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

To: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH]: xl: use libuuid to generate random UUID's
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 10 Aug 2010 12:43:59 -0700
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Gianni Tedesco \(3P\)" <gianni.tedesco@xxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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 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.


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