The Implementation of the ULIX Literate Operating System








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A diary documenting the implementation of ULIX-i386

Welcome to the ULIX blog.

Ulix (Literate Unix) is a Unix-like operating system developed at University of Erlangen-Nürnberg. I use D. E. Knuth's concept of Literate Programming for the implementation and documentation. The goal was a fully working system which can be used in operating system courses to show students how OS concepts (such as paging and scheduling) can be implemented. Literate programs are very accessible because they can be read like a book; the order of presentation is not enforced by program logic or compiler restrictions, but instead is guided by the implementer's creative process.

Ulix is written in C and assembler for the Intel architecture. The literate programming part is handled by noweb.

On this page I document my progress with the implementation.

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Having Fun with Minix (13.07.2013)

As I wrote in the last entry, I have implemented (parts of) the Minix filesystem. I used that one because Linux machines can create and mount Minix filesystem images. However, I use a Mac for development, and on those machines it is harder to access Minix volumes. The MacFUSE-based "minixfs" command can mount a Minix image, but only read-only, and I have not found software that can mount them writeable on the Mac.

So I created a small VirtualBox VM with Debian inside, shared the Mac's filesystem with the VM and created shell scripts which mount the Minix image and modify it. I had to learn that this approach doesn't work when the image resides on the vboxsf shared folder: Files kept disappearing from the image.

The solution was to first physically copy the image into the VM, mount it, make the changes, unmount it, and copy it back to the Mac. It works now :)

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v0.08: Floppies, Minix Filesystem (13.07.2013)

Ulix reads and writes floppy disks (via the FDC controller), it can handle parallel accesses from several processes (using a mutex to synchronize things). There's a basic implentation of the Minix (v2) filesystem: Via standard system calls, processes can open, read, write, lseek files, and single indirection for block numbers is possible. No double indirection, and currently no sub-directories. (The Minix code replaces the older simplefs filesystem which was a very basic FAT-type system.)

Next: Implementation of signals. There's already a kill() function and the corresponding system call, but the scheduler needs modification (for jumping into signal handlers when signals are found).

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