/*
* Copyright (c) 1990 The Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that the above copyright notice and this paragraph are
* duplicated in all such forms and that any documentation,
* advertising materials, and other materials related to such
* distribution and use acknowledge that the software was developed
* by the University of California, Berkeley. The name of the
* University may not be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*/
/*
FUNCTION
<<fseek>>, <<fseeko>>---set file position
INDEX
fseek
INDEX
fseeko
INDEX
_fseek_r
INDEX
_fseeko_r
ANSI_SYNOPSIS
#include <stdio.h>
int fseek(FILE *<[fp]>, long <[offset]>, int <[whence]>)
int fseeko(FILE *<[fp]>, off_t <[offset]>, int <[whence]>)
int _fseek_r(struct _reent *<[ptr]>, FILE *<[fp]>,
long <[offset]>, int <[whence]>)
int _fseeko_r(struct _reent *<[ptr]>, FILE *<[fp]>,
off_t <[offset]>, int <[whence]>)
TRAD_SYNOPSIS
#include <stdio.h>
int fseek(<[fp]>, <[offset]>, <[whence]>)
FILE *<[fp]>;
long <[offset]>;
int <[whence]>;
int fseeko(<[fp]>, <[offset]>, <[whence]>)
FILE *<[fp]>;
off_t <[offset]>;
int <[whence]>;
int _fseek_r(<[ptr]>, <[fp]>, <[offset]>, <[whence]>)
struct _reent *<[ptr]>;
FILE *<[fp]>;
long <[offset]>;
int <[whence]>;
int _fseeko_r(<[ptr]>, <[fp]>, <[offset]>, <[whence]>)
struct _reent *<[ptr]>;
FILE *<[fp]>;
off_t <[offset]>;
int <[whence]>;
DESCRIPTION
Objects of type <<FILE>> can have a ``position'' that records how much
of the file your program has already read. Many of the <<stdio>> functions
depend on this position, and many change it as a side effect.
You can use <<fseek>>/<<fseeko>> to set the position for the file identified by
<[fp]>. The value of <[offset]> determines the new position, in one
of three ways selected by the value of <[whence]> (defined as macros
in `<<stdio.h>>'):
<<SEEK_SET>>---<[offset]> is the absolute file position (an offset
from the beginning of the file) desired. <[offset]> must be positive.
<<SEEK_CUR>>---<[offset]> is relative to the current file position.
<[offset]> can meaningfully be either positive or negative.
<<SEEK_END>>---<[offset]> is relative to the current end of file.
<[offset]> can meaningfully be either positive (to increase the size
of the file) or negative.
See <<ftell>>/<<ftello>> to determine the current file position.
RETURNS
<<fseek>>/<<fseeko>> return <<0>> when successful. On failure, the
result is <<EOF>>. The reason for failure is indicated in <<errno>>:
either <<ESPIPE>> (the stream identified by <[fp]> doesn't support
repositioning) or <<EINVAL>> (invalid file position).
PORTABILITY
ANSI C requires <<fseek>>.
<<fseeko>> is defined by the Single Unix specification.
Supporting OS subroutines required: <<close>>, <<fstat>>, <<isatty>>,
<<lseek>>, <<read>>, <<sbrk>>, <<write>>.
*/
#include <_ansi.h>
#include <reent.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <fcntl.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/stat.h>
#include "local.h"
#define POS_ERR (-(_fpos_t)1)
/*
* Seek the given file to the given offset.
* `Whence' must be one of the three SEEK_* macros.
*/
int
_DEFUN(_fseek_r, (ptr, fp, offset, whence),
struct _reent *ptr _AND
register FILE *fp _AND
long offset _AND
int whence)
{
_fpos_t _EXFNPTR(seekfn, (struct _reent *, _PTR, _fpos_t, int));
_fpos_t target;
_fpos_t curoff = 0;
size_t n;
#ifdef __USE_INTERNAL_STAT64
struct stat64 st;
#else
struct stat st;
#endif
int havepos;
/* Make sure stdio is set up. */
CHECK_INIT (ptr, fp);
__sfp_lock_acquire ();
_flockfile (fp);
/* If we've been doing some writing, and we're in append mode
then we don't really know where the filepos is. */
if (fp->_flags & __SAPP && fp->_flags & __SWR)
{
/* So flush the buffer and seek to the end. */
_fflush_r (ptr, fp);
}
/* Have to be able to seek. */
if ((seekfn = fp->_seek) == NULL)
{
ptr->_errno = ESPIPE; /* ??? */
_funlockfile (fp);
__sfp_lock_release ();
return EOF;
}
/*
* Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
* After this, whence is either SEEK_SET or SEEK_END.
*/
switch (whence)
{
case SEEK_CUR:
/*
* In order to seek relative to the current stream offset,
* we have to first find the current stream offset a la
* ftell (see ftell for details).
*/
_fflush_r (ptr, fp); /* may adjust seek offset on append stream */
if (fp->_flags & __SOFF)
curoff = fp->_offset;
else
{
curoff = seekfn (ptr, fp->_cookie, (_fpos_t) 0, SEEK_CUR);
if (curoff == -1L)
{
_funlockfile (fp);
__sfp_lock_release ();
return EOF;
}
}
if (fp->_flags & __SRD)
{
curoff -= fp->_r;
if (HASUB (fp))
curoff -= fp->_ur;
}
else if (fp->_flags & __SWR && fp->_p != NULL)
curoff += fp->_p - fp->_bf._base;
offset += curoff;
whence = SEEK_SET;
havepos = 1;
break;
case SEEK_SET:
case SEEK_END:
havepos = 0;
break;
default:
ptr->_errno = EINVAL;
_funlockfile (fp);
__sfp_lock_release ();
return (EOF);
}
/*
* Can only optimise if:
* reading (and not reading-and-writing);
* not unbuffered; and
* this is a `regular' Unix file (and hence seekfn==__sseek).
