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;
re-issue without the flag for 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 v5 -> v6:

- Patch 1 (BPF_FIB_LOOKUP_VLAN: resolve a VLAN egress to its real
  device plus the tag): no code 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.
- Patch 3 (selftests for both flags, tc and XDP paths): comments
  restyled; dead skb.ifindex write removed.

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                      |  50 +-
 net/core/filter.c                             |  97 ++-
 tools/include/uapi/linux/bpf.h                |  50 +-
 .../selftests/bpf/prog_tests/fib_lookup.c     | 712 +++++++++++++++++-
 .../testing/selftests/bpf/progs/fib_lookup.c  |  36 +
 5 files changed, 931 insertions(+), 14 deletions(-)


base-commit: a975094bf98ca97be9146f9d3b5681a6f9cf5ce3
-- 
2.54.0