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Re: [Xen-devel] [PATCH] [Xend] Move some backend configuration

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] [Xend] Move some backend configuration
From: "Daniel P. Berrange" <berrange@xxxxxxxxxx>
Date: Tue, 30 Sep 2008 18:08:26 +0100
Cc: Pascal Bouchareine <pascal@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, John Levon <levon@xxxxxxxxxxxxxxxxx>
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On Tue, Sep 30, 2008 at 05:46:04PM +0100, Keir Fraser wrote:
> On 30/9/08 17:35, "Daniel P. Berrange" <berrange@xxxxxxxxxx> wrote:
> >> Duplicating this pair of nodes sounds fine to me, *but* then libvirt is
> >> simply remaining vulnerable to the kind of attack we're are looking to
> >> avoid? Can any good really come from keeping the old locations?
> > 
> > Given that this is security sensitive, I have no objection to updating
> > libvirt to read from the new locations. The only thing I need to work
> > out is a reliable way to choose when to use the new location, vs the
> > looking at old location (for compat with existing deployments).
> That's an interesting question. Obviously you don't want to race their
> creation and go down the unsafe path unnecessarily.
> We could add a node to xenstore, or append version/feature info to the pid
> file? Do you have a preference?

I think its probably best to have explicit "feature" info written into
somewhere in xenstore to indicate that the new layout is in use - "version" 
info would get too confusing when we inevitably have to backport this stuff.

To avoid a race condition we'd not want it in the per-VM areas. It'd want
to be a global feature flag we can probe once when libvirt connects, 
rather than probing  per guest.

I notice there's a  /tool area that's unused

  # xenstore-ls /tool
  xenstored = ""

Could put a little feature flag node there perhaps ?

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