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

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Message-Id: <20110112.234250.10542369.davem@davemloft.net>
Date:	Wed, 12 Jan 2011 23:42:50 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	tklauser@...tanz.ch
Cc:	cmetcalf@...era.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] netdev: tilepro: Use
 is_multicast_ether_addr helper

From: Tobias Klauser <tklauser@...tanz.ch>
Date: Thu, 13 Jan 2011 07:58:55 +0100

> 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.

Ok, this may be correct, but it makes the code hard to read.

I think the old code, whilst redundant, is easier to understand.

Why not add a function "is_unicast_ether_addr()" and use that
here instead?

That solves all of the issues I have with your change.
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