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

["Stephen C. Tweedie" <sct@xxxxxxxxxx>]

Hi,

On Fri, 2006-05-19 at 10:43 +0100, Christian Limpach wrote:

> This solution, as any solution which exposes the uuid to the guest,
> will break if/when we support VM forking.

Right.  But this isn't unique to Xen --- uuids in ext2/3 filesystem
superblocks have the same problem when you have LVM snapshots, for
example.  That doesn't mean they aren't useful --- it does mean you may
need to take care when creating forks/clones/snapshots.

There are just so many unique IDs out there.  The breakage opportunities
on VM fork are boundless.  You now have two VMs mounting the same on-
disk filesystems, which have the same UUIDs; your management agents' own
internal UUIDs are duplicated; you have duplicated IP connections out
over duplicate MAC addresses, etc.

So I think VM forking is not a major obstacle here, not because UUID
doesn't affect fork, but because fork is *so* hard, and will require so
much cooperation from the domU if you want to get these things right,
that domU-visible UUID is the least of your worries. :-)

--Stephen



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