]>
git.proxmox.com Git - mirror_ubuntu-hirsute-kernel.git/blob - include/linux/kref.h
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/spinlock.h>
19 #include <linux/refcount.h>
25 #define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }
28 * kref_init - initialize object.
29 * @kref: object in question.
31 static inline void kref_init(struct kref
*kref
)
33 refcount_set(&kref
->refcount
, 1);
36 static inline unsigned int kref_read(const struct kref
*kref
)
38 return refcount_read(&kref
->refcount
);
42 * kref_get - increment refcount for object.
45 static inline void kref_get(struct kref
*kref
)
47 refcount_inc(&kref
->refcount
);
51 * kref_put - decrement refcount for 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
56 * in as this function.
58 * Decrement the refcount, and if 0, call release().
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
64 static inline int kref_put(struct kref
*kref
, void (*release
)(struct kref
*kref
))
66 if (refcount_dec_and_test(&kref
->refcount
)) {
73 static inline int kref_put_mutex(struct kref
*kref
,
74 void (*release
)(struct kref
*kref
),
77 if (refcount_dec_and_mutex_lock(&kref
->refcount
, lock
)) {
84 static inline int kref_put_lock(struct kref
*kref
,
85 void (*release
)(struct kref
*kref
),
88 if (refcount_dec_and_lock(&kref
->refcount
, lock
)) {
96 * kref_get_unless_zero - Increment refcount for object unless it is zero.
99 * Return non-zero if the increment succeeded. Otherwise return 0.
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.
111 static inline int __must_check
kref_get_unless_zero(struct kref
*kref
)
113 return refcount_inc_not_zero(&kref
->refcount
);
115 #endif /* _KREF_H_ */