1/*
2 * kref.h - library routines for handling generic reference counted objects
3 *
4 * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
5 * Copyright (C) 2004 IBM Corp.
6 *
7 * based on kobject.h which was:
8 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
9 * Copyright (C) 2002-2003 Open Source Development Labs
10 *
11 * This file is released under the GPLv2.
12 *
13 */
14
15#ifndef _KREF_H_
16#define _KREF_H_
17
18#include <linux/spinlock.h>
19#include <linux/refcount.h>
20
21struct kref {
22 refcount_t refcount;
23};
24
25#define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }
26
27/**
28 * kref_init - initialize object.
29 * @kref: object in question.
30 */
31static inline void kref_init(struct kref *kref)
32{
33 refcount_set(&kref->refcount, 1);
34}
35
36static inline unsigned int kref_read(const struct kref *kref)
37{
38 return refcount_read(&kref->refcount);
39}
40
41/**
42 * kref_get - increment refcount for object.
43 * @kref: object.
44 */
45static inline void kref_get(struct kref *kref)
46{
47 refcount_inc(&kref->refcount);
48}
49
50/**
51 * kref_put - decrement refcount for object.
52 * @kref: object.
53 * @release: pointer to the function that will clean up the object when the
54 * last reference to the object is released.
55 * This pointer is required, and it is not acceptable to pass kfree
56 * in as this function.
57 *
58 * Decrement the refcount, and if 0, call release().
59 * Return 1 if the object was removed, otherwise return 0. Beware, if this
60 * function returns 0, you still can not count on the kref from remaining in
61 * memory. Only use the return value if you want to see if the kref is now
62 * gone, not present.
63 */
64static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
65{
66 if (refcount_dec_and_test(&kref->refcount)) {
67 release(kref);
68 return 1;
69 }
70 return 0;
71}
72
73static inline int kref_put_mutex(struct kref *kref,
74 void (*release)(struct kref *kref),
75 struct mutex *lock)
76{
77 if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
78 release(kref);
79 return 1;
80 }
81 return 0;
82}
83
84static inline int kref_put_lock(struct kref *kref,
85 void (*release)(struct kref *kref),
86 spinlock_t *lock)
87{
88 if (refcount_dec_and_lock(&kref->refcount, lock)) {
89 release(kref);
90 return 1;
91 }
92 return 0;
93}
94
95/**
96 * kref_get_unless_zero - Increment refcount for object unless it is zero.
97 * @kref: object.
98 *
99 * Return non-zero if the increment succeeded. Otherwise return 0.
100 *
101 * This function is intended to simplify locking around refcounting for
102 * objects that can be looked up from a lookup structure, and which are
103 * removed from that lookup structure in the object destructor.
104 * Operations on such objects require at least a read lock around
105 * lookup + kref_get, and a write lock around kref_put + remove from lookup
106 * structure. Furthermore, RCU implementations become extremely tricky.
107 * With a lookup followed by a kref_get_unless_zero *with return value check*
108 * locking in the kref_put path can be deferred to the actual removal from
109 * the lookup structure and RCU lookups become trivial.
110 */
111static inline int __must_check kref_get_unless_zero(struct kref *kref)
112{
113 return refcount_inc_not_zero(&kref->refcount);
114}
115#endif /* _KREF_H_ */
116