hsr: remove hsr interface if all slaves are removed

When all hsr slave interfaces are removed, hsr interface doesn't work.
At that moment, it's fine to remove an unused hsr interface automatically
for saving resources.
That's a common behavior of virtual interfaces.
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/hsr/hsr_main.c

@@ -15,12 +15,23 @@
 #include "hsr_framereg.h"
 #include "hsr_slave.h"
 
+static bool hsr_slave_empty(struct hsr_priv *hsr)
+{
+	struct hsr_port *port;
+
+	hsr_for_each_port(hsr, port)
+		if (port->type != HSR_PT_MASTER)
+			return false;
+	return true;
+}
+
 static int hsr_netdev_notify(struct notifier_block *nb, unsigned long event,
 			     void *ptr)
 {
-	struct net_device *dev;
 	struct hsr_port *port, *master;
+	struct net_device *dev;
 	struct hsr_priv *hsr;
+	LIST_HEAD(list_kill);
 	int mtu_max;
 	int res;
 
@@ -85,8 +96,15 @@ static int hsr_netdev_notify(struct notifier_block *nb, unsigned long event,
 		master->dev->mtu = mtu_max;
 		break;
 	case NETDEV_UNREGISTER:
-		if (!is_hsr_master(dev))
+		if (!is_hsr_master(dev)) {
+			master = hsr_port_get_hsr(port->hsr, HSR_PT_MASTER);
 			hsr_del_port(port);
+			if (hsr_slave_empty(master->hsr)) {
+				unregister_netdevice_queue(master->dev,
+							   &list_kill);
+				unregister_netdevice_many(&list_kill);
+			}
+		}
 		break;
 	case NETDEV_PRE_TYPE_CHANGE:
 		/* HSR works only on Ethernet devices. Refuse slave to change