Actually you missed a buzzword “USB sniffing“. 😉
Here are a few tutorials on USB sniffing on Linux, to get you started.
- Official Wireshark wiki for USB monitoring
- biot.com/blog/usb-sniffing-on-linux (InternetArchive)
- tjworld.net/wiki/Linux/Ubuntu/USBmonitoring
Essentially you use the usbmon Linux kernel module to capture the USB-packets and Wireshark as a front-end to display and analyse the captured USB stream.