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1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 * kref.h - library routines for handling generic reference counted objects
4 *
5 * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
6 * Copyright (C) 2004 IBM Corp.
7 *
8 * based on kobject.h which was:
9 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
10 * Copyright (C) 2002-2003 Open Source Development Labs
11 */
12
13#ifndef _KREF_H_
14#define _KREF_H_
15
16#include <linux/spinlock.h>
17#include <linux/refcount.h>
18
19struct kref {
20 refcount_t refcount;
21};
22
23#define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }
24
25/**
26 * kref_init - initialize object.
27 * @kref: object in question.
28 */
29static inline void kref_init(struct kref *kref)
30{
31 refcount_set(&kref->refcount, 1);
32}
33
34static inline unsigned int kref_read(const struct kref *kref)
35{
36 return refcount_read(&kref->refcount);
37}
38
39/**
40 * kref_get - increment refcount for object.
41 * @kref: object.
42 */
43static inline void kref_get(struct kref *kref)
44{
45 refcount_inc(&kref->refcount);
46}
47
48/**
49 * kref_put - Decrement refcount for object
50 * @kref: Object
51 * @release: Pointer to the function that will clean up the object when the
52 * last reference to the object is released.
53 *
54 * Decrement the refcount, and if 0, call @release. The caller may not
55 * pass NULL or kfree() as the release function.
56 *
57 * Return: 1 if this call removed the object, otherwise return 0. Beware,
58 * if this function returns 0, another caller may have removed the object
59 * by the time this function returns. The return value is only certain
60 * if you want to see if the object is definitely released.
61 */
62static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
63{
64 if (refcount_dec_and_test(&kref->refcount)) {
65 release(kref);
66 return 1;
67 }
68 return 0;
69}
70
71/**
72 * kref_put_mutex - Decrement refcount for object
73 * @kref: Object
74 * @release: Pointer to the function that will clean up the object when the
75 * last reference to the object is released.
76 * @mutex: Mutex which protects the release function.
77 *
78 * This variant of kref_lock() calls the @release function with the @mutex
79 * held. The @release function will release the mutex.
80 */
81static inline int kref_put_mutex(struct kref *kref,
82 void (*release)(struct kref *kref),
83 struct mutex *mutex)
84 __cond_acquires(true, mutex)
85{
86 if (refcount_dec_and_mutex_lock(&kref->refcount, mutex)) {
87 release(kref);
88 return 1;
89 }
90 return 0;
91}
92
93/**
94 * kref_put_lock - Decrement refcount for object
95 * @kref: Object
96 * @release: Pointer to the function that will clean up the object when the
97 * last reference to the object is released.
98 * @lock: Spinlock which protects the release function.
99 *
100 * This variant of kref_lock() calls the @release function with the @lock
101 * held. The @release function will release the lock.
102 */
103static inline int kref_put_lock(struct kref *kref,
104 void (*release)(struct kref *kref),
105 spinlock_t *lock)
106 __cond_acquires(true, lock)
107{
108 if (refcount_dec_and_lock(&kref->refcount, lock)) {
109 release(kref);
110 return 1;
111 }
112 return 0;
113}
114
115/**
116 * kref_get_unless_zero - Increment refcount for object unless it is zero.
117 * @kref: object.
118 *
119 * This function is intended to simplify locking around refcounting for
120 * objects that can be looked up from a lookup structure, and which are
121 * removed from that lookup structure in the object destructor.
122 * Operations on such objects require at least a read lock around
123 * lookup + kref_get, and a write lock around kref_put + remove from lookup
124 * structure. Furthermore, RCU implementations become extremely tricky.
125 * With a lookup followed by a kref_get_unless_zero *with return value check*
126 * locking in the kref_put path can be deferred to the actual removal from
127 * the lookup structure and RCU lookups become trivial.
128 *
129 * Return: non-zero if the increment succeeded. Otherwise return 0.
130 */
131static inline int __must_check kref_get_unless_zero(struct kref *kref)
132{
133 return refcount_inc_not_zero(&kref->refcount);
134}
135#endif /* _KREF_H_ */