1 /* $OpenBSD: fseek.c,v 1.11 2012/05/21 22:24:19 matthew Exp $ */ 2 /*- 3 * Copyright (c) 1990, 1993 4 * The Regents of the University of California. All rights reserved. 5 * 6 * This code is derived from software contributed to Berkeley by 7 * Chris Torek. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 3. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 */ 33 34 #include <sys/types.h> 35 #include <sys/stat.h> 36 #include <fcntl.h> 37 #include <stdio.h> 38 #include <stdlib.h> 39 #include <errno.h> 40 #include "local.h" 41 42 #define POS_ERR (-(fpos_t)1) 43 44 /* 45 * Seek the given file to the given offset. 46 * `Whence' must be one of the three SEEK_* macros. 47 */ 48 int 49 fseeko(FILE *fp, off_t offset, int whence) 50 { 51 fpos_t (*seekfn)(void *, fpos_t, int); 52 fpos_t target, curoff; 53 size_t n; 54 struct stat st; 55 int havepos; 56 57 /* make sure stdio is set up */ 58 if (!__sdidinit) 59 __sinit(); 60 61 /* 62 * Have to be able to seek. 63 */ 64 if ((seekfn = fp->_seek) == NULL) { 65 errno = ESPIPE; /* historic practice */ 66 return (EOF); 67 } 68 69 /* 70 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 71 * After this, whence is either SEEK_SET or SEEK_END. 72 */ 73 FLOCKFILE(fp); 74 switch (whence) { 75 76 case SEEK_CUR: 77 /* 78 * In order to seek relative to the current stream offset, 79 * we have to first find the current stream offset a la 80 * ftell (see ftell for details). 81 */ 82 __sflush(fp); /* may adjust seek offset on append stream */ 83 if (fp->_flags & __SOFF) 84 curoff = fp->_offset; 85 else { 86 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 87 if (curoff == (fpos_t)-1) { 88 FUNLOCKFILE(fp); 89 return (EOF); 90 } 91 } 92 if (fp->_flags & __SRD) { 93 curoff -= fp->_r; 94 if (HASUB(fp)) 95 curoff -= fp->_ur; 96 } else if (fp->_flags & __SWR && fp->_p != NULL) 97 curoff += fp->_p - fp->_bf._base; 98 99 offset += curoff; 100 whence = SEEK_SET; 101 havepos = 1; 102 break; 103 104 case SEEK_SET: 105 case SEEK_END: 106 curoff = 0; /* XXX just to keep gcc quiet */ 107 havepos = 0; 108 break; 109 110 default: 111 FUNLOCKFILE(fp); 112 errno = EINVAL; 113 return (EOF); 114 } 115 116 /* 117 * Can only optimise if: 118 * reading (and not reading-and-writing); 119 * not unbuffered; and 120 * this is a `regular' Unix file (and hence seekfn==__sseek). 121 * We must check __NBF first, because it is possible to have __NBF 122 * and __SOPT both set. 123 */ 124 if (fp->_bf._base == NULL) 125 __smakebuf(fp); 126 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 127 goto dumb; 128 if ((fp->_flags & __SOPT) == 0) { 129 if (seekfn != __sseek || 130 fp->_file < 0 || fstat(fp->_file, &st) || 131 (st.st_mode & S_IFMT) != S_IFREG) { 132 fp->_flags |= __SNPT; 133 goto dumb; 134 } 135 fp->_blksize = st.st_blksize; 136 fp->_flags |= __SOPT; 137 } 138 139 /* 140 * We are reading; we can try to optimise. 141 * Figure out where we are going and where we are now. 142 */ 143 if (whence == SEEK_SET) 144 target = offset; 145 else { 146 if (fstat(fp->_file, &st)) 147 goto dumb; 148 target = st.st_size + offset; 149 } 150 151 if (!havepos) { 152 if (fp->_flags & __SOFF) 153 curoff = fp->_offset; 154 else { 155 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 156 if (curoff == POS_ERR) 157 goto dumb; 158 } 159 curoff -= fp->_r; 160 if (HASUB(fp)) 161 curoff -= fp->_ur; 162 } 163 164 /* 165 * Compute the number of bytes in the input buffer (pretending 166 * that any ungetc() input has been discarded). Adjust current 167 * offset backwards by this count so that it represents the 168 * file offset for the first byte in the current input buffer. 169 */ 170 if (HASUB(fp)) { 171 curoff += fp->_r; /* kill off ungetc */ 172 n = fp->_up - fp->_bf._base; 173 curoff -= n; 174 n += fp->_ur; 175 } else { 176 n = fp->_p - fp->_bf._base; 177 curoff -= n; 178 n += fp->_r; 179 } 180 181 /* 182 * If the target offset is within the current buffer, 183 * simply adjust the pointers, clear EOF, undo ungetc(), 184 * and return. (If the buffer was modified, we have to 185 * skip this; see fgetln.c.) 186 */ 187 if ((fp->_flags & __SMOD) == 0 && 188 target >= curoff && target < curoff + n) { 189 int o = target - curoff; 190 191 fp->_p = fp->_bf._base + o; 192 fp->_r = n - o; 193 if (HASUB(fp)) 194 FREEUB(fp); 195 fp->_flags &= ~__SEOF; 196 FUNLOCKFILE(fp); 197 return (0); 198 } 199 200 /* 201 * The place we want to get to is not within the current buffer, 202 * but we can still be kind to the kernel copyout mechanism. 203 * By aligning the file offset to a block boundary, we can let 204 * the kernel use the VM hardware to map pages instead of 205 * copying bytes laboriously. Using a block boundary also 206 * ensures that we only read one block, rather than two. 207 */ 208 curoff = target & ~(fp->_blksize - 1); 209 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 210 goto dumb; 211 fp->_r = 0; 212 fp->_p = fp->_bf._base; 213 if (HASUB(fp)) 214 FREEUB(fp); 215 fp->_flags &= ~__SEOF; 216 n = target - curoff; 217 if (n) { 218 if (__srefill(fp) || fp->_r < n) 219 goto dumb; 220 fp->_p += n; 221 fp->_r -= n; 222 } 223 FUNLOCKFILE(fp); 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 FUNLOCKFILE(fp); 234 return (EOF); 235 } 236 /* success: clear EOF indicator and discard ungetc() data */ 237 if (HASUB(fp)) 238 FREEUB(fp); 239 fp->_p = fp->_bf._base; 240 fp->_r = 0; 241 /* fp->_w = 0; */ /* unnecessary (I think...) */ 242 fp->_flags &= ~__SEOF; 243 FUNLOCKFILE(fp); 244 return (0); 245 } 246 247 int 248 fseek(FILE *fp, long offset, int whence) 249 { 250 return (fseeko(fp, offset, whence)); 251 } 252
