This implementation is based on the Plan9 RFC. It is intended to provide the both client and server functionality in a kernel module.

p9fs also targets:

• Providing a means of filesystem passthrough for BHyVe virtual machines.
• FreeBSD guests to talk to the PCI device provided by KVM for that purpose. This is exported as a VirtIO driver.

Any reading of the 9P2000.u RFC requires reading the original RFC, as the RFC is defined largely as documenting modifications.

There are three different filesystem specifications in Plan9:

• 9P2000: Original, used by Plan9
• 9P2000.u: Modification of the original for Unix VFSs
• 9P2000.L: Modification of the original specifically for Linux.

This implementation targets 9P2000.u, but if feasible, may also support 9P2000.L, primarily for compatibility purposes.

Some other implementations offer useful documentation and tips:

• py9p offers a generic implementation in Python.
• The diod protocol spec is helpful.
• There is some v9fs documentation too.