[Patch, RFC] Remove bogus fflush

[Paolo Carlini <pcarlini at suse dot de>]

Hi,

the below stems from private discussion with kernel developer Andrea
Arcangeli: while explaining various issues related to I/O, he pointed
out that the read/write primitives are *unbuffered*.

Now, turns out that the library still has some, essentially bogus, we
believe, fflush, remnants of the old __basic_file<> implementation,
used in 3.3, which exploited the stdio API (i.e., fread, fwrite,
fflush, and so on).

Indeed, the below regtests OK on x86 and x86_64 linux.

Anyone can spot something wrong/dangerous with it? Otherwise I will
apply it soon, say 24 hours, to mainline for wider testing.

Paolo.

////////////
2004-09-16  Paolo Carlini  <pcarlini@suse.de>
	    Andrea Arcangeli  <andrea@suse.de>

	* config/io/basic_file_stdio.cc (__basic_file<>::close)): Don't
	call unnecessarily sync, that is fflush: the library, since 3.4.0
	does not use buffered fread/fwrite.
	* include/bits/fstream.tcc (basic_filebuf<>::overflow): Likewise.

diff -prN libstdc++-v3-orig/config/io/basic_file_stdio.cc libstdc++-v3/config/io/basic_file_stdio.cc
*** libstdc++-v3-orig/config/io/basic_file_stdio.cc	Mon Aug 30 13:33:54 2004
--- libstdc++-v3/config/io/basic_file_stdio.cc	Thu Sep 16 18:04:21 2004
*************** namespace std 
*** 259,281 ****
      __basic_file* __ret = static_cast<__basic_file*>(NULL);
      if (this->is_open())
        {
! 	// In general, no need to zero errno in advance if checking
! 	// for error first. However, C89/C99 (at variance with IEEE
! 	// 1003.1, f.i.) do not mandate that fclose/fflush must set
! 	// errno upon error.
! 	int __err;
! 	errno = 0;
  	if (_M_cfile_created)
! 	  do
! 	    __err = fclose(_M_cfile);
! 	  while (__err && errno == EINTR);
! 	else
! 	  do
! 	    __err = this->sync();
! 	  while (__err && errno == EINTR);
  	if (!__err)
  	  __ret = this;
- 	_M_cfile = 0;
        }
      return __ret;
    }
--- 259,279 ----
      __basic_file* __ret = static_cast<__basic_file*>(NULL);
      if (this->is_open())
        {
! 	int __err = 0;
  	if (_M_cfile_created)
! 	  {
! 	    // In general, no need to zero errno in advance if checking
! 	    // for error first. However, C89/C99 (at variance with IEEE
! 	    // 1003.1, f.i.) do not mandate that fclose must set errno
! 	    // upon error.
! 	    errno = 0;
! 	    do
! 	      __err = fclose(_M_cfile);
! 	    while (__err && errno == EINTR);
! 	  }
! 	_M_cfile = 0;
  	if (!__err)
  	  __ret = this;
        }
      return __ret;
    }
diff -prN libstdc++-v3-orig/include/bits/fstream.tcc libstdc++-v3/include/bits/fstream.tcc
*** libstdc++-v3-orig/include/bits/fstream.tcc	Tue Sep 14 20:41:02 2004
--- libstdc++-v3/include/bits/fstream.tcc	Thu Sep 16 17:07:20 2004
*************** namespace std
*** 396,403 ****
  	      // Convert pending sequence to external representation,
  	      // and output.
  	      if (_M_convert_to_external(this->pbase(),
! 					 this->pptr() - this->pbase())
! 		  && (!__testeof || !_M_file.sync()))
  		{
  		  _M_set_buffer(0);
  		  __ret = traits_type::not_eof(__c);
--- 396,402 ----
  	      // Convert pending sequence to external representation,
  	      // and output.
  	      if (_M_convert_to_external(this->pbase(),
! 					 this->pptr() - this->pbase()))
  		{
  		  _M_set_buffer(0);
  		  __ret = traits_type::not_eof(__c);