All problems in computer science can be solved by another level of indirection,” is a famous quote attributed to Butler Lampson, the scientist who in 1972 envisioned the modern personal computer. The quote rings in my head on various occasions: when I am forced to talk to a secretary instead of the person I wish to communicate with, when I first travel east to Frankfurt in order to finally fly west to Shanghai or Bangalore, and—yes—when I examine a complex system’s source code.
Let’s start this particular journey by considering the problem of a
typical operating system that supports disparate filesystem formats. An
operating system may use data residing on its native filesystem, a CD-ROM, or a USB stick. These storage devices may, in turn, employ
different filesystem organizations: NTFS or ext3fs for a
Windows or Linux native filesystem, ISO-9660 for the CD-ROM, and, often, the
legacy FAT-32 filesystem for the USB stick. Each filesystem uses
different data structures for managing free space, for storing file
metadata, and for organizing files into directories. Therefore, each
filesystem requires different code for each operation on a file (
open, read, write, seek, close, delete, and so
I grew up in an era where different computers more often than not had incompatible filesystems, forcing me to transfer data from one machine to another over serial links. Therefore, the ability to read on my PC a flash ...