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Date:   Mon, 24 Aug 2020 18:11:09 -0700 (PDT)
Message-Id: <20200824.181109.421299456838417383.davem@davemloft.net>
To:     ahabdels@gmail.com
Cc:     kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org, kuba@kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        andrea.mayer@uniroma2.it
Subject: Re: [net-next v4] seg6: using DSCP of inner IPv4 packets
From:   David Miller <davem@davemloft.net>
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From: Ahmed Abdelsalam <ahabdels@gmail.com>
Date: Mon, 24 Aug 2020 08:51:24 +0000

> This patch allows copying the DSCP from inner IPv4 header to the
> outer IPv6 header, when doing SRv6 Encapsulation.
> 
> This allows forwarding packet across the SRv6 fabric based on their
> original traffic class.
> 
> Signed-off-by: Ahmed Abdelsalam <ahabdels@gmail.com>

"Allows" sounds like the behavior is optional, but that is not what
is happening here.  You are making this DSCP inheritance behavior
unconditional.

I've stated that the current behavior matches what other ipv6
tunneling devices do, and therefore we should keep it that way.

Furthermore, this behavior has been in place for several releases
so you cannot change it by default.  People may be depending upon
how things work right now.

Also:

> @@ -130,6 +129,7 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
>  	struct ipv6_sr_hdr *isrh;
>  	int hdrlen, tot_len, err;
>  	__be32 flowlabel;
> +	u8 tos = 0, hop_limit;

Need to preserve reverse christmas tree here.