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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.
 57  *
 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
 62  * gone, not present.
 63  */
 64 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
 65 {
 66         if (refcount_dec_and_test(&kref->refcount)) {
 67                 release(kref);
 68                 return 1;
 69         }
 70         return 0;
 71 }
 72 
 73 static inline int kref_put_mutex(struct kref *kref,
 74                                  void (*release)(struct kref *kref),
 75                                  struct mutex *lock)
 76 {
 77         if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
 78                 release(kref);
 79                 return 1;
 80         }
 81         return 0;
 82 }
 83 
 84 static inline int kref_put_lock(struct kref *kref,
 85                                 void (*release)(struct kref *kref),
 86                                 spinlock_t *lock)
 87 {
 88         if (refcount_dec_and_lock(&kref->refcount, lock)) {
 89                 release(kref);
 90                 return 1;
 91         }
 92         return 0;
 93 }
 94 
 95 /**
 96  * kref_get_unless_zero - Increment refcount for object unless it is zero.
 97  * @kref: object.
 98  *
 99  * Return non-zero if the increment succeeded. Otherwise return 0.
100  *
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.
110  */
111 static inline int __must_check kref_get_unless_zero(struct kref *kref)
112 {
113         return refcount_inc_not_zero(&kref->refcount);
114 }
115 #endif /* _KREF_H_ */
116 

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