90 lines
3.4 KiB
Markdown
90 lines
3.4 KiB
Markdown
---
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layout: post
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title: "My first contribution to Linux Kernel: Step by step"
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date: 2021-11-06 00:00:00
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permalink: first-linux-contribution/
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categories: programming
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author: Mahdi
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published: false
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---
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November 6th:
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Create a virtual machine for Archlinux on my macOS using QEMU:
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- [Download the Archlinux iso image](https://archlinux.org/download/)
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- Create a qemu disk:
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{% highlight bash %}
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qemu-img create disk.img 15G
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{% endhighlight %}
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- Start the machine and [install Archlinux](https://wiki.archlinux.org/title/Installation_guide)
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{% highlight bash %}
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qemu-system-x86_64 -cdrom archlinux-2021.11.01-x86_64.iso -boot order=d -drive format=raw,file=disk.img -m 8G
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{% endhighlight %}
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- Start the machine after installing (note I forward 2222 to 22 so I can SSH/SCP to the virtual machine. I also set 4 CPUs so I can use threads for faster builds in the VM)
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{% highlight bash %}
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qemu-system-x86_64 -boot -drive format=raw,file=disk.img -m 8G -smp cpus=4 -net user,hostfwd=tcp::2222-:22 -net nic
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{% endhighlight %}
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- Install dependencies:
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{% highlight bash %}
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pacman -S gcc git make
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{% endhighlight %}
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- Clone linux:
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{% highlight bash %}
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git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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{% endhighlight %}
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- Install necessary dependencies
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{% highlight bash %}
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pacman -S flex base-devel xmlto kmod inetutils bc libelf git cpio perl tar xz
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{% endhighlight %}
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- Copy configuration of archlinux (optional: also [use modprobed-db to remove unnecessary modules](https://wiki.archlinux.org/title/Kernel/Traditional_compilation#Default_Arch_configuration))
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{% highlight bash %}
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zcat /proc/config.gz > .config
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{% endhighlight %}
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- Make! The `-j8` parameter specifies the number of threads to be used by the build. My CPU has 8 threads and so I use it all.
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{% highlight bash %}
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make -j8
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{% endhighlight %}
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- Install the newly built Kernel. I create this as a script file and run it after every build from the root of repository.
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{% highlight bash %}
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make -j8 modules_install
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RELEASE=$(cat include/config/kernel.release)
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cp -v arch/x86_64/boot/bzImage /boot/vmlinuz-linux${RELEASE}
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mkinitcpio -k $RELEASE -g /boot/initramfs-linux${RELEASE}.img
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mkinitcpio -k $RELEASE -s autodetect -g /boot/initramfs-linux-fallback${RELEASE}.img
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{% endhighlight %}
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- Run grub-mkconfig to add a menu option for this new kernel
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{% highlight bash %}
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grub-mkconfig -o /boot/grub/grub.cfg
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{% endhighlight %}
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- Reboot and choose the new kernel (might be under "Advanced" in the bootloader)
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- Setup your environment for development. Mine consists of setting up tmux so I can have multiple terminals and neovim.
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{% highlight bash %}
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pacman -S neovim openssh tmux
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echo '[[ -z "$TMUX" ]] && exec tmux' >> /etc/profile
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# also follow https://github.com/junegunn/vim-plug for Neovim
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{% endhighlight %}
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And in the host:
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{% highlight bash %}
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scp -P 2222 ~/.tmux.conf root@localhost:/root
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scp -r -P 2222 ~/.config/nvim root@localhost:/root/.config/
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{% endhighlight %}
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# Debugging Logs
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There is a `pr_debug` function used over the code, in order to enable those logs in `dmesg` for a specific module, you can do this:
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{% highlight bash %}
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echo 8 > /proc/sys/kernel/printk
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echo 'module ip_set +p' > /sys/kernel/debug/dynamic_debug/control
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{% endhighlight %}
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Note that, this works if you have dynamic debug enabled in your `.config`:
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{% highlight bash %}
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CONFIG_DYNAMIC_DEBUG=y
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CONFIG_DYNAMIC_DEBUG_CORE=y
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{% endhighlight %}
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You can then look at `dmesg` while running the code to see those logs:
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{% highlight bash %}
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dmesg
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{% endhighlight %}
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