1 /* $FreeBSD: src/lib/libstand/lseek.c,v 1.1.1.1.6.2 2001/08/30 03:14:16 jdp Exp $ */
2 /* $NetBSD: lseek.c,v 1.4 1997/01/22 00:38:10 cgd Exp $ */
6 * The Regents of the University of California. All rights reserved.
8 * This code is derived from software contributed to Berkeley by
9 * The Mach Operating System project at Carnegie-Mellon University.
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12 * modification, are permitted provided that the following conditions
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21 * This product includes software developed by the University of
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25 * without specific prior written permission.
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36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
39 * @(#)lseek.c 8.1 (Berkeley) 6/11/93
42 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
43 * All Rights Reserved.
45 * Author: Alessandro Forin
47 * Permission to use, copy, modify and distribute this software and its
48 * documentation is hereby granted, provided that both the copyright
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53 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
54 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
55 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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59 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
60 * School of Computer Science
61 * Carnegie Mellon University
62 * Pittsburgh PA 15213-3890
64 * any improvements or extensions that they make and grant Carnegie the
65 * rights to redistribute these changes.
71 lseek(int fd, off_t offset, int where)
73 off_t bufpos, filepos, target;
74 struct open_file *f = &files[fd];
76 if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
81 if (f->f_flags & F_RAW) {
83 * On RAW devices, update internal offset.
90 f->f_offset += offset;
101 * If there is some unconsumed data in the readahead buffer and it
102 * contains the desired offset, simply adjust the buffer offset and
103 * length. We don't bother with SEEK_END here, since the code to
104 * handle it would fail in the same cases where the non-readahead
105 * code fails (namely, for streams which cannot seek backward and whose
106 * size isn't known in advance).
108 if (f->f_ralen != 0 && where != SEEK_END) {
109 if ((filepos = (f->f_ops->fo_seek)(f, (off_t)0, SEEK_CUR)) == -1)
111 bufpos = filepos - f->f_ralen;
117 target = bufpos + offset;
123 if (bufpos <= target && target < filepos) {
124 f->f_raoffset += target - bufpos;
125 f->f_ralen -= target - bufpos;
131 * If this is a relative seek, we need to correct the offset for
132 * bytes that we have already read but the caller doesn't know
135 if (where == SEEK_CUR)
136 offset -= f->f_ralen;
139 * Invalidate the readahead buffer.
143 return (f->f_ops->fo_seek)(f, offset, where);