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

[Vincent Hanquez <vincent.hanquez@xxxxxxxxxxxxx>]

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).
--
Vincent

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