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 #include "stand.h" 65 66 off_t 67 lseek(int fd, off_t offset, int where) 68 { 69 off_t bufpos, filepos, target; 70 struct open_file *f; 71 72 f = fd2open_file(fd); 73 if (f == NULL || f->f_flags == 0) { 74 errno = EBADF; 75 return (-1); 76 } 77 78 if (f->f_flags & F_RAW) { 79 /* 80 * On RAW devices, update internal offset. 81 */ 82 switch (where) { 83 case SEEK_SET: 84 f->f_offset = offset; 85 break; 86 case SEEK_CUR: 87 f->f_offset += offset; 88 break; 89 default: 90 errno = EOFFSET; 91 return (-1); 92 } 93 return (f->f_offset); 94 } 95 96 /* 97 * If there is some unconsumed data in the readahead buffer and it 98 * contains the desired offset, simply adjust the buffer offset and 99 * length. We don't bother with SEEK_END here, since the code to 100 * handle it would fail in the same cases where the non-readahead 101 * code fails (namely, for streams which cannot seek backward and whose 102 * size isn't known in advance). 103 */ 104 if (f->f_ralen != 0 && where != SEEK_END) { 105 filepos = (f->f_ops->fo_seek)(f, 0, SEEK_CUR); 106 if (filepos == -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