VMM (e.g. QEMU) can receive a file descriptor of a vhost-vdpa character device already opened by the management layer (e.g. libvirt). This is useful especially when the device can only be accessed with certain privileges, more details here: https://bugzilla.redhat.com/show_bug.cgi?id=2180076
This series also adds a new fd test to check that property for the drivers
that support it.
Signed-off-by: Stefano Garzarella sgarzare@redhat.com