lib/libc/stdio/fseek.c

   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. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #if defined(LIBC_SCCS) && !defined(lint)
  34 static char sccsid[] = "@(#)fseek.c     8.3 (Berkeley) 1/2/94";
  35 #endif /* LIBC_SCCS and not lint */
  36 #include <sys/cdefs.h>
  37 __FBSDID("$FreeBSD$");
  38
  39 #include "namespace.h"
  40 #include <sys/types.h>
  41 #include <sys/stat.h>
  42 #include <errno.h>
  43 #include <fcntl.h>
  44 #include <limits.h>
  45 #include <stdio.h>
  46 #include <stdlib.h>
  47 #include "un-namespace.h"
  48 #include "local.h"
  49 #include "libc_private.h"
  50
  51 #define POS_ERR (-(fpos_t)1)
  52
  53 int
  54 fseek(FILE *fp, long offset, int whence)
  55 {
  56         int ret;
  57         int serrno = errno;
  58
  59         /* make sure stdio is set up */
  60         if (!__sdidinit)
  61                 __sinit();
  62
  63         FLOCKFILE(fp);
  64         ret = _fseeko(fp, (off_t)offset, whence, 1);
  65         FUNLOCKFILE(fp);
  66         if (ret == 0)
  67                 errno = serrno;
  68         return (ret);
  69 }
  70
  71 int
  72 fseeko(FILE *fp, off_t offset, int whence)
  73 {
  74         int ret;
  75         int serrno = errno;
  76
  77         /* make sure stdio is set up */
  78         if (!__sdidinit)
  79                 __sinit();
  80
  81         FLOCKFILE(fp);
  82         ret = _fseeko(fp, offset, whence, 0);
  83         FUNLOCKFILE(fp);
  84         if (ret == 0)
  85                 errno = serrno;
  86         return (ret);
  87 }
  88
  89 /*
  90  * Seek the given file to the given offset.
  91  * `Whence' must be one of the three SEEK_* macros.
  92  */
  93 int
  94 _fseeko(FILE *fp, off_t offset, int whence, int ltest)
  95 {
  96         fpos_t (*seekfn)(void *, fpos_t, int);
  97         fpos_t target, curoff, ret;
  98         size_t n;
  99         struct stat st;
 100         int havepos;
 101
 102         /*
 103          * Have to be able to seek.
 104          */
 105         if ((seekfn = fp->_seek) == NULL) {
 106                 errno = ESPIPE;         /* historic practice */
 107                 return (-1);
 108         }
 109
 110         /*
 111          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 112          * After this, whence is either SEEK_SET or SEEK_END.
 113          */
 114         switch (whence) {
 115
 116         case SEEK_CUR:
 117                 /*
 118                  * In order to seek relative to the current stream offset,
 119                  * we have to first find the current stream offset via
 120                  * ftell (see ftell for details).
 121                  */
 122                 if (_ftello(fp, &curoff))
 123                         return (-1);
 124                 if (curoff < 0) {
 125                         /* Unspecified position because of ungetc() at 0 */
 126                         errno = ESPIPE;
 127                         return (-1);
 128                 }
 129                 if (offset > 0 && curoff > OFF_MAX - offset) {
 130                         errno = EOVERFLOW;
 131                         return (-1);
 132                 }
 133                 offset += curoff;
 134                 if (offset < 0) {
 135                         errno = EINVAL;
 136                         return (-1);
 137                 }
 138                 if (ltest && offset > LONG_MAX) {
 139                         errno = EOVERFLOW;
 140                         return (-1);
 141                 }
 142                 whence = SEEK_SET;
 143                 havepos = 1;
 144                 break;
 145
 146         case SEEK_SET:
 147                 if (offset < 0) {
 148                         errno = EINVAL;
 149                         return (-1);
 150                 }
 151         case SEEK_END:
 152                 curoff = 0;             /* XXX just to keep gcc quiet */
 153                 havepos = 0;
 154                 break;
 155
 156         default:
 157                 errno = EINVAL;
 158                 return (-1);
 159         }
 160
 161         /*
 162          * Can only optimise if:
 163          *      reading (and not reading-and-writing);
 164          *      not unbuffered; and
 165          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 166          * We must check __NBF first, because it is possible to have __NBF
 167          * and __SOPT both set.
