int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
			struct ext4_map_blocks *map, int flags)
{
	struct ext4_ext_path *path = NULL;
	struct ext4_extent newex, *ex, *ex2;
	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
	ext4_fsblk_t newblock = 0, pblk;
	int err = 0, depth, ret;
	unsigned int allocated = 0, offset = 0;
	unsigned int allocated_clusters = 0;
	struct ext4_allocation_request ar;
	ext4_lblk_t cluster_offset;

	ext_debug(inode, "blocks %u/%u requested\n", map->m_lblk, map->m_len);
	trace_ext4_ext_map_blocks_enter(inode, map->m_lblk, map->m_len, flags);

	/* find extent for this block */
	path = ext4_find_extent(inode, map->m_lblk, NULL, 0);
	if (IS_ERR(path)) {
		err = PTR_ERR(path);
		path = NULL;
		goto out;
	}

	depth = ext_depth(inode);

	/*
	 * consistent leaf must not be empty;
	 * this situation is possible, though, _during_ tree modification;
	 * this is why assert can't be put in ext4_find_extent()
	 */
	if (unlikely(path[depth].p_ext == NULL && depth != 0)) {
		EXT4_ERROR_INODE(inode, "bad extent address "
				 "lblock: %lu, depth: %d pblock %lld",
				 (unsigned long) map->m_lblk, depth,
				 path[depth].p_block);
		err = -EFSCORRUPTED;
		goto out;
	}

	ex = path[depth].p_ext;
	if (ex) {
		ext4_lblk_t ee_block = le32_to_cpu(ex->ee_block);
		ext4_fsblk_t ee_start = ext4_ext_pblock(ex);
		unsigned short ee_len;


		/*
		 * unwritten extents are treated as holes, except that
		 * we split out initialized portions during a write.
		 */
		ee_len = ext4_ext_get_actual_len(ex);

		trace_ext4_ext_show_extent(inode, ee_block, ee_start, ee_len);

		/* if found extent covers block, simply return it */
		if (in_range(map->m_lblk, ee_block, ee_len)) {
			newblock = map->m_lblk - ee_block + ee_start;
			/* number of remaining blocks in the extent */
			allocated = ee_len - (map->m_lblk - ee_block);
			ext_debug(inode, "%u fit into %u:%d -> %llu\n",
				  map->m_lblk, ee_block, ee_len, newblock);

			/*
			 * If the extent is initialized check whether the
			 * caller wants to convert it to unwritten.
			 */
			if ((!ext4_ext_is_unwritten(ex)) &&
			    (flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN)) {
				err = convert_initialized_extent(handle,
					inode, map, &path, &allocated);
				goto out;
			} else if (!ext4_ext_is_unwritten(ex)) {
				map->m_flags |= EXT4_MAP_MAPPED;
				map->m_pblk = newblock;
				if (allocated > map->m_len)
					allocated = map->m_len;
				map->m_len = allocated;
				ext4_ext_show_leaf(inode, path);
				goto out;
			}

			ret = ext4_ext_handle_unwritten_extents(
				handle, inode, map, &path, flags,
				allocated, newblock);
			if (ret < 0)
				err = ret;
			else
				allocated = ret;
			goto out;
		}
	}

	/*
	 * requested block isn't allocated yet;
	 * we couldn't try to create block if create flag is zero
	 */
	if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
		ext4_lblk_t hole_start, hole_len;

		hole_start = map->m_lblk;
		hole_len = ext4_ext_determine_hole(inode, path, &hole_start);
		/*
		 * put just found gap into cache to speed up
		 * subsequent requests
		 */
		ext4_ext_put_gap_in_cache(inode, hole_start, hole_len);

		/* Update hole_len to reflect hole size after map->m_lblk */
		if (hole_start != map->m_lblk)
			hole_len -= map->m_lblk - hole_start;
		map->m_pblk = 0;
		map->m_len = min_t(unsigned int, map->m_len, hole_len);

		goto out;
	}

	/*
	 * Okay, we need to do block allocation.
	 */
	newex.ee_block = cpu_to_le32(map->m_lblk);
	cluster_offset = EXT4_LBLK_COFF(sbi, map->m_lblk);

	/*
	 * If we are doing bigalloc, check to see if the extent returned
	 * by ext4_find_extent() implies a cluster we can use.
	 */
	if (cluster_offset && ex &&
	    get_implied_cluster_alloc(inode->i_sb, map, ex, path)) {
		ar.len = allocated = map->m_len;
		newblock = map->m_pblk;
		goto got_allocated_blocks;
	}

	/* find neighbour allocated blocks */
	ar.lleft = map->m_lblk;
	err = ext4_ext_search_left(inode, path, &ar.lleft, &ar.pleft);
	if (err)
		goto out;
	ar.lright = map->m_lblk;
	ex2 = NULL;
	err = ext4_ext_search_right(inode, path, &ar.lright, &ar.pright, &ex2);
	if (err)
		goto out;

	/* Check if the extent after searching to the right implies a
	 * cluster we can use. */
	if ((sbi->s_cluster_ratio > 1) && ex2 &&
	    get_implied_cluster_alloc(inode->i_sb, map, ex2, path)) {
		ar.len = allocated = map->m_len;
		newblock = map->m_pblk;
		goto got_allocated_blocks;
	}

	/*
	 * See if request is beyond maximum number of blocks we can have in
	 * a single extent. For an initialized extent this limit is
	 * EXT_INIT_MAX_LEN and for an unwritten extent this limit is
	 * EXT_UNWRITTEN_MAX_LEN.
	 */
	if (map->m_len > EXT_INIT_MAX_LEN &&
	    !(flags & EXT4_GET_BLOCKS_UNWRIT_EXT))
		map->m_len = EXT_INIT_MAX_LEN;
	else if (map->m_len > EXT_UNWRITTEN_MAX_LEN &&
		 (flags & EXT4_GET_BLOCKS_UNWRIT_EXT))
		map->m_len = EXT_UNWRITTEN_MAX_LEN;

