newlib/libc/stdio/fseeko.c

   1 /*
   2  * Copyright (c) 1990 The Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms are permitted
   6  * provided that the above copyright notice and this paragraph are
   7  * duplicated in all such forms and that any documentation,
   8  * and/or other materials related to such
   9  * distribution and use acknowledge that the software was developed
  10  * by the University of California, Berkeley.  The name of the
  11  * University may not be used to endorse or promote products derived
  12  * from this software without specific prior written permission.
  13  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  15  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  16  */
  17
  18 /*
  19 FUNCTION
  20 <<fseek>>, <<fseeko>>---set file position
  21
  22 INDEX
  23         fseek
  24 INDEX
  25         fseeko
  26 INDEX
  27         _fseek_r
  28 INDEX
  29         _fseeko_r
  30
  31 SYNOPSIS
  32         #include <stdio.h>
  33         int fseek(FILE *<[fp]>, long <[offset]>, int <[whence]>)
  34         int fseeko(FILE *<[fp]>, off_t <[offset]>, int <[whence]>)
  35         int _fseek_r(struct _reent *<[ptr]>, FILE *<[fp]>,
  36                      long <[offset]>, int <[whence]>)
  37         int _fseeko_r(struct _reent *<[ptr]>, FILE *<[fp]>,
  38                      off_t <[offset]>, int <[whence]>)
  39
  40 DESCRIPTION
  41 Objects of type <<FILE>> can have a ``position'' that records how much
  42 of the file your program has already read.  Many of the <<stdio>> functions
  43 depend on this position, and many change it as a side effect.
  44
  45 You can use <<fseek>>/<<fseeko>> to set the position for the file identified by
  46 <[fp]>.  The value of <[offset]> determines the new position, in one
  47 of three ways selected by the value of <[whence]> (defined as macros
  48 in `<<stdio.h>>'):
  49
  50 <<SEEK_SET>>---<[offset]> is the absolute file position (an offset
  51 from the beginning of the file) desired.  <[offset]> must be positive.
  52
  53 <<SEEK_CUR>>---<[offset]> is relative to the current file position.
  54 <[offset]> can meaningfully be either positive or negative.
  55
  56 <<SEEK_END>>---<[offset]> is relative to the current end of file.
  57 <[offset]> can meaningfully be either positive (to increase the size
  58 of the file) or negative.
  59
  60 See <<ftell>>/<<ftello>> to determine the current file position.
  61
  62 RETURNS
  63 <<fseek>>/<<fseeko>> return <<0>> when successful.  On failure, the
  64 result is <<EOF>>.  The reason for failure is indicated in <<errno>>:
  65 either <<ESPIPE>> (the stream identified by <[fp]> doesn't support
  66 repositioning) or <<EINVAL>> (invalid file position).
  67
  68 PORTABILITY
  69 ANSI C requires <<fseek>>.
  70
  71 <<fseeko>> is defined by the Single Unix specification.
  72
  73 Supporting OS subroutines required: <<close>>, <<fstat>>, <<isatty>>,
  74 <<lseek>>, <<read>>, <<sbrk>>, <<write>>.
  75 */
  76
  77 #include <_ansi.h>
  78 #include <reent.h>
  79 #include <stdio.h>
  80 #include <string.h>
  81 #include <time.h>
  82 #include <fcntl.h>
  83 #include <stdlib.h>
  84 #include <errno.h>
  85 #include <sys/stat.h>
  86 #include "local.h"
  87
  88 #define POS_ERR (-(_fpos_t)1)
  89
  90 /*
  91  * Seek the given file to the given offset.
  92  * `Whence' must be one of the three SEEK_* macros.
