[xdp-hints] Re: [PATCH bpf-next v8 09/18] xdp: Add VLAN tag hint

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 12/5/23 22:08, Larysa Zaremba wrote:
> Implement functionality that enables drivers to expose VLAN tag
> to XDP code.
> 
> VLAN tag is represented by 2 variables:
> - protocol ID, which is passed to bpf code in BE
> - VLAN TCI, in host byte order
> 
> Acked-by: Stanislav Fomichev <sdf@google.com>
> Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> ---

Small doc nitpicks below, but it can go in-as-is

Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>

>   Documentation/netlink/specs/netdev.yaml      |  4 +++
>   Documentation/networking/xdp-rx-metadata.rst |  8 ++++-
>   include/net/xdp.h                            |  6 ++++
>   include/uapi/linux/netdev.h                  |  3 ++
>   net/core/xdp.c                               | 33 ++++++++++++++++++++
>   tools/include/uapi/linux/netdev.h            |  3 ++
>   tools/net/ynl/generated/netdev-user.c        |  1 +
>   7 files changed, 57 insertions(+), 1 deletion(-)
[...]

> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index b6f1d6dab3f2..4869c1c2d8f3 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -736,6 +736,39 @@ __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_proto: Destination pointer for VLAN Tag protocol identifier (TPID).

I would have written: Tag Protocol Identifier (TPID).
  - like e.g. CCNA exam https://study-ccna.com/ieee-802-1q/

Capital letters leading up to the short version, but I don't think this
is a requirement. I noticed that wikipedia also got this wrong. So, I it
doesn't really matter. If you need to do a respin, I would appreciate
this changed, but you got my ACK anyway.

> + * @vlan_tci: Destination pointer for VLAN TCI (VID + DEI + PCP)
> + *
> + * 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,

Drop Eligible Indicator (DEI)

> + * *Priority code point (PCP)* - 3 bits.

Priority Code Point (PCP)

> + * 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,
> +					     __be16 *vlan_proto, u16 *vlan_tci)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>   __bpf_kfunc_end_defs();