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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)

  • [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.