stdio/FreeBSD/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
  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: src/lib/libc/stdio/fseek.c,v 1.44 2008/04/17 22:17:54 jhb Exp $");
  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(fp, offset, whence)
  55         FILE *fp;
  56         long offset;
  57         int whence;
  58 {
  59         int ret;
  60         int serrno = errno;
  61
  62         /* make sure stdio is set up */
  63         if (!__sdidinit)
  64                 __sinit();
  65
  66         FLOCKFILE(fp);
  67         ret = _fseeko(fp, (off_t)offset, whence, 1);
  68         FUNLOCKFILE(fp);
  69         if (ret == 0)
  70                 errno = serrno;
  71         return (ret);
  72 }
  73
  74 int
  75 fseeko(fp, offset, whence)
  76         FILE *fp;
  77         off_t offset;
  78         int whence;
  79 {
  80         int ret;
  81         int serrno = errno;
  82
  83         /* make sure stdio is set up */
  84         if (!__sdidinit)
  85                 __sinit();
  86
  87         FLOCKFILE(fp);
  88         ret = _fseeko(fp, offset, whence, 0);
  89         FUNLOCKFILE(fp);
  90         if (ret == 0)
  91                 errno = serrno;
  92         return (ret);
  93 }
  94
  95 /*
  96  * Seek the given file to the given offset.
  97  * `Whence' must be one of the three SEEK_* macros.
  98  */
  99 int
 100 _fseeko(fp, offset, whence, ltest)
 101         FILE *fp;
 102         off_t offset;
 103         int whence;
 104         int ltest;
 105 {
 106         fpos_t (*seekfn)(void *, fpos_t, int);
 107         fpos_t target, curoff, ret;
 108         size_t n;
 109         struct stat st;
 110         int havepos;
 111
 112         /*
 113          * Have to be able to seek.
 114          */
 115         if ((seekfn = fp->_seek) == NULL) {
 116                 errno = ESPIPE;         /* historic practice */
 117                 return (-1);
 118         }
 119
 120         /*
 121          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 122          * After this, whence is either SEEK_SET or SEEK_END.
 123          */
 124         switch (whence) {
 125
 126         case SEEK_CUR:
 127                 /*
 128                  * In order to seek relative to the current stream offset,
 129                  * we have to first find the current stream offset via
 130                  * ftell (see ftell for details).
 131                  */
 132                 if (_ftello(fp, &curoff))
 133                         return (-1);
 134                 if (curoff < 0) {
 135                         /* Unspecified position because of ungetc() at 0 */
 136                         errno = ESPIPE;
 137                         return (-1);
 138                 }
 139                 if (offset > 0 && curoff > OFF_MAX - offset) {
 140                         errno = EOVERFLOW;
 141                         return (-1);
 142                 }
 143                 offset += curoff;
 144                 if (offset < 0) {
 145                         errno = EINVAL;
 146                         return (-1);
 147                 }
 148                 if (ltest && offset > LONG_MAX) {
 149                         errno = EOVERFLOW;
 150                         return (-1);
 151                 }
 152                 whence = SEEK_SET;
 153                 havepos = 1;
 154                 break;
 155
 156         case SEEK_SET:
 157                 if (offset < 0) {
 158                         errno = EINVAL;
 159                         return (-1);
 160                 }
 161         case SEEK_END:
 162                 curoff = 0;             /* XXX just to keep gcc quiet */
 163                 havepos = 0;
 164                 break;
 165
 166         default:
 167                 errno = EINVAL;
 168                 return (-1);
 169         }
 170
 171         /*
 172          * Can only optimise if:
 173          *      reading (and not reading-and-writing);
 174          *      not unbuffered; and
 175          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 176          * We must check __NBF first, because it is possible to have __NBF
 177          * and __SOPT both set.
 178          */
 179         if (fp->_bf._base == NULL)
 180                 __smakebuf(fp);
 181         if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 182                 goto dumb;
 183         if ((fp->_flags & __SOPT) == 0) {
 184                 if (seekfn != __sseek ||
 185                     fp->_file < 0 || _fstat(fp->_file, &st) ||
 186                     (st.st_mode & S_IFMT) != S_IFREG) {
 187                         fp->_flags |= __SNPT;
 188                         goto dumb;
 189                 }
 190                 fp->_blksize = st.st_blksize;
 191                 fp->_flags |= __SOPT;
 192         }
 193
 194         /*
 195          * We are reading; we can try to optimise.
