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

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Date: Wed, 6 Dec 2023 09:25:29 +0100
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Larysa Zaremba <larysa.zaremba@...el.com>, bpf@...r.kernel.org
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 martin.lau@...ux.dev, song@...nel.org, yhs@...com, john.fastabend@...il.com,
 kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
 David Ahern <dsahern@...il.com>, Jakub Kicinski <kuba@...nel.org>,
 Willem de Bruijn <willemb@...gle.com>,
 Anatoly Burakov <anatoly.burakov@...el.com>,
 Alexander Lobakin <alexandr.lobakin@...el.com>,
 Magnus Karlsson <magnus.karlsson@...il.com>,
 Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
 netdev@...r.kernel.org, Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>,
 Tariq Toukan <tariqt@...lanox.com>, Saeed Mahameed <saeedm@...lanox.com>,
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Subject: Re: [PATCH bpf-next v8 09/18] xdp: Add VLAN tag hint



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@...gle.com>
> Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> ---

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

Acked-by: Jesper Dangaard Brouer <hawk@...nel.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();