USB Port busy, or not

How to detect USB Port status connected with a USB Flash drive? (working or idle).

It seems no APIs or interfaces to get the status of a USB Port (working or idle).

As workarounds, it may work to force reflush cache by unmounting and re-mounting volume or remove and rescan usb key device.

1. Flush disk cache by unmounting and re-mounting volume

2. Devcon remove "USB\VID_XXXX&PID_XXXX" and then "devcon rescan"