Changes to basic_filebuf::sync and testsuite

[scott snyder <snyder at fnal dot gov>]

hi -

I noticed the following in the changelog:

1999-11-11  Benjamin Kosnik  <bkoz@gnu.org>

	* bits/std_fstream.h: Revert. Disable call to _M_file->sync as
	killing 27_io/filebuf.cc tests. . . need another solution.

I tried to investigate why this was failing.
It looks like the problem is due to a separate bug in the libio/libstdc++
interaction which is provoked by the change.

[For the record, i'm testing this on a redhat 6.0 linux system,
which uses glibc 2.1.1.]

The failure in filebuf.cc occurs here:

  pt_2 = fb_03.pubseekoff(2, std::ios_base::cur, std::ios_base::in|std::ios_base::out);
  off_2 = pt_2._M_position();
  test &= (off_2 == (off_1 + 2 + 1 + 1));

off_1 is 2; before the call we've seeked two chars further than off_1;
so pt_2 should return 6, but instead, it returns 2.

If i step through what's happening, i find myself in _IO_new_file_seekoff
in fileops.c of libio.  This code chooses to take the `dumb' path
(branching to the label of the same name), in which it ends up simply
calling basic_file::sys_seek.  (I think that it chooses this path due
to the addition of the sync call in basic_filebuf::sync, but i haven't
checked that.)  The call is here:

  result = _IO_SYSSEEK (fp, offset, dir);

The problem is that `offset' is declared as a _IO_off64_t, which is an
8-byte integer.  Meanwhile, the function which gets called in bits/basic_file.h
is declared as:

    virtual __c_streampos 
    sys_seek(streamoff __off, ios_base::seekdir __way);

Here, `streamoff' is a 4-byte integer.  Guess calling functions through
libio's jump tables doesn't enforce type safety...

So, _IO_new_file_seekoff is trying to call sys_seek with arguments
__off==2 and __way==1 (seek_cur).  But due to the type mismatch,
__way in sys_seek ends up being the high 4 bytes of __off, which
is 0, or seek_set.  So the seek goes to absolute position 2, rather then
relative position 2, as intended.

Following is an attempt at a fix.  With these changes, i don't see
any changes in the testsuite results, and my test of flush ordering
executes correctly.  However, i have not tested this on any other platforms.

thanks,
sss


1999-11-15  Scott Snyder  <snyder@fnal.gov>

	* bits/basic_file.h: Type of __off parm should be __c_streampos, to
	match how libio is calling us.
	* src/basic_file.cc (sys_seek): Likewise.
	* bits/std_fstream.h (basic_filebuf::sync): Restore sync call.


Index: bits/basic_file.h
===================================================================
RCS file: /cvs/libstdc++/libstdc++/bits/basic_file.h,v
retrieving revision 1.15
diff -u -p -r1.15 basic_file.h
--- basic_file.h	1999/06/25 03:55:23	1.15
+++ basic_file.h	1999/11/16 04:01:45
@@ -169,7 +169,7 @@ namespace std {
     // does no mucking around with or setting of the pointers or flags
     // in __c_file_type.
     virtual __c_streampos 
-    sys_seek(streamoff __off, ios_base::seekdir __way);
+    sys_seek(__c_streampos __off, ios_base::seekdir __way);
 
     virtual int 
     sys_close();
Index: bits/std_fstream.h
===================================================================
RCS file: /cvs/libstdc++/libstdc++/bits/std_fstream.h,v
retrieving revision 1.61
diff -u -p -r1.61 std_fstream.h
--- std_fstream.h	1999/11/12 08:06:48	1.61
+++ std_fstream.h	1999/11/16 04:01:45
@@ -170,7 +170,7 @@ namespace std {
 	    // flushed. Back up, so overflow doesn't append extra characters.
 	    this->_M_really_overflow();
 	  }
-	//	_M_file->sync();
+	_M_file->sync();
 	_M_last_overflowed = false;	
 	return 0;
       }
Index: src/basic_file.cc
===================================================================
RCS file: /cvs/libstdc++/libstdc++/src/basic_file.cc,v
retrieving revision 1.20
diff -u -p -r1.20 basic_file.cc
--- basic_file.cc	1999/10/18 18:57:13	1.20
+++ basic_file.cc	1999/11/16 04:01:45
@@ -224,7 +224,7 @@ namespace std {
   { return _IO_file_write(this, __s, __n); }
 
   __c_streampos 
-  __basic_file::sys_seek(streamoff __off, ios_base::seekdir __way)
+  __basic_file::sys_seek(__c_streampos __off, ios_base::seekdir __way)
   { return _IO_file_seek(this, __off, __way); }
   
   int