The linux kernel is very big, and hard to understand. Even if we are looking at just one component, the component can still be very complex. What's more, the component is not stand-alone, and we usually can't find how it works without finding its connections with other components. But thanks to the git version control tool used by the linux kernel, we can trace the history of how a component was added into the kernel, and changed gradually. Even a big component is developed from a very simple version, and code is added piece by piece. What's more, each commit of code usually has one central idea from the author. So it should be much easier to understand the first simple version, and catch each following code commits.
I just tried this method. Firstly, I download the linux kernel using `git clone` command. Then, I make a little change of a core file in the component I want to understand. The change can make me easier to trace down the first code commit. Then, use gitk to find the first commit. In the gitk GUI interface, you can see what is changed in a commit, by right click on a line that is changed, I can jump to the commit this line is added. By continuously jumping like this, I can finally arrive to the first commit of this component, or the first commit of the linux kernel when it starts using gitk. Whatever, the earliest commit you can find should be much easier to understand. Of course, if you can understand the component in the current linux kernel version, that's great, and you don't need to find how it arrives here. But if you are not smart enough, and have a great pain trying to understand something in the linux kernel like me, this article should provide a simpler way to climb the linux kernel code mountain!
