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#include <linux/slab.h>
17
18/**
19 * kref_init - initialize object.
20 * @kref: object in question.
21 */
22void kref_init(struct kref *kref)
23{
24	atomic_set(&kref->refcount, 1);
25	smp_mb();
26}
27
28/**
29 * kref_get - increment refcount for object.
30 * @kref: object.
31 */
32void kref_get(struct kref *kref)
33{
34	WARN_ON(!atomic_read(&kref->refcount));
35	atomic_inc(&kref->refcount);
36	smp_mb__after_atomic_inc();
37}
38
39/**
40 * kref_put - decrement refcount for object.
41 * @kref: object.
42 * @release: pointer to the function that will clean up the object when the
43 *	     last reference to the object is released.
44 *	     This pointer is required, and it is not acceptable to pass kfree
45 *	     in as this function.
46 *
47 * Decrement the refcount, and if 0, call release().
48 * Return 1 if the object was removed, otherwise return 0.  Beware, if this
49 * function returns 0, you still can not count on the kref from remaining in
50 * memory.  Only use the return value if you want to see if the kref is now
51 * gone, not present.
52 */
53int kref_put(struct kref *kref, void (*release)(struct kref *kref))
54{
55	WARN_ON(release == NULL);
56	WARN_ON(release == (void (*)(struct kref *))kfree);
57
58	if (atomic_dec_and_test(&kref->refcount)) {
59		release(kref);
60		return 1;
61	}
62	return 0;
63}
64
65
66/**
67 * kref_sub - subtract a number of refcounts for object.
68 * @kref: object.
69 * @count: Number of recounts to subtract.
70 * @release: pointer to the function that will clean up the object when the
71 *	     last reference to the object is released.
72 *	     This pointer is required, and it is not acceptable to pass kfree
73 *	     in as this function.
74 *
75 * Subtract @count from the refcount, and if 0, call release().
76 * Return 1 if the object was removed, otherwise return 0.  Beware, if this
77 * function returns 0, you still can not count on the kref from remaining in
78 * memory.  Only use the return value if you want to see if the kref is now
79 * gone, not present.
80 */
81int kref_sub(struct kref *kref, unsigned int count,
82	     void (*release)(struct kref *kref))
83{
84	WARN_ON(release == NULL);
85	WARN_ON(release == (void (*)(struct kref *))kfree);
86
87	if (atomic_sub_and_test((int) count, &kref->refcount)) {
88		release(kref);
89		return 1;
90	}
91	return 0;
92}
93
94EXPORT_SYMBOL(kref_init);
95EXPORT_SYMBOL(kref_get);
96EXPORT_SYMBOL(kref_put);
97EXPORT_SYMBOL(kref_sub);