source: GPL/trunk/include/linux/refcount.h

#ifndef _LINUX_REFCOUNT_H
#define _LINUX_REFCOUNT_H

/**
 * struct refcount_t - variant of atomic_t specialized for reference counts
 * @refs: atomic_t counter field
 *
 * The counter saturates at UINT_MAX and will not move once
 * there. This avoids wrapping the counter and causing 'spurious'
 * use-after-free bugs.
 */
typedef struct refcount_struct {
        atomic_t refs;
} refcount_t;

#define REFCOUNT_INIT(n)        { .refs = ATOMIC_INIT(n), }

/**
 * refcount_read - get a refcount's value
 * @r: the refcount
 *
 * Return: the refcount's value
 */
static inline unsigned int refcount_read(const refcount_t *r)
{
        return atomic_read(&r->refs);
}

/**
 * refcount_set - set a refcount's value
 * @r: the refcount
 * @n: value to which the refcount will be set
 */
static inline void refcount_set(refcount_t *r, unsigned int n)
{
        atomic_set(&r->refs, n);
}

static inline void refcount_add(unsigned int i, refcount_t *r)
{
        atomic_add(i, &r->refs);
}

static inline void refcount_inc(refcount_t *r)
{
        atomic_inc(&r->refs);
}

static inline __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r)
{
        return atomic_sub_and_test(i, &r->refs);
}

static inline __must_check bool refcount_dec_and_test(refcount_t *r)
{
        return atomic_dec_and_test(&r->refs);
}

static inline void refcount_dec(refcount_t *r)
{
        atomic_dec(&r->refs);
}

#endif /* _LINUX_REFCOUNT_H */