This series adds VLAN awareness to bpf_fib_lookup() in both directions.
BPF_FIB_LOOKUP_VLAN resolves a VLAN egress to its underlying real device
plus the VLAN tag (XDP programs need this because VLAN devices have no
XDP xmit), and BPF_FIB_LOOKUP_VLAN_INPUT runs the lookup as if a tagged
frame had arrived on the matching VLAN subinterface, for iif policy
routing and VRF table selection.

BPF_FIB_LOOKUP_VLAN opts in to replacing params->ifindex, whose value
existing programs consume since d1c362e1dd68 ("bpf: Always return
target ifindex in bpf_fib_lookup"); without it the output is unchanged.

An egress that does not reduce to a real device plus one tag (a QinQ
stack, or a parent in another network namespace) returns
BPF_FIB_LKUP_RET_VLAN_FAILURE with params->ifindex left at the input;
repeating the lookup without the flag, with a re-initialized params,
returns the VLAN device's own ifindex. A VLAN on a bond reduces to the
bond, which picks its egress slave at xmit.

The new return code is appended after BPF_FIB_LKUP_RET_NO_SRC_ADDR
(nothing renumbered, tools/ mirror updated) and is returned only when
the flag is set, so no existing caller can observe it.

Changes v6 -> v7:

- Patch 1 (BPF_FIB_LOOKUP_VLAN: resolve a VLAN egress to its real
  device plus the tag): uapi doc clarified, repeating the lookup after
  BPF_FIB_LKUP_RET_VLAN_FAILURE needs a re-initialized params, since
  output fields overwrite the inputs they share storage with. No
  functional change.
- Patch 2 (BPF_FIB_LOOKUP_VLAN_INPUT: run the lookup as if the tagged
  frame arrived on the matching VLAN subinterface): no code change; a
  commit message correction (an invalid proto returns -EINVAL under
  !CONFIG_VLAN_8021Q too).
- Patch 3 (selftests for both flags, tc and XDP paths): local defines
  for the netns subtest addresses (Emil's review); the netns input arm
  brings the moved device up first, so the namespace check is the only
  condition it can fail on; the live-frames subtest uses its own netns
  name (no collision under test_progs -j) and counts only the test's
  TCP frames, so background traffic cannot satisfy the delivery
  assertion; a stale mtu comment corrected.

v6: https://lore.kernel.org/all/20260704092159.1256823-1-avinash.duduskar@gmail.com/ (local)
v5: https://lore.kernel.org/all/20260624030530.3342884-1-avinash.duduskar@gmail.com/ (local)
v4: https://lore.kernel.org/all/20260623025147.1001664-1-avinash.duduskar@gmail.com/ (local)
v3: https://lore.kernel.org/all/20260617224729.1428662-1-avinash.duduskar@gmail.com/ (local)
v2: https://lore.kernel.org/all/20260616223426.3568080-1-avinash.duduskar@gmail.com/ (local)
v1: https://lore.kernel.org/all/20260609172052.81613-1-avinash.duduskar@gmail.com/ (local)

Avinash Duduskar (3):
  bpf: Add BPF_FIB_LOOKUP_VLAN flag to bpf_fib_lookup() helper
  bpf: Add BPF_FIB_LOOKUP_VLAN_INPUT flag to bpf_fib_lookup() helper
  selftests/bpf: Add bpf_fib_lookup() VLAN flag tests

 include/uapi/linux/bpf.h                      |  52 +-
 net/core/filter.c                             |  97 ++-
 tools/include/uapi/linux/bpf.h                |  52 +-
 .../selftests/bpf/prog_tests/fib_lookup.c     | 720 +++++++++++++++++-
 .../testing/selftests/bpf/progs/fib_lookup.c  |  57 ++
 5 files changed, 964 insertions(+), 14 deletions(-)


base-commit: a975094bf98ca97be9146f9d3b5681a6f9cf5ce3
-- 
2.54.0