/*
   * linux/ipc/ipcns_notifier.c
   * Copyright (C) 2007 BULL SA. Nadia Derbey
   *
   * Notification mechanism for ipc namespaces:
   * The callback routine registered in the memory chain invokes the ipcns
   * notifier chain with the IPCNS_MEMCHANGED event.
   * Each callback routine registered in the ipcns namespace recomputes msgmni
   * for the owning namespace.
   */
  
  #include <linux/msg.h>
  #include <linux/rcupdate.h>
  #include <linux/notifier.h>
  #include <linux/nsproxy.h>
  #include <linux/ipc_namespace.h>
  
  #include "util.h"
  
  
  
  static BLOCKING_NOTIFIER_HEAD(ipcns_chain);
  
  
  static int ipcns_callback(struct notifier_block *self,
  				unsigned long action, void *arg)
  {
  	struct ipc_namespace *ns;
  
  	switch (action) {
  	case IPCNS_MEMCHANGED:   /* amount of lowmem has changed */

  	case IPCNS_CREATED:
  	case IPCNS_REMOVED:

  		/*
  		 * It's time to recompute msgmni
  		 */
  		ns = container_of(self, struct ipc_namespace, ipcns_nb);
  		/*
  		 * No need to get a reference on the ns: the 1st job of
  		 * free_ipc_ns() is to unregister the callback routine.
  		 * blocking_notifier_chain_unregister takes the wr lock to do
  		 * it.
  		 * When this callback routine is called the rd lock is held by
  		 * blocking_notifier_call_chain.
  		 * So the ipc ns cannot be freed while we are here.
  		 */
  		recompute_msgmni(ns);
  		break;
  	default:
  		break;
  	}
  
  	return NOTIFY_OK;
  }
  
  int register_ipcns_notifier(struct ipc_namespace *ns)
  {
  	memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
  	ns->ipcns_nb.notifier_call = ipcns_callback;
  	ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
  	return blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
  }

  int cond_register_ipcns_notifier(struct ipc_namespace *ns)
  {
  	memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
  	ns->ipcns_nb.notifier_call = ipcns_callback;
  	ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
  	return blocking_notifier_chain_cond_register(&ipcns_chain,
  							&ns->ipcns_nb);
  }

  int unregister_ipcns_notifier(struct ipc_namespace *ns)
  {
  	return blocking_notifier_chain_unregister(&ipcns_chain,
  						&ns->ipcns_nb);
  }
  
  int ipcns_notify(unsigned long val)
  {
  	return blocking_notifier_call_chain(&ipcns_chain, val, NULL);
  }