From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751956Ab2IPQJt (ORCPT <rfc822;w@1wt.eu>);
	Sun, 16 Sep 2012 12:09:49 -0400
Received: from lxorguk.ukuu.org.uk ([81.2.110.251]:60231 "EHLO
	lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751331Ab2IPQJr (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sun, 16 Sep 2012 12:09:47 -0400
Date: Sun, 16 Sep 2012 17:13:16 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: ebiederm@xmission.com (Eric W. Biederman)
Cc: Serge Hallyn <serge@hallyn.com>, Aristeu Rozanski <aris@ruivo.org>,
        Neil Horman <nhorman@tuxdriver.com>,
        "Serge E. Hallyn" <serue@us.ibm.com>,
        containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        Michal Hocko <mhocko@suse.cz>, Thomas Graf <tgraf@suug.ch>,
        Paul Mackerras <paulus@samba.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>,
        cgroups@vger.kernel.org, Paul Turner <pjt@google.com>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: Controlling devices and device namespaces
Message-ID: <20120916171316.517ad0fd@pyramind.ukuu.org.uk>
In-Reply-To: <87k3vuqc5l.fsf@xmission.com>
References: <20120913205827.GO7677@google.com>
	<20120914183641.GA2191@cathedrallabs.org>
	<20120915022037.GA6438@mail.hallyn.com>
	<87wqzv7i08.fsf_-_@xmission.com>
	<20120915220520.GA11364@mail.hallyn.com>
	<87y5kazuez.fsf@xmission.com>
	<20120916122112.3f16178d@pyramind.ukuu.org.uk>
	<87sjaiuqp5.fsf@xmission.com>
	<87d31mupp3.fsf@xmission.com>
	<5055D4D1.3070407@hallyn.com>
	<87k3vuqc5l.fsf@xmission.com>
X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.8; x86_64-redhat-linux-gnu)
Face: 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
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> At least with a recent modern distro I can't imagine this to be an
> issue.  I expect we could have a kernel build option that removed the
> mknod system call and a modern distro wouldn't notice.

A few things beyond named pipes will break. PCMCIA I believe still
depends on ugly mknod hackery of its own. You also need it for some
classes of non detectable device.

Basically though you could.

> For migration with direct access to real hardware devices we must treat
> it as hardware hotunplug.  There is nothing else we can do.

That is demonstrably false for a shared bus or a network linked device.
Consider a firewire camera wired to two systems at once. Consider SAN
storage.

Alan