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LDD3 study note 0

This document shares a development environment to debug kernel using qemu.

0. How to learn Linux kernel

You maybe have many ways to learn Linux kernel, but I think the only way to learn

Linux kernel is keeping thinking and keeping writing codes. There are so many modules in kernel, maybe at first we do not know how to start, what to write. I think at first what to write is not important, the important thing is to understand basic kernel knowledge, as now everyday we will see so many open source codes, the only unchangeable or more stable thing is basic knowledge of kernel related. Let’s start up from the basic things

Here I suggest to use LDD3 to learn these basic knowledge. We will try to rewrite

the modules in this book to get a new understanding about Linux kernel.

1. Environment setting

Normally it is very hard to debug kernel, so here I suggest you to learn and

debug kernel using virtual machine, qemu is a good tool to help us to do this work.

In my previous blogs, this was one which tell us how to using qemu to debug

kernel in my way.

http://blog.csdn.net/scarecrow_byr/article/details/40707323

However, the file system in that blog is not a very good one

as there are some useful tools it did not have,

Now I got a new root file system, which includes the basic user space tools to

debug kernel. You can download it here:

https://github.com/wangzhou/kernel_debug_using_qemu.git

Above repo also includes a script to run qemu in command line. I just use the

root file system as a memory file system. So if you write something when the system is booting up, what you wrote will be lost when you shutdown your qemu.

There is another script called put_file_in_mini.sh. When you wrote a kernel

module and compiled it to a ko, you can use the script to put the ko to the root file system. The work flow of this script is very simple, it just extracts the compressed file system, put the file(e.g. your ko) to file system, and at last compress the file system back.

In fact, there is other ways to get a root file system for your debug environment,

for example, you can use a nfs as a root file system. In nfs way: 1. you need configure your networking for host and guest to let qemu be able to access one directory in you host, which includes the file system; 2. you need configure qemu to use nfs to get root file system. If having time, we can try this way later.