ipv6: add knob to send unsolicited ND on link-layer address change

This patch introduces a new knob ndisc_notify. If enabled, the kernel
will transmit an unsolicited neighbour advertisement on link-layer address
change to update the neighbour tables of the corresponding hosts more quickly.

This is the equivalent to arp_notify in ipv4 world.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ipv6.h

@@ -47,6 +47,7 @@ struct ipv6_devconf {
 	__s32		disable_ipv6;
 	__s32		accept_dad;
 	__s32		force_tllao;
+	__s32           ndisc_notify;
 	void		*sysctl;
 };
 

include/uapi/linux/ipv6.h

@@ -157,6 +157,7 @@ enum {
 	DEVCONF_DISABLE_IPV6,
 	DEVCONF_ACCEPT_DAD,
 	DEVCONF_FORCE_TLLAO,
+	DEVCONF_NDISC_NOTIFY,
 	DEVCONF_MAX
 };
 

net/ipv6/addrconf.c

@@ -4037,6 +4037,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
 	array[DEVCONF_DISABLE_IPV6] = cnf->disable_ipv6;
 	array[DEVCONF_ACCEPT_DAD] = cnf->accept_dad;
 	array[DEVCONF_FORCE_TLLAO] = cnf->force_tllao;
+	array[DEVCONF_NDISC_NOTIFY] = cnf->ndisc_notify;
 }
 
 static inline size_t inet6_ifla6_size(void)
@@ -4704,6 +4705,13 @@ static struct addrconf_sysctl_table
 			.mode           = 0644,
 			.proc_handler   = proc_dointvec
 		},
+		{
+			.procname       = "ndisc_notify",
+			.data           = &ipv6_devconf.ndisc_notify,
+			.maxlen         = sizeof(int),
+			.mode           = 0644,
+			.proc_handler   = proc_dointvec
+		},
 		{
 			/* sentinel */
 		}

net/ipv6/ndisc.c

@@ -1572,11 +1572,18 @@ static int ndisc_netdev_event(struct notifier_block *this, unsigned long event,
 {
 	struct net_device *dev = ptr;
 	struct net *net = dev_net(dev);
+	struct inet6_dev *idev;
 
 	switch (event) {
 	case NETDEV_CHANGEADDR:
 		neigh_changeaddr(&nd_tbl, dev);
 		fib6_run_gc(~0UL, net);
+		idev = in6_dev_get(dev);
+		if (!idev)
+			break;
+		if (idev->cnf.ndisc_notify)
+			ndisc_send_unsol_na(dev);
+		in6_dev_put(idev);
 		break;
 	case NETDEV_DOWN:
 		neigh_ifdown(&nd_tbl, dev);