Re: [PATCH bpf-next v3 03/12] bpf: XDP metadata RX kfuncs

[Jesper Dangaard Brouer <jbrouer@xxxxxxxxxx>]

On 06/12/2022 03.45, Stanislav Fomichev wrote:
> There is an ndo handler per kfunc, the verifier replaces a call to the
> generic kfunc with a call to the per-device one.
>
> For XDP, we define a new kfunc set (xdp_metadata_kfunc_ids) which
> implements all possible metatada kfuncs. Not all devices have to
> implement them. If kfunc is not supported by the target device,
> the default implementation is called instead.
>
> Upon loading, if BPF_F_XDP_HAS_METADATA is passed via prog_flags,
> we treat prog_index as target device for kfunc resolution.

[...cut...]
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 5aa35c58c342..2eabb9157767 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -74,6 +74,7 @@ struct udp_tunnel_nic_info;
>   struct udp_tunnel_nic;
>   struct bpf_prog;
>   struct xdp_buff;
> +struct xdp_md;
>   
>   void synchronize_net(void);
>   void netdev_set_default_ethtool_ops(struct net_device *dev,
> @@ -1611,6 +1612,10 @@ struct net_device_ops {
>   	ktime_t			(*ndo_get_tstamp)(struct net_device *dev,
>   						  const struct skb_shared_hwtstamps *hwtstamps,
>   						  bool cycles);
> +	bool			(*ndo_xdp_rx_timestamp_supported)(const struct xdp_md *ctx);
> +	u64			(*ndo_xdp_rx_timestamp)(const struct xdp_md *ctx);
> +	bool			(*ndo_xdp_rx_hash_supported)(const struct xdp_md *ctx);
> +	u32			(*ndo_xdp_rx_hash)(const struct xdp_md *ctx);
>   };
>   

Would it make sense to add a 'flags' parameter to ndo_xdp_rx_timestamp
and ndo_xdp_rx_hash ?

E.g. we could have a "STORE" flag that asks the kernel to store this
information for later. This will be helpful for both the SKB and
redirect use-cases.
For redirect e.g into a veth, then BPF-prog can use the same function
bpf_xdp_metadata_rx_hash() to receive the RX-hash, as it can obtain the
"stored" value (from the BPF-prog that did the redirect).

(p.s. Hopefully a const 'flags' variable can be optimized when unrolling
to eliminate store instructions when flags==0)

>   /**
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 55dbc68bfffc..c24aba5c363b 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -409,4 +409,33 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
>   
>   #define DEV_MAP_BULK_SIZE XDP_BULK_QUEUE_SIZE
>   
> +#define XDP_METADATA_KFUNC_xxx	\
> +	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_TIMESTAMP_SUPPORTED, \
> +			   bpf_xdp_metadata_rx_timestamp_supported) \
> +	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_TIMESTAMP, \
> +			   bpf_xdp_metadata_rx_timestamp) \
> +	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_HASH_SUPPORTED, \
> +			   bpf_xdp_metadata_rx_hash_supported) \
> +	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_HASH, \
> +			   bpf_xdp_metadata_rx_hash) \
> +
> +enum {
> +#define XDP_METADATA_KFUNC(name, str) name,
> +XDP_METADATA_KFUNC_xxx
> +#undef XDP_METADATA_KFUNC
> +MAX_XDP_METADATA_KFUNC,
> +};
> +
> +#ifdef CONFIG_NET
> +u32 xdp_metadata_kfunc_id(int id);
> +#else
> +static inline u32 xdp_metadata_kfunc_id(int id) { return 0; }
> +#endif
> +
> +struct xdp_md;
> +bool bpf_xdp_metadata_rx_timestamp_supported(const struct xdp_md *ctx);
> +u64 bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx);
> +bool bpf_xdp_metadata_rx_hash_supported(const struct xdp_md *ctx);
> +u32 bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx);
> +