To add Sukisu to your kernel, especially if you are building a custom kernel for your MI MIX 2S running Android 14 with LineageOS-21, you'll need to follow a series of steps. Since you're using a non-GKI kernel version 4.9, the process might be a bit different from the more recent GKI kernels. Here's a guide to help you integrate Sukisu and add SUSFS support.

Step 1: Obtain the Sukisu Source Code

First, you need to get the Sukisu source code. You can usually find this on the official Sukisu GitHub repository or other kernel development forums. Make sure to download the version that is compatible with your kernel version (4.9).

Step 2: Set Up Your Development Environment

Before you start modifying your kernel, ensure you have a proper development environment set up. This includes having the necessary tools like the Android SDK, ADB, fastboot, and a good code editor or IDE like Visual Studio Code with the C/C++ extension.

Step 3: Merge Sukisu with Your Kernel

Next, you will need to merge the Sukisu source code with your existing kernel source. This process involves copying the relevant Sukisu files into your kernel directory and ensuring they are compatible with your current kernel version. You may need to resolve any merge conflicts that arise.

Step 4: Add SUSFS Support

To add SUSFS support, you will need to locate the SUSFS source code and integrate it into your kernel. This typically involves adding SUSFS files to the appropriate directories in your kernel source and modifying the kernel configuration to include SUSFS support. You may need to recompile your kernel to apply these changes.

Step 5: Compile and Test Your Kernel

After integrating both Sukisu and SUSFS, you will need to compile your kernel. Use the following command in your kernel directory to compile the kernel:

make -j$(nproc --all) ARCH=arm64 CROSS_COMPILE=aarch64-linux-android- defconfig
make -j$(nproc --all) ARCH=arm64 CROSS_COMPILE=aarch64-linux-android- zImage

Once the compilation is complete, flash the new kernel onto your device using fastboot. After flashing, boot into your new kernel and test for any issues.

Step 6: Debugging and Further Customization

If you encounter any issues, use ADB to logcat and debug the kernel. You may need to make further adjustments to ensure everything works smoothly. Don't hesitate to seek help from the Sukisu community or other kernel development forums if you run into difficulties.

By following these steps, you should be able to add Sukisu and SUSFS support to your custom kernel. Good luck with your kernel development journey, and remember that patience and persistence are key in this process!