1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
|
#ifndef _LINUX_CALL_ONCE_H
#define _LINUX_CALL_ONCE_H
#include <linux/types.h>
#include <linux/mutex.h>
#define ONCE_NOT_STARTED 0
#define ONCE_RUNNING 1
#define ONCE_COMPLETED 2
struct once {
atomic_t state;
struct mutex lock;
};
static inline void __once_init(struct once *once, const char *name,
struct lock_class_key *key)
{
atomic_set(&once->state, ONCE_NOT_STARTED);
__mutex_init(&once->lock, name, key);
}
#define once_init(once) \
do { \
static struct lock_class_key __key; \
__once_init((once), #once, &__key); \
} while (0)
/*
* call_once - Ensure a function has been called exactly once
*
* @once: Tracking struct
* @cb: Function to be called
*
* If @once has never completed successfully before, call @cb and, if
* it returns a zero or positive value, mark @once as completed. Return
* the value returned by @cb
*
* If @once has completed succesfully before, return 0.
*
* The call to @cb is implicitly surrounded by a mutex, though for
* efficiency the * function avoids taking it after the first call.
*/
static inline int call_once(struct once *once, int (*cb)(struct once *))
{
int r, state;
/* Pairs with atomic_set_release() below. */
if (atomic_read_acquire(&once->state) == ONCE_COMPLETED)
return 0;
guard(mutex)(&once->lock);
state = atomic_read(&once->state);
if (unlikely(state != ONCE_NOT_STARTED))
return WARN_ON_ONCE(state != ONCE_COMPLETED) ? -EINVAL : 0;
atomic_set(&once->state, ONCE_RUNNING);
r = cb(once);
if (r < 0)
atomic_set(&once->state, ONCE_NOT_STARTED);
else
atomic_set_release(&once->state, ONCE_COMPLETED);
return r;
}
#endif /* _LINUX_CALL_ONCE_H */
|
