On Mon, Mar 04, 2013 at 03:04:53PM +0100, Kevin Wolf wrote:
Am 04.03.2013 um 14:09 hat Daniel P. Berrange geschrieben:
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.
I think it makes much more sense to deal with it the way qemu does instead of inventing new names. This has much more of an (incompatible) feature flag than of a different image format. So to fit it in your proposed syntax:
The issue is that QEMU is not the only thing that implements the qcow format. There are a number of other impls out there, and we can't just assume that they will all be providing a qcow2 driver that automagically opens a qcow3 image format. Just in the same way we didn't assume that a 'qcow' (version 1) driver would open a version 2 image. It so happens that with QEMU if you specify format=qcow2 and give it a qcow3 image, QEMU will open it, but libvirt can't assume that, since this is a mere implementation detail. Hence libvirt must explicitly refer to 'qcow3' in the XML and map it to qcow2 if applicable when talking to QEMU.
But I guess you call all VMDKs just "vmdk", despite the fact that they are really just a collection of different subformats. Right?
Yes, but that is really a bug in our representation of vmdk. Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|