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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> | |
1da177e4 LT |
37 | #endif |
38 | ||
1da177e4 LT |
39 | /* |
40 | * lock for reading | |
41 | */ | |
4ea2176d | 42 | extern void down_read(struct rw_semaphore *sem); |
1da177e4 LT |
43 | |
44 | /* | |
45 | * trylock for reading -- returns 1 if successful, 0 if contention | |
46 | */ | |
4ea2176d | 47 | extern int down_read_trylock(struct rw_semaphore *sem); |
1da177e4 LT |
48 | |
49 | /* | |
50 | * lock for writing | |
51 | */ | |
4ea2176d | 52 | extern void down_write(struct rw_semaphore *sem); |
1da177e4 LT |
53 | |
54 | /* | |
55 | * trylock for writing -- returns 1 if successful, 0 if contention | |
56 | */ | |
4ea2176d | 57 | extern int down_write_trylock(struct rw_semaphore *sem); |
1da177e4 LT |
58 | |
59 | /* | |
60 | * release a read lock | |
61 | */ | |
4ea2176d | 62 | extern void up_read(struct rw_semaphore *sem); |
1da177e4 LT |
63 | |
64 | /* | |
65 | * release a write lock | |
66 | */ | |
4ea2176d | 67 | extern void up_write(struct rw_semaphore *sem); |
1da177e4 LT |
68 | |
69 | /* | |
70 | * downgrade write lock to read lock | |
71 | */ | |
4ea2176d IM |
72 | extern void downgrade_write(struct rw_semaphore *sem); |
73 | ||
74 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
75 | /* | |
5fca80e8 IM |
76 | * nested locking. NOTE: rwsems are not allowed to recurse |
77 | * (which occurs if the same task tries to acquire the same | |
78 | * lock instance multiple times), but multiple locks of the | |
79 | * same lock class might be taken, if the order of the locks | |
80 | * is always the same. This ordering rule can be expressed | |
81 | * to lockdep via the _nested() APIs, but enumerating the | |
82 | * subclasses that are used. (If the nesting relationship is | |
83 | * static then another method for expressing nested locking is | |
84 | * the explicit definition of lock class keys and the use of | |
85 | * lockdep_set_class() at lock initialization time. | |
86 | * See Documentation/lockdep-design.txt for more details.) | |
4ea2176d IM |
87 | */ |
88 | extern void down_read_nested(struct rw_semaphore *sem, int subclass); | |
89 | extern void down_write_nested(struct rw_semaphore *sem, int subclass); | |
90 | /* | |
5fca80e8 IM |
91 | * Take/release a lock when not the owner will release it. |
92 | * | |
93 | * [ This API should be avoided as much as possible - the | |
94 | * proper abstraction for this case is completions. ] | |
4ea2176d IM |
95 | */ |
96 | extern void down_read_non_owner(struct rw_semaphore *sem); | |
97 | extern void up_read_non_owner(struct rw_semaphore *sem); | |
98 | #else | |
99 | # define down_read_nested(sem, subclass) down_read(sem) | |
100 | # define down_write_nested(sem, subclass) down_write(sem) | |
101 | # define down_read_non_owner(sem) down_read(sem) | |
102 | # define up_read_non_owner(sem) up_read(sem) | |
103 | #endif | |
1da177e4 | 104 | |
1da177e4 | 105 | #endif /* _LINUX_RWSEM_H */ |