ext4: only zero partial blocks in ext4_zero_partial_blocks()

{

	struct super_block *sb = inode->i_sb;

	struct address_space *mapping = inode->i_mapping;

	unsigned partial = lstart & (sb->s_blocksize - 1);

	unsigned partial_start, partial_end;

	ext4_fsblk_t start, end;

	loff_t byte_end = (lstart + length - 1);

	int err = 0;

	partial_start = lstart & (sb->s_blocksize - 1);

	partial_end = byte_end & (sb->s_blocksize - 1);

	start = lstart >> sb->s_blocksize_bits;

	end = byte_end >> sb->s_blocksize_bits;

	/* Handle partial zero within the single block */

	if (start == end) {

	if (start == end &&

	    (partial_start || (partial_end != sb->s_blocksize - 1))) {

		err = ext4_block_zero_page_range(handle, mapping,

						 lstart, length);

		return err;

	}

	/* Handle partial zero out on the start of the range */

	if (partial) {

	if (partial_start) {

		err = ext4_block_zero_page_range(handle, mapping,

						 lstart, sb->s_blocksize);

		if (err)

			return err;

	}

	/* Handle partial zero out on the end of the range */

	partial = byte_end & (sb->s_blocksize - 1);

	if (partial != sb->s_blocksize - 1)

	if (partial_end != sb->s_blocksize - 1)

		err = ext4_block_zero_page_range(handle, mapping,

						 byte_end - partial,

						 partial + 1);

						 byte_end - partial_end,

						 partial_end + 1);

	return err;

}