🚀 go-pugleaf

Subject: multiple NULLs read on BREAK if RAW/COOKED is toggled
Index:	sys/sys/tty.c or sys/{vaxuba,is68kdev}/dh.c

Type:	bug
Priority:	high

Description:
	When reading in RAW mode, multiple '\0' characters are read from
	the standard input when the line is toggled between RAW and COOKED
	in the loop that does the read if a BREAK is typed at the terminal
	(under certain conditions).  One '\0' is expected.

	NOTE: This problem is hardware dependent.  It has been
	reproduced on a VAX 8200 running Ultrix with a DEC DH/U board
	but does not occur on the same VAX 8200 with Emulex or Able
	boards running in DH emulation mode.
	The bug also occurs on an Integrated Solutions Optimum 5/10
	(QBus - 68010 CPU) running 4.2BSD (ISI3.05 distribution) with
	an Emulex DH board (CS02).

Repeat-By:
	Run the following program.
	(This test program demonstrates a problem with /etc/getty).
--------------------------CUT HERE-----------------------------------
/*
 *	just type your input and it will be echoed (parity bits and all)
 *	type EOT to exit
 */

#define	EOT	'\004'

#include <stdio.h>
#include <sys/ioctl.h>

main()
{
	char c;
	int ldisc = OTTYDISC;
	struct sgttyb ttybuf;

/*	ioctl(0, TIOCSETD, 0);		/* not really necessary - does
					   it for both old & new tty drivers */
	ioctl(0, TIOCGETP, &ttybuf);
	ttybuf.sg_flags |= RAW;				/* stty raw -echo */
	ttybuf.sg_flags &= ~ECHO;
	ioctl(0, TIOCSETP, &ttybuf);

	/* the read loop */
	do {
		ttybuf.sg_flags &= ~RAW;		/* stty -raw */
		ioctl(0, TIOCSETP, &ttybuf);
		ttybuf.sg_flags |= RAW;			/* stty raw */
		ioctl(0, TIOCSETP, &ttybuf);
		read(0, &c, 1);
		fprintf(stderr, "%c (== %#o)\r\n", c, c);
	} while ((c&0177) != EOT);

	ttybuf.sg_flags |= ECHO;			/* stty -raw echo */
	ttybuf.sg_flags &= ~RAW;
	ioctl(0, TIOCSETP, &ttybuf);
}
--------------------CUT HERE-------------------------------------------------

	If the problem exists with your hardware configuration, you will
	get multiple lines like
(== 0)
(== 0)
(== 0)
(== 0)
	when you type <BREAK> on your terminal.

Discussion:
	TIOCSETP should cause the interface to delay until the output
	is quiescent, then throw away any unread characters, before
	changing the modes.  It would appear that this is not happening.
	
	While it could be argued that this is a hard/firmware problem since
	it occurs with some hardware but not with other hardware, I believe
	that the problem is either in the tty driver or the dh driver.
-- 
 
NAME:     James P. Kiely                USPS:   Lown Cardiovascular Laboratory
USENET:   ...!harvard!lownlab!kiely             Harvard School of Public Health
PHONE:    +1 617 732 1307                       665 Huntington Avenue
                                                Boston, MA 02115-9915