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1da177e4 | 1 | /* |
932fb06b | 2 | * kref.h - library routines for handling generic reference counted objects |
1da177e4 LT |
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 | ||
0a13cd1a | 18 | #include <linux/spinlock.h> |
10383aea | 19 | #include <linux/refcount.h> |
1da177e4 LT |
20 | |
21 | struct kref { | |
10383aea | 22 | refcount_t refcount; |
1da177e4 LT |
23 | }; |
24 | ||
10383aea | 25 | #define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), } |
1e24edca | 26 | |
4af679cd PZ |
27 | /** |
28 | * kref_init - initialize object. | |
29 | * @kref: object in question. | |
30 | */ | |
31 | static inline void kref_init(struct kref *kref) | |
32 | { | |
10383aea | 33 | refcount_set(&kref->refcount, 1); |
4af679cd PZ |
34 | } |
35 | ||
10383aea | 36 | static inline unsigned int kref_read(const struct kref *kref) |
2c935bc5 | 37 | { |
10383aea | 38 | return refcount_read(&kref->refcount); |
2c935bc5 PZ |
39 | } |
40 | ||
4af679cd PZ |
41 | /** |
42 | * kref_get - increment refcount for object. | |
43 | * @kref: object. | |
44 | */ | |
45 | static inline void kref_get(struct kref *kref) | |
46 | { | |
10383aea | 47 | refcount_inc(&kref->refcount); |
4af679cd PZ |
48 | } |
49 | ||
50 | /** | |
bdfafc4f | 51 | * kref_put - decrement refcount for object. |
4af679cd PZ |
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 | |
186bddb2 | 56 | * in as this function. |
4af679cd | 57 | * |
bdfafc4f | 58 | * Decrement the refcount, and if 0, call release(). |
4af679cd PZ |
59 | * Return 1 if the object was removed, otherwise return 0. Beware, if this |
60 | * function returns 0, you still can not count on the kref from remaining in | |
61 | * memory. Only use the return value if you want to see if the kref is now | |
62 | * gone, not present. | |
63 | */ | |
bdfafc4f | 64 | static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) |
4af679cd | 65 | { |
10383aea | 66 | if (refcount_dec_and_test(&kref->refcount)) { |
4af679cd PZ |
67 | release(kref); |
68 | return 1; | |
69 | } | |
70 | return 0; | |
71 | } | |
72 | ||
8ad5db8a AV |
73 | static inline int kref_put_mutex(struct kref *kref, |
74 | void (*release)(struct kref *kref), | |
75 | struct mutex *lock) | |
76 | { | |
10383aea | 77 | if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) { |
0a13cd1a PZ |
78 | release(kref); |
79 | return 1; | |
80 | } | |
81 | return 0; | |
82 | } | |
83 | ||
84 | static inline int kref_put_lock(struct kref *kref, | |
85 | void (*release)(struct kref *kref), | |
86 | spinlock_t *lock) | |
87 | { | |
10383aea | 88 | if (refcount_dec_and_lock(&kref->refcount, lock)) { |
8ad5db8a AV |
89 | release(kref); |
90 | return 1; | |
91 | } | |
92 | return 0; | |
93 | } | |
4b20db3d TH |
94 | |
95 | /** | |
96 | * kref_get_unless_zero - Increment refcount for object unless it is zero. | |
97 | * @kref: object. | |
98 | * | |
99 | * Return non-zero if the increment succeeded. Otherwise return 0. | |
100 | * | |
101 | * This function is intended to simplify locking around refcounting for | |
102 | * objects that can be looked up from a lookup structure, and which are | |
103 | * removed from that lookup structure in the object destructor. | |
104 | * Operations on such objects require at least a read lock around | |
105 | * lookup + kref_get, and a write lock around kref_put + remove from lookup | |
106 | * structure. Furthermore, RCU implementations become extremely tricky. | |
107 | * With a lookup followed by a kref_get_unless_zero *with return value check* | |
108 | * locking in the kref_put path can be deferred to the actual removal from | |
109 | * the lookup structure and RCU lookups become trivial. | |
110 | */ | |
111 | static inline int __must_check kref_get_unless_zero(struct kref *kref) | |
112 | { | |
10383aea | 113 | return refcount_inc_not_zero(&kref->refcount); |
4b20db3d | 114 | } |
1da177e4 | 115 | #endif /* _KREF_H_ */ |