Vomit-induced implementations of the 9P protocol in Chicken Scheme (by alaric)
Last Saturday, I came down with what I suspect was Norovirus - the rest of the family (apart from the baby) having come down with it on Thursday and me having spent the past few days mopping up after them, this was probably unavoidable; although I'd tried my best by wearing a respirator when performing clean-up operations (it was also nice to not have to smell what I was clearing up...).
But, it meant I spent Monday off of work recuperating. I was too weak and exhausted to do any work from home, but I was bored senseless of just lying there on the sofa, so I decided to try and extend Chicken Scheme's 9p egg, which is a client implementation of the 9P2000 file server protocol, to also be able to act as a server.
This is something I want for Ugarit; it means that a Chicken Scheme app will be able to provide a virtual filesystem that can be mounted from a computer and used like your "real" filesystem. In particular, I want to be able to let people access their backed-up snapshots from a Ugarit vault as a live read-only filesystem, rather than needing to go in and manually "restore" their desired files back into the filesystem to access them. And it'll really come into its own when I implement archive mode, as it will make it possible to actually use the Ugarit archive seamlessly.
Unfortunately, being rather fuzzy-headed, I kept making rookie mistakes, but I eventually managed to get the core protocol implementation working. In doing so, I found out that a 9P server that puts incorrect lengths in the stat structures returned from directory reads causes 9P mounts in Linux to "hang" in a way that can't be unmounted and you need to power-cycle the machine as it won't even shut down cleanly... so be careful of that when mounting the few public 9P servers out there!
In order to test it, and as a utility for Chicken apps that would like to provide a 9P "control/status filesystem" in the manner of wmii et al, I started to write a simplified high-level virtual filesystem server library on top of the core server implementation. At the point where I made this status update to my friends in the Chicken Scheme IRC channel, directory listings weren't working (they now are), but you can see the idea - create a filesystem object from Scheme and register files and directories in it, and it appears as a live filesystem under UNIX.
Now I'm feeling a bit better today I've realised several other rookie errors I've made (not ones that cause bugs, I hope, but ones that complicated the code unnecessarily) - I'll fix those up before I submit all of my changes to the 9p egg's maintainer for merging in...
Then it'll be time to start on the Ugarit integration. THAT will be fun 🙂
Tue 24th Apr 2012 9:38 am 
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