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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 */