Realize the support of instance to usb device, that is, add, delete, change and check the function of usb device.

1. show the host's usb device:expand the interface of nova- API, and provide an API entry.For convenience, you can add an action to trigger the interface by calling /os-hypervisors/{host_name}/get_host_usblist by **GET**. The following code adds an API interface, which needs to be called by **GET** request.The code manager.py is modified in compute-manager to call libvirt to drive and filter out the system's own devices.Add the code in host (virsh nodedev-list,virsh nodedev-dumpxml ${usb}) to list all usb devices.

2: attach_usb: call API interface, input vendor and product values, call compute.Manager. Attach_usb method, call driver.py to modify conf file to increase vendor and product values, call nova/objects/ instance_usb.instanceusb.create (), and save data to instance_usb table.

3: detach_usb: with attach_usb.

4: show_usb: show the usb that has been mounted to the virtual machine,call API interface, input server_id, call nova/objects/ instance_usb.instanceusb.get_with_instance_uuid () method, data will be returned to the data, through the CONF

Note:
Rebuild, resize, delete, migrate/live-migrate, and evacuate for virtual machines will result in the loss of the usb and will need to be modified as well.