bonding: add netlink attributes to slave link dev

If link is IFF_SLAVE, extend link dev netlink attributes to include
slave attributes with new IFLA_SLAVE nest.  Add netlink notification
(RTM_NEWLINK) when slave status changes from backup to active, or
visa-versa.

Adds new ndo_get_slave op to net_device_ops to fill skb with IFLA_SLAVE
attributes.  Currently only used by bonding driver, but could be
used by other aggregating devices with slaves.

Signed-off-by: Scott Feldman <sfeldma@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
index 309757d..8a935f8 100644
--- a/drivers/net/bonding/bonding.h
+++ b/drivers/net/bonding/bonding.h
@@ -285,12 +285,18 @@
 
 static inline void bond_set_active_slave(struct slave *slave)
 {
-	slave->backup = 0;
+	if (slave->backup) {
+		slave->backup = 0;
+		rtmsg_ifinfo(RTM_NEWLINK, slave->dev, 0, GFP_KERNEL);
+	}
 }
 
 static inline void bond_set_backup_slave(struct slave *slave)
 {
-	slave->backup = 1;
+	if (!slave->backup) {
+		slave->backup = 1;
+		rtmsg_ifinfo(RTM_NEWLINK, slave->dev, 0, GFP_KERNEL);
+	}
 }
 
 static inline int bond_slave_state(struct slave *slave)
@@ -426,6 +432,7 @@
 void bond_sysfs_slave_del(struct slave *slave);
 int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev);
 int bond_release(struct net_device *bond_dev, struct net_device *slave_dev);
+int bond_get_slave(struct net_device *slave_dev, struct sk_buff *skb);
 int bond_xmit_hash(struct bonding *bond, struct sk_buff *skb, int count);
 int bond_parse_parm(const char *mode_arg, const struct bond_parm_tbl *tbl);
 int bond_parm_tbl_lookup(int mode, const struct bond_parm_tbl *tbl);