2 * kref.h - 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 kobject.h which was:
8 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
9 * Copyright (C) 2002-2003 Open Source Development Labs
11 * This file is released under the GPLv2.
18 #include <linux/bug.h>
19 #include <linux/atomic.h>
20 #include <linux/kernel.h>
21 #include <linux/mutex.h>
22 #include <linux/spinlock.h>
29 * kref_init - initialize object.
30 * @kref: object in question.
32 static inline void kref_init(struct kref *kref)
34 atomic_set(&kref->refcount, 1);
38 * kref_get - increment refcount for object.
41 static inline void kref_get(struct kref *kref)
43 WARN_ON(!atomic_read(&kref->refcount));
44 atomic_inc(&kref->refcount);
48 * kref_sub - subtract a number of refcounts for object.
50 * @count: Number of recounts to subtract.
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. If the caller does pass kfree to this
55 * function, you will be publicly mocked mercilessly by the kref
56 * maintainer, and anyone else who happens to notice it. You have
59 * Subtract @count from the refcount, and if 0, call release().
60 * Return 1 if the object was removed, otherwise return 0. Beware, if this
61 * function returns 0, you still can not count on the kref from remaining in
62 * memory. Only use the return value if you want to see if the kref is now
65 static inline int kref_sub(struct kref *kref, unsigned int count,
66 void (*release)(struct kref *kref))
68 WARN_ON(release == NULL);
70 if (atomic_sub_and_test((int) count, &kref->refcount)) {
78 * kref_put - decrement refcount for object.
80 * @release: pointer to the function that will clean up the object when the
81 * last reference to the object is released.
82 * This pointer is required, and it is not acceptable to pass kfree
83 * in as this function. If the caller does pass kfree to this
84 * function, you will be publicly mocked mercilessly by the kref
85 * maintainer, and anyone else who happens to notice it. You have
88 * Decrement the refcount, and if 0, call release().
89 * Return 1 if the object was removed, otherwise return 0. Beware, if this
90 * function returns 0, you still can not count on the kref from remaining in
91 * memory. Only use the return value if you want to see if the kref is now
94 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
96 return kref_sub(kref, 1, release);
100 * kref_put_spinlock_irqsave - decrement refcount for object.
102 * @release: pointer to the function that will clean up the object when the
103 * last reference to the object is released.
104 * This pointer is required, and it is not acceptable to pass kfree
105 * in as this function.
106 * @lock: lock to take in release case
108 * Behaves identical to kref_put with one exception. If the reference count
109 * drops to zero, the lock will be taken atomically wrt dropping the reference
110 * count. The release function has to call spin_unlock() without _irqrestore.
112 static inline int kref_put_spinlock_irqsave(struct kref *kref,
113 void (*release)(struct kref *kref),
118 WARN_ON(release == NULL);
119 if (atomic_add_unless(&kref->refcount, -1, 1))
121 spin_lock_irqsave(lock, flags);
122 if (atomic_dec_and_test(&kref->refcount)) {
124 local_irq_restore(flags);
127 spin_unlock_irqrestore(lock, flags);
131 static inline int kref_put_mutex(struct kref *kref,
132 void (*release)(struct kref *kref),
135 WARN_ON(release == NULL);
136 if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) {
138 if (unlikely(!atomic_dec_and_test(&kref->refcount))) {
149 * kref_get_unless_zero - Increment refcount for object unless it is zero.
152 * Return non-zero if the increment succeeded. Otherwise return 0.
154 * This function is intended to simplify locking around refcounting for
155 * objects that can be looked up from a lookup structure, and which are
156 * removed from that lookup structure in the object destructor.
157 * Operations on such objects require at least a read lock around
158 * lookup + kref_get, and a write lock around kref_put + remove from lookup
159 * structure. Furthermore, RCU implementations become extremely tricky.
160 * With a lookup followed by a kref_get_unless_zero *with return value check*
161 * locking in the kref_put path can be deferred to the actual removal from
162 * the lookup structure and RCU lookups become trivial.
164 static inline int __must_check kref_get_unless_zero(struct kref *kref)
166 return atomic_add_unless(&kref->refcount, 1, 0);
168 #endif /* _KREF_H_ */