firewire: net: add carrier detection

To make userland, e.g. NetworkManager work with firewire, we need to
detect whether cable is plugged or not.  Simple and correct way of doing
that is just counting number of peers.  No peers - no link and vice
versa.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/net.c

@@ -178,6 +178,7 @@ struct fwnet_device {
 
 	/* Number of tx datagrams that have been queued but not yet acked */
 	int queued_datagrams;
+	int peer_count;
 
 	struct list_head peer_list;
 	struct fw_card *card;
@@ -1405,6 +1406,10 @@ static int fwnet_change_mtu(struct net_device *net, int new_mtu)
 	return 0;
 }
 
+static const struct ethtool_ops fwnet_ethtool_ops = {
+	.get_link	= ethtool_op_get_link,
+};
+
 static const struct net_device_ops fwnet_netdev_ops = {
 	.ndo_open       = fwnet_open,
 	.ndo_stop	= fwnet_stop,
@@ -1423,6 +1428,8 @@ static void fwnet_init_dev(struct net_device *net)
 	net->hard_header_len	= FWNET_HLEN;
 	net->type		= ARPHRD_IEEE1394;
 	net->tx_queue_len	= FWNET_TX_QUEUE_LEN;
+	net->ethtool_ops	= &fwnet_ethtool_ops;
+
 }
 
 /* caller must hold fwnet_device_mutex */
@@ -1463,6 +1470,7 @@ static int fwnet_add_peer(struct fwnet_device *dev,
 
 	spin_lock_irq(&dev->lock);
 	list_add_tail(&peer->peer_link, &dev->peer_list);
+	dev->peer_count++;
 	spin_unlock_irq(&dev->lock);
 
 	return 0;
@@ -1534,6 +1542,9 @@ static int fwnet_probe(struct device *_dev)
 		unregister_netdev(net);
 		list_del(&dev->dev_link);
 	}
+
+	if (dev->peer_count > 1)
+		netif_carrier_on(net);
  out:
 	if (ret && allocated_netdev)
 		free_netdev(net);
@@ -1549,6 +1560,7 @@ static void fwnet_remove_peer(struct fwnet_peer *peer)
 
 	spin_lock_irq(&peer->dev->lock);
 	list_del(&peer->peer_link);
+	peer->dev->peer_count--;
 	spin_unlock_irq(&peer->dev->lock);
 
 	list_for_each_entry_safe(pd, pd_next, &peer->pd_list, pd_link)
@@ -1568,6 +1580,11 @@ static int fwnet_remove(struct device *_dev)
 
 	fwnet_remove_peer(peer);
 
+	/* If we serve just one node, that means we lost link
+		with outer world */
+	if (dev->peer_count == 1)
+		netif_carrier_off(dev->netdev);
+
 	if (list_empty(&dev->peer_list)) {
 		net = dev->netdev;
 		unregister_netdev(net);