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_set - initialize object and set refcount to requested number.
  19 * @kref: object in question.
  20 * @num: initial reference counter
  21 */
  22void 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 */
  32void 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 */
  41void 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 */
  62int 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
  74EXPORT_SYMBOL(kref_set);
  75EXPORT_SYMBOL(kref_init);
  76EXPORT_SYMBOL(kref_get);
  77EXPORT_SYMBOL(kref_put);
  78