Subject: Re: [PATCH RFC bpf-next v2 1/5] netlink: specs: Add XDP RX checksum capability to XDP metadata specs

From: Stanislav Fomichev <[email-masked]>
Date: Thu, 25 Sep 2025 21:20:57 -0700

On 09/25, Lorenzo Bianconi wrote:
> Introduce XDP RX checksum capability to XDP metadata specs. XDP RX
> checksum will be use by devices capable of exposing receive checksum
> result via bpf_xdp_metadata_rx_checksum().
> Moreover, 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 <[email-masked]>
> ---
>  Documentation/netlink/specs/netdev.yaml |  5 +++++
>  include/net/xdp.h                       | 14 ++++++++++++++
>  net/core/xdp.c                          | 29 +++++++++++++++++++++++++++++
>  3 files changed, 48 insertions(+)
> 
> diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
> index e00d3fa1c152d7165e9485d6d383a2cc9cef7cfd..00699bf4a7fdb67c6b9ee3548098b0c933fd39a4 100644
> --- a/Documentation/netlink/specs/netdev.yaml
> +++ b/Documentation/netlink/specs/netdev.yaml
> @@ -61,6 +61,11 @@ definitions:
>          doc: |
>            Device is capable of exposing receive packet VLAN tag via
>            bpf_xdp_metadata_rx_vlan_tag().
> +      -
> +        name: checksum
> +        doc: |
> +          Device is capable of exposing receive checksum result via
> +          bpf_xdp_metadata_rx_checksum().
>    -
>      type: flags
>      name: xsk-flags
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index aa742f413c358575396530879af4570dc3fc18de..9ab9ac10ae2074b70618a9d4f32544d8b9a30b63 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -586,6 +586,10 @@ 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,
> @@ -643,12 +647,22 @@ enum xdp_rss_hash_type {
>  	XDP_RSS_TYPE_L4_IPV6_SCTP_EX = XDP_RSS_TYPE_L4_IPV6_SCTP | XDP_RSS_L3_DYNHDR,
>  };
>  
> +enum xdp_checksum {
> +	XDP_CHECKSUM_NONE		= CHECKSUM_NONE,
> +	XDP_CHECKSUM_UNNECESSARY	= CHECKSUM_UNNECESSARY,
> +	XDP_CHECKSUM_COMPLETE		= CHECKSUM_COMPLETE,
> +	XDP_CHECKSUM_PARTIAL		= CHECKSUM_PARTIAL,
> +};

Btw, might be worth mentioning, awhile ago we had settled on a smaller set of
exposed types:

https://lore.kernel.org/netdev/[email-masked]/

Maybe go through the previous postings and check if the arguments are
still relevant? (or explain why we want more checksum now)