fseek.c revision 81818
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 81818 2001-08-17 10:06:46Z 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 whence = SEEK_SET; 159 havepos = 1; 160 break; 161 162 case SEEK_SET: 163 /* Disallow negative seeks per POSIX */ 164 if (offset < 0) { 165 errno = EINVAL; 166 return (EOF); 167 } 168 case SEEK_END: 169 curoff = 0; /* XXX just to keep gcc quiet */ 170 havepos = 0; 171 break; 172 173 default: 174 errno = EINVAL; 175 return (EOF); 176 } 177 178 /* 179 * Can only optimise if: 180 * reading (and not reading-and-writing); 181 * not unbuffered; and 182 * this is a `regular' Unix file (and hence seekfn==__sseek). 183 * We must check __NBF first, because it is possible to have __NBF 184 * and __SOPT both set. 185 */ 186 if (fp->_bf._base == NULL) 187 __smakebuf(fp); 188 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 189 goto dumb; 190 if ((fp->_flags & __SOPT) == 0) { 191 if (seekfn != __sseek || 192 fp->_file < 0 || _fstat(fp->_file, &st) || 193 (st.st_mode & S_IFMT) != S_IFREG) { 194 fp->_flags |= __SNPT; 195 goto dumb; 196 } 197 fp->_blksize = st.st_blksize; 198 fp->_flags |= __SOPT; 199 } 200 201 /* 202 * We are reading; we can try to optimise. 203 * Figure out where we are going and where we are now. 204 */ 205 if (whence == SEEK_SET) 206 target = offset; 207 else { 208 if (_fstat(fp->_file, &st)) 209 goto dumb; 210 /* st.st_size always >= 0 */ 211 if (offset > 0 && 212 st.st_size > (ltest ? LONG_MAX : OFF_MAX) - offset) { 213 errno = EOVERFLOW; 214 return (EOF); 215 } 216 target = st.st_size + offset; 217 /* Disallow negative seeks per POSIX */ 218 if ((off_t)target < 0) { 219 errno = EINVAL; 220 return (EOF); 221 } 222 } 223 224 if (!havepos) { 225 if (fp->_flags & __SOFF) 226 curoff = fp->_offset; 227 else { 228 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 229 if (curoff == POS_ERR) 230 goto dumb; 231 } 232 curoff -= fp->_r; 233 if (HASUB(fp)) 234 curoff -= fp->_ur; 235 } 236 237 /* 238 * Compute the number of bytes in the input buffer (pretending 239 * that any ungetc() input has been discarded). Adjust current 240 * offset backwards by this count so that it represents the 241 * file offset for the first byte in the current input buffer. 242 */ 243 if (HASUB(fp)) { 244 curoff += fp->_r; /* kill off ungetc */ 245 n = fp->_extra->_up - fp->_bf._base; 246 curoff -= n; 247 n += fp->_ur; 248 } else { 249 n = fp->_p - fp->_bf._base; 250 curoff -= n; 251 n += fp->_r; 252 } 253 254 /* 255 * If the target offset is within the current buffer, 256 * simply adjust the pointers, clear EOF, undo ungetc(), 257 * and return. (If the buffer was modified, we have to 258 * skip this; see fgetln.c.) 259 */ 260 if ((fp->_flags & __SMOD) == 0 && 261 target >= curoff && target < curoff + n) { 262 register int o = target - curoff; 263 264 fp->_p = fp->_bf._base + o; 265 fp->_r = n - o; 266 if (HASUB(fp)) 267 FREEUB(fp); 268 fp->_flags &= ~__SEOF; 269 return (0); 270 } 271 272 /* 273 * The place we want to get to is not within the current buffer, 274 * but we can still be kind to the kernel copyout mechanism. 275 * By aligning the file offset to a block boundary, we can let 276 * the kernel use the VM hardware to map pages instead of 277 * copying bytes laboriously. Using a block boundary also 278 * ensures that we only read one block, rather than two. 279 */ 280 curoff = target & ~(fp->_blksize - 1); 281 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 282 goto dumb; 283 fp->_r = 0; 284 fp->_p = fp->_bf._base; 285 if (HASUB(fp)) 286 FREEUB(fp); 287 fp->_flags &= ~__SEOF; 288 n = target - curoff; 289 if (n) { 290 if (__srefill(fp) || fp->_r < n) 291 goto dumb; 292 fp->_p += n; 293 fp->_r -= n; 294 } 295 return (0); 296 297 /* 298 * We get here if we cannot optimise the seek ... just 299 * do it. Allow the seek function to change fp->_bf._base. 300 */ 301dumb: 302 if (__sflush(fp) || 303 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) 304 return (EOF); 305 /* POSIX require long type resulting offset for fseek() */ 306 if (ltest && fp->_offset != (long)fp->_offset) { 307 errno = EOVERFLOW; 308 return (EOF); 309 } 310 /* success: clear EOF indicator and discard ungetc() data */ 311 if (HASUB(fp)) 312 FREEUB(fp); 313 fp->_p = fp->_bf._base; 314 fp->_r = 0; 315 /* fp->_w = 0; */ /* unnecessary (I think...) */ 316 fp->_flags &= ~__SEOF; 317 return (0); 318} 319