In message <Pine.NEB.4.44.0211011450030.376-100000@elation.immanent.net>, Frede
rick Bruckman writes:
>On Fri, 1 Nov 2002, Steven M. Bellovin wrote:
>
>> In message <Pine.NEB.4.33.0211011033400.20030-100000@vespasia.home-net.inter
>net
>> connect.net>, Bill Studenmund writes:
>> >
>> >> 2.  If I enable DSR/DTR handshaking, whenever the terminal tries to hands
>hak
>> >e,
>> >> it ends up causing getty to respawn - I suspect NetBSD is seeing it as a
>> >> break.
>> >
>> >That actually would be good. That means that DTR is getting mapped to CD,
>> >which is what mdmbuf wants. Mark the port local, and go for it.
>> >
>> I don't think so.  The "break" key on a terminal sends a "long space"
>> signal, i.e., an in-band "bit" that is stretched long enough that it
>> causes a framing error because there's no stop bit.  (We're getting far
>> afield here of NetBSD, but...  An RS-232 line in idle state is sending
>> a constant voltage equivalent to a 1-bit.  A start bit is one bit-time
>> worth of a 0-bit, followed by some number (usually 8) bit-times of 0 or
>> 1 bits, as needed.  That's followed by one (sometimes more) "stop bits"
>> -- idle time, really, when the signal value *must* be 1.  If it isn't,
>> a framing error is signaled.  The break key sends about 1/4 second of
>> 0-bit, enough to cause a framing error at any baud rate.  It's thus a
>> speed-independent signal of *something*.  It has nothing to do with DTR
>> or CD, and in fact can be sent on 3-wire interfaces with no control
>> leads.)
>
>A break wouldn't cause the getty to respawn, though -- it would drop
>into the debugger. So it isn't actually a break. Dropping CD would
>cause the getty to respawn, so it could actually be what Bill said, so
>"stty clocal -hup mdmbuf" might work.
>
A break is usually translated to SIGINT.  A very quick grep shows that 
getty is trying to handle SIGINT at certain points but not always, and I'm 
not inclined to wade through it now.

I agree with you about the effects of CD dropping.

		--Steve Bellovin, http://www.research.att.com/~smb (me)
		http://www.wilyhacker.com ("Firewalls" book)