On Mon, Aug 2, 2021 at 6:05 PM Ederson de Souza
[off-list ref] wrote:

An example of how to retrieve XDP hints/metadata from an XDP frame. To
get the xdp_hints struct, one can use:

$ bpftool net xdp show
  xdp:
  enp6s0(2) md_btf_id(44) md_btf_enabled(0)

To get the BTF id, and then:

$ bpftool btf dump id 44 format c > btf.h

But, in this example, to demonstrate BTF and CORE features, a simpler
struct was defined, containing the only field used by the sample.

A lowpoint is that it's not currently possible to use some CORE features
from "samples/bpf" directory, as those samples are currently built
without using "clang -target bpf". This way, it was not possible to use
"bpf_core_field_exists" macro to check, in runtime, the presence of a
given XDP hints field.
---

FYI, Kumar Kartikeya Dwivedi is adding vmlinux.h and CO-RE support to
samples/bpf in [0].

  [0] https://lore.kernel.org/bpf/20210728165552.435050-1-memxor@gmail.com/ (local)

 samples/bpf/xdp_sample_pkts_kern.c | 21 +++++++++++++++++++++
 samples/bpf/xdp_sample_pkts_user.c |  4 +++-
 2 files changed, 24 insertions(+), 1 deletion(-)

[...]