Re: [PATCH net-next v3] ipv6: add IFLA_INET6_RA_MTU to expose mtu value in the RA message

@@ -6129,6 +6136,66 @@ static void ipv6_ifa_notify(int event, struct inet6_ifaddr *ifp)
 		__ipv6_ifa_notify(event, ifp);
 }
 
+static inline size_t inet6_iframtu_msgsize(void)
+{
+	return NLMSG_ALIGN(sizeof(struct ifinfomsg))
+	     + nla_total_size(IFNAMSIZ)	/* IFLA_IFNAME */
+	     + nla_total_size(4);	/* IFLA_INET6_RA_MTU */
+}
+
+static int inet6_fill_iframtu(struct sk_buff *skb, struct inet6_dev *idev)
+{
+	struct net_device *dev = idev->dev;
+	struct ifinfomsg *hdr;
+	struct nlmsghdr *nlh;
+
+	nlh = nlmsg_put(skb, 0, 0, RTM_NEWLINK, sizeof(*hdr), 0);
+	if (!nlh)
+		return -EMSGSIZE;
+
+	hdr = nlmsg_data(nlh);
+	hdr->ifi_family = AF_INET6;
+	hdr->__ifi_pad = 0;
+	hdr->ifi_index = dev->ifindex;
+	hdr->ifi_flags = dev_get_flags(dev);
+	hdr->ifi_change = 0;
+
+	if (nla_put_string(skb, IFLA_IFNAME, dev->name) ||
+	    nla_put_u32(skb, IFLA_INET6_RA_MTU, idev->ra_mtu))
+		goto nla_put_failure;
+
+	nlmsg_end(skb, nlh);
+	return 0;
+
+nla_put_failure:
+	nlmsg_cancel(skb, nlh);
+	return -EMSGSIZE;
+}
+
+void inet6_iframtu_notify(struct inet6_dev *idev)
+{
+	struct sk_buff *skb;
+	struct net *net = dev_net(idev->dev);
+	int err = -ENOBUFS;
+
+	skb = nlmsg_new(inet6_iframtu_msgsize(), GFP_ATOMIC);
+	if (!skb)
+		goto errout;
+
+	err = inet6_fill_iframtu(skb, idev);
+	if (err < 0) {
+		/* -EMSGSIZE implies BUG in inet6_iframtu_msgsize() */
+		WARN_ON(err == -EMSGSIZE);
+		kfree_skb(skb);
+		goto errout;
+	}
+	rtnl_notify(skb, net, 0, RTNLGRP_IPV6_IFINFO, NULL, GFP_ATOMIC);
+	return;
+errout:
+	if (err < 0)
+		rtnl_set_sk_err(net, RTNLGRP_IPV6_IFINFO, err);
+}

+
 #ifdef CONFIG_SYSCTL
 
 static int addrconf_sysctl_forward(struct ctl_table *ctl, int write,

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index c467c6419893..a04164cbd77f 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c

@@ -1496,6 +1496,12 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 		memcpy(&n, ((u8 *)(ndopts.nd_opts_mtu+1))+2, sizeof(mtu));
 		mtu = ntohl(n);
 
+		if (in6_dev->ra_mtu != mtu) {
+			in6_dev->ra_mtu = mtu;
+			inet6_iframtu_notify(in6_dev);
+			ND_PRINTK(2, info, "update ra_mtu to %d\n", in6_dev->ra_mtu);
+		}
+
 		if (mtu < IPV6_MIN_MTU || mtu > skb->dev->mtu) {
 			ND_PRINTK(2, warn, "RA: invalid mtu: %d\n", mtu);
 		} else if (in6_dev->cnf.mtu6 != mtu) {