/*
   * kref.c - library routines for handling generic reference counted objects
   *
   * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
   * Copyright (C) 2004 IBM Corp.
   *
   * based on lib/kobject.c which was:
   * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
   *
   * This file is released under the GPLv2.
   *
   */
  
  #include <linux/kref.h>
  #include <linux/module.h>

  #include <linux/slab.h>

  
  /**
   * kref_init - initialize object.
   * @kref: object in question.
   */
  void kref_init(struct kref *kref)
  {

  	atomic_set(&kref->refcount, 1);
  	smp_mb();

  }
  
  /**
   * kref_get - increment refcount for object.
   * @kref: object.
   */
  void kref_get(struct kref *kref)
  {
  	WARN_ON(!atomic_read(&kref->refcount));
  	atomic_inc(&kref->refcount);

  	smp_mb__after_atomic_inc();

  }
  
  /**
   * kref_put - decrement refcount for object.
   * @kref: object.
   * @release: pointer to the function that will clean up the object when the
   *	     last reference to the object is released.
   *	     This pointer is required, and it is not acceptable to pass kfree
   *	     in as this function.
   *
   * Decrement the refcount, and if 0, call release().
   * Return 1 if the object was removed, otherwise return 0.  Beware, if this
   * function returns 0, you still can not count on the kref from remaining in
   * memory.  Only use the return value if you want to see if the kref is now
   * gone, not present.
   */
  int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  {
  	WARN_ON(release == NULL);
  	WARN_ON(release == (void (*)(struct kref *))kfree);

  	if (atomic_dec_and_test(&kref->refcount)) {

  		release(kref);
  		return 1;
  	}
  	return 0;
  }

  
  /**
   * kref_sub - subtract a number of refcounts for object.
   * @kref: object.
   * @count: Number of recounts to subtract.
   * @release: pointer to the function that will clean up the object when the
   *	     last reference to the object is released.
   *	     This pointer is required, and it is not acceptable to pass kfree
   *	     in as this function.
   *
   * Subtract @count from the refcount, and if 0, call release().
   * Return 1 if the object was removed, otherwise return 0.  Beware, if this
   * function returns 0, you still can not count on the kref from remaining in
   * memory.  Only use the return value if you want to see if the kref is now
   * gone, not present.
   */
  int kref_sub(struct kref *kref, unsigned int count,
  	     void (*release)(struct kref *kref))
  {
  	WARN_ON(release == NULL);
  	WARN_ON(release == (void (*)(struct kref *))kfree);
  
  	if (atomic_sub_and_test((int) count, &kref->refcount)) {
  		release(kref);
  		return 1;
  	}
  	return 0;
  }

  EXPORT_SYMBOL(kref_init);
  EXPORT_SYMBOL(kref_get);
  EXPORT_SYMBOL(kref_put);

  EXPORT_SYMBOL(kref_sub);