Subject: Re: [PATCH bpf-next v3 09/21] xdp: Add VLAN tag hint

From: Stanislav Fomichev <[email-masked]>
Date: Thu, 20 Jul 2023 14:49:58 -0700

On 07/19, Larysa Zaremba wrote:
> Implement functionality that enables drivers to expose VLAN tag
> to XDP code.
> 
> Signed-off-by: Larysa Zaremba <[email-masked]>

Acked-by: Stanislav Fomichev <[email-masked]>

Thank you for a super detailed kfunc kdoc!

> ---
>  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                               | 34 ++++++++++++++++++++
>  5 files changed, 47 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..1749f4f75c64 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_tci,
> +				   __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 8362130bf085..8b55419d332e 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -738,6 +738,40 @@ __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
> + * @ctx: XDP context pointer.
> + * @vlan_tci: Destination pointer for VLAN TCI (VID + DEI + PCP)
> + * @vlan_proto: Destination pointer for VLAN Tag protocol identifier (TPID).
> + *
> + * In case of success, ``vlan_proto`` contains *Tag protocol identifier (TPID)*,
> + * usually ``ETH_P_8021Q`` or ``ETH_P_8021AD``, but some networks can use
> + * custom TPIDs. ``vlan_proto`` is stored in **network byte order (BE)**
> + * and should be used as follows:
> + * ``if (vlan_proto == bpf_htons(ETH_P_8021Q)) do_something();``
> + *
> + * ``vlan_tci`` contains the remaining 16 bits of a VLAN tag.
> + * Driver is expected to provide those in **host byte order (usually LE)**,
> + * so the bpf program should not perform byte conversion.
> + * According to 802.1Q standard, *VLAN TCI (Tag control information)*
> + * is a bit field that contains:
> + * *VLAN identifier (VID)* that can be read with ``vlan_tci & 0xfff``,
> + * *Drop eligible indicator (DEI)* - 1 bit,
> + * *Priority code point (PCP)* - 3 bits.
> + * For detailed meaning of DEI and PCP, please refer to other sources.
> + *
> + * 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_tci,
> +					     __be16 *vlan_proto)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  __diag_pop();
>  
>  BTF_SET8_START(xdp_metadata_kfunc_ids)
> -- 
> 2.41.0
>