fseek.c revision 1.3
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[] = "from: @(#)fseek.c 5.7 (Berkeley) 2/24/91";*/ 47 static char rcsid[] = "$Id: fseek.c,v 1.3 1993/08/01 18:38:55 mycroft Exp $"; 48 #endif /* LIBC_SCCS and not lint */ 49 50 #include <sys/types.h> 51 #include <sys/stat.h> 52 #include <fcntl.h> 53 #include <stdio.h> 54 #include <stdlib.h> 55 #include <errno.h> 56 #include "local.h" 57 58 #define POS_ERR (-(fpos_t)1) 59 60 /* 61 * Seek the given file to the given offset. 62 * `Whence' must be one of the three SEEK_* macros. 63 */ 64 fseek(fp, offset, whence) 65 register FILE *fp; 66 long offset; 67 int whence; 68 { 69 #if __STDC__ 70 register fpos_t (*seekfn)(void *, fpos_t, int); 71 #else 72 register fpos_t (*seekfn)(); 73 #endif 74 fpos_t target, curoff; 75 size_t n; 76 struct stat st; 77 int havepos; 78 79 /* make sure stdio is set up */ 80 if (!__sdidinit) 81 __sinit(); 82 83 /* 84 * Have to be able to seek. 85 */ 86 if ((seekfn = fp->_seek) == NULL) { 87 errno = ESPIPE; /* historic practice */ 88 return (EOF); 89 } 90 91 /* 92 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 93 * After this, whence is either SEEK_SET or SEEK_END. 94 */ 95 switch (whence) { 96 97 case SEEK_CUR: 98 /* 99 * In order to seek relative to the current stream offset, 100 * we have to first find the current stream offset a la 101 * ftell (see ftell for details). 102 */ 103 if (fp->_flags & __SOFF) 104 curoff = fp->_offset; 105 else { 106 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); 107 if (curoff == -1L) 108 return (EOF); 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 return (EOF); 131 } 132 133 /* 134 * Can only optimise if: 135 * reading (and not reading-and-writing); 136 * not unbuffered; and 137 * this is a `regular' Unix file (and hence seekfn==__sseek). 138 * We must check __NBF first, because it is possible to have __NBF 139 * and __SOPT both set. 140 */ 141 if (fp->_bf._base == NULL) 142 __smakebuf(fp); 143 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 144 goto dumb; 145 if ((fp->_flags & __SOPT) == 0) { 146 if (seekfn != __sseek || 147 fp->_file < 0 || fstat(fp->_file, &st) || 148 (st.st_mode & S_IFMT) != S_IFREG) { 149 fp->_flags |= __SNPT; 150 goto dumb; 151 } 152 fp->_blksize = st.st_blksize; 153 fp->_flags |= __SOPT; 154 } 155 156 /* 157 * We are reading; we can try to optimise. 158 * Figure out where we are going and where we are now. 159 */ 160 if (whence == SEEK_SET) 161 target = offset; 162 else { 163 if (fstat(fp->_file, &st)) 164 goto dumb; 165 target = st.st_size + offset; 166 } 167 168 if (!havepos) { 169 if (fp->_flags & __SOFF) 170 curoff = fp->_offset; 171 else { 172 curoff = (*seekfn)(fp->_cookie, 0L, SEEK_CUR); 173 if (curoff == POS_ERR) 174 goto dumb; 175 } 176 curoff -= fp->_r; 177 if (HASUB(fp)) 178 curoff -= fp->_ur; 179 } 180 181 /* 182 * Compute the number of bytes in the input buffer (pretending 183 * that any ungetc() input has been discarded). Adjust current 184 * offset backwards by this count so that it represents the 185 * file offset for the first byte in the current input buffer. 186 */ 187 if (HASUB(fp)) { 188 n = fp->_up - fp->_bf._base; 189 curoff -= n; 190 n += fp->_ur; 191 } else { 192 n = fp->_p - fp->_bf._base; 193 curoff -= n; 194 n += fp->_r; 195 } 196 197 /* 198 * If the target offset is within the current buffer, 199 * simply adjust the pointers, clear EOF, undo ungetc(), 200 * and return. (If the buffer was modified, we have to 201 * skip this; see fgetline.c.) 202 */ 203 if ((fp->_flags & __SMOD) == 0 && 204 target >= curoff && target < curoff + n) { 205 register int o = target - curoff; 206 207 fp->_p = fp->_bf._base + o; 208 fp->_r = n - o; 209 if (HASUB(fp)) 210 FREEUB(fp); 211 fp->_flags &= ~__SEOF; 212 return (0); 213 } 214 215 /* 216 * The place we want to get to is not within the current buffer, 217 * but we can still be kind to the kernel copyout mechanism. 218 * By aligning the file offset to a block boundary, we can let 219 * the kernel use the VM hardware to map pages instead of 220 * copying bytes laboriously. Using a block boundary also 221 * ensures that we only read one block, rather than two. 222 */ 223 curoff = target & ~(fp->_blksize - 1); 224 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 225 goto dumb; 226 fp->_r = 0; 227 fp->_p = fp->_bf._base; 228 if (HASUB(fp)) 229 FREEUB(fp); 230 fp->_flags &= ~__SEOF; 231 n = target - curoff; 232 if (n) { 233 if (__srefill(fp) || fp->_r < n) 234 goto dumb; 235 fp->_p += n; 236 fp->_r -= n; 237 } 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, offset, whence) == POS_ERR) { 247 return (EOF); 248 } 249 /* success: clear EOF indicator and discard ungetc() data */ 250 if (HASUB(fp)) 251 FREEUB(fp); 252 fp->_p = fp->_bf._base; 253 fp->_r = 0; 254 /* fp->_w = 0; */ /* unnecessary (I think...) */ 255 fp->_flags &= ~__SEOF; 256 return (0); 257 } 258
Indexes created Tue Sep 30 10:09:55 GMT 2025