FreeBSD/Linux Kernel Cross Reference
sys/sys/sysref2.h

     /*
      * Copyright (c) 2007 The DragonFly Project.  All rights reserved.
      * 
      * This code is derived from software contributed to The DragonFly Project
      * by Matthew Dillon <dillon@backplane.com>
      * 
      * 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.
     * 3. Neither the name of The DragonFly Project nor the names of its
     *    contributors may be used to endorse or promote products derived
     *    from this software without specific, prior written permission.
     * 
     * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
     * COPYRIGHT HOLDERS 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.
     */
    /*
     * System resource registration, reference counter, and allocation
     * management subsystem.
     *
     * All major system resources use this structure and API to associate
     * a machine-unique sysref with a major system resource structure, to
     * reference count that structure, to register the structure and provide
     * a dictionary lookup feature for remote access, and to provide an
     * allocation and release backend.
     */
    
    #ifndef _SYS_SYSREF2_H_
    #define _SYS_SYSREF2_H_
    
    #ifndef _SYS_SYSREF_H_
    #include <sys/sysref.h>
    #endif
    #include <machine/atomic.h>
    
    void _sysref_put(struct sysref *);
    
    /*
     * Normally only 1+ transitions can occur.  Note that a negative ref count
     * is used as a marker to indicate that a structure is undergoing deletion
     * and that temporary refs during the process of deletion may occur.
     *
     * The get interface is the primary reference counting interface.
     */
    static __inline
    void
    sysref_get(struct sysref *sr)
    {
            KKASSERT((sr->flags & SRF_PUTAWAY) == 0);
            atomic_add_int(&sr->refcnt, 1);
    }
    
    /*
     * 1->0 transitions, and transitions occuring with negative ref counts,
     * require special handling.  All other transitions can be done with a
     * trivial locked bus cycle.
     */
    static __inline
    void
    sysref_put(struct sysref *sr)
    {
            int count = sr->refcnt;
    
            KKASSERT((sr->flags & SRF_PUTAWAY) == 0);
            if (count <= 1 || atomic_cmpset_int(&sr->refcnt, count, count - 1) == 0)
                    _sysref_put(sr);
    }
    
    /*
     * Return true of the object is fully active
     */
    static __inline
    int
    sysref_isactive(struct sysref *sr)
    {
            return(sr->refcnt > 0);
    }
    
    /*
     * Return true of the object is being deactivated
     */
    static __inline
   int
   sysref_isinactive(struct sysref *sr)
   {
           return(sr->refcnt <= 0);
   }
   
   /*
    * Return true if we control the last deactivation ref on the object
    */
   static __inline
   int
   sysref_islastdeactivation(struct sysref *sr)
   {
           return(sr->refcnt == -0x40000000);
   }
   
   #ifdef _KERNEL
   
   void sysref_init(struct sysref *sr, struct sysref_class *);
   void *sysref_alloc(struct sysref_class *class);
   void sysref_activate(struct sysref *);
   
   #endif
   
   #endif

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