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

["Toke Høiland-Jørgensen" <toke@redhat.com>]

David Ahern <dsahern@kernel.org> writes:

> 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.

There's no enforcement from the kernel side of the parameters being
zero, though? So we do need the flag for feature detection; unless we
expect applications to do that out of band? But then we'd need a
mechanism to do that which could be... the presence of the flag in the
ENUM (and thus in BTF)? :)

-Toke