needs a semaphore on 2.3.x
The registration code assigns minor numbers based on the type requested. -ENFILE is returned in all the device slots for this category are full. If not then the minor field is set and the driver initialize function is called (if non NULL).
Zero is returned on success.
Valid types are
VFL_TYPE_GRABBER - A frame grabber
VFL_TYPE_VTX - A teletext device
VFL_TYPE_VBI - Vertical blank data (undecoded)
VFL_TYPE_RADIO - A radio card