Understanding the Linux Kernel, 3rd Edition

Chapter 18. The Ext2 and Ext3 Filesystems

In this chapter, we finish our extensive discussion of I/O and filesystems by taking a look at the details the kernel has to take care of when interacting with a specific filesystem. Because the Second Extended Filesystem (Ext2) is native to Linux and is used on virtually every Linux system, it is a natural choice for this discussion. Furthermore, Ext2 illustrates a lot of good practices in its support for modern filesystem features with fast performance. To be sure, other filesystems supported by Linux include many interesting features, but we have no room to examine all of them.

After introducing Ext2 in the section "General Characteristics of Ext2,” we describe the data structures needed, just as in other chapters. Because we are looking at a specific way to store data on disk, we have to consider two versions of the same data structures. The section "Ext2 Disk Data Structures" shows the data structures stored by Ext2 on disk, while “Ext2 Memory Data Structures” shows the corresponding versions in memory.

Then we get to the operations performed on the filesystem. In the section "Creating the Ext2 Filesystem,” we discuss how Ext2 is created in a disk partition. The next sections describe the kernel activities performed whenever the disk is used. Most of these are relatively low-level activities dealing with the allocation of disk space to inodes and data blocks.

In the last section, we give a short description of the Ext3 filesystem, which ...