9P is a network protocol developed at Bell Labs for the Plan 9 from Bell Labs distributed operating system as the means of accessing and manipulating resources and applications transparently in a distributed environment. 9P works both as a distributed file system and as a network transparent and language agnostic ‘API’.^[1]

9p Now allows an host computer through USB to share an FS. The client at the other end of the USB can mount that FS. The use is in gadget on the USB device that can be programmed/dev in a fast/simple way. ^[2]