linux-kernel - Re: [PATCH] ip6_tunnel: Correct tos value in collect

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Message-Id: <142A1EF8-2274-47FD-BA8B-DFF99308E366@cmss.chinamobile.com>
Date:   Thu, 15 Jun 2017 08:58:41 +0800
From:   严海双 <yanhaishuang@...s.chinamobile.com>
To:     Peter Dawson <petedaws@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Patrick McHardy <kaber@...sh.net>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ip6_tunnel: Correct tos value in collect_md mode


> On 14 Jun 2017, at 1:28 PM, Peter Dawson <petedaws@...il.com> wrote:
> 
> On Wed, 14 Jun 2017 10:54:31 +0800
> 严海双 <yanhaishuang@...s.chinamobile.com> wrote:
> 
> 
>>> Changes since v2:
>>> * mask key->tos with RT_TOS() suggested by Daniel
> 
> Can you help me understand the rationale for this change? Is there are bug introduced by dsfield = ip6_tclass(key->label); ?
> 
> The RT_TOS masks out 4bits of the 8bit tos field in accordance with RFC1349 (obsoleted by RFC2474). IPv6 does not have a TOS field. So it dosen't make sense to apply a TOS value to the outer header of an IPv6 tunnel.
> 
> 

Hi, Peter

Here the tos also means Traffic Class in IPv6, see the define in struct ip_tunnel_key:

u8          tos;        /* TOS for IPv4, TC for IPv6 */

RT_TOS mask is suggested by Daniel, please refer to the implement in vxlan or geneve code:

fl6.flowlabel = ip6_make_flowinfo(RT_TOS(tos), label);

Thanks.