Subject: RE: [PATCH bpf-next v2 09/20] xdp: Add VLAN tag hint

From: John Fastabend <[email-masked]>
Date: Mon, 03 Jul 2023 13:15:34 -0700

Larysa Zaremba wrote:
> Implement functionality that enables drivers to expose VLAN tag
> to XDP code.
> 
> Signed-off-by: Larysa Zaremba <[email-masked]>
> ---
>  Documentation/networking/xdp-rx-metadata.rst |  8 +++++++-
>  include/linux/netdevice.h                    |  2 ++
>  include/net/xdp.h                            |  2 ++
>  kernel/bpf/offload.c                         |  2 ++
>  net/core/xdp.c                               | 20 ++++++++++++++++++++
>  5 files changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
> index 25ce72af81c2..ea6dd79a21d3 100644
> --- a/Documentation/networking/xdp-rx-metadata.rst
> +++ b/Documentation/networking/xdp-rx-metadata.rst
> @@ -18,7 +18,13 @@ Currently, the following kfuncs are supported. In the future, as more
>  metadata is supported, this set will grow:
>  
>  .. kernel-doc:: net/core/xdp.c
> -   :identifiers: bpf_xdp_metadata_rx_timestamp bpf_xdp_metadata_rx_hash
> +   :identifiers: bpf_xdp_metadata_rx_timestamp
> +
> +.. kernel-doc:: net/core/xdp.c
> +   :identifiers: bpf_xdp_metadata_rx_hash
> +
> +.. kernel-doc:: net/core/xdp.c
> +   :identifiers: bpf_xdp_metadata_rx_vlan_tag
>  
>  An XDP program can use these kfuncs to read the metadata into stack
>  variables for its own consumption. Or, to pass the metadata on to other
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index b828c7a75be2..4fa4380e6d89 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1658,6 +1658,8 @@ 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, u16 *vlan_tag,
> +				   __be16 *vlan_proto);
>  };
>  
>  /**
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 6381560efae2..89c58f56ffc6 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -389,6 +389,8 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
>  			   bpf_xdp_metadata_rx_timestamp) \
>  	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_HASH, \
>  			   bpf_xdp_metadata_rx_hash) \
> +	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_VLAN_TAG, \
> +			   bpf_xdp_metadata_rx_vlan_tag) \
>  
>  enum {
>  #define XDP_METADATA_KFUNC(name, _) name,
> diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
> index 8a26cd8814c1..986e7becfd42 100644
> --- a/kernel/bpf/offload.c
> +++ b/kernel/bpf/offload.c
> @@ -848,6 +848,8 @@ void *bpf_dev_bound_resolve_kfunc(struct bpf_prog *prog, u32 func_id)
>  		p = ops->xmo_rx_timestamp;
>  	else if (func_id == bpf_xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_HASH))
>  		p = ops->xmo_rx_hash;
> +	else if (func_id == bpf_xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_VLAN_TAG))
> +		p = ops->xmo_rx_vlan_tag;
>  out:
>  	up_read(&bpf_devs_lock);
>  
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 41e5ca8643ec..f6262c90e45f 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -738,6 +738,26 @@ __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash,
>  	return -EOPNOTSUPP;
>  }
>  
> +/**
> + * bpf_xdp_metadata_rx_vlan_tag - Get XDP packet outermost VLAN tag with protocol
> + * @ctx: XDP context pointer.
> + * @vlan_tag: Destination pointer for VLAN tag
> + * @vlan_proto: Destination pointer for VLAN protocol identifier in network byte order.
> + *
> + * In case of success, vlan_tag contains VLAN tag, including 12 least significant bytes
> + * containing VLAN ID, vlan_proto contains protocol identifier.

Above is a bit confusing to me at least.

The vlan tag would be both the 16bit TPID and 16bit TCI. What fields
are to be included here? The VlanID or the full 16bit TCI meaning the
PCP+DEI+VID? I think by "including 12 least significant bytes" you
mean bits, but also not clear about those 4 other bits.

I can likely figure it out in next patches from implementation but
would be nice to clean up docs.

> + *
> + * Return:
> + * * Returns 0 on success or ``-errno`` on error.
> + * * ``-EOPNOTSUPP`` : device driver doesn't implement kfunc
> + * * ``-ENODATA``    : VLAN tag was not stripped or is not available
> + */
> +__bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx, u16 *vlan_tag,
> +					     __be16 *vlan_proto)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  __diag_pop();
>  
>  BTF_SET8_START(xdp_metadata_kfunc_ids)
> -- 
> 2.41.0
>