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 *	@(#)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__FBSDID("$FreeBSD$");
65
66#include "stand.h"
67
68off_t
69lseek(int fd, off_t offset, int where)
70{
71    off_t bufpos, filepos, target;
72    struct open_file *f = &files[fd];
73
74    if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
75	errno = EBADF;
76	return (-1);
77    }
78
79    if (f->f_flags & F_RAW) {
80	/*
81	 * On RAW devices, update internal offset.
82	 */
83	switch (where) {
84	case SEEK_SET:
85	    f->f_offset = offset;
86	    break;
87	case SEEK_CUR:
88	    f->f_offset += offset;
89	    break;
90	default:
91	    errno = EOFFSET;
92	    return (-1);
93	}
94	return (f->f_offset);
95    }
96
97    /*
98     * If there is some unconsumed data in the readahead buffer and it
99     * contains the desired offset, simply adjust the buffer offset and
100     * length.  We don't bother with SEEK_END here, since the code to
101     * handle it would fail in the same cases where the non-readahead
102     * code fails (namely, for streams which cannot seek backward and whose
103     * size isn't known in advance).
104     */
105    if (f->f_ralen != 0 && where != SEEK_END) {
106	if ((filepos = (f->f_ops->fo_seek)(f, (off_t)0, SEEK_CUR)) == -1)
107	    return (-1);
108	bufpos = filepos - f->f_ralen;
109	switch (where) {
110	case SEEK_SET:
111	    target = offset;
112	    break;
113	case SEEK_CUR:
114	    target = bufpos + offset;
115	    break;
116	default:
117	    errno = EINVAL;
118	    return (-1);
119	}
120	if (bufpos <= target && target < filepos) {
121	    f->f_raoffset += target - bufpos;
122	    f->f_ralen -= target - bufpos;
123	    return (target);
124	}
125    }
126
127    /*
128     * If this is a relative seek, we need to correct the offset for
129     * bytes that we have already read but the caller doesn't know
130     * about.
131     */
132    if (where == SEEK_CUR)
133	offset -= f->f_ralen;
134
135    /*
136     * Invalidate the readahead buffer.
137     */
138    f->f_ralen = 0;
139
140    return (f->f_ops->fo_seek)(f, offset, where);
141}
142