VFIO virtual device
===================

Device types supported:
  KVM_DEV_TYPE_VFIO

Only one VFIO instance may be created per VM.  The created device
tracks VFIO groups in use by the VM and features of those groups
important to the correctness and acceleration of the VM.  As groups
are enabled and disabled for use by the VM, KVM should be updated
about their presence.  When registered with KVM, a reference to the
VFIO-group is held by KVM.

Groups:
  KVM_DEV_VFIO_GROUP

KVM_DEV_VFIO_GROUP attributes:
  KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
  KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking

For each, kvm_device_attr.addr points to an int32_t file descriptor
for the VFIO group.