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
  17 /**
  18  * kref_set - initialize object and set refcount to requested number.
  19  * @kref: object in question.
  20  * @num: initial reference counter
  21  */
  22 void kref_set(struct kref *kref, int num)
  23 {
  24         atomic_set(&kref->refcount, num);
  25         smp_mb();
  26 }
  27
  28 /**
  29  * kref_init - initialize object.
  30  * @kref: object in question.
  31  */
  32 void kref_init(struct kref *kref)
  33 {
  34         kref_set(kref, 1);
  35 }
  36
  37 /**
  38  * kref_get - increment refcount for object.
  39  * @kref: object.
  40  */
  41 void kref_get(struct kref *kref)
  42 {
  43         WARN_ON(!atomic_read(&kref->refcount));
  44         atomic_inc(&kref->refcount);
  45         smp_mb__after_atomic_inc();
  46 }
  47
  48 /**
  49  * kref_put - decrement refcount for object.
  50  * @kref: object.
  51  * @release: pointer to the function that will clean up the object when the
  52  *           last reference to the object is released.
  53  *           This pointer is required, and it is not acceptable to pass kfree
  54  *           in as this function.
  55  *
  56  * Decrement 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 int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  63 {
  64         WARN_ON(release == NULL);
  65         WARN_ON(release == (void (*)(struct kref *))kfree);
  66
  67         if (atomic_dec_and_test(&kref->refcount)) {
  68                 release(kref);
  69                 return 1;
  70         }
  71         return 0;
  72 }
  73
  74 EXPORT_SYMBOL(kref_set);
  75 EXPORT_SYMBOL(kref_init);
  76 EXPORT_SYMBOL(kref_get);
  77 EXPORT_SYMBOL(kref_put);