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. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)fseek.c 8.3 (Berkeley) 1/2/94 37 * $FreeBSD: src/lib/libc/stdio/fseek.c,v 1.9.2.1 2001/03/05 10:56:58 obrien Exp $ 38 * $DragonFly: src/lib/libc/stdio/fseek.c,v 1.5 2004/06/07 20:35:41 hmp Exp $ 39 */ 40 41 #include <sys/types.h> 42 #include <sys/stat.h> 43 #include <fcntl.h> 44 #include <stdio.h> 45 #include <stdlib.h> 46 #include <errno.h> 47 #include "local.h" 48 #include "libc_private.h" 49 50 #define POS_ERR (-(fpos_t)1) 51 52 int 53 fseek(FILE *fp, long offset, int whence) 54 { 55 return (fseeko(fp, offset, whence)); 56 } 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 fpos_t (*seekfn) (void *, fpos_t, int); 66 fpos_t target, curoff; 67 size_t n; 68 struct stat st; 69 int havepos; 70 71 /* make sure stdio is set up */ 72 if (!__sdidinit) 73 __sinit(); 74 75 FLOCKFILE(fp); 76 /* 77 * Have to be able to seek. 78 */ 79 if ((seekfn = fp->_seek) == NULL) { 80 errno = ESPIPE; /* historic practice */ 81 FUNLOCKFILE(fp); 82 return (EOF); 83 } 84 85 /* 86 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 87 * After this, whence is either SEEK_SET or SEEK_END. 88 */ 89 switch (whence) { 90 91 case SEEK_CUR: 92 /* 93 * In order to seek relative to the current stream offset, 94 * we have to first find the current stream offset a la 95 * ftell (see ftell for details). 96 */ 97 if (fp->_flags & __SOFF) 98 curoff = fp->_offset; 99 else { 100 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 101 if (curoff == -1) { 102 FUNLOCKFILE(fp); 103 return (EOF); 104 } 105 } 106 if (fp->_flags & __SRD) { 107 curoff -= fp->_r; 108 if (HASUB(fp)) 109 curoff -= fp->_ur; 110 } else if (fp->_flags & __SWR && fp->_p != NULL) 111 curoff += fp->_p - fp->_bf._base; 112 113 offset += curoff; 114 whence = SEEK_SET; 115 havepos = 1; 116 break; 117 118 case SEEK_SET: 119 case SEEK_END: 120 curoff = 0; /* XXX just to keep gcc quiet */ 121 havepos = 0; 122 break; 123 124 default: 125 errno = EINVAL; 126 FUNLOCKFILE(fp); 127 return (EOF); 128 } 129 130 /* 131 * Can only optimise if: 132 * reading (and not reading-and-writing); 133 * not unbuffered; and 134 * this is a `regular' Unix file (and hence seekfn==__sseek). 135 * We must check __NBF first, because it is possible to have __NBF 136 * and __SOPT both set. 137 */ 138 if (fp->_bf._base == NULL) 139 __smakebuf(fp); 140 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 141 goto dumb; 142 if ((fp->_flags & __SOPT) == 0) { 143 if (seekfn != __sseek || 144 fp->_file < 0 || fstat(fp->_file, &st) || 145 (st.st_mode & S_IFMT) != S_IFREG) { 146 fp->_flags |= __SNPT; 147 goto dumb; 148 } 149 fp->_blksize = st.st_blksize; 150 fp->_flags |= __SOPT; 151 } 152 153 /* 154 * We are reading; we can try to optimise. 155 * Figure out where we are going and where we are now. 156 */ 157 if (whence == SEEK_SET) 158 target = offset; 159 else { 160 if (fstat(fp->_file, &st)) 161 goto dumb; 162 target = st.st_size + offset; 163 } 164 165 if (!havepos) { 166 if (fp->_flags & __SOFF) 167 curoff = fp->_offset; 168 else { 169 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 170 if (curoff == POS_ERR) 171 goto dumb; 172 } 173 curoff -= fp->_r; 174 if (HASUB(fp)) 175 curoff -= fp->_ur; 176 } 177 178 /* 179 * Compute the number of bytes in the input buffer (pretending 180 * that any ungetc() input has been discarded). Adjust current 181 * offset backwards by this count so that it represents the 182 * file offset for the first byte in the current input buffer. 183 */ 184 if (HASUB(fp)) { 185 curoff += fp->_r; /* kill off ungetc */ 186 n = fp->_up - fp->_bf._base; 187 curoff -= n; 188 n += fp->_ur; 189 } else { 190 n = fp->_p - fp->_bf._base; 191 curoff -= n; 192 n += fp->_r; 193 } 194 195 /* 196 * If the target offset is within the current buffer, 197 * simply adjust the pointers, clear EOF, undo ungetc(), 198 * and return. (If the buffer was modified, we have to 199 * skip this; see fgetln.c.) 200 */ 201 if ((fp->_flags & __SMOD) == 0 && 202 target >= curoff && target < curoff + n) { 203 int o = target - curoff; 204 205 fp->_p = fp->_bf._base + o; 206 fp->_r = n - o; 207 if (HASUB(fp)) 208 FREEUB(fp); 209 fp->_flags &= ~__SEOF; 210 FUNLOCKFILE(fp); 211 return (0); 212 } 213 214 /* 215 * The place we want to get to is not within the current buffer, 216 * but we can still be kind to the kernel copyout mechanism. 217 * By aligning the file offset to a block boundary, we can let 218 * the kernel use the VM hardware to map pages instead of 219 * copying bytes laboriously. Using a block boundary also 220 * ensures that we only read one block, rather than two. 221 */ 222 curoff = target & ~(fp->_blksize - 1); 223 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 224 goto dumb; 225 fp->_r = 0; 226 fp->_p = fp->_bf._base; 227 if (HASUB(fp)) 228 FREEUB(fp); 229 fp->_flags &= ~__SEOF; 230 n = target - curoff; 231 if (n) { 232 if (__srefill(fp) || fp->_r < n) 233 goto dumb; 234 fp->_p += n; 235 fp->_r -= n; 236 } 237 FUNLOCKFILE(fp); 238 return (0); 239 240 /* 241 * We get here if we cannot optimise the seek ... just 242 * do it. Allow the seek function to change fp->_bf._base. 243 */ 244 dumb: 245 if (__sflush(fp) || 246 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) { 247 FUNLOCKFILE(fp); 248 return (EOF); 249 } 250 /* success: clear EOF indicator and discard ungetc() data */ 251 if (HASUB(fp)) 252 FREEUB(fp); 253 fp->_p = fp->_bf._base; 254 fp->_r = 0; 255 /* fp->_w = 0; */ /* unnecessary (I think...) */ 256 fp->_flags &= ~__SEOF; 257 FUNLOCKFILE(fp); 258 return (0); 259 } 260