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      1 /*	$NetBSD: kern_cfglock.c,v 1.1 2010/08/21 13:17:31 pgoyette Exp $ */
      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 of the Numerical Aerospace Simulation Facility,
      9  * NASA Ames Research Center, and by Andrew Doran.
     10  *
     11  * Redistribution and use in source and binary forms, with or without
     12  * modification, are permitted provided that the following conditions
     13  * are met:
     14  * 1. Redistributions of source code must retain the above copyright
     15  *    notice, this list of conditions and the following disclaimer.
     16  * 2. Redistributions in binary form must reproduce the above copyright
     17  *    notice, this list of conditions and the following disclaimer in the
     18  *    documentation and/or other materials provided with the distribution.
     19  *
     20  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     22  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     23  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     24  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     25  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     26  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     27  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     28  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     29  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     30  * POSSIBILITY OF SUCH DAMAGE.
     31  */
     32 
     33 #include <sys/cdefs.h>
     34 __KERNEL_RCSID(0, "$NetBSD: kern_cfglock.c,v 1.1 2010/08/21 13:17:31 pgoyette Exp $");
     35 
     36 #include <sys/param.h>
     37 #include <sys/cpu.h>
     38 #include <sys/mutex.h>
     39 #include <sys/lwp.h>
     40 #include <sys/systm.h>
     41 
     42 static kmutex_t kernconfig_mutex;
     43 static lwp_t *kernconfig_lwp;
     44 static int kernconfig_recurse;
     45 
     46 /*
     47  * Functions for manipulating the kernel configuration lock.  This
     48  * recursive lock should be used to protect all additions and removals
     49  * of kernel functionality, such as device configuration and loading
     50  * of modular kernel components.
     51  */
     52 
     53 void
     54 kernconfig_lock_init(void)
     55 {
     56 
     57 	mutex_init(&kernconfig_mutex, MUTEX_DEFAULT, IPL_NONE);
     58 	kernconfig_lwp = NULL;
     59 	kernconfig_recurse = 0;
     60 }
     61 
     62 void
     63 kernconfig_lock(void)
     64 {
     65 	lwp_t	*my_lwp;
     66 
     67 	/*
     68 	 * It's OK to check this unlocked, since it could only be set to
     69 	 * curlwp by the current thread itself, and not by an interrupt
     70 	 * or any other LWP.
     71 	 */
     72 	KASSERT(!cpu_intr_p());
     73 	my_lwp = curlwp;
     74 	if (kernconfig_lwp == my_lwp) {
     75 		kernconfig_recurse++;
     76 		KASSERT(kernconfig_recurse > 1);
     77 	} else {
     78 		mutex_enter(&kernconfig_mutex);
     79 		kernconfig_lwp = my_lwp;
     80 		kernconfig_recurse = 1;
     81 	}
     82 }
     83 
     84 void
     85 kernconfig_unlock(void)
     86 {
     87 
     88 	KASSERT(kernconfig_is_held());
     89 	KASSERT(kernconfig_recurse != 0);
     90 	if (--kernconfig_recurse == 0) {
     91 		kernconfig_lwp = NULL;
     92 		mutex_exit(&kernconfig_mutex);
     93 	}
     94 }
     95 
     96 bool
     97 kernconfig_is_held(void)
     98 {
     99 
    100 	return mutex_owned(&kernconfig_mutex);
    101 }
    102