  93  */
  94
  95 int
  96 _fseeko_r (struct _reent *ptr,
  97        register FILE *fp,
  98        _off_t offset,
  99        int whence)
 100 {
 101   _fpos_t (*seekfn) (struct _reent *, void *, _fpos_t, int);
 102   _fpos_t target;
 103   _fpos_t curoff = 0;
 104   size_t n;
 105 #ifdef __USE_INTERNAL_STAT64
 106   struct stat64 st;
 107 #else
 108   struct stat st;
 109 #endif
 110   int havepos;
 111
 112   /* Make sure stdio is set up.  */
 113
 114   CHECK_INIT (ptr, fp);
 115
 116   _newlib_flockfile_start (fp);
 117
 118   /* If we've been doing some writing, and we're in append mode
 119      then we don't really know where the filepos is.  */
 120
 121   if (fp->_flags & __SAPP && fp->_flags & __SWR)
 122     {
 123       /* So flush the buffer and seek to the end.  */
 124       _fflush_r (ptr, fp);
 125     }
 126
 127   /* Have to be able to seek.  */
 128
 129   if ((seekfn = fp->_seek) == NULL)
 130     {
 131       _REENT_ERRNO(ptr) = ESPIPE;       /* ??? */
 132       _newlib_flockfile_exit (fp);
 133       return EOF;
 134     }
 135
 136   /*
 137    * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 138    * After this, whence is either SEEK_SET or SEEK_END.
 139    */
 140
 141   switch (whence)
 142     {
 143     case SEEK_CUR:
 144       /*
 145        * In order to seek relative to the current stream offset,
 146        * we have to first find the current stream offset a la
 147        * ftell (see ftell for details).
 148        */
 149       _fflush_r (ptr, fp);   /* may adjust seek offset on append stream */
 150       if (fp->_flags & __SOFF)
 151         curoff = fp->_offset;
 152       else
 153         {
 154           curoff = seekfn (ptr, fp->_cookie, (_fpos_t) 0, SEEK_CUR);
 155           if (curoff == -1L)
 156             {
 157               _newlib_flockfile_exit (fp);
 158               return EOF;
 159             }
 160         }
 161       if (fp->_flags & __SRD)
 162         {
 163           curoff -= fp->_r;
 164           if (HASUB (fp))
 165             curoff -= fp->_ur;
 166         }
 167       else if (fp->_flags & __SWR && fp->_p != NULL)
 168         curoff += fp->_p - fp->_bf._base;
 169
 170       offset += curoff;
 171       whence = SEEK_SET;
 172       havepos = 1;
 173       break;
 174
 175     case SEEK_SET:
 176     case SEEK_END:
 177       havepos = 0;
 178       break;
 179
 180     default:
 181       _REENT_ERRNO(ptr) = EINVAL;
 182       _newlib_flockfile_exit (fp);
 183       return (EOF);
 184     }
 185
 186   /*
 187    * Can only optimise if:
 188    *    reading (and not reading-and-writing);
 189    *    not unbuffered; and
 190    *    this is a `regular' Unix file (and hence seekfn==__sseek).
 191    * We must check __NBF first, because it is possible to have __NBF
 192    * and __SOPT both set.
 193    */
 194
 195   if (fp->_bf._base == NULL)
 196     __smakebuf_r (ptr, fp);
 197
 198 #ifdef _FSEEK_OPTIMIZATION
 199   if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 200     goto dumb;
 201   if ((fp->_flags & __SOPT) == 0)
 202     {
 203       if (seekfn != __sseek
 204           || fp->_file < 0
 205 #ifdef __USE_INTERNAL_STAT64
 206           || _fstat64_r (ptr, fp->_file, &st)
 207 #else
 208           || _fstat_r (ptr, fp->_file, &st)
 209 #endif
 210           || (st.st_mode & S_IFMT) != S_IFREG)
 211         {
 212           fp->_flags |= __SNPT;
 213           goto dumb;
 214         }
 215 #ifdef  HAVE_BLKSIZE
 216       fp->_blksize = st.st_blksize;
 217 #else
 218       fp->_blksize = 1024;
 219 #endif
 220       fp->_flags |= __SOPT;
 221     }
 222
 223   /*
 224    * We are reading; we can try to optimise.
 225    * Figure out where we are going and where we are now.
 226    */
 227
 228   if (whence == SEEK_SET)
 229     target = offset;
 230   else
 231     {
 232 #ifdef __USE_INTERNAL_STAT64
 233       if (_fstat64_r (ptr, fp->_file, &st))
 234 #else
 235       if (_fstat_r (ptr, fp->_file, &st))
 236 #endif
 237         goto dumb;
 238       target = st.st_size + offset;
 239     }
 240
 241   if (!havepos)
 242     {
 243       if (fp->_flags & __SOFF)
 244         curoff = fp->_offset;
 245       else
 246         {
 247           curoff = seekfn (ptr, fp->_cookie, 0L, SEEK_CUR);
 248           if (curoff == POS_ERR)
 249             goto dumb;
 250         }
 251       curoff -= fp->_r;
 252       if (HASUB (fp))
 253         curoff -= fp->_ur;
 254     }
 255
 256   /*
 257    * Compute the number of bytes in the input buffer (pretending
 258    * that any ungetc() input has been discarded).  Adjust current
 259    * offset backwards by this count so that it represents the
 260    * file offset for the first byte in the current input buffer.
