On Fri, Oct 18, 2013 at 02:01:03PM +0200, Stefan Hajnoczi wrote:
> On Fri, Oct 11, 2013 at 02:17:31PM -0400, Jeff Cody wrote:
> > + /* check the payload block state */
> > + switch (s->bat[sinfo.bat_idx] & VHDX_BAT_STATE_BIT_MASK) {
> > + case PAYLOAD_BLOCK_ZERO:
> > + /* in this case, we need to preserve zero writes for
> > + * data that is not part of this write, so we must pad
> > + * the rest of the buffer to zeroes */
> > +
> > + /* if we are on a posix system with ftruncate() that
> > extends
> > + * a file, then it is zero-filled for us. On Win32, the
> > raw
> > + * layer uses SetFilePointer and SetFileEnd, which does not
> > + * zero fill AFAIK */
> > +
> > + /* Queue another write of zero buffers if the underlying
> > file
> > + * does not zero-fill on file extension */
> > +
> > + if (bdrv_has_zero_init(bs->file) == 0) {
>
> Maybe this should be done differently once Peter Lieven's thin
> provisioning patches are merged. I think bdrv_has_zero_init() only
> tells you whether the file is zeroed after creation. It doesn't
> guarantee zeroes for other operations like growing the file.
>
> I'm not 100% sure right now, will follow-up on this point later when
> I've reviewed Peter's series and thought more about it.
With Peter's thin provisioning patches this call would be changed to
bdrv_has_discard_zeroes(). We're discussing changing the name of that
function though.
Stefan
