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

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Message-ID: <8628FE4E7912BF47A96AE7DD7BAC0AADDDC69DDEB4@SJEXCHCCR02.corp.ad.broadcom.com>
Date:	Thu, 17 Jun 2010 07:08:52 -0700
From:	"Vladislav Zolotarov" <vladz@...adcom.com>
To:	"Eric Dumazet" <eric.dumazet@...il.com>
cc:	"Arnd Bergmann" <arnd@...db.de>,
	"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: Thursday, June 17, 2010 1:29 PM
> To: Vladislav Zolotarov
> Cc: Arnd Bergmann; 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 jeudi 17 juin 2010 à 01:56 -0700, Vladislav Zolotarov a écrit :
> >
> > > -----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.
> 
> 16bits vtag = 0 : there is no priority information.

According to IEEE 802.1p PCP=0 is legal priority, CFI bit is usually zero. So, VTAG=0 would mark a priority tagged frame with a priority 0 and it should be handled differently than a frame with no priority at all and your patch will prevent it.

> 
> 
> 
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