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 <sys/cdefs.h> 62 #include "stand.h" 63 64 off_t 65 lseek(int fd, off_t offset, int where) 66 { 67 off_t bufpos, filepos, target; 68 struct open_file *f; 69 70 f = fd2open_file(fd); 71 if (f == NULL || f->f_flags == 0) { 72 errno = EBADF; 73 return (-1); 74 } 75 76 if (f->f_flags & F_RAW) { 77 /* 78 * On RAW devices, update internal offset. 79 */ 80 switch (where) { 81 case SEEK_SET: 82 f->f_offset = offset; 83 break; 84 case SEEK_CUR: 85 f->f_offset += offset; 86 break; 87 default: 88 errno = EOFFSET; 89 return (-1); 90 } 91 return (f->f_offset); 92 } 93 94 /* 95 * If there is some unconsumed data in the readahead buffer and it 96 * contains the desired offset, simply adjust the buffer offset and 97 * length. We don't bother with SEEK_END here, since the code to 98 * handle it would fail in the same cases where the non-readahead 99 * code fails (namely, for streams which cannot seek backward and whose 100 * size isn't known in advance). 101 */ 102 if (f->f_ralen != 0 && where != SEEK_END) { 103 filepos = (f->f_ops->fo_seek)(f, 0, SEEK_CUR); 104 if (filepos == -1) 105 return (-1); 106 bufpos = filepos - f->f_ralen; 107 switch (where) { 108 case SEEK_SET: 109 target = offset; 110 break; 111 case SEEK_CUR: 112 target = bufpos + offset; 113 break; 114 default: 115 errno = EINVAL; 116 return (-1); 117 } 118 if (bufpos <= target && target < filepos) { 119 f->f_raoffset += target - bufpos; 120 f->f_ralen -= target - bufpos; 121 return (target); 122 } 123 } 124 125 /* 126 * If this is a relative seek, we need to correct the offset for 127 * bytes that we have already read but the caller doesn't know 128 * about. 129 */ 130 if (where == SEEK_CUR) 131 offset -= f->f_ralen; 132 133 /* 134 * Invalidate the readahead buffer. 135 */ 136 f->f_ralen = 0; 137 138 return (f->f_ops->fo_seek)(f, offset, where); 139 } 140