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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 | ||
1da177e4 LT |
17 | #include <asm/system.h> |
18 | #include <asm/atomic.h> | |
19 | ||
20 | struct rw_semaphore; | |
21 | ||
22 | #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK | |
23 | #include <linux/rwsem-spinlock.h> /* use a generic implementation */ | |
24 | #else | |
1c8ed640 TG |
25 | /* All arch specific implementations share the same struct */ |
26 | struct rw_semaphore { | |
27 | long count; | |
28 | spinlock_t wait_lock; | |
29 | struct list_head wait_list; | |
30 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
31 | struct lockdep_map dep_map; | |
32 | #endif | |
33 | }; | |
34 | ||
35 | /* Include the arch specific part */ | |
36 | #include <asm/rwsem.h> | |
41e5887f TG |
37 | |
38 | /* In all implementations count != 0 means locked */ | |
39 | static inline int rwsem_is_locked(struct rw_semaphore *sem) | |
40 | { | |
41 | return sem->count != 0; | |
42 | } | |
43 | ||
1da177e4 LT |
44 | #endif |
45 | ||
12249b34 TG |
46 | /* Common initializer macros and functions */ |
47 | ||
48 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
49 | # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } | |
50 | #else | |
51 | # define __RWSEM_DEP_MAP_INIT(lockname) | |
52 | #endif | |
53 | ||
54 | #define __RWSEM_INITIALIZER(name) \ | |
55 | { RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED(name.wait_lock), \ | |
56 | LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) } | |
57 | ||
58 | #define DECLARE_RWSEM(name) \ | |
59 | struct rw_semaphore name = __RWSEM_INITIALIZER(name) | |
60 | ||
61 | extern void __init_rwsem(struct rw_semaphore *sem, const char *name, | |
62 | struct lock_class_key *key); | |
63 | ||
64 | #define init_rwsem(sem) \ | |
65 | do { \ | |
66 | static struct lock_class_key __key; \ | |
67 | \ | |
68 | __init_rwsem((sem), #sem, &__key); \ | |
69 | } while (0) | |
70 | ||
1da177e4 LT |
71 | /* |
72 | * lock for reading | |
73 | */ | |
4ea2176d | 74 | extern void down_read(struct rw_semaphore *sem); |
1da177e4 LT |
75 | |
76 | /* | |
77 | * trylock for reading -- returns 1 if successful, 0 if contention | |
78 | */ | |
4ea2176d | 79 | extern int down_read_trylock(struct rw_semaphore *sem); |
1da177e4 LT |
80 | |
81 | /* | |
82 | * lock for writing | |
83 | */ | |
4ea2176d | 84 | extern void down_write(struct rw_semaphore *sem); |
1da177e4 LT |
85 | |
86 | /* | |
87 | * trylock for writing -- returns 1 if successful, 0 if contention | |
88 | */ | |
4ea2176d | 89 | extern int down_write_trylock(struct rw_semaphore *sem); |
1da177e4 LT |
90 | |
91 | /* | |
92 | * release a read lock | |
93 | */ | |
4ea2176d | 94 | extern void up_read(struct rw_semaphore *sem); |
1da177e4 LT |
95 | |
96 | /* | |
97 | * release a write lock | |
98 | */ | |
4ea2176d | 99 | extern void up_write(struct rw_semaphore *sem); |
1da177e4 LT |
100 | |
101 | /* | |
102 | * downgrade write lock to read lock | |
103 | */ | |
4ea2176d IM |
104 | extern void downgrade_write(struct rw_semaphore *sem); |
105 | ||
106 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
107 | /* | |
5fca80e8 IM |
108 | * nested locking. NOTE: rwsems are not allowed to recurse |
109 | * (which occurs if the same task tries to acquire the same | |
110 | * lock instance multiple times), but multiple locks of the | |
111 | * same lock class might be taken, if the order of the locks | |
112 | * is always the same. This ordering rule can be expressed | |
113 | * to lockdep via the _nested() APIs, but enumerating the | |
114 | * subclasses that are used. (If the nesting relationship is | |
115 | * static then another method for expressing nested locking is | |
116 | * the explicit definition of lock class keys and the use of | |
117 | * lockdep_set_class() at lock initialization time. | |
118 | * See Documentation/lockdep-design.txt for more details.) | |
4ea2176d IM |
119 | */ |
120 | extern void down_read_nested(struct rw_semaphore *sem, int subclass); | |
121 | extern void down_write_nested(struct rw_semaphore *sem, int subclass); | |
122 | /* | |
5fca80e8 IM |
123 | * Take/release a lock when not the owner will release it. |
124 | * | |
125 | * [ This API should be avoided as much as possible - the | |
126 | * proper abstraction for this case is completions. ] | |
4ea2176d IM |
127 | */ |
128 | extern void down_read_non_owner(struct rw_semaphore *sem); | |
129 | extern void up_read_non_owner(struct rw_semaphore *sem); | |
130 | #else | |
131 | # define down_read_nested(sem, subclass) down_read(sem) | |
132 | # define down_write_nested(sem, subclass) down_write(sem) | |
133 | # define down_read_non_owner(sem) down_read(sem) | |
134 | # define up_read_non_owner(sem) up_read(sem) | |
135 | #endif | |
1da177e4 | 136 | |
1da177e4 | 137 | #endif /* _LINUX_RWSEM_H */ |