ipc/ipcns_notifier.c

   1 /*
   2  * linux/ipc/ipcns_notifier.c
   3  * Copyright (C) 2007 BULL SA. Nadia Derbey
   4  *
   5  * Notification mechanism for ipc namespaces:
   6  * The callback routine registered in the memory chain invokes the ipcns
   7  * notifier chain with the IPCNS_MEMCHANGED event.
   8  * Each callback routine registered in the ipcns namespace recomputes msgmni
   9  * for the owning namespace.
  10  */
  11
  12 #include <linux/msg.h>
  13 #include <linux/rcupdate.h>
  14 #include <linux/notifier.h>
  15 #include <linux/nsproxy.h>
  16 #include <linux/ipc_namespace.h>
  17
  18 #include "util.h"
  19
  20
  21
  22 static BLOCKING_NOTIFIER_HEAD(ipcns_chain);
  23
  24
  25 static int ipcns_callback(struct notifier_block *self,
  26                                 unsigned long action, void *arg)
  27 {
  28         struct ipc_namespace *ns;
  29
  30         switch (action) {
  31         case IPCNS_MEMCHANGED:   /* amount of lowmem has changed */
  32                 /*
  33                  * It's time to recompute msgmni
  34                  */
  35                 ns = container_of(self, struct ipc_namespace, ipcns_nb);
  36                 /*
  37                  * No need to get a reference on the ns: the 1st job of
  38                  * free_ipc_ns() is to unregister the callback routine.
  39                  * blocking_notifier_chain_unregister takes the wr lock to do
  40                  * it.
  41                  * When this callback routine is called the rd lock is held by
  42                  * blocking_notifier_call_chain.
  43                  * So the ipc ns cannot be freed while we are here.
  44                  */
  45                 recompute_msgmni(ns);
  46                 break;
  47         default:
  48                 break;
  49         }
  50
  51         return NOTIFY_OK;
  52 }
  53
  54 int register_ipcns_notifier(struct ipc_namespace *ns)
  55 {
  56         memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
  57         ns->ipcns_nb.notifier_call = ipcns_callback;
  58         ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
  59         return blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
  60 }
  61
  62 int unregister_ipcns_notifier(struct ipc_namespace *ns)
  63 {
  64         return blocking_notifier_chain_unregister(&ipcns_chain,
  65                                                 &ns->ipcns_nb);
  66 }
  67
  68 int ipcns_notify(unsigned long val)
  69 {
  70         return blocking_notifier_call_chain(&ipcns_chain, val, NULL);
  71 }