Re: [PATCH net-next v5] ipv6: add IFLA_INET6_RA_MTU to expose mtu value

[David Ahern]

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.