Line data Source code
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 1 :
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 */
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