GLEP:49

Status
The council rejected this GLEP in favor of starting from a package manager API and requiring Gentoo package managers in the tree to support that API. (That API is still pending, however.)

Abstract
This GLEP describes four classes of package managers. What the requirements for them are, and what support they can receive.

Motivation
To set a standard that package managers that seek Gentoo project approval and support should adhere to.

Rationale
Currently Portage is showing its age. The code of Portage does not seem to be salvageable for new versions. As of the date of publication, there are two known alternative package managers that claim a level of Portage compatibility. These alternatives are paludis and pkgcore. Before these alternatives are developed further, a set of rules should be created to level the playing field and ensuring that decisions can be made clearly.

Backwards Compatibility
Not a problem for this GLEP. There is no previous standard as the issue did not exist before. This GLEP is to prevent future compatibility issues.

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We distinguish four categories of package managers. While a package manager can transition from one category to another, it can not be in two categories at the same time. It can be in a state of transition though.


 * Primary Package Manager
 * There is one primary package manager. Currently this position is held by Portage. The primary package manager is assigned by the council and all packages in the official tree must be installable by a usable version of the primary package manager.


 * Candidate Primary Package Managers
 * A candidate Primary Package Manager does aim, or show an aim, at replacing the current primary package manager. At a point where the package manager is deemed stable a decision must be made whether this package manager should become the new primary package manager. At that point the Primary package manager transition phase starts.


 * Secondary Package Managers
 * A secondary package manager is a package manager that coexists with the primary package manager, while not aiming to replace it. Examples of package managers that would fall into this category are:


 * Experimental package managers. Package managers whose purpose it is to try out new features.
 * Focused package managers. For example a package manager that allows the use of RPM formatted binary packages would be an example.
 * Alternate package managers. Package managers that aim to coexist with the primary package manager. They might for example offer a nicer user interface than the primary package manager (e.g. show a cow instead of compilation messages).


 * Third Party Package Managers
 * A third party package manager is any package manager that lacks recognition from Gentoo as being in any other category. A third party package manager may or may not have a Gentoo package, but is not supported beyond that.

Package manager requirements
As a package manager is in a state of higher support there are higher requirements to it. The purpose of these requirements is to ensure the unity of the distribution and the package tree. For this purpose it is needed that there is only one primary package manager. This is from Gentoo's perspective. From a user perspective it is perfectly possible to use another package manager. Candidate primary package managers and secondary package managers are also supported in regards to bugs etc.

Primary package manager requirements
The primary package manager is the package manager that sets the standards for the tree. All ebuilds in the tree must function with the primary package manager. As the primary package manager sets the standard it does not have to maintain compatibility with other package managers. This does not mean that the actual implementation is the standard, but that the maintainers have the ability to define new standards, together with the other involved Gentoo projects.

The primary package manager does however have the responsibility that it must be very stable. The primary package manager must maintain compatibility with old versions of itself for extended periods of time. This compatibility time is set by the council. The suggested time would be one year from the point that there is a compatible stable version for all supported architectures.

Another compatibility requirement for the primary package manager is a limited forward compatibility. It must always be possible to transition from the unstable version of the primary package manager to a stable version. This may be done either by first introducing reading compatibility for a new format and only having write support later. Another way would be the provision of a conversion tool that ensures that the on disk information maintained by the package manager is supported by the stable package manager.

The primary package manager maintainers further have the responsibility to allow competition. This means that reasonable patches from the maintainers of secondary or candidate primary package managers must be applied, given that these patches are as independent of that package manager as possible.

The primary package manager is maintained on official Gentoo infrastructure, under control of Gentoo developers.

Candidate primary package manager requirements
A candidate primary package manager aims to replace the primary package manager. The council is responsible for deciding whether this is done. The requirements are there to ensure that it is actually possible to transition a candidate primary package manager into the primary package manager.

First of all, there must exist a transition path. This means that the on disk data of the primary package manager can be used by (or converted to a format usable by) the candidate primary package manager.

Second, there must be a test path. It must be possible for the developers to test out the candidate primary package manager on their working systems. This means that the transition path must exist. This also means that there are no serious obstacles for reverting to the current primary package manager. This reverting must also be usable when it is decided that the candidate will not become primary package manager, for example because serious design flaws or bugs were found. Ideally, the Candidate Primary Package Manager and the Primary Package Manager can be installed simultaneously. If not, clear instructions must be provided for both ways of transitioning.

