netdev - RE: Question regarding MAC address configuraton with VLAN devices

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Date:	Wed, 8 Apr 2015 10:16:32 +0000
From:	Yuval Mintz <Yuval.Mintz@...gic.com>
To:	Michal Kubecek <mkubecek@...e.cz>
CC:	Alexander Duyck <alexander.h.duyck@...hat.com>,
	Manish Chopra <manish.chopra@...gic.com>,
	Patrick McHardy <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>
Subject: RE: Question regarding MAC address configuraton with VLAN devices

> > I think there's an even simpler question here - Today, if you'll have
> > a network interface with a vlan stacked on top of it and user calls
> > 'ip link set ... address ...' the end result would be that the vlan
> > interface retains the original MAC and push it downward [to base device].
> > You can claim this is harmless, but I don't really think anyone
> > intends this to happen.
> 
> If it wasn't intended, why would anyone write the code doing the sync (and
> switching to promiscuous mode as a fallback)?

I Didn't mean there's NO use-case where this is intended [e.g, this reflects
the logic behind the vlanmac configuration just fine] - I meant that it's
probably not the intended behavior for a plain vlan interface.

> The way I see it, there were two options:
> 
>   (a) add upper device's address to lower device's uc list
>   (b) propagate changed MAC address upwards
> 
> And the decision was to choose (a). While (b) might make some things simpler
> (and others more complicated), changing the behaviour now when people are
> used to it would be IMHO very unfortunate.
> 
>                                                         Michal Kubecek

I agree, although I'm not sure (a) and (b) can't co-exist under some strict set 
of rules.

I was thinking of perhaps marking the netdevice when eth_hw_addr_inherit() is
called, and unmark that flag on dev_set_mac_address(), assuming that as long
as a different MAC wasn't explicitly configured, the device should continue
inheriting the real dev MAC; But I think that would pose problems with APIs
that change the 'dev_addr' without the ndo, e.g., bonding devices.

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