1 /*- 2 * Copyright (c) 1990, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Chris Torek. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #if defined(LIBC_SCCS) && !defined(lint) 34 static char rcsid[] = "$OpenBSD: fseek.c,v 1.5 2003/06/02 20:18:37 millert Exp $"; 35 #endif /* LIBC_SCCS and not lint */ 36 37 #include <sys/types.h> 38 #include <sys/stat.h> 39 #include <fcntl.h> 40 #include <stdio.h> 41 #include <stdlib.h> 42 #include <errno.h> 43 #include "local.h" 44 45 #define POS_ERR (-(fpos_t)1) 46 47 /* 48 * Seek the given file to the given offset. 49 * `Whence' must be one of the three SEEK_* macros. 50 */ 51 int 52 fseeko(fp, offset, whence) 53 register FILE *fp; 54 off_t offset; 55 int whence; 56 { 57 register fpos_t (*seekfn)(void *, fpos_t, int); 58 fpos_t target, curoff; 59 size_t n; 60 struct stat st; 61 int havepos; 62 63 /* make sure stdio is set up */ 64 if (!__sdidinit) 65 __sinit(); 66 67 /* 68 * Have to be able to seek. 69 */ 70 if ((seekfn = fp->_seek) == NULL) { 71 errno = ESPIPE; /* historic practice */ 72 return (EOF); 73 } 74 75 /* 76 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 77 * After this, whence is either SEEK_SET or SEEK_END. 78 */ 79 switch (whence) { 80 81 case SEEK_CUR: 82 /* 83 * In order to seek relative to the current stream offset, 84 * we have to first find the current stream offset a la 85 * ftell (see ftell for details). 86 */ 87 __sflush(fp); /* may adjust seek offset on append stream */ 88 if (fp->_flags & __SOFF) 89 curoff = fp->_offset; 90 else { 91 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 92 if (curoff == (fpos_t)-1) 93 return (EOF); 94 } 95 if (fp->_flags & __SRD) { 96 curoff -= fp->_r; 97 if (HASUB(fp)) 98 curoff -= fp->_ur; 99 } else if (fp->_flags & __SWR && fp->_p != NULL) 100 curoff += fp->_p - fp->_bf._base; 101 102 offset += curoff; 103 whence = SEEK_SET; 104 havepos = 1; 105 break; 106 107 case SEEK_SET: 108 case SEEK_END: 109 curoff = 0; /* XXX just to keep gcc quiet */ 110 havepos = 0; 111 break; 112 113 default: 114 errno = EINVAL; 115 return (EOF); 116 } 117 118 /* 119 * Can only optimise if: 120 * reading (and not reading-and-writing); 121 * not unbuffered; and 122 * this is a `regular' Unix file (and hence seekfn==__sseek). 123 * We must check __NBF first, because it is possible to have __NBF 124 * and __SOPT both set. 125 */ 126 if (fp->_bf._base == NULL) 127 __smakebuf(fp); 128 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 129 goto dumb; 130 if ((fp->_flags & __SOPT) == 0) { 131 if (seekfn != __sseek || 132 fp->_file < 0 || fstat(fp->_file, &st) || 133 (st.st_mode & S_IFMT) != S_IFREG) { 134 fp->_flags |= __SNPT; 135 goto dumb; 136 } 137 fp->_blksize = st.st_blksize; 138 fp->_flags |= __SOPT; 139 } 140 141 /* 142 * We are reading; we can try to optimise. 143 * Figure out where we are going and where we are now. 144 */ 145 if (whence == SEEK_SET) 146 target = offset; 147 else { 148 if (fstat(fp->_file, &st)) 149 goto dumb; 150 target = st.st_size + offset; 151 } 152 153 if (!havepos) { 154 if (fp->_flags & __SOFF) 155 curoff = fp->_offset; 156 else { 157 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 158 if (curoff == POS_ERR) 159 goto dumb; 160 } 161 curoff -= fp->_r; 162 if (HASUB(fp)) 163 curoff -= fp->_ur; 164 } 165 166 /* 167 * Compute the number of bytes in the input buffer (pretending 168 * that any ungetc() input has been discarded). Adjust current 169 * offset backwards by this count so that it represents the 170 * file offset for the first byte in the current input buffer. 171 */ 172 if (HASUB(fp)) { 173 curoff += fp->_r; /* kill off ungetc */ 174 n = fp->_up - fp->_bf._base; 175 curoff -= n; 176 n += fp->_ur; 177 } else { 178 n = fp->_p - fp->_bf._base; 179 curoff -= n; 180 n += fp->_r; 181 } 182 183 /* 184 * If the target offset is within the current buffer, 185 * simply adjust the pointers, clear EOF, undo ungetc(), 186 * and return. (If the buffer was modified, we have to 187 * skip this; see fgetln.c.) 188 */ 189 if ((fp->_flags & __SMOD) == 0 && 190 target >= curoff && target < curoff + n) { 191 register int o = target - curoff; 192 193 fp->_p = fp->_bf._base + o; 194 fp->_r = n - o; 195 if (HASUB(fp)) 196 FREEUB(fp); 197 fp->_flags &= ~__SEOF; 198 return (0); 199 } 200 201 /* 202 * The place we want to get to is not within the current buffer, 203 * but we can still be kind to the kernel copyout mechanism. 204 * By aligning the file offset to a block boundary, we can let 205 * the kernel use the VM hardware to map pages instead of 206 * copying bytes laboriously. Using a block boundary also 207 * ensures that we only read one block, rather than two. 208 */ 209 curoff = target & ~(fp->_blksize - 1); 210 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 211 goto dumb; 212 fp->_r = 0; 213 fp->_p = fp->_bf._base; 214 if (HASUB(fp)) 215 FREEUB(fp); 216 fp->_flags &= ~__SEOF; 217 n = target - curoff; 218 if (n) { 219 if (__srefill(fp) || fp->_r < n) 220 goto dumb; 221 fp->_p += n; 222 fp->_r -= n; 223 } 224 return (0); 225 226 /* 227 * We get here if we cannot optimise the seek ... just 228 * do it. Allow the seek function to change fp->_bf._base. 229 */ 230 dumb: 231 if (__sflush(fp) || 232 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 233 return (EOF); 234 } 235 /* success: clear EOF indicator and discard ungetc() data */ 236 if (HASUB(fp)) 237 FREEUB(fp); 238 fp->_p = fp->_bf._base; 239 fp->_r = 0; 240 /* fp->_w = 0; */ /* unnecessary (I think...) */ 241 fp->_flags &= ~__SEOF; 242 return (0); 243 } 244 245 /* 246 * fseek()'s offset is a long and sizeof(off_t) != sizeof(long) on all arches 247 */ 248 #if defined(__alpha__) && defined(__indr_reference) 249 __indr_reference(fseeko, fseek); 250 #else 251 int 252 fseek(fp, offset, whence) 253 register FILE *fp; 254 long offset; 255 int whence; 256 { 257 off_t off = offset; 258 259 return(fseeko(fp, off, whence)); 260 } 261 #endif 262