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