fseek.c revision 82591
1208926Smjacob/*- 2208926Smjacob * Copyright (c) 1990, 1993 3208926Smjacob * The Regents of the University of California. All rights reserved. 4208926Smjacob * 5208926Smjacob * This code is derived from software contributed to Berkeley by 6208926Smjacob * Chris Torek. 7208926Smjacob * 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 82591 2001-08-30 20:49:47Z 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 a la 130 * ftell (see ftell for details). 131 */ 132 if (fp->_flags & __SOFF) 133 curoff = fp->_offset; 134 else { 135 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 136 if (curoff == -1) 137 return (-1); 138 } 139 if (fp->_flags & __SRD) { 140 curoff -= fp->_r; 141 if (curoff < 0) { 142 if (HASUB(fp)) { 143 fp->_p -= curoff; 144 fp->_r += curoff; 145 curoff = 0; 146 } else { 147 errno = EBADF; 148 return (-1); 149 } 150 } 151 if (HASUB(fp)) { 152 curoff -= fp->_ur; 153 if (curoff < 0) { 154 if (-curoff <= fp->_r) { 155 fp->_p -= curoff; 156 fp->_r += curoff; 157 curoff = 0; 158 } else { 159 errno = EBADF; 160 return (-1); 161 } 162 } 163 } 164 } else if ((fp->_flags & __SWR) && fp->_p != NULL) { 165 n = fp->_p - fp->_bf._base; 166 if (curoff > OFF_MAX - n) { 167 errno = EOVERFLOW; 168 return (-1); 169 } 170 curoff += n; 171 } 172 if (offset > 0 && curoff > OFF_MAX - offset) { 173 errno = EOVERFLOW; 174 return (-1); 175 } 176 offset += curoff; 177 if (offset < 0) { 178 errno = EINVAL; 179 return (-1); 180 } 181 if (ltest && offset > LONG_MAX) { 182 errno = EOVERFLOW; 183 return (-1); 184 } 185 whence = SEEK_SET; 186 havepos = 1; 187 break; 188 189 case SEEK_SET: 190 if (offset < 0) { 191 errno = EINVAL; 192 return (-1); 193 } 194 case SEEK_END: 195 curoff = 0; /* XXX just to keep gcc quiet */ 196 havepos = 0; 197 break; 198 199 default: 200 errno = EINVAL; 201 return (-1); 202 } 203 204 /* 205 * Can only optimise if: 206 * reading (and not reading-and-writing); 207 * not unbuffered; and 208 * this is a `regular' Unix file (and hence seekfn==__sseek). 209 * We must check __NBF first, because it is possible to have __NBF 210 * and __SOPT both set. 211 */ 212 if (fp->_bf._base == NULL) 213 __smakebuf(fp); 214 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 215 goto dumb; 216 if ((fp->_flags & __SOPT) == 0) { 217 if (seekfn != __sseek || 218 fp->_file < 0 || _fstat(fp->_file, &st) || 219 (st.st_mode & S_IFMT) != S_IFREG) { 220 fp->_flags |= __SNPT; 221 goto dumb; 222 } 223 fp->_blksize = st.st_blksize; 224 fp->_flags |= __SOPT; 225 } 226 227 /* 228 * We are reading; we can try to optimise. 229 * Figure out where we are going and where we are now. 230 */ 231 if (whence == SEEK_SET) 232 target = offset; 233 else { 234 if (_fstat(fp->_file, &st)) 235 goto dumb; 236 if (offset > 0 && st.st_size > OFF_MAX - offset) { 237 errno = EOVERFLOW; 238 return (-1); 239 } 240 target = st.st_size + offset; 241 if ((off_t)target < 0) { 242 errno = EINVAL; 243 return (-1); 244 } 245 if (ltest && (off_t)target > LONG_MAX) { 246 errno = EOVERFLOW; 247 return (-1); 248 } 249 } 250 251 if (!havepos) { 252 if (fp->_flags & __SOFF) 253 curoff = fp->_offset; 254 else { 255 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 256 if (curoff == POS_ERR) 257 goto dumb; 258 } 259 curoff -= fp->_r; 260 if (curoff < 0) { 261 if (HASUB(fp)) { 262 fp->_p -= curoff; 263 fp->_r += curoff; 264 curoff = 0; 265 } else 266 goto dumb; 267 } 268 if (HASUB(fp)) { 269 curoff -= fp->_ur; 270 if (curoff < 0) { 271 if (-curoff <= fp->_r) { 272 fp->_p -= curoff; 273 fp->_r += curoff; 274 curoff = 0; 275 } else 276 goto dumb; 277 } 278 } 279 } 280 281 /* 282 * Compute the number of bytes in the input buffer (pretending 283 * that any ungetc() input has been discarded). Adjust current 284 * offset backwards by this count so that it represents the 285 * file offset for the first byte in the current input buffer. 286 */ 287 if (HASUB(fp)) { 288 if (curoff > OFF_MAX - fp->_r) 289 goto abspos; 290 curoff += fp->_r; /* kill off ungetc */ 291 n = fp->_extra->_up - fp->_bf._base; 292 curoff -= n; 293 n += fp->_ur; 294 } else { 295 n = fp->_p - fp->_bf._base; 296 curoff -= n; 297 n += fp->_r; 298 } 299 /* curoff can be negative at this point. */ 300 301 /* 302 * If the target offset is within the current buffer, 303 * simply adjust the pointers, clear EOF, undo ungetc(), 304 * and return. (If the buffer was modified, we have to 305 * skip this; see fgetln.c.) 306 */ 307 if ((fp->_flags & __SMOD) == 0 && 308 target >= curoff && 309 (curoff <= 0 || curoff <= OFF_MAX - n) && 310 target < curoff + n) { 311 size_t o = target - curoff; 312 313 fp->_p = fp->_bf._base + o; 314 fp->_r = n - o; 315 if (HASUB(fp)) 316 FREEUB(fp); 317 fp->_flags &= ~__SEOF; 318 return (0); 319 } 320 321abspos: 322 /* 323 * The place we want to get to is not within the current buffer, 324 * but we can still be kind to the kernel copyout mechanism. 325 * By aligning the file offset to a block boundary, we can let 326 * the kernel use the VM hardware to map pages instead of 327 * copying bytes laboriously. Using a block boundary also 328 * ensures that we only read one block, rather than two. 329 */ 330 curoff = target & ~(fp->_blksize - 1); 331 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 332 goto dumb; 333 fp->_r = 0; 334 fp->_p = fp->_bf._base; 335 if (HASUB(fp)) 336 FREEUB(fp); 337 fp->_flags &= ~__SEOF; 338 n = target - curoff; 339 if (n) { 340 if (__srefill(fp) || fp->_r < n) 341 goto dumb; 342 fp->_p += n; 343 fp->_r -= n; 344 } 345 return (0); 346 347 /* 348 * We get here if we cannot optimise the seek ... just 349 * do it. Allow the seek function to change fp->_bf._base. 350 */ 351dumb: 352 if (__sflush(fp) || 353 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) 354 return (-1); 355 if (ltest && fp->_offset > LONG_MAX) { 356 errno = EOVERFLOW; 357 return (-1); 358 } 359 /* success: clear EOF indicator and discard ungetc() data */ 360 if (HASUB(fp)) 361 FREEUB(fp); 362 fp->_p = fp->_bf._base; 363 fp->_r = 0; 364 /* fp->_w = 0; */ /* unnecessary (I think...) */ 365 fp->_flags &= ~__SEOF; 366 return (0); 367} 368