p9fs: A 9P2000.U kernel filesystem driver for FreeBSD.

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.

Plan9 filesystem specifications

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.

Other References

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.