Re: Does skb_metadata_differs really need to stop GRO aggregation?

[Daniel Borkmann <daniel@iogearbox.net>]

On 11/30/23 2:55 PM, Toke Høiland-Jørgensen wrote:
> Daniel Borkmann <daniel@iogearbox.net> writes
>> On 11/29/23 10:52 PM, Toke Høiland-Jørgensen wrote:
>>> Edward Cree <ecree.xilinx@gmail.com> writes:
>>>> On 28/11/2023 14:39, Toke Høiland-Jørgensen wrote:
>>>>> I'm not quite sure what should be the semantics of that, though. I.e.,
>>>>> if you are trying to aggregate two packets that have the flag set, which
>>>>> packet do you take the value from? What if only one packet has the flag
>>
>> It would probably make sense if both packets have it set.
> 
> Right, so "aggregate only if both packets have the flag set, keeping the
> metadata area from the first packet", then?

Yes, sgtm.

>>>>> set? Or should we instead have a "metadata_xdp_only" flag that just
>>>>> prevents the skb metadata field from being set entirely?
>>
>> What would be the use case compared to resetting meta data right before
>> we return with XDP_PASS?
> 
> I was thinking it could save a call to xdp_adjust_meta() to reset it
> back to zero before PASSing the packet. But okay, that may be of
> marginal utility.

Agree, feels too marginal.

>>>> Sounds like what's actually needed is bpf progs inside the GRO engine
>>>>    to implement the metadata "protocol" prepare and coalesce callbacks?
>>>
>>> Hmm, yes, I guess that would be the most general solution :)
>>
>> Feels like a potential good fit, agree, although for just solving the
>> above sth not requiring extra BPF might be nice as well.
> 
> Yeah, I agree that just the flag makes sense on its own.
> 
> -Toke
>