include/net/netns/generic.h

   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
  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         BUG_ON(!ptr);
  45         return ptr;
  46 }
  47 #endif