1.3. Adding kernel modules to nodes

Procedure

1. Register a RHEL 8 system:

   # subscription-manager register

2. Attach a subscription to the RHEL 8 system:

   # subscription-manager attach --auto

3. Install software that is required to build the software and container:

   # yum install podman make git -y

4. Clone the kmod-via-containers repository:

   1. Create a folder for the repository:

      $ mkdir kmods; cd kmods

   2. Clone the repository:

      $ git clone https://github.com/kmods-via-containers/kmods-via-containers

5. Install a KVC framework instance on your RHEL 8 build host to test the module. This adds a kmods-via-container systemd service and loads it:

   1. Change to the kmod-via-containers directory:

      $ cd kmods-via-containers/

   2. Install the KVC framework instance:

      $ sudo make install

   3. Reload the systemd manager configuration:

      $ sudo systemctl daemon-reload

6. Get the kernel module source code. The source code might be used to build a third-party module that you do not have control over, but is supplied by others. You will need content similar to the content shown in the kvc-simple-kmod example that can be cloned to your system as follows:

   $ cd .. ; git clone https://github.com/kmods-via-containers/kvc-simple-kmod

7. Edit the configuration file, simple-kmod.conf file, in this example, and change the name of the Dockerfile to Dockerfile.rhel:

   1. Change to the kvc-simple-kmod directory:

      $ cd kvc-simple-kmod

   2. Rename the Dockerfile:

      $ cat simple-kmod.conf

      Example Dockerfile

      KMOD_CONTAINER_BUILD_CONTEXT="https://github.com/kmods-via-containers/kvc-simple-kmod.git"
      KMOD_CONTAINER_BUILD_FILE=Dockerfile.rhel
      KMOD_SOFTWARE_VERSION=dd1a7d4
      KMOD_NAMES="simple-kmod simple-procfs-kmod"

8. Create an instance of kmods-via-containers@.service for your kernel module, simple-kmod in this example:

   $ sudo make install

9. Enable the kmods-via-containers@.service instance:

   $ sudo kmods-via-containers build simple-kmod $(uname -r)

10. Enable and start the systemd service:

    $ sudo systemctl enable kmods-via-containers@simple-kmod.service --now

    1. Review the service status:

       $ sudo systemctl status kmods-via-containers@simple-kmod.service

       Example output

       ● kmods-via-containers@simple-kmod.service - Kmods Via Containers - simple-kmod
          Loaded: loaded (/etc/systemd/system/kmods-via-containers@.service;
                 enabled; vendor preset: disabled)
          Active: active (exited) since Sun 2020-01-12 23:49:49 EST; 5s ago...

11. To confirm that the kernel modules are loaded, use the lsmod command to list the modules:

    $ lsmod | grep simple_

    Example output

    simple_procfs_kmod     16384  0
    simple_kmod            16384  0

12. Optional. Use other methods to check that the simple-kmod example is working:

    • Look for a "Hello world" message in the kernel ring buffer with dmesg:

      $ dmesg | grep 'Hello world'

      Example output

      [ 6420.761332] Hello world from simple_kmod.

    • Check the value of simple-procfs-kmod in /proc:

      $ sudo cat /proc/simple-procfs-kmod

      Example output

      simple-procfs-kmod number = 0

    • Run the spkut command to get more information from the module:

      $ sudo spkut 44

      Example output

      KVC: wrapper simple-kmod for 4.21.0-147.3.1.el8_1.x86_64
      Running userspace wrapper using the kernel module container...
      + podman run -i --rm --privileged
         simple-kmod-dd1a7d4:4.21.0-147.3.1.el8_1.x86_64 spkut 44
      simple-procfs-kmod number = 0
      simple-procfs-kmod number = 44