net: add netdev_adjacent->private and allow to use it

Currently, even though we can access any linked device, we can't attach
anything to it, which is vital to properly manage them.

To fix this, add a new void *private to netdev_adjacent and functions
setting/getting it (per link), so that we can save, per example, bonding's
slave structures there, per slave device.

netdev_master_upper_dev_link_private(dev, upper_dev, private) links dev to
upper dev and populates the neighbour link only with private.

netdev_lower_dev_get_private{,_rcu}() returns the private, if found.

CC: "David S. Miller" <davem@davemloft.net>
CC: Eric Dumazet <edumazet@google.com>
CC: Jiri Pirko <jiri@resnulli.us>
CC: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -2839,8 +2839,15 @@ extern int netdev_upper_dev_link(struct net_device *dev,
 				 struct net_device *upper_dev);
 extern int netdev_master_upper_dev_link(struct net_device *dev,
 					struct net_device *upper_dev);
+extern int netdev_master_upper_dev_link_private(struct net_device *dev,
+						struct net_device *upper_dev,
+						void *private);
 extern void netdev_upper_dev_unlink(struct net_device *dev,
 				    struct net_device *upper_dev);
+extern void *netdev_lower_dev_get_private_rcu(struct net_device *dev,
+					      struct net_device *lower_dev);
+extern void *netdev_lower_dev_get_private(struct net_device *dev,
+					  struct net_device *lower_dev);
 extern int skb_checksum_help(struct sk_buff *skb);
 extern struct sk_buff *__skb_gso_segment(struct sk_buff *skb,
 	netdev_features_t features, bool tx_path);

net/core/dev.c

@@ -4376,6 +4376,9 @@ struct netdev_adjacent {
 	/* counter for the number of times this device was added to us */
 	u16 ref_nr;
 
+	/* private field for the users */
+	void *private;
+
 	struct list_head list;
 	struct rcu_head rcu;
 };
@@ -4510,7 +4513,7 @@ EXPORT_SYMBOL(netdev_master_upper_dev_get_rcu);
 static int __netdev_adjacent_dev_insert(struct net_device *dev,
 					struct net_device *adj_dev,
 					struct list_head *dev_list,
-					bool master)
+					void *private, bool master)
 {
 	struct netdev_adjacent *adj;
 
@@ -4528,6 +4531,7 @@ static int __netdev_adjacent_dev_insert(struct net_device *dev,
 	adj->dev = adj_dev;
 	adj->master = master;
 	adj->ref_nr = 1;
+	adj->private = private;
 	dev_hold(adj_dev);
 
 	pr_debug("dev_hold for %s, because of link added from %s to %s\n",
@@ -4574,15 +4578,17 @@ int __netdev_adjacent_dev_link_lists(struct net_device *dev,
 				     struct net_device *upper_dev,
 				     struct list_head *up_list,
 				     struct list_head *down_list,
-				     bool master)
+				     void *private, bool master)
 {
 	int ret;
 
-	ret = __netdev_adjacent_dev_insert(dev, upper_dev, up_list, master);
+	ret = __netdev_adjacent_dev_insert(dev, upper_dev, up_list, private,
+					   master);
 	if (ret)
 		return ret;
 
-	ret = __netdev_adjacent_dev_insert(upper_dev, dev, down_list, false);
+	ret = __netdev_adjacent_dev_insert(upper_dev, dev, down_list, private,
+					   false);
 	if (ret) {
 		__netdev_adjacent_dev_remove(dev, upper_dev, up_list);
 		return ret;
@@ -4597,7 +4603,7 @@ int __netdev_adjacent_dev_link(struct net_device *dev,
 	return __netdev_adjacent_dev_link_lists(dev, upper_dev,
 						&dev->all_adj_list.upper,
 						&upper_dev->all_adj_list.lower,
-						false);
+						NULL, false);
 }
 
 void __netdev_adjacent_dev_unlink_lists(struct net_device *dev,
@@ -4619,7 +4625,7 @@ void __netdev_adjacent_dev_unlink(struct net_device *dev,
 
 int __netdev_adjacent_dev_link_neighbour(struct net_device *dev,
 					 struct net_device *upper_dev,
-					 bool master)
+					 void *private, bool master)
 {
 	int ret = __netdev_adjacent_dev_link(dev, upper_dev);
 
