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 
21 struct 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  */
kref_init(struct kref * kref)31 static inline void kref_init(struct kref *kref)
32 {
33 	refcount_set(&kref->refcount, 1);
34 }
35 
kref_read(const struct kref * kref)36 static 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  */
kref_get(struct kref * kref)45 static 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.  If the caller does pass kfree to this
57  *	     function, you will be publicly mocked mercilessly by the kref
58  *	     maintainer, and anyone else who happens to notice it.  You have
59  *	     been warned.
60  *
61  * Decrement the refcount, and if 0, call release().
62  * Return 1 if the object was removed, otherwise return 0.  Beware, if this
63  * function returns 0, you still can not count on the kref from remaining in
64  * memory.  Only use the return value if you want to see if the kref is now
65  * gone, not present.
66  */
kref_put(struct kref * kref,void (* release)(struct kref * kref))67 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
68 {
69 	if (refcount_dec_and_test(&kref->refcount)) {
70 		release(kref);
71 		return 1;
72 	}
73 	return 0;
74 }
75 
kref_put_mutex(struct kref * kref,void (* release)(struct kref * kref),struct mutex * lock)76 static inline int kref_put_mutex(struct kref *kref,
77 				 void (*release)(struct kref *kref),
78 				 struct mutex *lock)
79 {
80 	if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
81 		release(kref);
82 		return 1;
83 	}
84 	return 0;
85 }
86 
kref_put_lock(struct kref * kref,void (* release)(struct kref * kref),spinlock_t * lock)87 static inline int kref_put_lock(struct kref *kref,
88 				void (*release)(struct kref *kref),
89 				spinlock_t *lock)
90 {
91 	if (refcount_dec_and_lock(&kref->refcount, lock)) {
92 		release(kref);
93 		return 1;
94 	}
95 	return 0;
96 }
97 
98 /**
99  * kref_get_unless_zero - Increment refcount for object unless it is zero.
100  * @kref: object.
101  *
102  * Return non-zero if the increment succeeded. Otherwise return 0.
103  *
104  * This function is intended to simplify locking around refcounting for
105  * objects that can be looked up from a lookup structure, and which are
106  * removed from that lookup structure in the object destructor.
107  * Operations on such objects require at least a read lock around
108  * lookup + kref_get, and a write lock around kref_put + remove from lookup
109  * structure. Furthermore, RCU implementations become extremely tricky.
110  * With a lookup followed by a kref_get_unless_zero *with return value check*
111  * locking in the kref_put path can be deferred to the actual removal from
112  * the lookup structure and RCU lookups become trivial.
113  */
kref_get_unless_zero(struct kref * kref)114 static inline int __must_check kref_get_unless_zero(struct kref *kref)
115 {
116 	return refcount_inc_not_zero(&kref->refcount);
117 }
118 #endif /* _KREF_H_ */
119