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  * @(#)fseek.c  8.3 (Berkeley) 1/2/94
  33  * $FreeBSD: src/lib/libc/stdio/fseek.c,v 1.44 2008/04/17 22:17:54 jhb Exp $
  34  */
  35
  36 #include "namespace.h"
  37 #include <sys/param.h>
  38 #include <sys/stat.h>
  39 #include <errno.h>
  40 #include <fcntl.h>
  41 #include <limits.h>
  42 #include <stdio.h>
  43 #include <stdlib.h>
  44 #include "un-namespace.h"
  45 #include "local.h"
  46 #include "libc_private.h"
  47
  48 #define POS_ERR (-(fpos_t)1)
  49
  50 int
  51 fseek(FILE *fp, long offset, int whence)
  52 {
  53         int ret;
  54         int serrno = errno;
  55
  56         /* make sure stdio is set up */
  57         if (!__sdidinit)
  58                 __sinit();
  59
  60         FLOCKFILE(fp);
  61         ret = _fseeko(fp, (off_t)offset, whence, 1);
  62         FUNLOCKFILE(fp);
  63         if (ret == 0)
  64                 errno = serrno;
  65         return (ret);
  66 }
  67
  68 int
  69 fseeko(FILE *fp, off_t offset, int whence)
  70 {
  71         int ret;
  72         int serrno = errno;
  73
  74         /* make sure stdio is set up */
  75         if (!__sdidinit)
  76                 __sinit();
  77
  78         FLOCKFILE(fp);
  79         ret = _fseeko(fp, offset, whence, 0);
  80         FUNLOCKFILE(fp);
  81         if (ret == 0)
  82                 errno = serrno;
  83         return (ret);
  84 }
  85
  86 /*
  87  * Seek the given file to the given offset.
  88  * `Whence' must be one of the three SEEK_* macros.
  89  */
  90 int
  91 _fseeko(FILE *fp, off_t offset, int whence, int ltest)
  92 {
  93         fpos_t (*seekfn)(void *, fpos_t, int);
  94         fpos_t target, curoff, ret;
  95         size_t n;
  96         struct stat st;
  97         int havepos;
  98
  99         /*
 100          * Have to be able to seek.
 101          */
 102         if ((seekfn = fp->_seek) == NULL) {
 103                 errno = ESPIPE;         /* historic practice */
 104                 return (-1);
 105         }
 106
 107         /*
 108          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 109          * After this, whence is either SEEK_SET or SEEK_END.
 110          */
 111         switch (whence) {
 112
 113         case SEEK_CUR:
 114                 /*
 115                  * In order to seek relative to the current stream offset,
 116                  * we have to first find the current stream offset via
 117                  * ftell (see ftell for details).
 118                  */
 119                 if (_ftello(fp, &curoff))
 120                         return (-1);
 121                 if (curoff < 0) {
 122                         /* Unspecified position because of ungetc() at 0 */
 123                         errno = ESPIPE;
 124                         return (-1);
 125                 }
 126                 if (offset > 0 && curoff > OFF_MAX - offset) {
 127                         errno = EOVERFLOW;
 128                         return (-1);
 129                 }
 130                 offset += curoff;
 131                 if (offset < 0) {
 132                         errno = EINVAL;
 133                         return (-1);
 134                 }
 135                 if (ltest && offset > LONG_MAX) {
 136                         errno = EOVERFLOW;
 137                         return (-1);
 138                 }
 139                 whence = SEEK_SET;
 140                 havepos = 1;
 141                 break;
 142
 143         case SEEK_SET:
 144                 if (offset < 0) {
 145                         errno = EINVAL;
 146                         return (-1);
 147                 }
 148         case SEEK_END:
 149                 curoff = 0;             /* XXX just to keep gcc quiet */
 150                 havepos = 0;
 151                 break;
 152
 153         default:
 154                 errno = EINVAL;
 155                 return (-1);
 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->pub._flags & (__SWR | __SRW | __SNBF | __SNPT))
 169                 goto dumb;
 170         if ((fp->pub._flags & __SOPT) == 0) {
 171                 if (seekfn != __sseek ||
 172                     fp->pub._fileno < 0 || _fstat(fp->pub._fileno, &st) ||
 173                     (st.st_mode & S_IFMT) != S_IFREG) {
 174                         fp->pub._flags |= __SNPT;
 175                         goto dumb;
 176                 }
 177                 fp->_blksize = st.st_blksize;
 178                 fp->pub._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->pub._fileno, &st))
 189                         goto dumb;
 190                 if (offset > 0 && st.st_size > OFF_MAX - offset) {
 191                         errno = EOVERFLOW;
 192                         return (-1);
 193                 }
 194                 target = st.st_size + offset;
 195                 if ((off_t)target < 0) {
 196                         errno = EINVAL;
 197                         return (-1);
 198                 }
 199                 if (ltest && (off_t)target > LONG_MAX) {
 200                         errno = EOVERFLOW;
 201                         return (-1);
 202                 }
 203         }
 204
 205         if (!havepos && _ftello(fp, &curoff))
 206                 goto dumb;
 207
 208         /*
 209          * (If the buffer was modified, we have to
 210          * skip this; see fgetln.c.)
