/*      $NetBSD: kern_cfglock.c,v 1.1 2010/08/21 13:17:31 pgoyette Exp $ */

/*-
* Copyright (c) 2002, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
* NASA Ames Research Center, and 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_cfglock.c,v 1.1 2010/08/21 13:17:31 pgoyette Exp $");

#include <sys/param.h>
#include <sys/cpu.h>
#include <sys/mutex.h>
#include <sys/lwp.h>
#include <sys/systm.h>

static kmutex_t kernconfig_mutex;
static lwp_t *kernconfig_lwp;
static int kernconfig_recurse;

/*
* Functions for manipulating the kernel configuration lock.  This
* recursive lock should be used to protect all additions and removals
* of kernel functionality, such as device configuration and loading
* of modular kernel components.
*/

void
kernconfig_lock_init(void)
{

       mutex_init(&kernconfig_mutex, MUTEX_DEFAULT, IPL_NONE);
       kernconfig_lwp = NULL;
       kernconfig_recurse = 0;
}

void
kernconfig_lock(void)
{
       lwp_t   *my_lwp;

       /*
        * It's OK to check this unlocked, since it could only be set to
        * curlwp by the current thread itself, and not by an interrupt
        * or any other LWP.
        */
       KASSERT(!cpu_intr_p());
       my_lwp = curlwp;
       if (kernconfig_lwp == my_lwp) {
               kernconfig_recurse++;
               KASSERT(kernconfig_recurse > 1);
       } else {
               mutex_enter(&kernconfig_mutex);
               kernconfig_lwp = my_lwp;
               kernconfig_recurse = 1;
       }
}

void
kernconfig_unlock(void)
{

       KASSERT(kernconfig_is_held());
       KASSERT(kernconfig_recurse != 0);
       if (--kernconfig_recurse == 0) {
               kernconfig_lwp = NULL;
               mutex_exit(&kernconfig_mutex);
       }
}

bool
kernconfig_is_held(void)
{

       return mutex_owned(&kernconfig_mutex);
}