最近发生一些事情，心情有所波动，没有更新，今天更新一下消息通知链。爷爷去世前的那个晚上正在看linux内核的消息通知链，今天，爷爷整整去世一个月了，前几天一直梦到爷爷，也奇怪，梦中我知道爷爷已经走了，但是还是显得那么自然。

通知链简单结构为：

linux内核中的消息通知链分为：

原始通知链
原子通知链（不受线程机制影响）
加锁通知链

他们的结构分别为：


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;
};

当然提供了一些宏

#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)

下面给出原始文件

notifier.h include\linux 8409 2/20/2019 9

/* 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 <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.*/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)    \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 }#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 =            \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 CONFIG_TREE_SRCU
#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)#else
#define _SRCU_NOTIFIER_HEAD(name, mod)              \mod struct srcu_notifier_head name =          \SRCU_NOTIFIER_INIT(name, name)#endif#define SRCU_NOTIFIER_HEAD(name)               \_SRCU_NOTIFIER_HEAD(name, /* not static */)#define SRCU_NOTIFIER_HEAD_STATIC(name)             \_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 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 */

对应的去查看.c文件就行了，需要注意的一点是，如果想要讲代码复制出来自己使用，可能只能弄出原始通知链（亲测可用有效），其他的则调用了大量的内核中的接口，不容易被“抠”出来。

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notifier.h include\linux 8409 2/20/2019 9

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