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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> | |
14 | #include <asm/system.h> | |
15 | #include <asm/atomic.h> | |
16 | ||
17 | struct rw_semaphore; | |
18 | ||
19 | #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK | |
20 | #include <linux/rwsem-spinlock.h> /* use a generic implementation */ | |
21 | #else | |
22 | #include <asm/rwsem.h> /* use an arch-specific implementation */ | |
23 | #endif | |
24 | ||
1da177e4 LT |
25 | /* |
26 | * lock for reading | |
27 | */ | |
4ea2176d | 28 | extern void down_read(struct rw_semaphore *sem); |
1da177e4 LT |
29 | |
30 | /* | |
31 | * trylock for reading -- returns 1 if successful, 0 if contention | |
32 | */ | |
4ea2176d | 33 | extern int down_read_trylock(struct rw_semaphore *sem); |
1da177e4 LT |
34 | |
35 | /* | |
36 | * lock for writing | |
37 | */ | |
4ea2176d | 38 | extern void down_write(struct rw_semaphore *sem); |
1da177e4 LT |
39 | |
40 | /* | |
41 | * trylock for writing -- returns 1 if successful, 0 if contention | |
42 | */ | |
4ea2176d | 43 | extern int down_write_trylock(struct rw_semaphore *sem); |
1da177e4 LT |
44 | |
45 | /* | |
46 | * release a read lock | |
47 | */ | |
4ea2176d | 48 | extern void up_read(struct rw_semaphore *sem); |
1da177e4 LT |
49 | |
50 | /* | |
51 | * release a write lock | |
52 | */ | |
4ea2176d | 53 | extern void up_write(struct rw_semaphore *sem); |
1da177e4 LT |
54 | |
55 | /* | |
56 | * downgrade write lock to read lock | |
57 | */ | |
4ea2176d IM |
58 | extern void downgrade_write(struct rw_semaphore *sem); |
59 | ||
60 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
61 | /* | |
5fca80e8 IM |
62 | * nested locking. NOTE: rwsems are not allowed to recurse |
63 | * (which occurs if the same task tries to acquire the same | |
64 | * lock instance multiple times), but multiple locks of the | |
65 | * same lock class might be taken, if the order of the locks | |
66 | * is always the same. This ordering rule can be expressed | |
67 | * to lockdep via the _nested() APIs, but enumerating the | |
68 | * subclasses that are used. (If the nesting relationship is | |
69 | * static then another method for expressing nested locking is | |
70 | * the explicit definition of lock class keys and the use of | |
71 | * lockdep_set_class() at lock initialization time. | |
72 | * See Documentation/lockdep-design.txt for more details.) | |
4ea2176d IM |
73 | */ |
74 | extern void down_read_nested(struct rw_semaphore *sem, int subclass); | |
75 | extern void down_write_nested(struct rw_semaphore *sem, int subclass); | |
76 | /* | |
5fca80e8 IM |
77 | * Take/release a lock when not the owner will release it. |
78 | * | |
79 | * [ This API should be avoided as much as possible - the | |
80 | * proper abstraction for this case is completions. ] | |
4ea2176d IM |
81 | */ |
82 | extern void down_read_non_owner(struct rw_semaphore *sem); | |
83 | extern void up_read_non_owner(struct rw_semaphore *sem); | |
84 | #else | |
85 | # define down_read_nested(sem, subclass) down_read(sem) | |
86 | # define down_write_nested(sem, subclass) down_write(sem) | |
87 | # define down_read_non_owner(sem) down_read(sem) | |
88 | # define up_read_non_owner(sem) up_read(sem) | |
89 | #endif | |
1da177e4 | 90 | |
1da177e4 | 91 | #endif /* _LINUX_RWSEM_H */ |