1. Preface

This document attempts to present an overview of the internal structure of the ext2 filesystem. It was written in summer 95, while I was working on the ext2 filesystem editor project (EXT2ED).

In the process of constructing EXT2ED, I acquired knowledge of the various design aspects of the the ext2 filesystem. This document is a result of an effort to document this knowledge.

This is only the initial version of this document. It is obviously neither error-prone nor complete, but at least it provides a starting point.

In the process of learning the subject, I have used the following sources / tools:

• Experimenting with EXT2ED, as it was developed.
• The ext2 kernel sources:
  • The main ext2 include file, /usr/include/linux/ext2_fs.h
  • The contents of the directory /usr/src/linux/fs/ext2.
  • The VFS layer sources (only a bit).
• The slides: The Second Extended File System, Current State, Future Development, by Remy Card.
• The slides: Optimisation in File Systems, by Stephen Tweedie.
• The various ext2 utilities.