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}
  25
  26/**
  27 * kref_get - increment refcount for object.
  28 * @kref: object.
  29 */
  30void kref_get(struct kref *kref)
  31{
  32        WARN_ON(!atomic_read(&kref->refcount));
  33        atomic_inc(&kref->refcount);
  34}
  35
  36/**
  37 * kref_put - decrement refcount for object.
  38 * @kref: object.
  39 * @release: pointer to the function that will clean up the object when the
  40 *           last reference to the object is released.
  41 *           This pointer is required, and it is not acceptable to pass kfree
  42 *           in as this function.
  43 *
  44 * Decrement the refcount, and if 0, call release().
  45 * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  46 * function returns 0, you still can not count on the kref from remaining in
  47 * memory.  Only use the return value if you want to see if the kref is now
  48 * gone, not present.
  49 */
  50int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  51{
  52        WARN_ON(release == NULL);
  53        WARN_ON(release == (void (*)(struct kref *))kfree);
  54
  55        /*
  56         * if current count is one, we are the last user and can release object
  57         * right now, avoiding an atomic operation on 'refcount'
  58         */
  59        if ((atomic_read(&kref->refcount) == 1) ||
  60            (atomic_dec_and_test(&kref->refcount))) {
  61                release(kref);
  62                return 1;
  63        }
  64        return 0;
  65}
  66
  67EXPORT_SYMBOL(kref_init);
  68EXPORT_SYMBOL(kref_get);
  69EXPORT_SYMBOL(kref_put);
  70