linux-kernel - Re: Controlling devices and device namespaces

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Date:	Sun, 16 Sep 2012 09:53:09 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Serge Hallyn <serge@...lyn.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Aristeu Rozanski <aris@...vo.org>,
	Neil Horman <nhorman@...driver.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

Serge Hallyn <serge@...lyn.com> writes:

>>> That's what I said a few emails ago :)  The device cgroup was meant as
>>> a short-term workaround for lack of user (and device) namespaces.
>>
>> I am saying something stronger.  The device cgroup doesn't seem to have
>> a practical function now.
>
> "Now" is wrong.  The user namespace is not complete and not yet usable for a
> full system container.  We still need the device control group.

Dropping cap mknod, and not having any device nodes you can mount
a filesystem with device nodes, plus mount namespace work to only allow
you to have access to proper device nodes should work today.  And I
admit the user namespace as I have it coded in my tree does make this
simpler.

But I agree "Now" is too soon until we have actually demonstrated
something else.

Eric
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