Re: [PATCH v4 07/30] qcow2: Document the Extended L2 Entries feature

[Alberto Garcia]

On Tue 14 Apr 2020 08:06:38 PM CEST, Vladimir Sementsov-Ogievskiy 
<address@hidden> wrote:
>>> In other words, cluster can't be unallocated with data file in use.
>> 
>> I still don't follow... clusters can be unallocated, and when you
>> create a new image they are indeed unallocated.
>
> with external data file? Than we probably need to fix spec..
>
> unallocated mean that offset is 0, and bit 63 is unset. But this can't
> be when and exernal data file is used, accordingly to the spec.
>
> Or what am I missing?

   $ qemu-img create -f qcow2 -o data_file=data.raw img.qcow2 1M
   $ qemu-io -c 'write 0 192k' img.qcow2 
   $ qemu-io -c 'write -z -u 64k 64k' img.qcow2 

Clusters #0 and #2 are allocated (offsets 0x00000 and 0x20000), cluster
#1 is unallocated (offset 0, bit 63 unset, bit 0 -all zeroes- set).

Berto