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

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Date:   Wed, 16 Nov 2022 12:51:09 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Martin KaFai Lau <martin.lau@...ux.dev>, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, 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, bpf@...r.kernel.org
Subject: Re: [xdp-hints] Re: [PATCH bpf-next 06/11] xdp: Carry over xdp
 metadata into skb context

On Wed, Nov 16, 2022 at 1:48 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Martin KaFai Lau <martin.lau@...ux.dev> writes:
>
> > On 11/14/22 7:02 PM, Stanislav Fomichev wrote:
> >> Implement new bpf_xdp_metadata_export_to_skb kfunc which
> >> prepares compatible xdp metadata for kernel consumption.
> >> This kfunc should be called prior to bpf_redirect
> >> or when XDP_PASS'ing the frame into the kernel (note, the drivers
> >> have to be updated to enable consuming XDP_PASS'ed metadata).
> >>
> >> veth driver is amended to consume this metadata when converting to skb.
> >>
> >> Internally, XDP_FLAGS_HAS_SKB_METADATA flag is used to indicate
> >> whether the frame has skb metadata. The metadata is currently
> >> stored prior to xdp->data_meta. bpf_xdp_adjust_meta refuses
> >> to work after a call to bpf_xdp_metadata_export_to_skb (can lift
> >> this requirement later on if needed, we'd have to memmove
> >> xdp_skb_metadata).
> >
> > It is ok to refuse bpf_xdp_adjust_meta() after bpf_xdp_metadata_export_to_skb()
> > for now.  However, it will also need to refuse bpf_xdp_adjust_head().
>
> I'm also OK with deferring this, although I'm wondering if it isn't just
> as easy to just add the memmove() straight away? :)

SG, let me try that! Martin also mentioned bpf_xdp_adjust_head needs
to be taken care of..