fseek.c revision 1.15
1 /* $NetBSD: fseek.c,v 1.15 1998/09/06 16:37:27 kleink 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 1.15 1998/09/06 16:37:27 kleink Exp $"); 45 #endif 46 #endif /* LIBC_SCCS and not lint */ 47 48 #include <sys/types.h> 49 #include <sys/stat.h> 50 #include <fcntl.h> 51 #include <stdio.h> 52 #include <stdlib.h> 53 #include <errno.h> 54 #include "local.h" 55 #include "reentrant.h" 56 57 #define POS_ERR (-(fpos_t)1) 58 59 /* 60 * Seek the given file to the given offset. 61 * `Whence' must be one of the three SEEK_* macros. 62 */ 63 int 64 fseek(fp, offset, whence) 65 FILE *fp; 66 long offset; 67 int whence; 68 { 69 fpos_t (*seekfn) __P((void *, fpos_t, int)); 70 fpos_t target, curoff; 71 size_t n; 72 struct stat st; 73 int havepos; 74 75 #ifdef __GNUC__ 76 /* This outrageous construct just to shut up a GCC warning. */ 77 (void) &curoff; 78 #endif 79 80 /* make sure stdio is set up */ 81 if (!__sdidinit) 82 __sinit(); 83 84 FLOCKFILE(fp); 85 86 /* 87 * Have to be able to seek. 88 */ 89 if ((seekfn = fp->_seek) == NULL) { 90 errno = ESPIPE; /* historic practice */ 91 FUNLOCKFILE(fp); 92 return (-1); 93 } 94 95 /* 96 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 97 * After this, whence is either SEEK_SET or SEEK_END. 98 */ 99 switch (whence) { 100 101 case SEEK_CUR: 102 /* 103 * In order to seek relative to the current stream offset, 104 * we have to first find the current stream offset a la 105 * ftell (see ftell for details). 106 */ 107 __sflush(fp); /* may adjust seek offset on append stream */ 108 if (fp->_flags & __SOFF) 109 curoff = fp->_offset; 110 else { 111 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 112 if (curoff == -1L) { 113 FUNLOCKFILE(fp); 114 return (-1); 115 } 116 } 117 if (fp->_flags & __SRD) { 118 curoff -= fp->_r; 119 if (HASUB(fp)) 120 curoff -= fp->_ur; 121 } else if (fp->_flags & __SWR && fp->_p != NULL) 122 curoff += fp->_p - fp->_bf._base; 123 124 offset += curoff; 125 whence = SEEK_SET; 126 havepos = 1; 127 break; 128 129 case SEEK_SET: 130 case SEEK_END: 131 curoff = 0; /* XXX just to keep gcc quiet */ 132 havepos = 0; 133 break; 134 135 default: 136 errno = EINVAL; 137 FUNLOCKFILE(fp); 138 return (-1); 139 } 140 141 /* 142 * Can only optimise if: 143 * reading (and not reading-and-writing); 144 * not unbuffered; and 145 * this is a `regular' Unix file (and hence seekfn==__sseek). 146 * We must check __NBF first, because it is possible to have __NBF 147 * and __SOPT both set. 148 */ 149 if (fp->_bf._base == NULL) 150 __smakebuf(fp); 151 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 152 goto dumb; 153 if ((fp->_flags & __SOPT) == 0) { 154 if (seekfn != __sseek || 155 fp->_file < 0 || fstat(fp->_file, &st) || 156 !S_ISREG(st.st_mode)) { 157 fp->_flags |= __SNPT; 158 goto dumb; 159 } 160 fp->_blksize = st.st_blksize; 161 fp->_flags |= __SOPT; 162 } 163 164 /* 165 * We are reading; we can try to optimise. 166 * Figure out where we are going and where we are now. 167 */ 168 if (whence == SEEK_SET) 169 target = offset; 170 else { 171 if (fstat(fp->_file, &st)) 172 goto dumb; 173 target = st.st_size + offset; 174 } 175 176 if (!havepos) { 177 if (fp->_flags & __SOFF) 178 curoff = fp->_offset; 179 else { 180 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 181 if (curoff == POS_ERR) 182 goto dumb; 183 } 184 curoff -= fp->_r; 185 if (HASUB(fp)) 186 curoff -= fp->_ur; 187 } 188 189 /* 190 * Compute the number of bytes in the input buffer (pretending 191 * that any ungetc() input has been discarded). Adjust current 192 * offset backwards by this count so that it represents the 193 * file offset for the first byte in the current input buffer. 194 */ 195 if (HASUB(fp)) { 196 curoff += fp->_r; /* kill off ungetc */ 197 n = fp->_up - fp->_bf._base; 198 curoff -= n; 199 n += fp->_ur; 200 } else { 201 n = fp->_p - fp->_bf._base; 202 curoff -= n; 203 n += fp->_r; 204 } 205 206 /* 207 * If the target offset is within the current buffer, 208 * simply adjust the pointers, clear EOF, undo ungetc(), 209 * and return. (If the buffer was modified, we have to 210 * skip this; see fgetln.c.) 211 */ 212 if ((fp->_flags & __SMOD) == 0 && 213 target >= curoff && target < curoff + n) { 214 int o = target - curoff; 215 216 fp->_p = fp->_bf._base + o; 217 fp->_r = n - o; 218 if (HASUB(fp)) 219 FREEUB(fp); 220 fp->_flags &= ~__SEOF; 221 FUNLOCKFILE(fp); 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 FUNLOCKFILE(fp); 249 return (0); 250 251 /* 252 * We get here if we cannot optimise the seek ... just 253 * do it. Allow the seek function to change fp->_bf._base. 254 */ 255 dumb: 256 if (__sflush(fp) || 257 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 258 FUNLOCKFILE(fp); 259 return (-1); 260 } 261 /* success: clear EOF indicator and discard ungetc() data */ 262 if (HASUB(fp)) 263 FREEUB(fp); 264 fp->_p = fp->_bf._base; 265 fp->_r = 0; 266 /* fp->_w = 0; */ /* unnecessary (I think...) */ 267 fp->_flags &= ~__SEOF; 268 FUNLOCKFILE(fp); 269 return (0); 270 } 271
Indexes created Tue Sep 23 02:09:52 GMT 2025