RE: [Xen-devel] [patch 3/5] xen: xm/create mac selection

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> > Please can you explain how the randomly generated MACs are kept
> > different -- I was expecting to see the vif number being 
> folded into the
> > random MAC generation.
> > 
> > (I'm not saying what you've done doesn't work, I'd just like an
> > explanation)
> 
> It doesn't prevent different domains from getting the same 
> random MACs,
> only within a domain. It keeps a list of generated MACs as it 
> processes
> the vifs, and loops until one is generated that hasn't been used yet.
> For some reason i'd usually get several copies of the same MAC without
> this code when creating multiple vifs within one domain.

Your patch certainly helps by rejecting duplicates, but I'd also like to
see the algorithm used to generate the MACs changed too.

We currently seed the random number generator with random.seed() which I
suspect seeds it with the system time in seconds. At the very least, we
should use something more fine grained to avoid other domains started in
quick succession getting the same MACs.

A better approach might be to seed it with a hash of the config file
plus any parameters passed into it (e.g. vmid), plus the vif number.

Would you mind knocking something up?

Thanks,
Ian




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