Date: Wed, 21 Nov 2007 22:00:02 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Dan Epure <gepu@iogyte.ro> Cc: freebsd-current@freebsd.org, freebsd-stable@freebsd.org, csjp@FreeBSD.org Subject: Re: pseudo terminals in 7.0 - pts implementation Message-ID: <20071121215807.F60495@fledge.watson.org> In-Reply-To: <20071118144243.B97497@fledge.watson.org> References: <20071118012616.GF19354@iogyte.ro> <20071118144243.B97497@fledge.watson.org>
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On Sun, 18 Nov 2007, Robert Watson wrote: > On Sun, 18 Nov 2007, Dan Epure wrote: > >> 7.0-BETA3 still has issues regarding the pts implementation . problems >> found: 1. - GNU screen: starting a screen, opening a few windows and >> quiting screen leaves the allocated pseudo terminal in use. 100 screen >> user, using each one opening 10 windows will deplete the default of 1000 >> pseudo terminals leaving the system unusable. 2. - 'ls /dev/ptmx' creates >> an additional entry in /dev/pty/. when the number of entries equals >> kern.pts.max the system became unusable. > > The first of these is likely a reference management bug of some sort -- I > find that if I close a pty in screen by exiting the shell, the pts device is > GC'd properly, but if I close it by killing the session with ctrl-k, then > the pts device is not properly GC'd and processes hung off it not properly > killed. I believe that closing the master device is not properly kicking > the slave device and causing its consumers to exit, hence the pts device not > being closd and released. Christian was taking a look at this a couple of > days ago, and I've CC'd him. > > The second problem is more tricky, and has to do with the cloning model. > Similar problems can exist with other variations on the ptmx implementation, > and I need to give some thought to how to address this. Dan, So, thinking a bit more about the second problem, I think it is inherrent to the way we've designed the /dev/ptmx cloning model, which is unfortunate. My current leaning is to disable the ptmx mechanism in 7.0 and put together a revised one for 7.1. The reason to do this is to avoid encoding the user<->kernel interface for allocating pty's via ptmx along the current lines, which we'd then need to continue supporting in future releases. I'm going to spend a bit of time over the next day or two looking at revising the interface to fix these problems. Robert N M Watson Computer Laboratory University of Cambridge
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