[RFC PATCH net-next 1/5] netns: allocate netns ids

@@ -121,6 +121,8 @@ struct net {
 #endif
 	struct net_generic __rcu	*gen;
 
+	struct idr		netns_ids;
+
 	/* Note : following structs are cache line aligned */
 #ifdef CONFIG_XFRM
 	struct netns_xfrm	xfrm;

@@ -289,6 +291,9 @@ static inline struct net *read_pnet(struct net * const *pnet)
 #define __net_initconst	__initconst
 #endif
 
+int net2id(struct net *net, struct net *peer);
+struct net *get_net_from_netnsid(struct net *net, int id);
+
 struct pernet_operations {
 	struct list_head list;
 	int (*init)(struct net *net);

@@ -144,6 +144,30 @@ static void ops_free_list(const struct pernet_operations *ops,
 	}
 }
 
+static int net_eq_idr(int id, void *net, void *peer)
+{
+	return net_eq(net, peer) ? id : 0;
+}
+
+int net2id(struct net *net, struct net *peer)
+{
+	ASSERT_RTNL();
+	return idr_for_each(&(net)->netns_ids, net_eq_idr, (peer)) ? : -ENOENT;
+}
+
+struct net *get_net_from_netnsid(struct net *net, int id)
+{
+	struct net *peer;
+
+	rcu_read_lock();
+	peer = idr_find(&(net)->netns_ids, id);
+	if (peer)
+		get_net(peer);
+	rcu_read_unlock();
+
+	return peer;
+}
+
 /*
  * setup_net runs the initializers for the network namespace object.
  */

@@ -158,6 +182,7 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 	atomic_set(&net->passive, 1);
 	net->dev_base_seq = 1;
 	net->user_ns = user_ns;
+	idr_init(&net->netns_ids);
 
 #ifdef NETNS_REFCNT_DEBUG
 	atomic_set(&net->use_count, 0);

@@ -253,7 +278,20 @@ struct net *copy_net_ns(unsigned long flags,
 	mutex_lock(&net_mutex);
 	rv = setup_net(net, user_ns);
 	if (rv == 0) {
+		struct net *tmp;
+
 		rtnl_lock();
+		idr_alloc_cyclic(&net->netns_ids, net, 1, 0, GFP_KERNEL);
+		for_each_net(tmp) {
+			/* Even if it fails, let's try to get ids for other
+			 * netns.
+			 */
+			idr_alloc_cyclic(&net->netns_ids, tmp, 1, 0,
+					 GFP_KERNEL);
+			idr_alloc_cyclic(&tmp->netns_ids, net, 1, 0,
+					 GFP_KERNEL);
+		}
+
 		list_add_tail_rcu(&net->list, &net_namespace_list);
 		rtnl_unlock();
 	}

@@ -288,6 +326,9 @@ static void cleanup_net(struct work_struct *work)
 	list_for_each_entry(net, &net_kill_list, cleanup_list) {
 		list_del_rcu(&net->list);
 		list_add_tail(&net->exit_list, &net_exit_list);
+		for_each_net(tmp)
+			idr_remove(&tmp->netns_ids, net2id(tmp, net));
+		idr_destroy(&net->netns_ids);
 	}
 	rtnl_unlock();
 

@@ -423,6 +464,7 @@ static int __init net_ns_init(void)
 		panic("Could not setup the initial network namespace");
 
 	rtnl_lock();
+	idr_alloc_cyclic(&init_net.netns_ids, &init_net, 1, 0, GFP_KERNEL);
 	list_add_tail_rcu(&init_net.list, &net_namespace_list);
 	rtnl_unlock();