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From: "GARY VANSICKLE" <g DOT r DOT vansickle AT worldnet DOT att DOT net>
To: <cygwin AT cygwin DOT com>
Subject: RE: working sync() code
Date: Sat, 10 Apr 2004 15:05:35 -0500
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In-Reply-To: <4078041C.1020AC42@karasik.eu.org>
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> Hi all,
> 
> I found a way to issue an actual sync() on win32, and as browsing
> through winsup directory gave me only this
> 
> 
> winsup/sygwin/syscalls.cc #1128
> extern "C" int
> sync ()
> {
>    return 0;
> }
> 
> 
> I think cygwin DLL might benefit from a code I found by looking in
> sync.exe by M.Russinovich, which is schematically as such:
> 
> 
> int
> sync( char drive)
> {
>    HANDLE f;
>    int ret;
>    char file[7] = "\\\\.\\X:";
>    file[5] = drive;
>    f = CreateFile( file, GENERIC_READ|GENERIC_WRITE,
> FILE_SHARE_READ|FILE_SHARE_WRITE,
> 		  NULL, OPEN_EXISTING, 0, NULL);
>    if ((int) f < 0)
>       return -1;
>    ret = FlushFileBuffers(f) ? 0 : -1;
>    CloseHandle(f);
>    return ret;
> }
> 

FlushFileBuffers() doesn't actually do much last I checked.  Despite its
misleading name, it is not a
"commit-to-disk-and-don't-return-until-its-done" at any rate, which is
what's needed here.  The only way I ever found to actually do this is to
open a handle to the underlying physical drive (and just try mapping drive
letters to physical drives!) and then there's an IOCTL_ that will do the
trick.  And as long as the account has the right privileges, you can do
that, otherwise you can't.


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