bug fixes to terminal handler of 4.1bsd

[utzoo!decvax!genradbo!linus!smk]

The following shows 2 bug fixes in /usr/sys/dev/tty.c.
I hope these are included in 4.2bsd.

	The first is a bug that is not noticed when 2 UNIX systems
are communicating, but appear when UNIX is connected to a machine
that does flow control but refuses to take 2 stop characters
without an intervening start character.  The fix looks to see
if the stop character was sent already.  If so, it is not sent again.
The fix now makes computer-compter communication possible
with flow control between 4.1 and any other machine (e.g., IBM)
that handles flow control with terminals.
	The second fix allows the stty hup to be undone.  We defined
TIOCCHPCL in /usr/include/sys/ioctl.h as:
#define	TIOCCHPCL	(('t'<<8)|113)	/* clear hangup line on close bit */
and changed stty.c to allow for it:
*** /usr/src/cmd/stty.c	Wed Jul  8 21:48:57 1981
--- /usr/src/new/stty.c	Sun May 16 10:45:20 1982
***************
*** 256,261
  			ioctl(1, TIOCHPCL, NULL);
  			continue;
  		}
  		for(i=0; speeds[i].string; i++)
  			if(eq(speeds[i].string)) {
  				mode.sg_ispeed = mode.sg_ospeed = speeds[i].speed;

--- 256,267 -----
  			ioctl(1, TIOCHPCL, NULL);
  			continue;
  		}
+ #ifdef MITRE
+ 		if (eq("-hup")) {
+ 			ioctl(1, TIOCCHPCL, NULL);
+ 			continue;
+ 		}
+ #endif
  		for(i=0; speeds[i].string; i++)
  			if(eq(speeds[i].string)) {
  				mode.sg_ispeed = mode.sg_ospeed = speeds[i].speed;


*** tty.c.orig	Sun May 16 10:32:55 1982
--- tty.c	Mon Dec 20 18:10:59 1982
***************
*** 142,147
  		flushtty(tp, FREAD|FWRITE);
  		tp->t_state &= ~TBLOCK;
  	}
  	if (x >= TTYHOG/2) {
  		if (putc(tun.t_stopc, &tp->t_outq)==0) {
  			tp->t_state |= TBLOCK;

--- 142,153 -----
  		flushtty(tp, FREAD|FWRITE);
  		tp->t_state &= ~TBLOCK;
  	}
+ #ifdef MITRE
+ 	/*	We should only block if we aren't in that state already.
+ 		We check for the blocked state before blocking, and
+ 		don't block if we already have.	*/
+     if (!(tp->t_state & TBLOCK))
+ #endif
  	if (x >= TTYHOG/2) {
  		if (putc(tun.t_stopc, &tp->t_outq)==0) {
  			tp->t_state |= TBLOCK;
***************
*** 369,374
  	case TIOCHPCL:
  		tp->t_state |= HUPCLS;
  		break;
  
  	case TIOCFLUSH: {
  		int flags;

--- 375,389 -----
  	case TIOCHPCL:
  		tp->t_state |= HUPCLS;
  		break;
+ 
+ #ifdef MITRE
+ 	/*
+ 	 * Do not hang up line on last close
+ 	 */
+ 	case TIOCCHPCL:
+ 		tp->t_state &= ~HUPCLS;
+ 		break;
+ #endif
  
  	case TIOCFLUSH: {
  		int flags;