TANDEM mode bugs in 4.3bsd

[Steve Feldman]

Index:	sys/sys/tty.c 4.3BSD +FIX


Description:
	There are two problems in the TANDEM mode handling in the
	4.3 bsd tty driver.  (They were in 4.2 as well.)

	First, if you have a device which is slow responding to
	a control-S, the driver can send additional control-S's
	when the last few characters arrive.

	Second, there is a deadlock condition possible if the tty
	is in cooked mode.  If input is stopped with more than TTYHOG/5
	characters left in the rawq, input can't ever be started again
	since the application won't see those characters.

Repeat-By:
	Send lots of data to a slow system in cooked mode.

Fix:
	Apply the following patch to /sys/sys/tty.c:
		(your line numbers will vary.)

*** tty.c.old	Thu Jan  8 11:09:58 1987
--- tty.c	Mon Jan  5 17:33:13 1987
***************
*** 191,197 ****
  	 * Current input > threshold AND input is available to user program
  	 */
  	if (x >= TTYHOG/2 && 
! 	    ((tp->t_flags & (RAW|CBREAK)) || (tp->t_canq.c_cc > 0))) {
  		if (putc(tp->t_stopc, &tp->t_outq)==0) {
  			tp->t_state |= TS_TBLOCK;
  			ttstart(tp);
--- 191,198 ----
  	 * Current input > threshold AND input is available to user program
  	 */
  	if (x >= TTYHOG/2 && 
! 	    ((tp->t_flags & (RAW|CBREAK)) || (tp->t_canq.c_cc > 0)) &&
! 	    (tp->t_state&TS_TBLOCK) == 0) {
  		if (putc(tp->t_stopc, &tp->t_outq)==0) {
  			tp->t_state |= TS_TBLOCK;
  			ttstart(tp);
***************
*** 1245,1251 ****
  	 * Look to unblock output now that (presumably)
  	 * the input queue has gone down.
  	 */
! 	if (tp->t_state&TS_TBLOCK && tp->t_rawq.c_cc < TTYHOG/5)
  		if (putc(tp->t_startc, &tp->t_outq) == 0) {
  			tp->t_state &= ~TS_TBLOCK;
  			ttstart(tp);
--- 1246,1254 ----
  	 * Look to unblock output now that (presumably)
  	 * the input queue has gone down.
  	 */
! 	if (tp->t_state&TS_TBLOCK &&
! 	    (tp->t_rawq.c_cc+tp->t_canq.c_cc < TTYHOG/5 ||
! 	    (t_flags&(RAW|CBREAK)) == 0 && tp->t_canq.c_cc == 0))
  		if (putc(tp->t_startc, &tp->t_outq) == 0) {
  			tp->t_state &= ~TS_TBLOCK;
  			ttstart(tp);