net: add change_carrier netdev op

This allows a driver to register change_carrier callback which will be
called whenever user will like to change carrier state. This is useful
for devices like dummy, gre, team and so on.
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -891,6 +891,14 @@ struct netdev_fcoe_hbainfo {
  * int (*ndo_bridge_setlink)(struct net_device *dev, struct nlmsghdr *nlh)
  * int (*ndo_bridge_getlink)(struct sk_buff *skb, u32 pid, u32 seq,
  *			     struct net_device *dev)
+ *
+ * int (*ndo_change_carrier)(struct net_device *dev, bool new_carrier);
+ *	Called to change device carrier. Soft-devices (like dummy, team, etc)
+ *	which do not represent real hardware may define this to allow their
+ *	userspace components to manage their virtual carrier state. Devices
+ *	that determine carrier state from physical hardware properties (eg
+ *	network cables) or protocol-dependent mechanisms (eg
+ *	USB_CDC_NOTIFY_NETWORK_CONNECTION) should NOT implement this function.
  */
 struct net_device_ops {
 	int			(*ndo_init)(struct net_device *dev);
@@ -1008,6 +1016,8 @@ struct net_device_ops {
 	int			(*ndo_bridge_getlink)(struct sk_buff *skb,
 						      u32 pid, u32 seq,
 						      struct net_device *dev);
+	int			(*ndo_change_carrier)(struct net_device *dev,
+						      bool new_carrier);
 };
 
 /*
@@ -2194,6 +2204,8 @@ extern int		dev_set_mtu(struct net_device *, int);
 extern void		dev_set_group(struct net_device *, int);
 extern int		dev_set_mac_address(struct net_device *,
 					    struct sockaddr *);
+extern int		dev_change_carrier(struct net_device *,
+					   bool new_carrier);
 extern int		dev_hard_start_xmit(struct sk_buff *skb,
 					    struct net_device *dev,
 					    struct netdev_queue *txq);

net/core/dev.c

@@ -5027,6 +5027,25 @@ int dev_set_mac_address(struct net_device *dev, struct sockaddr *sa)
 }
 EXPORT_SYMBOL(dev_set_mac_address);
 
+/**
+ *	dev_change_carrier - Change device carrier
+ *	@dev: device
+ *	@new_carries: new value
+ *
+ *	Change device carrier
+ */
+int dev_change_carrier(struct net_device *dev, bool new_carrier)
+{
+	const struct net_device_ops *ops = dev->netdev_ops;
+
+	if (!ops->ndo_change_carrier)
+		return -EOPNOTSUPP;
+	if (!netif_device_present(dev))
+		return -ENODEV;
+	return ops->ndo_change_carrier(dev, new_carrier);
+}
+EXPORT_SYMBOL(dev_change_carrier);
+
 /*
  *	Perform the SIOCxIFxxx calls, inside rcu_read_lock()
  */