Re: [PATCH bpf-next v5 1/3] bpf: Add BPF_FIB_LOOKUP_VLAN flag to bpf_fib_lookup() helper

[David Ahern <dsahern@kernel.org>]

On 6/23/26 9:05 PM, Avinash Duduskar wrote:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 89b36de5fdbb..e00f0392e728 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3532,6 +3532,29 @@ union bpf_attr {
>   *			Use the mark present in *params*->mark for the fib lookup.
>   *			This option should not be used with BPF_FIB_LOOKUP_DIRECT,
>   *			as it only has meaning for full lookups.
> + *		**BPF_FIB_LOOKUP_VLAN**

This flag should not be needed. Patches for vlan support were never
submitted (I have them in some old branch). Since the vlan params are
initialized to 0, no new flag should be needed. Besides, these are
output parameters.

> + *			If the fib lookup resolves to a VLAN device whose
> + *			parent is a real (non-VLAN) device, set
> + *			*params*->h_vlan_proto and *params*->h_vlan_TCI from
> + *			the VLAN device and replace *params*->ifindex with the
> + *			parent's ifindex. *params*->h_vlan_TCI carries the VID
> + *			only, with PCP and DEI bits zero; a consumer wanting to
> + *			set egress priority writes PCP itself. *params*->smac is
> + *			the VLAN device's own address, which can differ from the
> + *			parent's. Only the immediate parent is resolved; if it
> + *			is itself a VLAN device (QinQ) or in another namespace,
> + *			the egress cannot be reduced to a physical device plus
> + *			one tag and the lookup returns
> + *			**BPF_FIB_LKUP_RET_VLAN_FAILURE** with *params*->ifindex
> + *			left at the input. Re-issue without
> + *			**BPF_FIB_LOOKUP_VLAN** to obtain the VLAN device's own
> + *			ifindex. The swap and the vlan fields
> + *			are written only on success; other output fields keep
> + *			the helper's existing behaviour, so a frag-needed result
> + *			still reports the route mtu in *params*->mtu_result.
> + *			This flag is only valid for XDP programs; tc programs
> + *			receive -EINVAL since they can redirect to the VLAN
> + *			device directly.