/*
   *	Routines to manage notifier chains for passing status changes to any
   *	interested routines. We need this instead of hard coded call lists so
   *	that modules can poke their nose into the innards. The network devices
   *	needed them so here they are for the rest of you.
   *
   *				Alan Cox <Alan.Cox@linux.org>
   */
   
  #ifndef _LINUX_NOTIFIER_H
  #define _LINUX_NOTIFIER_H
  #include <linux/errno.h>
  #include <linux/mutex.h>
  #include <linux/rwsem.h>
  #include <linux/srcu.h>
  
  /*
   * Notifier chains are of four types:
   *
   *	Atomic notifier chains: Chain callbacks run in interrupt/atomic
   *		context. Callouts are not allowed to block.
   *	Blocking notifier chains: Chain callbacks run in process context.
   *		Callouts are allowed to block.
   *	Raw notifier chains: There are no restrictions on callbacks,
   *		registration, or unregistration.  All locking and protection
   *		must be provided by the caller.
   *	SRCU notifier chains: A variant of blocking notifier chains, with
   *		the same restrictions.
   *
   * atomic_notifier_chain_register() may be called from an atomic context,
   * but blocking_notifier_chain_register() and srcu_notifier_chain_register()
   * must be called from a process context.  Ditto for the corresponding
   * _unregister() routines.
   *
   * atomic_notifier_chain_unregister(), blocking_notifier_chain_unregister(),
   * and srcu_notifier_chain_unregister() _must not_ be called from within
   * the call chain.
   *
   * SRCU notifier chains are an alternative form of blocking notifier chains.
   * They use SRCU (Sleepable Read-Copy Update) instead of rw-semaphores for
   * protection of the chain links.  This means there is _very_ low overhead
   * in srcu_notifier_call_chain(): no cache bounces and no memory barriers.
   * As compensation, srcu_notifier_chain_unregister() is rather expensive.
   * SRCU notifier chains should be used when the chain will be called very
   * often but notifier_blocks will seldom be removed.  Also, SRCU notifier
   * chains are slightly more difficult to use because they require special
   * runtime initialization.
   */
  
  typedef	int (*notifier_fn_t)(struct notifier_block *nb,
  			unsigned long action, void *data);
  
  struct notifier_block {
  	notifier_fn_t notifier_call;
  	struct notifier_block __rcu *next;
  	int priority;
  };
  
  struct atomic_notifier_head {
  	spinlock_t lock;
  	struct notifier_block __rcu *head;
  };
  
  struct blocking_notifier_head {
  	struct rw_semaphore rwsem;
  	struct notifier_block __rcu *head;
  };
  
  struct raw_notifier_head {
  	struct notifier_block __rcu *head;
  };
  
  struct srcu_notifier_head {
  	struct mutex mutex;
  	struct srcu_struct srcu;
  	struct notifier_block __rcu *head;
  };
  
  #define ATOMIC_INIT_NOTIFIER_HEAD(name) do {	\
  		spin_lock_init(&(name)->lock);	\
  		(name)->head = NULL;		\
  	} while (0)
  #define BLOCKING_INIT_NOTIFIER_HEAD(name) do {	\
  		init_rwsem(&(name)->rwsem);	\
  		(name)->head = NULL;		\
  	} while (0)
  #define RAW_INIT_NOTIFIER_HEAD(name) do {	\
  		(name)->head = NULL;		\
  	} while (0)
  
  /* srcu_notifier_heads must be initialized and cleaned up dynamically */
  extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
  #define srcu_cleanup_notifier_head(name)	\
  		cleanup_srcu_struct(&(name)->srcu);
  
  #define ATOMIC_NOTIFIER_INIT(name) {				\
  		.lock = __SPIN_LOCK_UNLOCKED(name.lock),	\
  		.head = NULL }
  #define BLOCKING_NOTIFIER_INIT(name) {				\
  		.rwsem = __RWSEM_INITIALIZER((name).rwsem),	\
  		.head = NULL }
  #define RAW_NOTIFIER_INIT(name)	{				\
  		.head = NULL }
  /* srcu_notifier_heads cannot be initialized statically */
  
