Re: [RFC PATCH] ethtool: add FEC bins histogramm report

[Jakub Kicinski <kuba@kernel.org>]

On Tue, 29 Jul 2025 03:23:54 -0700 Vadim Fedorenko wrote:
> diff --git a/Documentation/netlink/specs/ethtool.yaml b/Documentation/netlink/specs/ethtool.yaml
> index 1063d5d32fea2..3781ced722fee 100644
> --- a/Documentation/netlink/specs/ethtool.yaml
> +++ b/Documentation/netlink/specs/ethtool.yaml
> @@ -1239,6 +1239,30 @@ attribute-sets:
>          name: corr-bits
>          type: binary
>          sub-type: u64
> +      -
> +        name: hist
> +        type: nest
> +        multi-attr: True
> +        nested-attributes: fec-hist
> +      -
> +        name: fec-hist-bin-low
> +        type: s32
> +      -
> +        name: fec-hist-bin-high
> +        type: s32
> +      -
> +        name: fec-hist-bin-val
> +        type: u64
> +  -
> +    name: fec-hist
> +    subset-of: fec-stat

no need to make this a subset, better to make it its own attr set

> +    attributes:
> +      -
> +        name: fec-hist-bin-low
> +      -
> +        name: fec-hist-bin-high
> +      -
> +        name: fec-hist-bin-val
>    -
>      name: fec
>      attr-cnt-name: __ethtool-a-fec-cnt

> +static const struct ethtool_fec_hist_range netdevsim_fec_ranges[] = {
> +	{  0,  0},
> +	{  1,  3},
> +	{  4,  7},
> +	{ -1, -1}
> +};

Let's add a define for the terminating element?

> +/**
> + * struct ethtool_fec_hist_range - byte range for FEC bins histogram statistics

byte range? thought these are bit errors..

> + * sentinel value of { -1, -1 } is used as marker for end of bins array
> + * @low: low bound of the bin (inclusive)
> + * @high: high bound of the bin (inclusive)
> + */

> +		len += nla_total_size_64bit(sizeof(u64) * ETHTOOL_FEC_HIST_MAX);

I don't think it's right, each attr is its own nla_total_size().
Add a nla_total_size(8) to the calculation below

> +		/* add FEC bins information */
> +		len += (nla_total_size(0) +  /* _A_FEC_HIST */
> +			nla_total_size(4) +  /* _A_FEC_HIST_BIN_LOW */
> +			nla_total_size(4)) * /* _A_FEC_HIST_BIN_HI */
> +			ETHTOOL_FEC_HIST_MAX;