
        if (test_bit(BTRFS_ORDERED_TRUNCATED, &oe->flags))
                num_bytes = ram_bytes = oe->truncated_len;
        btrfs_set_stack_file_extent_num_bytes(&stack_fi, num_bytes);
        btrfs_set_stack_file_extent_ram_bytes(&stack_fi, ram_bytes);
        btrfs_set_stack_file_extent_compression(&stack_fi, oe->compress_type);
        /* Encryption and other encoding is reserved and all 0 */

        /*
         * For delalloc, when completing an ordered extent we update the inode's
         * bytes when clearing the range in the inode's io tree, so pass false
         * as the argument 'update_inode_bytes' to insert_reserved_file_extent(),
         * except if the ordered extent was truncated.
         */
        update_inode_bytes = test_bit(BTRFS_ORDERED_DIRECT, &oe->flags) ||
                             test_bit(BTRFS_ORDERED_ENCODED, &oe->flags) ||
                             test_bit(BTRFS_ORDERED_TRUNCATED, &oe->flags);

        return insert_reserved_file_extent(trans, BTRFS_I(oe->inode),