  #define ATOMIC_NOTIFIER_HEAD(name)				\
  	struct atomic_notifier_head name =			\
  		ATOMIC_NOTIFIER_INIT(name)
  #define BLOCKING_NOTIFIER_HEAD(name)				\
  	struct blocking_notifier_head name =			\
  		BLOCKING_NOTIFIER_INIT(name)
  #define RAW_NOTIFIER_HEAD(name)					\
  	struct raw_notifier_head name =				\
  		RAW_NOTIFIER_INIT(name)
  
  #ifdef __KERNEL__
  
  extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
  		struct notifier_block *nb);
  extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
  		struct notifier_block *nb);
  extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
  		struct notifier_block *nb);
  extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
  		struct notifier_block *nb);
  
  extern int blocking_notifier_chain_cond_register(
  		struct blocking_notifier_head *nh,
  		struct notifier_block *nb);
  
  extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
  		struct notifier_block *nb);
  extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
  		struct notifier_block *nb);
  extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
  		struct notifier_block *nb);
  extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
  		struct notifier_block *nb);
  
  extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
  		unsigned long val, void *v);
  extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
  	unsigned long val, void *v, int nr_to_call, int *nr_calls);
  extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
  		unsigned long val, void *v);
  extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
  	unsigned long val, void *v, int nr_to_call, int *nr_calls);
  extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
  		unsigned long val, void *v);
  extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
  	unsigned long val, void *v, int nr_to_call, int *nr_calls);
  extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
  		unsigned long val, void *v);
  extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
  	unsigned long val, void *v, int nr_to_call, int *nr_calls);
  
  #define NOTIFY_DONE		0x0000		/* Don't care */
  #define NOTIFY_OK		0x0001		/* Suits me */
  #define NOTIFY_STOP_MASK	0x8000		/* Don't call further */
  #define NOTIFY_BAD		(NOTIFY_STOP_MASK|0x0002)
  						/* Bad/Veto action */
  /*
   * Clean way to return from the notifier and stop further calls.
   */
  #define NOTIFY_STOP		(NOTIFY_OK|NOTIFY_STOP_MASK)
  
  /* Encapsulate (negative) errno value (in particular, NOTIFY_BAD <=> EPERM). */
  static inline int notifier_from_errno(int err)
  {
  	if (err)
  		return NOTIFY_STOP_MASK | (NOTIFY_OK - err);
  
  	return NOTIFY_OK;
  }
  
  /* Restore (negative) errno value from notify return value. */
  static inline int notifier_to_errno(int ret)
  {
  	ret &= ~NOTIFY_STOP_MASK;
  	return ret > NOTIFY_OK ? NOTIFY_OK - ret : 0;
  }
  
  /*
   *	Declared notifiers so far. I can imagine quite a few more chains
   *	over time (eg laptop power reset chains, reboot chain (to clean 
   *	device units up), device [un]mount chain, module load/unload chain,
   *	low memory chain, screenblank chain (for plug in modular screenblankers) 
   *	VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
   */
   
  /* CPU notfiers are defined in include/linux/cpu.h. */
  
  /* netdevice notifiers are defined in include/linux/netdevice.h */
  
  /* reboot notifiers are defined in include/linux/reboot.h. */
  
  /* Hibernation and suspend events are defined in include/linux/suspend.h. */
  
  /* Virtual Terminal events are defined in include/linux/vt.h. */
  
  #define NETLINK_URELEASE	0x0001	/* Unicast netlink socket released */
  
  /* Console keyboard events.
   * Note: KBD_KEYCODE is always sent before KBD_UNBOUND_KEYCODE, KBD_UNICODE and
   * KBD_KEYSYM. */
  #define KBD_KEYCODE		0x0001 /* Keyboard keycode, called before any other */
  #define KBD_UNBOUND_KEYCODE	0x0002 /* Keyboard keycode which is not bound to any other */
  #define KBD_UNICODE		0x0003 /* Keyboard unicode */
  #define KBD_KEYSYM		0x0004 /* Keyboard keysym */
  #define KBD_POST_KEYSYM		0x0005 /* Called after keyboard keysym interpretation */
  
  extern struct blocking_notifier_head reboot_notifier_list;
  
  #endif /* __KERNEL__ */
  #endif /* _LINUX_NOTIFIER_H */