pseudo terminals in 7.0 - pts implementation

John Baldwin jhb at FreeBSD.org
Mon Nov 26 14:13:35 PST 2007


On Thursday 22 November 2007 10:47:41 am Dan Epure wrote:
> Hi,
> 
> For the moment this feature is only available in HEAD. I think the limit 
is "only" 512 master/slave pairs.
> Should be enough for this year. Is it going to be merged  in 6.3 ? 
> Thanks again.

The 512 ptys can easily be merged.  We actually are using 1152 ptys at work
using a similar patch (just more pty letters).

> On Thu, Nov 22, 2007 at 08:53:36AM +0000, Robert Watson wrote:
> >
> > On Thu, 22 Nov 2007, Dan Epure wrote:
> >
> >> Thank you for your answer. In this case the first problem (gnu screen) 
> >> does not deserve any attention because it is related to the ptmx clonig. 
> >> My goal is to find a way to increase the number os pseudo terminal. the 
> >> traditional 256 pty is not sufficient for my needs. Is there any way to 
do 
> >> this on freebsd other than using ptmx cloning ?
> >
> > John Baldwin has just merged support for up to 1024 ptys using the 
> > traditional pty driver, I believe, to HEAD, and plans (or perhaps has 
> > already) merged it to 7.0.  I see no reason not to further merge it to 
6.x. 
> >  I've stuck him on the CC list also.
> >
> > Robert N M Watson
> > Computer Laboratory
> > University of Cambridge
> >
> >>
> >>
> >> On Wed, Nov 21, 2007 at 10:00:02PM +0000, Robert Watson wrote:
> >>>
> >>> 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
> >>
> > _______________________________________________
> > freebsd-current at freebsd.org mailing list
> > http://lists.freebsd.org/mailman/listinfo/freebsd-current
> > To unsubscribe, send any mail to "freebsd-current-unsubscribe at freebsd.org"
> 



-- 
John Baldwin


More information about the freebsd-current mailing list