1 /*- 2 * Copyright (c) 1990 The Regents of the University of California. 3 * 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 * PATCHES MAGIC LEVEL PATCH THAT GOT US HERE 37 * -------------------- ----- ---------------------- 38 * CURRENT PATCH LEVEL: 1 00109 39 * -------------------- ----- ---------------------- 40 * 41 * 02 Mar 93 Branko Lankester Update internal buffer pointer 42 * 43 */ 44 45 #if defined(LIBC_SCCS) && !defined(lint) 46 static char sccsid[] = "@(#)fseek.c 5.7 (Berkeley) 2/24/91"; 47 #endif /* LIBC_SCCS and not lint */ 48 49 #include <sys/types.h> 50 #include <sys/stat.h> 51 #include <fcntl.h> 52 #include <stdio.h> 53 #include <stdlib.h> 54 #include <errno.h> 55 #include "local.h" 56 57 #define POS_ERR (-(fpos_t)1) 58 59 /* 60 * Seek the given file to the given offset. 61 * `Whence' must be one of the three SEEK_* macros. 62 */ 63 fseek(fp, offset, whence) 64 register FILE *fp; 65 long offset; 66 int whence; 67 { 68 #if __STDC__ 69 register fpos_t (*seekfn)(void *, fpos_t, int); 70 #else 71 register fpos_t (*seekfn)(); 72 #endif 73 fpos_t target, curoff; 74 size_t n; 75 struct stat st; 76 int havepos; 77 78 /* make sure stdio is set up */ 79 if (!__sdidinit) 80 __sinit(); 81 82 /* 83 * Have to be able to seek. 84 */ 85 if ((seekfn = fp->_seek) == NULL) { 86 errno = ESPIPE; /* historic practice */ 87 return (EOF); 88 } 89 90 /* 91 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 92 * After this, whence is either SEEK_SET or SEEK_END. 93 */ 94 switch (whence) { 95 96 case SEEK_CUR: 97 /* 98 * In order to seek relative to the current stream offset, 99 * we have to first find the current stream offset a la 100 * ftell (see ftell for details). 101 */ 102 if (fp->_flags & __SOFF) 103 curoff = fp->_offset; 104 else { 105 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 106 if (curoff == -1L) 107 return (EOF); 108 } 109 if (fp->_flags & __SRD) { 110 curoff -= fp->_r; 111 if (HASUB(fp)) 112 curoff -= fp->_ur; 113 } else if (fp->_flags & __SWR && fp->_p != NULL) 114 curoff += fp->_p - fp->_bf._base; 115 116 offset += curoff; 117 whence = SEEK_SET; 118 havepos = 1; 119 break; 120 121 case SEEK_SET: 122 case SEEK_END: 123 curoff = 0; /* XXX just to keep gcc quiet */ 124 havepos = 0; 125 break; 126 127 default: 128 errno = EINVAL; 129 return (EOF); 130 } 131 132 /* 133 * Can only optimise if: 134 * reading (and not reading-and-writing); 135 * not unbuffered; and 136 * this is a `regular' Unix file (and hence seekfn==__sseek). 137 * We must check __NBF first, because it is possible to have __NBF 138 * and __SOPT both set. 139 */ 140 if (fp->_bf._base == NULL) 141 __smakebuf(fp); 142 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 143 goto dumb; 144 if ((fp->_flags & __SOPT) == 0) { 145 if (seekfn != __sseek || 146 fp->_file < 0 || fstat(fp->_file, &st) || 147 (st.st_mode & S_IFMT) != S_IFREG) { 148 fp->_flags |= __SNPT; 149 goto dumb; 150 } 151 fp->_blksize = st.st_blksize; 152 fp->_flags |= __SOPT; 153 } 154 155 /* 156 * We are reading; we can try to optimise. 157 * Figure out where we are going and where we are now. 158 */ 159 if (whence == SEEK_SET) 160 target = offset; 161 else { 162 if (fstat(fp->_file, &st)) 163 goto dumb; 164 target = st.st_size + offset; 165 } 166 167 if (!havepos) { 168 if (fp->_flags & __SOFF) 169 curoff = fp->_offset; 170 else { 171 curoff = (*seekfn)(fp->_cookie, 0L, SEEK_CUR); 172 if (curoff == POS_ERR) 173 goto dumb; 174 } 175 curoff -= fp->_r; 176 if (HASUB(fp)) 177 curoff -= fp->_ur; 178 } 179 180 /* 181 * Compute the number of bytes in the input buffer (pretending 182 * that any ungetc() input has been discarded). Adjust current 183 * offset backwards by this count so that it represents the 184 * file offset for the first byte in the current input buffer. 185 */ 186 if (HASUB(fp)) { 187 n = fp->_up - fp->_bf._base; 188 curoff -= n; 189 n += fp->_ur; 190 } else { 191 n = fp->_p - fp->_bf._base; 192 curoff -= n; 193 n += fp->_r; 194 } 195 196 /* 197 * If the target offset is within the current buffer, 198 * simply adjust the pointers, clear EOF, undo ungetc(), 199 * and return. (If the buffer was modified, we have to 200 * skip this; see fgetline.c.) 201 */ 202 if ((fp->_flags & __SMOD) == 0 && 203 target >= curoff && target < curoff + n) { 204 register int o = target - curoff; 205 206 fp->_p = fp->_bf._base + o; 207 fp->_r = n - o; 208 if (HASUB(fp)) 209 FREEUB(fp); 210 fp->_flags &= ~__SEOF; 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 return (0); 238 239 /* 240 * We get here if we cannot optimise the seek ... just 241 * do it. Allow the seek function to change fp->_bf._base. 242 */ 243 dumb: 244 if (__sflush(fp) || 245 (*seekfn)(fp->_cookie, offset, whence) == POS_ERR) { 246 return (EOF); 247 } 248 /* success: clear EOF indicator and discard ungetc() data */ 249 if (HASUB(fp)) 250 FREEUB(fp); 251 fp->_p = fp->_bf._base; 252 fp->_r = 0; 253 /* fp->_w = 0; */ /* unnecessary (I think...) */ 254 fp->_flags &= ~__SEOF; 255 return (0); 256 } 257