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Path: utzoo!linus!security!genrad!grkermit!masscomp!clyde!ihnp4!fortune!rpw3
From: rpw3@fortune.UUCP
Newsgroups: net.wanted
Subject: Re: un-dedicating a line to a dialer, an - (nf)
Message-ID: <2058@fortune.UUCP>
Date: Tue, 20-Dec-83 15:07:46 EST
Article-I.D.: fortune.2058
Posted: Tue Dec 20 15:07:46 1983
Date-Received: Thu, 22-Dec-83 04:52:48 EST
Sender: notes@fortune.UUCP
Organization: Fortune Systems, Redwood City, CA
Lines: 31

#R:denelcor:-25000:fortune:12300008:000:1031
fortune!rpw3    Dec 19 20:33:00 1983

Re: Outbound and inbound lines (getty, etc)

While I cannot give you the code, I can tell you what we did, since
it is in our published tty(4) page (FOR:PRO 1.7 version).

A new sub-device, whose minor number is 128 greater than the normal device,
is created for every tty. the "x"+128 device is used for calling out, and
the "x" device is used for hanging getty on. The trick is,

	1. If the getty line is opened "successfully" (carrier up),
	   an open to the +128 line will fail (busy).

	2. If the getty line is "hanging" waiting for carrier, and
	   an open to the +128 port occurs, the +128 open succeeds,
	   and the getty port continues to hang.

	3. The kernel makes sure there are no races.

If /dev/tty131 (say) is in L.sys for some uucp hosts, and
   /dev/tty03 (131-128) is in /etc/ttys for init to find, then
they can share the port quite nicely.

Rob Warnock

UUCP:	{sri-unix,amd70,hpda,harpo,ihnp4,allegra}!fortune!rpw3
DDD:	(415)595-8444
USPS:	Fortune Systems Corp, 101 Twin Dolphins Drive, Redwood City, CA 94065