Two fixes for pseudo-ttys

[jim at haring.UUCP]

Subject: Two fixes for pseudo-ttys
Index:	sys/sys/tty_pty.c 4.2BSD

Description:
	1) When the slave end of a pseudo-tty closes, the controlling
	   side is not informed if it is already trying to read from
	   the device.

	2) As it says in the manual, it should be but isn't possible to
	   send an end-of-file to the slave side by the controlling side
	   doing a 0-length write in TIOCREMOTE mode.
Repeat-By:
	1) The following short program may or may not cause the parent to
	   wait forever in the read(), depending on whether it gets there
	   before the child exits. It is always possible to put a sleep()
	   in the child process before the exit to ensure the parent gets
	   to read.
	
	main()
	{
		switch(fork()){

		case -1:
			perror("fork");
			break;

		case 0:
			child();
			/*NOTREACHED*/

		default:
			parent();
			/*NOTREACHED*/
		}
		exit(1);
	}

	child()
	{
		register int fd;

		if((fd = open("/dev/ttyp4", 1)) == -1){
			perror("/dev/ttyp4");
			exit(1);
		}
		(void) write(fd, "Hello world\n", 12);
		exit(0);
	}

	parent()
	{
		register int fd, n;
		char buf[100];

		if((fd = open("/dev/ptyp4", 2)) == -1){
			perror("/dev/ptyp4");
			exit(1);
		}
		while((n = read(fd, buf, sizeof(buf))) > 0)
			(void) write(1, buf, n);
		if(n == -1)
			perror("read");
		else
			printf("EOF");
		exit(0);
	}
	
	2) Typing EOF to a process expecting input from a shell window in
	   EMACS - the process is undisturbed.
Fix:
	The following is a diff -c of the original 4.2BSD module with the
	current one.

	The EOF fix comes from David Rosenthal, David.Rosenthal at CMU-CS-A.ARPA

*** sys.gen/sys/tty_pty.c	Tue Mar 27 15:12:08 1984
--- sys/sys/tty_pty.c	Sun Apr  1 20:42:26 1984
***************
*** 78,83
  	tp = &pt_tty[minor(dev)];
  	(*linesw[tp->t_line].l_close)(tp);
  	ttyclose(tp);
  }
  
  ptsread(dev, uio)

--- 78,84 -----
  	tp = &pt_tty[minor(dev)];
  	(*linesw[tp->t_line].l_close)(tp);
  	ttyclose(tp);
+ 	ptcwakeup(tp);
  }
  
  ptsread(dev, uio)
***************
*** 236,242
  		error = ureadc(0, uio);
  	}
  	while (tp->t_outq.c_cc == 0 || (tp->t_state&TS_TTSTOP)) {
! 		if (pti->pt_flags&PF_NBIO)
  			return (EWOULDBLOCK);
  		sleep((caddr_t)&tp->t_outq.c_cf, TTIPRI);
  	}

--- 237,243 -----
  		error = ureadc(0, uio);
  	}
  	while (tp->t_outq.c_cc == 0 || (tp->t_state&TS_TTSTOP)) {
! 		if (((tp->t_state&TS_CARR_ON) == 0) || (pti->pt_flags&PF_NBIO))
  			return (EWOULDBLOCK);
  		sleep((caddr_t)&tp->t_outq.c_cf, TTIPRI);
  	}
***************
*** 337,342
  			break;
  		iov = uio->uio_iov;
  		if (iov->iov_len == 0) {
  			uio->uio_iovcnt--;	
  			uio->uio_iov++;
  			if (uio->uio_iovcnt < 0)

--- 338,349 -----
  			break;
  		iov = uio->uio_iov;
  		if (iov->iov_len == 0) {
+ 			while((pti->pt_flags&PF_REMOTE) && tp->t_rawq.c_cc != 0)
+ 				sleep((caddr_t)&tp->t_rawq.c_cf, TTIPRI);
+ 			if(pti->pt_flags&PF_REMOTE){
+ 				(void) putc(0, &tp->t_rawq);
+ 				wakeup((caddr_t)&tp->t_rawq);
+ 			}
  			uio->uio_iovcnt--;	
  			uio->uio_iov++;
  			if (uio->uio_iovcnt < 0)