fseek.c revision 1.19
1 /* $NetBSD: fseek.c,v 1.19 2003/01/18 11:29:53 thorpej 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 1.19 2003/01/18 11:29:53 thorpej 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 "reentrant.h" 57 #include "local.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 79 #ifdef __GNUC__ 80 /* This outrageous construct just to shut up a GCC warning. */ 81 (void) &curoff; 82 #endif 83 84 /* make sure stdio is set up */ 85 if (!__sdidinit) 86 __sinit(); 87 88 FLOCKFILE(fp); 89 90 /* 91 * Have to be able to seek. 92 */ 93 if ((seekfn = fp->_seek) == NULL) { 94 errno = ESPIPE; /* historic practice */ 95 FUNLOCKFILE(fp); 96 return (-1); 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 __sflush(fp); /* may adjust seek offset on append stream */ 112 if (fp->_flags & __SOFF) 113 curoff = fp->_offset; 114 else { 115 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 116 if (curoff == -1L) { 117 FUNLOCKFILE(fp); 118 return (-1); 119 } 120 } 121 if (fp->_flags & __SRD) { 122 curoff -= fp->_r; 123 if (HASUB(fp)) 124 curoff -= fp->_ur; 125 } else if (fp->_flags & __SWR && fp->_p != NULL) 126 curoff += fp->_p - fp->_bf._base; 127 128 offset += (long)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 FUNLOCKFILE(fp); 142 return (-1); 143 } 144 145 /* 146 * Can only optimise if: 147 * reading (and not reading-and-writing); 148 * not unbuffered; and 149 * this is a `regular' Unix file (and hence seekfn==__sseek). 150 * We must check __NBF first, because it is possible to have __NBF 151 * and __SOPT both set. 152 */ 153 if (fp->_bf._base == NULL) 154 __smakebuf(fp); 155 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 156 goto dumb; 157 if ((fp->_flags & __SOPT) == 0) { 158 if (seekfn != __sseek || 159 fp->_file < 0 || fstat(fp->_file, &st) || 160 !S_ISREG(st.st_mode)) { 161 fp->_flags |= __SNPT; 162 goto dumb; 163 } 164 fp->_blksize = st.st_blksize; 165 fp->_flags |= __SOPT; 166 } 167 168 /* 169 * We are reading; we can try to optimise. 170 * Figure out where we are going and where we are now. 171 */ 172 if (whence == SEEK_SET) 173 target = offset; 174 else { 175 if (fstat(fp->_file, &st)) 176 goto dumb; 177 target = st.st_size + offset; 178 } 179 180 if (!havepos) { 181 if (fp->_flags & __SOFF) 182 curoff = fp->_offset; 183 else { 184 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 185 if (curoff == POS_ERR) 186 goto dumb; 187 } 188 curoff -= fp->_r; 189 if (HASUB(fp)) 190 curoff -= fp->_ur; 191 } 192 193 /* 194 * Compute the number of bytes in the input buffer (pretending 195 * that any ungetc() input has been discarded). Adjust current 196 * offset backwards by this count so that it represents the 197 * file offset for the first byte in the current input buffer. 198 */ 199 if (HASUB(fp)) { 200 curoff += fp->_r; /* kill off ungetc */ 201 n = fp->_up - fp->_bf._base; 202 curoff -= n; 203 n += fp->_ur; 204 } else { 205 n = fp->_p - fp->_bf._base; 206 curoff -= n; 207 n += fp->_r; 208 } 209 210 /* 211 * If the target offset is within the current buffer, 212 * simply adjust the pointers, clear EOF, undo ungetc(), 213 * and return. (If the buffer was modified, we have to 214 * skip this; see fgetln.c.) 215 */ 216 if ((fp->_flags & __SMOD) == 0 && 217 target >= curoff && target < curoff + n) { 218 int o = (int)(target - curoff); 219 220 fp->_p = fp->_bf._base + o; 221 fp->_r = n - o; 222 if (HASUB(fp)) 223 FREEUB(fp); 224 fp->_flags &= ~__SEOF; 225 FUNLOCKFILE(fp); 226 return (0); 227 } 228 229 /* 230 * The place we want to get to is not within the current buffer, 231 * but we can still be kind to the kernel copyout mechanism. 232 * By aligning the file offset to a block boundary, we can let 233 * the kernel use the VM hardware to map pages instead of 234 * copying bytes laboriously. Using a block boundary also 235 * ensures that we only read one block, rather than two. 236 */ 237 curoff = target & ~(fp->_blksize - 1); 238 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 239 goto dumb; 240 fp->_r = 0; 241 fp->_p = fp->_bf._base; 242 if (HASUB(fp)) 243 FREEUB(fp); 244 fp->_flags &= ~__SEOF; 245 n = (int)(target - curoff); 246 if (n) { 247 if (__srefill(fp) || fp->_r < n) 248 goto dumb; 249 fp->_p += n; 250 fp->_r -= n; 251 } 252 FUNLOCKFILE(fp); 253 return (0); 254 255 /* 256 * We get here if we cannot optimise the seek ... just 257 * do it. Allow the seek function to change fp->_bf._base. 258 */ 259 dumb: 260 if (__sflush(fp) || 261 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 262 FUNLOCKFILE(fp); 263 return (-1); 264 } 265 /* success: clear EOF indicator and discard ungetc() data */ 266 if (HASUB(fp)) 267 FREEUB(fp); 268 fp->_p = fp->_bf._base; 269 fp->_r = 0; 270 /* fp->_w = 0; */ /* unnecessary (I think...) */ 271 fp->_flags &= ~__SEOF; 272 FUNLOCKFILE(fp); 273 return (0); 274 } 275
Indexes created Tue Sep 23 07:09:52 GMT 2025