netdev - Re: vlan missing with AF

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Message-ID: <f8a4855240c23dd03e936ba270126ad5@walle.cc>
Date:   Mon, 24 Sep 2018 16:25:03 +0200
From:   Michael Walle <michael@...le.cc>
To:     Jan Grashöfer <jan.grashoefer@...il.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        "Steinar H. Gunderson" <sesse@...gle.com>, heiko.thiery@...il.com
Subject: Re: vlan missing with AF_PACKET and auxdata

Am 2018-09-24 14:22, schrieb Jan Grashöfer:
> Hi Michael,
> 
> On 24/09/2018 14:01, Michael Walle wrote:
>> I'm using the AF_PACKET socket with setsockopt(PACKET_AUXDATA) to get 
>> the incoming VLAN tag. Correct me if I'm wrong, but as far as I see 
>> the first VLAN tag is always stripped - either in hardware or in 
>> net/core/dev.c in __netif_receive_skb_core() - and stored in 
>> skb->vlan_tci. Therefore, it won't be in the packet data anymore.
> 
> although the documentation says "SOCK_RAW packets are passed to and
> from the device driver without any changes in the packet data." [1]
> that's correct and was discussed here:
> https://www.spinics.net/lists/netdev/msg440313.html
> 
> Result of the discussion: Won't fix, too complicated.

Hi Jan,

thanks for the pointer. I'm fine with this decision, because the VLAN 
tag should be available through metadata. And this was my original 
question, because the metadata is only available in case of proto == 
ETH_P_ALL, but not for proto != ETH_P_ALL because of the commit in 
question.

-michael