xref: /freebsd/stand/libsa/lseek.c (revision a970610a3af63b3f4df5b69d91c6b4093a00ed8f)
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
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