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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 * This pointer is required, and it is not acceptable to pass kfree
54 * in as this function.
55 *
56 * Decrement the refcount, and if 0, call release().
57 * Return 1 if the object was removed, otherwise return 0. Beware, if this
58 * function returns 0, you still can not count on the kref from remaining in
59 * memory. Only use the return value if you want to see if the kref is now
60 * gone, not present.
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
71static inline int kref_put_mutex(struct kref *kref,
72 void (*release)(struct kref *kref),
73 struct mutex *lock)
74{
75 if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
76 release(kref);
77 return 1;
78 }
79 return 0;
80}
81
82static inline int kref_put_lock(struct kref *kref,
83 void (*release)(struct kref *kref),
84 spinlock_t *lock)
85{
86 if (refcount_dec_and_lock(&kref->refcount, lock)) {
87 release(kref);
88 return 1;
89 }
90 return 0;
91}
92
93/**
94 * kref_get_unless_zero - Increment refcount for object unless it is zero.
95 * @kref: object.
96 *
97 * Return non-zero if the increment succeeded. Otherwise return 0.
98 *
99 * This function is intended to simplify locking around refcounting for
100 * objects that can be looked up from a lookup structure, and which are
101 * removed from that lookup structure in the object destructor.
102 * Operations on such objects require at least a read lock around
103 * lookup + kref_get, and a write lock around kref_put + remove from lookup
104 * structure. Furthermore, RCU implementations become extremely tricky.
105 * With a lookup followed by a kref_get_unless_zero *with return value check*
106 * locking in the kref_put path can be deferred to the actual removal from
107 * the lookup structure and RCU lookups become trivial.
108 */
109static inline int __must_check kref_get_unless_zero(struct kref *kref)
110{
111 return refcount_inc_not_zero(&kref->refcount);
112}
113#endif /* _KREF_H_ */
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/bug.h>
19#include <linux/atomic.h>
20#include <linux/kernel.h>
21
22struct kref {
23 atomic_t refcount;
24};
25
26/**
27 * kref_init - initialize object.
28 * @kref: object in question.
29 */
30static inline void kref_init(struct kref *kref)
31{
32 atomic_set(&kref->refcount, 1);
33}
34
35/**
36 * kref_get - increment refcount for object.
37 * @kref: object.
38 */
39static inline void kref_get(struct kref *kref)
40{
41 WARN_ON(!atomic_read(&kref->refcount));
42 atomic_inc(&kref->refcount);
43}
44
45/**
46 * kref_sub - subtract a number of refcounts for object.
47 * @kref: object.
48 * @count: Number of recounts to subtract.
49 * @release: pointer to the function that will clean up the object when the
50 * last reference to the object is released.
51 * This pointer is required, and it is not acceptable to pass kfree
52 * in as this function. If the caller does pass kfree to this
53 * function, you will be publicly mocked mercilessly by the kref
54 * maintainer, and anyone else who happens to notice it. You have
55 * been warned.
56 *
57 * Subtract @count from the refcount, and if 0, call release().
58 * Return 1 if the object was removed, otherwise return 0. Beware, if this
59 * function returns 0, you still can not count on the kref from remaining in
60 * memory. Only use the return value if you want to see if the kref is now
61 * gone, not present.
62 */
63static inline int kref_sub(struct kref *kref, unsigned int count,
64 void (*release)(struct kref *kref))
65{
66 WARN_ON(release == NULL);
67
68 if (atomic_sub_and_test((int) count, &kref->refcount)) {
69 release(kref);
70 return 1;
71 }
72 return 0;
73}
74
75/**
76 * kref_put - decrement refcount for object.
77 * @kref: object.
78 * @release: pointer to the function that will clean up the object when the
79 * last reference to the object is released.
80 * This pointer is required, and it is not acceptable to pass kfree
81 * in as this function. If the caller does pass kfree to this
82 * function, you will be publicly mocked mercilessly by the kref
83 * maintainer, and anyone else who happens to notice it. You have
84 * been warned.
85 *
86 * Decrement the refcount, and if 0, call release().
87 * Return 1 if the object was removed, otherwise return 0. Beware, if this
88 * function returns 0, you still can not count on the kref from remaining in
89 * memory. Only use the return value if you want to see if the kref is now
90 * gone, not present.
91 */
92static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
93{
94 return kref_sub(kref, 1, release);
95}
96#endif /* _KREF_H_ */