static void echo_char(unsigned char c, struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (c == ECHO_OP_START) {
		add_echo_byte(ECHO_OP_START, ldata);
		add_echo_byte(ECHO_OP_START, ldata);
	} else {
		if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
			add_echo_byte(ECHO_OP_START, ldata);
		add_echo_byte(c, ldata);
	}
}
Unknown