Date: Tue, 20 Jul 2010 14:18:16 -0700
From: Stephen Hemminger <shemminger@vyatta.com>
To: David Miller <davem@davemloft.net>
Cc: bhutchings@solarflare.com, sassmann@redhat.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, gospo@redhat.com,
        gregory.v.rose@intel.com, alexander.h.duyck@intel.com,
        leedom@chelsio.com, harald@redhat.com
Subject: Re: [PATCH net-next] sysfs: add entry to indicate network
 interfaces with random MAC address
Message-ID: <20100720141816.16f0a939@nehalam>
In-Reply-To: <20100720.131748.51255156.davem@davemloft.net>
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	<4C45996B.3000003@redhat.com>
	<1279636194.2110.45.camel@achroite.uk.solarflarecom.com>
	<20100720.131748.51255156.davem@davemloft.net>
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On Tue, 20 Jul 2010 13:17:48 -0700 (PDT)
David Miller <davem@davemloft.net> wrote:

> From: Ben Hutchings <bhutchings@solarflare.com>
> Date: Tue, 20 Jul 2010 15:29:54 +0100
> 
> > On Tue, 2010-07-20 at 14:41 +0200, Stefan Assmann wrote:
> >> Btw, the driver itself could also alter the flag. Then we'd have a well
> >> defined way of setting a stable address.
> > 
> > The driver can't know whether an address assigned by the user is stable.
> 
> If userspace can somehow obtain a persistent address, it can kick
> udev too.
> 
> I really don't see any real value provided by letting userspace mess
> with this.  Because the permanence communicated in this value is from
> the perspective of the kernel driver, it's really therefore about the
> thing that's in ->perm_addr[] not what happens to be in ->addr[] right
> now.

No one mentioned that the first octet of an Ethernet address already
indicates "software generated" Ethernet address. Per the standard,
if bit 1 is set it means address is locally assigned.

static inline bool is_locally_assigned_ether(const u8 *addr)
{
	return (addr[0] & 0x2) != 0;
}
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