2 * kref.c - library routines for handling generic reference counted objects
4 * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
5 * Copyright (C) 2004 IBM Corp.
7 * based on lib/kobject.c which was:
8 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
10 * This file is released under the GPLv2.
14 #include <linux/kref.h>
15 #include <linux/module.h>
16 #include <linux/slab.h>
19 * kref_init - initialize object.
20 * @kref: object in question.
22 void kref_init(struct kref *kref)
24 atomic_set(&kref->refcount, 1);
29 * kref_get - increment refcount for object.
32 void kref_get(struct kref *kref)
34 WARN_ON(!atomic_read(&kref->refcount));
35 atomic_inc(&kref->refcount);
36 smp_mb__after_atomic_inc();
40 * kref_put - decrement refcount for 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.
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
53 int kref_put(struct kref *kref, void (*release)(struct kref *kref))
55 WARN_ON(release == NULL);
56 WARN_ON(release == (void (*)(struct kref *))kfree);
58 if (atomic_dec_and_test(&kref->refcount)) {
67 * kref_sub - subtract a number of refcounts for 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.
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
81 int kref_sub(struct kref *kref, unsigned int count,
82 void (*release)(struct kref *kref))
84 WARN_ON(release == NULL);
85 WARN_ON(release == (void (*)(struct kref *))kfree);
87 if (atomic_sub_and_test((int) count, &kref->refcount)) {
94 EXPORT_SYMBOL(kref_init);
95 EXPORT_SYMBOL(kref_get);
96 EXPORT_SYMBOL(kref_put);
97 EXPORT_SYMBOL(kref_sub);