britney2-ubuntu/doc/hints.md

#! TITLE: Britney hints documentation #! SUBTITLE: How to override the britney policies

Britney hints

This document describes the "britney hints". These are basically small instructions to britney. The vast majority of them involve overriding a quality gating policy in britney. However, there are a few hints that assist britney into finding solutions that it cannot compute itself.

Related configuration

The configuration HINTSDIR determines which directory contains the so called "hints files". This is complimented with the HINTS_<NAME> configurations that defines a "hint file" and the related hint permissions for it.

For each HINTS_<NAME> configuration, britney will attempt to read <HINTSDIR>/<name>. Note that it lowercases <NAME> when looking for the file.

Configuration example:

HINTSDIR = /etc/britney2/hints
HINTS_ANNA = ALL
HINTS_JOHN = STANDARD
HINTS_FREEZE = block block-all block-udeb
HINTS_AUTO-REMOVALS = remove

There are no fixed rules for how to use hints files. Though usually, each person with permissions to give hints to britney will have their own hint file along with write permissions for that file. It can also make sense to create hint files for "roles". Like in the above example there are two human hints (anna and john) plus two non-human hinters (freeze and auto-removals).

Format of the hint file

The hint file is a plain text file with line-based content. Empty and whitespace-only lines are ignored. If the first (non-whitespace) character is a #, then britney considers it a comment and ignores it. However, other tooling may interpret these comments (as is the case for e.g. some parts of the Debian infrastructure).

The remaining lines are considered space-separated lists, where the first element must be a known hint. The remaining elements will be interpreted as its arguments. Britney generally warns on and then discards unknown hints or hints with invalid arguments.

The following are common types of arguments for hints:

• Unversioned item, format: <item name>
• Versioned item, format: <item name>/<version>
• Architecture-qualified versioned item: <item name>/<version>/<architecture>

(The above-mentioned types correspond to britney migration item types)

Generally, for hints, all item names will be names of source packages. Furthermore, some hints also accept a - before the item name. This generally refers to the removal of said item rather than the migration of the hint.

Hints

There are the following type of hints:

• Policy overrides
• Migration selections (with or without overrides)
• Other

Policy override hints

The policy override hints are used to disable or tweak various policies in britney. Their effects are generally very precise ways of accepting specific regressions or disabling various checks.

Some of these items are built-in while others are related to specific policies. In the latter case, they are only valid if the given policy is enabled (as the policy registers them when it is enabled).

block-all <type>

Usually used during freezes to prevent migrations by default.

The <type> can be one of:

• source: Blocks all source migrations. This is a superset of new-source.
• new-source: Block source migrations if the given source is not already in the target suite. (Side-effect: Removed packages will not re-enter the taget suite automatically).

All variants of these can be overruled by a valid unblock-hint.

Note that this does not and cannot restrict architecture specific migrations (e.g. binNMUs or first time builds for architectures).

block <action list>, block-udeb <action list>

Prevent the items in the <action list> from migrating until the hint is removed or overruled by the equivalent unblock hint (or a remove-hint). All items in the <action list> must be unversioned items and can be prefixed with - to prevent removal by built-in policies. However, it will not prevent removals requested by a removal-hint.

The block-udeb is mainly intended for preventing accidental migration of installer-related packages during the later stages of the release cycle.

Note that this does not and cannot restrict architecture specific migrations (e.g. binNMUs or first time builds for architectures).

unblock <action list>, unblock-udeb <action list>

Enable the items in <action list> to migrate by overriding block-, block-all- or block-udeb-hints. The unblock-hint (often under its synonym approve) is also used to approve migrations from source suites that require approval.

The items in <action list> must all be versioned items.

The unblock-udeb is mainly intended for preventing accidental migration of installer-related packages during the later stages of the release cycle.

The two types of block hint must be paired with their corresponding unblock hint - i.e. an unblock-udeb does not override a block.

approve <action list>

A synonym of unblock. The variant is generally used for approving migrations from suites that require approvals.

