1 /*
2  * generic net pointers
3  */
4 
5 #ifndef __NET_GENERIC_H__
6 #define __NET_GENERIC_H__
7 
8 #include <linux/rcupdate.h>
9 
10 /*
11  * Generic net pointers are to be used by modules to put some private
12  * stuff on the struct net without explicit struct net modification
13  *
14  * The rules are simple:
15  * 1. set pernet_operations->id.  After register_pernet_device you
16  *    will have the id of your private pointer.
17  * 2. set pernet_operations->size to have the code allocate and free
18  *    a private structure pointed to from struct net.
19  * 3. do not change this pointer while the net is alive;
20  * 4. do not try to have any private reference on the net_generic object.
21  *
22  * After accomplishing all of the above, the private pointer can be
23  * accessed with the net_generic() call.
24  */
25 
26 struct net_generic {
27 	unsigned int len;
28 	struct rcu_head rcu;
29 
30 	void *ptr[0];
31 };
32 
net_generic(const struct net * net,int id)33 static inline void *net_generic(const struct net *net, int id)
34 {
35 	struct net_generic *ng;
36 	void *ptr;
37 
38 	rcu_read_lock();
39 	ng = rcu_dereference(net->gen);
40 	BUG_ON(id == 0 || id > ng->len);
41 	ptr = ng->ptr[id - 1];
42 	rcu_read_unlock();
43 
44 	return ptr;
45 }
46 #endif
47