Re: [Qemu-devel] [PATCH] qcow2: Metadata preallocation

[Jamie Lokier]

Jamie Lokier wrote:
> Filip Navara wrote:
> > FILE_ATTRIBUTE_SPARSE_FILE? You can't actually set it when
> > opening/creating the file, a separate call to
> > DeviceIoControl/FSCTL_SET_SPARSE is needed.
> 
> I see that you increase the file size by writing zeros to the end.
> 
> Can't you use the Windows equivalent of unix ftruncate() to extend the
> file instead, after FSCTL_SET_SPARSE?

Specifically: 

    SetEndOfFile
        Use this after SetFilePointer to change the length of a file
        or stream.  If used on a sparse file or stream, increasing
        the length creates a sparse region.

-- Jamie