# Introduction

Devices in POSIX Systems are files in /dev directory. As with any files
in POSIX, they may be opened, closed, read from, written to, seeked,
ioctl'd, and others.

Examples of device files:

* /dev/sda - A SCSI block device
* /dev/ttyS0 - A Serial terminal device

# POSIX I/O calls

POSIX systems have some standard calls for I/O. Since devices are files,
these same system calls are used to work with devices. We are gonna work
with the following calls:

* open
* read
* write
* close
* lseek
* ioctl

# Device types and numbers

Linux devices may be of different types, including character devices,
block devices or network devices. Both character and block devices have
identifying numbers, a major and a minor number.

# Character devices allocation

In Linux, major and minor numbers have to be requested or allocated. The
calls to do that for character devices are:


* int register\\_chrdev\\_region (dev\\_t first, unsigned int count, char
*name);
* int alloc\\_chrdev\\_region (dev\\_t *dev, unsigned int firstminor,
unsigned int count, char *name);
* void unregister\\_chrdev\\_region (dev\\_t dev, unsigned int count);