Device drivers provide an interface between operating systems and hardware devices. They are split into character, block, and network modules. Character drivers handle streams of bytes like files and implement open, close, read, and write functions. Block drivers are similar but differ in how the kernel manages data internally. Network drivers send and receive data supervised by the device subsystem. Device drivers provide mechanisms and not policies, and security is enforced by kernel code to avoid encoding policies directly into drivers. Loadable modules can add functionality while the system is running.

1. Linux Device Driver
Chapter 1
Anupam Datta

2. Advised Reading
LDD3 Chapter 1 : https://static.lwn.net/images/pdf/LDD3/ch01.pdf

3. Role
Device driver provides mechanism, not policy.
Splitting kernel :
● Process management
● Memory management
● Filesystem
● Device control
● Networking
Loadable module - add functionality while system running.

4. Class of device and module
Character, block & network module
➔ Character - stream of bytes like file. Implements open, close, read, write.
Example : /dev/console, /dev/ttyS0. Sequential access by filesystem node, no
back forth unlike regular file.
➔ Block - Almost like char but differs how kernel manages data internally
➔ Network - Send-receive supervised by device subsystem.

5. Security
Security enforced by kernel code
Avoid encoding security policy in code. Exception - If affects global resource such
as hardware, ie. setting interrupt line.
Module loading can be disabled in kernel.
Even numbered kernels are stable.