netdev - Re: [RFC] ethernet: avoid pre-assigned OUI values in random_ether

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Date:	Sun, 15 May 2011 23:10:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>, netdev@...r.kernel.org
Subject: Re: [RFC] ethernet: avoid pre-assigned OUI values in
 random_ether_addr

Le dimanche 15 mai 2011 à 13:20 -0700, Joe Perches a écrit :
> On Sun, 2011-05-15 at 21:46 +0200, Eric Dumazet wrote:
> > Le vendredi 13 mai 2011 à 17:17 -0700, Stephen Hemminger a écrit :
> > > There are some addresses in the assigned vendor block that don't obey
> > > the locally assigned convention. These should be avoided by random_ether_addr
> > > assignment.
> > We call random_ether_addr() for some virtual devices, maybe we can add a
> > __random_ether_addr() helper for them and not avoid these OUI ?
> 
> Unless it's speed critical, it's probably not worthwhile.
> 

Speed was not my concern, but getting idea of why avoiding pre-assigned
OUI was a concern for them, if they dont hit a real Ethernet domain.

> I think that using get_random_bytes, because it can drain
> the entropy pool, may not be a great thing to do.
> 

This has litle to do with Stephen patch. You could discuss this with
Matt Mackall.

By the way, since 2.6.29 every exec() gets 16 bytes from
get_random_bytes() for PRNG seeding.

Typical machine starts far more programs than network interfaces ;)


Anyway, it seems to have no impact at all, even gathering 128*6 bytes
here : 

# cat /proc/sys/kernel/random/entropy_avail
142
# modprobe dummy numdummies=128 
# cat /proc/sys/kernel/random/entropy_avail
156



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