From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757323Ab2AXSTh (ORCPT ); Tue, 24 Jan 2012 13:19:37 -0500 Received: from 50-56-35-84.static.cloud-ips.com ([50.56.35.84]:36216 "EHLO mail.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752828Ab2AXSTg (ORCPT ); Tue, 24 Jan 2012 13:19:36 -0500 Date: Tue, 24 Jan 2012 18:21:16 +0000 From: "Serge E. Hallyn" To: Al Viro Cc: Linus Torvalds , containers@lists.linux-foundation.org, Dave Hansen , linux-kernel@vger.kernel.org, Andy Whitcroft , sukadev@linux.vnet.ibm.com Subject: Re: [RFC] fix devpts mount behavior Message-ID: <20120124182116.GA11715@hallyn.com> References: <20120124000517.GA28878@sergelap> <20120124002555.GA29534@sergelap> <20120124010758.GJ23916@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120124010758.GJ23916@ZenIV.linux.org.uk> 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 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? -serge