The Virtual File System in the last chapter depends on lower-level functions to carry out each read, write, or other operation in a manner suited to each device. The previous chapter included a brief discussion of how operations are handled by different filesystems. In this chapter, we'll look at how the kernel invokes the operations on actual devices.
In Section 13.1 we give a brief survey of the Intel 80x86 I/O architecture. In Section 13.2 we show how the VFS associates a "device file" with each different hardware device so that application programs can use all kinds of devices in the same way. Most of the chapter focuses on the two types of drivers, character and block.
The aim of this chapter is to illustrate the overall organization of device drivers in Linux. Readers interested in developing device drivers on their own may want to refer to Alessandro Rubini's Linux Device Drivers book from O'Reilly.