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  */
  21 void 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  */
  30 void 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  */
  50 int 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
  67 EXPORT_SYMBOL(kref_init);
  68 EXPORT_SYMBOL(kref_get);
  69 EXPORT_SYMBOL(kref_put);