netdev - Re: [xdp-hints] [PATCH bpf-next 06/11] xdp: Carry over xdp metadata into skb context

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Date:   Tue, 15 Nov 2022 19:49:21 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
        haoluo@...gle.com, jolsa@...nel.org,
        David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
        netdev@...r.kernel.org
Subject: Re: [xdp-hints] [PATCH bpf-next 06/11] xdp: Carry over xdp metadata
 into skb context

On Tue, Nov 15, 2022 at 3:20 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index b444b1118c4f..71e3bc7ad839 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -6116,6 +6116,12 @@ enum xdp_action {
> >       XDP_REDIRECT,
> >  };
> >
> > +/* Subset of XDP metadata exported to skb context.
> > + */
> > +struct xdp_skb_metadata {
> > +     __u64 rx_timestamp;
> > +};
>
> Okay, so given Alexei's comment about __randomize_struct not actually
> working, I think we need to come up with something else for this. Just
> sticking this in a regular UAPI header seems like a bad idea; we'd just
> be inviting people to use it as-is.
>
> Do we actually need the full definition here? It's just a pointer
> declaration below, so is an opaque forward-definition enough? Then we
> could have the full definition in an internal header, moving the full
> definition back to being in vmlinux.h only?

Looks like having a uapi-declaration only (and moving the definition
into the kernel headers) might work. At least it does in my limited
testing :-) So let's go with that for now. Alexei, thanks for the
context on __randomize_struct!