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Subject: Re: [PATCH 05/10] Core checkpoint/restart support code
From: Nathan Lynch <ntl@pobox.com>
To: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org,
        Oren Laadan <orenl@cs.columbia.edu>,
        Alexey Dobriyan <adobriyan@gmail.com>
In-Reply-To: <20110404151017.GA4857@hallyn.com>
References: <1298936432-29607-1-git-send-email-ntl@pobox.com>
 <1298936432-29607-6-git-send-email-ntl@pobox.com>
 <20110403190324.GD15044@hallyn.com> <1301929228.31531.39.camel@tp-t61>
 <20110404151017.GA4857@hallyn.com>
Content-Type: text/plain; charset="UTF-8"
Date: Mon, 04 Apr 2011 10:40:08 -0500
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On Mon, 2011-04-04 at 10:10 -0500, Serge E. Hallyn wrote:
> Quoting Nathan Lynch (ntl@pobox.com):
> > On Sun, 2011-04-03 at 14:03 -0500, Serge E. Hallyn wrote:
> > > Quoting ntl@pobox.com (ntl@pobox.com):
> > > > Only a pid namespace init task - the child process produced by a call
> > > > to clone(2) with CLONE_NEWPID - is allowed to call these.  The state
> > > 
> > > So you make this useful for your cases by only using this with
> > > application containers - created using lxc-execute, or, more precisely,
> > > using lxc-init as the container's init.  So a container running a stock
> > > distro can't be checkpointed.
> > 
> > Correct, a conventional distro init won't work, and application
> > containers are my focus for now, at least.
> > 
> > 
> > > Is this just to keep the patch simple for now, or is there some reason
> > > to keep this limitation in place?
> > 
> > I guess you're asking whether non-pid-init processes could be allowed to
> > use the syscalls?
> 
> No.  I'm asking whether you are intending to later on change the checkpoint
> API to allow an external task to checkpoint a pid-init process, rather than
> the pid-init process having to initiate it itself.

No, that is not the intention.  I can see how that would be problematic
for those wanting to run minimally-modified distro containers, but I
think running a patched pid-init is a reasonable tradeoff to ask users
to make in order to get c/r.  And there's nothing to keep the standard
distro inits from growing c/r capability.


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