Command line tool to build rootfs images

How to build a rootfs image using kci_rootfs

You will be using kernelci/debos:kernelci docker image for this purpose.

  1. Pull the docker image docker pull kernelci/debos:kernelci

  2. Clone the kernelci-core repo.

    git clone https://github.com/kernelci/kernelci-core.git
  3. Start the docker and get into it.

    $ sudo docker run -it \
      -v $(pwd)/kernelci-core:/kernelci-core \
      --device /dev/kvm -v /dev:/dev \
      --privileged kernelci/debos:kernelci /bin/bash
    $ cd /kernelci-core/
  4. Now to check if everything works, type ./kci_rootfs --help it should produce below help message.

    usage: kci_rootfs [-h] [--yaml-configs YAML_CONFIGS]
                      {validate,list_configs,list_variants,build,upload} ...
    optional arguments:
      -h, --help            show this help message and exit
      --yaml-configs YAML_CONFIGS
                            Path to the YAML configs file
                            List of available commands
        validate            Validate the rootfs YAML configuration
        list_configs        List all rootfs config names
        list_variants       List all rootfs variants
        build               Build a rootfs image
        upload              Upload a rootfs image
  5. To list available rootfs configuration, you can use list_configs option.

    $ ./kci_rootfs list_configs

    By default kci_rootfs reads entries from rootfs-configs.yaml. This file acts as a rootfs config file.

  6. Let’s list all available rootfs images using ./kci_rootfs list_variants. It should show existing rootfs name along with its architecture. Here are a few examples taken from the full list:

    buildroot-baseline riscv
    buildroot-baseline x86
    bullseye mips64el
    bullseye-libcamera amd64
    bullseye-ltp amd64
    bullseye-rt armhf

    It also comes with couple of options --rootfs-config and --arch to filter the results based on config name or arch type.

    $ ./kci_rootfs list_variants --rootfs-config bullseye --arch i386
    bullseye i386
    $ ./kci_rootfs list_variants --rootfs-config bullseye
    bullseye amd64
    bullseye arm64
    bullseye armel
    bullseye armhf
    bullseye i386
    bullseye mips64el
    bullseye mipsel
    $ ./kci_rootfs list_variants --arch amd64
    bullseye amd64
    bullseye-cros-ec amd64
    bullseye-igt amd64
    bullseye-libcamera amd64
    bullseye-ltp amd64
    bullseye-rt amd64
    bullseye-v4l2 amd64
  7. Now it’s time to re-build existing rootfs image using kci_rootfs build. It takes three arguments:

    • --rootfs-config refers to rootfs name which you want to build
    • --data-path points to debos files location
    • --arch refers to CPU arch you want to build

    For example, to build a bullseye rootfs image for i386, you can run

    ./kci_rootfs build \
        --rootfs-config bullseye \
        --data-path config/rootfs/debos \
        --arch i386 \
        --output /tmp

    depending on your network speed, this will take some time to complete.

  8. If build is successful you should see message like

    cd ${ROOTDIR} ; find -H  |  cpio -H newc -v -o | gzip -c - > ${ARTIFACTDIR}/bullseye/i386/rootfs.cpio.gz | ./build_info.json
    cd ${ROOTDIR} ; find -H  |  cpio -H newc -v -o | gzip -c - > ${ARTIFACTDIR}/bullseye/i386/rootfs.cpio.gz | 79539 blocks
    Powering off.
    ==== Recipe done ====

    Finally newly built rootfs images can be found under the directory pointed by --output. In our case, its /tmp.

    $ ls /tmp/_install_/bullseye/i386/
    build_info.json  full.rootfs.cpio.gz  full.rootfs.tar.xz  initrd.cpio.gz  rootfs.cpio.gz  rootfs.ext4.xz

Create a new rootfs image

Now you know how to build default kci_rootfs images. Let’s look at how to add simple bullseye rootfs image.

  1. First you need to add appropriate entries to rootfs_config.yml file.

        rootfs_type: debos
        debian_release: bullseye
          - amd64
          - arm64
          - e2fslibs
          - e2fsprogs

Above entry will create rootfs named bullseye-example for CPU amd64 and arm64 architectures without e2fslibs and e2fsprogs packages. List of possible rootfs-config yaml entries and its description are listed below:

bullseye-exampleUnique rootfs configuration name.
rootfs_typeTool used for rootfs creation.
debian_releaseDesired Debian OS version.
arch_listDesired list of CPU architecture.
extra_packages_removeSpecifies list of packages to remove from rootfs.
scriptCustom script to be executed during rootfs image creation.
test_overlayCreate a directory layout on final rootfs image as provided.
extra_packagesInstalls specified packages on rootfs image.
extra_firmwareInstalls specified linux-firmware files into rootfs image.
linux_fw_versionIf extra_firmware is specified, selects the linux-firmware version to fetch.
extra_files_removeRemoves specified files from rootfs image.

Please note at the moment, only debos is supported as rootfs_type and above options are debos specific.

  1. Now validate rootfs-config.yml entries using ./kci_rootfs validate and verify that it didn’t report any errors.

  2. If no issues reported during validation, start the build process using,

    ./kci_rootfs build \
        --rootfs-config bullseye-example \
        --data-path config/rootfs/debos \
        --arch amd64

    and wait for its completion. If everything went fine you should see something like below under config/rootfs/debos/bullseye-example/amd64/ directory.

    ls config/rootfs/debos/bullseye-example/amd64/
    build_info.json  full.rootfs.cpio.gz  full.rootfs.tar.xz  initrd.cpio.gz  rootfs.cpio.gz  rootfs.ext4.xz
Last modified August 5, 2021