fseek.c revision 82197
16735Samurai/*- 26059Samurai * Copyright (c) 1990, 1993 36059Samurai * The Regents of the University of California. All rights reserved. 46059Samurai * 56059Samurai * This code is derived from software contributed to Berkeley by 66059Samurai * Chris Torek. 76735Samurai * 86059Samurai * Redistribution and use in source and binary forms, with or without 96059Samurai * modification, are permitted provided that the following conditions 106059Samurai * are met: 116059Samurai * 1. Redistributions of source code must retain the above copyright 126059Samurai * 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 82197 2001-08-23 14:49:02Z 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' is always >= 0 */ 147 if (offset > 0 && curoff > OFF_MAX - offset) { 148 errno = EOVERFLOW; 149 return (EOF); 150 } 151 offset += curoff; 152 /* Disallow negative seeks per POSIX */ 153 if (offset < 0) { 154 errno = EINVAL; 155 return (EOF); 156 } 157 if (ltest && offset > LONG_MAX) { 158 errno = EOVERFLOW; 159 return (EOF); 160 } 161 whence = SEEK_SET; 162 havepos = 1; 163 break; 164 165 case SEEK_SET: 166 /* Disallow negative seeks per POSIX */ 167 if (offset < 0) { 168 errno = EINVAL; 169 return (EOF); 170 } 171 case SEEK_END: 172 curoff = 0; /* XXX just to keep gcc quiet */ 173 havepos = 0; 174 break; 175 176 default: 177 errno = EINVAL; 178 return (EOF); 179 } 180 181 /* 182 * Can only optimise if: 183 * reading (and not reading-and-writing); 184 * not unbuffered; and 185 * this is a `regular' Unix file (and hence seekfn==__sseek). 186 * We must check __NBF first, because it is possible to have __NBF 187 * and __SOPT both set. 188 */ 189 if (fp->_bf._base == NULL) 190 __smakebuf(fp); 191 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 192 goto dumb; 193 if ((fp->_flags & __SOPT) == 0) { 194 if (seekfn != __sseek || 195 fp->_file < 0 || _fstat(fp->_file, &st) || 196 (st.st_mode & S_IFMT) != S_IFREG) { 197 fp->_flags |= __SNPT; 198 goto dumb; 199 } 200 fp->_blksize = st.st_blksize; 201 fp->_flags |= __SOPT; 202 } 203 204 /* 205 * We are reading; we can try to optimise. 206 * Figure out where we are going and where we are now. 207 */ 208 if (whence == SEEK_SET) 209 target = offset; 210 else { 211 if (_fstat(fp->_file, &st)) 212 goto dumb; 213 /* 'st.st_size' is always >= 0 */ 214 if (offset > 0 && st.st_size > OFF_MAX - offset) { 215 errno = EOVERFLOW; 216 return (EOF); 217 } 218 target = st.st_size + offset; 219 /* Disallow negative seeks per POSIX */ 220 if ((off_t)target < 0) { 221 errno = EINVAL; 222 return (EOF); 223 } 224 if (ltest && (off_t)target > LONG_MAX) { 225 errno = EOVERFLOW; 226 return (EOF); 227 } 228 } 229 230 if (!havepos) { 231 if (fp->_flags & __SOFF) 232 curoff = fp->_offset; 233 else { 234 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 235 if (curoff == POS_ERR) 236 goto dumb; 237 } 238 curoff -= fp->_r; 239 if (HASUB(fp)) 240 curoff -= fp->_ur; 241 } 242 243 /* 244 * Compute the number of bytes in the input buffer (pretending 245 * that any ungetc() input has been discarded). Adjust current 246 * offset backwards by this count so that it represents the 247 * file offset for the first byte in the current input buffer. 248 */ 249 if (HASUB(fp)) { 250 curoff += fp->_r; /* kill off ungetc */ 251 n = fp->_extra->_up - fp->_bf._base; 252 curoff -= n; 253 n += fp->_ur; 254 } else { 255 n = fp->_p - fp->_bf._base; 256 curoff -= n; 257 n += fp->_r; 258 } 259 260 /* 261 * If the target offset is within the current buffer, 262 * simply adjust the pointers, clear EOF, undo ungetc(), 263 * and return. (If the buffer was modified, we have to 264 * skip this; see fgetln.c.) 265 */ 266 if ((fp->_flags & __SMOD) == 0 && 267 target >= curoff && target < curoff + n) { 268 register int o = target - curoff; 269 270 fp->_p = fp->_bf._base + o; 271 fp->_r = n - o; 272 if (HASUB(fp)) 273 FREEUB(fp); 274 fp->_flags &= ~__SEOF; 275 return (0); 276 } 277 278 /* 279 * The place we want to get to is not within the current buffer, 280 * but we can still be kind to the kernel copyout mechanism. 281 * By aligning the file offset to a block boundary, we can let 282 * the kernel use the VM hardware to map pages instead of 283 * copying bytes laboriously. Using a block boundary also 284 * ensures that we only read one block, rather than two. 285 */ 286 curoff = target & ~(fp->_blksize - 1); 287 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 288 goto dumb; 289 fp->_r = 0; 290 fp->_p = fp->_bf._base; 291 if (HASUB(fp)) 292 FREEUB(fp); 293 fp->_flags &= ~__SEOF; 294 n = target - curoff; 295 if (n) { 296 if (__srefill(fp) || fp->_r < n) 297 goto dumb; 298 fp->_p += n; 299 fp->_r -= n; 300 } 301 return (0); 302 303 /* 304 * We get here if we cannot optimise the seek ... just 305 * do it. Allow the seek function to change fp->_bf._base. 306 */ 307dumb: 308 if (__sflush(fp) || 309 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) 310 return (EOF); 311 /* POSIX require long type resulting offset for fseek() */ 312 if (ltest && fp->_offset != (long)fp->_offset) { 313 errno = EOVERFLOW; 314 return (EOF); 315 } 316 /* success: clear EOF indicator and discard ungetc() data */ 317 if (HASUB(fp)) 318 FREEUB(fp); 319 fp->_p = fp->_bf._base; 320 fp->_r = 0; 321 /* fp->_w = 0; */ /* unnecessary (I think...) */ 322 fp->_flags &= ~__SEOF; 323 return (0); 324} 325