stdio/fseek.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /*
  26  * Copyright (c) 1990, 1993
  27  *      The Regents of the University of California.  All rights reserved.
  28  *
  29  * This code is derived from software contributed to Berkeley by
  30  * Chris Torek.
  31  *
  32  * Redistribution and use in source and binary forms, with or without
  33  * modification, are permitted provided that the following conditions
  34  * are met:
  35  * 1. Redistributions of source code must retain the above copyright
  36  *    notice, this list of conditions and the following disclaimer.
  37  * 2. Redistributions in binary form must reproduce the above copyright
  38  *    notice, this list of conditions and the following disclaimer in the
  39  *    documentation and/or other materials provided with the distribution.
  40  * 3. All advertising materials mentioning features or use of this software
  41  *    must display the following acknowledgement:
  42  *      This product includes software developed by the University of
  43  *      California, Berkeley and its contributors.
  44  * 4. Neither the name of the University nor the names of its contributors
  45  *    may be used to endorse or promote products derived from this software
  46  *    without specific prior written permission.
  47  *
  48  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  49  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  50  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  51  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  52  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  53  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  54  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  55  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  56  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  57  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  58  * SUCH DAMAGE.
  59  */
  60
  61
  62 #include <sys/types.h>
  63 #include <sys/types.h>
  64 #include <sys/stat.h>
  65 #include <fcntl.h>
  66 #include <stdio.h>
  67 #include <stdlib.h>
  68 #include <errno.h>
  69 #include "local.h"
  70
  71 #define POS_ERR (-(fpos_t)1)
  72
  73 int
  74 fseek(fp, offset, whence)
  75         register FILE *fp;
  76         long offset;
  77         int whence;
  78 {
  79         return (fseeko(fp, offset, whence));
  80 }
  81
  82
  83 /*
  84  * Seek the given file to the given offset.
  85  * `Whence' must be one of the three SEEK_* macros.
  86  */
  87 int
  88 fseeko(fp, offset, whence)
  89         register FILE *fp;
  90         off_t offset;
  91         int whence;
  92 {
  93         register fpos_t (*seekfn) __P((void *, fpos_t, int));
  94         fpos_t target, curoff;
  95         size_t n;
  96         struct stat st;
  97         int havepos;
  98
  99         /* make sure stdio is set up */
 100         if (!__sdidinit)
 101                 __sinit();
 102
 103         /* FLOCKFILE(fp); */
 104         /*
 105          * Have to be able to seek.
 106          */
 107         if ((seekfn = fp->_seek) == NULL) {
 108                 errno = ESPIPE;                 /* historic practice */
 109                 /* FUNLOCKFILE(fp); */
 110                 return (EOF);
 111         }
 112
 113         /*
 114          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 115          * After this, whence is either SEEK_SET or SEEK_END.
 116          */
 117         switch (whence) {
 118
 119         case SEEK_CUR:
 120                 /*
 121                  * In order to seek relative to the current stream offset,
 122                  * we have to first find the current stream offset a la
 123                  * ftell (see ftell for details).
 124                  */
 125                 if (fp->_flags & __SOFF)
 126                         curoff = fp->_offset;
 127                 else {
 128                         curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 129                         if (curoff == -1) {
 130                                 /* FUNLOCKFILE(fp); */
 131                                 return (EOF);
 132                         }
 133                 }
 134                 if (fp->_flags & __SRD) {
 135                         curoff -= fp->_r;
 136                         if (HASUB(fp))
 137                                 curoff -= fp->_ur;
 138                 } else if (fp->_flags & __SWR && fp->_p != NULL)
 139                         curoff += fp->_p - fp->_bf._base;
 140
 141                 offset += curoff;
 142                 whence = SEEK_SET;
 143                 havepos = 1;
 144                 break;
 145
 146         case SEEK_SET:
 147         case SEEK_END:
 148                 curoff = 0;             /* XXX just to keep gcc quiet */
 149                 havepos = 0;
 150                 break;
 151
 152         default:
 153                 errno = EINVAL;
 154                 /* FUNLOCKFILE(fp); */
 155                 return (EOF);
 156         }
 157
 158         /*
 159          * Can only optimise if:
 160          *      reading (and not reading-and-writing);
 161          *      not unbuffered; and
 162          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 163          * We must check __NBF first, because it is possible to have __NBF
 164          * and __SOPT both set.
