[MisterTea]

9p is not a file system but a byte oriented file based RPC protocol for transferring data. In plan 9 the idea is files are objects in the programming sense which you create/open/read/write/remove/close. Example: your mouse is a file, /dev/mouse, which you open to read the coordinates and click events.

In plan 9 files are served by file servers, programs which speak 9p. The plan 9 kernel knows nothing of disks or file systems living on those disks. In fact, you don't mount disks in plan 9, you mount 9p connections. So to access files on a Fat formatted disk you need a file server program called dossrv(4) which opens the disk file and listens for 9p messages and performs the necessary Fat operations.

Fun fact: A common plan 9 newbie mistake is to mount a disk file directly as in Unix. This causes the kernel to write a 9p T_attach message to the beginning of the disk overwriting the boot sector. http://man.postnix.pw/9front/5/attach