| 1 | #ifndef _LINUX_CALL_ONCE_H |
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| 2 | #define _LINUX_CALL_ONCE_H |
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| 3 | |
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| 4 | #include <linux/types.h> |
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| 5 | #include <linux/mutex.h> |
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| 6 | |
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| 7 | #define ONCE_NOT_STARTED 0 |
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| 8 | #define ONCE_RUNNING 1 |
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| 9 | #define ONCE_COMPLETED 2 |
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| 10 | |
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| 11 | struct once { |
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| 12 | atomic_t state; |
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| 13 | struct mutex lock; |
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| 14 | }; |
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| 15 | |
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| 16 | static inline void __once_init(struct once *once, const char *name, |
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| 17 | struct lock_class_key *key) |
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| 18 | { |
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| 19 | atomic_set(v: &once->state, ONCE_NOT_STARTED); |
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| 20 | __mutex_init(lock: &once->lock, name, key); |
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| 21 | } |
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| 22 | |
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| 23 | #define once_init(once) \ |
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| 24 | do { \ |
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| 25 | static struct lock_class_key __key; \ |
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| 26 | __once_init((once), #once, &__key); \ |
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| 27 | } while (0) |
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| 28 | |
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| 29 | /* |
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| 30 | * call_once - Ensure a function has been called exactly once |
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| 31 | * |
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| 32 | * @once: Tracking struct |
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| 33 | * @cb: Function to be called |
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| 34 | * |
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| 35 | * If @once has never completed successfully before, call @cb and, if |
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| 36 | * it returns a zero or positive value, mark @once as completed. Return |
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| 37 | * the value returned by @cb |
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| 38 | * |
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| 39 | * If @once has completed succesfully before, return 0. |
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| 40 | * |
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| 41 | * The call to @cb is implicitly surrounded by a mutex, though for |
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| 42 | * efficiency the * function avoids taking it after the first call. |
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| 43 | */ |
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| 44 | static inline int call_once(struct once *once, int (*cb)(struct once *)) |
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| 45 | { |
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| 46 | int r, state; |
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| 47 | |
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| 48 | /* Pairs with atomic_set_release() below. */ |
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| 49 | if (atomic_read_acquire(v: &once->state) == ONCE_COMPLETED) |
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| 50 | return 0; |
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| 51 | |
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| 52 | guard(mutex)(T: &once->lock); |
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| 53 | state = atomic_read(v: &once->state); |
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| 54 | if (unlikely(state != ONCE_NOT_STARTED)) |
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| 55 | return WARN_ON_ONCE(state != ONCE_COMPLETED) ? -EINVAL : 0; |
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| 56 | |
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| 57 | atomic_set(v: &once->state, ONCE_RUNNING); |
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| 58 | r = cb(once); |
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| 59 | if (r < 0) |
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| 60 | atomic_set(v: &once->state, ONCE_NOT_STARTED); |
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| 61 | else |
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| 62 | atomic_set_release(v: &once->state, ONCE_COMPLETED); |
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| 63 | return r; |
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| 64 | } |
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| 65 | |
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| 66 | #endif /* _LINUX_CALL_ONCE_H */ |
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| 67 | |
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