netdev - Re: [PATCH RFC bpf-next 2/6] net: xdp: Add xmo_rx

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Message-ID: <aNFupGy1QxlhRSUE@mini-arch>
Date: Mon, 22 Sep 2025 08:43:32 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>
Cc: Donald Hunter <donald.hunter@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>,
	netdev@...r.kernel.org, bpf@...r.kernel.org,
	intel-wired-lan@...ts.osuosl.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC bpf-next 2/6] net: xdp: Add xmo_rx_checksum callback

On 09/20, Lorenzo Bianconi wrote:
> Introduce xmo_rx_checksum netdev callback in order allow the eBPF
> program bounded to the device to retrieve the RX checksum result computed
> by the hw NIC.
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  include/net/xdp.h |  6 ++++++
>  net/core/xdp.c    | 29 +++++++++++++++++++++++++++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 6fd294fa6841d59c3d7dc4475e09e731996566b0..481b39976ac8c8d4db2de39055c72ba8d0d511c3 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -581,6 +581,10 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
>  			   NETDEV_XDP_RX_METADATA_VLAN_TAG, \
>  			   bpf_xdp_metadata_rx_vlan_tag, \
>  			   xmo_rx_vlan_tag) \
> +	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_CHECKSUM, \
> +			   NETDEV_XDP_RX_METADATA_CHECKSUM, \
> +			   bpf_xdp_metadata_rx_checksum, \
> +			   xmo_rx_checksum)
>  
>  enum xdp_rx_metadata {
>  #define XDP_METADATA_KFUNC(name, _, __, ___) name,
> @@ -644,6 +648,8 @@ struct xdp_metadata_ops {
>  			       enum xdp_rss_hash_type *rss_type);
>  	int	(*xmo_rx_vlan_tag)(const struct xdp_md *ctx, __be16 *vlan_proto,
>  				   u16 *vlan_tci);
> +	int	(*xmo_rx_checksum)(const struct xdp_md *ctx, u8 *ip_summed,
> +				   u32 *cksum_meta);
>  };
>  
>  #ifdef CONFIG_NET
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 9100e160113a9a1e2cb88e7602e85c5f36a9f3b9..3edab2d5e5c7c2013b1ef98c949a83655eb94349 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -961,6 +961,35 @@ __bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx,
>  	return -EOPNOTSUPP;
>  }
>  
> +/**
> + * bpf_xdp_metadata_rx_checksum - Read XDP frame RX checksum.
> + * @ctx: XDP context pointer.
> + * @ip_summed: Return value pointer indicating checksum result.
> + * @cksum_meta: Return value pointer indicating checksum result metadata.
> + *
> + * In case of success, ``ip_summed`` is set to the RX checksum result. Possible
> + * values are:
> + * ``CHECKSUM_NONE``
> + * ``CHECKSUM_UNNECESSARY``
> + * ``CHECKSUM_COMPLETE``
> + * ``CHECKSUM_PARTIAL``

What do you think about adding new UAPI enum here? Similar to
xdp_rss_hash_type for the hash. The values can match the internal
CHECKSUM_XXX ones with (BUILD_BUG_ONs to enforce the relationship).
Will be a bit nicer api-wise to have an enum than an opaque u8.