[libvirt] [PATCH 3/5] domaincaps: Report graphics spiceGL

[Daniel P. Berrange]

On Tue, May 10, 2016 at 11:26:29AM -0400, Cole Robinson wrote:
> On 05/10/2016 05:10 AM, Daniel P. Berrange wrote:
> > On Mon, May 09, 2016 at 06:53:01PM -0400, Cole Robinson wrote:
> >> On 05/09/2016 09:48 AM, Daniel P. Berrange wrote:
> > 
> > IMHO it is a total failure if we require the application to extend its
> > parser every time we add a new enum to the domain capabilities. We have
> > the ability to design something that is data driven - we should not build
> > something it is forced to be code driven with code changes for every
> > libvirt addition.
> 
> This is ignoring the point I made previously that the schema is not already
> fully introspectable. Most of the current enums cannot be programmatically
> consumed anyways, because there's no way to map an enum name to its domain XML
> property. So if that's our goal to be data driven, we should address that
> issue first.

Knowing the mapping of the capabilities enums to the domain schema is
a pre-requisite for consuming the capabilities data, no matter which
approach discussed in this thread is chosen. Assuming the app knows
that mapping, then the enum conditionals can be programmatically
handled with the approach I describe.

Providing a way for the app to automatically determine the mapping
from capabilities enums to the domain schema would be a nice
addition, but it isn't a pre-requisite blocker for what's discussed
here. It is something that can be deal with in parallel.

> I can't really think of a good way to represent that without nesting
> deeply or using specially formatted strings. Do you have a suggestion
> for that?

Probably the best thing is to use a very simplified xpath style notation.
If we add a 'mapping' attribute to the <enum> that expresses the attribute
or element it is associated with, relative to the parent container element.

eg, consider the tests/domaincapsschemadata/domaincaps-qemu_1.6.50-1.xml
data file with the mapping info:

<domainCapabilities>
  <path>/usr/bin/qemu-system-x86_64</path>
  <domain>kvm</domain>
  <machine>pc-1.2</machine>
  <arch>x86_64</arch>
  <os supported='yes'>
    <loader supported='yes'>
      <value>/usr/share/AAVMF/AAVMF_CODE.fd</value>
      <value>/usr/share/OVMF/OVMF_CODE.fd</value>
      <enum name='type' mapping="@type">
        <value>rom</value>
        <value>pflash</value>
      </enum>
      <enum name='readonly' mapping="@readonly">
        <value>yes</value>
        <value>no</value>
      </enum>
    </loader>
  </os>
  <devices>
    <disk supported='yes'>
      <enum name='diskDevice' mapping="@device">
        <value>disk</value>
        <value>cdrom</value>
        <value>floppy</value>
        <value>lun</value>
      </enum>
      <enum name='bus' mapping="target/@bus">
        <value>ide</value>
        <value>fdc</value>
        <value>scsi</value>
        <value>virtio</value>
        <value>usb</value>
      </enum>
    </disk>
    <hostdev supported='yes'>
      <enum name='mode' mapping="@mode">
        <value>subsystem</value>
      </enum>
      <enum name='startupPolicy' mapping="source/@startupPolicy">
        <value>default</value>
        <value>mandatory</value>
        <value>requisite</value>
        <value>optional</value>
      </enum>
      <enum name='subsysType' mapping="@type">
        <value>usb</value>
        <value>pci</value>
        <value>scsi</value>
      </enum>
      <enum name='capsType' mapping="@type"/>
      <enum name='pciBackend' mapping="driver/@name">
        <value>default</value>
        <value>kvm</value>
        <value>vfio</value>
      </enum>
    </hostdev>
  </devices>
  <features>
    <gic supported='no'/>
  </features>
</domainCapabilities>


NB, with my proposed conditionals, the hostdev enums above would actually
want to be different. eg it would want to look like this:

      <enum name='mode' mapping="@mode">
        <value>subsystem</value>
      </enum>
      <enum name='startupPolicy' mapping="source/@startupPolicy">
        <value>default</value>
        <value>mandatory</value>
        <value>requisite</value>
        <value>optional</value>
      </enum>
      <enum name='type' mapping="@type">
        <condition>
	  <enum name='mode' value='subsystem'/>
	</condition>
        <value>usb</value>
        <value>pci</value>
        <value>scsi</value>
      </enum>
      <enum name='driver' mapping="driver/@name">
        <condition>
	  <enum name='mode' value='subsystem'/>
	  <enum name='type' value='pci'/>
	</condition>
        <value>default</value>
        <value>kvm</value>
        <value>vfio</value>
      </enum>


Regards,
Daniel
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