From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757438Ab2AXUwI (ORCPT ); Tue, 24 Jan 2012 15:52:08 -0500 Received: from 50-56-35-84.static.cloud-ips.com ([50.56.35.84]:44768 "EHLO mail.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756902Ab2AXUwF (ORCPT ); Tue, 24 Jan 2012 15:52:05 -0500 Date: Tue, 24 Jan 2012 20:53:45 +0000 From: "Serge E. Hallyn" To: Sukadev Bhattiprolu Cc: Al Viro , containers@lists.linux-foundation.org, Dave Hansen , linux-kernel@vger.kernel.org, Andy Whitcroft , Linus Torvalds Subject: Re: [RFC] fix devpts mount behavior Message-ID: <20120124205345.GA4861@hallyn.com> References: <20120124000517.GA28878@sergelap> <20120124002555.GA29534@sergelap> <20120124010758.GJ23916@ZenIV.linux.org.uk> <20120124182116.GA11715@hallyn.com> <20120124201600.GB20039@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120124201600.GB20039@us.ibm.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Sukadev Bhattiprolu (sukadev@linux.vnet.ibm.com): > Serge Hallyn [serge@hallyn.com] wrote: > | Quoting Al Viro (viro@ZenIV.linux.org.uk): > | > On Mon, Jan 23, 2012 at 04:41:25PM -0800, Linus Torvalds wrote: > | > > | > > Right. I think the opportunity for problems should be pretty small. > | > > > | > > And it's not like the pty itself wouldn't continue to work - it's just > | > > that programs like /usr/bin/tty wouldn't be able to *find* it. > | > > > | > > Although who knows - maybe there is some other subtle interaction. > | > > | > FWIW, the subtle and nasty part in all that is that you can mknod /dev/ptmx > | > and it *will* work, refering to the "initial" instance. That's what > | > concerns me about the chroot scenarios - > | > mknod /jail/dev/ptmx c 5 2 > | > mkdir /jail/dev/pts > | > mount -t devpts /jail/dev/pts > | > chroot /jail > | > works fine right now, but with that change behaviour will be all wrong - > | > opening /dev/ptmx inside of jail will grab you a pts, all right, but > | > it will *not* show up in (jail) /dev/pts/* as it does with the current > | > kernel. > | > > | > Note that if you replace that mknod with symlink pts/ptmx /jail/dev/ptmx > | > the things will keep working. However, that will _only_ work for kernels > | > with DEVPTS_MULTIPLE_INSTANCES - without it you won't get ptmx inside > | > devpts (which is arguably wrong, BTW) > | > | Should /dev/pts/ptmx be created for DEVPTS_MULTIPLE_INSTANCES=n? > > With DEVPTS_MULTIPLE_INSTANCES=n, there is only _one_ (global) instance > right ? Why would we need a 'pts/ptmx' node ? To keep the symlink (i.e > user space scripts) valid for both single and multiple instance cases ? Exactly