1 /* $NetBSD: fseeko.c,v 1.4 2003/08/07 16:43:25 agc 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. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 #if defined(LIBC_SCCS) && !defined(lint) 37 __RCSID("$NetBSD: fseeko.c,v 1.4 2003/08/07 16:43:25 agc Exp $"); 38 #endif /* LIBC_SCCS and not lint */ 39 40 #include "namespace.h" 41 #include <sys/types.h> 42 #include <sys/stat.h> 43 44 #include <assert.h> 45 #include <errno.h> 46 #include <fcntl.h> 47 #include <stdio.h> 48 #include <stdlib.h> 49 #include "reentrant.h" 50 #include "local.h" 51 52 #ifdef __weak_alias 53 __weak_alias(fseeko, _fseeko) 54 #endif 55 56 #define POS_ERR (-(fpos_t)1) 57 58 /* 59 * Seek the given file to the given offset. 60 * `Whence' must be one of the three SEEK_* macros. 61 */ 62 int 63 fseeko(fp, offset, whence) 64 FILE *fp; 65 off_t offset; 66 int whence; 67 { 68 fpos_t (*seekfn) __P((void *, fpos_t, int)); 69 fpos_t target, curoff; 70 size_t n; 71 struct stat st; 72 int havepos; 73 74 _DIAGASSERT(fp != NULL); 75 76 #ifdef __GNUC__ 77 /* This outrageous construct just to shut up a GCC warning. */ 78 (void) &curoff; 79 #endif 80 81 /* make sure stdio is set up */ 82 if (!__sdidinit) 83 __sinit(); 84 85 FLOCKFILE(fp); 86 87 /* 88 * Have to be able to seek. 89 */ 90 if ((seekfn = fp->_seek) == NULL) { 91 errno = ESPIPE; /* historic practice */ 92 FUNLOCKFILE(fp); 93 return (-1); 94 } 95 96 /* 97 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 98 * After this, whence is either SEEK_SET or SEEK_END. 99 */ 100 switch (whence) { 101 102 case SEEK_CUR: 103 /* 104 * In order to seek relative to the current stream offset, 105 * we have to first find the current stream offset a la 106 * ftell (see ftell for details). 107 */ 108 __sflush(fp); /* may adjust seek offset on append stream */ 109 if (fp->_flags & __SOFF) 110 curoff = fp->_offset; 111 else { 112 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 113 if (curoff == POS_ERR) { 114 FUNLOCKFILE(fp); 115 return (-1); 116 } 117 } 118 if (fp->_flags & __SRD) { 119 curoff -= fp->_r; 120 if (HASUB(fp)) 121 curoff -= fp->_ur; 122 } else if (fp->_flags & __SWR && fp->_p != NULL) 123 curoff += fp->_p - fp->_bf._base; 124 125 offset += curoff; 126 whence = SEEK_SET; 127 havepos = 1; 128 break; 129 130 case SEEK_SET: 131 case SEEK_END: 132 curoff = 0; /* XXX just to keep gcc quiet */ 133 havepos = 0; 134 break; 135 136 default: 137 errno = EINVAL; 138 FUNLOCKFILE(fp); 139 return (-1); 140 } 141 142 /* 143 * Can only optimise if: 144 * reading (and not reading-and-writing); 145 * not unbuffered; and 146 * this is a `regular' Unix file (and hence seekfn==__sseek). 147 * We must check __NBF first, because it is possible to have __NBF 148 * and __SOPT both set. 149 */ 150 if (fp->_bf._base == NULL) 151 __smakebuf(fp); 152 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 153 goto dumb; 154 if ((fp->_flags & __SOPT) == 0) { 155 if (seekfn != __sseek || 156 fp->_file < 0 || fstat(fp->_file, &st) || 157 !S_ISREG(st.st_mode)) { 158 fp->_flags |= __SNPT; 159 goto dumb; 160 } 161 fp->_blksize = st.st_blksize; 162 fp->_flags |= __SOPT; 163 } 164 165 /* 166 * We are reading; we can try to optimise. 167 * Figure out where we are going and where we are now. 168 */ 169 if (whence == SEEK_SET) 170 target = offset; 171 else { 172 if (fstat(fp->_file, &st)) 173 goto dumb; 174 target = st.st_size + offset; 175 } 176 177 if (!havepos) { 178 if (fp->_flags & __SOFF) 179 curoff = fp->_offset; 180 else { 181 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 182 if (curoff == POS_ERR) 183 goto dumb; 184 } 185 curoff -= fp->_r; 186 if (HASUB(fp)) 187 curoff -= fp->_ur; 188 } 189 190 /* 191 * Compute the number of bytes in the input buffer (pretending 192 * that any ungetc() input has been discarded). Adjust current 193 * offset backwards by this count so that it represents the 194 * file offset for the first byte in the current input buffer. 195 */ 196 if (HASUB(fp)) { 197 curoff += fp->_r; /* kill off ungetc */ 198 n = fp->_up - fp->_bf._base; 199 curoff -= n; 200 n += fp->_ur; 201 } else { 202 n = fp->_p - fp->_bf._base; 203 curoff -= n; 204 n += fp->_r; 205 } 206 207 /* 208 * If the target offset is within the current buffer, 209 * simply adjust the pointers, clear EOF, undo ungetc(), 210 * and return. (If the buffer was modified, we have to 211 * skip this; see fgetln.c.) 212 */ 213 if ((fp->_flags & __SMOD) == 0 && 214 target >= curoff && target < curoff + n) { 215 int o = (int)(target - curoff); 216 217 fp->_p = fp->_bf._base + o; 218 fp->_r = n - o; 219 if (HASUB(fp)) 220 FREEUB(fp); 221 fp->_flags &= ~__SEOF; 222 FUNLOCKFILE(fp); 223 return (0); 224 } 225 226 /* 227 * The place we want to get to is not within the current buffer, 228 * but we can still be kind to the kernel copyout mechanism. 229 * By aligning the file offset to a block boundary, we can let 230 * the kernel use the VM hardware to map pages instead of 231 * copying bytes laboriously. Using a block boundary also 232 * ensures that we only read one block, rather than two. 233 */ 234 curoff = target & ~(fp->_blksize - 1); 235 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 236 goto dumb; 237 fp->_r = 0; 238 fp->_p = fp->_bf._base; 239 if (HASUB(fp)) 240 FREEUB(fp); 241 fp->_flags &= ~__SEOF; 242 n = (int)(target - curoff); 243 if (n) { 244 if (__srefill(fp) || fp->_r < n) 245 goto dumb; 246 fp->_p += n; 247 fp->_r -= n; 248 } 249 FUNLOCKFILE(fp); 250 return (0); 251 252 /* 253 * We get here if we cannot optimise the seek ... just 254 * do it. Allow the seek function to change fp->_bf._base. 255 */ 256 dumb: 257 if (__sflush(fp) || 258 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 259 FUNLOCKFILE(fp); 260 return (-1); 261 } 262 /* success: clear EOF indicator and discard ungetc() data */ 263 if (HASUB(fp)) 264 FREEUB(fp); 265 fp->_p = fp->_bf._base; 266 fp->_r = 0; 267 /* fp->_w = 0; */ /* unnecessary (I think...) */ 268 fp->_flags &= ~__SEOF; 269 FUNLOCKFILE(fp); 270 return (0); 271 } 272