lib/kref.c

   1 /*
   2  * kref.c - 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 lib/kobject.c which was:
   8  * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
   9  *
  10  * This file is released under the GPLv2.
  11  *
  12  */
  13
  14 #include <linux/kref.h>
  15 #include <linux/module.h>
  16 #include <linux/slab.h>
  17
  18 /**
  19  * kref_init - initialize object.
  20  * @kref: object in question.
  21  */
  22 void kref_init(struct kref *kref)
  23 {
  24         atomic_set(&kref->refcount, 1);
  25         smp_mb();
  26 }
  27
  28 /**
  29  * kref_get - increment refcount for object.
  30  * @kref: object.
  31  */
  32 void kref_get(struct kref *kref)
  33 {
  34         WARN_ON(!atomic_read(&kref->refcount));
  35         atomic_inc(&kref->refcount);
  36         smp_mb__after_atomic_inc();
  37 }
  38
  39 /**
  40  * kref_put - decrement refcount for object.
  41  * @kref: object.
  42  * @release: pointer to the function that will clean up the object when the
  43  *           last reference to the object is released.
  44  *           This pointer is required, and it is not acceptable to pass kfree
  45  *           in as this function.
  46  *
  47  * Decrement the refcount, and if 0, call release().
  48  * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  49  * function returns 0, you still can not count on the kref from remaining in
  50  * memory.  Only use the return value if you want to see if the kref is now
  51  * gone, not present.
  52  */
  53 int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  54 {
  55         WARN_ON(release == NULL);
  56         WARN_ON(release == (void (*)(struct kref *))kfree);
  57
  58         if (atomic_dec_and_test(&kref->refcount)) {
  59                 release(kref);
  60                 return 1;
  61         }
  62         return 0;
  63 }
  64
  65
  66 /**
  67  * kref_sub - subtract a number of refcounts for object.
  68  * @kref: object.
  69  * @count: Number of recounts to subtract.
  70  * @release: pointer to the function that will clean up the object when the
  71  *           last reference to the object is released.
  72  *           This pointer is required, and it is not acceptable to pass kfree
  73  *           in as this function.
  74  *
  75  * Subtract @count from the refcount, and if 0, call release().
  76  * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  77  * function returns 0, you still can not count on the kref from remaining in
  78  * memory.  Only use the return value if you want to see if the kref is now
  79  * gone, not present.
  80  */
  81 int kref_sub(struct kref *kref, unsigned int count,
  82              void (*release)(struct kref *kref))
  83 {
  84         WARN_ON(release == NULL);
  85         WARN_ON(release == (void (*)(struct kref *))kfree);
  86
  87         if (atomic_sub_and_test((int) count, &kref->refcount)) {
  88                 release(kref);
  89                 return 1;
  90         }
  91         return 0;
  92 }
  93
  94 EXPORT_SYMBOL(kref_init);
  95 EXPORT_SYMBOL(kref_get);
  96 EXPORT_SYMBOL(kref_put);
  97 EXPORT_SYMBOL(kref_sub);