FlashKernelTester

This is my attempt to make compiling of custom linux kernel(for kernel dev) followed by their testing really easy and fast.

Prereq:

• Install docker on your system. (The downside)

  • For Ubuntu: https://docs.docker.com/install/linux/docker-ce/ubuntu/ (It takes about 6 commans to install it)
  • For Windows 10:https://docs.docker.com/toolbox/toolbox_install_windows/ (God save you guys)
  • For Mac users: https://docs.docker.com/docker-for-mac/install/ (Stable)
  • For anythother system, just google "install docker in X"

• [Optional] Check your installation of docker using -

  • sudo docker run -it ubuntu (for windows)
  • This will take some time as it will download ubuntu image.
  • It will change your prompt to something like root@4d4c9750e9e0:/#. This is the shell of an full fledged ubuntu running on docker.

• You should have downloaded the linux kernel on your system (Test on kernel verion v3.13)

• Make the test file required to run on bootup (This is the only code that will run on the new kernal) and store it in a folder with name of the .c file as test.c

Usage:

NOTE: ktest.sh may not work on your sytem if it Mac or Windows. Therefore I've provided alternative commands for almost everything. Therefore this can run on any x86/x86_64 system with virtualization enabled(using boot menu) and docker installed regardless of the OS(a few changes might be required).

• Clone this repo on your system using: git clone https://github.com/geekSiddharth/FlashKernelTester.git

• Open ktest.sh to edit the following variable

  • KERNEL_SOURCE
    It refers to the absolute linux kernal path. (Path should end in /)
    Example: KERNEL_SOURCE=/home/sid/linux-master/ where /home/sid/linux-master/ is the absolute linux kernal path
  • TEST_SOURCE
    It refers to the absolute path of the testing code. (Path should end in /)
    The pointed folder must constain a file called test.c
    (You can leave it to its default value for seeing if everything is working fine)

• Make ktest.sh executable by using: chmod +x ktest.sh

• If you are making the kernel for the first time, use:

  ./ktest.sh make1
  

  OR

    KERNEL_SOURCE=/home/sid/linux-master/
  
    docker run -it -v $KERNEL_SOURCE:/shared_kernel geeksid/kernel_tester bash ./make_first.sh
  

  Note this may take A LOT OF TIME if you are executing ktest.sh for the first time on you system.

• To test the kernel, use:

  ./ktest.sh test
  

  OR

    KERNEL_SOURCE=/home/sid/linux-master/
    TEST_SOURCE=$PWD/hello_world_test
  
     docker run  --privileged -it -v $KERNEL_SOURCE:/shared_kernel/ -v $TEST_SOURCE:/test/ geeksid/kernel_tester bash ./test.sh
  

• If you want to recompile on a part of kernel which resides in a folder with relative path within the linux folder as ./fold, use this to build,

  ./ktest.sh makes ./fold
  

  OR

    KERNEL_SOURCE=/home/sid/linux-master/
    TEST_SOURCE=$PWD/hello_world_test
    CHANGE_FOLDER=./fold
    docker run -it -v $KERNEL_SOURCE:/shared_kernel geeksid/kernel_tester bash ./make_small.sh $CHANGE_FOLDER
  
  

  This is much faster.

?

Why so fast?

• We are not building the whole kernel. config file in docker/ stores aprx minimum configurations.
  • drastically reduces building time
  • fast bootup time
• makes only builds the folder. If you are making changes to the sys call, whose code reside in particular folder, it is much faster to use makes <relative(to Linux Source folder) path to the folder>
• The building is done on the docker platform, which has almost no performace overhead. Therefore full utilization of your system resources and hence much faster booting time(than building inside a slow VM)

What is happening with the testing thing?

You remember the init process? It is the first process to be executed. Before init starts to execute , the kernel is executing. The test.c file is changed to a static binary and is passed to the kernel as the init process. The kernel executes the the static binary and it exits.