1 /* $NetBSD: lseek.c,v 1.4 1997/01/22 00:38:10 cgd Exp $ */
2
3 /*-
4 * Copyright (c) 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * The Mach Operating System project at Carnegie-Mellon University.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 4. Neither the name of the University nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 * @(#)lseek.c 8.1 (Berkeley) 6/11/93
35 *
36 *
37 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
38 * All Rights Reserved.
39 *
40 * Author: Alessandro Forin
41 *
42 * Permission to use, copy, modify and distribute this software and its
43 * documentation is hereby granted, provided that both the copyright
44 * notice and this permission notice appear in all copies of the
45 * software, derivative works or modified versions, and any portions
46 * thereof, and that both notices appear in supporting documentation.
47 *
48 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
49 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
50 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
51 *
52 * Carnegie Mellon requests users of this software to return to
53 *
54 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
55 * School of Computer Science
56 * Carnegie Mellon University
57 * Pittsburgh PA 15213-3890
58 *
59 * any improvements or extensions that they make and grant Carnegie the
60 * rights to redistribute these changes.
61 */
62
63 #include <sys/cdefs.h>
64 #include "stand.h"
65
66 off_t
lseek(int fd,off_t offset,int where)67 lseek(int fd, off_t offset, int where)
68 {
69 off_t bufpos, filepos, target;
70 struct open_file *f = &files[fd];
71
72 if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
73 errno = EBADF;
74 return (-1);
75 }
76
77 if (f->f_flags & F_RAW) {
78 /*
79 * On RAW devices, update internal offset.
80 */
81 switch (where) {
82 case SEEK_SET:
83 f->f_offset = offset;
84 break;
85 case SEEK_CUR:
86 f->f_offset += offset;
87 break;
88 default:
89 errno = EOFFSET;
90 return (-1);
91 }
92 return (f->f_offset);
93 }
94
95 /*
96 * If there is some unconsumed data in the readahead buffer and it
97 * contains the desired offset, simply adjust the buffer offset and
98 * length. We don't bother with SEEK_END here, since the code to
99 * handle it would fail in the same cases where the non-readahead
100 * code fails (namely, for streams which cannot seek backward and whose
101 * size isn't known in advance).
102 */
103 if (f->f_ralen != 0 && where != SEEK_END) {
104 if ((filepos = (f->f_ops->fo_seek)(f, (off_t)0, SEEK_CUR)) == -1)
105 return (-1);
106 bufpos = filepos - f->f_ralen;
107 switch (where) {
108 case SEEK_SET:
109 target = offset;
110 break;
111 case SEEK_CUR:
112 target = bufpos + offset;
113 break;
114 default:
115 errno = EINVAL;
116 return (-1);
117 }
118 if (bufpos <= target && target < filepos) {
119 f->f_raoffset += target - bufpos;
120 f->f_ralen -= target - bufpos;
121 return (target);
122 }
123 }
124
125 /*
126 * If this is a relative seek, we need to correct the offset for
127 * bytes that we have already read but the caller doesn't know
128 * about.
129 */
130 if (where == SEEK_CUR)
131 offset -= f->f_ralen;
132
133 /*
134 * Invalidate the readahead buffer.
135 */
136 f->f_ralen = 0;
137
138 return (f->f_ops->fo_seek)(f, offset, where);
139 }
140