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
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 */
29 static inline void kref_init(struct kref *kref)
30 {
31 refcount_set(&kref->refcount, 1);
32 }
33
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 */
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 * 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 */
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 static 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
82 static 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 */
109 static 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_ */
114
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