From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754714Ab2AXBIF (ORCPT ); Mon, 23 Jan 2012 20:08:05 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:45424 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752743Ab2AXBID (ORCPT ); Mon, 23 Jan 2012 20:08:03 -0500 Date: Tue, 24 Jan 2012 01:07:58 +0000 From: Al Viro To: Linus Torvalds Cc: Serge Hallyn , Dave Hansen , sukadev@linux.vnet.ibm.com, Andy Whitcroft , Matt Helsley , linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org Subject: Re: [RFC] fix devpts mount behavior Message-ID: <20120124010758.GJ23916@ZenIV.linux.org.uk> References: <20120124000517.GA28878@sergelap> <20120124002555.GA29534@sergelap> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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)