This article will focus on how to contribute to the Linux kernel contribution workflow. The Linux kernel is a free and open-source software project that anyone can contribute. Workflow, which contributes to the Linux kernel, is unlike any other open-source project. You can not contribute code using GitHub or GitLab. Submit kernel patches via Git and Email using the Linux Kernel Mailing List (LKML) on the Linux kernel. Kernel Maintainers will review via email and merge the code to Linux kernel source tree after discuss.
In short, make a list
- Setup Email Client
- Make Fixes
- Build Kernel Code
- Git diff
- Git commit
- Git show
- Git format-patch
- Check Kernel Patch
- Get Kernel Maintainers
- Git send-mail
There will be Below is a step-by-step guide for each.
Setup Email Client
Firstly you need to set up the Email Client in gitconfig.
Set up an Email Client to use ~/.gitconfig using a Text Editor.
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zawzaw@ubuntu-linux:~$ vim ~/.gitconfig
For example: Gmail
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[user]
name = Your Name
email = youremailaddr@mail.com
# Setup Eamil Client for using git send-mail.
[sendemail]
smtpuser = youremailaddr@mail.com
smptpass = yourpassword
smtpserver = smtp.googlemail.com
smtpencryption = tls
smtpserverport = 587
[core]
editor = vim
[color]
ui = auto
Make Fixes
You can get the source code Linux kernel main source tree via https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git. It’s hard to say what to fix and what parts to fix and contribute. Like any other software project, you learn something. If you are interested in kernel hacking, you can learn more at Linux Kernel Newbies. It depends on your interests. Initially, you do not have to follow the entire subsystem of the entire Linux kernel. Linux kernel subsystems are categorized as File Systems: /linux/fs, Kernel Device Drivers / Modules:/linux/drivers, Networking: /linux/net, Kernel Security (eg SELinux, Kernel lockdown and etc .. There are many kernel subsystems, such as /linux/security. You should specialize in something from the beginning. Writing kernel device drivers / modules for embedded hardware devices is more popular in the real Embedded Linux World than any other kernel subsystem.
About Linux Kernel Device Drivers: There is a book I would recommend. Linux Device Drivers, Third Edition is a great book to learn about Linux Kernel Device Drivers. The O’Reilly Open Books Project is now available as a free book under the Creative Commons Attribution-ShareAlike 2.0 license.
O’Reilly Open Book: Linux Device Drivers Book, Third Edition.
LWN.net: Linux Device Drivers Book, Third Edition.
Book Cover Photo by: O’Reilly Open Books Project
In this blog post, I will give an example of a build error that was fixed when building Linux kernel with LLVM / Clang Compiler version 9.
Create a new dev/zawzaw branch from the original master branch locally.
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git branch dev/zawzaw
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git checkout dev/zawzaw
Fixed kernel build error in LLVM / Clang compiler version 9: linux/arch/x86/include/asm/bitops.h
Build Kernel Code
This is the part that compiles and tests whether it exists or not.
Go to the Kernel source tree and configure the kernel and compile it. I use Clang/LLVM, so I added CC=clang to compile kernel. I wrote Compiling Linux Kernel with Clang/LLVM article on how to build Linux Kernel with Clang/LLVM toolchain.
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make CC=clang defconfig
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make CC=clang -j$(nproc --all)
Git diff
Let’s do git diff and look at the changes first.
Git commit
You need to write meaningful commit message.
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git commit -a
Git show
You can view the commit messages and changes you made with git show
Git format-patch
Here you will generate a patch for the fixes you made. The next step is to submit the generated kernel patches via email.
Let’s look at your local branch first with git branch.
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zawzaw@ubuntu-linux:~/Linux-kernel/linux$ git branch
* dev/zawzaw
master
Generate a patch.
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git format-patch master..dev/zawzaw
If you open the generated patch file with a text editor, you will see something like this: In other words, it will be sent git send-mail.
Check Kernel Patch
The Linux kernel source tree has many useful tools and scripts. What are the errors before submitting your Kernel Patch via Email? You can check what Warnings are with checkpatch.pl.
You need to run checkpatch.pl in the Linux kernel source tree.
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./scripts/checkpatch.pl 0001-arch-x86-asm-Fix-arch-x86-kernel-build-error-in-clan.patch
Get Kernel Maintainers
You do not have to worry about which kernel patch to send the kernel patch to. Before you submit your patch via email, you can see which maintainer it will send to with ‘get_maintainer.pl’. Each Linux kernel subsystem has its own maintainers. Before sending the patch, you need to know which maintainer to send your patch to.
You need to run get_maintainer.pl in the Linux kernel tree.
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./scripts/get_maintainer.pl 0001-arch-x86-asm-Fix-arch-x86-kernel-build-error-in-clan.patch
Git send-mail
After completing the above steps, the patch will be sent to the relevant maintainers with git send-mail.
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git send-mail --to mingo@redhat.com --cc hpa@zytor.com --cc jesse.brandeburg@intel.com --cc linux-kernel@vger.kernel.org --cc clang-built-linux@googlegroups.com 0001-arch-x86-asm-Fix-arch-x86-kernel-build-error-in-clan.patch
When sending a kernel patch with git send-mail, --to must be the main maintainer of the kernel subsystem to which you want to send it. --cc should be Reviewers and Open Public Mailing Lists. An Open List is a mailing list for each kernel subsystem.
For example : linux-kernel@vger.kernel.org is the main Linux Kernel Mailing List (LKML). clang-built-linux @ googlegroups.com is a mailing list for submission of builds using the Clang compiler for the Linux kernel. Email addresses of all mailing lists can be accessed at http://vger.kernel.org/vger-lists.html. You can then subscribe to the mailing list of your favorite kernel subsystems with the email you want to use.
The generated kernel patch will be sent to kernel maintainers via git send-mail. Eamil will then review your patch. Email Feedback software can be used to communicate with Kernel Maintainers and CCed Reviewers for feedback. You can also use [Mutt] (http://www.mutt.org/) for Email Client Software or see Email Clients for Linux. When all is said and done, the Kernel Maintainers will review your patch via email and approve it. That way you can contribute to the Linux kernel.