* We must check __NBF first, because it is possible to have __NBF
* and __SOPT both set.
*/
if (fp->_bf._base == NULL)
__smakebuf_r (ptr, fp);
if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
goto dumb;
if ((fp->_flags & __SOPT) == 0)
{
if (seekfn != __sseek
|| fp->_file < 0
#ifdef __USE_INTERNAL_STAT64
|| _fstat64_r (ptr, fp->_file, &st)
#else
|| _fstat_r (ptr, fp->_file, &st)
#endif
|| (st.st_mode & S_IFMT) != S_IFREG)
{
fp->_flags |= __SNPT;
goto dumb;
}
#ifdef HAVE_BLKSIZE
fp->_blksize = st.st_blksize;
#else
fp->_blksize = 1024;
#endif
fp->_flags |= __SOPT;
}
/*
* We are reading; we can try to optimise.
* Figure out where we are going and where we are now.
*/
if (whence == SEEK_SET)
target = offset;
else
{
#ifdef __USE_INTERNAL_STAT64
if (_fstat64_r (ptr, fp->_file, &st))
#else
if (_fstat_r (ptr, fp->_file, &st))
#endif
goto dumb;
target = st.st_size + offset;
}
if ((long)target != target)
{
ptr->_errno = EOVERFLOW;
_funlockfile (fp);
__sfp_lock_release ();
return EOF;
}
if (!havepos)
{
if (fp->_flags & __SOFF)
curoff = fp->_offset;
else
{
curoff = seekfn (ptr, fp->_cookie, 0L, SEEK_CUR);
if (curoff == POS_ERR)
goto dumb;
}
curoff -= fp->_r;
if (HASUB (fp))
curoff -= fp->_ur;
}
/*
* Compute the number of bytes in the input buffer (pretending
* that any ungetc() input has been discarded). Adjust current
* offset backwards by this count so that it represents the
* file offset for the first byte in the current input buffer.
*/
if (HASUB (fp))
{
curoff += fp->_r; /* kill off ungetc */
n = fp->_up - fp->_bf._base;
curoff -= n;
n += fp->_ur;
}
else
{
n = fp->_p - fp->_bf._base;
curoff -= n;
n += fp->_r;
}
/*
* If the target offset is within the current buffer,
* simply adjust the pointers, clear EOF, undo ungetc(),
* and return.
*/
if (target >= curoff && target < curoff + n)
{
register int o = target - curoff;
fp->_p = fp->_bf._base + o;
fp->_r = n - o;
if (HASUB (fp))
FREEUB (ptr, fp);
fp->_flags &= ~__SEOF;
memset (&fp
->_mbstate
, 0, sizeof (_mbstate_t
)); _funlockfile (fp);
__sfp_lock_release ();
return 0;
}
/*
* The place we want to get to is not within the current buffer,
* but we can still be kind to the kernel copyout mechanism.
* By aligning the file offset to a block boundary, we can let
* the kernel use the VM hardware to map pages instead of
* copying bytes laboriously. Using a block boundary also
* ensures that we only read one block, rather than two.
*/
curoff = target & ~(fp->_blksize - 1);
if (seekfn (ptr, fp->_cookie, curoff, SEEK_SET) == POS_ERR)
goto dumb;
fp->_r = 0;
fp->_p = fp->_bf._base;
if (HASUB (fp))
FREEUB (ptr, fp);
fp->_flags &= ~__SEOF;
n = target - curoff;
if (n)
{
if (__srefill_r (ptr, fp) || fp->_r < n)
goto dumb;
fp->_p += n;
fp->_r -= n;
}
memset (&fp
->_mbstate
, 0, sizeof (_mbstate_t
)); _funlockfile (fp);
__sfp_lock_release ();
return 0;
/*
* We get here if we cannot optimise the seek ... just
* do it. Allow the seek function to change fp->_bf._base.
*/
dumb:
if (_fflush_r (ptr, fp)
|| seekfn (ptr, fp->_cookie, offset, whence) == POS_ERR)
{
_funlockfile (fp);
__sfp_lock_release ();
return EOF;
}
/* success: clear EOF indicator and discard ungetc() data */
if (HASUB (fp))
FREEUB (ptr, fp);
fp->_p = fp->_bf._base;
fp->_r = 0;
/* fp->_w = 0; *//* unnecessary (I think...) */
fp->_flags &= ~__SEOF;
/* Reset no-optimization flag after successful seek. The
no-optimization flag may be set in the case of a read
stream that is flushed which by POSIX/SUSv3 standards,
means that a corresponding seek must not optimize. The
optimization is then allowed if no subsequent flush
is performed. */
fp->_flags &= ~__SNPT;
memset (&fp
->_mbstate
, 0, sizeof (_mbstate_t
)); _funlockfile (fp);
__sfp_lock_release ();
return 0;
}
#ifndef _REENT_ONLY
int
_DEFUN
(fseek, (fp
, offset
, whence
), register FILE *fp _AND
long offset _AND
int whence)
{
return _fseek_r (_REENT, fp, offset, whence);
}
#endif /* !_REENT_ONLY */