netdev - Re: VLAN packets silently dropped in promiscuous mode

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Date:	Mon, 4 Oct 2010 13:21:44 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Roger Luethi <rl@...lgate.ch>, netdev@...r.kernel.org,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: VLAN packets silently dropped in promiscuous mode

On Fri, Oct 1, 2010 at 1:41 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le vendredi 01 octobre 2010 à 07:10 +0200, Eric Dumazet a écrit :
>> Le jeudi 30 septembre 2010 à 19:37 -0700, Jesse Gross a écrit :
>>
>> > That's true.  Dropping here seems roughly equivalent to the effects of
>> > a hardware VLAN filter, which will also not be tracked by a counter,
>> > so that seems not too bad to me.
>> >
>> > The thing that concerns me though is why so many drivers seem to have
>> > this problem with completely dropping the VLAN header.  I know that
>> > even several of the ones that work now were broken initially and had
>> > to be fixed.  Seeing as the driver drops the VLAN information before
>> > it gets to the general networking code I don't see a generic fix to
>> > this as it is currently setup.  However, perhaps we could make it so
>> > that it is harder to get wrong.  Something like this:
>> >
>> > * Allow vlan_gro_receive() to take a NULL VLAN group and a tag of 0
>> > (and do the same thing for vlan_hwaccel_rx())
>> > * Now that the vlan functions can deal with non-VLAN packets, merge
>> > them into their non-VLAN counterparts.
>> > * We can now demultiplex between the VLAN/non-VLAN case in core
>> > networking.  This is done anyways, it just prevents every driver from
>> > needing that code block I copied above and allows us to fix these
>> > types of problems centrally.
>> > * Dump the VLAN tag into the SKB and hand off the packet to the
>> > various consumers: VLAN devices, libpcap, bridge hook (not currently
>> > done but should be for trunking).
>> >
>> > I see a number of advantages of this:
>> > * Fixes all the problems with cards dropping VLAN headers at once.
>> > * Avoids having to disable VLAN acceleration when in promiscuous mode
>> > (good for bridging since it always puts devices in promiscuous mode).
>> > * Keeps VLAN tag separate until given to ultimate consumer, which
>> > avoids needing to do header reconstruction as in tg3 unless absolutely
>> > necessary.
>> > * Consolidates common driver code in core networking.
>>
>> This seems very reasonable ;)
>
> Jesse, do you plan to work on this stuff yourself in a near future ?

I'm a little bit busy at the moment but I'm hoping to have some time
to work on it towards the end of this week/beginning of next week.

Thanks for looking over the idea.
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