Re: [Qemu-devel] [RFC] qcow3 format in libvirt

[Daniel P. Berrange]

On Mon, Mar 04, 2013 at 01:58:12PM +0100, Ján Tomko wrote:
> Before posting another version of my patches [1], attempting to add
> support for the new qcow format to libvirt, I would like to know if this
> sounds reasonable:
> 
> A new format named 'qcow3' would be added, along with a <features>
> sub-element for target.
> 
> <volume>
>   <name>qcow3test</name>
>   <source>
>   </source>
>   <capacity unit='GiB'>8</capacity>
>   <target>
>     <path>/var/lib/libvirt/images/qcow3test</path>
>     <format type='qcow3'/>
>     <features>
>       <lazy_refcounts/>
>     </features>
>   </target>
> </volume>
> 
> I think that libvirt shouldn't care if the features are compatible or
> incompatible, as we don't know what features are supported by the
> hypervisor. Would the features be any good as tri-state (on, off, default?).
> 
> While the qcow3 format is handled by the qcow2 driver in QEMU,
> <driver name='qemu' type='qcow2'/> should be enough for domains,

We should use qcow3 everywhere IMHO, regardless of whether qcow2
technically works in this context.

> but in snapshot XML we treat the driver type as the format:
> 
> <disk name='/path/to/old'>
>   <driver type='qcow3'/>
>   <source file='/path/to/new'/>
>   <features>
>     <lazy_refcounts/>
>   </features>
> </disk>
> 
> So I think we should allow the qcow3 driver type as well and translate
> it to qcow2 for QEMU.
> 
> Jan
> 
> [1] v2 here:
> https://www.redhat.com/archives/libvir-list/2013-February/msg00212.html
> 

Daniel
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