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

[Stanislav Fomichev <sdf@google.com>]

On Wed, Nov 16, 2022 at 1:48 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Martin KaFai Lau <martin.lau@linux.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..