14.1. Device Special Files (Devices)

This chapter frequently mentions disk devices, so we start with a brief overview of the concept of a device file.

A device special file corresponds to a device on the system. Within the kernel, each device type has a corresponding device driver, which handles all I/O requests for the device. A device driver is a unit of kernel code that implements a set of operations that (normally) correspond to input and output actions on an associated piece of hardware. The API provided by device drivers is fixed, and includes operations corresponding to the system calls open(), close(), read(), write(), mmap(), and ioctl(). The fact that each device driver provides a consistent interface, hiding the differences in operation of individual devices, allows for universality of I/O (Section 4.2).