Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver

[Dietmar Maurer]

> > >> This should call bdrv_is_allocated_above like the other block jobs do.
> > >> It would be needed later anyway to backup only the topmost image.
> > >
> > > I do not need that information now, so why do you want that I add dead
> code?
> >
> > I think you do.  You're wasting time reading unallocated clusters and
> > checking that they are zero.  bdrv_is_allocated_above gives you the
> > same information much more efficiently.
> 
> I thought that just returns information if the data is allocated, or if data 
> is on
> backing file?
> 
> Or is data guaranteed to be zero if bdrv_is_allocated_above() return 0?

Oh, I need to pass NULL for base to get that information?