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;
	int free_on_err = 0, err = 0, depth, ret;
	unsigned int allocated = 0, offset = 0;
	unsigned int allocated_clusters = 0;
	struct ext4_allocation_request ar;
	ext4_io_end_t *io = ext4_inode_aio(inode);
	ext4_lblk_t cluster_offset;
	int set_unwritten = 0;
	bool map_from_cluster = false;

	ext_debug("blocks %u/%u requested for inode %lu\n",
		  map->m_lblk, map->m_len, inode->i_ino);
	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 out2;
	}

	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 out2;
	}

	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("%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)) {
				allocated = convert_initialized_extent(
						handle, inode, map, &path,
						flags, allocated, newblock);
				goto out2;
			} else if (!ext4_ext_is_unwritten(ex))
				goto out;

			ret = ext4_ext_handle_unwritten_extents(
				handle, inode, map, &path, flags,
				allocated, newblock);
			if (ret < 0)
				err = ret;
			else
				allocated = ret;
			goto out2;
		}
	}

	/*
	 * 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) {
		/*
		 * put just found gap into cache to speed up
		 * subsequent requests
		 */
		ext4_ext_put_gap_in_cache(inode, path, map->m_lblk);
		goto out2;
	}

	/*
	 * 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;
		map_from_cluster = true;
		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 out2;
	ar.lright = map->m_lblk;
	ex2 = NULL;
	err = ext4_ext_search_right(inode, path, &ar.lright, &ar.pright, &ex2);
	if (err)
		goto out2;

	/* 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;
		map_from_cluster = true;
		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 out2;
	ext_debug("allocate new block: goal %llu, found %llu/%u\n",
		  ar.goal, newblock, allocated);
	free_on_err = 1;
	allocated_clusters = ar.len;
	ar.len = EXT4_C2B(sbi, ar.len) - offset;
	if (ar.len > allocated)
		ar.len = allocated;

got_allocated_blocks:
	/* try to insert new extent into found leaf and return */
	ext4_ext_store_pblock(&newex, newblock + offset);
	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;
		/*
		 * io_end structure was created for every IO write to an
		 * unwritten extent. To avoid unnecessary conversion,
		 * here we flag the IO that really needs the conversion.
		 * For non asycn direct IO case, flag the inode state
		 * that we need to perform conversion when IO is done.
		 */
		if (flags & EXT4_GET_BLOCKS_PRE_IO)
			set_unwritten = 1;
	}

	err = 0;
	if ((flags & EXT4_GET_BLOCKS_KEEP_SIZE) == 0)
		err = check_eofblocks_fl(handle, inode, map->m_lblk,
					 path, ar.len);
	if (!err)
		err = ext4_ext_insert_extent(handle, inode, &path,
					     &newex, flags);

	if (!err && set_unwritten) {
		if (io)
			ext4_set_io_unwritten_flag(inode, io);
		else
			ext4_set_inode_state(inode,
					     EXT4_STATE_DIO_UNWRITTEN);
	}

	if (err && free_on_err) {
		int fb_flags = flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE ?
			EXT4_FREE_BLOCKS_NO_QUOT_UPDATE : 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);
		ext4_free_blocks(handle, inode, NULL, newblock,
				 EXT4_C2B(sbi, allocated_clusters), fb_flags);
		goto out2;
	}

	/* previous routine could use block we allocated */
	newblock = ext4_ext_pblock(&newex);
	allocated = ext4_ext_get_actual_len(&newex);
	if (allocated > map->m_len)
		allocated = map->m_len;
	map->m_flags |= EXT4_MAP_NEW;

	/*
	 * Update reserved blocks/metadata blocks after successful
	 * block allocation which had been deferred till now.
	 */
	if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) {
		unsigned int reserved_clusters;
		/*
		 * Check how many clusters we had reserved this allocated range
		 */
		reserved_clusters = get_reserved_cluster_alloc(inode,
						map->m_lblk, allocated);
		if (!map_from_cluster) {
			BUG_ON(allocated_clusters < reserved_clusters);
			if (reserved_clusters < allocated_clusters) {
				struct ext4_inode_info *ei = EXT4_I(inode);
				int reservation = allocated_clusters -
						  reserved_clusters;
				/*
				 * It seems we claimed few clusters outside of
				 * the range of this allocation. We should give
				 * it back to the reservation pool. This can
				 * happen in the following case:
				 *
				 * * Suppose s_cluster_ratio is 4 (i.e., each
				 *   cluster has 4 blocks. Thus, the clusters
				 *   are [0-3],[4-7],[8-11]...
				 * * First comes delayed allocation write for
				 *   logical blocks 10 & 11. Since there were no
				 *   previous delayed allocated blocks in the
				 *   range [8-11], we would reserve 1 cluster
				 *   for this write.
				 * * Next comes write for logical blocks 3 to 8.
				 *   In this case, we will reserve 2 clusters
				 *   (for [0-3] and [4-7]; and not for [8-11] as
				 *   that range has a delayed allocated blocks.
				 *   Thus total reserved clusters now becomes 3.
				 * * Now, during the delayed allocation writeout
				 *   time, we will first write blocks [3-8] and
				 *   allocate 3 clusters for writing these
				 *   blocks. Also, we would claim all these
				 *   three clusters above.
				 * * Now when we come here to writeout the
				 *   blocks [10-11], we would expect to claim
				 *   the reservation of 1 cluster we had made
				 *   (and we would claim it since there are no
				 *   more delayed allocated blocks in the range
				 *   [8-11]. But our reserved cluster count had
				 *   already gone to 0.
				 *
				 *   Thus, at the step 4 above when we determine
				 *   that there are still some unwritten delayed
				 *   allocated blocks outside of our current
				 *   block range, we should increment the
				 *   reserved clusters count so that when the
				 *   remaining blocks finally gets written, we
				 *   could claim them.
				 */
				dquot_reserve_block(inode,
						EXT4_C2B(sbi, reservation));
				spin_lock(&ei->i_block_reservation_lock);
				ei->i_reserved_data_blocks += reservation;
				spin_unlock(&ei->i_block_reservation_lock);
			}
			/*
			 * We will claim quota for all newly allocated blocks.
			 * We're updating the reserved space *after* the
			 * correction above so we do not accidentally free
			 * all the metadata reservation because we might
			 * actually need it later on.
			 */
			ext4_da_update_reserve_space(inode, allocated_clusters,
							1);
		}
	}

	/*
	 * 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);
out:
	if (allocated > map->m_len)
		allocated = map->m_len;
	ext4_ext_show_leaf(inode, path);
	map->m_flags |= EXT4_MAP_MAPPED;
	map->m_pblk = newblock;
	map->m_len = allocated;
out2:
	ext4_ext_drop_refs(path);
	kfree(path);

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