[xdp-hints] Re: [PATCH bpf-next V3] xdp: bpf_xdp_metadata use EOPNOTSUPP for no driver support

[Stanislav Fomichev <sdf@google.com>]

On Sat, Feb 18, 2023 at 7:34 AM Jesper Dangaard Brouer
<brouer@redhat.com> wrote:
>
> When driver doesn't implement a bpf_xdp_metadata kfunc the default
> implementation returns EOPNOTSUPP, which indicate device driver doesn't
> implement this kfunc.
>
> Currently many drivers also return EOPNOTSUPP when the hint isn't
> available. Instead change drivers to return ENODATA in these cases.
> There can be natural cases why a driver doesn't provide any hardware
> info for a specific hint, even on a frame to frame basis (e.g. PTP).
> Lets keep these cases as separate return codes.
>
> When describing the return values, adjust the function kernel-doc layout
> to get proper rendering for the return values.

Acked-by: Stanislav Fomichev <sdf@google.com>

Thanks! ENODATA seems like a better fit for the actual implementation.
Long term probably still makes sense to export this info via xdp-features?
Not sure how long we can 100% ensure EOPNOTSUPP vs ENODATA convention :-)

> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
>  Documentation/networking/xdp-rx-metadata.rst     |    7 +++++--
>  drivers/net/ethernet/mellanox/mlx4/en_rx.c       |    4 ++--
>  drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c |    4 ++--
>  drivers/net/veth.c                               |    4 ++--
>  net/core/xdp.c                                   |   10 ++++++++--
>  5 files changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
> index aac63fc2d08b..25ce72af81c2 100644
> --- a/Documentation/networking/xdp-rx-metadata.rst
> +++ b/Documentation/networking/xdp-rx-metadata.rst
> @@ -23,10 +23,13 @@ metadata is supported, this set will grow:
>  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
>  consumers, an XDP program can store it into the metadata area carried
> -ahead of the packet.
> +ahead of the packet. Not all packets will necessary have the requested
> +metadata available in which case the driver returns ``-ENODATA``.
>
>  Not all kfuncs have to be implemented by the device driver; when not
> -implemented, the default ones that return ``-EOPNOTSUPP`` will be used.
> +implemented, the default ones that return ``-EOPNOTSUPP`` will be used
> +to indicate the device driver have not implemented this kfunc.
> +
>
>  Within an XDP frame, the metadata layout (accessed via ``xdp_buff``) is
>  as follows::
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index 0869d4fff17b..4b5e459b6d49 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -674,7 +674,7 @@ int mlx4_en_xdp_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
>         struct mlx4_en_xdp_buff *_ctx = (void *)ctx;
>
>         if (unlikely(_ctx->ring->hwtstamp_rx_filter != HWTSTAMP_FILTER_ALL))
> -               return -EOPNOTSUPP;
> +               return -ENODATA;
>
>         *timestamp = mlx4_en_get_hwtstamp(_ctx->mdev,
>                                           mlx4_en_get_cqe_ts(_ctx->cqe));
> @@ -686,7 +686,7 @@ int mlx4_en_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash)
>         struct mlx4_en_xdp_buff *_ctx = (void *)ctx;
>
>         if (unlikely(!(_ctx->dev->features & NETIF_F_RXHASH)))
> -               return -EOPNOTSUPP;
> +               return -ENODATA;
>
>         *hash = be32_to_cpu(_ctx->cqe->immed_rss_invalid);
>         return 0;
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> index f7d52b1d293b..32c444c01906 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> @@ -161,7 +161,7 @@ static int mlx5e_xdp_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
>         const struct mlx5e_xdp_buff *_ctx = (void *)ctx;
>
>         if (unlikely(!mlx5e_rx_hw_stamp(_ctx->rq->tstamp)))
> -               return -EOPNOTSUPP;
> +               return -ENODATA;
>
>         *timestamp =  mlx5e_cqe_ts_to_ns(_ctx->rq->ptp_cyc2time,
>                                          _ctx->rq->clock, get_cqe_ts(_ctx->cqe));
> @@ -173,7 +173,7 @@ static int mlx5e_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash)
>         const struct mlx5e_xdp_buff *_ctx = (void *)ctx;
>
>         if (unlikely(!(_ctx->xdp.rxq->dev->features & NETIF_F_RXHASH)))
> -               return -EOPNOTSUPP;
> +               return -ENODATA;
>
>         *hash = be32_to_cpu(_ctx->cqe->rss_hash_result);
>         return 0;
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index 1bb54de7124d..046461ee42ea 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -1610,7 +1610,7 @@ static int veth_xdp_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
>         struct veth_xdp_buff *_ctx = (void *)ctx;
>
>         if (!_ctx->skb)
> -               return -EOPNOTSUPP;
> +               return -ENODATA;
>
>         *timestamp = skb_hwtstamps(_ctx->skb)->hwtstamp;
>         return 0;
> @@ -1621,7 +1621,7 @@ static int veth_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash)
>         struct veth_xdp_buff *_ctx = (void *)ctx;
>
>         if (!_ctx->skb)
> -               return -EOPNOTSUPP;
> +               return -ENODATA;
>
>         *hash = skb_get_hash(_ctx->skb);
>         return 0;
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 26483935b7a4..b71fe21b5c3e 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -721,7 +721,10 @@ __diag_ignore_all("-Wmissing-prototypes",
>   * @ctx: XDP context pointer.
>   * @timestamp: Return value pointer.
>   *
> - * Returns 0 on success or ``-errno`` on error.
> + * Return:
> + * * Returns 0 on success or ``-errno`` on error.
> + * * ``-EOPNOTSUPP`` : means device driver does not implement kfunc
> + * * ``-ENODATA``    : means no RX-timestamp available for this frame
>   */
>  __bpf_kfunc int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
>  {
> @@ -733,7 +736,10 @@ __bpf_kfunc int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *tim
>   * @ctx: XDP context pointer.
>   * @hash: Return value pointer.
>   *
> - * Returns 0 on success or ``-errno`` on error.
> + * Return:
> + *  * Returns 0 on success or ``-errno`` on error.
> + *  * ``-EOPNOTSUPP`` : means device driver doesn't implement kfunc
> + *  * ``-ENODATA``    : means no RX-hash available for this frame
>   */
>  __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash)
>  {
>
>