netdev - Re: [PATCH v7 bpf-next 05/10] veth: Handle xdp

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Message-ID: <20180802134548.2230455b@redhat.com>
Date:   Thu, 2 Aug 2018 13:45:48 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        John Fastabend <john.fastabend@...il.com>, brouer@...hat.com
Subject: Re: [PATCH v7 bpf-next 05/10] veth: Handle xdp_frames in xdp napi
 ring

On Thu,  2 Aug 2018 19:55:09 +0900
Toshiaki Makita <makita.toshiaki@....ntt.co.jp> wrote:

> +	headroom = frame->data - delta - (void *)frame;

Your calculation of headroom is still adding an assumption that
xdp_frame is located in the top of data area, that is unnecessary.

The headroom can be calculated as:

 headroom = sizeof(struct xdp_frame) + frame->headroom - delta;

> +	skb = veth_build_skb(frame, headroom, len, 0);
> +	if (!skb) {
> +		xdp_return_frame(frame);
> +		goto err;
> +	}
> +
> +	xdp_scrub_frame(frame);

Thanks you for adding a xdp_scrub_frame() instead.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer