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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 | * Counting semaphores allow up to <n> tasks to acquire the semaphore | |
8 | * simultaneously. | |
9 | */ | |
10 | #ifndef __LINUX_SEMAPHORE_H | |
11 | #define __LINUX_SEMAPHORE_H | |
12 | ||
13 | #include <linux/list.h> | |
14 | #include <linux/spinlock.h> | |
15 | ||
16 | /* | |
17 | * The spinlock controls access to the other members of the semaphore. | |
18 | * 'count' is decremented by every task which calls down*() and incremented | |
19 | * by every call to up(). Thus, if it is positive, it indicates how many | |
20 | * more tasks may acquire the lock. If it is negative, it indicates how | |
21 | * many tasks are waiting for the lock. Tasks waiting for the lock are | |
22 | * kept on the wait_list. | |
23 | */ | |
24 | struct semaphore { | |
25 | spinlock_t lock; | |
26 | int count; | |
27 | struct list_head wait_list; | |
28 | }; | |
29 | ||
30 | #define __SEMAPHORE_INITIALIZER(name, n) \ | |
31 | { \ | |
32 | .lock = __SPIN_LOCK_UNLOCKED((name).lock), \ | |
33 | .count = n, \ | |
34 | .wait_list = LIST_HEAD_INIT((name).wait_list), \ | |
35 | } | |
36 | ||
37 | #define __DECLARE_SEMAPHORE_GENERIC(name, count) \ | |
38 | struct semaphore name = __SEMAPHORE_INITIALIZER(name, count) | |
39 | ||
40 | #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1) | |
41 | ||
42 | static inline void sema_init(struct semaphore *sem, int val) | |
43 | { | |
44 | static struct lock_class_key __key; | |
45 | *sem = (struct semaphore) __SEMAPHORE_INITIALIZER(*sem, val); | |
46 | lockdep_init_map(&sem->lock.dep_map, "semaphore->lock", &__key, 0); | |
47 | } | |
48 | ||
49 | #define init_MUTEX(sem) sema_init(sem, 1) | |
50 | #define init_MUTEX_LOCKED(sem) sema_init(sem, 0) | |
51 | ||
52 | /* | |
53 | * Attempt to acquire the semaphore. If another task is already holding the | |
54 | * semaphore, sleep until the semaphore is released. | |
55 | */ | |
56 | extern void down(struct semaphore *sem); | |
57 | ||
58 | /* | |
59 | * As down(), except the sleep may be interrupted by a signal. If it is, | |
60 | * this function will return -EINTR. | |
61 | */ | |
62 | extern int __must_check down_interruptible(struct semaphore *sem); | |
63 | ||
64 | /* | |
65 | * As down(), except this function will not sleep. It will return 0 if it | |
66 | * acquired the semaphore and 1 if the semaphore was contended. This | |
67 | * function may be called from any context, including interrupt and softirq. | |
68 | */ | |
69 | extern int __must_check down_trylock(struct semaphore *sem); | |
70 | ||
71 | /* | |
72 | * Release the semaphore. Unlike mutexes, up() may be called from any | |
73 | * context and even by tasks which have never called down(). | |
74 | */ | |
75 | extern void up(struct semaphore *sem); | |
76 | ||
77 | #endif /* __LINUX_SEMAPHORE_H */ |