@@ -4629,7 +4635,7 @@ int __netdev_adjacent_dev_link_neighbour(struct net_device *dev,
 	ret = __netdev_adjacent_dev_link_lists(dev, upper_dev,
 					       &dev->adj_list.upper,
 					       &upper_dev->adj_list.lower,
-					       master);
+					       private, master);
 	if (ret) {
 		__netdev_adjacent_dev_unlink(dev, upper_dev);
 		return ret;
@@ -4648,7 +4654,8 @@ void __netdev_adjacent_dev_unlink_neighbour(struct net_device *dev,
 }
 
 static int __netdev_upper_dev_link(struct net_device *dev,
-				   struct net_device *upper_dev, bool master)
+				   struct net_device *upper_dev, bool master,
+				   void *private)
 {
 	struct netdev_adjacent *i, *j, *to_i, *to_j;
 	int ret = 0;
@@ -4668,7 +4675,8 @@ static int __netdev_upper_dev_link(struct net_device *dev,
 	if (master && netdev_master_upper_dev_get(dev))
 		return -EBUSY;
 
-	ret = __netdev_adjacent_dev_link_neighbour(dev, upper_dev, master);
+	ret = __netdev_adjacent_dev_link_neighbour(dev, upper_dev, private,
+						   master);
 	if (ret)
 		return ret;
 
@@ -4759,7 +4767,7 @@ static int __netdev_upper_dev_link(struct net_device *dev,
 int netdev_upper_dev_link(struct net_device *dev,
 			  struct net_device *upper_dev)
 {
-	return __netdev_upper_dev_link(dev, upper_dev, false);
+	return __netdev_upper_dev_link(dev, upper_dev, false, NULL);
 }
 EXPORT_SYMBOL(netdev_upper_dev_link);
 
@@ -4777,10 +4785,18 @@ EXPORT_SYMBOL(netdev_upper_dev_link);
 int netdev_master_upper_dev_link(struct net_device *dev,
 				 struct net_device *upper_dev)
 {
-	return __netdev_upper_dev_link(dev, upper_dev, true);
+	return __netdev_upper_dev_link(dev, upper_dev, true, NULL);
 }
 EXPORT_SYMBOL(netdev_master_upper_dev_link);
 
+int netdev_master_upper_dev_link_private(struct net_device *dev,
+					 struct net_device *upper_dev,
+					 void *private)
+{
+	return __netdev_upper_dev_link(dev, upper_dev, true, private);
+}
+EXPORT_SYMBOL(netdev_master_upper_dev_link_private);
+
 /**
  * netdev_upper_dev_unlink - Removes a link to upper device
  * @dev: device
@@ -4818,6 +4834,36 @@ void netdev_upper_dev_unlink(struct net_device *dev,
 }
 EXPORT_SYMBOL(netdev_upper_dev_unlink);
 
+void *netdev_lower_dev_get_private_rcu(struct net_device *dev,
+				       struct net_device *lower_dev)
+{
+	struct netdev_adjacent *lower;
+
+	if (!lower_dev)
+		return NULL;
+	lower = __netdev_find_adj_rcu(dev, lower_dev, &dev->adj_list.lower);
+	if (!lower)
+		return NULL;
+
+	return lower->private;
+}
+EXPORT_SYMBOL(netdev_lower_dev_get_private_rcu);
+
+void *netdev_lower_dev_get_private(struct net_device *dev,
+				   struct net_device *lower_dev)
+{
+	struct netdev_adjacent *lower;
+
+	if (!lower_dev)
+		return NULL;
+	lower = __netdev_find_adj(dev, lower_dev, &dev->adj_list.lower);
+	if (!lower)
+		return NULL;
+
+	return lower->private;
+}
+EXPORT_SYMBOL(netdev_lower_dev_get_private);
+
 static void dev_change_rx_flags(struct net_device *dev, int flags)
 {
 	const struct net_device_ops *ops = dev->netdev_ops;