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

[Paolo Bonzini]

On 02/09/2016 22:19, John Ferlan wrote:
> We don't have such a pool for GPU's (yet) - although I suppose they
> could just become a class of storage pools.
> 
> The issue being nodedev device objects are not saved between reboots.
> They are generated on the fly. Hence the "create-nodedev' API - notice
> there's no "define-nodedev' API, although I suppose one could be
> created. It's just more work to get this all to work properly.

It can all be made transient to begin with.  The VM can be defined but
won't start unless the mdev(s) exist with the right UUIDs.

>> After creating the vGPU, if required by the host driver, all the other
>> type ids would disappear from "virsh nodedev-dumpxml pci_0000_86_00_0" too.
> 
> Not wanting to make assumptions, but this reads as if I create one type
> 11 vGPU, then I can create no others on the host.  Maybe I'm reading it
> wrong - it's been a long week.

Correct, at least for NVIDIA.

> PCI devices have the "managed='yes|no'" attribute as well. That's what
> determines whether the device is to be detached from the host or not.
> That's been something very painful to manage for vfio and well libvirt!

mdevs do not exist on the host (they do not have a driver on the host
because they are not PCI devices) so they do need any management.  At
least I hope that's good news. :)

Paolo