ext4_fc_reserve_space
dst = ext4_fc_reserve_space(sb, EXT4_FC_TAG_BASE_LEN + sizeof(tail), &crc);
dst = ext4_fc_reserve_space(sb, EXT4_FC_TAG_BASE_LEN + len, crc);
u8 *dst = ext4_fc_reserve_space(sb,
dst = ext4_fc_reserve_space(inode->i_sb,