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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