GLEP 72: Architecture stability status file
|Author||Andreas K. Hüttel <firstname.lastname@example.org>, Michał Górny <email@example.com>|
|Posting history||2017-05-06, 2020-04-10|
- Specifications for profiles/arches.desc
- Backwards Compatibility
This GLEP provides specifications for a new file in the profiles base directory, arches.desc. Its intent is to allow more fine-grained repoman check control, and in particular to help moving architectures from stable to testing while keeping the testing dependency tree consistent, or moving architectures from testing to stable while easily preparing a consistent stable dependency tree.
arches.desc specifies whether an architecture, as opposed to a profile, is to be considered stable. It does not replace profiles.desc, but supplements it; profiles.desc still describes the profiles of each architecture.
We use the term architecture here in the colloquial sense, as also used by the Package Manager Specification in section 4.4.1 (describing profiles.desc), and corresponding in the terminology of GLEP 53 to a "keyword" (which, however, even if more precise is not consistently used in practice).
At the moment we have several cases where repoman finds its limits:
An architecture loses its stable status (imagine c128), but the architecture team doesn't want to drop all the stable keywords since they are useful for stage building. Since the stable keywords on c128 are only an arch-team-internal thing, everyone is allowed to drop the latest stable version of a package, and it's the arch team's responsibility to keep their "unofficial stable tree" straight. This is how at the time of the writing of this GLEP s390, sh, and m68k are handled.
Right now this means that we have to set all profiles of this arch to profile status exp in profiles.desc, otherwise repoman throws errors about a broken stable dependency tree. If we do that, repoman does however also not check ~c128 consistency, meaning that the ~c128 dependency tree will soon be broken as well due to negligence. Given arches.conf as described below, one could set the architecture c128 to "transitional" status and keep stable profiles. This results in stable keywords being ignored, but consistency of the ~c128 dependency tree is still enforced.
An architecture prepares for becoming a stable architecture (think arm64). So, first the ~arm64 dependency tree should be fine, and then stable keywords can be added. However, to avoid repoman errors as long as the stable dependency tree is not complete yet, the profiles need to be set to dev/exp, and again this brings the danger of the ~arm64 dependency tree getting inadvertently broken. Again the combination of setting the architecture to "transitional" in arches.desc and profiles to stable helps.
Finally, at the moment the "semi-official" algorithm to figure out if an architecture is stable in the colloquial sense (e.g., requires stabilization requests) is to check if the architecture has any stable profile. This makes non-stable arches which want to keep a consistent dependency tree (think mips) impossible. Reading the architecture status from arches.desc instead solves this problem.
In the main profiles directory, a file arches.desc is added. Name and location are chosen in analogy to the existing profiles.desc file. The format of arches.desc is as follows:
Every # starts a comment; the character and the rest of the line are ignored. Every blank line is ignored. Otherwise the file consists of two whitespace-separated columns:
- first column: architecture name (keyword), which must be unique
- second column: one of the three values stable, transitional, testing
Additional columns are ignored to allow for future revisions of this document.
If the file does not exist, it is treated as if it were empty.
An example arches.desc file might look as follows:
# Example arches.desc file amd64 stable x86 stable # not for long sparc transitional m68k testing
On introduction, the setting will be stable for all architectures using stable keywords, and testing for those that do not (alpha, mips, riscv, Prefix profiles at the moment).
Stable means that the architecture is actively maintaining stable keywords. When dependency graphs of packages with stable keywords are tested, they are tested separately for arch and ~arch systems.
Stable architectures are listed first in keyword-relevant contexts (eshowkw, Bugzilla) and developers are expected to file stabilization requests on these arches.
This is the current behaviour and shall be the default if nothing is specified for an architecture.
Transitional means that the architecture does not maintain a consistent stable dependency graph but uses stable keywords on some packages. When dependency graphs of packages with stable keywords are tested, they are tested only for ~arch systems, i.e. stable keywords are ignored.
Transitional architectures are generally listed after stable architectures, possibly mixed with testing. Developers are expected to file stabilization requests.
A new switch for linting tools may be provided to temporarily upgrade an architecture from transitional to stable status (for architecture team work).
Testing means that the architecture does not use stable keywords at all. Presence of such keywords is considered an error. Consistency is tested only for ~arch.
If arches.desc is present in several repositories, then each file affects packages in the repository in question. If the file does not specify a value for given arch, the value from the master repository is used. However, using it in multiple repositories is discouraged.
Note that the stability status override affects only packages in the slave repository and their direct dependencies. If an arch is set to testing, then master repositories are still permitted to use stable keywords. If it is set to stable, then missing stable keywords in dependencies from the master repository will cause dependency graph inconsistency.
Essentially two cases need to be discussed. Here "old system" designates a Gentoo installation where package manager and/or utilities do not provide arches.desc support yet, "new system" an installation where they do.
Utilities ignore the unknown file.
Repoman and other tools may emit surplus dependency errors when profiles are checked on arches that are transitional (they check the consistency of the stable tree alone, which may fail, since arch is supposed to be treated like ~arch). This affects only development work and can be fixed by updating repoman.
Arches are treated as "stable" by repoman (the current behaviour), with profile status according to profiles.desc. Gentoolkit and other tools trying to determine a list of stable arches shall fall back to the current method of determining stable arches by scanning profiles.desc for stable profiles.