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Re: [Xen-devel] xenstore -- read UUID

To: "dinesh chandrasekaran" <dinesh_chan8@xxxxxxxxxxx>
Subject: Re: [Xen-devel] xenstore -- read UUID
From: "Derek Murray" <Derek.Murray@xxxxxxxxxxxx>
Date: Wed, 10 Sep 2008 12:49:54 +0100
Cc: xen developers community <xen-devel@xxxxxxxxxxxxxxxxxxx>, xen users community <xen-users@xxxxxxxxxxxxxxxxxxx>
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Reply-to: Derek.Murray@xxxxxxxxxxxx
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Hi Dinesh,

On Wed, Sep 10, 2008 at 1:24 AM, dinesh chandrasekaran
<dinesh_chan8@xxxxxxxxxxx> wrote:
> they were 2 seperate questions... sorry for the typos...
> How to access xenstore from Dom-0? -- which you said 'YES'...

Yes, this is certainly possible: your code should work (I haven't
tested it) in Dom0 user-space. For another example, see
tools/xenstore/xsls.c, which implements ls functionality for xenstore
using the same interface.

> And How to access xenstore from hypervosor?

There is no code to do this in Xen at the moment.

> If the hypervisor has no knowledge about XenStore, Dom-0 must have the full
> control over the xenstore.

Correct. XenStore is simply implemented as a user-space daemon
(xenstored), running as root in Dom0.

> I need to build a table with some fields one of which should never change
> during a VMs lifetime.
> For example, if I chose the domain_id whose value is transient, If the VM
> reboots, its domain_id changes.
> That is the reason why I opted for the UUID of a domain that persists over
> time even after migration to another machine.
> The only way I could get a domain's UUID is through the xenstore and want to
> take away domain-0 from the picture, which
> according to you is almost impossible.

Instead of Dom0, you could possibly do this in a stubdomain. It is
possible to access XenStore from a MiniOS-based domain.


Derek Murray.

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