1 /* $NetBSD: fseeko.c,v 1.2 2000/07/26 08:52:57 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 __RCSID("$NetBSD: fseeko.c,v 1.2 2000/07/26 08:52:57 kleink Exp $"); 42 #endif /* LIBC_SCCS and not lint */ 43 44 #include "namespace.h" 45 #include <sys/types.h> 46 #include <sys/stat.h> 47 48 #include <assert.h> 49 #include <errno.h> 50 #include <fcntl.h> 51 #include <stdio.h> 52 #include <stdlib.h> 53 #include "local.h" 54 #include "reentrant.h" 55 56 #ifdef __weak_alias 57 __weak_alias(fseeko, _fseeko) 58 #endif 59 60 #define POS_ERR (-(fpos_t)1) 61 62 /* 63 * Seek the given file to the given offset. 64 * `Whence' must be one of the three SEEK_* macros. 65 */ 66 int 67 fseeko(fp, offset, whence) 68 FILE *fp; 69 off_t offset; 70 int whence; 71 { 72 fpos_t (*seekfn) __P((void *, fpos_t, int)); 73 fpos_t target, curoff; 74 size_t n; 75 struct stat st; 76 int havepos; 77 78 _DIAGASSERT(fp != NULL); 79 80 #ifdef __GNUC__ 81 /* This outrageous construct just to shut up a GCC warning. */ 82 (void) &curoff; 83 #endif 84 85 /* make sure stdio is set up */ 86 if (!__sdidinit) 87 __sinit(); 88 89 FLOCKFILE(fp); 90 91 /* 92 * Have to be able to seek. 93 */ 94 if ((seekfn = fp->_seek) == NULL) { 95 errno = ESPIPE; /* historic practice */ 96 FUNLOCKFILE(fp); 97 return (-1); 98 } 99 100 /* 101 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 102 * After this, whence is either SEEK_SET or SEEK_END. 103 */ 104 switch (whence) { 105 106 case SEEK_CUR: 107 /* 108 * In order to seek relative to the current stream offset, 109 * we have to first find the current stream offset a la 110 * ftell (see ftell for details). 111 */ 112 __sflush(fp); /* may adjust seek offset on append stream */ 113 if (fp->_flags & __SOFF) 114 curoff = fp->_offset; 115 else { 116 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 117 if (curoff == POS_ERR) { 118 FUNLOCKFILE(fp); 119 return (-1); 120 } 121 } 122 if (fp->_flags & __SRD) { 123 curoff -= fp->_r; 124 if (HASUB(fp)) 125 curoff -= fp->_ur; 126 } else if (fp->_flags & __SWR && fp->_p != NULL) 127 curoff += fp->_p - fp->_bf._base; 128 129 offset += curoff; 130 whence = SEEK_SET; 131 havepos = 1; 132 break; 133 134 case SEEK_SET: 135 case SEEK_END: 136 curoff = 0; /* XXX just to keep gcc quiet */ 137 havepos = 0; 138 break; 139 140 default: 141 errno = EINVAL; 142 FUNLOCKFILE(fp); 143 return (-1); 144 } 145 146 /* 147 * Can only optimise if: 148 * reading (and not reading-and-writing); 149 * not unbuffered; and 150 * this is a `regular' Unix file (and hence seekfn==__sseek). 151 * We must check __NBF first, because it is possible to have __NBF 152 * and __SOPT both set. 153 */ 154 if (fp->_bf._base == NULL) 155 __smakebuf(fp); 156 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 157 goto dumb; 158 if ((fp->_flags & __SOPT) == 0) { 159 if (seekfn != __sseek || 160 fp->_file < 0 || fstat(fp->_file, &st) || 161 !S_ISREG(st.st_mode)) { 162 fp->_flags |= __SNPT; 163 goto dumb; 164 } 165 fp->_blksize = st.st_blksize; 166 fp->_flags |= __SOPT; 167 } 168 169 /* 170 * We are reading; we can try to optimise. 171 * Figure out where we are going and where we are now. 172 */ 173 if (whence == SEEK_SET) 174 target = offset; 175 else { 176 if (fstat(fp->_file, &st)) 177 goto dumb; 178 target = st.st_size + offset; 179 } 180 181 if (!havepos) { 182 if (fp->_flags & __SOFF) 183 curoff = fp->_offset; 184 else { 185 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 186 if (curoff == POS_ERR) 187 goto dumb; 188 } 189 curoff -= fp->_r; 190 if (HASUB(fp)) 191 curoff -= fp->_ur; 192 } 193 194 /* 195 * Compute the number of bytes in the input buffer (pretending 196 * that any ungetc() input has been discarded). Adjust current 197 * offset backwards by this count so that it represents the 198 * file offset for the first byte in the current input buffer. 199 */ 200 if (HASUB(fp)) { 201 curoff += fp->_r; /* kill off ungetc */ 202 n = fp->_up - fp->_bf._base; 203 curoff -= n; 204 n += fp->_ur; 205 } else { 206 n = fp->_p - fp->_bf._base; 207 curoff -= n; 208 n += fp->_r; 209 } 210 211 /* 212 * If the target offset is within the current buffer, 213 * simply adjust the pointers, clear EOF, undo ungetc(), 214 * and return. (If the buffer was modified, we have to 215 * skip this; see fgetln.c.) 216 */ 217 if ((fp->_flags & __SMOD) == 0 && 218 target >= curoff && target < curoff + n) { 219 int o = (int)(target - curoff); 220 221 fp->_p = fp->_bf._base + o; 222 fp->_r = n - o; 223 if (HASUB(fp)) 224 FREEUB(fp); 225 fp->_flags &= ~__SEOF; 226 FUNLOCKFILE(fp); 227 return (0); 228 } 229 230 /* 231 * The place we want to get to is not within the current buffer, 232 * but we can still be kind to the kernel copyout mechanism. 233 * By aligning the file offset to a block boundary, we can let 234 * the kernel use the VM hardware to map pages instead of 235 * copying bytes laboriously. Using a block boundary also 236 * ensures that we only read one block, rather than two. 237 */ 238 curoff = target & ~(fp->_blksize - 1); 239 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 240 goto dumb; 241 fp->_r = 0; 242 fp->_p = fp->_bf._base; 243 if (HASUB(fp)) 244 FREEUB(fp); 245 fp->_flags &= ~__SEOF; 246 n = (int)(target - curoff); 247 if (n) { 248 if (__srefill(fp) || fp->_r < n) 249 goto dumb; 250 fp->_p += n; 251 fp->_r -= n; 252 } 253 FUNLOCKFILE(fp); 254 return (0); 255 256 /* 257 * We get here if we cannot optimise the seek ... just 258 * do it. Allow the seek function to change fp->_bf._base. 259 */ 260 dumb: 261 if (__sflush(fp) || 262 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 263 FUNLOCKFILE(fp); 264 return (-1); 265 } 266 /* success: clear EOF indicator and discard ungetc() data */ 267 if (HASUB(fp)) 268 FREEUB(fp); 269 fp->_p = fp->_bf._base; 270 fp->_r = 0; 271 /* fp->_w = 0; */ /* unnecessary (I think...) */ 272 fp->_flags &= ~__SEOF; 273 FUNLOCKFILE(fp); 274 return (0); 275 } 276