rtnetlink: handle rtnl_link netlink notifications manually

In order to support specifying device flags during device creation,
we must be able to roll back device registration in case setting the
flags fails without sending any notifications related to the device
to userspace.

This patch changes rollback_registered_many() and register_netdevice()
to manually send netlink notifications for devices not handled by
rtnl_link and allows to defer notifications for devices handled by
rtnl_link until setup is complete.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -924,7 +924,12 @@ struct net_device {
 	       NETREG_UNREGISTERED,	/* completed unregister todo */
 	       NETREG_RELEASED,		/* called free_netdev */
 	       NETREG_DUMMY,		/* dummy device for NAPI poll */
-	} reg_state;
+	} reg_state:16;
+
+	enum {
+		RTNL_LINK_INITIALIZED,
+		RTNL_LINK_INITIALIZING,
+	} rtnl_link_state:16;
 
 	/* Called from unregister, can be used to call free_netdev */
 	void (*destructor)(struct net_device *dev);

net/core/dev.c

@@ -4865,6 +4865,10 @@ static void rollback_registered_many(struct list_head *head)
 		*/
 		call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
 
+		if (!dev->rtnl_link_ops ||
+		    dev->rtnl_link_state == RTNL_LINK_INITIALIZED)
+			rtmsg_ifinfo(RTM_DELLINK, dev, ~0U);
+
 		/*
 		 *	Flush the unicast and multicast chains
 		 */
@@ -5091,7 +5095,9 @@ int register_netdevice(struct net_device *dev)
 	 *	Prevent userspace races by waiting until the network
 	 *	device is fully setup before sending notifications.
 	 */
-	rtmsg_ifinfo(RTM_NEWLINK, dev, ~0U);
+	if (!dev->rtnl_link_ops ||
+	    dev->rtnl_link_state == RTNL_LINK_INITIALIZED)
+		rtmsg_ifinfo(RTM_NEWLINK, dev, ~0U);
 
 out:
 	return ret;

net/core/rtnetlink.c

@@ -1425,9 +1425,6 @@ static int rtnetlink_event(struct notifier_block *this, unsigned long event, voi
 	struct net_device *dev = ptr;
 
 	switch (event) {
-	case NETDEV_UNREGISTER:
-		rtmsg_ifinfo(RTM_DELLINK, dev, ~0U);
-		break;
 	case NETDEV_UP:
 	case NETDEV_DOWN:
 		rtmsg_ifinfo(RTM_NEWLINK, dev, IFF_UP|IFF_RUNNING);
@@ -1437,6 +1434,7 @@ static int rtnetlink_event(struct notifier_block *this, unsigned long event, voi
 	case NETDEV_REGISTER:
 	case NETDEV_CHANGE:
 	case NETDEV_GOING_DOWN:
+	case NETDEV_UNREGISTER:
 	case NETDEV_UNREGISTER_BATCH:
 		break;
 	default: