What do you think ?: How should pseundo terminals behave ...

[Martin Blapp]

... 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 at imp.ch> <mbr at FreeBSD.org>
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