Merge branch 'xdp: hints via kfuncs'

Stanislav Fomichev says:

====================

Please see the first patch in the series for the overall
design and use-cases.

See the following email from Toke for the per-packet metadata overhead:
https://lore.kernel.org/bpf/20221206024554.3826186-1-sdf@google.com/T/#m49d48ea08d525ec88360c7d14c4d34fb0e45e798

Recent changes:
- Keep new functions in en/xdp.c, do 'extern mlx5_xdp_metadata_ops' (Tariq)

- Remove mxbuf pointer and use xsk_buff_to_mxbuf (Tariq)

- Clarify xdp_buff vs 'XDP frame' (Jesper)

- Explicitly mention that AF_XDP RX descriptor lacks metadata size (Jesper)

- Drop libbpf_flags/xdp_flags from selftests and use ifindex instead
  of ifname (due to recent xsk.h refactoring)

Prior art (to record pros/cons for different approaches):

- Stable UAPI approach:
  https://lore.kernel.org/bpf/20220628194812.1453059-1-alexandr.lobakin@intel.com/
- Metadata+BTF_ID appoach:
  https://lore.kernel.org/bpf/166256538687.1434226.15760041133601409770.stgit@firesoul/
- v7:
  https://lore.kernel.org/bpf/20230112003230.3779451-1-sdf@google.com/
- v6:
  https://lore.kernel.org/bpf/20230104215949.529093-1-sdf@google.com/
- v5:
  https://lore.kernel.org/bpf/20221220222043.3348718-1-sdf@google.com/
- v4:
  https://lore.kernel.org/bpf/20221213023605.737383-1-sdf@google.com/
- v3:
  https://lore.kernel.org/bpf/20221206024554.3826186-1-sdf@google.com/
- v2:
  https://lore.kernel.org/bpf/20221121182552.2152891-1-sdf@google.com/
- v1:
  https://lore.kernel.org/bpf/20221115030210.3159213-1-sdf@google.com/
- kfuncs v2 RFC:
  https://lore.kernel.org/bpf/20221027200019.4106375-1-sdf@google.com/
- kfuncs v1 RFC:
  https://lore.kernel.org/bpf/20221104032532.1615099-1-sdf@google.com/

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Anatoly Burakov <anatoly.burakov@intel.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
Cc: Maryam Tahhan <mtahhan@redhat.com>
Cc: xdp-hints@xdp-project.net
Cc: netdev@vger.kernel.org
Stanislav Fomichev (13):
  bpf: Document XDP RX metadata
  bpf: Rename bpf_{prog,map}_is_dev_bound to is_offloaded
  bpf: Move offload initialization into late_initcall
  bpf: Reshuffle some parts of bpf/offload.c
  bpf: Introduce device-bound XDP programs
  selftests/bpf: Update expected test_offload.py messages
  bpf: XDP metadata RX kfuncs
  veth: Introduce veth_xdp_buff wrapper for xdp_buff
  veth: Support RX XDP metadata
  selftests/bpf: Verify xdp_metadata xdp->af_xdp path
  net/mlx4_en: Introduce wrapper for xdp_buff
  net/mlx4_en: Support RX XDP metadata
  selftests/bpf: Simple program to dump XDP RX metadata
====================

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>