From mboxrd@z Thu Jan 1 00:00:00 1970 From: sukadev@us.ibm.com Subject: Re: Per-instance devpts Date: Sat, 2 Aug 2008 22:08:00 -0700 Message-ID: <20080803050800.GA4322@us.ibm.com> References: <20080412172933.GA19295@us.ibm.com> <1208027215.28187.17.camel@x61.ebiederm.org> <48935205.3090807@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <48935205.3090807@zytor.com> Sender: linux-kernel-owner@vger.kernel.org To: "H. Peter Anvin" Cc: "Eric W. Biederman" , Andrew Morton , serue@us.ibm.com, matthltc@us.ibm.com, Pavel Emelyanov , Containers , linux-kernel@vger.kernel.org, Alan Cox , Greg KH , sukadev@us.ibm.com List-Id: containers.vger.kernel.org H. Peter Anvin [hpa@zytor.com] wrote: > Since the issue of PTY namespaces came up (and was rejected) back in April, > I have thought a little bit about changing ptys to be tied directly into a > devpts instance. devpts would then be a "normal" filesystem, which can be > mounted multiple times (or not at all). pty's would then become private to > a devpts instance. Sorry, I thought we were going with a complete device namespace - since that would address other devices as well and would avoid the following user-space issue. I guess this issue came up in OLS recently and have been looking into this again. I have some helper patches to explore multiple mounts of devpts without namespace stuff and can send them out in a couple of days. > > This is what it would appear would have to change, and I'd like to get > people's feeing for the user-space impact: > > 1. /dev/ptmx would have to change to a symlink, ptmx -> pts/ptmx. IIRC, /dev/tty also needs a similar symlink. > 2. Permissions on /dev/ptmx would not be persistent, and would have to > be set via devpts mount options (unless they're 0666 root.tty, which > would presumably be the default.) > 3. The /proc/sys/kernel/pty limit would be global; a per-filesystem > limit could be added on top or instead (presumably via a filesystem > mount options.) > > I worry #1 would have substantial user-space impact, but I don't see a way > around it, since there would be no obvious way to associate /dev/ptmx with > a filesystem. Sukadev