netdev - RE: [PATCH] vlan_dev: VLAN 0 should be treated as "no vlan tag" (802.1p packet)

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Message-ID: <8628FE4E7912BF47A96AE7DD7BAC0AADDDC69DDE7E@SJEXCHCCR02.corp.ad.broadcom.com>
Date:	Thu, 17 Jun 2010 01:56:26 -0700
From:	"Vladislav Zolotarov" <vladz@...adcom.com>
To:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Arnd Bergmann" <arnd@...db.de>
cc:	"Patrick McHardy" <kaber@...sh.net>,
	"Pedro Garcia" <pedro.netdev@...devamos.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Ben Hutchings" <bhutchings@...arflare.com>
Subject: RE: [PATCH] vlan_dev: VLAN 0 should be treated as "no vlan tag"
 (802.1p packet)



> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On
> Behalf Of Eric Dumazet
> Sent: Wednesday, June 16, 2010 9:58 PM
> To: Arnd Bergmann
> Cc: Patrick McHardy; Pedro Garcia; netdev@...r.kernel.org; Ben Hutchings
> Subject: Re: [PATCH] vlan_dev: VLAN 0 should be treated as "no vlan tag"
> (802.1p packet)
> 
> Le mercredi 16 juin 2010 à 20:26 +0200, Arnd Bergmann a écrit :
> > On Wednesday 16 June 2010 17:28:23 Patrick McHardy wrote:
> >
> > > Since we don't have any special VLAN handling in the bridging code, I
> > > guess it comes down to optionally using a different ethertype value
> > > (0x88a8) in the VLAN code. We probably also need some indication from
> > > device drivers whether they are able to add these headers to avoid
> > > trying to offload tagging in case they're not.
> >
> > It's probably a little more than just supporting the new ethertype, but not
> > much. The outer tag can be handled like our current VLAN module does,
> > but the standard does not allow a regular frame to be encapsulated
> directly,
> > but rather requires one of
> >
> > 1. In 802.1ad: an 802.1Q VLAN tag (ethertype 0x8100) followed by the frame
> > 2. In 802.1ah: A service tag (ethertype 0x88e7) followed by the 802.1Q VLAN
> tag
> >    and then the frame.
> >
> > Maybe what we can do is extend the vlan code to understand all three frame
> > formats (q, ad and ah) or at least the first two so we configure both the
> > provider VID and the Customer VID for the interface in case of 802.1ad but
> > only the regular VID in 802.1Q.
> >
> > Device drivers can then flag whether they support both formats or just
> > the regular Q tag.
> >
> > 	Arnd
> 
> Speaking of device drivers, I see bnx2 (hardware accelerated) is able to
> insert a 8021q tag in case no vlgrp is defined (the 8201q tag that was
> removed by NIC)... interesting ping pong games, since our 8021q stack
> will remove it again, eventually.
> 
> So VLAN 0 'problem' on bnx2 could be solved with following patch
> (avoiding this insert if vtag==0)
> 
> 
> 
> diff --git a/drivers/net/bnx2.c b/drivers/net/bnx2.c
> index 522de9f..b5d4d05 100644
> --- a/drivers/net/bnx2.c
> +++ b/drivers/net/bnx2.c
> @@ -3192,7 +3192,7 @@ bnx2_rx_int(struct bnx2 *bp, struct bnx2_napi *bnapi,
> int budget)
>  				hw_vlan = 1;
>  			else
>  #endif
> -			{
> +			if (vtag) {
>  				struct vlan_ethhdr *ve = (struct vlan_ethhdr *)
>  					__skb_push(skb, 4);
> 
> 
> 
> --

This way u will loose all the priority information that was on the VLAN header.

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