Linux Kernel Development
Part 1
by:
Sameer Rahmani
Chapter 1
Basics
Overview
- What is Linux Kernel ?
- Why I need to learn about Kernel ?
- Linux Kernel development process
- Basic Linux Kernel internals
What is kernel anyway?
Kernel is responsible for communication
with hardware
Kernel Provides a unique interface for
software to use hardware
Kernel is responsible to handle network
communications
Kernel schedules processes to use CPU time
Kernel shares resources between processes
Very Basic Schema of an operating system
Why software need
kernel?
- Without a kernel each software has to implement its own interface to use hardware
- With lots of interfaces around, there will be huge number of software bugs around.
- There is no warranty for performance of each interface.
Why do i need to know about
Kernel?
- You can improve your system performance
- You can install some device drivers by yourself *
- It's good to know about your Linux box
- If you are a developer or want to be one you have to know how your operating system operates.
Why Linux Kernel ?
- It's totally free ( under GPL v2)
- Monolithic with support for loadable modules
- True multi-tasking
- Support for hardware and filesystem
- Multi-arch
- Robust community
- People watching, So no backdoor
- Configurable
- ........
that's Enough, let's begin
First Step
Build a custom kernel
Requirements for build
1. Linux kernel source code. Get it from www.kernel.org
$ wget https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.x.y.tar.xz 2. A bootloader. You definitely have one already.
3.ncurses library and build tools (on a debian box)
# apt install libncurses5 build-essential Lets Do it
Extract the source code.
$ tar Jxvf linux-3.x.y.tar.xz Create a build directoy
$ mkdir build Configure the kernel ( It's the hard part )
$ cd linux-3.x.y && make O=../build menuconfig build the kernel
$ make O=../build -j 4 Installation
Install new kernel image
# make O=../build modules_install install update your bootloader configuration to load new image.
# update-grub2 * In case of a grub2 bootloader on a debian compatible boxes
Reboot & Enjoy new kernel
Initial Ram disk
Installer script probably created it for you.
Manual creation of initrd:
# cd /boot/ && mkinitramfs -v -o ./initrd-3.x.y 3.x.y
Understanding
Start up Process
BIOS -> Bootloader -> Kernel
Bios
BIOS performs hardware-platform specific
startup tasks
BIOS loads and executes the partition boot code
from the designated boot device
(Phase 1 of a Linux bootloader)
Bootloader
Phase 1 loads phase 2 (the bulk of the boot loader code).
Some bootloaders use a phase called "Phase 1.5"
Without is some modern disks may not be
fully available.
Decompress OS into memory and load it.
Prepare hardware and memory before calling
'start_kernel()'
Kernel
'start_kernel()' perform OS setup
( Interrupts, Memory management, Drivers, etc )
Kernel spawns idle process, scheduler and systemd
systemd sets up and load the user space world
Wait until next chapter To learn about startup process in nutshell
End of Chapter 1
References:
-
https://www.kernel.org/doc/
- Linux Kernel Development (3rd Edition) ISBN: 978-0672329463
-
Linux kernel documentation (documents directory in source tree)
Contact me
Website : www.lxsameer.com
IRC: irc://irc.freenode.net/#5hit
Email: lxsameer@gnu.org
twitter: @lxsameer
Linux Kernel Development
By Sameer Rahmani
