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1da177e4 LT |
1 | /* rwsem.h: R/W semaphores, public interface |
2 | * | |
3 | * Written by David Howells (dhowells@redhat.com). | |
4 | * Derived from asm-i386/semaphore.h | |
5 | */ | |
6 | ||
7 | #ifndef _LINUX_RWSEM_H | |
8 | #define _LINUX_RWSEM_H | |
9 | ||
10 | #include <linux/linkage.h> | |
11 | ||
1da177e4 LT |
12 | #include <linux/types.h> |
13 | #include <linux/kernel.h> | |
c16a87ce TG |
14 | #include <linux/list.h> |
15 | #include <linux/spinlock.h> | |
16 | ||
60063497 | 17 | #include <linux/atomic.h> |
1da177e4 LT |
18 | |
19 | struct rw_semaphore; | |
20 | ||
21 | #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK | |
22 | #include <linux/rwsem-spinlock.h> /* use a generic implementation */ | |
23 | #else | |
1c8ed640 TG |
24 | /* All arch specific implementations share the same struct */ |
25 | struct rw_semaphore { | |
26 | long count; | |
ddb6c9b5 | 27 | raw_spinlock_t wait_lock; |
1c8ed640 TG |
28 | struct list_head wait_list; |
29 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
30 | struct lockdep_map dep_map; | |
31 | #endif | |
32 | }; | |
33 | ||
d1233754 TG |
34 | extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); |
35 | extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); | |
36 | extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); | |
37 | extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); | |
aac72277 | 38 | |
1c8ed640 TG |
39 | /* Include the arch specific part */ |
40 | #include <asm/rwsem.h> | |
41e5887f TG |
41 | |
42 | /* In all implementations count != 0 means locked */ | |
43 | static inline int rwsem_is_locked(struct rw_semaphore *sem) | |
44 | { | |
45 | return sem->count != 0; | |
46 | } | |
47 | ||
1da177e4 LT |
48 | #endif |
49 | ||
12249b34 TG |
50 | /* Common initializer macros and functions */ |
51 | ||
52 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
53 | # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } | |
54 | #else | |
55 | # define __RWSEM_DEP_MAP_INIT(lockname) | |
56 | #endif | |
57 | ||
ddb6c9b5 TG |
58 | #define __RWSEM_INITIALIZER(name) \ |
59 | { RWSEM_UNLOCKED_VALUE, \ | |
60 | __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \ | |
61 | LIST_HEAD_INIT((name).wait_list) \ | |
62 | __RWSEM_DEP_MAP_INIT(name) } | |
12249b34 TG |
63 | |
64 | #define DECLARE_RWSEM(name) \ | |
65 | struct rw_semaphore name = __RWSEM_INITIALIZER(name) | |
66 | ||
67 | extern void __init_rwsem(struct rw_semaphore *sem, const char *name, | |
68 | struct lock_class_key *key); | |
69 | ||
70 | #define init_rwsem(sem) \ | |
71 | do { \ | |
72 | static struct lock_class_key __key; \ | |
73 | \ | |
74 | __init_rwsem((sem), #sem, &__key); \ | |
75 | } while (0) | |
76 | ||
1da177e4 LT |
77 | /* |
78 | * lock for reading | |
79 | */ | |
4ea2176d | 80 | extern void down_read(struct rw_semaphore *sem); |
1da177e4 LT |
81 | |
82 | /* | |
83 | * trylock for reading -- returns 1 if successful, 0 if contention | |
84 | */ | |
4ea2176d | 85 | extern int down_read_trylock(struct rw_semaphore *sem); |
1da177e4 LT |
86 | |
87 | /* | |
88 | * lock for writing | |
89 | */ | |
4ea2176d | 90 | extern void down_write(struct rw_semaphore *sem); |
1da177e4 LT |
91 | |
92 | /* | |
93 | * trylock for writing -- returns 1 if successful, 0 if contention | |
94 | */ | |
4ea2176d | 95 | extern int down_write_trylock(struct rw_semaphore *sem); |
1da177e4 LT |
96 | |
97 | /* | |
98 | * release a read lock | |
99 | */ | |
4ea2176d | 100 | extern void up_read(struct rw_semaphore *sem); |
1da177e4 LT |
101 | |
102 | /* | |
103 | * release a write lock | |
104 | */ | |
4ea2176d | 105 | extern void up_write(struct rw_semaphore *sem); |
1da177e4 LT |
106 | |
107 | /* | |
108 | * downgrade write lock to read lock | |
109 | */ | |
4ea2176d IM |
110 | extern void downgrade_write(struct rw_semaphore *sem); |
111 | ||
112 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
113 | /* | |
5fca80e8 IM |
114 | * nested locking. NOTE: rwsems are not allowed to recurse |
115 | * (which occurs if the same task tries to acquire the same | |
116 | * lock instance multiple times), but multiple locks of the | |
117 | * same lock class might be taken, if the order of the locks | |
118 | * is always the same. This ordering rule can be expressed | |
119 | * to lockdep via the _nested() APIs, but enumerating the | |
120 | * subclasses that are used. (If the nesting relationship is | |
121 | * static then another method for expressing nested locking is | |
122 | * the explicit definition of lock class keys and the use of | |
123 | * lockdep_set_class() at lock initialization time. | |
124 | * See Documentation/lockdep-design.txt for more details.) | |
4ea2176d IM |
125 | */ |
126 | extern void down_read_nested(struct rw_semaphore *sem, int subclass); | |
127 | extern void down_write_nested(struct rw_semaphore *sem, int subclass); | |
4ea2176d IM |
128 | #else |
129 | # define down_read_nested(sem, subclass) down_read(sem) | |
130 | # define down_write_nested(sem, subclass) down_write(sem) | |
4ea2176d | 131 | #endif |
1da177e4 | 132 | |
1da177e4 | 133 | #endif /* _LINUX_RWSEM_H */ |