USB device passthrough implementation

[Wojciech Puchar]

> We want to implement the USB pass through feature for bhyve so that users
> will be able to pass through individual USB devices like in QEMU. We are

i want to be your beta tester.

> trying to emulate the USB controller and pass to the virtual machine only
> one port.
>
> * We need to disconnect the USB device from host: we are currently not very
> familiar with the kernel API to perform this

in most cases you actually don't have to.
just use /dev/ugen/* devices
simply make it as a parameter for bhyve

usbpassthrough=a/device

where a is virtual USB device number (i don't think you want to emulate 
more than one bus - one xhci is already done in bhyve),  and device would 
be like /dev/ugenX.Y