linux-kernel - Re: [PATCH net-next] sysfs: add entry to indicate network interfaces with random MAC address

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Message-ID: <20100721150732.GR7497@gospo.rdu.redhat.com>
Date:	Wed, 21 Jul 2010 11:07:32 -0400
From:	Andy Gospodarek <andy@...yhouse.net>
To:	Harald Hoyer <harald@...hat.com>
Cc:	David Miller <davem@...emloft.net>, shemminger@...tta.com,
	bhutchings@...arflare.com, sassmann@...hat.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	gospo@...hat.com, gregory.v.rose@...el.com,
	alexander.h.duyck@...el.com, leedom@...lsio.com
Subject: Re: [PATCH net-next] sysfs: add entry to indicate network
	interfaces with random MAC address

On Wed, Jul 21, 2010 at 08:47:36AM +0200, Harald Hoyer wrote:
> On 07/21/2010 08:34 AM, David Miller wrote:
>> From: Harald Hoyer<harald@...hat.com>
>> Date: Wed, 21 Jul 2010 08:26:27 +0200
>>
>>> On 07/20/2010 11:20 PM, David Miller wrote:
>>>> From: Stephen Hemminger<shemminger@...tta.com>
>>>> Date: Tue, 20 Jul 2010 14:18:16 -0700
>>>>
>>>>> 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;
>>>>> }
>>>>
>>>> W00t!
>>>>
>>>> Indeed, can udev just use that?  :-)
>>>
>>> It already does:
>>> see /lib/udev/rules.d/75-persistent-net-generator.rules
>>
>> So... why doesn't this work?
>
> It works.. but the information, that the MAC is randomly generated would 
> be valuable. So, for the non-random locally assigned MAC (with bit 1), we 
> could easily make persistent rules based on the MAC, instead of 
> completely ignoring them, like we do currently.

Agreed.  The subtle difference between a locally assigned address that
is persistent and one that is random would be helpful.

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