static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
			      struct ext4_map_blocks *map,
			      struct buffer_head *bh)
{
	struct extent_status es;
	int retval;
	sector_t invalid_block = ~((sector_t) 0xffff);
#ifdef ES_AGGRESSIVE_TEST
	struct ext4_map_blocks orig_map;

	memcpy(&orig_map, map, sizeof(*map));
#endif

	if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
		invalid_block = ~0;

	map->m_flags = 0;
	ext_debug("ext4_da_map_blocks(): inode %lu, max_blocks %u,"
		  "logical block %lu\n", inode->i_ino, map->m_len,
		  (unsigned long) map->m_lblk);

	/* Lookup extent status tree firstly */
	if (ext4_es_lookup_extent(inode, iblock, &es)) {
		if (ext4_es_is_hole(&es)) {
			retval = 0;
			down_read(&EXT4_I(inode)->i_data_sem);
			goto add_delayed;
		}

		/*
		 * Delayed extent could be allocated by fallocate.
		 * So we need to check it.
		 */
		if (ext4_es_is_delayed(&es) && !ext4_es_is_unwritten(&es)) {
			map_bh(bh, inode->i_sb, invalid_block);
			set_buffer_new(bh);
			set_buffer_delay(bh);
			return 0;
		}

		map->m_pblk = ext4_es_pblock(&es) + iblock - es.es_lblk;
		retval = es.es_len - (iblock - es.es_lblk);
		if (retval > map->m_len)
			retval = map->m_len;
		map->m_len = retval;
		if (ext4_es_is_written(&es))
			map->m_flags |= EXT4_MAP_MAPPED;
		else if (ext4_es_is_unwritten(&es))
			map->m_flags |= EXT4_MAP_UNWRITTEN;
		else
			BUG_ON(1);

#ifdef ES_AGGRESSIVE_TEST
		ext4_map_blocks_es_recheck(NULL, inode, map, &orig_map, 0);
#endif
		return retval;
	}

	/*
	 * Try to see if we can get the block without requesting a new
	 * file system block.
	 */
	down_read(&EXT4_I(inode)->i_data_sem);
	if (ext4_has_inline_data(inode))
		retval = 0;
	else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
		retval = ext4_ext_map_blocks(NULL, inode, map, 0);
	else
		retval = ext4_ind_map_blocks(NULL, inode, map, 0);

add_delayed:
	if (retval == 0) {
		int ret;
		/*
		 * XXX: __block_prepare_write() unmaps passed block,
		 * is it OK?
		 */
		/*
		 * If the block was allocated from previously allocated cluster,
		 * then we don't need to reserve it again. However we still need
		 * to reserve metadata for every block we're going to write.
		 */
		if (EXT4_SB(inode->i_sb)->s_cluster_ratio == 1 ||
		    !ext4_find_delalloc_cluster(inode, map->m_lblk)) {
			ret = ext4_da_reserve_space(inode);
			if (ret) {
				/* not enough space to reserve */
				retval = ret;
				goto out_unlock;
			}
		}

		ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
					    ~0, EXTENT_STATUS_DELAYED);
		if (ret) {
			retval = ret;
			goto out_unlock;
		}

		map_bh(bh, inode->i_sb, invalid_block);
		set_buffer_new(bh);
		set_buffer_delay(bh);
	} else if (retval > 0) {
		int ret;
		unsigned int status;

		if (unlikely(retval != map->m_len)) {
			ext4_warning(inode->i_sb,
				     "ES len assertion failed for inode "
				     "%lu: retval %d != map->m_len %d",
				     inode->i_ino, retval, map->m_len);
			WARN_ON(1);
		}

		status = map->m_flags & EXT4_MAP_UNWRITTEN ?
				EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
		ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
					    map->m_pblk, status);
		if (ret != 0)
			retval = ret;
	}

out_unlock:
	up_read((&EXT4_I(inode)->i_data_sem));

	return retval;
}