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From: jhc@mtune.UUCP (Jonathan Clark)
Newsgroups: net.unix-wizards
Subject: Re: tty w/wo modem control inquiry
Message-ID: <588@mtune.UUCP>
Date: Wed, 23-Apr-86 23:41:53 EST
Article-I.D.: mtune.588
Posted: Wed Apr 23 23:41:53 1986
Date-Received: Sat, 26-Apr-86 05:49:36 EST
References: <979@rlgvax.UUCP> <350@ptsfb.UUCP> <418@hropus.UUCP>
Reply-To: jhc@mtune.UUCP (Jonathan Clark)
Organization: AT&T ISL Middletown NJ USA
Lines: 23
Summary: 

Having come late to this question (our news feed having been down
for a few days), but being slightly familiar with the USG tty driver,
I can comment that if you read the termio man page many things are
possible. As I read the VAX 5.0 code the following scenario will
occur every time:

	dcd is down throughout all this
	proc 1 opens line with O_NDELAY
	proc 1 sets CLOCAL (which I read as 'ignore DCD')
	proc 1 does a write and blocks
	proc 2 does a !O_NDELAY open (which succeeds)
	proc 2 does a write which succeeds
	pric 1 is still blocked...

Apparently this is fixed in 3b2 SVR2. I'm very close to fixing it for
the UNIX PC. But the set of interactions inside the tty driver
is heavily religious. Informed comments are welcomed.

-- 
Jonathan Clark
[NAC]!mtune!jhc

My walk has become rather more silly lately.