1 /*
2 * kref.c - 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 lib/kobject.c which was:
8 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
9 *
10 * This file is released under the GPLv2.
11 *
12 */
13
14 #include <linux/kref.h>
15 #include <linux/module.h>
16
17 /**
18 * kref_set - initialize object and set refcount to requested number.
19 * @kref: object in question.
20 * @num: initial reference counter
21 */
22 void kref_set(struct kref *kref, int num)
23 {
24 atomic_set(&kref->refcount, num);
25 smp_mb();
26 }
27
28 /**
29 * kref_init - initialize object.
30 * @kref: object in question.
31 */
32 void kref_init(struct kref *kref)
33 {
34 kref_set(kref, 1);
35 }
36
37 /**
38 * kref_get - increment refcount for object.
39 * @kref: object.
40 */
41 void kref_get(struct kref *kref)
42 {
43 WARN_ON(!atomic_read(&kref->refcount));
44 atomic_inc(&kref->refcount);
45 smp_mb__after_atomic_inc();
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 int kref_put(struct kref *kref, void (*release)(struct kref *kref))
63 {
64 WARN_ON(release == NULL);
65 WARN_ON(release == (void (*)(struct kref *))kfree);
66
67 if (atomic_dec_and_test(&kref->refcount)) {
68 release(kref);
69 return 1;
70 }
71 return 0;
72 }
73
74 EXPORT_SYMBOL(kref_set);
75 EXPORT_SYMBOL(kref_init);
76 EXPORT_SYMBOL(kref_get);
77 EXPORT_SYMBOL(kref_put);
78
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