Merge pull request #25875 from codyhoag/rn-4-6-rhcos

RHCOS release note additions

release_notes/ocp-4-6-release-notes.adoc

@@ -60,6 +60,70 @@ This release adds improvements related to the following components and concepts.
 [id="ocp-4-6-rhcos"]
 === {op-system-first}
 
+[id="ocp-4-6-live-env-with-coreos-installer"]
+==== {op-system} PXE and ISO now live environment
+
+The PXE media and ISO available for {op-system} are now a fully live
+environment. Unlike the previous dedicated PXE media and ISO used for
+installation, the {product-title} live environment can be configured with
+Ignition and contains all the same packages as the main {op-system}, such as
+podman. This allows arbitrary scripting of pre- or post-installation workflows. For
+example, you could run `coreos-installer` and then make an HTTP request to
+signal success to a provisioning server. PXE boots use the normal
+`ignition.config.url`. The ISO can be configured with Ignition by using the
+following command:
+
+[source,terminal]
+----
+$ coreos-installer iso ignition embed
+----
+
+[id="ocp-4-6-coreos-installer-rewritten"]
+==== `coreos-installer` has been rewritten
+
+The `coreos-installer` is now rewritten to support more features including:
+
+* Modifying the kernel arguments of the installed system.
+* Fetching Ignition configs.
+* Preserving previously existing partitions.
+* Configuring Ignition for the new live ISO using the `coreos-installer iso ignition` command.
+
+[id="ocp-4-6-ignition-spect-updated-v3"]
+==== Ignition Spec updated to v3
+
+{op-system} now uses Ignition spec v3 as the only supported spec
+version of Ignition. This allows for more complex disk configuration support
+in the future.
+
+The change should be mostly transparent for those using installer-provisioned
+infrastructure. For user-provisioned infrastructure installations, you must
+adapt any custom Ignition configurations to use Ignition spec 3. The
+`openshift-install` program now generates Ignition spec 3.
+
+If you are creating Machine Configs for day 1 or day 2 operations that use
+Ignition snippets, they should be created using Ignition spec v3. However, the
+Machine Config Operator (MCO) still supports Ignition spec v2.
+
+[id="ocp-4-6-extensions-supported-for-rhcos-mco"]
+==== Extensions now supported for {op-system} and MCO 
+
+{op-system} and the MCO now support the following extensions to the default
+{op-system} installation.
+
+* `kernel-devel`
+* `usbguard`
+
+[id="ocp-4-6-4kn-disk-support"]
+==== 4Kn Disks now supported
+
+{op-system} now supports installing to disks that use 4K sector sizes.
+
+[id="ocp-4-6-4k-var-partition-support"]
+==== `/var` partitions now supported
+
+{op-system} now supports `/var` being a separate partition, as well as any other
+subdirectory of `/var`.
+
 [id="ocp-4-6-static-ip-config-with-ova"]
 ==== Static IP configuration for vSphere using OVA