[libvirt] RFC: Extending UEFI XML specification

[Peter Krempa]

On Wed, Mar 28, 2018 at 16:15:50 +0530, Prerna wrote:
> Hi Michal,
> The <loader>,<nvram> tags of os element in domain XML (
> https://libvirt.org/formatdomain.html#elementsOSBIOS) currently expects
> absolute path of the local file which would be used to back the the pflash
> disk representing the non-volatile RAM:
> 
> <loader readonly='yes' secure='no'
> type='rom'>/usr/lib/xen/boot/hvmloader</loader>
> <nvram
> template='/usr/share/OVMF/OVMF_VARS.fd'>/var/lib/libvirt/nvram/guest_VARS.fd</nvram>
> 
> However, given that for virtualized environments, it is possible that the
> VM could be started on different hosts at various points in time, and so we
> need to expose the firmware/nvram tuple over a network device so as to be
> accessible from various hosts.
> I propose extending of the existing config by adding a new element,
> "backing". This could be one of :
> - 'file': for local filesystem paths
> - 'network': for network-attached storage.

Since this is as any other storage volume for the hypervisor, you should
treat it as a virStorageSource, including the 'block' and 'volume'
types.

> 
> As an example:
> 
> <loader readonly='yes' secure='no' type='rom' backing =
> 'file'>/usr/share/OVMF/OVMF_CODE.fd</loader>
> <nvram backing='file'
> template='/usr/share/OVMF/OVMF_VARS.fd'>/var/lib/libvirt/nvram/guest_VARS.fd</nvram>
> 
> For network-attached storage:
> <loader readonly='yes' secure='no' type='rom' backing =
> 'network'>/usr/share/OVMF/OVMF_CODE.fd</loader>

I presume you wanted to add the <source> section here as well.

> <nvram backing='network'>
>     <source protocol='XXX'  name='YYY'>
>         <host name='x.x.x.x' port=xxxx/>
>      </source>
> </nvram>

In addition to this we should also support the 'storage-source' like
definition for backing='file' too:

<nvram backing='file'>
  <source file='/path/to/blah'/>
</nvram>

With that encryption of the image can be defined as well.

> 
> Note that 'template' attribute in NVRAM should be explicitly disallowed for
> backing type "network". This is because libvirtd may not be able to access
> the backing store to copy the contents of the template.

This should be hypervisor-defined. While it will not be easy, you can
use qemu-img in the qemu driver to populate network disks via the
'convert' command.

> I would like to capture thoughts from the community to extend the current
> firmware spec.
> 
> Regards,
> Prerna
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