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

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Date:   Wed, 16 Nov 2022 00:20:26 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Stanislav Fomichev <sdf@...gle.com>, bpf@...r.kernel.org
Cc:     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, sdf@...gle.com,
        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

> 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?

-Toke