Aside from the tab-completion in the hint testing interface, which will give different suggestions to approve and unblock, the rest of britney will consider them identical.

age-days <days> <action list>

Set the length of time which the listed action items must have been in unstable before they can be considered candidates. This may be used to either lengthen or reduce the default time period. All items in <action list> must be versioned items.

If multiple age-days hints for a single package are available, whichever is encountered first during parsing overrides the others.

Provided by the age policy.

urgent <action list>

Approximately equivalent to age-days 0 <action list>, with the distinction that an "urgent" hint overrides any "age-days" hint for the same action item.

Provided by the age policy.

ignore-rc-bugs <bugs> <action list>

The <bugs> argument is a comma separated list of bugs that affect the items in <action list>. Britney will ignore these bugs when determining whether the migration items have regressed compared to the target suite. All items in <action list> must be versioned items.

Currently britney supports at most one active ignore-rc-bugs per migration item.

Provided by the bugs policy

ignore-piuparts <action list>

The items in <action list> will not be blocked by regressions in results from piuparts tests. All items in <action list> must be versioned items.

Provided by the piuparts policy

force <action list>

Override all policies that claim the items in <action list> have regressions or are otherwise not ready to migrate. All items in the <action list> must be versioned items or architecture qualified versioned items.

This hint does not guarantee that they will migrate. To ensure that, you will have to combine it with a force-hint. However, please read the warning in the documentation for force-hint before you do this.

Migration selection hints

All migration selection hints work on an "action list". This consists of at least 1 or more of the following (in any combination):

• Versioned item (e.g. coreutils/8.27)
• Architecture qualified versioned item (e.g. coreutils/8.27-1/amd64)
• The removal of either of the above (e.g. -coreutils/8.27-1 or -coreutils/8.27-1/amd64)

All elements in the action list must be valid at the time the hint is attempted. Notably, if one action has already been completed, the entire hint is rejected as invalid.

easy <action list>

Perform all the migrations and removals denoted by <action list> as if it were a single migration group. If the end result is equal or better compared to the original situation, the action is committed.

This hint is primarily useful if britney fails to compute a valid solution for a concrete problem with a valid solution. Although, in many cases, britney will generally figure out the solution on its own.

Note that for easy the <action list> must have at least two elements. There is no use-case where a single element for easy will make sense (as britney always tries those).

hint <action list>

Perform all the migrations and removals denoted by <action list> as if it were a single migration group. After that, process all remaining (unmigrated) items and accept any that can now be processed. If the end result is equal or better compared to the original situation, the result is committed. Otherwise, all actions triggered by the hint are rolled back.

The primary difference between easy and hint is who carries the burden of finding the solution. In an easy hint, the hinter must provide a full valid and self-contained solution. Whereas with a hint, the hinter can basically say "I want X to migrate, try to figure out a solution for it". For the same reason, hint-hints are rather expensive and should be used sparingly.

This hint is primarily useful if britney fails to compute a valid solution for a concrete problem with a valid solution. Although, in many cases, britney will generally figure out the solution on its own.

Caveat: Due to "uninstallability trading", this hint may cause undesireable changes to the target suite. In practise, this is rather rare but the hinter is letting britney decide what "repairs" the situation.

force-hint <action list>

The provided <action list> is migrated as-is regardless of what is broken by said migration. This often needs to be paired with a force-hint to ensure that the actions are considered as valid candidates.

This hint is generally useful when the provided <action list> is more desirable than the resulting breakage.

Caveat: Be sure to test the outcome of these hints. A last minute change can have long lasting undesireable consequences on the end result.

Other hints

This section cover hints that have no other grouping.

remove <action list>

Britney should attempt to remove all items in the <action list> from the target suite. The <action list> must consist entirely of versioned items (note the items should not be prefixed with "-").

If an item in <action list> is not in the target suite that item is silently ignored.

Note: It is not possible to do architecture specific removals via remove-hints.