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/*
* Copyright (c) 2008 Intel Corporation
* Author: Matthew Wilcox <willy@linux.intel.com>
*
* Distributed under the terms of the GNU GPL, version 2
*
* Counting semaphores allow up to <n> tasks to acquire the semaphore
* simultaneously.
*/
#ifndef __LINUX_SEMAPHORE_H
#define __LINUX_SEMAPHORE_H
#include <linux/list.h>
#include <linux/spinlock.h>
/*
* The spinlock controls access to the other members of the semaphore.
* 'count' is decremented by every task which calls down*() and incremented
* by every call to up(). Thus, if it is positive, it indicates how many
* more tasks may acquire the lock. If it is negative, it indicates how
* many tasks are waiting for the lock. Tasks waiting for the lock are
* kept on the wait_list.
*/
struct semaphore {
spinlock_t lock;
int count;
struct list_head wait_list;
};
#define __SEMAPHORE_INITIALIZER(name, n) \
{ \
.lock = __SPIN_LOCK_UNLOCKED((name).lock), \
.count = n, \
.wait_list = LIST_HEAD_INIT((name).wait_list), \
}
#define __DECLARE_SEMAPHORE_GENERIC(name, count) \
struct semaphore name = __SEMAPHORE_INITIALIZER(name, count)
#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1)
static inline void sema_init(struct semaphore *sem, int val)
{
static struct lock_class_key __key;
*sem = (struct semaphore) __SEMAPHORE_INITIALIZER(*sem, val);
lockdep_init_map(&sem->lock.dep_map, "semaphore->lock", &__key, 0);
}
#define init_MUTEX(sem) sema_init(sem, 1)
#define init_MUTEX_LOCKED(sem) sema_init(sem, 0)
/*
* Attempt to acquire the semaphore. If another task is already holding the
* semaphore, sleep until the semaphore is released.
*/
extern void down(struct semaphore *sem);
/*
* As down(), except the sleep may be interrupted by a signal. If it is,
* this function will return -EINTR.
*/
extern int __must_check down_interruptible(struct semaphore *sem);
/*
* As down(), except this function will not sleep. It will return 0 if it
* acquired the semaphore and 1 if the semaphore was contended. This
* function may be called from any context, including interrupt and softirq.
*/
extern int __must_check down_trylock(struct semaphore *sem);
/*
* Release the semaphore. Unlike mutexes, up() may be called from any
* context and even by tasks which have never called down().
*/
extern void up(struct semaphore *sem);
#endif /* __LINUX_SEMAPHORE_H */
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