1 /* $NetBSD: lseek.c,v 1.4 1997/01/22 00:38:10 cgd Exp $ */
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34 * @(#)lseek.c 8.1 (Berkeley) 6/11/93
37 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
38 * All Rights Reserved.
40 * Author: Alessandro Forin
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54 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
55 * School of Computer Science
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59 * any improvements or extensions that they make and grant Carnegie the
60 * rights to redistribute these changes.
63 #include <sys/cdefs.h>
64 __FBSDID("$FreeBSD$");
69 lseek(int fd, off_t offset, int where)
71 off_t bufpos, filepos, target;
72 struct open_file *f = &files[fd];
74 if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
79 if (f->f_flags & F_RAW) {
81 * On RAW devices, update internal offset.
88 f->f_offset += offset;
99 * If there is some unconsumed data in the readahead buffer and it
100 * contains the desired offset, simply adjust the buffer offset and
101 * length. We don't bother with SEEK_END here, since the code to
102 * handle it would fail in the same cases where the non-readahead
103 * code fails (namely, for streams which cannot seek backward and whose
104 * size isn't known in advance).
106 if (f->f_ralen != 0 && where != SEEK_END) {
107 if ((filepos = (f->f_ops->fo_seek)(f, (off_t)0, SEEK_CUR)) == -1)
109 bufpos = filepos - f->f_ralen;
115 target = bufpos + offset;
121 if (bufpos <= target && target < filepos) {
122 f->f_raoffset += target - bufpos;
123 f->f_ralen -= target - bufpos;
129 * If this is a relative seek, we need to correct the offset for
130 * bytes that we have already read but the caller doesn't know
133 if (where == SEEK_CUR)
134 offset -= f->f_ralen;
137 * Invalidate the readahead buffer.
141 return (f->f_ops->fo_seek)(f, offset, where);