netdev - Re: [PATCH v2 net] net: Always untag vlan-tagged traffic on input.

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Message-ID: <54296577.6050401@6wind.com>
Date:	Mon, 29 Sep 2014 15:58:15 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	vyasevic@...hat.com, Jiri Pirko <jiri@...nulli.us>
CC:	netdev@...r.kernel.org, Patrick McHardy <kaber@...sh.net>,
	Nithin Nayak Sujir <nsujir@...adcom.com>,
	Michael Chan <mchan@...adcom.com>
Subject: Re: [PATCH v2 net] net: Always untag vlan-tagged traffic on input.

Le 29/09/2014 15:54, Vlad Yasevich a écrit :
> On 09/29/2014 09:46 AM, Nicolas Dichtel wrote:
>> Le 29/09/2014 15:05, Jiri Pirko a écrit :
>>> Mon, Sep 29, 2014 at 02:44:57PM CEST, nicolas.dichtel@...nd.com wrote:
>>>> Le 08/08/2014 20:42, Vladislav Yasevich a écrit :
>>>> [snip]
>>>>>
>>>>> The patch attempt to fix this another way.  It moves the vlan header
>>>>> stipping code out of the vlan module and always builds it into the
>>>>> kernel network core.  This way, even if vlan is not supported on
>>>>> a virtualizatoin host, the virtual machines running on top of such
>>>>> host will still work with VLANs enabled.
>>>> After this patch (0d5501c1c828 ("net: Always untag vlan-tagged traffic on
>>>> input.")), tcpdump will not be able to display the VLAN header on input path.
>>>> Is this really intended?
>>>
>>> I assume you are talking about the case when CONFIG_VLAN_8021Q is "n"
>>> right? Because if it is "m" of "y" I see no change in the code.
>> Right.
>>
>>>
>>> In case of CONFIG_VLAN_8021Q is "n" the only change is that for
>>> non-accelerated path, skb->vlan_tci is set and vlan header is stripped.
>>> This makes the path same to accelerated path.
>>>
>>> tcpdump should be able to cope with skb->vlan_tci
>> My fault, I've tested with a quite old tcpdump version, with a recent one it
>> works perfectly!
>
> Thanks.   BTW,  did that old tcpdump version work correctly when CONFIG_VLAN_8021Q
> was y or m?  My guess is that it would not.
Your guess is right ;-)


Nicolas
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