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

To: Vincent Hanquez <Vincent.Hanquez@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH]: xl: use libuuid to generate random UUID's
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Thu, 5 Aug 2010 11:34:20 +0100
Cc: Ian, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Gianni Tedesco \(3P\)" <gianni.tedesco@xxxxxxxxxx>
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On Thu, 5 Aug 2010, Vincent Hanquez wrote:
> On 05/08/10 03:19, Ian Pratt wrote:
> >> Link to libuuid in xl et al and bring in the header file. Use libuuid to
> >> generate UUID's which are actually UU and not merely pseudo-random :)
> >>
> >> As a side-effect I have also used libuuid to generate more random MAC
> >> addresses rather than keeping the old code and simply xoring getpid() in
> >> to the PRNG seed.
> >
> > The MAC generation scheme in xend was awful -- it might be a good idea to 
> > take this opportunity to fix things in libxl.
> >
> > The best approach is to generate locally administered MAC addresses hence 
> > giving us 46 bits of freedom rather than XenSource registered OUI addresses 
> > which have just 24 bits -- collisions will be *much* less likely. Further, 
> > it's best not to generate random addresses every time, but to derive the 
> > MAC address from a good hash of the VM UUID and the NIC number so that they 
> > are deterministic.
> Adding some details here...
> In general it would be a good idea to recopy already *existing* schemes 
> (unless it can be proven to be the wrong thing to do) already available 
> in XCP and XCI into libxl, instead of reinventing new square wheels like 
> here. (although this square wheel is in xl not in libxl actually)
> The MAC generation, as the one Ian mentioned, is already available in 
> the XCI toolstack and in the XCP toolstack (the code there is a bit more 
> scattered so i'ld recommend reading the XCI one).
since you seem to know exactly where the code is, would you like to
submit a patch for that? ;)

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