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 <[email protected]>
6 * Copyright (C) 2004 IBM Corp.
7 *
8 * based on kobject.h which was:
9 * Copyright (C) 2002-2003 Patrick Mochel <[email protected]>
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
19 struct 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 */
kref_init(struct kref * kref)29 static inline void kref_init(struct kref *kref)
30 {
31 refcount_set(&kref->refcount, 1);
32 }
33
kref_read(const struct kref * kref)34 static 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 */
kref_get(struct kref * kref)43 static 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 */
kref_put(struct kref * kref,void (* release)(struct kref * kref))62 static 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 */
kref_put_mutex(struct kref * kref,void (* release)(struct kref * kref),struct mutex * mutex)81 static inline int kref_put_mutex(struct kref *kref,
82 void (*release)(struct kref *kref),
83 struct mutex *mutex)
84 {
85 if (refcount_dec_and_mutex_lock(&kref->refcount, mutex)) {
86 release(kref);
87 return 1;
88 }
89 return 0;
90 }
91
92 /**
93 * kref_put_lock - Decrement refcount for object
94 * @kref: Object
95 * @release: Pointer to the function that will clean up the object when the
96 * last reference to the object is released.
97 * @lock: Spinlock which protects the release function.
98 *
99 * This variant of kref_lock() calls the @release function with the @lock
100 * held. The @release function will release the lock.
101 */
kref_put_lock(struct kref * kref,void (* release)(struct kref * kref),spinlock_t * lock)102 static inline int kref_put_lock(struct kref *kref,
103 void (*release)(struct kref *kref),
104 spinlock_t *lock)
105 {
106 if (refcount_dec_and_lock(&kref->refcount, lock)) {
107 release(kref);
108 return 1;
109 }
110 return 0;
111 }
112
113 /**
114 * kref_get_unless_zero - Increment refcount for object unless it is zero.
115 * @kref: object.
116 *
117 * This function is intended to simplify locking around refcounting for
118 * objects that can be looked up from a lookup structure, and which are
119 * removed from that lookup structure in the object destructor.
120 * Operations on such objects require at least a read lock around
121 * lookup + kref_get, and a write lock around kref_put + remove from lookup
122 * structure. Furthermore, RCU implementations become extremely tricky.
123 * With a lookup followed by a kref_get_unless_zero *with return value check*
124 * locking in the kref_put path can be deferred to the actual removal from
125 * the lookup structure and RCU lookups become trivial.
126 *
127 * Return: non-zero if the increment succeeded. Otherwise return 0.
128 */
kref_get_unless_zero(struct kref * kref)129 static inline int __must_check kref_get_unless_zero(struct kref *kref)
130 {
131 return refcount_inc_not_zero(&kref->refcount);
132 }
133 #endif /* _KREF_H_ */
134