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      1 /*
      2  * CDDL HEADER START
      3  *
      4  * The contents of this file are subject to the terms of the
      5  * Common Development and Distribution License, Version 1.0 only
      6  * (the "License").  You may not use this file except in compliance
      7  * with the License.
      8  *
      9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
     10  * or http://www.opensolaris.org/os/licensing.
     11  * See the License for the specific language governing permissions
     12  * and limitations under the License.
     13  *
     14  * When distributing Covered Code, include this CDDL HEADER in each
     15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     16  * If applicable, add the following below this CDDL HEADER, with the
     17  * fields enclosed by brackets "[]" replaced with your own identifying
     18  * information: Portions Copyright [yyyy] [name of copyright owner]
     19  *
     20  * CDDL HEADER END
     21  */
     22 /*
     23  * Copyright 1989 Sun Microsystems, Inc.  All rights reserved.
     24  * Use is subject to license terms.
     25  */
     26 
     27 /*	Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T	*/
     28 /*	  All Rights Reserved  	*/
     29 
     30 /*
     31  * Portions of this source code were derived from Berkeley 4.3 BSD
     32  * under license from the Regents of the University of California.
     33  */
     34 
     35 #ident	"%Z%%M%	%I%	%E% SMI"
     36 /* from ufs_dsort.c	2.12	89/07/24 SMI"	*/
     37 /*
     38  * Seek sort for disks.  We depend on the driver
     39  * which calls us using b_resid as the current cylinder number.
     40  *
     41  * The argument dp structure holds a b_actf activity chain pointer
     42  * on which we keep two queues, sorted in ascending cylinder order.
     43  * The first queue holds those requests which are positioned after
     44  * the current cylinder (in the first request); the second holds
     45  * requests which came in after their cylinder number was passed.
     46  * Thus we implement a one way scan, retracting after reaching the
     47  * end of the drive to the first request on the second queue,
     48  * at which time it becomes the first queue.
     49  *
     50  * A one-way scan is natural because of the way UNIX read-ahead
     51  * blocks are allocated.
     52  */
     53 
     54 #include <sys/types.h>
     55 #include <sys/param.h>
     56 #include <sys/systm.h>
     57 #include <sys/buf.h>
     58 
     59 #define	b_cylin	b_resid
     60 
     61 void
     62 disksort(dp, bp)
     63 	register struct diskhd *dp;
     64 	register struct buf *bp;
     65 {
     66 	register struct buf *ap;
     67 
     68 	/*
     69 	 * If nothing on the activity queue, then
     70 	 * we become the only thing.
     71 	 */
     72 	ap = dp->b_actf;
     73 	if (ap == NULL) {
     74 		dp->b_actf = bp;
     75 		dp->b_actl = bp;
     76 		bp->av_forw = NULL;
     77 		return;
     78 	}
     79 	/*
     80 	 * If we lie after the first (currently active)
     81 	 * request, then we must locate the second request list
     82 	 * and add ourselves to it.
     83 	 */
     84 	if (bp->b_cylin < ap->b_cylin) {
     85 		while (ap->av_forw) {
     86 			/*
     87 			 * Check for an ``inversion'' in the
     88 			 * normally ascending cylinder numbers,
     89 			 * indicating the start of the second request list.
     90 			 */
     91 			if (ap->av_forw->b_cylin < ap->b_cylin) {
     92 				/*
     93 				 * Search the second request list
     94 				 * for the first request at a larger
     95 				 * cylinder number.  We go before that;
     96 				 * if there is no such request, we go at end.
     97 				 */
     98 				do {
     99 					if (bp->b_cylin < ap->av_forw->b_cylin)
    100 						goto insert;
    101 					ap = ap->av_forw;
    102 				} while (ap->av_forw);
    103 				goto insert;		/* after last */
    104 			}
    105 			ap = ap->av_forw;
    106 		}
    107 		/*
    108 		 * No inversions... we will go after the last, and
    109 		 * be the first request in the second request list.
    110 		 */
    111 		goto insert;
    112 	}
    113 	/*
    114 	 * Request is at/after the current request...
    115 	 * sort in the first request list.
    116 	 */
    117 	while (ap->av_forw) {
    118 		/*
    119 		 * We want to go after the current request
    120 		 * if there is an inversion after it (i.e. it is
    121 		 * the end of the first request list), or if
    122 		 * the next request is a larger cylinder than our request.
    123 		 */
    124 		if (ap->av_forw->b_cylin < ap->b_cylin ||
    125 		    bp->b_cylin < ap->av_forw->b_cylin)
    126 			goto insert;
    127 		ap = ap->av_forw;
    128 	}
    129 	/*
    130 	 * Neither a second list nor a larger
    131 	 * request... we go at the end of the first list,
    132 	 * which is the same as the end of the whole schebang.
    133 	 */
    134 insert:
    135 	bp->av_forw = ap->av_forw;
    136 	ap->av_forw = bp;
    137 	if (ap == dp->b_actl)
    138 		dp->b_actl = bp;
    139 }
    140