Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!mailrus!cornell!rochester!ritcv!moscom!jgp
From: jgp@moscom.UUCP (Jim Prescott)
Newsgroups: comp.dcom.modems
Subject: Re: Solution to Problems with UUCP/modems.
Summary: Dialin/out is trivial with a little kernel help
Keywords: modems ACU driver
Message-ID: <1260@moscom.UUCP>
Date: 14 Sep 88 06:43:24 GMT
References: <14170@comp.vuw.ac.nz> <323@uncle.UUCP> <37899@pyramid.pyramid.com> <324@telly.UUCP> <310@impch.UUCP>
Reply-To: jgp@moscom.UUCP (Jim Prescott)
Organization: Moscom Corp., E. Rochester, NY
Lines: 36

In article <310@impch.UUCP> boxdiger@impch.UUCP (Patrick Guelat) writes:
>In article <324@telly.UUCP> evan@telly.UUCP (Evan Leibovitch) writes:
>% In article <37899@pyramid.pyramid.com>, csg@pyramid.pyramid.com (Carl S. Gutekunst) writes:
>%> Standard OSx does not provide acucntrl. The 4.3BSD version is highly VAX...
>% There is also a System V acucntrl which does the same thing, but not as
>% ....
>% program edits /etc/inittab to change the entry from 'respawn' to 'off',
>% and then kills the getty.
>Another solution has been done by SCO in their XENIX.
>There is a program called 'ungetty'. It looks up in /etc/utmp if there
>is a user on the line, if there isn't it sends a SIGUSR1-signal to getty

There sure are a lot of complex solutions that perform the same function
as the so called Sun hacks which work as follows:
	- a modem gets 2 names, /dev/ttyd0 (for getty) and /dev/cua0 (for
		dialout with uucp, kermit, tip or whatever).
	- an open on ttyd0 blocks until DCD gets raised.  getty spends
		most of it's life waiting for someone to call in and raise
		DCD so it can complete the open.
	- an open on cua0 succeeds without DCD
	- the kernel ensures that only 1 of ttyd0 and cua0 can be open at
		the same time.  If someone is logged in then an open of cua0
		fails.  If cua0 gets opened by someone then getty won't see
		DCD until cua0 gets closed.

This isolates all the changes in the tty driver.  No changes to any programs
are required and it works with both modems and direct connections.  The only
disadvantage that I've heard about it is that since it can be done in user
mode it shouldn't be in the kernel.  Since it came with our 9/84 release
of HCR V7 for a pdp-11 I don't think that it can add all that much code.

Anybody know why everyone hasn't picked up on this?  I know that some of
the PC Unix systems use it.
-- 
Jim Prescott	moscom!jgp@cs.rochester.edu
		{rutgers,ames,harvard}!rochester!moscom!jgp