net: ipv4: Notify about changes to ip_forward_update_priority

Drivers may make offloading decision based on whether
ip_forward_update_priority is enabled or not. Therefore distribute
netevent notifications to give them a chance to react to a change.

Signed-off-by: Petr Machata <[e-mail]>
Reviewed-by: Ido Schimmel <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/netevent.h

···
 	NETEVENT_DELAY_PROBE_TIME_UPDATE, /* arg is struct neigh_parms ptr */
 	NETEVENT_IPV4_MPATH_HASH_UPDATE, /* arg is struct net ptr */
 	NETEVENT_IPV6_MPATH_HASH_UPDATE, /* arg is struct net ptr */
+	NETEVENT_IPV4_FWD_UPDATE_PRIORITY_UPDATE, /* arg is struct net ptr */
 };
 
 int register_netevent_notifier(struct notifier_block *nb);

net/ipv4/sysctl_net_ipv4.c

···
 	return ret;
 }
 
+static int ipv4_fwd_update_priority(struct ctl_table *table, int write,
+				    void __user *buffer,
+				    size_t *lenp, loff_t *ppos)
+{
+	struct net *net;
+	int ret;
+
+	net = container_of(table->data, struct net,
+			   ipv4.sysctl_ip_fwd_update_priority);
+	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	if (write && ret == 0)
+		call_netevent_notifiers(NETEVENT_IPV4_FWD_UPDATE_PRIORITY_UPDATE,
+					net);
+
+	return ret;
+}
+
 static int proc_tcp_congestion_control(struct ctl_table *ctl, int write,
 				       void __user *buffer, size_t *lenp, loff_t *ppos)
 {
···
 		.data		= &init_net.ipv4.sysctl_ip_fwd_update_priority,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler   = proc_dointvec_minmax,
+		.proc_handler   = ipv4_fwd_update_priority,
 		.extra1		= &zero,
 		.extra2		= &one,
 	},