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  * 4. 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  * $DragonFly: src/lib/libc/stdio/fseek.c,v 1.10 2005/11/20 11:07:30 swildner Exp $
  35  */
  36
  37 #include "namespace.h"
  38 #include <sys/types.h>
  39 #include <sys/stat.h>
  40 #include <errno.h>
  41 #include <fcntl.h>
  42 #include <limits.h>
  43 #include <stdio.h>
  44 #include <stdlib.h>
  45 #include "un-namespace.h"
  46 #include "local.h"
  47 #include "libc_private.h"
  48 #include "priv_stdio.h"
  49
  50 #define POS_ERR (-(fpos_t)1)
  51
  52 int
  53 fseek(FILE *fp, long offset, int whence)
  54 {
  55         int ret;
  56         int serrno = errno;
  57
  58         /* make sure stdio is set up */
  59         if (!__sdidinit)
  60                 __sinit();
  61
  62         FLOCKFILE(fp);
  63         ret = _fseeko(fp, (off_t)offset, whence, 1);
  64         FUNLOCKFILE(fp);
  65         if (ret == 0)
  66                 errno = serrno;
  67         return (ret);
  68 }
  69
  70 int
  71 fseeko(FILE *fp, off_t offset, int whence)
  72 {
  73         int ret;
  74         int serrno = errno;
  75
  76         /* make sure stdio is set up */
  77         if (!__sdidinit)
  78                 __sinit();
  79
  80         FLOCKFILE(fp);
  81         ret = _fseeko(fp, offset, whence, 0);
  82         FUNLOCKFILE(fp);
  83         if (ret == 0)
  84                 errno = serrno;
  85         return (ret);
  86 }
  87
  88 /*
  89  * Seek the given file to the given offset.
  90  * `Whence' must be one of the three SEEK_* macros.
  91  */
  92 int
  93 _fseeko(FILE *fp, off_t offset, int whence, int ltest)
  94 {
  95         fpos_t (*seekfn)(void *, fpos_t, int);
  96         fpos_t target, curoff, ret;
  97         size_t n;
  98         struct stat st;
  99         int havepos;
 100
 101         /*
 102          * Have to be able to seek.
 103          */
 104         if ((seekfn = fp->_seek) == NULL) {
 105                 errno = ESPIPE;         /* historic practice */
 106                 return (-1);
 107         }
 108
 109         /*
 110          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 111          * After this, whence is either SEEK_SET or SEEK_END.
 112          */
 113         switch (whence) {
 114
 115         case SEEK_CUR:
 116                 /*
 117                  * In order to seek relative to the current stream offset,
 118                  * we have to first find the current stream offset via
 119                  * ftell (see ftell for details).
 120                  */
 121                 if (_ftello(fp, &curoff))
 122                         return (-1);
 123                 if (curoff < 0) {
 124                         /* Unspecified position because of ungetc() at 0 */
 125                         errno = ESPIPE;
 126                         return (-1);
 127                 }
 128                 if (offset > 0 && curoff > OFF_MAX - offset) {
 129                         errno = EOVERFLOW;
 130                         return (-1);
 131                 }
 132                 offset += curoff;
 133                 if (offset < 0) {
 134                         errno = EINVAL;
 135                         return (-1);
 136                 }
 137                 if (ltest && offset > LONG_MAX) {
 138                         errno = EOVERFLOW;
 139                         return (-1);
 140                 }
 141                 whence = SEEK_SET;
 142                 havepos = 1;
 143                 break;
 144
 145         case SEEK_SET:
 146                 if (offset < 0) {
 147                         errno = EINVAL;
 148                         return (-1);
 149                 }
 150         case SEEK_END:
 151                 curoff = 0;             /* XXX just to keep gcc quiet */
 152                 havepos = 0;
 153                 break;
 154
 155         default:
 156                 errno = EINVAL;
 157                 return (-1);
 158         }
 159
 160         /*
 161          * Can only optimise if:
 162          *      reading (and not reading-and-writing);
 163          *      not unbuffered; and
 164          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 165          * We must check __NBF first, because it is possible to have __NBF
 166          * and __SOPT both set.
