fseek.c revision 82709
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 82709 2001-09-01 01:56:54Z 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 (_ftello(fp, &curoff)) 133 return (-1); 134 if ((offset > 0 && curoff > OFF_MAX - offset) || 135 (offset < 0 && curoff < OFF_MIN - offset)) { 136 errno = EOVERFLOW; 137 return (-1); 138 } 139 offset += curoff; 140 if (offset < 0) { 141 errno = EINVAL; 142 return (-1); 143 } 144 if (ltest && offset > LONG_MAX) { 145 errno = EOVERFLOW; 146 return (-1); 147 } 148 whence = SEEK_SET; 149 havepos = 1; 150 break; 151 152 case SEEK_SET: 153 if (offset < 0) { 154 errno = EINVAL; 155 return (-1); 156 } 157 case SEEK_END: 158 curoff = 0; /* XXX just to keep gcc quiet */ 159 havepos = 0; 160 break; 161 162 default: 163 errno = EINVAL; 164 return (-1); 165 } 166 167 /* 168 * Can only optimise if: 169 * reading (and not reading-and-writing); 170 * not unbuffered; and 171 * this is a `regular' Unix file (and hence seekfn==__sseek). 172 * We must check __NBF first, because it is possible to have __NBF 173 * and __SOPT both set. 174 */ 175 if (fp->_bf._base == NULL) 176 __smakebuf(fp); 177 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 178 goto dumb; 179 if ((fp->_flags & __SOPT) == 0) { 180 if (seekfn != __sseek || 181 fp->_file < 0 || _fstat(fp->_file, &st) || 182 (st.st_mode & S_IFMT) != S_IFREG) { 183 fp->_flags |= __SNPT; 184 goto dumb; 185 } 186 fp->_blksize = st.st_blksize; 187 fp->_flags |= __SOPT; 188 } 189 190 /* 191 * We are reading; we can try to optimise. 192 * Figure out where we are going and where we are now. 193 */ 194 if (whence == SEEK_SET) 195 target = offset; 196 else { 197 if (_fstat(fp->_file, &st)) 198 goto dumb; 199 if (offset > 0 && st.st_size > OFF_MAX - offset) { 200 errno = EOVERFLOW; 201 return (-1); 202 } 203 target = st.st_size + offset; 204 if ((off_t)target < 0) { 205 errno = EINVAL; 206 return (-1); 207 } 208 if (ltest && (off_t)target > LONG_MAX) { 209 errno = EOVERFLOW; 210 return (-1); 211 } 212 } 213 214 if (!havepos && _ftello(fp, &curoff)) 215 goto dumb; 216 217 /* 218 * (If the buffer was modified, we have to 219 * skip this; see fgetln.c.) 220 */ 221 if (fp->_flags & __SMOD) 222 goto abspos; 223 224 /* 225 * Compute the number of bytes in the input buffer (pretending 226 * that any ungetc() input has been discarded). Adjust current 227 * offset backwards by this count so that it represents the 228 * file offset for the first byte in the current input buffer. 229 */ 230 if (HASUB(fp)) { 231 if (curoff > 0 && fp->_r > OFF_MAX - curoff) 232 goto abspos; 233 curoff += fp->_r; /* kill off ungetc */ 234 n = fp->_extra->_up - fp->_bf._base; 235 if (curoff < 0 && -((off_t)n) < OFF_MIN - curoff) 236 goto abspos; 237 curoff -= n; 238 n += fp->_ur; 239 } else { 240 n = fp->_p - fp->_bf._base; 241 if (curoff < 0 && -((off_t)n) < OFF_MIN - curoff) 242 goto abspos; 243 curoff -= n; 244 n += fp->_r; 245 } 246 247 /* 248 * If the target offset is within the current buffer, 249 * simply adjust the pointers, clear EOF, undo ungetc(), 250 * and return. 251 */ 252 if (target >= curoff && 253 (curoff <= 0 || n <= OFF_MAX - curoff) && 254 target < curoff + n) { 255 size_t o = target - curoff; 256 257 fp->_p = fp->_bf._base + o; 258 fp->_r = n - o; 259 if (HASUB(fp)) 260 FREEUB(fp); 261 fp->_flags &= ~__SEOF; 262 return (0); 263 } 264 265abspos: 266 /* 267 * The place we want to get to is not within the current buffer, 268 * but we can still be kind to the kernel copyout mechanism. 269 * By aligning the file offset to a block boundary, we can let 270 * the kernel use the VM hardware to map pages instead of 271 * copying bytes laboriously. Using a block boundary also 272 * ensures that we only read one block, rather than two. 273 */ 274 curoff = target & ~(fp->_blksize - 1); 275 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 276 goto dumb; 277 fp->_r = 0; 278 fp->_p = fp->_bf._base; 279 if (HASUB(fp)) 280 FREEUB(fp); 281 n = target - curoff; 282 if (n) { 283 if (__srefill(fp) || fp->_r < n) 284 goto dumb; 285 fp->_p += n; 286 fp->_r -= n; 287 } 288 fp->_flags &= ~__SEOF; 289 return (0); 290 291 /* 292 * We get here if we cannot optimise the seek ... just 293 * do it. Allow the seek function to change fp->_bf._base. 294 */ 295dumb: 296 if (__sflush(fp) || 297 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) 298 return (-1); 299 if (ltest && fp->_offset > LONG_MAX) { 300 errno = EOVERFLOW; 301 return (-1); 302 } 303 /* success: clear EOF indicator and discard ungetc() data */ 304 if (HASUB(fp)) 305 FREEUB(fp); 306 fp->_p = fp->_bf._base; 307 fp->_r = 0; 308 /* fp->_w = 0; */ /* unnecessary (I think...) */ 309 fp->_flags &= ~__SEOF; 310 return (0); 311} 312