netdev - Re: [PATCH] macvlan: Don't propagate IFF_ALLMULTI changes on down interfaces.

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Date:	Mon, 12 May 2014 09:59:53 +0200
From:	Peter Christensen <pch@...bogen.com>
To:	David Miller <davem@...emloft.net>
Cc:	kaber@...sh.net, netdev@...r.kernel.org
Subject: Re: [PATCH] macvlan: Don't propagate IFF_ALLMULTI changes on down
 interfaces.

On Fri, 09 May 2014 16:02:25 -0400 (EDT)
David Miller <davem@...emloft.net> wrote:

> From: Peter Christensen <pch@...bogen.com>
> Date: Thu,  8 May 2014 11:15:37 +0200
> 
> > Clearing the IFF_ALLMULTI flag on a down interface could cause an
> > allmulti overflow on the underlying interface.
> > 
> > Attempting the set IFF_ALLMULTI on the underlying interface would
> > cause an error and the log message:
> > 
> > "allmulti touches root, set allmulti failed."
> > 
> > Signed-off-by: Peter Christensen <pch@...bogen.com>
> 
> Hmmm, but won't we lose this event once the interface is brought
> back up?

No, macvlan_open and macvlan_stop already takes care of that (which is
part of the reason the allmulti counter overflowed). Either
macvlan_open and macvlan_close shouldn't touch the flag on the
underlying interface, or
macvlan_change_rx_flags shouldn't touch the underlying interface if the
MACVLAN interface is down.

I though that it was probably better to make MACVLAN as non-intrusive
to the underlying interface when the MACVLAN interface is down, so I
opted for this solution.

Apparently the 802.1Q VLAN driver behaves
exactly like that, and back in 2011 it got a patch similar to this one
(commit deede2fabe24e00bd7e246eb81cd5767dc6fcfc7).
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