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