netdev - Re: [PATCH net v4] igb: Fix XDP with PTP enabled

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Date:   Tue, 4 May 2021 10:28:27 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
Cc:     brouer@...hat.com, Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Sven Auhagen <sven.auhagen@...eatech.de>,
        intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Richard Cochran <richardcochran@...il.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Tyler S <tylerjstachecki@...il.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Subject: Re: [PATCH net v4] igb: Fix XDP with PTP enabled

On Mon,  3 May 2021 09:28:00 +0200
Kurt Kanzenbach <kurt@...utronix.de> wrote:

> When using native XDP with the igb driver, the XDP frame data doesn't point to
> the beginning of the packet. It's off by 16 bytes. Everything works as expected
> with XDP skb mode.
> 
> Actually these 16 bytes are used to store the packet timestamps. Therefore, pull
> the timestamp before executing any XDP operations and adjust all other code
> accordingly. The igc driver does it like that as well.
> 
> Tested with Intel i210 card and AF_XDP sockets.
> 
> Fixes: 9cbc948b5a20 ("igb: add XDP support")
> Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>

Thanks for fixing this!

Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>

I expect that we/I will (soon) play with getting this area that is
stored in front of the packet (the XDP data_meta area) described via
BTF.  This way both xdp_frame and AF_XDP can get structured access (e.g.
to the PTP timestamp in this case).

I'll be adding my notes on this project here:
 https://github.com/xdp-project/xdp-project/blob/master/areas/tsn/

Looking forward to collaborate on this with you :-)
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer