Subject: Re: [PATCH bpf-next v3 1/5] netlink: specs: Add XDP RX checksum capability to XDP metadata specs

From: Jakub Kicinski <[email-masked]>
Date: Wed, 18 Feb 2026 17:47:42 -0800

On Tue, 17 Feb 2026 09:33:56 +0100 Lorenzo Bianconi wrote:
> + * In case of success, ``ip_summed`` is set to the RX checksum result. Possible
> + * values are:
> + * ``XDP_CHECKSUM_NONE``
> + * ``XDP_CHECKSUM_UNNECESSARY``
> + * ``XDP_CHECKSUM_COMPLETE``
> + *
> + * In case of success, ``cksum_meta`` contains the hw computed checksum value
> + * for ``XDP_CHECKSUM_COMPLETE`` or the ``csum_level`` for
> + * ``XDP_CHECKSUM_UNNECESSARY``. It is set to 0 for ``XDP_CHECKSUM_NONE``

It's fairly common for NICs to report both csum complete and
unnecessary. Which one should the driver return in that case?
What if the user prefers the other one?..