Re: Optimizing away "ReadFile" calls when Make calls stat()

[Warren Young <warren at etr-usa dot com>]

Egor Duda wrote:
> 
> the  only problem with this approach i can see is that if we introduce
> new  API  and applications start to use it we became "bound" to it and
> it'll  be  not too easy to deprecate ad remove it afterwards. OTOH, we
> can  always  make stat_lite() a simple wrapper to stat() if the latter
> become fast enough.

I like the idea of stat_lite(), and I don't see a reason to ever
deprecate it: it's simply a fact that stat() is a bad interface to Win32
functionality.  It exposes a Unix filesystem's inode element, and
therefore makes programs dependent on it.  To eliminate the need for a
stat_lite(), you'd have to redesign Win32, which is out of our hands.

Here's how I think stat_lite() should be designed: give it one extra
parameter, a bitfield, over regular stat().  This declares what fields
are important to the caller.  

All the code in the DLL's current stat() implementation would move to
stat_lite().  Then add 'if's checking the bitfield flags before making
Win32 calls to look up field values.  The DLL's stat() implementation
then becomes a wrapper around stat_lite(): it just sets all the bitfield
flags, telling it to look up every field value.

If this design is used, stat_lite() would be a misleading name.  How
about stat_select(), since it would behave like select(2)?

Example code:

	struct stat st;
	stat_select("foo", &st, ST_MODE | ST_MTIME);

Cygwin.DLL:
	int stat(const char* file, struct stat* pst) 
	{
		return stat_select(file, pst, 0xFFFFFFFF);
	}

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