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/*
* 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
*
* This file is released under the GPLv2.
*
*/
#ifndef _KREF_H_
#define _KREF_H_
#include <linux/bug.h>
#include <linux/atomic.h>
#include <linux/kernel.h>
struct kref {
atomic_t refcount;
};
static inline void kref_init(struct kref *kref)
{
atomic_set(&kref->refcount, 1);
}
static inline void kref_get(struct kref *kref)
{
WARN_ON(!atomic_read(&kref->refcount));
atomic_inc(&kref->refcount);
}
static inline int kref_sub(struct kref *kref, unsigned int count,
void (*release)(struct kref *kref))
{
WARN_ON(release == NULL);
if (atomic_sub_and_test((int) count, &kref->refcount)) {
release(kref);
return 1;
}
return 0;
}
static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
{
return kref_sub(kref, 1, release);
}
/**
* kref_get_unless_zero - Increment refcount for object unless it is zero.
* @kref: object.
*
* Return non-zero if the increment succeeded. Otherwise return 0.
*
* 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.
*/
static inline int __must_check kref_get_unless_zero(struct kref *kref)
{
return atomic_add_unless(&kref->refcount, 1, 0);
}
#endif /* _KREF_H_ */
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