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kref.h revision 1.1.2.2 
      1 /*	$NetBSD: kref.h,v 1.1.2.2 2013/07/24 01:51:36 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2013 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Taylor R. Campbell.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #ifndef _LINUX_KREF_H_
     33 #define _LINUX_KREF_H_
     34 
     35 #include <sys/types.h>
     36 #include <sys/atomic.h>
     37 #include <sys/systm.h>
     38 
     39 #include <linux/mutex.h>
     40 
     41 struct kref {
     42 	unsigned int kr_count;
     43 };
     44 
     45 static inline void
     46 kref_init(struct kref *kref)
     47 {
     48 	kref->kr_count = 1;
     49 }
     50 
     51 static inline void
     52 kref_get(struct kref *kref)
     53 {
     54 	const unsigned int count __unused =
     55 	    atomic_inc_uint_nv(&kref->kr_count);
     56 
     57 	KASSERT(count > 1);
     58 }
     59 
     60 static inline int
     61 kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *))
     62 {
     63 	unsigned int old, new;
     64 
     65 	do {
     66 		old = kref->kr_count;
     67 		KASSERT(count <= old);
     68 		new = (old - count);
     69 	} while (atomic_cas_uint(&kref->kr_count, old, new) == old);
     70 
     71 	if (new == 0) {
     72 		(*release)(kref);
     73 		return 1;
     74 	}
     75 
     76 	return 0;
     77 }
     78 
     79 static inline int
     80 kref_put(struct kref *kref, void (*release)(struct kref *))
     81 {
     82 
     83 	return kref_sub(kref, 1, release);
     84 }
     85 
     86 static inline int
     87 kref_put_mutex(struct kref *kref, void (*release)(struct kref *),
     88     struct mutex *interlock)
     89 {
     90 	unsigned int old, new;
     91 
     92 	do {
     93 		old = kref->kr_count;
     94 		KASSERT(old > 0);
     95 		if (old == 1) {
     96 			mutex_lock(interlock);
     97 			if (atomic_add_int_nv(&kref->kr_count, -1) == 0) {
     98 				(*release)(kref);
     99 				return 1;
    100 			}
    101 			mutex_unlock(interlock);
    102 			return 0;
    103 		}
    104 		new = (old - 1);
    105 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
    106 
    107 	return 0;
    108 }
    109 
    110 #endif  /* _LINUX_KREF_H_ */
    111