Re: [Qemu-devel] Re: KVM call agenda for Jan 25

[Dushyant Bansal <cs5070214@cse.iitd.ac.in>]

>> 1. header_size: variable in qed, equals to cluster size in qcow2:
>> When will it be larger than 1 cluster in qed? So, what will happen to
>> that extra data on qed->qcow2 conversion.
>>      
> If you have an feature that is used in the original image, but cannot be
> represented in the new format, I think you should just get an error.
>
>    
>> 2. L2 table size: equals to L1 table size in qed, equals to cluster size
>> in qcow2:
>> we need to take it into account during conversion.
>>      
> Right. I think we'll have to rewrite all of the metadata.
>
> I wonder if we can manage to have a nice block driver interface for
> in-place image conversions so that we don't only get a qed<->qcow2
> converter, but also can implement the interface in e.g. VMDK and get
> VMDK<->qcow2 and VMDK<->qed as well.
>    
>> 3. refcount table:
>> qcow2->qed:we do not keep refcount structure
>> qed->qcow2: initialize refcount structure
>>      
> Yes, refcounts can be rebuilt after the mapping has been converted.
>
>    
>> So, a qcow2->qed->qcow2 conversion means if earlier, qcow2 image was
>> using additional features{1-4}, all information related to that will be
>> lost.
>>      
> We shouldn't lose anything but just abort if a conversion isn't
> possible. The user can still use qemu-img convert for the more
> complicated cases, for example for removing encryption or compression.
>
>    
Thanks for clearing up those issues.

--
Dushyant