fseek.c revision 81730
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 81730 2001-08-15 20:10:38Z 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 return (fseeko(fp, offset, whence)); 66} 67 68int 69fseeko(fp, offset, whence) 70 FILE *fp; 71 off_t offset; 72 int whence; 73{ 74 int ret; 75 76 /* make sure stdio is set up */ 77 if (!__sdidinit) 78 __sinit(); 79 80 FLOCKFILE(fp); 81 ret = _fseeko(fp, offset, whence); 82 FUNLOCKFILE(fp); 83 return (ret); 84} 85 86/* 87 * Seek the given file to the given offset. 88 * `Whence' must be one of the three SEEK_* macros. 89 */ 90int 91_fseeko(fp, offset, whence) 92 FILE *fp; 93 off_t offset; 94 int whence; 95{ 96 register fpos_t (*seekfn) __P((void *, fpos_t, int)); 97 fpos_t target, curoff; 98 size_t n; 99 struct stat st; 100 int havepos; 101 102 /* 103 * Have to be able to seek. 104 */ 105 if ((seekfn = fp->_seek) == NULL) { 106 errno = ESPIPE; /* historic practice */ 107 return (EOF); 108 } 109 110 /* 111 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 112 * After this, whence is either SEEK_SET or SEEK_END. 113 */ 114 switch (whence) { 115 116 case SEEK_CUR: 117 /* 118 * In order to seek relative to the current stream offset, 119 * we have to first find the current stream offset a la 120 * ftell (see ftell for details). 121 */ 122 if (fp->_flags & __SOFF) 123 curoff = fp->_offset; 124 else { 125 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 126 if (curoff == -1) 127 return (EOF); 128 } 129 if (fp->_flags & __SRD) { 130 curoff -= fp->_r; 131 if (HASUB(fp)) 132 curoff -= fp->_ur; 133 } else if (fp->_flags & __SWR && fp->_p != NULL) 134 curoff += fp->_p - fp->_bf._base; 135 136 /* curoff always >= 0 */ 137 if (offset > 0 && curoff > OFF_MAX - offset) { 138 errno = EOVERFLOW; 139 return (EOF); 140 } 141 offset += curoff; 142 /* Disallow negative seeks per POSIX */ 143 if (offset < 0) { 144 errno = EINVAL; 145 return (EOF); 146 } 147 whence = SEEK_SET; 148 havepos = 1; 149 break; 150 151 case SEEK_SET: 152 /* Disallow negative seeks per POSIX */ 153 if (offset < 0) { 154 errno = EINVAL; 155 return (EOF); 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 (EOF); 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 /* st.st_size always >= 0 */ 200 if (offset > 0 && st.st_size > OFF_MAX - offset) { 201 errno = EOVERFLOW; 202 return (EOF); 203 } 204 target = st.st_size + offset; 205 /* Disallow negative seeks per POSIX */ 206 if ((off_t)target < 0) { 207 errno = EINVAL; 208 return (EOF); 209 } 210 } 211 212 if (!havepos) { 213 if (fp->_flags & __SOFF) 214 curoff = fp->_offset; 215 else { 216 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 217 if (curoff == POS_ERR) 218 goto dumb; 219 } 220 curoff -= fp->_r; 221 if (HASUB(fp)) 222 curoff -= fp->_ur; 223 } 224 225 /* 226 * Compute the number of bytes in the input buffer (pretending 227 * that any ungetc() input has been discarded). Adjust current 228 * offset backwards by this count so that it represents the 229 * file offset for the first byte in the current input buffer. 230 */ 231 if (HASUB(fp)) { 232 curoff += fp->_r; /* kill off ungetc */ 233 n = fp->_extra->_up - fp->_bf._base; 234 curoff -= n; 235 n += fp->_ur; 236 } else { 237 n = fp->_p - fp->_bf._base; 238 curoff -= n; 239 n += fp->_r; 240 } 241 242 /* 243 * If the target offset is within the current buffer, 244 * simply adjust the pointers, clear EOF, undo ungetc(), 245 * and return. (If the buffer was modified, we have to 246 * skip this; see fgetln.c.) 247 */ 248 if ((fp->_flags & __SMOD) == 0 && 249 target >= curoff && target < curoff + n) { 250 register int o = target - curoff; 251 252 fp->_p = fp->_bf._base + o; 253 fp->_r = n - o; 254 if (HASUB(fp)) 255 FREEUB(fp); 256 fp->_flags &= ~__SEOF; 257 return (0); 258 } 259 260 /* 261 * The place we want to get to is not within the current buffer, 262 * but we can still be kind to the kernel copyout mechanism. 263 * By aligning the file offset to a block boundary, we can let 264 * the kernel use the VM hardware to map pages instead of 265 * copying bytes laboriously. Using a block boundary also 266 * ensures that we only read one block, rather than two. 267 */ 268 curoff = target & ~(fp->_blksize - 1); 269 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 270 goto dumb; 271 fp->_r = 0; 272 fp->_p = fp->_bf._base; 273 if (HASUB(fp)) 274 FREEUB(fp); 275 fp->_flags &= ~__SEOF; 276 n = target - curoff; 277 if (n) { 278 if (__srefill(fp) || fp->_r < n) 279 goto dumb; 280 fp->_p += n; 281 fp->_r -= n; 282 } 283 return (0); 284 285 /* 286 * We get here if we cannot optimise the seek ... just 287 * do it. Allow the seek function to change fp->_bf._base. 288 */ 289dumb: 290 if (__sflush(fp) || 291 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) 292 return (EOF); 293 /* success: clear EOF indicator and discard ungetc() data */ 294 if (HASUB(fp)) 295 FREEUB(fp); 296 fp->_p = fp->_bf._base; 297 fp->_r = 0; 298 /* fp->_w = 0; */ /* unnecessary (I think...) */ 299 fp->_flags &= ~__SEOF; 300 return (0); 301} 302