[libvirt] Xen device section defaults miss name='qemu'

[Jim Fehlig]

On 07/11/2017 08:15 AM, Christian Ehrhardt wrote:
> Hi,

Hi,

Thanks for the report and sorry for delayed response. I'm slowly catching up on 
libvirt mail after being away for a while...

> we have found an issue caused by 321a28c6 "libxl: set default disk format in 
> device post-parse" (and maybe more changes I couldn't identify yet).
> 
> TL;DR: The auto-added driver section in xen changed and now causes issues.
>
> An example to to trigger:
> 1. Create a  XEN xml with a disk device of type cdrom, but do not add a driver 
> section, like.
>      <disk type='file' device='cdrom'>
>        <target dev='hdb' bus='ide'/>
>        <readonly/>
>      </disk>
> 2. on virsh define if that XML
> 2b. You could also "virsh edit" any working xml file, remove the <driver../> 
> which will trigger the same
> 2c. You could also define via virt-manager as it does not explicitly specify the 
> device section
> 
> What happens is that before the changes this auto-added a driver section like:
>     <driver name='qemu' type='raw'/>
> But now it does only add
>     <driver type='raw'/>
> Which fails to verify like:

I think you forgot to paste the example here, but I assume it is something like

# virt-xml-validate test.xml
Relax-NG validity error : Extra element devices in interleave
test.xml:21: element devices: Relax-NG validity error : Element domain failed to 
validate content
test.xml fails to validate

where test.xml contains disk config

     <disk type='file' device='cdrom'>
       <driver type='raw'/>
       <target dev='hdb' bus='ide'/>
       <readonly/>
       <address type='drive' controller='0' bus='0' target='0' unit='1'/>
     </disk>

It is not clear to me if 'name' is a required attribute of <disk>. The doc says 
"If the hypervisor supports multiple backend drivers, then the name attribute 
selects the primary backend driver name". It doesn't mention "required" or 
"mandatory". We'd have a schema bug if 'name' is optional. I guess it is a good 
question for danpb. Dan, is disk/driver/@name a required attribute?

Regards,
Jim