fseek.c revision 1.17
1 /* $NetBSD: fseek.c,v 1.17 1999/09/16 11:45:27 lukem Exp $ */ 2 3 /*- 4 * Copyright (c) 1990, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * Chris Torek. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 */ 38 39 #include <sys/cdefs.h> 40 #if defined(LIBC_SCCS) && !defined(lint) 41 #if 0 42 static char sccsid[] = "@(#)fseek.c 8.3 (Berkeley) 1/2/94"; 43 #else 44 __RCSID("$NetBSD: fseek.c,v 1.17 1999/09/16 11:45:27 lukem Exp $"); 45 #endif 46 #endif /* LIBC_SCCS and not lint */ 47 48 #include <sys/types.h> 49 #include <sys/stat.h> 50 51 #include <assert.h> 52 #include <errno.h> 53 #include <fcntl.h> 54 #include <stdio.h> 55 #include <stdlib.h> 56 #include "local.h" 57 #include "reentrant.h" 58 59 #define POS_ERR (-(fpos_t)1) 60 61 /* 62 * Seek the given file to the given offset. 63 * `Whence' must be one of the three SEEK_* macros. 64 */ 65 int 66 fseek(fp, offset, whence) 67 FILE *fp; 68 long offset; 69 int whence; 70 { 71 fpos_t (*seekfn) __P((void *, fpos_t, int)); 72 fpos_t target, curoff; 73 size_t n; 74 struct stat st; 75 int havepos; 76 77 _DIAGASSERT(fp != NULL); 78 #ifdef _DIAGNOSTIC 79 if (fp == NULL) { 80 errno = EBADF; 81 return (-1); 82 } 83 #endif 84 85 #ifdef __GNUC__ 86 /* This outrageous construct just to shut up a GCC warning. */ 87 (void) &curoff; 88 #endif 89 90 /* make sure stdio is set up */ 91 if (!__sdidinit) 92 __sinit(); 93 94 FLOCKFILE(fp); 95 96 /* 97 * Have to be able to seek. 98 */ 99 if ((seekfn = fp->_seek) == NULL) { 100 errno = ESPIPE; /* historic practice */ 101 FUNLOCKFILE(fp); 102 return (-1); 103 } 104 105 /* 106 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 107 * After this, whence is either SEEK_SET or SEEK_END. 108 */ 109 switch (whence) { 110 111 case SEEK_CUR: 112 /* 113 * In order to seek relative to the current stream offset, 114 * we have to first find the current stream offset a la 115 * ftell (see ftell for details). 116 */ 117 __sflush(fp); /* may adjust seek offset on append stream */ 118 if (fp->_flags & __SOFF) 119 curoff = fp->_offset; 120 else { 121 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 122 if (curoff == -1L) { 123 FUNLOCKFILE(fp); 124 return (-1); 125 } 126 } 127 if (fp->_flags & __SRD) { 128 curoff -= fp->_r; 129 if (HASUB(fp)) 130 curoff -= fp->_ur; 131 } else if (fp->_flags & __SWR && fp->_p != NULL) 132 curoff += fp->_p - fp->_bf._base; 133 134 offset += (long)curoff; 135 whence = SEEK_SET; 136 havepos = 1; 137 break; 138 139 case SEEK_SET: 140 case SEEK_END: 141 curoff = 0; /* XXX just to keep gcc quiet */ 142 havepos = 0; 143 break; 144 145 default: 146 errno = EINVAL; 147 FUNLOCKFILE(fp); 148 return (-1); 149 } 150 151 /* 152 * Can only optimise if: 153 * reading (and not reading-and-writing); 154 * not unbuffered; and 155 * this is a `regular' Unix file (and hence seekfn==__sseek). 156 * We must check __NBF first, because it is possible to have __NBF 157 * and __SOPT both set. 158 */ 159 if (fp->_bf._base == NULL) 160 __smakebuf(fp); 161 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 162 goto dumb; 163 if ((fp->_flags & __SOPT) == 0) { 164 if (seekfn != __sseek || 165 fp->_file < 0 || fstat(fp->_file, &st) || 166 !S_ISREG(st.st_mode)) { 167 fp->_flags |= __SNPT; 168 goto dumb; 169 } 170 fp->_blksize = st.st_blksize; 171 fp->_flags |= __SOPT; 172 } 173 174 /* 175 * We are reading; we can try to optimise. 