Re: [Qemu-devel] [libvirt] [PATCH v7 0/4] Add Mediated device support

[John Ferlan <jferlan@redhat.com>]

On 09/02/2016 05:48 PM, Paolo Bonzini wrote:
> 
> 
> On 02/09/2016 20:33, Kirti Wankhede wrote:
>> <Alex> We could even do:
>>>>
>>>> echo $UUID1:$GROUPA > create
>>>>
>>>> where $GROUPA is the group ID of a previously created mdev device into
>>>> which $UUID1 is to be created and added to the same group.
>> </Alex>
> 
>>From the point of view of libvirt, I think I prefer Alex's idea.
> <group> could be an additional element in the nodedev-create XML:
> 
>     <device>
>       <name>my-vgpu</name>
>       <parent>pci_0000_86_00_0</parent>
>       <capability type='mdev'>
>         <type id='11'/>
>         <uuid>0695d332-7831-493f-9e71-1c85c8911a08</uuid>
>         <group>group1</group>
>       </capability>
>     </device>
> 
> (should group also be a UUID?)

As long as create_group handles all the work and all libvirt does is
call it, get the return status/error, and handle deleting the vGPU on
error, then I guess it's doable.

Alternatively having multiple <type id='#'> in the XML and performing a
single *mdev/create_group is an option. I suppose it all depends on the
arguments to create_group and the expected output and how that's
expected to be used.

That is, what is the "output" from create_group that gets added to the
domain XML?  How is that found? Also, once the domain is running can a
vGPU be added to the group?  Removed?  What allows/prevents?

> 
> Since John brought up the topic of minimal XML, in this case it will be
> like this:
> 
>     <device>
>       <name>my-vgpu</name>
>       <parent>pci_0000_86_00_0</parent>
>       <capability type='mdev'>
>         <type id='11'/>
>       </capability>
>     </device>
> 
> The uuid will be autogenerated by libvirt and if there's no <group> (as
> is common for VMs with only 1 vGPU) it will be a single-device group.
> 

The <name> could be ignored as it seems existing libvirt code wants to
generate a name via udevGenerateDeviceName for other devices. I haven't
studied it long enough, but I believe that's how those pci_####* names
created.

John