Basic Linux kernel

Linux Kernel
Morteza Noorelahi Alamdari(Ipo)


Linux kernel history

Structure

What we need

Configuring / Building / Installing / Upgrading

Customizing

History:
Linux is a clone of the operating system Unix, written from scratch by Linus Torvalds
with assistance from a loosely-knit team of hackers across the Net. It aims towards
POSIX and Single UNIX Specification compliance.
License : GNU General Public License
Although originally developed first for 32-bit x86-based PCs (386 or higher), today
Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and UltraSPARC,
Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell, IBM S/390,
MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS, Xtensa, Tilera
TILE, AVR32 and Renesas M32R architectures.

What we need:
GCC is a C compiler
Make is a tools that walks the kernel source tree to determine which files need to be compiled.
Binutils is linking and assembling of source files.
Git is version controller [optional]

Getting Kernel source code :

$ wget http://www.kernel.org/pub/linux/kernel/v3.0/linux-3.6.6.tar.bz2

Or :

$ curl http://www.kernel.org/pub/linux/kernel/v3.0/linux-3.6.6.tar.bz2 -o linux-3.6.6.tar.bz2

Then :
$ tar -xjzf linux-3.6.6.tar.bz2
$ cd linux-3.6.6

What is Git?
Git is a free and open source distributed version control system designed to handle
everything from small to very large projects with speed and efficiency.

Redhat:
# yum install git
Debian:
# apt-get install git
OpenSuse:
# zypper install git
Arch:
# pacman -S git

Simple example about Git:
You can get clone projects via this command:
$ git clone https://github.com/torvalds/linux.git

Redirect to linux directory:
$ cd linux

For showing list of logs:
$ git log

For showing list of versions:
$ git tags

For getting last update from the git server:
$ git pull

Simple example about Git:
For pushing changed parts to the git server:
$ git push

For showing status of project:
$ git status

For configing git :
$ git config [--global] user.name “your name”
$ git config [--global] user.email “your email”

Configuring:
For showing help:
$ make help

We have several ways for configuring kernel:
1- For configuring step by step:
$ make config
2- For configuring with default config:
$ make defconfig
3- For configuring in graphical mode:
$ make menuconfig/gconfig/xconfig
4- see `make help` ...

For removing all generated files + config + various backup files:
$ make mrproper

Building:
For building kernel:
$ make

Advanced building options:
$ make -j4
$ make -j8
$ make -j

For getting iso file:
$ make isoimage

For making deb package:
$ make deb-pkg
For making rpm package:
$ make rpm-pkg
For making targz file:
$ make targz-pkg

Installing:
For install any modules that we want:
# make module_install

Then for installing kernel in your system:
# make install

Updating:
For updating this version we need to get patch files from the official site:
$ wget http://kernel.org/patches/patch-3.6.6.7.10.bz

Redirect to the directory of kernel source:
$ cd linux-3.6.6

And for adding patch in the kernel:
$ bzip2 -dv patch-3.6.6.7.10.bz | patch -p1

Or:

$ bzip2 -dv patch-3.6.6.7.10.bz
$ cd linux-3.6.6
$ patch -p1 < ../patch-3.6.6.7.10

Config file:
Sometimes you want to use other distributions config file, Like ubuntu.
You can find config file of ubuntu via live cd!

$ cp /proc/config.gz .
$ gzip -dv config.gz
$ cp config linux-3.6.6/.config

And then you can run `make` command.

Customizing:
Determining the driver:
Example network driver:
ls /sys/class/net

$ basename $(readlink /sys/class/net/eth0/device/driver/module)
$ r8169 << output
$ cd linux-3.6.6
$ fine . -type f -a -name Makefile | grep -i r8169
$ ./drivers/net/ethernet/realtek/Makefile:obj-$(CONFIG_R8169) += r8169.o
$ make menuconfig
=> press /
=> type module name: r8169

Now you can enable this module in the kernel.

Determining the correct module from scratch:
PCI devices:
# lspci | grep -i ethernet
# 13:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B
PCI Express Gigabit Ethernet controller (rev 06)
$ cd /sys/bus/pci/devices/
$ ls
$
0000:00:00.0 0000:00:1a.0 0000:00:1c.1 0000:00:1d.0 0000:00:1f.2 0000:12:00.0 0000:ff:00.1
0000:ff:02.2 0000:00:02.0 0000:00:1b.0 0000:00:1c.2 0000:00:1e.0 0000:00:1f.3 0000:13:00.0
0000:ff:02.0 0000:ff:02.3 0000:00:16.0 0000:00:1c.0 0000:00:1c.4 0000:00:1f.0 0000:00:1f.6
0000:ff:00.0 0000:ff:02.1
$ cd cd 0000:13:00.0/
$ cat vendor
$ 0x10ec << output
$ cat device
$ 0x8168 << output
$ cd linux-3.6.6
$ grep -i 0x10ec include/linux/pci_ids.h
$ #define PCI_VENDOR_ID_REALTEK 0x10ec

$ grep -R1 PCI_VENDOR_ID_REALTEK * | less
/0x8168 << search device
Result:
--
drivers/net/ethernet/realtek/r8169.c-static DEFINE_PCI_DEVICE_TABLE(rtl8169_pci_tbl) = {
drivers/net/ethernet/realtek/r8169.c: { PCI_DEVICE(PCI_VENDOR_ID_REALTEK, 0x8129), 0, 0, RTL_CFG_0 },
drivers/net/ethernet/realtek/r8169.c- { PCI_DEVICE(PCI_VENDOR_ID_DLINK, 0x4300), 0, 0, RTL_CFG_0 },
--

All PCI drivers contain a list of different devices that ther support.
Vendor id matches with device.

Summery:
Here are steps needed in order to find which pci driver can control a specific PCI device:

1.Find the PCI bus ID of the device for which you want to find the driver , using lspci.
2.Go into the /sys/bus/pci/devices/0000:bus_id directory , where bus_id is the PCI bus ID
found in the previous step.
3.Read the values of the vendor and device file in the PCI device directory.
4.Move back the kernel source tree and look in include/linux/pci_ids.h for the PCI vendor and
device IDs found in the previous step.
5.Search the kernel source tree for references to those values in drivers . Both the vendor
and device ID should be in a struct pci_device_id definition.
6.Search the kernel Makefile for the CONFIG_ rule that builds this driver by using find and
grep: $ find . -type f -a -name Makefile | xargs grep DRIVER_NAME
7.Search in the kernel configuration system for that configuration value and go to the location
in the menu that it specifies to enable that driver to be built.

References:
Oreilly : Linux Kernel in the nutshell
http://www.wikipedia.org/
https://github.com/torvalds/linux
http://kernel.org/

Basic Linux kernel

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Basic Linux kernel