Re: [RFC PATCH bpf-next v1 0/7] xdp: RX checksum metadata hint and checksum assertion over redirect

Hi Lorenzo,

Sorry -- I blindly missed your earlier RX-checksum series before I posted
mine, thanks Stanislav for the pointer.

To answer your question: yes, I'm happy to take on the driver selftest
Jakub asked for.

As for my own series, the read side clearly overlaps yours and you own it,
so I'll drop my bpf_xdp_metadata_rx_csum() hint and its driver bits.

What's left that is genuinely separate is the "assertion" half -- a non-dev-bound
bpf_xdp_assert_rx_csum() that preserves the HW verdict across a
cpumap/redirect: it sets a flag on the xdp_buff that rides into the
xdp_frame and becomes skb->ip_summed = CHECKSUM_UNNECESSARY in
__xdp_build_skb_from_frame().

Should I resend that as a small standalone series (v2, assert-only)?
It also looks like a PoC that you and Jakub discussed on v3 [1].

A few things I'd like to confirm before writing the test:

1. API for v4. In the v3 discussion you agreed to rework the API to report
   both COMPLETE and UNNECESSARY (+ csum_level), per Jakub. Do you plan to
   send that in v4, or should the driver selftest target the current v3
   signature (enum xdp_checksum + cksum_meta)? I'd rather write the test
   against the API you intend to keep.

2. Documented behavior. The selftest is meant to "check the documented
   expectation", so which rule should it assert -- "a driver must never
   report CHECKSUM_COMPLETE while an XDP program is attached", or that the
   driver downgrades/repairs COMPLETE on the XDP_PASS path? I'll write the
   doc paragraph and the test to match whatever we settle on.

3. Drivers. Your series adds veth and ice; I don't see mlx5e -- was that
   intentional (left to the driver maintainers)? I had an mlx5e
   implementation in my v1 and I'm happy to contribute it to your series if
   it's useful.

For the test itself I was thinking of extending
tools/testing/selftests/drivers/net/hw/xdp_metadata.py, gated on the new
"checksum" xdp-rx-metadata feature, with good-csum / bad-csum / modify +
XDP_PASS cases. Does that match what you and Jakub had in mind?

[1] https://lore.kernel.org/bpf/20260217-bpf-xdp-meta-rxcksum-v3-0-30024c50ba71@kernel.org/ (local)

Thanks,
Vladimir