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The RFC Process
Curtis Millar
2020 seL4 Project a Series of LF Projects, LLC.

seL4 Request for Comments (RFC) Process

We have introduced the request for comments (RFC) process for the following reasons:

  • to allow the community to discuss design changes in seL4,
  • to gather valuable feedback from the community on changes the Foundation is considering,
  • to allow members of the seL4 community to get support and approval to propose and implement their own changes to the seL4 ecosystem,
  • to ensure that all changes made to core components of the seL4 ecosystem or that have wide and varying impacts on users of seL4 undergo rigorous review, and
  • to ensure large changes are well advertised and can viewed publicly before contributors commit to implementing them.

This helps the seL4 community ensure that such changes are made with the goal of the best outcome for the most users of seL4 whilst maintaining the seL4 guarantees of isolation and security.

To see all current RFCs, go check out the RFC dashboard.

You can also stay notified of new RFCs and updates to RFCs by joining the RFC announcement mailing list. You can then use you Atlassian Cloud account to keep track of and contribute to discussion on each of the RFCs.

When to follow the RFC process

All substantial changes to the seL4 ecosystem must be made using the RFC process. Substantial changes are those that that impact a large number of users of seL4 in a way that may require them to change their own projects, changes the operation of toolchain used to build projects on seL4, changes the underlying model of one or more software components within the ecosystem.

Examples of changes that must follow the RFC process include:

{% comment %} Over time this list may change, as we find certain kinds of changes should be made via the RFC process to benefit from the wider publicity and the documentation artefact it generates. {% endcomment %}

  • Removing support for a platform
  • Changing the versioning system used for libraries
  • Adding a new major API feature to the kernel
  • Adding a new operation/invocation to an existing capability type, or removing one
  • Adding or removing a capability or object type

Changes such as bug-fixes, refactorings, optimisations, or those that do not affect the functional requirements of the kernel, supporting tooling, infrastructure, or system components can be made through the existing pull-request process on the relevant repository.

Examples of changes that should not involve the RFC process include:

  • Fixing a typo in existing code,
  • Clarifying code or documentation,
  • Adding a driver to an existing layer of the system.

If you try to make a substantial change via the pull-request process, your request is likely to be rejected and you will be asked to use the RFC process to propose your change.

If you are unsure whether a change requires an RFC, ask on the seL4 Mattermost chat or post a question to the development mailing list.

The RFC Process

Before creating a new RFC

Before proposing a new RFC it is important to determine whether it will be supported and what possible options exist to solve the particular problem.

This should be done through discussion one one of the many community forums such as the seL4 Mattermost chat or the development mailing list.

This part of the process should help you determine whether your idea has already been proposed, whether or not it fits with the near-term goals of the ecosystem, and how to propose it with the best chances of acceptance.

You should make sure that during this discussion you address each of the sections in the template below. This will ensure that your proposal is well prepared before it is formally presented as an RFC and will speed up much of the RFC process.

Once you have the support of some existing seL4 developers they can help you take your idea through the rest of the RFC process.

After discussion, RFCs will ultimately be approved, postponed, or rejected by a decision of the Technical Steering Committee of the seL4 Foundation.

Proposing an new RFC

An RFC exists in the form of an RFC issue on the RFC project of the seL4 Jira instance. Anyone who has an Atlassian Cloud account is able to create an RFC.

You should check the postponed RFCs to see if your idea has already been proposed but was previously postponed. You can adopt a postponed RFC which will return it to the proposal stage and you will become responsible for it.

Once you create an RFC, you are the one responsible for maintaining it throughout the approval process. You will be able to modify it in response to discussion and feedback up until the point it is either approved or rejected.

Every RFC should use the template below, omitting sections that are not relevant for the RFC.

The RFC template

You should consider each section of the RFC template in depth before determining that it is not relevant.

You will probably want to work on this offline during the initial discussion so that you can paste the final document into the issue description when you create the RFC issue.

{% comment %} This template has been taken from the Rust RFCs repository ( under the following MIT license:

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.


h1. Summary

One paragraph explanation of the change.

h1. Motivation

- Why are we doing this?
- What use cases does it support?
- What is the expected outcome?

h1. Guide-level explanation

Explain the change or feature as you would to another user of seL4.

