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TOMOYO Linux Cross Reference
Linux/include/linux/kref.h

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  1 /*
  2  * kref.h - 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 kobject.h which was:
  8  * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
  9  * Copyright (C) 2002-2003 Open Source Development Labs
 10  *
 11  * This file is released under the GPLv2.
 12  *
 13  */
 14 
 15 #ifndef _KREF_H_
 16 #define _KREF_H_
 17 
 18 #include <linux/spinlock.h>
 19 #include <linux/refcount.h>
 20 
 21 struct kref {
 22         refcount_t refcount;
 23 };
 24 
 25 #define KREF_INIT(n)    { .refcount = REFCOUNT_INIT(n), }
 26 
 27 /**
 28  * kref_init - initialize object.
 29  * @kref: object in question.
 30  */
 31 static inline void kref_init(struct kref *kref)
 32 {
 33         refcount_set(&kref->refcount, 1);
 34 }
 35 
 36 static inline unsigned int kref_read(const struct kref *kref)
 37 {
 38         return refcount_read(&kref->refcount);
 39 }
 40 
 41 /**
 42  * kref_get - increment refcount for object.
 43  * @kref: object.
 44  */
 45 static inline void kref_get(struct kref *kref)
 46 {
 47         refcount_inc(&kref->refcount);
 48 }
 49 
 50 /**
 51  * kref_put - decrement refcount for object.
 52  * @kref: 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.  If the caller does pass kfree to this
 57  *           function, you will be publicly mocked mercilessly by the kref
 58  *           maintainer, and anyone else who happens to notice it.  You have
 59  *           been warned.
 60  *
 61  * Decrement the refcount, and if 0, call release().
 62  * Return 1 if the object was removed, otherwise return 0.  Beware, if this
 63  * function returns 0, you still can not count on the kref from remaining in
 64  * memory.  Only use the return value if you want to see if the kref is now
 65  * gone, not present.
 66  */
 67 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
 68 {
 69         if (refcount_dec_and_test(&kref->refcount)) {
 70                 release(kref);
 71                 return 1;
 72         }
 73         return 0;
 74 }
 75 
 76 static inline int kref_put_mutex(struct kref *kref,
 77                                  void (*release)(struct kref *kref),
 78                                  struct mutex *lock)
 79 {
 80         if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
 81                 release(kref);
 82                 return 1;
 83         }
 84         return 0;
 85 }
 86 
 87 static inline int kref_put_lock(struct kref *kref,
 88                                 void (*release)(struct kref *kref),
 89                                 spinlock_t *lock)
 90 {
 91         if (refcount_dec_and_lock(&kref->refcount, lock)) {
 92                 release(kref);
 93                 return 1;
 94         }
 95         return 0;
 96 }
 97 
 98 /**
 99  * kref_get_unless_zero - Increment refcount for object unless it is zero.
100  * @kref: object.
101  *
102  * Return non-zero if the increment succeeded. Otherwise return 0.
103  *
104  * This function is intended to simplify locking around refcounting for
105  * objects that can be looked up from a lookup structure, and which are
106  * removed from that lookup structure in the object destructor.
107  * Operations on such objects require at least a read lock around
108  * lookup + kref_get, and a write lock around kref_put + remove from lookup
109  * structure. Furthermore, RCU implementations become extremely tricky.
110  * With a lookup followed by a kref_get_unless_zero *with return value check*
111  * locking in the kref_put path can be deferred to the actual removal from
112  * the lookup structure and RCU lookups become trivial.
113  */
114 static inline int __must_check kref_get_unless_zero(struct kref *kref)
115 {
116         return refcount_inc_not_zero(&kref->refcount);
117 }
118 #endif /* _KREF_H_ */
119 

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