Re: [Qemu-devel] proposed qcow2 extension: cluster reservations [was: [RFC] Proposed qcow2 extension: subcluster allocation

[Alberto Garcia]

On Sat 22 Apr 2017 07:56:57 PM CEST, Max Reitz wrote:
>> So, if you got this far in reading, the question becomes whether
>> having a mode where you can mark a cluster as
>> mapping-reserved-but-unallocated has enough use case to be worth
>> pursuing, knowing that it will burn an incompatible feature bit; or
>> if it should be rolled into the subcluster proposal, or whether it's
>> not a feature that anyone needs after all.
>
> I just forgot that just saying !ALLOCATED will be enough, regardless
> of the ZERO flag... Yeah, subclusters will give us this for free, and
> I think it's therefore reasonable to just require them if you want
> this feature (preallocation with a backing file).

I agree with Max here.

Berto