[PATCH bpf-next v4 0/6] bpf: decap flags and GSO state updates

[Nick Hudson <nhudson@akamai.com>]

This series extends bpf_skb_adjust_room() with decapsulation-specific
flags and tunnel GSO state updates for decap use cases.

Motivation
----------

When BPF decapsulates tunneled packets, skb GSO state needs to be updated
to match the removed tunnel layer. This includes clearing the corresponding
tunnel GSO type bits and resetting encapsulation state once no tunnel GSO
flags remain.

Series Overview
---------------

- Name the adjust_room flag enum for CO-RE lookups.
- Refactor adjust_room helper masks for maintainable validation logic.
- Add new DECAP flags to UAPI.
- Add guard rails for incompatible/invalid decap flag combinations.
- Implement decap GSO flag clearing.
- Add selftests to validate decap GSO state transitions.

Changes v3 -> v4:
- Patch 5: drop SKB_GSO_TUNNEL_REMCSUM handling from this series.
- Patch 5: clear encap_hdr_csum and remcsum_offload directly on UDP decap.

Changes v2 -> v3:
- Add a new selftests patch to validate decap GSO state behavior.
- Reorder the series so helper-mask refactoring precedes UAPI DECAP flag additions.
- Refresh patch 2 and patch 3 split to keep refactoring behavior-neutral.
- Patch 5: add decap tunnel GSO-state checks in
  "bpf: clear decap tunnel GSO state in skb_adjust_room" (per Gemini/sashiko).

Changes v1 -> v2:
- Patch 3: decap flag acceptance intentionally remains L3-only while adding helper masks.
- Patch 4: decap with L4/IPXIP support enabled with guard rails.

Co-developed-by: Max Tottenham <mtottenh@akamai.com>
Signed-off-by: Max Tottenham <mtottenh@akamai.com>
Co-developed-by: Anna Glasgall <aglasgal@akamai.com>
Signed-off-by: Anna Glasgall <aglasgal@akamai.com>
Signed-off-by: Nick Hudson <nhudson@akamai.com>

Nick Hudson (6):
  bpf: name the enum for BPF_FUNC_skb_adjust_room flags
  bpf: refactor masks for ADJ_ROOM flags and encap validation
  bpf: add BPF_F_ADJ_ROOM_DECAP_* flags for tunnel decapsulation
  bpf: allow new DECAP flags and add guard rails
  bpf: clear decap tunnel GSO state in skb_adjust_room
  selftests/bpf: tc_tunnel validate decap GSO state

 include/uapi/linux/bpf.h                      |  36 +++++-
 net/core/filter.c                             | 118 +++++++++++++++---
 tools/include/uapi/linux/bpf.h                |  36 +++++-
 .../selftests/bpf/progs/test_tc_tunnel.c      |  58 +++++++++
 4 files changed, 225 insertions(+), 23 deletions(-)

-- 
2.34.1