fseek.c revision 1.12
1 /* $NetBSD: fseek.c,v 1.12 1998/01/19 07:38:48 jtc 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 1.12 1998/01/19 07:38:48 jtc 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 /* make sure stdio is set up */ 76 if (!__sdidinit) 77 __sinit(); 78 79 FLOCKFILE(fp); 80 81 /* 82 * Have to be able to seek. 83 */ 84 if ((seekfn = fp->_seek) == NULL) { 85 errno = ESPIPE; /* historic practice */ 86 return (-1); 87 } 88 89 /* 90 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 91 * After this, whence is either SEEK_SET or SEEK_END. 92 */ 93 switch (whence) { 94 95 case SEEK_CUR: 96 /* 97 * In order to seek relative to the current stream offset, 98 * we have to first find the current stream offset a la 99 * ftell (see ftell for details). 100 */ 101 __sflush(fp); /* may adjust seek offset on append stream */ 102 if (fp->_flags & __SOFF) 103 curoff = fp->_offset; 104 else { 105 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 106 if (curoff == -1L) { 107 FUNLOCKFILE(fp); 108 return (-1); 109 } 110 } 111 if (fp->_flags & __SRD) { 112 curoff -= fp->_r; 113 if (HASUB(fp)) 114 curoff -= fp->_ur; 115 } else if (fp->_flags & __SWR && fp->_p != NULL) 116 curoff += fp->_p - fp->_bf._base; 117 118 offset += curoff; 119 whence = SEEK_SET; 120 havepos = 1; 121 break; 122 123 case SEEK_SET: 124 case SEEK_END: 125 curoff = 0; /* XXX just to keep gcc quiet */ 126 havepos = 0; 127 break; 128 129 default: 130 errno = EINVAL; 131 FUNLOCKFILE(fp); 132 return (-1); 133 } 134 135 /* 136 * Can only optimise if: 137 * reading (and not reading-and-writing); 138 * not unbuffered; and 139 * this is a `regular' Unix file (and hence seekfn==__sseek). 140 * We must check __NBF first, because it is possible to have __NBF 141 * and __SOPT both set. 142 */ 143 if (fp->_bf._base == NULL) 144 __smakebuf(fp); 145 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 146 goto dumb; 147 if ((fp->_flags & __SOPT) == 0) { 148 if (seekfn != __sseek || 149 fp->_file < 0 || fstat(fp->_file, &st) || 150 !S_ISREG(st.st_mode)) { 151 fp->_flags |= __SNPT; 152 goto dumb; 153 } 154 fp->_blksize = st.st_blksize; 155 fp->_flags |= __SOPT; 156 } 157 158 /* 159 * We are reading; we can try to optimise. 160 * Figure out where we are going and where we are now. 161 */ 162 if (whence == SEEK_SET) 163 target = offset; 164 else { 165 if (fstat(fp->_file, &st)) 166 goto dumb; 167 target = st.st_size + offset; 168 } 169 170 if (!havepos) { 171 if (fp->_flags & __SOFF) 172 curoff = fp->_offset; 173 else { 174 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 175 if (curoff == POS_ERR) 176 goto dumb; 177 } 178 curoff -= fp->_r; 179 if (HASUB(fp)) 180 curoff -= fp->_ur; 181 } 182 183 /* 184 * Compute the number of bytes in the input buffer (pretending 185 * that any ungetc() input has been discarded). Adjust current 186 * offset backwards by this count so that it represents the 187 * file offset for the first byte in the current input buffer. 188 */ 189 if (HASUB(fp)) { 190 curoff += fp->_r; /* kill off ungetc */ 191 n = fp->_up - fp->_bf._base; 192 curoff -= n; 193 n += fp->_ur; 194 } else { 195 n = fp->_p - fp->_bf._base; 196 curoff -= n; 197 n += fp->_r; 198 } 199 200 /* 201 * If the target offset is within the current buffer, 202 * simply adjust the pointers, clear EOF, undo ungetc(), 203 * and return. (If the buffer was modified, we have to 204 * skip this; see fgetln.c.) 205 */ 206 if ((fp->_flags & __SMOD) == 0 && 207 target >= curoff && target < curoff + n) { 208 register int o = target - curoff; 209 210 fp->_p = fp->_bf._base + o; 211 fp->_r = n - o; 212 if (HASUB(fp)) 213 FREEUB(fp); 214 fp->_flags &= ~__SEOF; 215 FUNLOCKFILE(fp); 216 return (0); 217 } 218 219 /* 220 * The place we want to get to is not within the current buffer, 221 * but we can still be kind to the kernel copyout mechanism. 222 * By aligning the file offset to a block boundary, we can let 223 * the kernel use the VM hardware to map pages instead of 224 * copying bytes laboriously. Using a block boundary also 225 * ensures that we only read one block, rather than two. 226 */ 227 curoff = target & ~(fp->_blksize - 1); 228 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 229 goto dumb; 230 fp->_r = 0; 231 fp->_p = fp->_bf._base; 232 if (HASUB(fp)) 233 FREEUB(fp); 234 fp->_flags &= ~__SEOF; 235 n = target - curoff; 236 if (n) { 237 if (__srefill(fp) || fp->_r < n) 238 goto dumb; 239 fp->_p += n; 240 fp->_r -= n; 241 } 242 FUNLOCKFILE(fp); 243 return (0); 244 245 /* 246 * We get here if we cannot optimise the seek ... just 247 * do it. Allow the seek function to change fp->_bf._base. 248 */ 249 dumb: 250 if (__sflush(fp) || 251 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 252 FUNLOCKFILE(fp); 253 return (-1); 254 } 255 /* success: clear EOF indicator and discard ungetc() data */ 256 if (HASUB(fp)) 257 FREEUB(fp); 258 fp->_p = fp->_bf._base; 259 fp->_r = 0; 260 /* fp->_w = 0; */ /* unnecessary (I think...) */ 261 fp->_flags &= ~__SEOF; 262 FUNLOCKFILE(fp); 263 return (0); 264 } 265
Indexes created Thu Sep 25 02:09:54 GMT 2025