minix_last_byte
limit = kaddr + minix_last_byte(inode, n) - chunk_size;
limit = kaddr + minix_last_byte(dir, n) - sbi->s_dirsize;
dir_end = kaddr + minix_last_byte(dir, n);
limit = kaddr + minix_last_byte(inode, i) - sbi->s_dirsize;