net: add for_each iterators through neighbour lower link's private

Add a possibility to iterate through netdev_adjacent's private, currently
only for lower neighbours.

Add both RCU and RTNL/other locking variants of iterators, and make the
non-rcu variant to be safe from removal.

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

@@ -2833,6 +2833,23 @@ extern struct net_device *netdev_all_upper_get_next_dev_rcu(struct net_device *d
 	     updev; \
 	     updev = netdev_all_upper_get_next_dev_rcu(dev, &(iter)))
 
+extern void *netdev_lower_get_next_private(struct net_device *dev,
+					   struct list_head **iter);
+extern void *netdev_lower_get_next_private_rcu(struct net_device *dev,
+					       struct list_head **iter);
+
+#define netdev_for_each_lower_private(dev, priv, iter) \
+	for (iter = (dev)->adj_list.lower.next, \
+	     priv = netdev_lower_get_next_private(dev, &(iter)); \
+	     priv; \
+	     priv = netdev_lower_get_next_private(dev, &(iter)))
+
+#define netdev_for_each_lower_private_rcu(dev, priv, iter) \
+	for (iter = &(dev)->adj_list.lower, \
+	     priv = netdev_lower_get_next_private_rcu(dev, &(iter)); \
+	     priv; \
+	     priv = netdev_lower_get_next_private_rcu(dev, &(iter)))
+
 extern struct net_device *netdev_master_upper_dev_get(struct net_device *dev);
 extern struct net_device *netdev_master_upper_dev_get_rcu(struct net_device *dev);
 extern int netdev_upper_dev_link(struct net_device *dev,

net/core/dev.c

@@ -4466,7 +4466,8 @@ struct net_device *netdev_master_upper_dev_get(struct net_device *dev)
 }
 EXPORT_SYMBOL(netdev_master_upper_dev_get);
 
-/* netdev_all_upper_get_next_dev_rcu - Get the next dev from upper list
+/**
+ * netdev_all_upper_get_next_dev_rcu - Get the next dev from upper list
  * @dev: device
  * @iter: list_head ** of the current position
  *
@@ -4491,6 +4492,63 @@ struct net_device *netdev_all_upper_get_next_dev_rcu(struct net_device *dev,
 }
 EXPORT_SYMBOL(netdev_all_upper_get_next_dev_rcu);
 
+/**
+ * netdev_lower_get_next_private - Get the next ->private from the
+ *				   lower neighbour list
+ * @dev: device
+ * @iter: list_head ** of the current position
+ *
+ * Gets the next netdev_adjacent->private from the dev's lower neighbour
+ * list, starting from iter position. The caller must hold either hold the
+ * RTNL lock or its own locking that guarantees that the neighbour lower
+ * list will remain unchainged.
+ */
+void *netdev_lower_get_next_private(struct net_device *dev,
+				    struct list_head **iter)
+{
+	struct netdev_adjacent *lower;
+
+	lower = list_entry(*iter, struct netdev_adjacent, list);
+
+	if (&lower->list == &dev->adj_list.lower)
+		return NULL;
+
+	if (iter)
+		*iter = lower->list.next;
+
+	return lower->private;
+}
+EXPORT_SYMBOL(netdev_lower_get_next_private);
+
+/**
+ * netdev_lower_get_next_private_rcu - Get the next ->private from the
+ *				       lower neighbour list, RCU
+ *				       variant
+ * @dev: device
+ * @iter: list_head ** of the current position
+ *
+ * Gets the next netdev_adjacent->private from the dev's lower neighbour
+ * list, starting from iter position. The caller must hold RCU read lock.
+ */
+void *netdev_lower_get_next_private_rcu(struct net_device *dev,
+					struct list_head **iter)
+{
+	struct netdev_adjacent *lower;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
+	lower = list_entry_rcu((*iter)->next, struct netdev_adjacent, list);
+
+	if (&lower->list == &dev->adj_list.lower)
+		return NULL;
+
+	if (iter)
+		*iter = &lower->list;
+
+	return lower->private;
+}
+EXPORT_SYMBOL(netdev_lower_get_next_private_rcu);
+
 /**
  * netdev_master_upper_dev_get_rcu - Get master upper device
  * @dev: device