176 * Figure out where we are going and where we are now. 177 */ 178 if (whence == SEEK_SET) 179 target = offset; 180 else { 181 if (fstat(fp->_file, &st)) 182 goto dumb; 183 target = st.st_size + offset; 184 } 185 186 if (!havepos) { 187 if (fp->_flags & __SOFF) 188 curoff = fp->_offset; 189 else { 190 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 191 if (curoff == POS_ERR) 192 goto dumb; 193 } 194 curoff -= fp->_r; 195 if (HASUB(fp)) 196 curoff -= fp->_ur; 197 } 198 199 /* 200 * Compute the number of bytes in the input buffer (pretending 201 * that any ungetc() input has been discarded). Adjust current 202 * offset backwards by this count so that it represents the 203 * file offset for the first byte in the current input buffer. 204 */ 205 if (HASUB(fp)) { 206 curoff += fp->_r; /* kill off ungetc */ 207 n = fp->_up - fp->_bf._base; 208 curoff -= n; 209 n += fp->_ur; 210 } else { 211 n = fp->_p - fp->_bf._base; 212 curoff -= n; 213 n += fp->_r; 214 } 215 216 /* 217 * If the target offset is within the current buffer, 218 * simply adjust the pointers, clear EOF, undo ungetc(), 219 * and return. (If the buffer was modified, we have to 220 * skip this; see fgetln.c.) 221 */ 222 if ((fp->_flags & __SMOD) == 0 && 223 target >= curoff && target < curoff + n) { 224 int o = (int)(target - curoff); 225 226 fp->_p = fp->_bf._base + o; 227 fp->_r = n - o; 228 if (HASUB(fp)) 229 FREEUB(fp); 230 fp->_flags &= ~__SEOF; 231 FUNLOCKFILE(fp); 232 return (0); 233 } 234 235 /* 236 * The place we want to get to is not within the current buffer, 237 * but we can still be kind to the kernel copyout mechanism. 238 * By aligning the file offset to a block boundary, we can let 239 * the kernel use the VM hardware to map pages instead of 240 * copying bytes laboriously. Using a block boundary also 241 * ensures that we only read one block, rather than two. 242 */ 243 curoff = target & ~(fp->_blksize - 1); 244 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 245 goto dumb; 246 fp->_r = 0; 247 fp->_p = fp->_bf._base; 248 if (HASUB(fp)) 249 FREEUB(fp); 250 fp->_flags &= ~__SEOF; 251 n = (int)(target - curoff); 252 if (n) { 253 if (__srefill(fp) || fp->_r < n) 254 goto dumb; 255 fp->_p += n; 256 fp->_r -= n; 257 } 258 FUNLOCKFILE(fp); 259 return (0); 260 261 /* 262 * We get here if we cannot optimise the seek ... just 263 * do it. Allow the seek function to change fp->_bf._base. 264 */ 265 dumb: 266 if (__sflush(fp) || 267 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 268 FUNLOCKFILE(fp); 269 return (-1); 270 } 271 /* success: clear EOF indicator and discard ungetc() data */ 272 if (HASUB(fp)) 273 FREEUB(fp); 274 fp->_p = fp->_bf._base; 275 fp->_r = 0; 276 /* fp->_w = 0; */ /* unnecessary (I think...) */ 277 fp->_flags &= ~__SEOF; 278 FUNLOCKFILE(fp); 279 return (0); 280 } 281
Indexes created Tue Sep 30 10:09:55 GMT 2025