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' 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 */