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_test_and_get - increment refcount for object only if refcount is not
  41  * zero.
  42  * @kref: object.
  43  *
  44  * Return non-zero if the refcount was incremented, 0 otherwise
  45  */
  46 int kref_test_and_get(struct kref *kref)
  47 {
  48         return atomic_inc_not_zero(&kref->refcount);
  49 }
  50
  51 /**
  52  * kref_put - decrement refcount for object.
  53  * @kref: object.
  54  * @release: pointer to the function that will clean up the object when the
  55  *           last reference to the object is released.
  56  *           This pointer is required, and it is not acceptable to pass kfree
  57  *           in as this function.
  58  *
  59  * Decrement the refcount, and if 0, call release().
  60  * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  61  * function returns 0, you still can not count on the kref from remaining in
  62  * memory.  Only use the return value if you want to see if the kref is now
  63  * gone, not present.
  64  */
  65 int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  66 {
  67         WARN_ON(release == NULL);
  68         WARN_ON(release == (void (*)(struct kref *))kfree);
  69
  70         if (atomic_dec_and_test(&kref->refcount)) {
  71                 release(kref);
  72                 return 1;
  73         }
  74         return 0;
  75 }
  76
  77 EXPORT_SYMBOL(kref_init);
  78 EXPORT_SYMBOL(kref_get);
  79 EXPORT_SYMBOL(kref_put);