Chapter 15

Drivers for Character Devices

A character device does not have physically addressable storage media, such as tape drives or serial ports, where I/O is normally performed in a byte stream. This chapter describes the structure of a character device driver, focusing in particular on entry points for character drivers. In addition, this chapter describes the use of physio(9F) and aphysio(9F) in the context of synchronous and asynchronous I/O transfers.

This chapter provides information on the following subjects:

• Overview of the Character Driver Structure

• Character Device Autoconfiguration

• Device Access (Character Drivers)

• I/O Request Handling

• Mapping Device Memory

• Multiplexing I/O on File Descriptors

• Miscellaneous I/O Control

• 32-bit and 64-bit Data Structure Macros