fseek.c revision 82668
1/*- 2 * Copyright (c) 1990, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Chris Torek. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 */ 36 37#if defined(LIBC_SCCS) && !defined(lint) 38#if 0 39static char sccsid[] = "@(#)fseek.c 8.3 (Berkeley) 1/2/94"; 40#endif 41static const char rcsid[] = 42 "$FreeBSD: head/lib/libc/stdio/fseek.c 82668 2001-08-31 18:23:29Z ache $"; 43#endif /* LIBC_SCCS and not lint */ 44 45#include "namespace.h" 46#include <sys/types.h> 47#include <sys/stat.h> 48#include <errno.h> 49#include <fcntl.h> 50#include <limits.h> 51#include <stdio.h> 52#include <stdlib.h> 53#include "un-namespace.h" 54#include "local.h" 55#include "libc_private.h" 56 57#define POS_ERR (-(fpos_t)1) 58 59int 60fseek(fp, offset, whence) 61 register FILE *fp; 62 long offset; 63 int whence; 64{ 65 int ret; 66 67 /* make sure stdio is set up */ 68 if (!__sdidinit) 69 __sinit(); 70 71 FLOCKFILE(fp); 72 ret = _fseeko(fp, (off_t)offset, whence, 1); 73 FUNLOCKFILE(fp); 74 return (ret); 75} 76 77int 78fseeko(fp, offset, whence) 79 FILE *fp; 80 off_t offset; 81 int whence; 82{ 83 int ret; 84 85 /* make sure stdio is set up */ 86 if (!__sdidinit) 87 __sinit(); 88 89 FLOCKFILE(fp); 90 ret = _fseeko(fp, offset, whence, 0); 91 FUNLOCKFILE(fp); 92 return (ret); 93} 94 95/* 96 * Seek the given file to the given offset. 97 * `Whence' must be one of the three SEEK_* macros. 98 */ 99int 100_fseeko(fp, offset, whence, ltest) 101 FILE *fp; 102 off_t offset; 103 int whence; 104 int ltest; 105{ 106 register fpos_t (*seekfn) __P((void *, fpos_t, int)); 107 fpos_t target, curoff; 108 size_t n; 109 struct stat st; 110 int havepos; 111 112 /* 113 * Have to be able to seek. 114 */ 115 if ((seekfn = fp->_seek) == NULL) { 116 errno = ESPIPE; /* historic practice */ 117 return (-1); 118 } 119 120 /* 121 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 122 * After this, whence is either SEEK_SET or SEEK_END. 123 */ 124 switch (whence) { 125 126 case SEEK_CUR: 127 /* 128 * In order to seek relative to the current stream offset, 129 * we have to first find the current stream offset via 130 * ftell (see ftell for details). 131 */ 132 if ((curoff = _ftello(fp)) == -1) 133 return (-1); 134 if (offset > 0 && curoff > OFF_MAX - offset) { 135 errno = EOVERFLOW; 136 return (-1); 137 } 138 offset += curoff; 139 if (offset < 0) { 140 errno = EINVAL; 141 return (-1); 142 } 143 if (ltest && offset > LONG_MAX) { 144 errno = EOVERFLOW; 145 return (-1); 146 } 147 whence = SEEK_SET; 148 havepos = 1; 149 break; 150 151 case SEEK_SET: 152 if (offset < 0) { 153 errno = EINVAL; 154 return (-1); 155 } 156 case SEEK_END: 157 curoff = 0; /* XXX just to keep gcc quiet */ 158 havepos = 0; 159 break; 160 161 default: 162 errno = EINVAL; 163 return (-1); 164 } 165 166 /* 167 * Can only optimise if: 168 * reading (and not reading-and-writing); 169 * not unbuffered; and 170 * this is a `regular' Unix file (and hence seekfn==__sseek). 171 * We must check __NBF first, because it is possible to have __NBF 172 * and __SOPT both set. 173 */ 174 if (fp->_bf._base == NULL) 175 __smakebuf(fp); 176 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 177 goto dumb; 178 if ((fp->_flags & __SOPT) == 0) { 179 if (seekfn != __sseek || 180 fp->_file < 0 || _fstat(fp->_file, &st) || 181 (st.st_mode & S_IFMT) != S_IFREG) { 182 fp->_flags |= __SNPT; 183 goto dumb; 184 } 185 fp->_blksize = st.st_blksize; 186 fp->_flags |= __SOPT; 187 } 188 189 /* 190 * We are reading; we can try to optimise. 