	/* Check if we can really insert (m_lblk)::(m_lblk + m_len) extent */
	newex.ee_len = cpu_to_le16(map->m_len);
	err = ext4_ext_check_overlap(sbi, inode, &newex, path);
	if (err)
		allocated = ext4_ext_get_actual_len(&newex);
	else
		allocated = map->m_len;

	/* allocate new block */
	ar.inode = inode;
	ar.goal = ext4_ext_find_goal(inode, path, map->m_lblk);
	ar.logical = map->m_lblk;
	/*
	 * We calculate the offset from the beginning of the cluster
	 * for the logical block number, since when we allocate a
	 * physical cluster, the physical block should start at the
	 * same offset from the beginning of the cluster.  This is
	 * needed so that future calls to get_implied_cluster_alloc()
	 * work correctly.
	 */
	offset = EXT4_LBLK_COFF(sbi, map->m_lblk);
	ar.len = EXT4_NUM_B2C(sbi, offset+allocated);
	ar.goal -= offset;
	ar.logical -= offset;
	if (S_ISREG(inode->i_mode))
		ar.flags = EXT4_MB_HINT_DATA;
	else
		/* disable in-core preallocation for non-regular files */
		ar.flags = 0;
	if (flags & EXT4_GET_BLOCKS_NO_NORMALIZE)
		ar.flags |= EXT4_MB_HINT_NOPREALLOC;
	if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
		ar.flags |= EXT4_MB_DELALLOC_RESERVED;
	if (flags & EXT4_GET_BLOCKS_METADATA_NOFAIL)
		ar.flags |= EXT4_MB_USE_RESERVED;
	newblock = ext4_mb_new_blocks(handle, &ar, &err);
	if (!newblock)
		goto out;
	allocated_clusters = ar.len;
	ar.len = EXT4_C2B(sbi, ar.len) - offset;
	ext_debug(inode, "allocate new block: goal %llu, found %llu/%u, requested %u\n",
		  ar.goal, newblock, ar.len, allocated);
	if (ar.len > allocated)
		ar.len = allocated;

got_allocated_blocks:
	/* try to insert new extent into found leaf and return */
	pblk = newblock + offset;
	ext4_ext_store_pblock(&newex, pblk);
	newex.ee_len = cpu_to_le16(ar.len);
	/* Mark unwritten */
	if (flags & EXT4_GET_BLOCKS_UNWRIT_EXT) {
		ext4_ext_mark_unwritten(&newex);
		map->m_flags |= EXT4_MAP_UNWRITTEN;
	}

	err = ext4_ext_insert_extent(handle, inode, &path, &newex, flags);
	if (err) {
		if (allocated_clusters) {
			int fb_flags = 0;

			/*
			 * free data blocks we just allocated.
			 * not a good idea to call discard here directly,
			 * but otherwise we'd need to call it every free().
			 */
			ext4_discard_preallocations(inode);
			if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
				fb_flags = EXT4_FREE_BLOCKS_NO_QUOT_UPDATE;
			ext4_free_blocks(handle, inode, NULL, newblock,
					 EXT4_C2B(sbi, allocated_clusters),
					 fb_flags);
		}
		goto out;
	}

	/*
	 * Reduce the reserved cluster count to reflect successful deferred
	 * allocation of delayed allocated clusters or direct allocation of
	 * clusters discovered to be delayed allocated.  Once allocated, a
	 * cluster is not included in the reserved count.
	 */
	if (test_opt(inode->i_sb, DELALLOC) && allocated_clusters) {
		if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) {
			/*
			 * When allocating delayed allocated clusters, simply
			 * reduce the reserved cluster count and claim quota
			 */
			ext4_da_update_reserve_space(inode, allocated_clusters,
							1);
		} else {
			ext4_lblk_t lblk, len;
			unsigned int n;

			/*
			 * When allocating non-delayed allocated clusters
			 * (from fallocate, filemap, DIO, or clusters
			 * allocated when delalloc has been disabled by
			 * ext4_nonda_switch), reduce the reserved cluster
			 * count by the number of allocated clusters that
			 * have previously been delayed allocated.  Quota
			 * has been claimed by ext4_mb_new_blocks() above,
			 * so release the quota reservations made for any
			 * previously delayed allocated clusters.
			 */
			lblk = EXT4_LBLK_CMASK(sbi, map->m_lblk);
			len = allocated_clusters << sbi->s_cluster_bits;
			n = ext4_es_delayed_clu(inode, lblk, len);
			if (n > 0)
				ext4_da_update_reserve_space(inode, (int) n, 0);
		}
	}

	/*
	 * Cache the extent and update transaction to commit on fdatasync only
	 * when it is _not_ an unwritten extent.
	 */
	if ((flags & EXT4_GET_BLOCKS_UNWRIT_EXT) == 0)
		ext4_update_inode_fsync_trans(handle, inode, 1);
	else
		ext4_update_inode_fsync_trans(handle, inode, 0);

	map->m_flags |= (EXT4_MAP_NEW | EXT4_MAP_MAPPED);
	map->m_pblk = pblk;
	map->m_len = ar.len;
	allocated = map->m_len;
	ext4_ext_show_leaf(inode, path);

out:
	ext4_ext_drop_refs(path);
	kfree(path);

	trace_ext4_ext_map_blocks_exit(inode, flags, map,
				       err ? err : allocated);
	return err ? err : allocated;
}