Marko Bolowski, the chap behind the Sony Librie translation project, gave in to our desire to explore the Librie’s internals and released a tool which allows us to open a root console via USB to the Sony device. USBPD consists of a console program (that runs on the USBPD host device, i.e. any Linux computer) and a server program (that runs on the USBPD target device, i.e. our Sony Librie); the precompiled binaries (including sources, of course) can be downloaded here- Link.
Root console on Sony Librie with USBPD