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

On Fri, 2021-08-27 at 13:28 +0800, David Ahern wrote:

On 8/25/21 11:46 PM, Rocco Yue wrote:

quoted

@@ -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))

Hi David,

Thanks for your pretty suggestion.

When ra_mtu = 0, notify userspace is really unnecessary. At first
I did this because when userspace get ra_mtu = 0 through getlink,
then the corresponding operation can be performed.

After adding the restriction of "idev->ra_mtu", I think userspace can
judge whether the mtu option is carried in the RA by judging whether it
can be parsed to IFLA_INET6_RA_MTU after getlink, and perform the
corresponding operation.

I will push the next version.

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

will do.

Thanks
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