Re: [PATCH]: xl: use libuuid to generate random UUID's

[Jeremy Fitzhardinge <jeremy@goop.org>]

  On 08/10/2010 08:23 AM, Ian Jackson wrote:
> Gianni Tedesco (3P) writes ("RE: [Xen-devel] [PATCH]: xl: use libuuid to generate random UUID's"):
>> On Mon, 2010-08-09 at 11:51 +0100, Ian Jackson wrote:
>>> VM uuids are not stable in xend nor xl.  Perhaps xl should hash the VM
>>> name, which is stable and supposedly unique.
>> But they can be made to be stable and I suppose this is the point here.
> No, I don't think VM uuids can be made stable in xl.  If for no other
> reason than that localhost migration would be impossible.

Stable uuids are a primary requirement.  Localhost migration is a 
parlour trick which is useful for testing but little else.  Therefore, 
localhost migration should work around stable uuids rather than the 
other way around (failing if you've got a stable uuid defined would be a 
reasonable answer).

xl's current behaviour of ignoring the config file uuid is an 
unequivocal bug.

> I think the only way to have stable MAC addresses is to derive them
> from the VM name, or for the user to explicitly write a MAC address in
> the config file.

Deriving from the vm name makes sense as a fallback if they haven't 
specified a uuid.  But I think in that case it would make more sense to 
derive the uuid from the domain name, and then everything else from that 
uuid.

> Users who do the latter will find things continue to work no matter
> how we change the default scheme, and the default is already somewhat
> broken, so perhaps we should indeed consider changing it.

If the default uuid is random at the moment, then it should be pretty 
safe to change it to anything else.

     J