How does litout work

[Chris Torek]

In article <170 at brl-tgr.ARPA> gwyn at brl-tgr.ARPA (Doug Gwyn <gwyn>) writes:

>> I seem to recall that LITOUT was slightly buggy and you had to go
>> thru some special contortions to get it to work properly.

> The word was that LITOUT would not stick unless you set it a
> second time.

No:  The problem was that the device drivers did not call the
`param' routine when changing the local mode word.  Only TIOCSETP
and TIOCSETN would force a call.  With one of these buggy drivers,
to set LITOUT mode, use something like the routine below.

#include <ioctl.h>

/*
 * Set LITOUT mode on the tty line corresponding to the
 * descriptor `fd'.  Since you may not have installed the
 * (trivial) fix in your kernel for the bug, we use a
 * kludge.
 *
 * The fix:  In each tty device driver, find the code for
 * ioctl (e.g., `dhioctl' or `dzioctl').  There will be a
 * bit of code that looks like this:
 *
 *	if (cmd == TIOCSETP || cmd == TIOCSETN)
 *
 * Change the `if' statement to read:
 *
 *	if (cmd == TIOCSETP || cmd == TIOCSETN || cmd == TIOCLSET ||
 *	    cmd == TIOCLBIS || cmd == TIOCLBIC)
 *
 */
set_litout_with_bug_workaround(fd)
	int fd;
{
	int litout = LITOUT;
	struct sgttyb sg;

	if (ioctl(fd, TIOCLBIS, &litout))
		return (-1);	/* probably not a tty line */
	/*
	 * Here is the workaround.
	 */
	if (ioctl(fd, TIOCGETP, &sg))
		return (-1);
	if (ioctl(fd, TIOCSETP, &sg))
		return (-1);
	return (0);
}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 4251)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris at umcp-cs		ARPA:	chris at mimsy.umd.edu