netdev - Re: [PATCH iproute2-next 1/3] tc: p_ip6: Support pedit of IPv6 dsfield

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Date:   Fri, 27 Mar 2020 17:51:23 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Petr Machata <petrm@...lanox.com>
Cc:     netdev@...r.kernel.org, David Ahern <dsahern@...il.com>
Subject: Re: [PATCH iproute2-next 1/3] tc: p_ip6: Support pedit of IPv6
 dsfield

On Fri, 27 Mar 2020 20:55:08 +0300
Petr Machata <petrm@...lanox.com> wrote:

> Support keywords dsfield, traffic_class and tos in the IPv6 context.
> 
> Signed-off-by: Petr Machata <petrm@...lanox.com>
> ---
>  man/man8/tc-pedit.8 | 14 ++++++++++++--
>  tc/p_ip6.c          | 16 ++++++++++++++++
>  2 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/man/man8/tc-pedit.8 b/man/man8/tc-pedit.8
> index bbd725c4..b44b0263 100644
> --- a/man/man8/tc-pedit.8
> +++ b/man/man8/tc-pedit.8
> @@ -60,8 +60,8 @@ pedit - generic packet editor action
>  
>  .ti -8
>  .IR IP6HDR_FIELD " := { "
> -.BR src " | " dst " | " flow_lbl " | " payload_len " | " nexthdr " |"
> -.BR hoplimit " }"
> +.BR src " | " dst " | " tos " | " dsfield " | " traffic_class " | "
> +.BR flow_lbl " | " payload_len " | " nexthdr " |" hoplimit " }"
>  
>  .ti -8
>  .IR TCPHDR_FIELD " := { "
> @@ -228,6 +228,16 @@ are:
>  .B src
>  .TQ
>  .B dst
> +.TP
> +.B tos
> +.TQ
> +.B dsfield
> +.TQ
> +.B traffic_class
> +Traffic Class, an 8-bit quantity. Because the field is shifted by 4 bits,
> +it is necessary to specify the full 16-bit halfword, with the actual
> +dsfield value sandwiched between 4-bit zeroes.
> +.TP
>  .TQ
>  .B flow_lbl
>  .TQ
> diff --git a/tc/p_ip6.c b/tc/p_ip6.c
> index 7cc7997b..b6fe81f5 100644
> --- a/tc/p_ip6.c
> +++ b/tc/p_ip6.c
> @@ -56,6 +56,22 @@ parse_ip6(int *argc_p, char ***argv_p,
>  		res = parse_cmd(&argc, &argv, 4, TU32, 0x0007ffff, sel, tkey);
>  		goto done;
>  	}
> +	if (strcmp(*argv, "traffic_class") == 0 ||
> +	    strcmp(*argv, "tos") == 0 ||
> +	    strcmp(*argv, "dsfield") == 0) {
> +		NEXT_ARG();
> +		tkey->off = 1;
> +		res = parse_cmd(&argc, &argv, 1, TU32, RU8, sel, tkey);
> +
> +		/* Shift the field by 4 bits on success. */
> +		if (!res) {
> +			int nkeys = sel->sel.nkeys;
> +			struct tc_pedit_key *key = &sel->sel.keys[nkeys - 1];
> +			key->mask = htonl(ntohl(key->mask) << 4 | 0xf);
> +			key->val = htonl(ntohl(key->val) << 4);
> +		}
> +		goto done;
> +	}
Why in the middle of the list? Why three aliases for the same value?
Since this is new code choose one and make it match what IPv6 standard
calls that field.