call_once.h

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