 165          */
 166         if (fp->_bf._base == NULL)
 167                 __smakebuf(fp);
 168         if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 169                 goto dumb;
 170         if ((fp->_flags & __SOPT) == 0) {
 171                 if (seekfn != __sseek ||
 172                     fp->_file < 0 || fstat(fp->_file, &st) ||
 173                     (st.st_mode & S_IFMT) != S_IFREG) {
 174                         fp->_flags |= __SNPT;
 175                         goto dumb;
 176                 }
 177                 fp->_blksize = st.st_blksize;
 178                 fp->_flags |= __SOPT;
 179         }
 180
 181         /*
 182          * We are reading; we can try to optimise.
 183          * Figure out where we are going and where we are now.
 184          */
 185         if (whence == SEEK_SET)
 186                 target = offset;
 187         else {
 188                 if (fstat(fp->_file, &st))
 189                         goto dumb;
 190                 target = st.st_size + offset;
 191         }
 192
 193         if (!havepos) {
 194                 if (fp->_flags & __SOFF)
 195                         curoff = fp->_offset;
 196                 else {
 197                         curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 198                         if (curoff == POS_ERR)
 199                                 goto dumb;
 200                 }
 201                 curoff -= fp->_r;
 202                 if (HASUB(fp))
 203                         curoff -= fp->_ur;
 204         }
 205
 206         /*
 207          * Compute the number of bytes in the input buffer (pretending
 208          * that any ungetc() input has been discarded).  Adjust current
 209          * offset backwards by this count so that it represents the
 210          * file offset for the first byte in the current input buffer.
 211          */
 212         if (HASUB(fp)) {
 213                 curoff += fp->_r;       /* kill off ungetc */
 214                 n = fp->_up - fp->_bf._base;
 215                 curoff -= n;
 216                 n += fp->_ur;
 217         } else {
 218                 n = fp->_p - fp->_bf._base;
 219                 curoff -= n;
 220                 n += fp->_r;
 221         }
 222
 223         /*
 224          * If the target offset is within the current buffer,
 225          * simply adjust the pointers, clear EOF, undo ungetc(),
 226          * and return.  (If the buffer was modified, we have to
 227          * skip this; see fgetln.c.)
 228          */
 229         if ((fp->_flags & __SMOD) == 0 &&
 230             target >= curoff && target < curoff + n) {
 231                 register int o = target - curoff;
 232
 233                 fp->_p = fp->_bf._base + o;
 234                 fp->_r = n - o;
 235                 if (HASUB(fp))
 236                         FREEUB(fp);
 237                 fp->_flags &= ~__SEOF;
 238                 /* FUNLOCKFILE(fp); */
 239                 return (0);
 240         }
 241
 242         /*
 243          * The place we want to get to is not within the current buffer,
 244          * but we can still be kind to the kernel copyout mechanism.
 245          * By aligning the file offset to a block boundary, we can let
 246          * the kernel use the VM hardware to map pages instead of
 247          * copying bytes laboriously.  Using a block boundary also
 248          * ensures that we only read one block, rather than two.
 249          */
 250         curoff = target & ~(fp->_blksize - 1);
 251         if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
 252                 goto dumb;
 253         fp->_r = 0;
 254         fp->_p = fp->_bf._base;
 255         if (HASUB(fp))
 256                 FREEUB(fp);
 257         fp->_flags &= ~__SEOF;
 258         n = target - curoff;
 259         if (n) {
 260                 if (__srefill(fp) || fp->_r < n)
 261                         goto dumb;
 262                 fp->_p += n;
 263                 fp->_r -= n;
 264         }
 265         /* FUNLOCKFILE(fp); */
 266         return (0);
 267
 268         /*
 269          * We get here if we cannot optimise the seek ... just
 270          * do it.  Allow the seek function to change fp->_bf._base.
 271          */
 272 dumb:
 273         if (__sflush(fp) ||
 274             (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
 275                 /* FUNLOCKFILE(fp); */
 276                 return (EOF);
 277         }
 278         /* success: clear EOF indicator and discard ungetc() data */
 279         if (HASUB(fp))
 280                 FREEUB(fp);
 281         fp->_p = fp->_bf._base;
 282         fp->_r = 0;
 283         /* fp->_w = 0; */       /* unnecessary (I think...) */
 284         fp->_flags &= ~__SEOF;
 285         /* FUNLOCKFILE(fp); */
 286         return (0);
 287 }