 196          * Figure out where we are going and where we are now.
 197          */
 198         if (whence == SEEK_SET)
 199                 target = offset;
 200         else {
 201                 if (_fstat(fp->_file, &st))
 202                         goto dumb;
 203                 if (offset > 0 && st.st_size > OFF_MAX - offset) {
 204                         errno = EOVERFLOW;
 205                         return (-1);
 206                 }
 207                 target = st.st_size + offset;
 208                 if ((off_t)target < 0) {
 209                         errno = EINVAL;
 210                         return (-1);
 211                 }
 212                 if (ltest && (off_t)target > LONG_MAX) {
 213                         errno = EOVERFLOW;
 214                         return (-1);
 215                 }
 216         }
 217
 218         if (!havepos && _ftello(fp, &curoff))
 219                 goto dumb;
 220
 221         /*
 222          * (If the buffer was modified, we have to
 223          * skip this; see fgetln.c.)
 224          */
 225         if (fp->_flags & __SMOD)
 226                 goto abspos;
 227
 228         /*
 229          * Compute the number of bytes in the input buffer (pretending
 230          * that any ungetc() input has been discarded).  Adjust current
 231          * offset backwards by this count so that it represents the
 232          * file offset for the first byte in the current input buffer.
 233          */
 234         if (HASUB(fp)) {
 235                 curoff += fp->_r;       /* kill off ungetc */
 236                 n = fp->_up - fp->_bf._base;
 237                 curoff -= n;
 238                 n += fp->_ur;
 239         } else {
 240                 n = fp->_p - fp->_bf._base;
 241                 curoff -= n;
 242                 n += fp->_r;
 243         }
 244
 245         /*
 246          * If the target offset is within the current buffer,
 247          * simply adjust the pointers, clear EOF, undo ungetc(),
 248          * and return.
 249          */
 250         if (target >= curoff && target < curoff + n) {
 251                 size_t o = target - curoff;
 252
 253                 fp->_p = fp->_bf._base + o;
 254                 fp->_r = n - o;
 255                 if (HASUB(fp))
 256                         FREEUB(fp);
 257                 fp->_flags &= ~__SEOF;
 258                 memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 259                 return (0);
 260         }
 261
 262 abspos:
 263         /*
 264          * The place we want to get to is not within the current buffer,
 265          * but we can still be kind to the kernel copyout mechanism.
 266          * By aligning the file offset to a block boundary, we can let
 267          * the kernel use the VM hardware to map pages instead of
 268          * copying bytes laboriously.  Using a block boundary also
 269          * ensures that we only read one block, rather than two.
 270          */
 271         curoff = target & ~(fp->_blksize - 1);
 272         if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
 273                 goto dumb;
 274         fp->_r = 0;
 275         fp->_p = fp->_bf._base;
 276         if (HASUB(fp))
 277                 FREEUB(fp);
 278         n = target - curoff;
 279         if (n) {
 280                 if (__srefill(fp) || fp->_r < n)
 281                         goto dumb;
 282                 fp->_p += n;
 283                 fp->_r -= n;
 284         }
 285         fp->_flags &= ~__SEOF;
 286         memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 287         return (0);
 288
 289         /*
 290          * We get here if we cannot optimise the seek ... just
 291          * do it.  Allow the seek function to change fp->_bf._base.
 292          */
 293 dumb:
 294         if (__sflush(fp) ||
 295             (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
 296                 return (-1);
 297         if (ltest && ret > LONG_MAX) {
 298                 fp->_flags |= __SERR;
 299                 errno = EOVERFLOW;
 300                 return (-1);
 301         }
 302         /* success: clear EOF indicator and discard ungetc() data */
 303         if (HASUB(fp))
 304                 FREEUB(fp);
 305         fp->_p = fp->_bf._base;
 306         fp->_r = 0;
 307         /* fp->_w = 0; */       /* unnecessary (I think...) */
 308         fp->_flags &= ~__SEOF;
 309         memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 310         return (0);
 311 }