在新版本的linux内核中，init_mutex已经被废除了，新版本使用sema_init函数。查了一下早期版本的定义：
平台：X86 32位
内核：2.6.30
定义：
Linux/include/linux/semaphore.h
1 /*
2 * Copyright (c) 2008 Intel Corporation
3 * Author: Matthew Wilcox <willy@linux.intel.com>
4 *
5 * Distributed under the terms of the GNU GPL, version 2
6 *
7 * Please see kernel/semaphore.c for documentation of these functions
8 */
9 #ifndef __LINUX_SEMAPHORE_H
10 #define __LINUX_SEMAPHORE_H
11
12 #include <linux/list.h>
13 #include <linux/spinlock.h>
14
15 /* Please don't access any members of this structure directly */
16 struct semaphore {
17 spinlock_t lock;
18 unsigned int count;
19 struct list_head wait_list;
20 };
21
22 #define __SEMAPHORE_INITIALIZER(name, n) \
23 { \
24 .lock = __SPIN_LOCK_UNLOCKED((name).lock), \
25 .count = n, \
26 .wait_list = LIST_HEAD_INIT((name).wait_list), \
27 }
28
29 #define DECLARE_MUTEX(name) \
30 struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1)
31
32 static inline void sema_init(struct semaphore *sem, int val)
33 {
34 static struct lock_class_key __key;
35 *sem = (struct semaphore) __SEMAPHORE_INITIALIZER(*sem, val);
36 lockdep_init_map(&sem->lock.dep_map, "semaphore->lock", &__key, 0);
37 }
38
39 #define init_MUTEX(sem) sema_init(sem, 1)//在最新的版本中没有这两个宏定义了
40 #define init_MUTEX_LOCKED(sem) sema_init(sem, 0)
41
42 extern void down(struct semaphore *sem);
43 extern int __must_check down_interruptible(struct semaphore *sem);
44 extern int __must_check down_killable(struct semaphore *sem);
45 extern int __must_check down_trylock(struct semaphore *sem);
46 extern int __must_check down_timeout(struct semaphore *sem, long jiffies);
47 extern void up(struct semaphore *sem);
48
49 #endif /* __LINUX_SEMAPHORE_H */
50
说明：Init_MUTEX()函数初始化信号量为互斥量。 互斥量为信号量的特例，它可以防止数据被两个不同系统调用读写。
sema_init (sem, 1) 定义为：
平台：X86 32位
内核：3.0.xx
定义：
Linux/include/linux/semaphore.h
1 /*
2 * Copyright (c) 2008 Intel Corporation
3 * Author: Matthew Wilcox <willy@linux.intel.com>
4 *
5 * Distributed under the terms of the GNU GPL, version 2
6 *
7 * Please see kernel/semaphore.c for documentation of these functions
8 */
9 #ifndef __LINUX_SEMAPHORE_H
10 #define __LINUX_SEMAPHORE_H
11
12 #include <linux/list.h>
13 #include <linux/spinlock.h>
14
15 /* Please don't access any members of this structure directly */
16 struct semaphore {
17 spinlock_t lock;
18 unsigned int count;
19 struct list_head wait_list;
20 };
21
22 #define __SEMAPHORE_INITIALIZER(name, n) \
23 { \
24 .lock = __SPIN_LOCK_UNLOCKED((name).lock), \
25 .count = n, \
26 .wait_list = LIST_HEAD_INIT((name).wait_list), \
27 }
28
29 #define DEFINE_SEMAPHORE(name) \
30 struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1)
31
32 static inline void sema_init(struct semaphore *sem, int val)
33 {
34 static struct lock_class_key __key;
35 *sem = (struct semaphore) __SEMAPHORE_INITIALIZER(*sem, val);
36 lockdep_init_map(&sem->lock.dep_map, "semaphore->lock", &__key, 0);
37 }
38
39 extern void down(struct semaphore *sem);
40 extern int __must_check down_interruptible(struct semaphore *sem);
41 extern int __must_check down_killable(struct semaphore *sem);
42 extern int __must_check down_trylock(struct semaphore *sem);
43 extern int __must_check down_timeout(struct semaphore *sem, long jiffies);
44 extern void up(struct semaphore *sem);
45
46 #endif /* __LINUX_SEMAPHORE_H */
47