code: func DeviceCount() (uint, error) {
  	if C.nvmlHandle == nil {
  		return 0, errLibraryNotLoaded
  	}
  	var n C.uint
  	r := C.nvmlDeviceGetCount(&n)
  	return uint(n), errorString(r)
  }
docs: // DeviceCount returns the number of nvidia devices on the system.