1 /* 2 * Copyright (c) 2008 Intel Corporation 3 * Author: Matthew Wilcox <[email protected]> 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_interruptible(), except the sleep may only be interrupted by 66 * signals which are fatal to this process. 67 */ 68 extern int __must_check down_killable(struct semaphore *sem); 69 70 /* 71 * As down(), except this function will not sleep. It will return 0 if it 72 * acquired the semaphore and 1 if the semaphore was contended. This 73 * function may be called from any context, including interrupt and softirq. 74 */ 75 extern int __must_check down_trylock(struct semaphore *sem); 76 77 /* 78 * Release the semaphore. Unlike mutexes, up() may be called from any 79 * context and even by tasks which have never called down(). 80 */ 81 extern void up(struct semaphore *sem); 82 83 #endif /* __LINUX_SEMAPHORE_H */ 84