kernel-hacking.pdf

Unreliable Guide To Hacking The Linux

Kernel

Paul Rusty Russell

rusty@linuxcare.com

Unreliable Guide To Hacking The Linux Kernel

by Paul Rusty Russell

This documentation is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc.,

59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

For more details see the ﬁle COPYING in the source distribution of Linux.

Table of Contents

1. Introduction............................................................................................................................................5

2. The Players .............................................................................................................................................6

User Context.......................................................................................................................................6

Hardware Interrupts (Hard IRQs) ......................................................................................................6

Software Interrupt Context: Bottom Halves, Tasklets, softirqs..........................................................7

3. Some Basic Rules ...................................................................................................................................9

4. ioctls: Not writing a new system call ..................................................................................................10

5. Recipes for Deadlock ...........................................................................................................................11

6. Common Routines ...............................................................................................................................12

printk() include/linux/kernel.h ........................................................................................12

copy_[to/from]_user() / get_user() / put_user() include/asm/uaccess.h .............12

kmalloc() / kfree() include/linux/slab.h ..........................................................................13

current include/asm/current.h ............................................................................................14

local_irq_save() / local_irq_restore() include/asm/system.h .................................14

local_bh_disable() / local_bh_enable() include/asm/softirq.h ...............................14

smp_processor_id ()/ cpu_[number/logical]_map() include/asm/smp.h .....................14

__init/__exit/__initdata include/linux/init.h ........................................................................14

__initcall() / module_init() include/linux/init.h ......................................................15

module_exit() include/linux/init.h .................................................................................15

MOD_INC_USE_COUNT / MOD_DEC_USE_COUNT include/linux/module.h ...............................15

7. Wait Queues include/linux/wait.h .............................................................................................17

Declaring ..........................................................................................................................................17

Queuing ............................................................................................................................................17

Waking Up Queued Tasks ................................................................................................................17

8. Atomic Operations...............................................................................................................................18

9. Symbols .................................................................................................................................................19

EXPORT_SYMBOL() include/linux/module.h .........................................................................19

EXPORT_SYMTAB ..............................................................................................................................19

10. Routines and Conventions.................................................................................................................20

Double-linked lists include/linux/list.h ...............................................................................20

Return Conventions ..........................................................................................................................20

Breaking Compilation ......................................................................................................................20

Initializing structure members .........................................................................................................20

GNU Extensions ..............................................................................................................................21

C++...................................................................................................................................................21

#if .....................................................................................................................................................21

11. Putting Your Stuff in the Kernel ......................................................................................................23

12. Kernel Cantrips..................................................................................................................................24

13. Thanks ................................................................................................................................................26

Chapter 1. Introduction

Welcome, gentle reader, to Rusty’s Unreliable Guide to Linux Kernel Hacking. This document describes

the common routines and general requirements for kernel code: its goal is to serve as a primer for Linux

kernel development for experienced C programmers. I avoid implementation details: that’s what the code

is for, and I ignore whole tracts of useful routines.

Before you read this, please understand that I never wanted to write this document, being grossly

under-qualiﬁed, but I always wanted to read it, and this was the only way. I hope it will grow into a

compendium of best practice, common starting points and random information.

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