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 * 3. 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 *
35 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
36 * All Rights Reserved.
37 *
38 * Author: Alessandro Forin
39 *
40 * Permission to use, copy, modify and distribute this software and its
41 * documentation is hereby granted, provided that both the copyright
42 * notice and this permission notice appear in all copies of the
43 * software, derivative works or modified versions, and any portions
44 * thereof, and that both notices appear in supporting documentation.
45 *
46 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
47 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
48 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
49 *
50 * Carnegie Mellon requests users of this software to return to
51 *
52 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
53 * School of Computer Science
54 * Carnegie Mellon University
55 * Pittsburgh PA 15213-3890
56 *
57 * any improvements or extensions that they make and grant Carnegie the
58 * rights to redistribute these changes.
59 */
60
61 #include "stand.h"
62
63 off_t
lseek(int fd,off_t offset,int where)64 lseek(int fd, off_t offset, int where)
65 {
66 off_t bufpos, filepos, target;
67 struct open_file *f;
68
69 f = fd2open_file(fd);
70 if (f == NULL || f->f_flags == 0) {
71 errno = EBADF;
72 return (-1);
73 }
74
75 if (f->f_flags & F_RAW) {
76 /*
77 * On RAW devices, update internal offset.
78 */
79 switch (where) {
80 case SEEK_SET:
81 f->f_offset = offset;
82 break;
83 case SEEK_CUR:
84 f->f_offset += offset;
85 break;
86 default:
87 errno = EOFFSET;
88 return (-1);
89 }
90 return (f->f_offset);
91 }
92
93 /*
94 * If there is some unconsumed data in the readahead buffer and it
95 * contains the desired offset, simply adjust the buffer offset and
96 * length. We don't bother with SEEK_END here, since the code to
97 * handle it would fail in the same cases where the non-readahead
98 * code fails (namely, for streams which cannot seek backward and whose
99 * size isn't known in advance).
100 */
101 if (f->f_ralen != 0 && where != SEEK_END) {
102 filepos = (f->f_ops->fo_seek)(f, 0, SEEK_CUR);
103 if (filepos == -1)
104 return (-1);
105 bufpos = filepos - f->f_ralen;
106 switch (where) {
107 case SEEK_SET:
108 target = offset;
109 break;
110 case SEEK_CUR:
111 target = bufpos + offset;
112 break;
113 default:
114 errno = EINVAL;
115 return (-1);
116 }
117 if (bufpos <= target && target < filepos) {
118 f->f_raoffset += target - bufpos;
119 f->f_ralen -= target - bufpos;
120 return (target);
121 }
122 }
123
124 /*
125 * If this is a relative seek, we need to correct the offset for
126 * bytes that we have already read but the caller doesn't know
127 * about.
128 */
129 if (where == SEEK_CUR)
130 offset -= f->f_ralen;
131
132 /*
133 * Invalidate the readahead buffer.
134 */
135 f->f_ralen = 0;
136
137 return (f->f_ops->fo_seek)(f, offset, where);
138 }
139