191 * Figure out where we are going and where we are now. 192 */ 193 if (whence == SEEK_SET) 194 target = offset; 195 else { 196 if (_fstat(fp->_file, &st)) 197 goto dumb; 198 if (offset > 0 && st.st_size > OFF_MAX - offset) { 199 errno = EOVERFLOW; 200 return (-1); 201 } 202 target = st.st_size + offset; 203 if ((off_t)target < 0) { 204 errno = EINVAL; 205 return (-1); 206 } 207 if (ltest && (off_t)target > LONG_MAX) { 208 errno = EOVERFLOW; 209 return (-1); 210 } 211 } 212 213 if (!havepos && (curoff = _ftello(fp)) == -1) 214 goto dumb; 215 216 /* 217 * Compute the number of bytes in the input buffer (pretending 218 * that any ungetc() input has been discarded). Adjust current 219 * offset backwards by this count so that it represents the 220 * file offset for the first byte in the current input buffer. 221 */ 222 if (HASUB(fp)) { 223 if (curoff > OFF_MAX - fp->_r) 224 goto abspos; 225 curoff += fp->_r; /* kill off ungetc */ 226 n = fp->_extra->_up - fp->_bf._base; 227 curoff -= n; 228 n += fp->_ur; 229 } else { 230 n = fp->_p - fp->_bf._base; 231 curoff -= n; 232 n += fp->_r; 233 } 234 /* curoff can be negative at this point. */ 235 236 /* 237 * If the target offset is within the current buffer, 238 * simply adjust the pointers, clear EOF, undo ungetc(), 239 * and return. (If the buffer was modified, we have to 240 * skip this; see fgetln.c.) 241 */ 242 if ((fp->_flags & __SMOD) == 0 && 243 target >= curoff && 244 (curoff <= 0 || curoff <= OFF_MAX - n) && 245 target < curoff + n) { 246 size_t o = target - curoff; 247 248 fp->_p = fp->_bf._base + o; 249 fp->_r = n - o; 250 if (HASUB(fp)) 251 FREEUB(fp); 252 fp->_flags &= ~__SEOF; 253 return (0); 254 } 255 256abspos: 257 /* 258 * The place we want to get to is not within the current buffer, 259 * but we can still be kind to the kernel copyout mechanism. 260 * By aligning the file offset to a block boundary, we can let 261 * the kernel use the VM hardware to map pages instead of 262 * copying bytes laboriously. Using a block boundary also 263 * ensures that we only read one block, rather than two. 264 */ 265 curoff = target & ~(fp->_blksize - 1); 266 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 267 goto dumb; 268 fp->_r = 0; 269 fp->_p = fp->_bf._base; 270 if (HASUB(fp)) 271 FREEUB(fp); 272 n = target - curoff; 273 if (n) { 274 if (__srefill(fp) || fp->_r < n) 275 goto dumb; 276 fp->_p += n; 277 fp->_r -= n; 278 } 279 fp->_flags &= ~__SEOF; 280 return (0); 281 282 /* 283 * We get here if we cannot optimise the seek ... just 284 * do it. Allow the seek function to change fp->_bf._base. 285 */ 286dumb: 287 if (__sflush(fp) || 288 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) 289 return (-1); 290 if (ltest && fp->_offset > LONG_MAX) { 291 errno = EOVERFLOW; 292 return (-1); 293 } 294 /* success: clear EOF indicator and discard ungetc() data */ 295 if (HASUB(fp)) 296 FREEUB(fp); 297 fp->_p = fp->_bf._base; 298 fp->_r = 0; 299 /* fp->_w = 0; */ /* unnecessary (I think...) */ 300 fp->_flags &= ~__SEOF; 301 return (0); 302} 303