[NETNS]: The net-subsys IDs generator.

To make some per-net generic pointers, we need some way to address
them, i.e. - IDs. This is simple IDA-based IDs generator for pernet
subsystems.

Addressing questions about potential checkpoint/restart problems: 
these IDs are "lite-offsets" within the net structure and are by no 
means supposed to be exported to the userspace.

Since it will be used in the nearest future by devices only (tun,
vlan, tunnels, bridge, etc), I make it resemble the functionality
of register_pernet_device().

The new ids is stored in the *id pointer _before_ calling the init
callback to make this id available in this callback.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index e2aee26..72fad1a 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -185,6 +185,8 @@
 extern void unregister_pernet_subsys(struct pernet_operations *);
 extern int register_pernet_device(struct pernet_operations *);
 extern void unregister_pernet_device(struct pernet_operations *);
+extern int register_pernet_gen_device(int *id, struct pernet_operations *);
+extern void unregister_pernet_gen_device(int id, struct pernet_operations *);
 
 struct ctl_path;
 struct ctl_table;