linux-kernel - Re: [PATCH net-next v5] ipv6: add IFLA_INET6_RA

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Date:   Thu, 26 Aug 2021 22:28:29 -0700
From:   David Ahern <dsahern@...il.com>
To:     Rocco Yue <rocco.yue@...iatek.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     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 v5] ipv6: add IFLA_INET6_RA_MTU to expose mtu
 value

On 8/25/21 11:46 PM, Rocco Yue wrote:
> @@ -5651,6 +5654,9 @@ static int inet6_fill_ifla6_attrs(struct sk_buff *skb, struct inet6_dev *idev,
>  	if (nla_put_u8(skb, IFLA_INET6_ADDR_GEN_MODE, idev->cnf.addr_gen_mode))
>  		goto nla_put_failure;
>  
> +	if (nla_put_u32(skb, IFLA_INET6_RA_MTU, idev->ra_mtu))

I should have seen this earlier. The intent here is to only notify
userspace if the RA contains an MTU in which case this should be

	if (idev->ra_mtu &&
	    nla_put_u32(skb, IFLA_INET6_RA_MTU, idev->ra_mtu))

and in which case idev->ra_mtu should be initialized to 0 explicitly,
not U32_MIN.