linux-kernel - Re: [PATCH net-next v4] ipv6: add IFLA_INET6_RA_MTU to expose mtu value in the RA message

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Message-ID: <a4a52162-c645-b369-a9f3-120f48115cde@gmail.com>
Date:   Sun, 22 Aug 2021 20:01:44 -0700
From:   David Ahern <dsahern@...il.com>
To:     Rocco Yue <rocco.yue@...iatek.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, rocco.yue@...il.com,
        chao.song@...iatek.com, zhuoliang.zhang@...iatek.com
Subject: Re: [PATCH net-next v4] ipv6: add IFLA_INET6_RA_MTU to expose mtu
 value in the RA message

On 8/21/21 12:10 AM, Rocco Yue wrote:
> In this patch, if an RA no longer carries an MTU or if accept_ra_mtu is reset,
> in6_dev->ra_mtu will not be reset to 0, its value will remain the previous
> accept_ra_mtu=1 and the value of the mtu carried in the RA msg. This behavior
> is same with mtu6. This should be reasonable, it would show that the device
> had indeed received the ra_mtu before set accept_ra_mtu to 0 or an RA no longer
> carries an mtu value. I am willing to listen to your suggestions and make
> changes if needed, maybe it needs to add a new separate proc handler for
> accept_ra_mtu.

fair point. Consistency is important.


> 
> In addition, at your prompt, I find that this patch maybe have a defect for
> some types of virtual devices, that is, when the state of the virtual device
> updates the value of ra_mtu during the UP period, when its state is set to
> DOWN, ra_mtu is not reset to 0, so that its ra_mtu value remains the previous
> value after the interface is re-UP. I think I need to fix it.
> 

Please do. Also, that problem should apply to all netdev's not just
virtual devices if you are referring to admin down (e.g., ip link set
$DEV down)