Third, there must exist an ebuild test path. It must be possible for package managers to test ebuilds in one tree for both the primary as well as the candidate primary package manager. It is not an issue if this requires a special mode for the candidate primary package manager. It is not an issue either if compatibility can be achieved by having the candidate primary package manager unmerge the package.

Fourth, there must be support. This means that the package manager is actively maintained under control of Gentoo. If it is not maintained on Gentoo infrastructure, the means must be there to move the package manager, with its change history, to Gentoo infrastructure. This means that it must be maintained on a Gentoo supported versioning system, or on a version system whose history can be converted to a Gentoo supported versioning system.

Fifth, release capabilities. There must exist automated tools that use the candidate primary package manager to create release media that have similar capabilities as those released using the old primary package manager. The exact requirements are determined by the Release Engineering project, but should not be significantly beyond what is currently implemented using the primary package manager.

Secondary package manager requirements
A secondary package manager is a package manager that instead of directly aiming at replacing the current primary package manager as primary package manager aims to cooperate with the primary package manager. As such a secondary package manager does not set the standard on the tree, but follows the standard set by the primary package manager.

There are two kinds of secondary package managers. The first kind is formed by those that do not maintain their own installed package database, but work with the package database of the primary package manager. While these package managers can put additional information in the database, these entries must remain compatible with the primary package managers. Verification, reference, and deinstallation by the primary package manager must remain functional.

The second kind is formed by those package managers that maintain their own package database, or a package database incompatible with the primary package manager. To ensure the secondary role of these package managers the support in the tree for these package managers is provided along with restrictions.

The first restriction is that no packages in the tree must rely on the secondary package manager. While packages may provide a level of support (while being compatible with the primary package manager) this may not result in a significant increase of features. If this were allowed, this would mean that while they technically work with the primary package manager, there would be significant incentive to use the secondary package manager. As the use of this secondary package manager disallows the parallel use of the primary package manager, this would result in users using the secondary package manager as their primary package manager.

Users are allowed to make their own choices. However by making the tree favour a package manager that is not the primary package manager, this will lead to the secondary package manager becoming the effective primary package manager. As this will be a decision by default instead of a conscious choice by the council, this is an undesirable result.

There is one exclusion for the restriction of packages that only work with or have significant improvements with the secondary package manager. That is packages that by their nature are only usable with this secondary package manager. An example would be a graphical front-end to the secondary package manager.

If a secondary package manager works along the primary package manager, but by itself does not have the capabilities of becoming a primary package manager the risks of choice by default are lower. As a result, the council could choose to allow the inclusion of packages that work only or significantly better with this secondary package manager. For example at a point where there is a stable, functional, package manager that can handle RPM format packages, the council could decide to include these packages directly in the tree, instead of using wrapper scripts for those packages that are only provided in the RPM format. Such a decision does imply that the maintainers of the primary package manager must take this secondary package manager into account.

Third party package manager requirements
A third party package manager is just that. It is a package manager without any support within Gentoo. As there is no control by Gentoo over the package manager this means that there are no requirements on the package manager.

This complete lack of control however also translates to the fact that Gentoo can not make package manager specific changes to support this package manager. Package manager specific means that it is possible to request changes that make the tree more independent of the primary package manager. These changes must however be agnostic of the package manager, and only make it easier to have alternative package managers.

Primary package manager transition phase
A candidate primary package manager can be chosen to become primary package manager. This can only happen by council decision. This decision can only be made when the candidate primary package manager is stable on all stable architectures (all architectures except experimental ones). There is a incubation period of at least 3 months before a candidate primary package manager can become the primary package manager.

After the decision has been made to replace the primary package manager, the transition phase starts. The use of the old stable package manager must remain supported for a period of 6 months. This means that core packages must be installable by this package manager. Further the possibility to convert the system automatically to the new primary package manager must be available for at least 18 months, but preferably longer (enable installing the new package manager from the old one).

During the transition phase packages are allowed in the tree that use the new features of the new primary package manager. While backward compatibility with the previous primary package manager must be maintained a forward compatibility is no longer needed.

Secondary package manager to candidate primary package manager transition
The transition from secondary package manager to candidate primary package manager is straightforward. The secondary package manager must satisfy all requirements for a candidate primary package manager. At that point its maintainers can announce that they are changing the status to candidate primary package manager. This allows a greater support from Gentoo in achieving that goal.

Third party to other transition
When a third party package manager wants to transition into one of the other categories (except primary package manager) it must satisfy all requirements for that category.

Copyright
This document is copyright 2006 by Paul de Vrieze and licensed under the Open Publication License.