 261    */
 262
 263   if (HASUB (fp))
 264     {
 265       curoff += fp->_r;       /* kill off ungetc */
 266       n = fp->_up - fp->_bf._base;
 267       curoff -= n;
 268       n += fp->_ur;
 269     }
 270   else
 271     {
 272       n = fp->_p - fp->_bf._base;
 273       curoff -= n;
 274       n += fp->_r;
 275     }
 276
 277   /*
 278    * If the target offset is within the current buffer,
 279    * simply adjust the pointers, clear EOF, undo ungetc(),
 280    * and return.
 281    */
 282
 283   if (target >= curoff && target < curoff + n)
 284     {
 285       register int o = target - curoff;
 286
 287       fp->_p = fp->_bf._base + o;
 288       fp->_r = n - o;
 289       if (HASUB (fp))
 290         FREEUB (ptr, fp);
 291       fp->_flags &= ~__SEOF;
 292       memset (&fp->_mbstate, 0, sizeof (_mbstate_t));
 293       _newlib_flockfile_exit (fp);
 294       return 0;
 295     }
 296
 297   /*
 298    * The place we want to get to is not within the current buffer,
 299    * but we can still be kind to the kernel copyout mechanism.
 300    * By aligning the file offset to a block boundary, we can let
 301    * the kernel use the VM hardware to map pages instead of
 302    * copying bytes laboriously.  Using a block boundary also
 303    * ensures that we only read one block, rather than two.
 304    */
 305
 306   curoff = target & ~(fp->_blksize - 1);
 307   if (seekfn (ptr, fp->_cookie, curoff, SEEK_SET) == POS_ERR)
 308     goto dumb;
 309   fp->_r = 0;
 310   fp->_p = fp->_bf._base;
 311   if (HASUB (fp))
 312     FREEUB (ptr, fp);
 313   fp->_flags &= ~__SEOF;
 314   n = target - curoff;
 315   if (n)
 316     {
 317       if (__srefill_r (ptr, fp) || fp->_r < n)
 318         goto dumb;
 319       fp->_p += n;
 320       fp->_r -= n;
 321     }
 322   memset (&fp->_mbstate, 0, sizeof (_mbstate_t));
 323   _newlib_flockfile_exit (fp);
 324   return 0;
 325
 326   /*
 327    * We get here if we cannot optimise the seek ... just
 328    * do it.  Allow the seek function to change fp->_bf._base.
 329    */
 330 #endif
 331
 332 dumb:
 333   if (_fflush_r (ptr, fp)
 334       || seekfn (ptr, fp->_cookie, offset, whence) == POS_ERR)
 335     {
 336       _newlib_flockfile_exit (fp);
 337       return EOF;
 338     }
 339   /* success: clear EOF indicator and discard ungetc() data */
 340   if (HASUB (fp))
 341     FREEUB (ptr, fp);
 342   fp->_p = fp->_bf._base;
 343   fp->_r = 0;
 344   /* fp->_w = 0; *//* unnecessary (I think...) */
 345   fp->_flags &= ~__SEOF;
 346   /* Reset no-optimization flag after successful seek.  The
 347      no-optimization flag may be set in the case of a read
 348      stream that is flushed which by POSIX/SUSv3 standards,
 349      means that a corresponding seek must not optimize.  The
 350      optimization is then allowed if no subsequent flush
 351      is performed.  */
 352   fp->_flags &= ~__SNPT;
 353   memset (&fp->_mbstate, 0, sizeof (_mbstate_t));
 354   _newlib_flockfile_end (fp);
 355   return 0;
 356 }
 357
 358 #ifndef _REENT_ONLY
 359
 360 int
 361 fseeko (register FILE *fp,
 362        _off_t offset,
 363        int whence)
 364 {
 365   return _fseeko_r (_REENT, fp, offset, whence);
 366 }
 367
 368 #endif /* !_REENT_ONLY */