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         smp_mb();
  25 }
  26
  27 /**
  28  * kref_get - increment refcount for object.
  29  * @kref: object.
  30  */
  31 void 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  */
  52 int 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
  64 EXPORT_SYMBOL(kref_init);
  65 EXPORT_SYMBOL(kref_get);
  66 EXPORT_SYMBOL(kref_put);