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 * @(#)fseek.c 8.3 (Berkeley) 1/2/94 37 * $FreeBSD: src/lib/libc/stdio/fseek.c,v 1.9.2.1 2001/03/05 10:56:58 obrien Exp $ 38 * $DragonFly: src/lib/libc/stdio/fseek.c,v 1.9 2005/07/23 23:14:44 joerg Exp $ 39 */ 40 41 #include "namespace.h" 42 #include <sys/types.h> 43 #include <sys/stat.h> 44 #include <fcntl.h> 45 #include <stdio.h> 46 #include <stdlib.h> 47 #include <errno.h> 48 #include "un-namespace.h" 49 50 #include "local.h" 51 #include "libc_private.h" 52 #include "priv_stdio.h" 53 54 #define POS_ERR (-(fpos_t)1) 55 56 int 57 fseek(FILE *fp, long offset, int whence) 58 { 59 return (fseeko(fp, offset, whence)); 60 } 61 62 int 63 fseeko(fp, offset, whence) 64 FILE *fp; 65 off_t offset; 66 int whence; 67 { 68 int ret; 69 70 /* make sure stdio is set up */ 71 if (!__sdidinit) 72 __sinit(); 73 74 FLOCKFILE(fp); 75 ret = _fseeko(fp, offset, whence); 76 FUNLOCKFILE(fp); 77 return (ret); 78 } 79 80 /* 81 * Seek the given file to the given offset. 82 * `Whence' must be one of the three SEEK_* macros. 83 */ 84 int 85 _fseeko(FILE *fp, off_t offset, int whence) 86 { 87 fpos_t (*seekfn) (void *, fpos_t, int); 88 fpos_t target, curoff; 89 size_t n; 90 struct stat st; 91 int havepos; 92 93 /* 94 * Have to be able to seek. 95 */ 96 if ((seekfn = fp->_seek) == NULL) { 97 errno = ESPIPE; /* historic practice */ 98 return (EOF); 99 } 100 101 /* 102 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 103 * After this, whence is either SEEK_SET or SEEK_END. 104 */ 105 switch (whence) { 106 107 case SEEK_CUR: 108 /* 109 * In order to seek relative to the current stream offset, 110 * we have to first find the current stream offset a la 111 * ftell (see ftell for details). 112 */ 113 if (fp->pub._flags & __SOFF) 114 curoff = fp->_offset; 115 else { 116 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 117 if (curoff == -1) { 118 return (EOF); 119 } 120 } 121 if (fp->pub._flags & __SRD) { 122 curoff -= fp->pub._r; 123 if (HASUB(fp)) 124 curoff -= fp->_ur; 125 } else if (fp->pub._flags & __SWR && fp->pub._p != NULL) 126 curoff += fp->pub._p - fp->_bf._base; 127 128 offset += curoff; 129 whence = SEEK_SET; 130 havepos = 1; 131 break; 132 133 case SEEK_SET: 134 case SEEK_END: 135 curoff = 0; /* XXX just to keep gcc quiet */ 136 havepos = 0; 137 break; 138 139 default: 140 errno = EINVAL; 141 return (EOF); 142 } 143 144 /* 145 * Can only optimise if: 146 * reading (and not reading-and-writing); 147 * not unbuffered; and 148 * this is a `regular' Unix file (and hence seekfn==__sseek). 149 * We must check __NBF first, because it is possible to have __NBF 150 * and __SOPT both set. 151 */ 152 if (fp->_bf._base == NULL) 153 __smakebuf(fp); 154 if (fp->pub._flags & (__SWR | __SRW | __SNBF | __SNPT)) 155 goto dumb; 156 if ((fp->pub._flags & __SOPT) == 0) { 157 if (seekfn != __sseek || 158 fp->pub._fileno < 0 || _fstat(fp->pub._fileno, &st) || 159 (st.st_mode & S_IFMT) != S_IFREG) { 160 fp->pub._flags |= __SNPT; 161 goto dumb; 162 } 163 fp->_blksize = st.st_blksize; 164 fp->pub._flags |= __SOPT; 165 } 166 167 /* 168 * We are reading; we can try to optimise. 169 * Figure out where we are going and where we are now. 170 */ 171 if (whence == SEEK_SET) 172 target = offset; 173 else { 174 if (_fstat(fp->pub._fileno, &st)) 175 goto dumb; 176 target = st.st_size + offset; 177 } 178 179 if (!havepos) { 180 if (fp->pub._flags & __SOFF) 181 curoff = fp->_offset; 182 else { 183 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 184 if (curoff == POS_ERR) 185 goto dumb; 186 } 187 curoff -= fp->pub._r; 188 if (HASUB(fp)) 189 curoff -= fp->_ur; 190 } 191 192 /* 193 * Compute the number of bytes in the input buffer (pretending 194 * that any ungetc() input has been discarded). Adjust current 195 * offset backwards by this count so that it represents the 196 * file offset for the first byte in the current input buffer. 197 */ 198 if (HASUB(fp)) { 199 curoff += fp->pub._r; /* kill off ungetc */ 200 n = fp->_up - fp->_bf._base; 201 curoff -= n; 202 n += fp->_ur; 203 } else { 204 n = fp->pub._p - fp->_bf._base; 205 curoff -= n; 206 n += fp->pub._r; 207 } 208 209 /* 210 * If the target offset is within the current buffer, 211 * simply adjust the pointers, clear EOF, undo ungetc(), 212 * and return. (If the buffer was modified, we have to 213 * skip this; see fgetln.c.) 214 */ 215 if ((fp->pub._flags & __SMOD) == 0 && 216 target >= curoff && target < curoff + n) { 217 int o = target - curoff; 218 219 fp->pub._p = fp->_bf._base + o; 220 fp->pub._r = n - o; 221 if (HASUB(fp)) 222 FREEUB(fp); 223 fp->pub._flags &= ~__SEOF; 224 return (0); 225 } 226 227 /* 228 * The place we want to get to is not within the current buffer, 229 * but we can still be kind to the kernel copyout mechanism. 230 * By aligning the file offset to a block boundary, we can let 231 * the kernel use the VM hardware to map pages instead of 232 * copying bytes laboriously. Using a block boundary also 233 * ensures that we only read one block, rather than two. 234 */ 235 curoff = target & ~(fp->_blksize - 1); 236 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 237 goto dumb; 238 fp->pub._r = 0; 239 fp->pub._p = fp->_bf._base; 240 if (HASUB(fp)) 241 FREEUB(fp); 242 fp->pub._flags &= ~__SEOF; 243 n = target - curoff; 244 if (n) { 245 if (__srefill(fp) || fp->pub._r < n) 246 goto dumb; 247 fp->pub._p += n; 248 fp->pub._r -= n; 249 } 250 return (0); 251 252 /* 253 * We get here if we cannot optimise the seek ... just 254 * do it. Allow the seek function to change fp->_bf._base. 255 */ 256 dumb: 257 if (__sflush(fp) || 258 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 259 return (EOF); 260 } 261 /* success: clear EOF indicator and discard ungetc() data */ 262 if (HASUB(fp)) 263 FREEUB(fp); 264 fp->pub._p = fp->_bf._base; 265 fp->pub._r = 0; 266 /* fp->pub._w = 0; */ /* unnecessary (I think...) */ 267 fp->pub._flags &= ~__SEOF; 268 return (0); 269 } 270