Subject: Re: /dev/ptmx
To: Christos Zoulas <>
From: Sean Davis <>
List: tech-kern
Date: 05/24/2004 18:55:59
On Mon, 24 May 2004 18:34:27 -0400, Christos Zoulas <> wrote:
> On May 24,  6:19pm, (Sean Davis) wrote:
> -- Subject: Re: /dev/ptmx
> | Would we, then, also get /dev/pts/<number> for name <-> pty mapping?
> | That's one of the few things I like better about Linux than BSD...
> | There are only so many /dev/ttyXY's you can use, and it looks quite
> | obnoxious in 'w' or 'who' compared to Linux, where you just see
> | 'pts/whatever'. Of course, I don't claim to know what the official
> | stance on any of this is, so I'm just tossing out an opinion.
> I'd love that but it will break too much software...
> christos

I don't see how... certainly software would need changing, but we're
talking about making our pty implementation meet POSIX 2001 standards
anyway, right? If the change to the pty allocation/deallocation stuff
is as different as is implied by this thread, the software is going to
be broken one way or another, isn't it?

As it is.. all I can think of that this would break would be things
that mess with utmp/utmpx, and I would imagine utmp/utmpx could be
fixed easily enough. I haven't looked that deeply into the pty code
personally, but it seems like we might as well go all the way if we're
going to do the 'Unix98 ptys' thing in the first place. I don't know
if POSIX 2001 specifies a pts/etc filesystem, I don't think it does
(but again, I'm getting this from implication earlier in the thread, I
haven't read the standard myself)... but it looks so much nicer to

dive     pts/7    ip68-100-173-33. Fri 1pm  0.00s  0.03s  0.02s  screen 
dive     pts/23   ip68-100-173-33.  3:51pm 13.00s  0.01s  0.01s  -tcsh 
dive     pts/27   ip68-100-173-33.  3:51pm  9.00s  0.01s  0.01s  -tcsh 
dive     pts/28   ip68-100-173-33.  3:51pm  6.00s  0.01s  0.01s  -tcsh 
dive     pts/29   ip68-100-173-33.  3:51pm  2.00s  0.03s  0.03s  -tcsh 

in 'w' output than:

dive     pc -                 6:50PM     0 -tcsh 
dive     pd -                 6:50PM     0 -tcsh 
dive     pe -                 6:50PM     0 -tcsh 
dive     pf -                 6:50PM     0 -tcsh 
dive     pg -                 6:50PM     0 -tcsh 
dive     ph -                 6:50PM     0 -tcsh 
dive     pi -                 6:50PM     0 -tcsh 

(although the rest of the linux w output, the cputime stuff, can go,
as far as i'm concerned)

I'm not saying a cosmetic change is worth breaking tons of software, I
just don't see how it's going to break "too much" stuff. If it's not
too much trouble, can you explain what it'll break and why? I'd be
happy to devote some time to looking at how badly it'd break those
things and seeing about fixing them. Our utmp/utmpx already breaks
things in some instances - the major one being's sshd2 on
-current. Sometimes when a user logs out, it never pulls them out of
utmp, even though it's been modified to use logoutx() in exactly the
same manner as OpenSSH sshd.