/include/linux/rwsem-spinlock.h

 1/* rwsem-spinlock.h: fallback C implementation
 2 *
 3 * Copyright (c) 2001   David Howells (dhowells@redhat.com).
 4 * - Derived partially from ideas by Andrea Arcangeli <andrea@suse.de>
 5 * - Derived also from comments by Linus
 6 */
 7
 8#ifndef _LINUX_RWSEM_SPINLOCK_H
 9#define _LINUX_RWSEM_SPINLOCK_H
10
11#ifndef _LINUX_RWSEM_H
12#error "please don't include linux/rwsem-spinlock.h directly, use linux/rwsem.h instead"
13#endif
14
15#ifdef __KERNEL__
16/*
17 * the rw-semaphore definition
18 * - if activity is 0 then there are no active readers or writers
19 * - if activity is +ve then that is the number of active readers
20 * - if activity is -1 then there is one active writer
21 * - if wait_list is not empty, then there are processes waiting for the semaphore
22 */
23struct rw_semaphore {
24	__s32			activity;
25	raw_spinlock_t		wait_lock;
26	struct list_head	wait_list;
27#ifdef CONFIG_DEBUG_LOCK_ALLOC
28	struct lockdep_map dep_map;
29#endif
30};
31
32#define RWSEM_UNLOCKED_VALUE		0x00000000
33
34extern void __down_read(struct rw_semaphore *sem);
35extern int __down_read_trylock(struct rw_semaphore *sem);
36extern void __down_write(struct rw_semaphore *sem);
37extern void __down_write_nested(struct rw_semaphore *sem, int subclass);
38extern int __down_write_trylock(struct rw_semaphore *sem);
39extern void __up_read(struct rw_semaphore *sem);
40extern void __up_write(struct rw_semaphore *sem);
41extern void __downgrade_write(struct rw_semaphore *sem);
42extern int rwsem_is_locked(struct rw_semaphore *sem);
43
44#endif /* __KERNEL__ */
45#endif /* _LINUX_RWSEM_SPINLOCK_H */