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From: olson@fortune.UUCP (Dave Olson)
Newsgroups: net.unix-wizards
Subject: Re: TTY Inquiry
Message-ID: <5647@fortune.UUCP>
Date: Thu, 10-Oct-85 21:21:06 EDT
Article-I.D.: fortune.5647
Posted: Thu Oct 10 21:21:06 1985
Date-Received: Sat, 12-Oct-85 21:26:51 EDT
References: <482@scirtp.UUCP>
Reply-To: olson@fortune.UUCP (Dave olson)
Distribution: net
Organization: Fortune Systems, Redwood City, CA
Lines: 17

One approach that can be taken to allow bi-directional use
of tty lines is to have 2 minor #'s for each physical port.

This is the approach that was take at Fortune Systems.  If
one has a tty port with maj/min of 8/0, then the device
with 8/128 would be the corresponding outgoing port.  A few new
ioctl's were added to allow you to say that the outgoing line
should not complete open till carrier is up, the same for the 
incoming line, or neither.

When either minor # is opened, attempts to open the other mode
fail with EBUSY.  The changes that need to made are relatively
minor (but are unfortunately proprietary code, so I can't post
them).

	Dave Olson
	Fortune Systems