 211          */
 212         if (fp->pub._flags & __SMOD)
 213                 goto abspos;
 214
 215         /*
 216          * Compute the number of bytes in the input buffer (pretending
 217          * that any ungetc() input has been discarded).  Adjust current
 218          * offset backwards by this count so that it represents the
 219          * file offset for the first byte in the current input buffer.
 220          */
 221         if (HASUB(fp)) {
 222                 curoff += fp->pub._r;   /* kill off ungetc */
 223                 n = fp->_up - fp->_bf._base;
 224                 curoff -= n;
 225                 n += fp->_ur;
 226         } else {
 227                 n = fp->pub._p - fp->_bf._base;
 228                 curoff -= n;
 229                 n += fp->pub._r;
 230         }
 231
 232         /*
 233          * If the target offset is within the current buffer,
 234          * simply adjust the pointers, clear EOF, undo ungetc(),
 235          * and return.
 236          */
 237         if (target >= curoff && target < curoff + n) {
 238                 size_t o = target - curoff;
 239
 240                 fp->pub._p = fp->_bf._base + o;
 241                 fp->pub._r = n - o;
 242                 if (HASUB(fp))
 243                         FREEUB(fp);
 244                 fp->pub._flags &= ~__SEOF;
 245                 memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
 246                 return (0);
 247         }
 248
 249 abspos:
 250         /*
 251          * The place we want to get to is not within the current buffer,
 252          * but we can still be kind to the kernel copyout mechanism.
 253          * By aligning the file offset to a block boundary, we can let
 254          * the kernel use the VM hardware to map pages instead of
 255          * copying bytes laboriously.  Using a block boundary also
 256          * ensures that we only read one block, rather than two.
 257          */
 258         curoff = rounddown2(target, fp->_blksize);
 259         if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
 260                 goto dumb;
 261         fp->pub._r = 0;
 262         fp->pub._p = fp->_bf._base;
 263         if (HASUB(fp))
 264                 FREEUB(fp);
 265         n = target - curoff;
 266         if (n) {
 267                 if (__srefill(fp) || fp->pub._r < n)
 268                         goto dumb;
 269                 fp->pub._p += n;
 270                 fp->pub._r -= n;
 271         }
 272         fp->pub._flags &= ~__SEOF;
 273         memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
 274         return (0);
 275
 276         /*
 277          * We get here if we cannot optimise the seek ... just
 278          * do it.  Allow the seek function to change fp->_bf._base.
 279          */
 280 dumb:
 281         if (__sflush(fp) ||
 282             (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
 283                 return (-1);
 284         if (ltest && ret > LONG_MAX) {
 285                 fp->pub._flags |= __SERR;
 286                 errno = EOVERFLOW;
 287                 return (-1);
 288         }
 289         /* success: clear EOF indicator and discard ungetc() data */
 290         if (HASUB(fp))
 291                 FREEUB(fp);
 292         fp->pub._p = fp->_bf._base;
 293         fp->pub._r = 0;
 294         /* fp->pub._w = 0; */   /* unnecessary (I think...) */
 295         fp->pub._flags &= ~__SEOF;
 296         memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
 297         return (0);
 298 }