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Re: [Xen-devel] [PATCH] /sys/hypervisor/uuid

To: "Chris Wright" <chrisw@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] /sys/hypervisor/uuid
From: "Christian Limpach" <christian.limpach@xxxxxxxxx>
Date: Fri, 19 May 2006 10:43:18 +0100
Cc: Xen devel list <xen-devel@xxxxxxxxxxxxxxxxxxx>, Markus Armbruster <armbru@xxxxxxxxxx>, Christian Limpach <chris@xxxxxxxxxxxxx>
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On 5/19/06, Chris Wright <chrisw@xxxxxxxxxxxx> wrote:
* Keir Fraser (Keir.Fraser@xxxxxxxxxxxx) wrote:
> Christian has a fair point that, if you're just reading it out of
> xenstore, you could do that directly from user space. I suppose there
> is an argument of necessary privileges to do so however, since you need
> to be root to open the xenstore device file.

Privileges part is a bit annoying.  But if the envisioned user
is unprivilged, some init script could always stash uuid in a
world readable file.

This solution, as any solution which exposes the uuid to the guest,
will break if/when we support VM forking.  Nevertheless, at this point
I'd almost prefer adding a version sub hypercall since that gives you
at least a chance at getting an up to date value.  Alternatively, you
could add some code to the xenstore dev driver to only allow read-only
access for non-root users.

Also, the guest domain xenstore interface was never really intended to
be used in anger, it was only added to support driver domains getting
information about the devices to configure.  The immediate issue would
be that access to xenstore is through a file in /proc/xen and I'd
expect that to change at some point.  Might be good to already add the
new path to all tools as a fallback option now.  Any suggestions for
where this would end up in /sys I presume?


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