LXR linux/include/linux/kref.h

   1/*
   2 * kref.h - 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 kobject.h which was:
   8 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
   9 * Copyright (C) 2002-2003 Open Source Development Labs
  10 *
  11 * This file is released under the GPLv2.
  12 *
  13 */
  14
  15#ifndef _KREF_H_
  16#define _KREF_H_
  17
  18#include <linux/spinlock.h>
  19#include <linux/refcount.h>
  20
  21struct kref {
  22        refcount_t refcount;
  23};
  24
  25#define KREF_INIT(n)    { .refcount = REFCOUNT_INIT(n), }
  26
  27/**
  28 * kref_init - initialize object.
  29 * @kref: object in question.
  30 */
  31static inline void kref_init(struct kref *kref)
  32{
  33        refcount_set(&kref->refcount, 1);
  34}
  35
  36static inline unsigned int kref_read(const struct kref *kref)
  37{
  38        return refcount_read(&kref->refcount);
  39}
  40
  41/**
  42 * kref_get - increment refcount for object.
  43 * @kref: object.
  44 */
  45static inline void kref_get(struct kref *kref)
  46{
  47        refcount_inc(&kref->refcount);
  48}
  49
  50/**
  51 * kref_put - decrement refcount for object.
  52 * @kref: object.
  53 * @release: pointer to the function that will clean up the object when the
  54 *           last reference to the object is released.
  55 *           This pointer is required, and it is not acceptable to pass kfree
  56 *           in as this function.
  57 *
  58 * Decrement the refcount, and if 0, call release().
  59 * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  60 * function returns 0, you still can not count on the kref from remaining in
  61 * memory.  Only use the return value if you want to see if the kref is now
  62 * gone, not present.
  63 */
  64static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  65{
  66        if (refcount_dec_and_test(&kref->refcount)) {
  67                release(kref);
  68                return 1;
  69        }
  70        return 0;
  71}
  72
  73static inline int kref_put_mutex(struct kref *kref,
  74                                 void (*release)(struct kref *kref),
  75                                 struct mutex *lock)
  76{
  77        if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
  78                release(kref);
  79                return 1;
  80        }
  81        return 0;
  82}
  83
  84static inline int kref_put_lock(struct kref *kref,
  85                                void (*release)(struct kref *kref),
  86                                spinlock_t *lock)
  87{
  88        if (refcount_dec_and_lock(&kref->refcount, lock)) {
  89                release(kref);
  90                return 1;
  91        }
  92        return 0;
  93}
  94
  95/**
  96 * kref_get_unless_zero - Increment refcount for object unless it is zero.
  97 * @kref: object.
  98 *
  99 * Return non-zero if the increment succeeded. Otherwise return 0.
 100 *
 101 * This function is intended to simplify locking around refcounting for
 102 * objects that can be looked up from a lookup structure, and which are
 103 * removed from that lookup structure in the object destructor.
 104 * Operations on such objects require at least a read lock around
 105 * lookup + kref_get, and a write lock around kref_put + remove from lookup
 106 * structure. Furthermore, RCU implementations become extremely tricky.
 107 * With a lookup followed by a kref_get_unless_zero *with return value check*
 108 * locking in the kref_put path can be deferred to the actual removal from
 109 * the lookup structure and RCU lookups become trivial.
 110 */
 111static inline int __must_check kref_get_unless_zero(struct kref *kref)
 112{
 113        return refcount_inc_not_zero(&kref->refcount);
 114}
 115#endif /* _KREF_H_ */
 116