include/net/netns/generic.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * generic net pointers
   4  */
   5
   6 #ifndef __NET_GENERIC_H__
   7 #define __NET_GENERIC_H__
   8
   9 #include <linux/bug.h>
  10 #include <linux/rcupdate.h>
  11
  12 /*
  13  * Generic net pointers are to be used by modules to put some private
  14  * stuff on the struct net without explicit struct net modification
  15  *
  16  * The rules are simple:
  17  * 1. set pernet_operations->id.  After register_pernet_device you
  18  *    will have the id of your private pointer.
  19  * 2. set pernet_operations->size to have the code allocate and free
  20  *    a private structure pointed to from struct net.
  21  * 3. do not change this pointer while the net is alive;
  22  * 4. do not try to have any private reference on the net_generic object.
  23  *
  24  * After accomplishing all of the above, the private pointer can be
  25  * accessed with the net_generic() call.
  26  */
  27
  28 struct net_generic {
  29         union {
  30                 struct {
  31                         unsigned int len;
  32                         struct rcu_head rcu;
  33                 } s;
  34
  35                 void *ptr[0];
  36         };
  37 };
  38
  39 static inline void *net_generic(const struct net *net, unsigned int id)
  40 {
  41         struct net_generic *ng;
  42         void *ptr;
  43
  44         rcu_read_lock();
  45         ng = rcu_dereference(net->gen);
  46         ptr = ng->ptr[id];
  47         rcu_read_unlock();
  48
  49         return ptr;
  50 }
  51 #endif