Date: Tue, 26 Sep 2006 11:33:59 +0200 (CEST) From: Martin Blapp <mb@imp.ch> To: current@freebsd.org Subject: What do you think ?: How should pseundo terminals behave ... Message-ID: <20060926111452.J91466@godot.imp.ch>
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... if there is no slave and master anymore, both sides are closed (for example
after we did type exit in our term) and we open a slave and write something to
the closed pty ?
What we currently do:
If we have no slave and master ttypX ttytX anymore and we try to write to the
ttypX like:
echo "BLUBBER" > /dev/ttypX
We get currently blocked in ptsopen(). That's ok so far.
But after we ssh into the box again, THE SAME ! tty gets opened too,
leading to a tty livelock for 5 minutes.
Sometimes we gets then EOPNOTSUPP when the writer gets aborted, sometimes
we get two ptsclose(). After we exit this pty the refcounts are off by one, we
make one ttyrel() too much so the tty structure gets completly freed in ttyrel()
and the next ptsopen/ptcopen panics our box this is FreeBSD6 behaviour. With my
fixes CURRENT doesn not panic anymore, but it leaks ptys.
So how should ptys behave ?
1.) Block until the tty is really opened again and there is
a master available again. Then write to the freshly opened
pty. (not easy to do)
2.) Block forever since the tty will not be reopened anymore since
we leak ptys.
3.) Detect that there is no master around anymore and
return ENXIO:
# echo "BLUBBER" > /dev/ttypX
# /dev/ttypX: Device not configured
(easy to do, i've got a fix. IMHO this is the best thing to
do. This allows fast error recovery in case the master
has been gone away)
4.) Keep the current behaviour, leak terminals or panic.
(the simplest thing to do. Let's keep the bugs)
Please vote for any of those choice. Thank you for your
participation.
Martin
Martin Blapp, <mb@imp.ch> <mbr@FreeBSD.org>
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