Implement RWO/RWX SELinux context mounts (TechPreview)

Feature Overview (aka. Goal Summary)  

An elevator pitch (value statement) that describes the Feature in a clear, concise way.  Complete during New status.

Provide a long term solution to SELinux context labeling in OCP. Continue the implementation with RWO/RWX PVs which are the most expected from the field. Start with a TechPreview support grade.

Goals (aka. expected user outcomes)

The observable functionality that the user now has as a result of receiving this feature. Include the anticipated primary user type/persona and which existing features, if any, will be expanded. Complete during New status.

As of today when selinux is enabled, the PV's files are relabeled when attaching the PV to the pod, this can cause timeout when the PVs contains lot of files as well as overloading the storage backend.

https://access.redhat.com/solutions/6221251 provides few workarounds until the proper fix is implemented. Unfortunately these workaround are not perfect and we need a long term seamless optimised solution.

This feature tracks the long term solution where the PV FS will be mounted with the right selinux context thus avoiding to relabel every file. This covers RWO/RWX PVs, RWOP is already being implemented and should GA in 4.17.

Requirements (aka. Acceptance Criteria):

A list of specific needs or objectives that a feature must deliver in order to be considered complete.  Be sure to include nonfunctional requirements such as security, reliability, performance, maintainability, scalability, usability, etc.  Initial completion during Refinement status.

Should pass all regular regression CI. All the drivers we ship should have it enabled and partners may enable it if they want it to be consumed.

Performances should drascillaly improved and security should remain the same as the legacy chcon approach.

Anyone reviewing this Feature needs to know which deployment configurations that the Feature will apply to (or not) once it's been completed.  Describe specific needs (or indicate N/A) for each of the following deployment scenarios. For specific configurations that are out-of-scope for a given release, ensure you provide the OCPSTRAT (for the future to be supported configuration) as well.

Use Cases (Optional):

Include use case diagrams, main success scenarios, alternative flow scenarios.  Initial completion during Refinement status.

Provide details for user scenarios including actions to be performed, platform specifications, and user personas.  

1. Apply new context when there is none
2. Change context of all files/folders when changing context
3. RWO & RWX PVs

As we are relying on mount context there should not be any relabeling (chcon) because all files / folders will inherit the context from the mount context

More on design & scenarios in the KEP

Questions to Answer (Optional):

Include a list of refinement / architectural questions that may need to be answered before coding can begin.  Initial completion during Refinement status.

<your text here>

Out of Scope

High-level list of items that are out of scope.  Initial completion during Refinement status.

RWOP PVs

Background

Provide any additional context is needed to frame the feature.  Initial completion during Refinement status.

Lots of support cases due to pod taking too long to start because of selinux relabeling with chcon. This epics covers the most "unpopular" RWX case specially for PVs with lots of files and backends that are "slow" at updating metadata.

Customer Considerations

Provide any additional customer-specific considerations that must be made when designing and delivering the Feature.  Initial completion during Refinement status.

Most cases / concerns are on RWX, RWOP was the first step and has limited customer's impact though it is easier to implement first and gather feedback / metrics. https://access.redhat.com/solutions/6221251

This feature track TP for RWO/RWX PVs

Documentation Considerations

Provide information that needs to be considered and planned so that documentation will meet customer needs.  If the feature extends existing functionality, provide a link to its current documentation. Initial completion during Refinement status.

Relnotes + table of drivers supporting it.

Interoperability Considerations

Which other projects, including ROSA/OSD/ARO, and versions in our portfolio does this feature impact?  What interoperability test scenarios should be factored by the layered products?  Initial completion during Refinement status.

Partners may want to enable the feature.