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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 | |
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 | |
25 | /* |
26 | * lock for reading |
27 | */ |
28 | extern void down_read(struct rw_semaphore *sem); |
29 | |
30 | /* |
31 | * trylock for reading -- returns 1 if successful, 0 if contention |
32 | */ |
33 | extern int down_read_trylock(struct rw_semaphore *sem); |
34 | |
35 | /* |
36 | * lock for writing |
37 | */ |
38 | extern void down_write(struct rw_semaphore *sem); |
39 | |
40 | /* |
41 | * trylock for writing -- returns 1 if successful, 0 if contention |
42 | */ |
43 | extern int down_write_trylock(struct rw_semaphore *sem); |
44 | |
45 | /* |
46 | * release a read lock |
47 | */ |
48 | extern void up_read(struct rw_semaphore *sem); |
49 | |
50 | /* |
51 | * release a write lock |
52 | */ |
53 | extern void up_write(struct rw_semaphore *sem); |
54 | |
55 | /* |
56 | * downgrade write lock to read lock |
57 | */ |
58 | extern void downgrade_write(struct rw_semaphore *sem); |
59 | |
60 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
61 | /* |
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.) |
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 | /* |
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. ] |
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 |
90 | |
91 | #endif /* _LINUX_RWSEM_H */ |
92 |
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