1 /* $NetBSD: fseeko.c,v 1.12 2012/03/27 15:05:42 christos 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 1.12 2012/03/27 15:05:42 christos 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 ((off_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(FILE *fp, off_t offset, int whence) 64 { 65 off_t (*seekfn)(void *, off_t, int); 66 off_t target, curoff; 67 size_t n; 68 struct stat st; 69 int havepos; 70 71 _DIAGASSERT(fp != NULL); 72 73 /* make sure stdio is set up */ 74 if (!__sdidinit) 75 __sinit(); 76 77 FLOCKFILE(fp); 78 79 /* 80 * Have to be able to seek. 81 */ 82 if ((seekfn = fp->_seek) == NULL) { 83 errno = ESPIPE; /* historic practice */ 84 FUNLOCKFILE(fp); 85 return -1; 86 } 87 88 /* 89 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 90 * After this, whence is either SEEK_SET or SEEK_END. 91 */ 92 switch (whence) { 93 94 case SEEK_CUR: 95 /* 96 * In order to seek relative to the current stream offset, 97 * we have to first find the current stream offset a la 98 * ftell (see ftell for details). 99 */ 100 (void)__sflush(fp); /* may adjust seek offset on append stream */ 101 if (fp->_flags & __SOFF) 102 curoff = fp->_offset; 103 else { 104 curoff = (*seekfn)(fp->_cookie, (off_t)0, SEEK_CUR); 105 if (curoff == POS_ERR) { 106 FUNLOCKFILE(fp); 107 return -1; 108 } 109 } 110 if (fp->_flags & __SRD) { 111 curoff -= fp->_r; 112 if (HASUB(fp)) 113 curoff -= fp->_ur; 114 } else if (fp->_flags & __SWR && fp->_p != NULL) 115 curoff += fp->_p - fp->_bf._base; 116 117 offset += curoff; 118 whence = SEEK_SET; 119 havepos = 1; 120 break; 121 122 case SEEK_SET: 123 case SEEK_END: 124 curoff = 0; /* XXX just to keep gcc quiet */ 125 havepos = 0; 126 break; 127 128 default: 129 errno = EINVAL; 130 FUNLOCKFILE(fp); 131 return -1; 132 } 133 134 /* 135 * Can only optimise if: 136 * reading (and not reading-and-writing); 137 * not unbuffered; and 138 * this is a `regular' Unix file (and hence seekfn==__sseek). 139 * We must check __NBF first, because it is possible to have __NBF 140 * and __SOPT both set. 141 */ 142 if (fp->_bf._base == NULL) 143 __smakebuf(fp); 144 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 145 goto dumb; 146 if ((fp->_flags & __SOPT) == 0) { 147 if (seekfn != __sseek || 148 __sfileno(fp) == -1 || fstat(__sfileno(fp), &st) || 149 !S_ISREG(st.st_mode)) { 150 fp->_flags |= __SNPT; 151 goto dumb; 152 } 153 #ifdef __minix 154 if (st.st_blksize == 0) { 155 /* 0 in 2 cases: upgrade from old to new struct stat or 156 * there is a bug in underlying fs. 157 */ 158 fp->_blksize = MINIX_ST_BLKSIZE; 159 } else 160 #endif 161 fp->_blksize = st.st_blksize; 162 163 fp->_flags |= __SOPT; 164 } 165 166 /* 167 * We are reading; we can try to optimise. 168 * Figure out where we are going and where we are now. 169 */ 170 if (whence == SEEK_SET) 171 target = offset; 172 else { 173 if (fstat(__sfileno(fp), &st)) 174 goto dumb; 175 target = st.st_size + offset; 176 } 177 178 if (!havepos) { 179 if (fp->_flags & __SOFF) 180 curoff = fp->_offset; 181 else { 182 curoff = (*seekfn)(fp->_cookie, (off_t)0, SEEK_CUR); 183 if (curoff == POS_ERR) 184 goto dumb; 185 } 186 curoff -= fp->_r; 187 if (HASUB(fp)) 188 curoff -= fp->_ur; 189 } 190 191 /* 192 * Compute the number of bytes in the input buffer (pretending 193 * that any ungetc() input has been discarded). Adjust current 194 * offset backwards by this count so that it represents the 195 * file offset for the first byte in the current input buffer. 196 */ 197 if (HASUB(fp)) { 198 curoff += fp->_r; /* kill off ungetc */ 199 n = fp->_up - fp->_bf._base; 200 curoff -= n; 201 n += fp->_ur; 202 } else { 203 n = fp->_p - fp->_bf._base; 204 curoff -= n; 205 n += fp->_r; 206 } 207 208 /* 209 * If the target offset is within the current buffer, 210 * simply adjust the pointers, clear EOF, undo ungetc(), 211 * and return. (If the buffer was modified, we have to 212 * skip this; see fgetln.c.) 213 */ 214 if ((fp->_flags & __SMOD) == 0 && 215 target >= curoff && target < curoff + (off_t)n) { 216 int o = (int)(target - curoff); 217 218 fp->_p = fp->_bf._base + o; 219 _DIAGASSERT(__type_fit(int, n - o)); 220 fp->_r = (int)(n - o); 221 if (HASUB(fp)) 222 FREEUB(fp); 223 fp->_flags &= ~__SEOF; 224 FUNLOCKFILE(fp); 225 return 0; 226 } 227 228 /* 229 * The place we want to get to is not within the current buffer, 230 * but we can still be kind to the kernel copyout mechanism. 231 * By aligning the file offset to a block boundary, we can let 232 * the kernel use the VM hardware to map pages instead of 233 * copying bytes laboriously. Using a block boundary also 234 * ensures that we only read one block, rather than two. 235 */ 236 curoff = target & ~(fp->_blksize - 1); 237 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 238 goto dumb; 239 fp->_r = 0; 240 fp->_p = fp->_bf._base; 241 if (HASUB(fp)) 242 FREEUB(fp); 243 fp->_flags &= ~__SEOF; 244 n = (int)(target - curoff); 245 if (n) { 246 if (__srefill(fp) || (size_t)fp->_r < n) 247 goto dumb; 248 fp->_p += n; 249 _DIAGASSERT(__type_fit(int, fp->_r - n)); 250 fp->_r -= (int)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, 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