netdev - Re: [PATCH bpf-next V2 1/6] bpf: Remove MTU check in __bpf_skb_max

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Date:   Thu, 8 Oct 2020 08:33:04 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Maciej Żenczykowski <maze@...gle.com>,
        bpf <bpf@...r.kernel.org>, Linux NetDev <netdev@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Shaun Crampton <shaun@...era.io>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Marek Majkowski <marek@...udflare.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eyal Birger <eyal.birger@...il.com>
Subject: Re: [PATCH bpf-next V2 1/6] bpf: Remove MTU check in __bpf_skb_max_len

On Thu, Oct 8, 2020 at 7:06 AM Jesper Dangaard Brouer <brouer@...hat.com> wrote:
>
> On Wed, 7 Oct 2020 16:46:10 -0700
> Maciej Żenczykowski <maze@...gle.com> wrote:
>
> > >  static u32 __bpf_skb_max_len(const struct sk_buff *skb)
> > >  {
> > > -       return skb->dev ? skb->dev->mtu + skb->dev->hard_header_len :
> > > -                         SKB_MAX_ALLOC;
> > > +       return IP_MAX_MTU;
> > >  }
> >
> > Shouldn't we just delete this helper instead and replace call sites?
>
> It does seem wrong to pass argument skb into this function, as it is
> no-longer used...
>
> Guess I can simply replace __bpf_skb_max_len with IP_MAX_MTU.

Should that be IP6_MAX_MTU, which is larger than IP_MAX_MTU?