ext4_swap_extents(handle_t *handle, struct inode *inode1,
		  struct inode *inode2, ext4_lblk_t lblk1, ext4_lblk_t lblk2,
		  ext4_lblk_t count, int unwritten, int *erp)
{
	struct ext4_ext_path *path1 = NULL;
	struct ext4_ext_path *path2 = NULL;
	int replaced_count = 0;

	BUG_ON(!rwsem_is_locked(&EXT4_I(inode1)->i_data_sem));
	BUG_ON(!rwsem_is_locked(&EXT4_I(inode2)->i_data_sem));
	BUG_ON(!inode_is_locked(inode1));
	BUG_ON(!inode_is_locked(inode2));

	*erp = ext4_es_remove_extent(inode1, lblk1, count);
	if (unlikely(*erp))
		return 0;
	*erp = ext4_es_remove_extent(inode2, lblk2, count);
	if (unlikely(*erp))
		return 0;

	while (count) {
		struct ext4_extent *ex1, *ex2, tmp_ex;
		ext4_lblk_t e1_blk, e2_blk;
		int e1_len, e2_len, len;
		int split = 0;

		path1 = ext4_find_extent(inode1, lblk1, NULL, EXT4_EX_NOCACHE);
		if (IS_ERR(path1)) {
			*erp = PTR_ERR(path1);
			path1 = NULL;
		finish:
			count = 0;
			goto repeat;
		}
		path2 = ext4_find_extent(inode2, lblk2, NULL, EXT4_EX_NOCACHE);
		if (IS_ERR(path2)) {
			*erp = PTR_ERR(path2);
			path2 = NULL;
			goto finish;
		}
		ex1 = path1[path1->p_depth].p_ext;
		ex2 = path2[path2->p_depth].p_ext;
		/* Do we have something to swap ? */
		if (unlikely(!ex2 || !ex1))
			goto finish;

		e1_blk = le32_to_cpu(ex1->ee_block);
		e2_blk = le32_to_cpu(ex2->ee_block);
		e1_len = ext4_ext_get_actual_len(ex1);
		e2_len = ext4_ext_get_actual_len(ex2);

		/* Hole handling */
		if (!in_range(lblk1, e1_blk, e1_len) ||
		    !in_range(lblk2, e2_blk, e2_len)) {
			ext4_lblk_t next1, next2;

			/* if hole after extent, then go to next extent */
			next1 = ext4_ext_next_allocated_block(path1);
			next2 = ext4_ext_next_allocated_block(path2);
			/* If hole before extent, then shift to that extent */
			if (e1_blk > lblk1)
				next1 = e1_blk;
			if (e2_blk > lblk2)
				next2 = e2_blk;
			/* Do we have something to swap */
			if (next1 == EXT_MAX_BLOCKS || next2 == EXT_MAX_BLOCKS)
				goto finish;
			/* Move to the rightest boundary */
			len = next1 - lblk1;
			if (len < next2 - lblk2)
				len = next2 - lblk2;
			if (len > count)
				len = count;
			lblk1 += len;
			lblk2 += len;
			count -= len;
			goto repeat;
		}

		/* Prepare left boundary */
		if (e1_blk < lblk1) {
			split = 1;
			*erp = ext4_force_split_extent_at(handle, inode1,
						&path1, lblk1, 0);
			if (unlikely(*erp))
				goto finish;
		}
		if (e2_blk < lblk2) {
			split = 1;
			*erp = ext4_force_split_extent_at(handle, inode2,
						&path2,  lblk2, 0);
			if (unlikely(*erp))
				goto finish;
		}
		/* ext4_split_extent_at() may result in leaf extent split,
		 * path must to be revalidated. */
		if (split)
			goto repeat;

		/* Prepare right boundary */
		len = count;
		if (len > e1_blk + e1_len - lblk1)
			len = e1_blk + e1_len - lblk1;
		if (len > e2_blk + e2_len - lblk2)
			len = e2_blk + e2_len - lblk2;

		if (len != e1_len) {
			split = 1;
			*erp = ext4_force_split_extent_at(handle, inode1,
						&path1, lblk1 + len, 0);
			if (unlikely(*erp))
				goto finish;
		}
		if (len != e2_len) {
			split = 1;
			*erp = ext4_force_split_extent_at(handle, inode2,
						&path2, lblk2 + len, 0);
			if (*erp)
				goto finish;
		}
		/* ext4_split_extent_at() may result in leaf extent split,
		 * path must to be revalidated. */
		if (split)
			goto repeat;

		BUG_ON(e2_len != e1_len);
		*erp = ext4_ext_get_access(handle, inode1, path1 + path1->p_depth);
		if (unlikely(*erp))
			goto finish;
		*erp = ext4_ext_get_access(handle, inode2, path2 + path2->p_depth);
		if (unlikely(*erp))
			goto finish;

		/* Both extents are fully inside boundaries. Swap it now */
		tmp_ex = *ex1;
		ext4_ext_store_pblock(ex1, ext4_ext_pblock(ex2));
		ext4_ext_store_pblock(ex2, ext4_ext_pblock(&tmp_ex));
		ex1->ee_len = cpu_to_le16(e2_len);
		ex2->ee_len = cpu_to_le16(e1_len);
		if (unwritten)
			ext4_ext_mark_unwritten(ex2);
		if (ext4_ext_is_unwritten(&tmp_ex))
			ext4_ext_mark_unwritten(ex1);

		ext4_ext_try_to_merge(handle, inode2, path2, ex2);
		ext4_ext_try_to_merge(handle, inode1, path1, ex1);
		*erp = ext4_ext_dirty(handle, inode2, path2 +
				      path2->p_depth);
		if (unlikely(*erp))
			goto finish;
		*erp = ext4_ext_dirty(handle, inode1, path1 +
				      path1->p_depth);
		/*
		 * Looks scarry ah..? second inode already points to new blocks,
		 * and it was successfully dirtied. But luckily error may happen
		 * only due to journal error, so full transaction will be
		 * aborted anyway.
		 */
		if (unlikely(*erp))
			goto finish;
		lblk1 += len;
		lblk2 += len;
		replaced_count += len;
		count -= len;

	repeat:
		ext4_ext_drop_refs(path1);
		kfree(path1);
		ext4_ext_drop_refs(path2);
		kfree(path2);
		path1 = path2 = NULL;
	}
	return replaced_count;
}