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/* SPDX-License-Identifier: GPL-2.0 */
* 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 <>
#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.
struct notifier_block;
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 cleaned up dynamically */
extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
#define srcu_cleanup_notifier_head(name) \
#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 }
#define SRCU_NOTIFIER_INIT(name, pcpu) \
{ \
.mutex = __MUTEX_INITIALIZER(name.mutex), \
.head = NULL, \
.srcu = __SRCU_STRUCT_INIT(name.srcu, pcpu), \
#define ATOMIC_NOTIFIER_HEAD(name) \
struct atomic_notifier_head name = \
struct blocking_notifier_head name = \
#define RAW_NOTIFIER_HEAD(name) \
struct raw_notifier_head name = \
#define _SRCU_NOTIFIER_HEAD(name, mod) \
static DEFINE_PER_CPU(struct srcu_data, name##_head_srcu_data); \
mod struct srcu_notifier_head name = \
SRCU_NOTIFIER_INIT(name, name##_head_srcu_data)
#define _SRCU_NOTIFIER_HEAD(name, mod) \
mod struct srcu_notifier_head name = \
#define SRCU_NOTIFIER_HEAD(name) \
_SRCU_NOTIFIER_HEAD(name, /* not static */)
_SRCU_NOTIFIER_HEAD(name, static)
#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 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 blocking_notifier_call_chain(struct blocking_notifier_head *nh,
unsigned long val, void *v);
extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
unsigned long val, void *v);
extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
unsigned long val, void *v);
extern int atomic_notifier_call_chain_robust(struct atomic_notifier_head *nh,
unsigned long val_up, unsigned long val_down, void *v);
extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
unsigned long val_up, unsigned long val_down, void *v);
extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
unsigned long val_up, unsigned long val_down, void *v);
#define NOTIFY_DONE 0x0000 /* Don't care */
#define NOTIFY_OK 0x0001 /* Suits me */
#define NOTIFY_STOP_MASK 0x8000 /* Don't call further */
/* Bad/Veto action */
* Clean way to return from the notifier and stop further calls.
/* 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)
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
#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 */