22 Feb
2021
22 Feb
'21
10:41 p.m.
Lately, I've been playing around in v6 unix and mini-unix with a goal of
better understanding how things work and maybe doing a little hacking.
As my fooling around progressed, it became clear that moving files into
and out of the v6 unix world was a bit tedious. So it occurred to me
that having a way to mount a v6 filesystem under linux or another modern
unix would be kind of ideal. At the same time it also occurred to me
that writing such a tool would be a great way to sink my teeth into the
details of old Unix code.
I am aware of Amit Singh's ancientfs tool for osxfuse, which implements
a user-space v6 filesystem (among other things) for MacOS. However,
being read-only, it's not particularly useful for my problem. So I set
out to create my own FUSE-based filesystem capable of both reading and
writing v6 disk images. The result is a project I call retro-fuse,
which is now up on github for anyone to enjoy
(https://github.com/jaylogue/retro-fuse).
A novel (or perhaps just peculiar) feature of retro-fuse is that, rather
than being a wholesale re-implementation of the v6 filesystem, it
incorporates the actual v6 kernel code itself, "lightly" modernized to
work with current compilers, and reconfigured to run as a Unix process.
Most of file-handling code of the kernel is there, down to a trivial
block device driver that reflects I/O into the host OS. There's also a
filesystem initialization feature that incorporates code from the
original mkfs tool.
Currently, retro-fuse only works on linux. But once I get access to my
mac again in a couple weeks, I'll port it to MacOS as well. I also hope
to expand it to support other filesystems as well, such as v7 or the
early BSDs, but we'll see when that happens.
As I expected, this was a fun and very educational project to work on.
It forced me to really understand what was going in the kernel (and to
really pay attention to what Lions was saying). It also gave me a
little view into what it was like to work on Unix back in the day.
Hopefully someone else will find my little self-education project useful
as well.
--Jay