include/linux/kref.h

   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/bug.h>
  19 #include <linux/atomic.h>
  20
  21 struct kref {
  22         atomic_t refcount;
  23 };
  24
  25 /**
  26  * kref_init - initialize object.
  27  * @kref: object in question.
  28  */
  29 static inline void kref_init(struct kref *kref)
  30 {
  31         atomic_set(&kref->refcount, 1);
  32 }
  33
  34 /**
  35  * kref_get - increment refcount for object.
  36  * @kref: object.
  37  */
  38 static inline void kref_get(struct kref *kref)
  39 {
  40         WARN_ON(!atomic_read(&kref->refcount));
  41         atomic_inc(&kref->refcount);
  42 }
  43
  44 /**
  45  * kref_sub - subtract a number of refcounts for object.
  46  * @kref: object.
  47  * @count: Number of recounts to subtract.
  48  * @release: pointer to the function that will clean up the object when the
  49  *           last reference to the object is released.
  50  *           This pointer is required, and it is not acceptable to pass kfree
  51  *           in as this function.  If the caller does pass kfree to this
  52  *           function, you will be publicly mocked mercilessly by the kref
  53  *           maintainer, and anyone else who happens to notice it.  You have
  54  *           been warned.
  55  *
  56  * Subtract @count from the refcount, and if 0, call release().
  57  * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  58  * function returns 0, you still can not count on the kref from remaining in
  59  * memory.  Only use the return value if you want to see if the kref is now
  60  * gone, not present.
  61  */
  62 static inline int kref_sub(struct kref *kref, unsigned int count,
  63              void (*release)(struct kref *kref))
  64 {
  65         WARN_ON(release == NULL);
  66
  67         if (atomic_sub_and_test((int) count, &kref->refcount)) {
  68                 release(kref);
  69                 return 1;
  70         }
  71         return 0;
  72 }
  73
  74 /**
  75  * kref_put - decrement refcount for object.
  76  * @kref: object.
  77  * @release: pointer to the function that will clean up the object when the
  78  *           last reference to the object is released.
  79  *           This pointer is required, and it is not acceptable to pass kfree
  80  *           in as this function.  If the caller does pass kfree to this
  81  *           function, you will be publicly mocked mercilessly by the kref
  82  *           maintainer, and anyone else who happens to notice it.  You have
  83  *           been warned.
  84  *
  85  * Decrement the refcount, and if 0, call release().
  86  * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  87  * function returns 0, you still can not count on the kref from remaining in
  88  * memory.  Only use the return value if you want to see if the kref is now
  89  * gone, not present.
  90  */
  91 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  92 {
  93         return kref_sub(kref, 1, release);
  94 }
  95 #endif /* _KREF_H_ */