kref - the reference counter

A kref is a simple structure

struct kref {
        atomic_t refcount;
};

There are three kref operations:

void kref_init(struct kref *kref);
void kref_get(struct kref *kref);
int kref_put(struct kref *kref, 
             void (*release) (struct kref *kref));

Calls to kref_put() must be serialized externally