netdev - Re: [tcpdump-workers] vlan tagged packets and libpcap breakage

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Date:	Thu, 6 Dec 2012 14:40:03 -0800
From:	Ani Sinha <ani@...stanetworks.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Michael Richardson <mcr@...delman.ca>,
	tcpdump-workers@...ts.tcpdump.org, netdev@...r.kernel.org,
	Francesco Ruggeri <fruggeri@...stanetworks.com>
Subject: Re: [tcpdump-workers] vlan tagged packets and libpcap breakage

On Thu, Dec 6, 2012 at 2:19 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Ani Sinha <ani@...stanetworks.com> writes:
>
>> On Sat, Nov 17, 2012 at 3:33 PM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>> the vlan header in packets as we receive them.
>>>
>>> The code is correct except for the case of packets in vlan 0.  Currently
>>> the packet reconstruction is ambiguous.  The most recent kernels have
>>> a TP_STATUS_VLAN_VALID flag that can be checked to see if the packet was
>>> in vlan 0 or if there was no vlan at all.  libpcap probably should be
>>> taught how to handle TP_STATUS_VLAN_VALID so that it can get the vlan 0
>>> handling correct.
>>>
>>
>> May be this?
>
> Two things.
>
> - TP_STATUS_VLAN_VALID lives in the tp_status field not the tp_vlan_tci field.
> - To work on older kernels with binaries compiled with newer headers you
>   first want to test for tp_vlan_tci == 0 and then look at the status field for
>   TP_STATUS_VALID.

yes you are right Eric on both counts. I will resend the patch again in a bit.

ani
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