[libvirt] [PATCH 3/5] domaincaps: Report graphics spiceGL
Daniel P. Berrange
berrange at redhat.com
Wed May 11 15:30:56 UTC 2016
On Wed, May 11, 2016 at 11:25:50AM -0400, Cole Robinson wrote:
> On 05/11/2016 04:49 AM, Daniel P. Berrange wrote:
> > On Tue, May 10, 2016 at 07:15:01PM -0400, Cole Robinson wrote:
> >> On 05/10/2016 11:50 AM, Daniel P. Berrange wrote:
> >>> 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>
> >>>
> >>
> >> Yeah that mapping= bit makes sense to me.
> >>
> >> I don't have time to see pick this up now though, so I've stuffed it in a bug:
> >
> > Thinking about this some more last night, I realize that once we have
> > the 'mapping' attribute, then the choice of values in the 'name' attribute
> > becomes totally irrelevant.
> >
> > IOW, we could use your suggestion for giving each enum a unique name,
> > eg 'spiceGL', 'vncGL', etc, etc. So apps which want to consume this
> > data have a choice between just matching on explicit enum names and
> > ignoring the <condition> rules, or they can match on the 'mapping'
> > attribute and use the <condition> rules.. So we get the best of both
> > ideas.
>
> Hmm, but does that mean that once we assign an enum name, its semantics are
> locked in stone? Can we add new conditions to an existing enum to clarify
> semantics, or does extending the condition list always mandate a new enum?
Hmm, that's a good question - to too sure really, but I'd probably be
inclined to say the latter.
Regards,
Daniel
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