fseek.c revision 81819
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 81819 2001-08-17 10:22:03Z 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 (EOF); 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 (EOF); 138 } 139 if (fp->_flags & __SRD) { 140 curoff -= fp->_r; 141 if (HASUB(fp)) 142 curoff -= fp->_ur; 143 } else if (fp->_flags & __SWR && fp->_p != NULL) 144 curoff += fp->_p - fp->_bf._base; 145 146 /* curoff always >= 0 */ 147 if (offset > 0 && 148 curoff > (ltest ? LONG_MAX : OFF_MAX) - offset) { 149 errno = EOVERFLOW; 150 return (EOF); 151 } 152 offset += curoff; 153 /* Disallow negative seeks per POSIX */ 154 if (offset < 0) { 155 errno = EINVAL; 156 return (EOF); 157 } 158 if (ltest && offset > LONG_MAX) { 159 errno = EOVERFLOW; 160 return (EOF); 161 } 162 whence = SEEK_SET; 163 havepos = 1; 164 break; 165 166 case SEEK_SET: 167 /* Disallow negative seeks per POSIX */ 168 if (offset < 0) { 169 errno = EINVAL; 170 return (EOF); 171 } 172 case SEEK_END: 173 curoff = 0; /* XXX just to keep gcc quiet */ 174 havepos = 0; 175 break; 176 177 default: 178 errno = EINVAL; 179 return (EOF); 180 } 181 182 /* 183 * Can only optimise if: 184 * reading (and not reading-and-writing); 185 * not unbuffered; and 186 * this is a `regular' Unix file (and hence seekfn==__sseek). 187 * We must check __NBF first, because it is possible to have __NBF 188 * and __SOPT both set. 189 */ 190 if (fp->_bf._base == NULL) 191 __smakebuf(fp); 192 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 193 goto dumb; 194 if ((fp->_flags & __SOPT) == 0) { 195 if (seekfn != __sseek || 196 fp->_file < 0 || _fstat(fp->_file, &st) || 197 (st.st_mode & S_IFMT) != S_IFREG) { 198 fp->_flags |= __SNPT; 199 goto dumb; 200 } 201 fp->_blksize = st.st_blksize; 202 fp->_flags |= __SOPT; 203 } 204 205 /* 206 * We are reading; we can try to optimise. 207 * Figure out where we are going and where we are now. 208 */ 209 if (whence == SEEK_SET) 210 target = offset; 211 else { 212 if (_fstat(fp->_file, &st)) 213 goto dumb; 214 /* st.st_size always >= 0 */ 215 if (offset > 0 && 216 st.st_size > (ltest ? LONG_MAX : OFF_MAX) - offset) { 217 errno = EOVERFLOW; 218 return (EOF); 219 } 220 target = st.st_size + offset; 221 /* Disallow negative seeks per POSIX */ 222 if ((off_t)target < 0) { 223 errno = EINVAL; 224 return (EOF); 225 } 226 if (ltest && (off_t)target > LONG_MAX) { 227 errno = EOVERFLOW; 228 return (EOF); 229 } 230 } 231 232 if (!havepos) { 233 if (fp->_flags & __SOFF) 234 curoff = fp->_offset; 235 else { 236 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 237 if (curoff == POS_ERR) 238 goto dumb; 239 } 240 curoff -= fp->_r; 241 if (HASUB(fp)) 242 curoff -= fp->_ur; 243 } 244 245 /* 246 * Compute the number of bytes in the input buffer (pretending 247 * that any ungetc() input has been discarded). Adjust current 248 * offset backwards by this count so that it represents the 249 * file offset for the first byte in the current input buffer. 250 */ 251 if (HASUB(fp)) { 252 curoff += fp->_r; /* kill off ungetc */ 253 n = fp->_extra->_up - fp->_bf._base; 254 curoff -= n; 255 n += fp->_ur; 256 } else { 257 n = fp->_p - fp->_bf._base; 258 curoff -= n; 259 n += fp->_r; 260 } 261 262 /* 263 * If the target offset is within the current buffer, 264 * simply adjust the pointers, clear EOF, undo ungetc(), 265 * and return. (If the buffer was modified, we have to 266 * skip this; see fgetln.c.) 267 */ 268 if ((fp->_flags & __SMOD) == 0 && 269 target >= curoff && target < curoff + n) { 270 register int o = target - curoff; 271 272 fp->_p = fp->_bf._base + o; 273 fp->_r = n - o; 274 if (HASUB(fp)) 275 FREEUB(fp); 276 fp->_flags &= ~__SEOF; 277 return (0); 278 } 279 280 /* 281 * The place we want to get to is not within the current buffer, 282 * but we can still be kind to the kernel copyout mechanism. 283 * By aligning the file offset to a block boundary, we can let 284 * the kernel use the VM hardware to map pages instead of 285 * copying bytes laboriously. Using a block boundary also 286 * ensures that we only read one block, rather than two. 287 */ 288 curoff = target & ~(fp->_blksize - 1); 289 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 290 goto dumb; 291 fp->_r = 0; 292 fp->_p = fp->_bf._base; 293 if (HASUB(fp)) 294 FREEUB(fp); 295 fp->_flags &= ~__SEOF; 296 n = target - curoff; 297 if (n) { 298 if (__srefill(fp) || fp->_r < n) 299 goto dumb; 300 fp->_p += n; 301 fp->_r -= n; 302 } 303 return (0); 304 305 /* 306 * We get here if we cannot optimise the seek ... just 307 * do it. Allow the seek function to change fp->_bf._base. 308 */ 309dumb: 310 if (__sflush(fp) || 311 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) 312 return (EOF); 313 /* POSIX require long type resulting offset for fseek() */ 314 if (ltest && fp->_offset != (long)fp->_offset) { 315 errno = EOVERFLOW; 316 return (EOF); 317 } 318 /* success: clear EOF indicator and discard ungetc() data */ 319 if (HASUB(fp)) 320 FREEUB(fp); 321 fp->_p = fp->_bf._base; 322 fp->_r = 0; 323 /* fp->_w = 0; */ /* unnecessary (I think...) */ 324 fp->_flags &= ~__SEOF; 325 return (0); 326} 327