/*      $NetBSD: kern_rwlock_obj.c,v 1.13 2023/10/02 21:03:55 ad Exp $  */

/*-
* Copyright (c) 2008, 2009, 2019, 2023 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Andrew Doran.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_rwlock_obj.c,v 1.13 2023/10/02 21:03:55 ad Exp $");

#include <sys/param.h>
#include <sys/atomic.h>
#include <sys/kmem.h>
#include <sys/rwlock.h>

/* Mutex cache */
#define RW_OBJ_MAGIC    0x85d3c85d
struct krwobj {
       krwlock_t       ro_lock;
       u_int           ro_magic;
       u_int           ro_refcnt;
       uint8_t         mo_pad[COHERENCY_UNIT - sizeof(krwlock_t) -
           sizeof(u_int) * 2];
};

/*
* rw_obj_alloc:
*
*      Allocate a single lock object, waiting for memory if needed.
*/
krwlock_t *
rw_obj_alloc(void)
{
       struct krwobj *ro;

       ro = kmem_intr_alloc(sizeof(*ro), KM_SLEEP);
       KASSERT(ALIGNED_POINTER(ro, coherency_unit));
       _rw_init(&ro->ro_lock, (uintptr_t)__builtin_return_address(0));
       ro->ro_magic = RW_OBJ_MAGIC;
       ro->ro_refcnt = 1;

       return (krwlock_t *)ro;
}

/*
* rw_obj_tryalloc:
*
*      Allocate a single lock object, but fail if no memory is available.
*/
krwlock_t *
rw_obj_tryalloc(void)
{
       struct krwobj *ro;

       ro = kmem_intr_alloc(sizeof(*ro), KM_NOSLEEP);
       KASSERT(ALIGNED_POINTER(ro, coherency_unit));
       if (__predict_true(ro != NULL)) {
               _rw_init(&ro->ro_lock, (uintptr_t)__builtin_return_address(0));
               ro->ro_magic = RW_OBJ_MAGIC;
               ro->ro_refcnt = 1;
       }

       return (krwlock_t *)ro;
}

/*
* rw_obj_hold:
*
*      Add a single reference to a lock object.  A reference to the object
*      must already be held, and must be held across this call.
*/
void
rw_obj_hold(krwlock_t *lock)
{
       struct krwobj *ro = (struct krwobj *)lock;

       KASSERT(ro->ro_magic == RW_OBJ_MAGIC);
       KASSERT(ro->ro_refcnt > 0);

       atomic_inc_uint(&ro->ro_refcnt);
}

/*
* rw_obj_free:
*
*      Drop a reference from a lock object.  If the last reference is being
*      dropped, free the object and return true.  Otherwise, return false.
*/
bool
rw_obj_free(krwlock_t *lock)
{
       struct krwobj *ro = (struct krwobj *)lock;

       KASSERT(ro->ro_magic == RW_OBJ_MAGIC);
       KASSERT(ro->ro_refcnt > 0);

       membar_release();
       if (atomic_dec_uint_nv(&ro->ro_refcnt) > 0) {
               return false;
       }
       membar_acquire();
       rw_destroy(&ro->ro_lock);
       kmem_intr_free(ro, sizeof(*ro));
       return true;
}

/*
* rw_obj_refcnt:
*
*      Return the reference count for a lock object.
*/
u_int
rw_obj_refcnt(krwlock_t *lock)
{
       struct krwobj *ro = (struct krwobj *)lock;

       return ro->ro_refcnt;
}