net: Introduce unregister_netdevice_queue()

This patchs adds an unreg_list anchor to struct net_device, and
introduces an unregister_netdevice_queue() function, able to queue
a net_device to a list instead of immediately unregister it.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -683,6 +683,7 @@ struct net_device
 
 	struct list_head	dev_list;
 	struct list_head	napi_list;
+	struct list_head	unreg_list;
 
 	/* Net device features */
 	unsigned long		features;
@@ -1116,7 +1117,13 @@ extern int		dev_close(struct net_device *dev);
 extern void		dev_disable_lro(struct net_device *dev);
 extern int		dev_queue_xmit(struct sk_buff *skb);
 extern int		register_netdevice(struct net_device *dev);
-extern void		unregister_netdevice(struct net_device *dev);
+extern void		unregister_netdevice_queue(struct net_device *dev,
+						   struct list_head *head);
+static inline void unregister_netdevice(struct net_device *dev)
+{
+	unregister_netdevice_queue(dev, NULL);
+}
+
 extern void		free_netdev(struct net_device *dev);
 extern void		synchronize_net(void);
 extern int 		register_netdevice_notifier(struct notifier_block *nb);

net/core/dev.c

@@ -5245,25 +5245,31 @@ void synchronize_net(void)
 EXPORT_SYMBOL(synchronize_net);
 
 /**
- *	unregister_netdevice - remove device from the kernel
+ *	unregister_netdevice_queue - remove device from the kernel
  *	@dev: device
- *
+ *	@head: list
+
  *	This function shuts down a device interface and removes it
  *	from the kernel tables.
+ *	If head not NULL, device is queued to be unregistered later.
  *
  *	Callers must hold the rtnl semaphore.  You may want
  *	unregister_netdev() instead of this.
  */
 
-void unregister_netdevice(struct net_device *dev)
+void unregister_netdevice_queue(struct net_device *dev, struct list_head *head)
 {
 	ASSERT_RTNL();
 
-	rollback_registered(dev);
-	/* Finish processing unregister after unlock */
-	net_set_todo(dev);
+	if (head) {
+		list_add_tail(&dev->unreg_list, head);
+	} else {
+		rollback_registered(dev);
+		/* Finish processing unregister after unlock */
+		net_set_todo(dev);
+	}
 }
-EXPORT_SYMBOL(unregister_netdevice);
+EXPORT_SYMBOL(unregister_netdevice_queue);
 
 /**
  *	unregister_netdev - remove device from the kernel