netdev - Re: [PATCH net-next-2.6] netdev: tilepro: Use is_multicast_ether

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Message-ID: <20110113065855.GU29757@distanz.ch>
Date:	Thu, 13 Jan 2011 07:58:55 +0100
From:	Tobias Klauser <tklauser@...tanz.ch>
To:	David Miller <davem@...emloft.net>
Cc:	cmetcalf@...era.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] netdev: tilepro: Use
	is_multicast_ether_addr helper

On 2011-01-13 at 03:45:01 +0100, David Miller <davem@...emloft.net> wrote:
> From: Chris Metcalf <cmetcalf@...era.com>
> Date: Wed, 12 Jan 2011 12:49:03 -0500
> 
> > On 1/12/2011 4:31 AM, Tobias Klauser wrote:
> >> Use is_multicast_ether_addr from linux/etherdevice.h instead of a custom
> >> macro. Also remove the broadcast address check, as it is considered a
> >> multicast address too.
> >>
> >> Signed-off-by: Tobias Klauser <tklauser@...tanz.ch>
> >> ---
> >>  drivers/net/tile/tilepro.c |   10 +---------
> >>  1 files changed, 1 insertions(+), 9 deletions(-)
> > 
> > Thanks, I've taken this into the Tilera tree!
> 
> Don't, his transformation is buggy.

Why?

Doesn't the code want to make sure that only unicast addresses get
filtered?

> You can't get rid of the broadcast check, it needs to be there.
> Think about it.

If a unicast address is in buf, is_multicast_ether_addr returns false
(and is_broadcast_addr would too) and thus it would get filtered.

If a multicast address is in buf, is_multicast_ether_addr returns
true, so the it won't get filtered (no matter what is_broadcast_addr
would tell).

If a broadcast address is in buf, is_multicast_ether_addr returns true,
so it won't get filtered (no matter what is_broadcast_addr would tell).

Are there any special addresses I missed? Or did I didn't get the above
right?
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