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Subject: Re: [PATCH net-next v2] ipv6: add IFLA_INET6_RA_MTU to expose mtu
 value in the RA message
To:     Rocco Yue <rocco.yue@mediatek.com>,
        David Ahern <dsahern@kernel.org>
Cc:     "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, rocco.yue@gmail.com,
        chao.song@mediatek.com, zhuoliang.zhang@mediatek.com
References: <20210802031924.3256-1-rocco.yue@mediatek.com>
 <20210802124039.13231-1-rocco.yue@mediatek.com>
From:   David Ahern <dsahern@gmail.com>
Message-ID: <c20aa306-81a9-f083-25e8-85002063b4cc@gmail.com>
Date:   Mon, 2 Aug 2021 07:35:39 -0600
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On 8/2/21 6:40 AM, Rocco Yue wrote:
> On Sat, 2021-07-31 at 11:17 -0600, David Ahern wrote:
> On 7/30/21 7:52 PM, Rocco Yue wrote:
> 
>> IFLA_INET6_RA_MTU set. You can set "reject_message" in the policy to
>> return a message that "IFLA_INET6_RA_MTU can not be set".
> 
> Hi David,
> 
> Regarding setting "reject_message" in the policy, after reviewing
> the code, I fell that it is unnecessary, because the cost of
> implementing it seems to be a bit high, which requires modifying
> the function interface. The reasons is as follows:

The policy can be setup now to do the right thing once the extack
argument is available.

do_setlink() has an extack argument. It calls validate_linkmsg which
calls validate_link_af meaning support can be added in a single patch.
If you decide to do it, then it should be a separate patch preceding
this one.