Custom Kernel: Implement filesystem

Question

As a out of course project, I am currently developing a kernel in an attempt to better understand all the aspects of an actual OS. So far, I am done setting up a flat physical memory model with support for paging and the basic interrupts (keyboard and perhaps trackpad/mouse next). I thought the step forward would be to implement a filesystem and I am keen about the ext2. I have looked around, even on SO but there isn't anything explicit that answers my questions:

1. Is it possible to write a driver to access an ext2 filesystem in C or do I need to go lower?
2. If I plan to access the filesystem off a USB device, I am assuming I will need to get the device driver for USB running first. Any help on this would be greatly appreciated.
3. I know the code for detecting a filesystem is already available on the MINIX and other kernels but what I really want to know is if I want to build a custom albeit simple filesystem, how do I go about it? I am considering this possibility too.

My apologies if the question and details sound a little ignorant but I am still in the learning process.

Thanks :)

Answer 1

I'll try to give you a few tips/hints - a clear answer isn't that simple:

1. An ext2 filesystem written in C is just C. C is just a programming language - you can use C++, plain assembly or a few others (A few os'dever use D) - but not a "managed" language etc. But it is important that you have a rock solid understanding of this language. In my opinion assembly is a MUST (Take a look at the scheduler in an operating system -> plain assembly)

2. Do you really want to write an USB driver ? It isn't "just" a simple USB driver (Layer of abstractions). Why a USB driver and not a floppy disk or CD driver (Believe me - a floppy driver in 32 bit protected mode isn't that hard) ?

3. Please focus on your project. Of course Linux (Early versions) and Minix have example code, but take care of the design structure (Monolithic/Microkernel or hybrid-kernel) - and don't mix it, write your own code.

Please make on step after the other. You wrote a basic IRQ handling and the plan is to write a keyboard/mouse driver - write the keyboard driver ! Don't dream about loading and executing files (Rom wasn't built in one day).

You have to read documentations, for example the Intel manuals or other "books". A very popular forum is osdev.org - take a look at the wiki. As twalberg said, it's a very huge module - stay focused on the main parts of your operating system.

I know, this is not the answer to your question - but it's important not to go in the wrong direction and dream of a fancy UI or something like this ;)

osdev.org forum
osdev.org wiki
Intel manuals

And a few other books in my book shelf can you find here (Tanenbaum, Silberschatz with Peter Galvin - great books!):

Books