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