To test against existing implementation I wanted some existing tool that can be used to access 9p server. Kamid has `kamiftp` tool that is FTP-like client for 9p servers. It needs some patches to work on macOS so I add these changes in Nix derivation. Unfortunately this will not work for client tests, but it is way easier to find simple 9p server than it is to find simple 9p client for some reason.