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Date: Wed, 18 Feb 2026 17:47:42 -0800
From: Jakub Kicinski <kuba@kernel.org>
To: Lorenzo Bianconi <lorenzo@kernel.org>
Cc: Donald Hunter <donald.hunter@gmail.com>, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Paolo Abeni
 <pabeni@redhat.com>, Simon Horman <horms@kernel.org>, Alexei Starovoitov
 <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, Jesper Dangaard
 Brouer <hawk@kernel.org>, John Fastabend <john.fastabend@gmail.com>,
 Stanislav Fomichev <sdf@fomichev.me>, Andrew Lunn <andrew+netdev@lunn.ch>,
 Tony Nguyen <anthony.l.nguyen@intel.com>, Przemek Kitszel
 <przemyslaw.kitszel@intel.com>, Alexander Lobakin
 <aleksander.lobakin@intel.com>, Andrii Nakryiko <andrii@kernel.org>, Martin
 KaFai Lau <martin.lau@linux.dev>, Eduard Zingerman <eddyz87@gmail.com>,
 Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, KP
 Singh <kpsingh@kernel.org>, Hao Luo <haoluo@google.com>, Jiri Olsa
 <jolsa@kernel.org>, Shuah Khan <shuah@kernel.org>, Maciej Fijalkowski
 <maciej.fijalkowski@intel.com>, Jakub Sitnicki <jakub@cloudflare.com>,
 netdev@vger.kernel.org, bpf@vger.kernel.org,
 intel-wired-lan@lists.osuosl.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf-next v3 1/5] netlink: specs: Add XDP RX checksum
 capability to XDP metadata specs
Message-ID: <20260218174742.62a4074f@kernel.org>
In-Reply-To: <20260217-bpf-xdp-meta-rxcksum-v3-1-30024c50ba71@kernel.org>
References: <20260217-bpf-xdp-meta-rxcksum-v3-0-30024c50ba71@kernel.org>
	<20260217-bpf-xdp-meta-rxcksum-v3-1-30024c50ba71@kernel.org>
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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?..