Feature and driver maintainers¶
The term "maintainer" spans a very wide range of levels of engagement from people handling patches and pull requests as almost a full time job to people responsible for a small feature or a driver.
Unlike most of the chapter, this section is meant for the latter (more populous) group. It provides tips and describes the expectations and responsibilities of maintainers of a small(ish) section of the code.
Drivers and alike most often do not have their own mailing lists and git trees but instead send and review patches on the list of a larger subsystem.
The amount of maintenance work is usually proportional to the size and popularity of the code base. Small features and drivers should require relatively small amount of care and feeding. Nonetheless when the work does arrive (in form of patches which need review, user bug reports etc.) it has to be acted upon promptly. Even when a particular driver only sees one patch a month, or a quarter, a subsystem could well have a hundred such drivers. Subsystem maintainers cannot afford to wait a long time to hear from reviewers.
The exact expectations on the response time will vary by subsystem. The patch review SLA the subsystem had set for itself can sometimes be found in the subsystem documentation. Failing that as a rule of thumb reviewers should try to respond quicker than what is the usual patch review delay of the subsystem maintainer. The resulting expectations may range from two working days for fast-paced subsystems (e.g. networking) to as long as a few weeks in slower moving parts of the kernel.
Mailing list participation¶
Linux kernel uses mailing lists as the primary form of communication. Maintainers must be subscribed and follow the appropriate subsystem-wide mailing list. Either by subscribing to the whole list or using more modern, selective setup like lei.
Maintainers must know how to communicate on the list (plain text, no invasive legal footers, no top posting, etc.)
Maintainers must review all patches touching exclusively their drivers, no matter how trivial. If the patch is a tree wide change and modifies multiple drivers - whether to provide a review is left to the maintainer.
When there are multiple maintainers for a piece of code an
Reviewed-by tag (or review comments) from a single maintainer is
enough to satisfy this requirement.
If the review process or validation for a particular change will take longer than the expected review timeline for the subsystem, maintainer should reply to the submission indicating that the work is being done, and when to expect full results.
Refactoring and core changes¶
Occasionally core code needs to be changed to improve the maintainability of the kernel as a whole. Maintainers are expected to be present and help guide and test changes to their code to fit the new infrastructure.
Maintainers must ensure severe problems in their code reported to them are resolved in a timely manner: regressions, kernel crashes, kernel warnings, compilation errors, lockups, data loss, and other bugs of similar scope.
Maintainers furthermore should respond to reports about other kinds of bugs as well, if the report is of reasonable quality or indicates a problem that might be severe -- especially if they have Supported status of the codebase in the MAINTAINERS file.
Selecting the maintainer¶
The previous section described the expectations of the maintainer, this section provides guidance on selecting one and describes common misconceptions.
Modern best practices dictate that there should be at least two maintainers for any piece of code, no matter how trivial. It spreads the burden, helps people take vacations and prevents burnout, trains new members of the community etc. etc. Even when there is clearly one perfect candidate, another maintainer should be found.
Maintainers must be human, therefore, it is not acceptable to add a mailing list or a group email as a maintainer. Trust and understanding are the foundation of kernel maintenance and one cannot build trust with a mailing list. Having a mailing list in addition to humans is perfectly fine.
To an outsider the Linux kernel may resemble a hierarchical organization with Linus as the CEO. While the code flows in a hierarchical fashion, the corporate template does not apply here. Linux is an anarchy held together by (rarely expressed) mutual respect, trust and convenience.
All that is to say that managers almost never make good maintainers. The maintainer position more closely matches an on-call rotation than a position of power.
The following characteristics of a person selected as a maintainer are clear red flags:
unknown to the community, never sent an email to the list before
did not author any of the code
(when development is contracted) works for a company which paid for the development rather than the company which did the work
Subsystem maintainers may remove inactive maintainers from the MAINTAINERS file. If the maintainer was a significant author or played an important role in the development of the code, they should be moved to the CREDITS file.
Removing an inactive maintainer should not be seen as a punitive action. Having an inactive maintainer has a real cost as all developers have to remember to include the maintainers in discussions and subsystem maintainers spend brain power figuring out how to solicit feedback.
Subsystem maintainers may remove code for lacking maintenance.
Subsystem maintainers may refuse accepting code from companies which repeatedly neglected their maintainership duties.