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  * 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' represents how many more tasks can acquire this semaphore.
  19  * Tasks waiting for the lock are kept on the wait_list.
  20  */
  21 struct semaphore {
  22         spinlock_t              lock;
  23         unsigned int            count;
  24         struct list_head        wait_list;
  25 };
  26
  27 #define __SEMAPHORE_INITIALIZER(name, n)                                \
  28 {                                                                       \
  29         .lock           = __SPIN_LOCK_UNLOCKED((name).lock),            \
  30         .count          = n,                                            \
  31         .wait_list      = LIST_HEAD_INIT((name).wait_list),             \
  32 }
  33
  34 #define __DECLARE_SEMAPHORE_GENERIC(name, count) \
  35         struct semaphore name = __SEMAPHORE_INITIALIZER(name, count)
  36
  37 #define DECLARE_MUTEX(name)     __DECLARE_SEMAPHORE_GENERIC(name, 1)
  38
  39 static inline void sema_init(struct semaphore *sem, int val)
  40 {
  41         static struct lock_class_key __key;
  42         *sem = (struct semaphore) __SEMAPHORE_INITIALIZER(*sem, val);
  43         lockdep_init_map(&sem->lock.dep_map, "semaphore->lock", &__key, 0);
  44 }
  45
  46 #define init_MUTEX(sem)         sema_init(sem, 1)
  47 #define init_MUTEX_LOCKED(sem)  sema_init(sem, 0)
  48
  49 /*
  50  * Attempt to acquire the semaphore.  If another task is already holding the
  51  * semaphore, sleep until the semaphore is released.
  52  */
  53 extern void down(struct semaphore *sem);
  54
  55 /*
  56  * As down(), except the sleep may be interrupted by a signal.  If it is,
  57  * this function will return -EINTR.
  58  */
  59 extern int __must_check down_interruptible(struct semaphore *sem);
  60
  61 /*
  62  * As down_interruptible(), except the sleep may only be interrupted by
  63  * signals which are fatal to this process.
  64  */
  65 extern int __must_check down_killable(struct semaphore *sem);
  66
  67 /*
  68  * As down(), except this function will not sleep.  It will return 0 if it
  69  * acquired the semaphore and 1 if the semaphore was contended.  This
  70  * function may be called from any context, including interrupt and softirq.
  71  */
  72 extern int __must_check down_trylock(struct semaphore *sem);
  73
  74 /*
  75  * As down(), except this function will return -ETIME if it fails to
  76  * acquire the semaphore within the specified number of jiffies.
  77  */
  78 extern int __must_check down_timeout(struct semaphore *sem, long jiffies);
  79
  80 /*
  81  * Release the semaphore.  Unlike mutexes, up() may be called from any
  82  * context and even by tasks which have never called down().
  83  */
  84 extern void up(struct semaphore *sem);
  85
  86 #endif /* __LINUX_SEMAPHORE_H */