bridge: control carrier based on ports online

This makes the bridge device behave like a physical device.
In earlier releases the bridge always asserted carrier. This
changes the behavior so that bridge device carrier is on only
if one or more ports are in the forwarding state. This
should help IPv6 autoconfiguration, DHCP, and routing daemons.

I did brief testing with Network and Virt manager and they
seem fine, but since this changes behavior of bridge, it should
wait until net-next (2.6.39).
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Reviewed-by: Nicolas de Pesloüan <nicolas.2p.debian@free.fr>
Tested-By: Adam Majer <adamm@zombino.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_device.c

@@ -78,6 +78,8 @@ static int br_dev_open(struct net_device *dev)
 {
 	struct net_bridge *br = netdev_priv(dev);
 
+	netif_carrier_off(dev);
+
 	br_features_recompute(br);
 	netif_start_queue(dev);
 	br_stp_enable_bridge(br);
@@ -94,6 +96,8 @@ static int br_dev_stop(struct net_device *dev)
 {
 	struct net_bridge *br = netdev_priv(dev);
 
+	netif_carrier_off(dev);
+
 	br_stp_disable_bridge(br);
 	br_multicast_stop(br);
 

net/bridge/br_stp.c

@@ -397,13 +397,16 @@ static void br_make_forwarding(struct net_bridge_port *p)
 void br_port_state_selection(struct net_bridge *br)
 {
 	struct net_bridge_port *p;
+	unsigned int liveports = 0;
 
 	/* Don't change port states if userspace is handling STP */
 	if (br->stp_enabled == BR_USER_STP)
 		return;
 
 	list_for_each_entry(p, &br->port_list, list) {
-		if (p->state != BR_STATE_DISABLED) {
+		if (p->state == BR_STATE_DISABLED)
+			continue;
+
 		if (p->port_no == br->root_port) {
 			p->config_pending = 0;
 			p->topology_change_ack = 0;
@@ -416,9 +419,15 @@ void br_port_state_selection(struct net_bridge *br)
 			p->topology_change_ack = 0;
 			br_make_blocking(p);
 		}
-		}
 
+		if (p->state == BR_STATE_FORWARDING)
+			++liveports;
 	}
+
+	if (liveports == 0)
+		netif_carrier_off(br->dev);
+	else
+		netif_carrier_on(br->dev);
 }
 
 /* called under bridge lock */

net/bridge/br_stp_timer.c

@@ -94,6 +94,7 @@ static void br_forward_delay_timer_expired(unsigned long arg)
 		p->state = BR_STATE_FORWARDING;
 		if (br_is_designated_for_some_port(br))
 			br_topology_change_detection(br);
+		netif_carrier_on(br->dev);
 	}
 	br_log_state(p);
 	spin_unlock(&br->lock);