undocumented stty fields, visible bell, and su (sunos 3.2)

[Guy Harris]

> I also notice that here there seem to be a couple of undocumented
> stty options -- noflsh, nopost, noisig.  All seem to be -'ed, ie.,
> I normally have -noflsh, -nopost, and -noisig show up in `stty everything`.
> Can someone enlighten me on those options?  None of them seem to control
> the visible bell entirely, but I do notice that if I stty noisig,
> the vb sequence takes longer -- the screen changes, stays, then changes back.

You're imagining things.  "noisig" can't cause what you see.

"noflsh" is from 4.3BSD.  Berkeley didn't bother documenting it in STTY(1), but
in TTY(4) they document it as:

	LNOFLSH	100000	Inhibit flushing of pending I/O when an interrupt
			character is typed.

which means that if it is set, interrupt characters (for example, ^C) do not
cause any unread input or untransmitted output to be flushed.

"nopost" and "noisig" were added in 3.2 to make life easier for the code that
emulates much of the System V tty driver behavior.  "nopost" turns off all
output post-processing; it's like "litout", except that it doesn't put the
hardware into 8 bits, no parity mode.  "noisig" disables all interrupt
characters.  (If anybody wants to tweak those bits in a program, they are in an
"extra" mode word, fetched with TIOCGETX and set with TIOCSETX.)