LXR linux/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_init - initialize object.
  19 * @kref: object in question.
  20 */
  21void kref_init(struct kref *kref)
  22{
  23        atomic_set(&kref->refcount,1);
  24        smp_mb();
  25}
  26
  27/**
  28 * kref_get - increment refcount for object.
  29 * @kref: object.
  30 */
  31void kref_get(struct kref *kref)
  32{
  33        WARN_ON(!atomic_read(&kref->refcount));
  34        atomic_inc(&kref->refcount);
  35        smp_mb__after_atomic_inc();
  36}
  37
  38/**
  39 * kref_put - decrement refcount for object.
  40 * @kref: object.
  41 * @release: pointer to the function that will clean up the object when the
  42 *           last reference to the object is released.
  43 *           This pointer is required, and it is not acceptable to pass kfree
  44 *           in as this function.
  45 *
  46 * Decrement the refcount, and if 0, call release().
  47 * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  48 * function returns 0, you still can not count on the kref from remaining in
  49 * memory.  Only use the return value if you want to see if the kref is now
  50 * gone, not present.
  51 */
  52int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  53{
  54        WARN_ON(release == NULL);
  55        WARN_ON(release == (void (*)(struct kref *))kfree);
  56
  57        if (atomic_dec_and_test(&kref->refcount)) {
  58                release(kref);
  59                return 1;
  60        }
  61        return 0;
  62}
  63
  64EXPORT_SYMBOL(kref_init);
  65EXPORT_SYMBOL(kref_get);
  66EXPORT_SYMBOL(kref_put);
  67