netdev - Re: [PATCH] macvlan: Support creating macvlans from macvlans

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Date:	Fri, 06 Mar 2009 16:56:23 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] macvlan: Support creating macvlans from macvlans

Eric W. Biederman wrote:
> Patrick McHardy <kaber@...sh.net> writes:
> 
>> Eric W. Biederman wrote:
>>> Patrick McHardy <kaber@...sh.net> writes:
>>>
>>>>> Hmm.  Actually that appears to be a macvlan bug.  It looks like if I
>>>>> change the macaddress on a macvlan we don't update the hash chains.
>>>>> So unless we have the same low byte we will be on the wrong hash chain
>>>>> and not receive the packets for the mac we specified.  Ouch!
>>>> The address can only be changed while the device is down and unhashed.
>>> Point.  The dev_unicast/dev_unicast_delete in macvlan_set_mac_address
>>> appears to be completely unnecessary then.
>> I think thats correct.
> 
> Actually it is really weird.  We can change the mac address while
> the devices is running but the code is broken because it does
> not update the hash table.

Thats strange. I know the assumption was that this can't be done.
But I can't find anything preventing it, not even in older versions.

>> Refusing duplicate MACs (on one underlying device) makes sense, the
>> results are undefined currently.
> 
> Then I will do that just for consistency.

Thanks.
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