linux-kernel - Re: Controlling devices and device namespaces

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Message-ID: <20120916171316.517ad0fd@pyramind.ukuu.org.uk>
Date:	Sun, 16 Sep 2012 17:13:16 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	Serge Hallyn <serge@...lyn.com>, Aristeu Rozanski <aris@...vo.org>,
	Neil Horman <nhorman@...driver.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	Thomas Graf <tgraf@...g.ch>, Paul Mackerras <paulus@...ba.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
	Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...hat.com>
Subject: Re: Controlling devices and device namespaces

> 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
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