[libvirt PATCH v2 05/16] nodedev: add ability to list and parse defined mdevs

[Bjoern Walk]

Jonathon Jongsma <jjongsma at redhat.com> [2020-08-18, 09:47AM -0500]:
> diff --git a/tests/nodedevmdevctldata/mdevctl-list-single.out.xml b/tests/nodedevmdevctldata/mdevctl-list-single.out.xml
> new file mode 100644
> index 0000000000..cb443346ef
> --- /dev/null
> +++ b/tests/nodedevmdevctldata/mdevctl-list-single.out.xml
> @@ -0,0 +1,14 @@
> +<device>
> +  <name>mdev_783e6dbb_ea0e_411f_94e2_717eaad438bf</name>
> +  <parent>matrix</parent>
> +  <capability type='mdev'>
> +    <type id='vfio_ap-passthrough'/>
> +    <iommuGroup number='0'/>
> +    <attr name='assign_adapter' value='5'/>
> +    <attr name='assign_adapter' value='6'/>
> +    <attr name='assign_domain' value='0xab'/>
> +    <attr name='assign_control_domain' value='0xab'/>
> +    <attr name='assign_domain' value='4'/>
> +    <attr name='assign_control_domain' value='4'/>
> +  </capability>
> +</device>

I find this XML design for the an AP mdev rather unfortunate. First of
all, it is really noisy and requires a lot of boiler-plate for the end
user.

Secondly, which I think it more important, it introduces a completely
new and different nomenclature compared to what we currently already
have for AP-related devices, i.e. cards

	virsh # nodedev-dumpxml ap_card05
	<device>
	  <name>ap_card05</name>
	  <path>/sys/devices/ap/card05</path>
	  <parent>computer</parent>
	  <driver>
		<name>cex4card</name>
	  </driver>
	  <capability type='ap_card'>
		<ap-adapter>0x05</ap-adapter>
	  </capability>
	</device>

and queues

	virsh # nodedev-dumpxml ap_05_002a
	<device>
	  <name>ap_05_002a</name>
	  <path>/sys/devices/ap/card05/05.002a</path>
	  <parent>ap_card05</parent>
	  <driver>
		<name>cex4queue</name>
	  </driver>
	  <capability type='ap_queue'>
		<ap-adapter>0x05</ap-adapter>
		<ap-domain>0x002a</ap-domain>
	  </capability>
	</device>

This is really inconsistent and can be confusing for the end user.

Can we instead propose something along the lines

	<device>
	  <name>mdev_783e6dbb_ea0e_411f_94e2_717eaad438bf</name>
	  <parent>matrix</parent>
	  <capability type='mdev'>
		<type id='vfio_ap-passthrough'/>
		<iommuGroup number='0'/>
		<ap-adapter>0x05</ap-adapter>
		<ap-adapter>0x06</ap-adapter>
		<ap-domain>0x002a</ap-domain>
		<ap-domain>0x0004</ap-domain>
		<ap-domain>0x00ab</ap-domain>
		<ap-control>0x04</ap-control>
	  </capability>
	</device>

plus any number of enclosing elements that we like for better readability?

Best,
Bjoern

PS: I haven't read the whole patch series, we just have an internal
discussion about AP support and the XML design came up. I know that we'd
like to generically treat all mdevs as the same but we also should allow
for vendor-specific attributes to be represented individually to what
makes sense.

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