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

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 17 Feb 2026 17:01:07 -0800

On 02/17, 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 to allow
> the eBPF program bound 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                       | 13 +++++++++++++
>  include/uapi/linux/netdev.h             |  3 +++
>  net/core/xdp.c                          | 28 ++++++++++++++++++++++++++++
>  tools/include/uapi/linux/netdev.h       |  3 +++
>  5 files changed, 52 insertions(+)
> 
> diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
> index 596c306ce52b8303b20680ff0cd34d4fd9db0e48..58eda634668a07860447a65d9fc2284839af6244 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..00abb2e1e85514b4080d0e4e6e3b8f5f67f73b61 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 +647,21 @@ 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,
> +};
> +
>  struct xdp_metadata_ops {
>  	int	(*xmo_rx_timestamp)(const struct xdp_md *ctx, u64 *timestamp);
>  	int	(*xmo_rx_hash)(const struct xdp_md *ctx, u32 *hash,
>  			       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,
> +				   enum xdp_checksum *ip_summed,
> +				   u32 *cksum_meta);
>  };
>  
>  #ifdef CONFIG_NET
> diff --git a/include/uapi/linux/netdev.h b/include/uapi/linux/netdev.h
> index e0b579a1df4f2126acec6c44c299e97bbbefe640..d20da430cfd57bc26b5ea2f406c27b48d8a81693 100644
> --- a/include/uapi/linux/netdev.h
> +++ b/include/uapi/linux/netdev.h
> @@ -47,11 +47,14 @@ enum netdev_xdp_act {
>   *   hash via bpf_xdp_metadata_rx_hash().
>   * @NETDEV_XDP_RX_METADATA_VLAN_TAG: Device is capable of exposing receive
>   *   packet VLAN tag via bpf_xdp_metadata_rx_vlan_tag().
> + * @NETDEV_XDP_RX_METADATA_CHECKSUM: Device is capable of exposing receive
> + *   checksum result via bpf_xdp_metadata_rx_checksum().
>   */
>  enum netdev_xdp_rx_metadata {
>  	NETDEV_XDP_RX_METADATA_TIMESTAMP = 1,
>  	NETDEV_XDP_RX_METADATA_HASH = 2,
>  	NETDEV_XDP_RX_METADATA_VLAN_TAG = 4,
> +	NETDEV_XDP_RX_METADATA_CHECKSUM = 8,
>  };
>  
>  /**
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index fee6d080ee85fc2d278bfdddfd1365633058ec06..7d1e08d8ab4151ab42c91203def2afafc66d3149 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -961,6 +961,34 @@ __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:
> + * ``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``

The only thing I'm still not sure about is the csum_level and whether
we need to export it or just start with csum_level=0 and extend later
when needed. The rest looks good.

Jesper, Lorenzo mentioned that you might need it? Can you clarify?