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

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Date:	Tue, 28 Sep 2010 11:48:34 -0700
From:	Sridhar Samudrala <sri@...ibm.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	"Michael S. Tsirkin" <mst@...hat.com>,
	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
Subject: Re: [PATCH v11 13/17] Add mp(mediate passthru) device.

  On 9/28/2010 8:18 AM, Arnd Bergmann wrote:
> 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?
tun_get_user() does call eth_type_trans(). Not sure why i didn't use it 
in macvtap code.
Need to test it with guest VLAN tagging to make sure it works.
> 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?
> 	
I would think If both guest and host do VLAN tagging, the tags will be 
nested.

Thanks
Sridhar



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