Quelle kref.h Sprache: C

/* SPDX-License-Identifier: GPL-2.0-only */
/*
* kref.h - library routines for handling generic reference counted objects
*
* Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
* Copyright (C) 2004 IBM Corp.
*
* based on kobject.h which was:
* Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
* Copyright (C) 2002-2003 Open Source Development Labs
*/

#ifndef _KREF_H_
#define _KREF_H_

#include <linux/spinlock.h>
#include <linux/refcount.h>

struct kref {
refcount_t refcount;
};

#define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }

/**
* kref_init - initialize object.
* @kref: object in question.
*/
static inline void kref_init(struct kref *kref)
{
refcount_set(&kref->refcount, 1);
}

static inline unsigned int kref_read(const struct kref *kref)
{
return refcount_read(&kref->refcount);
}

/**
* kref_get - increment refcount for object.
* @kref: object.
*/
static inline void kref_get(struct kref *kref)
{
refcount_inc(&kref->refcount);
}

/**
* 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.
*
* Decrement the refcount, and if 0, call @release.  The caller may not
* pass NULL or kfree() as the release function.
*
* Return: 1 if this call removed the object, otherwise return 0.  Beware,
* if this function returns 0, another caller may have removed the object
* by the time this function returns.  The return value is only certain
* if you want to see if the object is definitely released.
*/
static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
{
if (refcount_dec_and_test(&kref->refcount)) {
  release(kref);
  return 1;
}
return 0;
}

/**
* kref_put_mutex - 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.
* @mutex: Mutex which protects the release function.
*
* This variant of kref_lock() calls the @release function with the @mutex
* held.  The @release function will release the mutex.
*/
static inline int kref_put_mutex(struct kref *kref,
     void (*release)(struct kref *kref),
     struct mutex *mutex)
{
if (refcount_dec_and_mutex_lock(&kref->refcount, mutex)) {
  release(kref);
  return 1;
}
return 0;
}

/**
* kref_put_lock - 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.
* @lock: Spinlock which protects the release function.
*
* This variant of kref_lock() calls the @release function with the @lock
* held.  The @release function will release the lock.
*/
static inline int kref_put_lock(struct kref *kref,
    void (*release)(struct kref *kref),
    spinlock_t *lock)
{
if (refcount_dec_and_lock(&kref->refcount, lock)) {
  release(kref);
  return 1;
}
return 0;
}

/**
* kref_get_unless_zero - Increment refcount for object unless it is zero.
* @kref: object.
*
* This function is intended to simplify locking around refcounting for
* objects that can be looked up from a lookup structure, and which are
* removed from that lookup structure in the object destructor.
* Operations on such objects require at least a read lock around
* lookup + kref_get, and a write lock around kref_put + remove from lookup
* structure. Furthermore, RCU implementations become extremely tricky.
* With a lookup followed by a kref_get_unless_zero *with return value check*
* locking in the kref_put path can be deferred to the actual removal from
* the lookup structure and RCU lookups become trivial.
*
* Return: non-zero if the increment succeeded. Otherwise return 0.
*/
static inline int __must_check kref_get_unless_zero(struct kref *kref)
{
return refcount_inc_not_zero(&kref->refcount);
}
#endif /* _KREF_H_ */

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