Linux kernel mirror (for testing)
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1#ifndef __LINUX_LOCKREF_H
2#define __LINUX_LOCKREF_H
3
4/*
5 * Locked reference counts.
6 *
7 * These are different from just plain atomic refcounts in that they
8 * are atomic with respect to the spinlock that goes with them. In
9 * particular, there can be implementations that don't actually get
10 * the spinlock for the common decrement/increment operations, but they
11 * still have to check that the operation is done semantically as if
12 * the spinlock had been taken (using a cmpxchg operation that covers
13 * both the lock and the count word, or using memory transactions, for
14 * example).
15 */
16
17#include <linux/spinlock.h>
18
19struct lockref {
20 spinlock_t lock;
21 unsigned int count;
22};
23
24/**
25 * lockref_get - Increments reference count unconditionally
26 * @lockcnt: pointer to lockref structure
27 *
28 * This operation is only valid if you already hold a reference
29 * to the object, so you know the count cannot be zero.
30 */
31static inline void lockref_get(struct lockref *lockref)
32{
33 spin_lock(&lockref->lock);
34 lockref->count++;
35 spin_unlock(&lockref->lock);
36}
37
38/**
39 * lockref_get_not_zero - Increments count unless the count is 0
40 * @lockcnt: pointer to lockref structure
41 * Return: 1 if count updated successfully or 0 if count is 0
42 */
43static inline int lockref_get_not_zero(struct lockref *lockref)
44{
45 int retval = 0;
46
47 spin_lock(&lockref->lock);
48 if (lockref->count) {
49 lockref->count++;
50 retval = 1;
51 }
52 spin_unlock(&lockref->lock);
53 return retval;
54}
55
56/**
57 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
58 * @lockcnt: pointer to lockref structure
59 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
60 */
61static inline int lockref_put_or_lock(struct lockref *lockref)
62{
63 spin_lock(&lockref->lock);
64 if (lockref->count <= 1)
65 return 0;
66 lockref->count--;
67 spin_unlock(&lockref->lock);
68 return 1;
69}
70
71#endif /* __LINUX_LOCKREF_H */