linux-kernel - Re: [PATCH 3/5] device_cgroup: keep track of local group settings

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Date:	Thu, 6 Dec 2012 04:31:30 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Aristeu Rozanski <aris@...hat.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	cgroups@...r.kernel.org
Subject: Re: [PATCH 3/5] device_cgroup: keep track of local group settings

Quoting Aristeu Rozanski (aris@...hat.com):
> On Mon, Dec 03, 2012 at 06:01:25PM +0000, Serge E. Hallyn wrote:
> > First, generally, I don't think 'allows' added to parent should be 
> > automatically propagated to descendents.
> 
> that's what I think too and what I tried to do
> 
> > In devcgroup_update_access: (around line 625)
> > 	there is a period of time where cgroup members have
> > 	default allow without the parent's exceptions.
> 
> true, will fix that one and look for more cases
> 
> > propagate_behavior (line 505):
> > 	1. doesn't follow the same ordering as devcgroup_update_access(), in
> > 	particular cleaning exceptions before setting behavior.
> 
> I see, will update that
> 
> > 	2. When changing a parent from deny to allow, I don't think children
> > 	should be updated.
> 
> I disagree on this one. since there'll be local preferences, it'll try
> to revalidate them everytime there's a change. so, for example, an
> exception that might not be possible now, will be possible when its
> parent changes in a way that allows that.

My concern is just practical - if I've started a bunch of containers,
and another admin decides to make a change to the root devices cgroup,
I don't want the container's device accesses now changing.

Maybe that's better solved by having all of userspace sit in /system
while containers and vms sit under /lxc and /libvirt...

-serge
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