Re: [PATCH] qemu-{img,nbd}: Don't report zeroed cluster as a hole

[Eric Blake]

On Fri, Jun 11, 2021 at 01:21:45PM +0200, Kevin Wolf wrote:
> > Did you consider just add a new field?
> > 
> > So, "depth" keeps its meaning "which level provides data".
> > 
> > And we add additional optional field like
> > 
> > absolutely-completely-absent: bool
> > 
> > Which is true if data is nowhere in the backing chain.
> 
> Or how about exposing BDRV_BLOCK_ALLOCATED as 'allocated': 'bool'? Which
> I think is what the conclusion was already for NBD, so doing the same in
> 'qemu-img map' would be consistent.
> 
> This is, of course, almost the same as 'absolutely-completely-absent',
> just without the negating the flag.

If we want to bikeshed on a new name, I think "allocated" is going to
cause more confusion than it solves.  And "hole" is wrong.  Better
would be "backing":true for portions of the file that would derive
from a backing file, if a backing file had been present.

But that still feels like more work than just exposing n+1 in depth.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org