 168          */
 169         if (fp->_bf._base == NULL)
 170                 __smakebuf(fp);
 171         if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 172                 goto dumb;
 173         if ((fp->_flags & __SOPT) == 0) {
 174                 if (seekfn != __sseek ||
 175                     fp->_file < 0 || _fstat(fp->_file, &st) ||
 176                     (st.st_mode & S_IFMT) != S_IFREG) {
 177                         fp->_flags |= __SNPT;
 178                         goto dumb;
 179                 }
 180                 fp->_blksize = st.st_blksize;
 181                 fp->_flags |= __SOPT;
 182         }
 183
 184         /*
 185          * We are reading; we can try to optimise.
 186          * Figure out where we are going and where we are now.
 187          */
 188         if (whence == SEEK_SET)
 189                 target = offset;
 190         else {
 191                 if (_fstat(fp->_file, &st))
 192                         goto dumb;
 193                 if (offset > 0 && st.st_size > OFF_MAX - offset) {
 194                         errno = EOVERFLOW;
 195                         return (-1);
 196                 }
 197                 target = st.st_size + offset;
 198                 if ((off_t)target < 0) {
 199                         errno = EINVAL;
 200                         return (-1);
 201                 }
 202                 if (ltest && (off_t)target > LONG_MAX) {
 203                         errno = EOVERFLOW;
 204                         return (-1);
 205                 }
 206         }
 207
 208         if (!havepos && _ftello(fp, &curoff))
 209                 goto dumb;
 210
 211         /*
 212          * (If the buffer was modified, we have to
 213          * skip this; see fgetln.c.)
 214          */
 215         if (fp->_flags & __SMOD)
 216                 goto abspos;
 217
 218         /*
 219          * Compute the number of bytes in the input buffer (pretending
 220          * that any ungetc() input has been discarded).  Adjust current
 221          * offset backwards by this count so that it represents the
 222          * file offset for the first byte in the current input buffer.
 223          */
 224         if (HASUB(fp)) {
 225                 curoff += fp->_r;       /* kill off ungetc */
 226                 n = fp->_up - fp->_bf._base;
 227                 curoff -= n;
 228                 n += fp->_ur;
 229         } else {
 230                 n = fp->_p - fp->_bf._base;
 231                 curoff -= n;
 232                 n += fp->_r;
 233         }
 234
 235         /*
 236          * If the target offset is within the current buffer,
 237          * simply adjust the pointers, clear EOF, undo ungetc(),
 238          * and return.
 239          */
 240         if (target >= curoff && target < curoff + n) {
 241                 size_t o = target - curoff;
 242
 243                 fp->_p = fp->_bf._base + o;
 244                 fp->_r = n - o;
 245                 if (HASUB(fp))
 246                         FREEUB(fp);
 247                 fp->_flags &= ~__SEOF;
 248                 memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 249                 return (0);
 250         }
 251
 252 abspos:
 253         /*
 254          * The place we want to get to is not within the current buffer,
 255          * but we can still be kind to the kernel copyout mechanism.
 256          * By aligning the file offset to a block boundary, we can let
 257          * the kernel use the VM hardware to map pages instead of
 258          * copying bytes laboriously.  Using a block boundary also
 259          * ensures that we only read one block, rather than two.
 260          */
 261         curoff = target & ~(fp->_blksize - 1);
 262         if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
 263                 goto dumb;
 264         fp->_r = 0;
 265         fp->_p = fp->_bf._base;
 266         if (HASUB(fp))
 267                 FREEUB(fp);
 268         n = target - curoff;
 269         if (n) {
 270                 if (__srefill(fp) || fp->_r < n)
 271                         goto dumb;
 272                 fp->_p += n;
 273                 fp->_r -= n;
 274         }
 275         fp->_flags &= ~__SEOF;
 276         memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 277         return (0);
 278
 279         /*
 280          * We get here if we cannot optimise the seek ... just
 281          * do it.  Allow the seek function to change fp->_bf._base.
 282          */
 283 dumb:
 284         if (__sflush(fp) ||
 285             (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
 286                 return (-1);
 287         if (ltest && ret > LONG_MAX) {
 288                 fp->_flags |= __SERR;
 289                 errno = EOVERFLOW;
 290                 return (-1);
 291         }
 292         /* success: clear EOF indicator and discard ungetc() data */
 293         if (HASUB(fp))
 294                 FREEUB(fp);
 295         fp->_p = fp->_bf._base;
 296         fp->_r = 0;
 297         /* fp->_w = 0; */       /* unnecessary (I think...) */
 298         fp->_flags &= ~__SEOF;
 299         memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 300         return (0);
 301 }