down(&bus->root_hub->serialize);
ret = usb_device_dump(&buf, &nbytes, &skip_bytes, ppos, bus->root_hub, bus, 0, 0, 0);
up(&bus->root_hub->serialize);
down(&bus->root_hub->serialize);
ret = usb_device_dump(&buf, &nbytes, &skip_bytes, ppos, bus->root_hub, bus, 0, 0, 0);
up(&bus->root_hub->serialize);