netdev - Re: [PATCH v11 13/17] Add mp(mediate passthru) device.

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Message-Id: <201009281718.15813.arnd@arndb.de>
Date:	Tue, 28 Sep 2010 17:18:15 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>, xiaohui.xin@...el.com,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, davem@...emloft.net,
	herbert@...dor.hengli.com.au, jdike@...ux.intel.com,
	Sridhar Samudrala <sri@...ibm.com>
Subject: Re: [PATCH v11 13/17] Add mp(mediate passthru) device.

On Tuesday 28 September 2010, Michael S. Tsirkin wrote:
> On Tue, Sep 28, 2010 at 04:39:59PM +0200, Arnd Bergmann wrote:
> > Can you be more specific what the problem is? Do you think
> > it breaks when a guest sends VLAN tagged frames or when macvtap
> > is connected to a VLAN interface that adds another tag (or
> > only the combination)?
>
> I expect the protocol value to be wrong when guest sends vlan tagged
> frames as 802.1q frames have a different format.

Ok, I see. Would that be fixed by using eth_type_trans()? I don't
see any code in there that tries to deal with the VLAN tag, so
do we have the same problem in the tun/tap driver?

Also, I wonder how we handle the case where both the guest and
the host do VLAN tagging. Does the host transparently override
the guest tag, or does it add a nested tag? More importantly,
what should it do?

	Arnd
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