fseek.c revision 1.13
1 /* $NetBSD: fseek.c,v 1.13 1998/02/03 01:40:49 mycroft 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 1.13 1998/02/03 01:40:49 mycroft 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 register FILE *fp; 66 long offset; 67 int whence; 68 { 69 register 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 return (-1); 92 } 93 94 /* 95 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 96 * After this, whence is either SEEK_SET or SEEK_END. 97 */ 98 switch (whence) { 99 100 case SEEK_CUR: 101 /* 102 * In order to seek relative to the current stream offset, 103 * we have to first find the current stream offset a la 104 * ftell (see ftell for details). 105 */ 106 __sflush(fp); /* may adjust seek offset on append stream */ 107 if (fp->_flags & __SOFF) 108 curoff = fp->_offset; 109 else { 110 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 111 if (curoff == -1L) { 112 FUNLOCKFILE(fp); 113 return (-1); 114 } 115 } 116 if (fp->_flags & __SRD) { 117 curoff -= fp->_r; 118 if (HASUB(fp)) 119 curoff -= fp->_ur; 120 } else if (fp->_flags & __SWR && fp->_p != NULL) 121 curoff += fp->_p - fp->_bf._base; 122 123 offset += curoff; 124 whence = SEEK_SET; 125 havepos = 1; 126 break; 127 128 case SEEK_SET: 129 case SEEK_END: 130 curoff = 0; /* XXX just to keep gcc quiet */ 131 havepos = 0; 132 break; 133 134 default: 135 errno = EINVAL; 136 FUNLOCKFILE(fp); 137 return (-1); 138 } 139 140 /* 141 * Can only optimise if: 142 * reading (and not reading-and-writing); 143 * not unbuffered; and 144 * this is a `regular' Unix file (and hence seekfn==__sseek). 145 * We must check __NBF first, because it is possible to have __NBF 146 * and __SOPT both set. 147 */ 148 if (fp->_bf._base == NULL) 149 __smakebuf(fp); 150 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 151 goto dumb; 152 if ((fp->_flags & __SOPT) == 0) { 153 if (seekfn != __sseek || 154 fp->_file < 0 || fstat(fp->_file, &st) || 155 !S_ISREG(st.st_mode)) { 156 fp->_flags |= __SNPT; 157 goto dumb; 158 } 159 fp->_blksize = st.st_blksize; 160 fp->_flags |= __SOPT; 161 } 162 163 /* 164 * We are reading; we can try to optimise. 165 * Figure out where we are going and where we are now. 166 */ 167 if (whence == SEEK_SET) 168 target = offset; 169 else { 170 if (fstat(fp->_file, &st)) 171 goto dumb; 172 target = st.st_size + offset; 173 } 174 175 if (!havepos) { 176 if (fp->_flags & __SOFF) 177 curoff = fp->_offset; 178 else { 179 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 180 if (curoff == POS_ERR) 181 goto dumb; 182 } 183 curoff -= fp->_r; 184 if (HASUB(fp)) 185 curoff -= fp->_ur; 186 } 187 188 /* 189 * Compute the number of bytes in the input buffer (pretending 190 * that any ungetc() input has been discarded). Adjust current 191 * offset backwards by this count so that it represents the 192 * file offset for the first byte in the current input buffer. 193 */ 194 if (HASUB(fp)) { 195 curoff += fp->_r; /* kill off ungetc */ 196 n = fp->_up - fp->_bf._base; 197 curoff -= n; 198 n += fp->_ur; 199 } else { 200 n = fp->_p - fp->_bf._base; 201 curoff -= n; 202 n += fp->_r; 203 } 204 205 /* 206 * If the target offset is within the current buffer, 207 * simply adjust the pointers, clear EOF, undo ungetc(), 208 * and return. (If the buffer was modified, we have to 209 * skip this; see fgetln.c.) 210 */ 211 if ((fp->_flags & __SMOD) == 0 && 212 target >= curoff && target < curoff + n) { 213 register int o = target - curoff; 214 215 fp->_p = fp->_bf._base + o; 216 fp->_r = n - o; 217 if (HASUB(fp)) 218 FREEUB(fp); 219 fp->_flags &= ~__SEOF; 220 FUNLOCKFILE(fp); 221 return (0); 222 } 223 224 /* 225 * The place we want to get to is not within the current buffer, 226 * but we can still be kind to the kernel copyout mechanism. 227 * By aligning the file offset to a block boundary, we can let 228 * the kernel use the VM hardware to map pages instead of 229 * copying bytes laboriously. Using a block boundary also 230 * ensures that we only read one block, rather than two. 231 */ 232 curoff = target & ~(fp->_blksize - 1); 233 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 234 goto dumb; 235 fp->_r = 0; 236 fp->_p = fp->_bf._base; 237 if (HASUB(fp)) 238 FREEUB(fp); 239 fp->_flags &= ~__SEOF; 240 n = target - curoff; 241 if (n) { 242 if (__srefill(fp) || fp->_r < n) 243 goto dumb; 244 fp->_p += n; 245 fp->_r -= n; 246 } 247 FUNLOCKFILE(fp); 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 FUNLOCKFILE(fp); 258 return (-1); 259 } 260 /* success: clear EOF indicator and discard ungetc() data */ 261 if (HASUB(fp)) 262 FREEUB(fp); 263 fp->_p = fp->_bf._base; 264 fp->_r = 0; 265 /* fp->_w = 0; */ /* unnecessary (I think...) */ 266 fp->_flags &= ~__SEOF; 267 FUNLOCKFILE(fp); 268 return (0); 269 } 270
Indexes created Tue Sep 23 22:09:46 GMT 2025