From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752977Ab2DGWDq (ORCPT ); Sat, 7 Apr 2012 18:03:46 -0400 Received: from terminus.zytor.com ([198.137.202.10]:53951 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751640Ab2DGWDp (ORCPT ); Sat, 7 Apr 2012 18:03:45 -0400 Message-ID: <4F80B9AC.2010103@zytor.com> Date: Sat, 07 Apr 2012 15:03:24 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120209 Thunderbird/10.0.1 MIME-Version: 1.0 To: "Ted Ts'o" , Alan Cox , Linux Kernel Mailing List , Al Viro , Konstantin Khlebnikov , Greg Kroah-Hartman , Kay Sievers , Sukadev Bhattiprolu Subject: Re: RFC: deprecating/removing the legacy mode of devpts References: <4F80892A.7050104@zytor.com> <20120407202056.472d8ad9@pyramind.ukuu.org.uk> <20120407212705.GD11295@thunk.org> In-Reply-To: <20120407212705.GD11295@thunk.org> X-Enigmail-Version: 1.3.5 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/07/2012 02:27 PM, Ted Ts'o wrote: > On Sat, Apr 07, 2012 at 01:02:33PM -0700, H. Peter Anvin wrote: >> The problem is that the lack of migration at the root causes real >> problems for the people who need the extra funkiness, and unlike BSD >> ttys it's not an application-level change at all. > > Could you explain what the issues are? I haven't been following > devpts all that carefully. > The issue is that to make the "ptys are private to an instance of the devpts filesystem", /dev/ptmx has to live inside the /dev/pts filesystem. This was traditionally not the case. To avoid breaking everything all at once, we have a legacy mode which supports the "all devpts instances are the same" (effectively bind mounts) and which support a /dev/ptmx outside /dev/pts. The problem is that anyone who wants to take advantage of the new functionality has to make sure *all* instances of devpts work with the new protocol. This means modifying your distro to: 1. Add "newinstance" and "ptmxmode" to /etc/fstab [easy] 2. Make /dev/ptmx a symlink to /dev/pts/ptmx. 2 would be easy if it wasn't for udev, which makes it very hard. It is not reasonable for udev to support both modes, so the *only* mode that is reasonable for it to support is the new mode. However, it is increasingly obvious that if we don't force it, this will never happen. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.