net: Avoid extra wakeups of threads blocked in wait_for_packet()
[linux-2.6.git] / include / linux / rwsem-spinlock.h
1 /* rwsem-spinlock.h: fallback C implementation
2  *
3  * Copyright (c) 2001   David Howells (dhowells@redhat.com).
4  * - Derived partially from ideas by Andrea Arcangeli <andrea@suse.de>
5  * - Derived also from comments by Linus
6  */
7
8 #ifndef _LINUX_RWSEM_SPINLOCK_H
9 #define _LINUX_RWSEM_SPINLOCK_H
10
11 #ifndef _LINUX_RWSEM_H
12 #error "please don't include linux/rwsem-spinlock.h directly, use linux/rwsem.h instead"
13 #endif
14
15 #include <linux/spinlock.h>
16 #include <linux/list.h>
17
18 #ifdef __KERNEL__
19
20 #include <linux/types.h>
21
22 struct rwsem_waiter;
23
24 /*
25  * the rw-semaphore definition
26  * - if activity is 0 then there are no active readers or writers
27  * - if activity is +ve then that is the number of active readers
28  * - if activity is -1 then there is one active writer
29  * - if wait_list is not empty, then there are processes waiting for the semaphore
30  */
31 struct rw_semaphore {
32         __s32                   activity;
33         spinlock_t              wait_lock;
34         struct list_head        wait_list;
35 #ifdef CONFIG_DEBUG_LOCK_ALLOC
36         struct lockdep_map dep_map;
37 #endif
38 };
39
40 #ifdef CONFIG_DEBUG_LOCK_ALLOC
41 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
42 #else
43 # define __RWSEM_DEP_MAP_INIT(lockname)
44 #endif
45
46 #define __RWSEM_INITIALIZER(name) \
47 { 0, __SPIN_LOCK_UNLOCKED(name.wait_lock), LIST_HEAD_INIT((name).wait_list) \
48   __RWSEM_DEP_MAP_INIT(name) }
49
50 #define DECLARE_RWSEM(name) \
51         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
52
53 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
54                          struct lock_class_key *key);
55
56 #define init_rwsem(sem)                                         \
57 do {                                                            \
58         static struct lock_class_key __key;                     \
59                                                                 \
60         __init_rwsem((sem), #sem, &__key);                      \
61 } while (0)
62
63 extern void __down_read(struct rw_semaphore *sem);
64 extern int __down_read_trylock(struct rw_semaphore *sem);
65 extern void __down_write(struct rw_semaphore *sem);
66 extern void __down_write_nested(struct rw_semaphore *sem, int subclass);
67 extern int __down_write_trylock(struct rw_semaphore *sem);
68 extern void __up_read(struct rw_semaphore *sem);
69 extern void __up_write(struct rw_semaphore *sem);
70 extern void __downgrade_write(struct rw_semaphore *sem);
71
72 static inline int rwsem_is_locked(struct rw_semaphore *sem)
73 {
74         return (sem->activity != 0);
75 }
76
77 #endif /* __KERNEL__ */
78 #endif /* _LINUX_RWSEM_SPINLOCK_H */