sys/kern/kern_rwlock_obj.c

   1 /*      $NetBSD$        */
   2
   3 /*-
   4  * Copyright (c) 2002, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
   5  * All rights reserved.
   6  *
   7  * This code is derived from software contributed to The NetBSD Foundation
   8  * by Jason R. Thorpe and Andrew Doran.
   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 #include <sys/cdefs.h>
  33 __KERNEL_RCSID(0, "$NetBSD$");
  34
  35 #include <sys/param.h>
  36 #include <sys/atomic.h>
  37 #include <sys/pool.h>
  38 #include <sys/rwlock.h>
  39
  40 /* Mutex cache */
  41 #define RW_OBJ_MAGIC    0x85d3c85d
  42 struct krwobj {
  43         krwlock_t       ro_lock;
  44         u_int           ro_magic;
  45         u_int           ro_refcnt;
  46 };
  47
  48 static int      rw_obj_ctor(void *, void *, int);
  49
  50 static pool_cache_t     rw_obj_cache;
  51
  52 /*
  53  * rw_obj_init:
  54  *
  55  *      Initialize the rw object store.
  56  */
  57 void
  58 rw_obj_init(void)
  59 {
  60
  61         rw_obj_cache = pool_cache_init(sizeof(struct krwobj),
  62             coherency_unit, 0, 0, "rwlock", NULL, IPL_NONE, rw_obj_ctor,
  63             NULL, NULL);
  64 }
  65
  66 /*
  67  * rw_obj_ctor:
  68  *
  69  *      Initialize a new lock for the cache.
  70  */
  71 static int
  72 rw_obj_ctor(void *arg, void *obj, int flags)
  73 {
  74         struct krwobj * ro = obj;
  75
  76         ro->ro_magic = RW_OBJ_MAGIC;
  77
  78         return 0;
  79 }
  80
  81 /*
  82  * rw_obj_alloc:
  83  *
  84  *      Allocate a single lock object.
  85  */
  86 krwlock_t *
  87 rw_obj_alloc(void)
  88 {
  89         struct krwobj *ro;
  90
  91         ro = pool_cache_get(rw_obj_cache, PR_WAITOK);
  92         rw_init(&ro->ro_lock);
  93         ro->ro_refcnt = 1;
  94
  95         return (krwlock_t *)ro;
  96 }
  97
  98 /*
  99  * rw_obj_hold:
 100  *
 101  *      Add a single reference to a lock object.  A reference to the object
 102  *      must already be held, and must be held across this call.
 103  */
 104 void
 105 rw_obj_hold(krwlock_t *lock)
 106 {
 107         struct krwobj *ro = (struct krwobj *)lock;
 108
 109         KASSERT(ro->ro_magic == RW_OBJ_MAGIC);
 110         KASSERT(ro->ro_refcnt > 0);
 111
 112         atomic_inc_uint(&ro->ro_refcnt);
 113 }
 114
 115 /*
 116  * rw_obj_free:
 117  *
 118  *      Drop a reference from a lock object.  If the last reference is being
 119  *      dropped, free the object and return true.  Otherwise, return false.
 120  */
 121 bool
 122 rw_obj_free(krwlock_t *lock)
 123 {
 124         struct krwobj *ro = (struct krwobj *)lock;
 125
 126         KASSERT(ro->ro_magic == RW_OBJ_MAGIC);
 127         KASSERT(ro->ro_refcnt > 0);
 128
 129         if (atomic_dec_uint_nv(&ro->ro_refcnt) > 0) {
 130                 return false;
 131         }
 132         rw_destroy(&ro->ro_lock);
 133         pool_cache_put(rw_obj_cache, ro);
 134         return true;
 135 }