netdev - Re: [PATCH net-next] net: bridge: pop vlan from skb if filtering is disabled but it's a pvid

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Date:   Sat, 12 Sep 2020 07:37:42 +0000
From:   Nikolay Aleksandrov <nikolay@...dia.com>
To:     "olteanv@...il.com" <olteanv@...il.com>
CC:     "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        Roopa Prabhu <roopa@...dia.com>
Subject: Re: [PATCH net-next] net: bridge: pop vlan from skb if filtering is
 disabled but it's a pvid

On Sat, 2020-09-12 at 10:23 +0300, Vladimir Oltean wrote:
> On Sat, Sep 12, 2020 at 06:56:12AM +0000, Nikolay Aleksandrov wrote:
> > Could you point me to a thread where these problems were discussed and why
> > they couldn't be resolved within DSA in detail ?
> 
> See my discussion with Florian in this thread:
> http://patchwork.ozlabs.org/project/netdev/patch/20200907182910.1285496-5-olteanv@gmail.com/
> There's a bunch of unrelated stuff going on there, hope you'll manage.
> 

Thanks!
I'm traveling and will be back on Sun evening, will go through the thread then.

> > > - the bridge API only offers a race-free API for determining the pvid of
> > >   a port, br_vlan_get_pvid(), under RTNL.
> > > 
> > 
> > The API can be easily extended.
> > 
> 
> If you can help, cool.
> 
> > > And in fact this might not even be a situation unique to DSA. Any driver
> > > that receives untagged frames as pvid-tagged is now able to communicate
> > > without needing an 8021q upper for the pvid.
> > > 
> > 
> > I would prefer we don't add hardware/driver-specific fixes in the bridge, when
> > vlan filtering is disabled there should be no vlan manipulation/filtering done
> > by the bridge. This could potentially break users who have added 8021q devices
> > as bridge ports. At the very least this needs to be hidden behind a new option,
> > but I would like to find a way to actually push it back to DSA. But again adding
> > hardware/driver-specific options should be avoided.
> > 
> > Can you use tc to pop the vlan on ingress ? I mean the cases above are visible
> > to the user, so they might decide to add the ingress vlan rule.
> > 
> > Thanks,
> >  Nik
> 
> I can, but I think that all in all it's a bit strange for the bridge to
> not untag pvid-tagged frames.
> 
> Thanks!
> -Vladimir

If vlan filtering is disabled the bridge shouldn't do any vlan processing,
that's the expected behaviour. If tc is a viable option then I'd explore that
further and avoid adding more code.