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Date: Fri, 29 Nov 1996 21:18:36 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199611291018.VAA21638@godzilla.zeta.org.au>
To: j@uriah.heep.sax.de, moke@winternet.com
Subject: Re: kern/2118: failure to write to vc w/o input
Cc: freebsd-bugs@FreeBSD.ORG, sos@FreeBSD.ORG
Sender: owner-bugs@FreeBSD.ORG
X-Loop: FreeBSD.org
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>> 	Text written to virtual consoles that are not waiting for input is
>> 	not displayed. However once input is asked for, all lines pending
>> 	will display.
>
>Uh, so perhaps _this_ is the reason why the emergency holographic
>shell of 2.2's sysinstall vanishes when typing a command while the
>installation is in progress?

The tty plumbing for this is very strange:

	$ cat >/dev/ttyv9		# on unused ttyv9
	1
	2
	3
	[pause]

This gives no output on /dev/ttyv9.  Then on another tty:

	$ cat /dev/ttyv9
	1
	2
	3
	$

ttyv9 is acting like a pty.

	$ cat /dev/ttyv9
	1
	2
	3
	$

A buggy pty :-).  Now with the first cat terminated by ^D:

	$ cat /dev/ttyv9
	1
	2
	3
	$

A very buggy pty :-).

Bruce