The documentation available here: https://docs.openshift.com/container-platform/4.12/post_installation_configuration/coreos-layering.html instructs how to prepare RHCOS image layering. Unfortunately it doesn't explain how  to build the image. I did it just using podman:

```
[root@quay-oc-mirror kernel-patch]# cat Containerfile
FROM quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:71658b50c68fdc974de2271f0ab166c663bc475e4626b4871f292e6a21ca1c41ADD kernel-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm ./
ADD kernel-core-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm ./
ADD kernel-modules-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm ./
ADD kernel-modules-extra-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm ./RUN rpm-ostree override replace kernel-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm \
    kernel-core-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm kernel-modules-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm \
    kernel-modules-extra-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm && \
    rpm-ostree cleanup -m && \
    ostree container commit
```


```
[root@quay-oc-mirror kernel-patch]# podman build .
STEP 1/6: FROM quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:71658b50c68fdc974de2271f0ab166c663bc475e4626b4871f292e6a21ca1c41
STEP 2/6: ADD kernel-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm ./
--> 60ff647cf7b
STEP 3/6: ADD kernel-core-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm ./
--> f0f27e9e506
STEP 4/6: ADD kernel-modules-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm ./
--> f5d4e03b60b
STEP 5/6: ADD kernel-modules-extra-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm ./
--> 16dbf08d57c
STEP 6/6: RUN rpm-ostree override replace kernel-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm     kernel-core-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm kernel-modules-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm     kernel-modules-extra-4.18.0-372.38.1.el8_6pittimerpinned.x86_64.rpm &&     rpm-ostree cleanup -m &&     ostree container commit
Enabled rpm-md repositories: rhel-8-for-x86_64-baseos-rpms rhel-8-for-x86_64-appstream-rpms
Updating metadata for 'rhel-8-for-x86_64-baseos-rpms'...done
Updating metadata for 'rhel-8-for-x86_64-appstream-rpms'...done
Importing rpm-md...done
rpm-md repo 'rhel-8-for-x86_64-baseos-rpms'; generated: 2023-04-05T14:04:21Z solvables: 14635
rpm-md repo 'rhel-8-for-x86_64-appstream-rpms'; generated: 2023-04-04T12:42:56Z solvables: 32053
Resolving dependencies...done
Installing 4 packages:
  kernel-4.18.0-372.38.1.el8_6pittimerpinned.x86_64 (@commandline)
  kernel-core-4.18.0-372.38.1.el8_6pittimerpinned.x86_64 (@commandline)
  kernel-modules-4.18.0-372.38.1.el8_6pittimerpinned.x86_64 (@commandline)
  kernel-modules-extra-4.18.0-372.38.1.el8_6pittimerpinned.x86_64 (@commandline)
Downgrading: kernel-core;4.18.0-372.38.1.el8_6pittimerpinned;x86_64;local
Downgrading: kernel-modules;4.18.0-372.38.1.el8_6pittimerpinned;x86_64;local
Downgrading: kernel;4.18.0-372.38.1.el8_6pittimerpinned;x86_64;local
Downgrading: kernel-modules-extra;4.18.0-372.38.1.el8_6pittimerpinned;x86_64;local
Cleanup: kernel;4.18.0-372.46.1.el8_6;x86_64;installed
Cleanup: kernel-modules-extra;4.18.0-372.46.1.el8_6;x86_64;installed
Cleanup: kernel-modules;4.18.0-372.46.1.el8_6;x86_64;installed
Cleanup: kernel-core;4.18.0-372.46.1.el8_6;x86_64;installed
COMMIT
--> 10e26b349fa
10e26b349fa0d6a818f9c5138def3a35451709080c0bd23b6eecd2472e7442cb
```

then tagged image and push it to the registry, created MachineConfig following the docs:


```
[root@quay-oc-mirror ~]# cat machineconfig-custom-image.yaml
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: master
  name: pittimerpinned
spec:
  osImageURL: ocp-mirror.local:8443/rafal-test/custom-image@sha256:08548f85691593864fb61b9e9186767f181e9cef949c25292f95e9d3f1f04bc0
```

but when node got rebooted, it kernel panicked.

Now I'm unsure if I did something wrong with the image build process or something else is broken. 

I'd like to have precise instructions including image build process for RHCOS image layering procedure.
 

1.
2.
3.

Incomplete RHCOS image layering instruction.