xref: /illumos-gate/usr/src/uts/common/os/bdev_dsort.c (revision 7c478bd9)
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
disksort(dp,bp)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