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

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Date:	Fri, 06 Mar 2009 16:33:08 +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:
> 
>>> 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.

>> No, they're not, but it seemed worth pointing out. Your patch
>> looks perfectly fine.
> 
> Thanks.
> 
> Would you be opposed to changes that made macvlan more robust.
> Such as refusing to come up if the macaddress is already in use.
> And perhaps denying the sending of packets with the wrong source
> mac?

Refusing duplicate MACs (on one underlying device) makes sense, the
results are undefined currently. About the filtering - I don't like
the idea too much given that we already have multiple possiblities
to do that.
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