On Apr 3, 2018, at 11:27 AM, Michael S. Tsirkin <mst@redhat.com> wrote:

>> I'm not sure why you would need a feature bit. The capability is
>> controlled via PCI configuration space. If it is present the device
>> has the capability. If it is not then it does not.
>>
>> Basically if the PCI configuration space is not present then the sysfs
>> entries will not be spawned and nothing will attempt to use this
>> function.
>>
>> - ALex
>
> It's about compability with older guests which ignore the
> capability.
>
> The feature is thus helpful so host knows whether guest supports VFs.

This is not about a guest creating its own VFs. This is about a host PF  
that happens to have a virtio interface to be able to create virtio VFs  
that can be assigned to guests. Nothing changes at all from a guest  
perspective. Or maybe I am not understanding what you mean by "whether  
guest supports VFs".

--
Mark Rustad, Networking Division, Intel Corporation