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

     /*      $NetBSD: bufq_disksort.c,v 1.3 2004/11/25 04:52:24 yamt Exp $   */
     /*      NetBSD: subr_disk.c,v 1.61 2004/09/25 03:30:44 thorpej Exp      */
     
     /*-
      * Copyright (c) 1996, 1997, 1999, 2000 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.
     *
     * 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. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the NetBSD
     *      Foundation, Inc. and its contributors.
     * 4. Neither the name of The NetBSD Foundation 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 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.
     */
    
    /*
     * Copyright (c) 1982, 1986, 1988, 1993
     *      The Regents of the University of California.  All rights reserved.
     * (c) UNIX System Laboratories, Inc.
     * All or some portions of this file are derived from material licensed
     * to the University of California by American Telephone and Telegraph
     * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * 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 University 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 REGENTS 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 REGENTS 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.
     *
     *      @(#)ufs_disksubr.c      8.5 (Berkeley) 1/21/94
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: bufq_disksort.c,v 1.3 2004/11/25 04:52:24 yamt Exp $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/buf.h>
    #include <sys/bufq.h>
    #include <sys/malloc.h>
    
    /*
     * Seek sort for disks.
     *
     * There are actually two queues, sorted in ascendening order.  The first
     * queue holds those requests which are positioned after the current block;
     * the second holds requests which came in after their position was passed.
     * Thus we implement a one-way scan, retracting after reaching the end of
     * the drive to the first request on the second queue, at which time it
     * becomes the first queue.
     *
     * A one-way scan is natural because of the way UNIX read-ahead blocks are
     * allocated.
     */
    
   struct bufq_disksort {
           TAILQ_HEAD(, buf) bq_head;      /* actual list of buffers */
   };
   
   static void bufq_disksort_init(struct bufq_state *);
   static void bufq_disksort_put(struct bufq_state *, struct buf *);
   static struct buf *bufq_disksort_get(struct bufq_state *, int);
   
   BUFQ_DEFINE(disksort, BUFQ_DISKSORT, bufq_disksort_init);
   
   static void
   bufq_disksort_put(struct bufq_state *bufq, struct buf *bp)
   {
           struct bufq_disksort *disksort = bufq->bq_private;
           struct buf *bq, *nbq;
           int sortby;
   
           sortby = bufq->bq_flags & BUFQ_SORT_MASK;
   
           bq = TAILQ_FIRST(&disksort->bq_head);
   
           /*
            * If the queue is empty it's easy; we just go on the end.
            */
           if (bq == NULL) {
                   TAILQ_INSERT_TAIL(&disksort->bq_head, bp, b_actq);
                   return;
           }
   
           /*
            * If we lie before the currently active request, then we
            * must locate the second request list and add ourselves to it.
            */
           if (buf_inorder(bp, bq, sortby)) {
                   while ((nbq = TAILQ_NEXT(bq, b_actq)) != NULL) {
                           /*
                            * Check for an ``inversion'' in the normally ascending
                            * block numbers, indicating the start of the second
                            * request list.
                            */
                           if (buf_inorder(nbq, bq, sortby)) {
                                   /*
                                    * Search the second request list for the first
                                    * request at a larger block number.  We go
                                    * after that; if there is no such request, we
                                    * go at the end.
                                    */
                                   do {
                                           if (buf_inorder(bp, nbq, sortby))
                                                   goto insert;
                                           bq = nbq;
                                   } while ((nbq =
                                       TAILQ_NEXT(bq, b_actq)) != NULL);
                                   goto insert;            /* after last */
                           }
                           bq = nbq;
                   }
                   /*
                    * No inversions... we will go after the last, and
                    * be the first request in the second request list.
                    */
                   goto insert;
           }
           /*
            * Request is at/after the current request...
            * sort in the first request list.
            */
           while ((nbq = TAILQ_NEXT(bq, b_actq)) != NULL) {
                   /*
                    * We want to go after the current request if there is an
                    * inversion after it (i.e. it is the end of the first
                    * request list), or if the next request is a larger cylinder
                    * than our request.
                    */
                   if (buf_inorder(nbq, bq, sortby) ||
                       buf_inorder(bp, nbq, sortby))
                           goto insert;
                   bq = nbq;
           }
           /*
            * Neither a second list nor a larger request... we go at the end of
            * the first list, which is the same as the end of the whole schebang.
            */
   insert: TAILQ_INSERT_AFTER(&disksort->bq_head, bq, bp, b_actq);
   }
   
   static struct buf *
   bufq_disksort_get(struct bufq_state *bufq, int remove)
   {
           struct bufq_disksort *disksort = bufq->bq_private;
           struct buf *bp;
   
           bp = TAILQ_FIRST(&disksort->bq_head);
   
           if (bp != NULL && remove)
                   TAILQ_REMOVE(&disksort->bq_head, bp, b_actq);
   
           return (bp);
   }
   
   static void
   bufq_disksort_init(struct bufq_state *bufq)
   {
           struct bufq_disksort *disksort;
   
           bufq->bq_get = bufq_disksort_get;
           bufq->bq_put = bufq_disksort_put;
           MALLOC(bufq->bq_private, struct bufq_disksort *,
               sizeof(struct bufq_disksort), M_DEVBUF, M_ZERO);
           disksort = (struct bufq_disksort *)bufq->bq_private;
           TAILQ_INIT(&disksort->bq_head);
   }

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