FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_cfglock.c

     /*      $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);
   }

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