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.  If the caller does pass kfree to this
  57 *           function, you will be publicly mocked mercilessly by the kref
  58 *           maintainer, and anyone else who happens to notice it.  You have
  59 *           been warned.
  60 *
  61 * Decrement the refcount, and if 0, call release().
  62 * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  63 * function returns 0, you still can not count on the kref from remaining in
  64 * memory.  Only use the return value if you want to see if the kref is now
  65 * gone, not present.
  66 */
  67static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
  68{
  69        if (refcount_dec_and_test(&kref->refcount)) {
  70                release(kref);
  71                return 1;
  72        }
  73        return 0;
  74}
  75
  76static inline int kref_put_mutex(struct kref *kref,
  77                                 void (*release)(struct kref *kref),
  78                                 struct mutex *lock)
  79{
  80        if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
  81                release(kref);
  82                return 1;
  83        }
  84        return 0;
  85}
  86
  87static inline int kref_put_lock(struct kref *kref,
  88                                void (*release)(struct kref *kref),
  89                                spinlock_t *lock)
  90{
  91        if (refcount_dec_and_lock(&kref->refcount, lock)) {
  92                release(kref);
  93                return 1;
  94        }
  95        return 0;
  96}
  97
  98/**
  99 * kref_get_unless_zero - Increment refcount for object unless it is zero.
 100 * @kref: object.
 101 *
 102 * Return non-zero if the increment succeeded. Otherwise return 0.
 103 *
 104 * This function is intended to simplify locking around refcounting for
 105 * objects that can be looked up from a lookup structure, and which are
 106 * removed from that lookup structure in the object destructor.
 107 * Operations on such objects require at least a read lock around
 108 * lookup + kref_get, and a write lock around kref_put + remove from lookup
 109 * structure. Furthermore, RCU implementations become extremely tricky.
 110 * With a lookup followed by a kref_get_unless_zero *with return value check*
 111 * locking in the kref_put path can be deferred to the actual removal from
 112 * the lookup structure and RCU lookups become trivial.
 113 */
 114static inline int __must_check kref_get_unless_zero(struct kref *kref)
 115{
 116        return refcount_inc_not_zero(&kref->refcount);
 117}
 118#endif /* _KREF_H_ */
 119