netdev - Re: [PATCH][bpf-next] bpf: change bpf_skb_generic

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Message-ID: <CAPhsuW6z+jh0xofi8FCA0uvTJ5jSL_ZGpwPu1Eg566XeJ03pZA@mail.gmail.com>
Date:   Fri, 3 Jan 2020 11:18:28 -0800
From:   Song Liu <liu.song.a23@...il.com>
To:     Simon Horman <simon.horman@...ronome.com>
Cc:     Li RongQing <lirongqing@...du.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH][bpf-next] bpf: change bpf_skb_generic_push type as void

On Fri, Jan 3, 2020 at 12:27 AM Simon Horman <simon.horman@...ronome.com> wrote:
>
> On Fri, Jan 03, 2020 at 02:02:33PM +0800, Li RongQing wrote:
> > bpf_skb_generic_push always returns 0, not need to check
> > its return, so change its type as void
> >
> > Signed-off-by: Li RongQing <lirongqing@...du.com>
>
> Reviewed-by: Simon Horman <simon.horman@...ronome.com>
Acked-by: Song Liu <songliubraving@...com>

>
> > ---
> >  net/core/filter.c | 30 ++++++++++--------------------
> >  1 file changed, 10 insertions(+), 20 deletions(-)
> >
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 42fd17c48c5f..1cbac34a4e11 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
>
> ...
>
> > @@ -5144,7 +5134,7 @@ BPF_CALL_3(bpf_lwt_seg6_adjust_srh, struct sk_buff *, skb, u32, offset,
> >               if (unlikely(ret < 0))
> >                       return ret;
> >
> > -             ret = bpf_skb_net_hdr_push(skb, offset, len);
> > +             bpf_skb_net_hdr_push(skb, offset, len);
>
> There is a check for (ret < 0) just below this if block.
> That is ok becuase in order to get to here (ret < 0) must
> be true as per the check a few lines above.
>
> So I think this is ok although the asymmetry with the else arm
> of this if statement is not ideal IMHO.

Agreed with this concern. But I cannot think of any free solution. I guess we
will just live with assumption that skb_cow_head() never return >0.

Thanks,
Song