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