The three main authors and designers of ext2fs have written
an excellent paper on it, and have contributed it to the KHG.
This paper was first published in the Proceedings of the First
Dutch International Symposium on Linux, ISBN 90-367-0385-9.
It may be a long time before I get around to writing a tutorial
on how to write a Linux filesystem; after all, I've never done it.
Would someone else like to help?