windows-server-2003/base/crts/crtw32/lowio/lseek.c

/***
*lseek.c - change file position
*
*       Copyright (c) 1989-2001, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       defines _lseek() - move the file pointer
*
*Revision History:
*       06-20-89  PHG   Module created, based on asm version
*       03-12-90  GJF   Made calling type _CALLTYPE2 (for now), added #include
*                       <cruntime.h> and fixed the copyright. Also, cleaned up
*                       the formatting a bit.
*       04-03-90  GJF   Now _CALLTYPE1.
*       07-24-90  SBM   Removed '32' from API names
*       08-14-90  SBM   Compiles cleanly with -W3
*       09-28-90  GJF   New-style function declarators.
*       12-04-90  GJF   Appended Win32 version with #ifdef-s. It's probably
*                       worth coming back and doing a more complete merge later
*                       (much later).
*       12-04-90  SRW   Changed to include <oscalls.h> instead of <doscalls.h>
*       12-06-90  SRW   Changed to use _osfile and _osfhnd instead of _osfinfo
*       01-16-91  GJF   ANSI naming.
*       02-07-91  SRW   Changed to call _get_osfhandle [_WIN32_]
*       04-09-91  PNT   Added _MAC_ conditional
*       02-13-92  GJF   Replaced _nfile by _nhandle for Win32.
*       04-06-93  SKS   Replace _CRTAPI* with __cdecl
*       09-06-94  CFW   Remove Cruiser support.
*       09-06-94  CFW   Replace MTHREAD with _MT.
*       12-03-94  SKS   Clean up OS/2 references
*       01-04-95  GJF   _WIN32_ -> _WIN32
*       02-15-95  GJF   Appended Mac version of source file (somewhat cleaned
*                       up), with appropriate #ifdef-s.
*       03-13-95  CFW   Verify handles before passing to OS.
*       06-06-95  GJF   Replaced _osfile[] with _osfile() (macro referencing
*                       field in ioinfo struct).
*       06-27-95  GJF   Added check that the file handle is open.
*       07-08-96  GJF   Replaced defined(_WIN32) with !defined(_MAC), and
*                       defined(_M_M68K) || defined(_M_MPPC) with 
*                       defined(_MAC). Also, detab-ed and cleaned up the 
*                       format a bit.
*       12-30-97  GJF   Exception-safe locking.
*       05-17-99  PML   Remove all Macintosh support.
*
*******************************************************************************/

#include <cruntime.h>
#include <oscalls.h>
#include <mtdll.h>
#include <io.h>
#include <internal.h>
#include <stdlib.h>
#include <errno.h>
#include <msdos.h>
#include <stdio.h>

/***
*long _lseek(fh,pos,mthd) - move the file pointer
*
*Purpose:
*       Moves the file pointer associated with fh to a new position.
*       The new position is pos bytes (pos may be negative) away
*       from the origin specified by mthd.
*
*       If mthd == SEEK_SET, the origin in the beginning of file
*       If mthd == SEEK_CUR, the origin is the current file pointer position
*       If mthd == SEEK_END, the origin is the end of the file
*
*       Multi-thread:
*       _lseek()    = locks/unlocks the file
*       _lseek_lk() = does NOT lock/unlock the file (it is assumed that
*                     the caller has the aquired the file lock,if needed).
*
*Entry:
*       int fh - file handle to move file pointer on
*       long pos - position to move to, relative to origin
*       int mthd - specifies the origin pos is relative to (see above)
*
*Exit:
*       returns the offset, in bytes, of the new position from the beginning
*       of the file.
*       returns -1L (and sets errno) if fails.
*       Note that seeking beyond the end of the file is not an error.
*       (although seeking before the beginning is.)
*
*Exceptions:
*
*******************************************************************************/

#ifdef  _MT

/* define locking/validating lseek */
long __cdecl _lseek (
        int fh,
        long pos,
        int mthd
        )
{
        int r;

        /* validate fh */
        if ( ((unsigned)fh >= (unsigned)_nhandle) ||
             !(_osfile(fh) & FOPEN) )
        {
                /* bad file handle */
                errno = EBADF;
                _doserrno = 0;  /* not o.s. error */
                return -1;
        }

        _lock_fh(fh);                   /* lock file handle */

        __try {
                if ( _osfile(fh) & FOPEN )
                        r = _lseek_lk(fh, pos, mthd);   /* seek */
                else {
                        errno = EBADF;
                        _doserrno = 0;
                        r = -1;
                }
        }
        __finally {
                _unlock_fh(fh);         /* unlock file handle */
        }

        return r;
}

/* define core _lseek -- doesn't lock or validate fh */
long __cdecl _lseek_lk (
        int fh,
        long pos,
        int mthd
        )
{
        ULONG newpos;                   /* new file position */
        ULONG dosretval;                /* o.s. return value */
        HANDLE osHandle;        /* o.s. handle value */

#else

/* define normal _lseek */
long __cdecl _lseek (
        int fh,
        long pos,
        int mthd
        )
{
        ULONG newpos;                   /* new file position */
        ULONG dosretval;                /* o.s. return value */
        HANDLE osHandle;        /* o.s. handle value */

        /* validate fh */
        if ( ((unsigned)fh >= (unsigned)_nhandle) ||
             !(_osfile(fh) & FOPEN) )
        {
                /* bad file handle */
                errno = EBADF;
                _doserrno = 0;  /* not o.s. error */
                return -1;
        }

#endif

        /* tell o.s. to seek */

#if SEEK_SET != FILE_BEGIN || SEEK_CUR != FILE_CURRENT || SEEK_END != FILE_END /*IFSTRIP=IGN*/
    #error Xenix and Win32 seek constants not compatible
#endif
        if ((osHandle = (HANDLE)_get_osfhandle(fh)) == (HANDLE)-1)
        {
            errno = EBADF;
            return -1;
        }

        if ((newpos = SetFilePointer(osHandle, pos, NULL, mthd)) == -1)
                dosretval = GetLastError();
        else
                dosretval = 0;

        if (dosretval) {
                /* o.s. error */
                _dosmaperr(dosretval);
                return -1;
        }

        _osfile(fh) &= ~FEOFLAG;        /* clear the ctrl-z flag on the file */
        return newpos;                  /* return */
}