Linux Kernel  3.7.1
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rwsem-spinlock.h
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1 /* rwsem-spinlock.h: fallback C implementation
2  *
3  * Copyright (c) 2001 David Howells ([email protected]).
4  * - Derived partially from ideas by Andrea Arcangeli <[email protected]>
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  */
23 struct rw_semaphore {
24  __s32 activity;
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 
34 extern void __down_read(struct rw_semaphore *sem);
35 extern int __down_read_trylock(struct rw_semaphore *sem);
36 extern void __down_write(struct rw_semaphore *sem);
37 extern void __down_write_nested(struct rw_semaphore *sem, int subclass);
38 extern int __down_write_trylock(struct rw_semaphore *sem);
39 extern void __up_read(struct rw_semaphore *sem);
40 extern void __up_write(struct rw_semaphore *sem);
41 extern void __downgrade_write(struct rw_semaphore *sem);
42 extern int rwsem_is_locked(struct rw_semaphore *sem);
43 
44 #endif /* __KERNEL__ */
45 #endif /* _LINUX_RWSEM_SPINLOCK_H */