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 1.6 2005/01/31 22:29:40 dillon 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 #include "local.h" 50 #include "libc_private.h" 51 52 #define POS_ERR (-(fpos_t)1) 53 54 int 55 fseek(FILE *fp, long offset, int whence) 56 { 57 return (fseeko(fp, offset, whence)); 58 } 59 60 int 61 fseeko(fp, offset, whence) 62 FILE *fp; 63 off_t offset; 64 int whence; 65 { 66 int ret; 67 68 /* make sure stdio is set up */ 69 if (!__sdidinit) 70 __sinit(); 71 72 FLOCKFILE(fp); 73 ret = _fseeko(fp, offset, whence); 74 FUNLOCKFILE(fp); 75 return (ret); 76 } 77 78 /* 79 * Seek the given file to the given offset. 80 * `Whence' must be one of the three SEEK_* macros. 81 */ 82 int 83 _fseeko(FILE *fp, off_t offset, int whence) 84 { 85 fpos_t (*seekfn) (void *, fpos_t, int); 86 fpos_t target, curoff; 87 size_t n; 88 struct stat st; 89 int havepos; 90 91 /* 92 * Have to be able to seek. 93 */ 94 if ((seekfn = fp->_seek) == NULL) { 95 errno = ESPIPE; /* historic practice */ 96 return (EOF); 97 } 98 99 /* 100 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 101 * After this, whence is either SEEK_SET or SEEK_END. 102 */ 103 switch (whence) { 104 105 case SEEK_CUR: 106 /* 107 * In order to seek relative to the current stream offset, 108 * we have to first find the current stream offset a la 109 * ftell (see ftell for details). 110 */ 111 if (fp->_flags & __SOFF) 112 curoff = fp->_offset; 113 else { 114 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 115 if (curoff == -1) { 116 return (EOF); 117 } 118 } 119 if (fp->_flags & __SRD) { 120 curoff -= fp->_r; 121 if (HASUB(fp)) 122 curoff -= fp->_ur; 123 } else if (fp->_flags & __SWR && fp->_p != NULL) 124 curoff += fp->_p - fp->_bf._base; 125 126 offset += curoff; 127 whence = SEEK_SET; 128 havepos = 1; 129 break; 130 131 case SEEK_SET: 132 case SEEK_END: 133 curoff = 0; /* XXX just to keep gcc quiet */ 134 havepos = 0; 135 break; 136 137 default: 138 errno = EINVAL; 139 return (EOF); 140 } 141 142 /* 143 * Can only optimise if: 144 * reading (and not reading-and-writing); 145 * not unbuffered; and 146 * this is a `regular' Unix file (and hence seekfn==__sseek). 147 * We must check __NBF first, because it is possible to have __NBF 148 * and __SOPT both set. 149 */ 150 if (fp->_bf._base == NULL) 151 __smakebuf(fp); 152 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 153 goto dumb; 154 if ((fp->_flags & __SOPT) == 0) { 155 if (seekfn != __sseek || 156 fp->_file < 0 || _fstat(fp->_file, &st) || 157 (st.st_mode & S_IFMT) != S_IFREG) { 158 fp->_flags |= __SNPT; 159 goto dumb; 160 } 161 fp->_blksize = st.st_blksize; 162 fp->_flags |= __SOPT; 163 } 164 165 /* 166 * We are reading; we can try to optimise. 167 * Figure out where we are going and where we are now. 168 */ 169 if (whence == SEEK_SET) 170 target = offset; 171 else { 172 if (_fstat(fp->_file, &st)) 173 goto dumb; 174 target = st.st_size + offset; 175 } 176 177 if (!havepos) { 178 if (fp->_flags & __SOFF) 179 curoff = fp->_offset; 180 else { 181 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 182 if (curoff == POS_ERR) 183 goto dumb; 184 } 185 curoff -= fp->_r; 186 if (HASUB(fp)) 187 curoff -= fp->_ur; 188 } 189 190 /* 191 * Compute the number of bytes in the input buffer (pretending 192 * that any ungetc() input has been discarded). Adjust current 193 * offset backwards by this count so that it represents the 194 * file offset for the first byte in the current input buffer. 195 */ 196 if (HASUB(fp)) { 197 curoff += fp->_r; /* kill off ungetc */ 198 n = fp->_up - fp->_bf._base; 199 curoff -= n; 200 n += fp->_ur; 201 } else { 202 n = fp->_p - fp->_bf._base; 203 curoff -= n; 204 n += fp->_r; 205 } 206 207 /* 208 * If the target offset is within the current buffer, 209 * simply adjust the pointers, clear EOF, undo ungetc(), 210 * and return. (If the buffer was modified, we have to 211 * skip this; see fgetln.c.) 212 */ 213 if ((fp->_flags & __SMOD) == 0 && 214 target >= curoff && target < curoff + n) { 215 int o = target - curoff; 216 217 fp->_p = fp->_bf._base + o; 218 fp->_r = n - o; 219 if (HASUB(fp)) 220 FREEUB(fp); 221 fp->_flags &= ~__SEOF; 222 return (0); 223 } 224 225 /* 226 * The place we want to get to is not within the current buffer, 227 * but we can still be kind to the kernel copyout mechanism. 228 * By aligning the file offset to a block boundary, we can let 229 * the kernel use the VM hardware to map pages instead of 230 * copying bytes laboriously. Using a block boundary also 231 * ensures that we only read one block, rather than two. 232 */ 233 curoff = target & ~(fp->_blksize - 1); 234 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 235 goto dumb; 236 fp->_r = 0; 237 fp->_p = fp->_bf._base; 238 if (HASUB(fp)) 239 FREEUB(fp); 240 fp->_flags &= ~__SEOF; 241 n = target - curoff; 242 if (n) { 243 if (__srefill(fp) || fp->_r < n) 244 goto dumb; 245 fp->_p += n; 246 fp->_r -= n; 247 } 248 return (0); 249 250 /* 251 * We get here if we cannot optimise the seek ... just 252 * do it. Allow the seek function to change fp->_bf._base. 253 */ 254 dumb: 255 if (__sflush(fp) || 256 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 257 return (EOF); 258 } 259 /* success: clear EOF indicator and discard ungetc() data */ 260 if (HASUB(fp)) 261 FREEUB(fp); 262 fp->_p = fp->_bf._base; 263 fp->_r = 0; 264 /* fp->_w = 0; */ /* unnecessary (I think...) */ 265 fp->_flags &= ~__SEOF; 266 return (0); 267 } 268