netdev - Re: VLAN packets silently dropped in promiscuous mode

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Date:	Fri, 01 Oct 2010 07:10:31 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesse Gross <jesse@...ira.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

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 ;)

I'll add a counter, a core generalization of 
commit 8990f468a (net: rx_dropped accounting)

Because we can drop packets _after_ netif_rx() if RPS is in action
anyway.



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