 167          */
 168         if (fp->_bf._base == NULL)
 169                 __smakebuf(fp);
 170         if (fp->pub._flags & (__SWR | __SRW | __SNBF | __SNPT))
 171                 goto dumb;
 172         if ((fp->pub._flags & __SOPT) == 0) {
 173                 if (seekfn != __sseek ||
 174                     fp->pub._fileno < 0 || _fstat(fp->pub._fileno, &st) ||
 175                     (st.st_mode & S_IFMT) != S_IFREG) {
 176                         fp->pub._flags |= __SNPT;
 177                         goto dumb;
 178                 }
 179                 fp->_blksize = st.st_blksize;
 180                 fp->pub._flags |= __SOPT;
 181         }
 182
 183         /*
 184          * We are reading; we can try to optimise.
 185          * Figure out where we are going and where we are now.
 186          */
 187         if (whence == SEEK_SET)
 188                 target = offset;
 189         else {
 190                 if (_fstat(fp->pub._fileno, &st))
 191                         goto dumb;
 192                 if (offset > 0 && st.st_size > OFF_MAX - offset) {
 193                         errno = EOVERFLOW;
 194                         return (-1);
 195                 }
 196                 target = st.st_size + offset;
 197                 if ((off_t)target < 0) {
 198                         errno = EINVAL;
 199                         return (-1);
 200                 }
 201                 if (ltest && (off_t)target > LONG_MAX) {
 202                         errno = EOVERFLOW;
 203                         return (-1);
 204                 }
 205         }
 206
 207         if (!havepos && _ftello(fp, &curoff))
 208                 goto dumb;
 209
 210         /*
 211          * (If the buffer was modified, we have to
 212          * skip this; see fgetln.c.)
 213          */
 214         if (fp->pub._flags & __SMOD)
 215                 goto abspos;
 216
 217         /*
 218          * Compute the number of bytes in the input buffer (pretending
 219          * that any ungetc() input has been discarded).  Adjust current
 220          * offset backwards by this count so that it represents the
 221          * file offset for the first byte in the current input buffer.
 222          */
 223         if (HASUB(fp)) {
 224                 curoff += fp->pub._r;   /* kill off ungetc */
 225                 n = fp->_up - fp->_bf._base;
 226                 curoff -= n;
 227                 n += fp->_ur;
 228         } else {
 229                 n = fp->pub._p - fp->_bf._base;
 230                 curoff -= n;
 231                 n += fp->pub._r;
 232         }
 233
 234         /*
 235          * If the target offset is within the current buffer,
 236          * simply adjust the pointers, clear EOF, undo ungetc(),
 237          * and return.
 238          */
 239         if (target >= curoff && target < curoff + n) {
 240                 size_t o = target - curoff;
 241
 242                 fp->pub._p = fp->_bf._base + o;
 243                 fp->pub._r = n - o;
 244                 if (HASUB(fp))
 245                         FREEUB(fp);
 246                 fp->pub._flags &= ~__SEOF;
 247                 memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
 248                 return (0);
 249         }
 250
 251 abspos:
 252         /*
 253          * The place we want to get to is not within the current buffer,
 254          * but we can still be kind to the kernel copyout mechanism.
 255          * By aligning the file offset to a block boundary, we can let
 256          * the kernel use the VM hardware to map pages instead of
 257          * copying bytes laboriously.  Using a block boundary also
 258          * ensures that we only read one block, rather than two.
 259          */
 260         curoff = target & ~(fp->_blksize - 1);
 261         if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
 262                 goto dumb;
 263         fp->pub._r = 0;
 264         fp->pub._p = fp->_bf._base;
 265         if (HASUB(fp))
 266                 FREEUB(fp);
 267         n = target - curoff;
 268         if (n) {
 269                 if (__srefill(fp) || fp->pub._r < n)
 270                         goto dumb;
 271                 fp->pub._p += n;
 272                 fp->pub._r -= n;
 273         }
 274         fp->pub._flags &= ~__SEOF;
 275         memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
 276         return (0);
 277
 278         /*
 279          * We get here if we cannot optimise the seek ... just
 280          * do it.  Allow the seek function to change fp->_bf._base.
 281          */
 282 dumb:
 283         if (__sflush(fp) ||
 284             (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
 285                 return (-1);
 286         if (ltest && ret > LONG_MAX) {
 287                 fp->pub._flags |= __SERR;
 288                 errno = EOVERFLOW;
 289                 return (-1);
 290         }
 291         /* success: clear EOF indicator and discard ungetc() data */
 292         if (HASUB(fp))
 293                 FREEUB(fp);
 294         fp->pub._p = fp->_bf._base;
 295         fp->pub._r = 0;
 296         /* fp->pub._w = 0; */   /* unnecessary (I think...) */
 297         fp->pub._flags &= ~__SEOF;
 298         memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
 299         return (0);
 300 }