Re: [PATCH net] veth: xdp: use head instead of hard_start

[Toshiaki Makita]

Hi Mao & Jesper
(Resending with plain text...)

On 2020/03/30 20:34, Jesper Dangaard Brouer wrote:
> On Mon, 30 Mar 2020 18:26:31 +0800
> Mao Wenan <maowenan@xxxxxxxxxx> wrote:
>
> > xdp.data_hard_start is mapped to the first
> > address of xdp_frame, but the pointer hard_start
> > is the offset(sizeof(struct xdp_frame)) of xdp_frame,
> > it should use head instead of hard_start to
> > set xdp.data_hard_start. Otherwise, if BPF program
> > calls helper_function such as bpf_xdp_adjust_head, it
> > will be confused for xdp_frame_end.
>
> I have noticed this[1] and have a patch in my current patchset for
> fixing this.  IMHO is is not so important fix right now, as the effect
> is that you currently only lose 32 bytes of headroom.
>
> [1] https://lore.kernel.org/netdev/158446621887.702578.17234304084556809684.stgit@firesoul/

You are right, the subtraction is not necessary here.
Thank you for working on this.

Toshiaki Makita