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         case IPCNS_CREATED:
  33         case IPCNS_REMOVED:
  34                 /*
  35                  * It's time to recompute msgmni
  36                  */
  37                 ns = container_of(self, struct ipc_namespace, ipcns_nb);
  38                 /*
  39                  * No need to get a reference on the ns: the 1st job of
  40                  * free_ipc_ns() is to unregister the callback routine.
  41                  * blocking_notifier_chain_unregister takes the wr lock to do
  42                  * it.
  43                  * When this callback routine is called the rd lock is held by
  44                  * blocking_notifier_call_chain.
  45                  * So the ipc ns cannot be freed while we are here.
  46                  */
  47                 recompute_msgmni(ns);
  48                 break;
  49         default:
  50                 break;
  51         }
  52
  53         return NOTIFY_OK;
  54 }
  55
  56 int register_ipcns_notifier(struct ipc_namespace *ns)
  57 {
  58         int rc;
  59
  60         memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
  61         ns->ipcns_nb.notifier_call = ipcns_callback;
  62         ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
  63         rc = blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
  64         if (!rc)
  65                 ns->auto_msgmni = 1;
  66         return rc;
  67 }
  68
  69 int cond_register_ipcns_notifier(struct ipc_namespace *ns)
  70 {
  71         int rc;
  72
  73         memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
  74         ns->ipcns_nb.notifier_call = ipcns_callback;
  75         ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
  76         rc = blocking_notifier_chain_cond_register(&ipcns_chain,
  77                                                         &ns->ipcns_nb);
  78         if (!rc)
  79                 ns->auto_msgmni = 1;
  80         return rc;
  81 }
  82
  83 void unregister_ipcns_notifier(struct ipc_namespace *ns)
  84 {
  85         blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
  86         ns->auto_msgmni = 0;
  87 }
  88
  89 int ipcns_notify(unsigned long val)
  90 {
  91         return blocking_notifier_call_chain(&ipcns_chain, val, NULL);
  92 }