Re: [virtio-dev] [pci PATCH v7 2/5] virtio_pci: Add support for unmanaged SR-IOV on virtio_pci devices

["Rustad, Mark D" <mark.d.rustad@intel.com>]

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

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