This section should clearly outline new named concepts, provide some examples of how it will be used, and explain how users should *think* about it.

You should describe the change in a manner that is clear to both existing seL4 users and to new users of the ecosystem.

Any changes that existing users need to make either as a result of the RFC or such that the can use the feature should be clearly stated here.

h1. Reference-level explanation

Explain the change or feature as you would to the maintainers of the seL4 ecosystem.

This section should provide sufficient technical detail to guide any related implementation and ongoing maintenance.

This section should clearly describe how this change will interact with the existing ecosystem, describe particular complex examples that may complicate the implementation, and describe how the implementation should support the examples in the previous section.

h1. Drawbacks

Outline any arguments that have been made against this proposal and discuss why we may not want to accept it.  Also discuss any complications that may arise from the proposed change that may require specific consideration.

h1. Rationale and alternatives

- Why is this design the best in the space of possible designs?
- What other designs have been considered and what is the rationale for not choosing them?
- What is the impact of not doing this?

h1. Prior art

Discuss prior art, both the good and the bad, in relation to this proposal.  A few examples of what this can include are:

- For ecosystem proposals: Does this feature exist in similar systems and what experience have their community had?
- For community proposals: Is this done by some other community and what were their experiences with it?
- What lessons can we learn from what other communities have done here?
- Are there any published papers or great posts that discuss this?  If you have some relevant papers to refer to, this can serve as a more detailed theoretical background.

This section is intended to encourage you as an author to think about the lessons from other systems, provide readers of your RFC with a fuller picture.  If there is no prior art, that is fine - your ideas are interesting to us whether they are brand new or if it is an adaptation from other systems.

Note that while precedent set by other systems is some motivation, it does not on its own motivate an RFC.

h1. Unresolved questions

- What needs to be resolved in further discussion before the RFC is approved?
- What needs to resolved during the implementation of this RFC?
- What related questions are beyond the scope of this RFC that should be addressed beyond its implementation?

Getting an RFC approved

After you propose an RFC, it is likely to undergo several rounds of changes in response to the discussion on Jira. Anyone is allowed to engage in this discussion.

Once the discussion phase is concluded, for instance because consensus has been reached or it has become clear that there will not be a consensus, the Technical Steering Committee of the seL4 Foundation will make a decision on the RFC.

The Steering Committee will either give stage 1 approval, fully approve, postpone, defer, require changes, or reject the RFC. When this occurs, a disposition will be added to the RFC outlining the reason for the particular ruling. If the discussion of an RFC has been particularly long, a summary comment will be made on the RFC before the given ruling is made.

Postponement of an RFC

When an RFC has a moderate amount of support and is generally accepted as a good idea but lacks someone to shepherd it to the point where it can be accepted it is postponed.

This indicates that the RFC may be revived in the future when someone can be found to take it through the remainder of the approval process. Anyone may adopt a postponed RFC if they wish to see it approved and want to rally support for it.

Stage 1 approval

In some cases, an RFC may require an implementation or very detailed design to properly judge its merits. When the TSC decides that an RFC is likely to get accepted if a convincing implementation can be shown, the TSC may give stage 1 approval for this RFC. Stage 1 approval means a candidate implementation should go ahead, but will need to be reviewed again, e.g. for performance and usability, before it can be fully accepted.

Implementation of an approved RFC

Once the Steering Committee approves an RFC, it is marked as active. They may then assign it to a contributor for implementation. Issues for the implementation of the necessary components will be created and linked to the RFC.

The implementation of an RFC may lead to the resolution of many issues that were present in the RFC when it was approved. As such, the RFC may be subject to further changes throughout this part of the process. These changes should not change the overall goals or design of the RFC but should merely resolve issues or extend the design to cope with unanticipated corner cases.

Deferment of an approved RFC

There may not be sufficient resources to implement an RFC when it is approved or resources may be diverted from the implementation of an RFC when higher priority work arises. In either case, the RFC will be deferred. A deferred RFC is lower priority than an active one and will generally see no progress on its implementation.

Anyone can request that a deferred RFC be given priority be demonstrating increased demand or urgency for its implementation, volunteering to work on the implementation, or find funding for the Foundation to implement it.