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Build Fedora with DNF 5

Summary

We are proposing to change the Mock configuration in Mock (mock-core-configs), Koji, and Copr to use DNF 5 as Mock's package manager instead of DNF 4. DNF 5 would be used by Mock to install build dependencies into chroots for package builds. This change is related to the build infrastructure and is distinct from changing the default package manager in Fedora.

Owner

Current status

Detailed Description

DNF 5 is a new package manager intended to replace DNF: https://dnf5.readthedocs.io/en/latest/about.html. It offers significant performance improvements over DNF while achieving lower memory usage and disk footprint. The switch to DNF 5 was originally planned for Fedora 39, but it's been postponed to (likely) Fedora 41: https://pagure.io/fesco/issue/3039.

In the meantime, we would like to start building Fedora with DNF 5. The set of package management features that Mock needs for setting up buildroots is small compared to the full capabilities of DNF, so it's a good place to start deploying DNF 5. We will be able to test the stability of DNF 5 at a large scale and gather data about its performance.

The Mock developers have been working alongside the DNF 5 developers for a while to ensure Mock can use DNF 5, per this tracking issue: https://github.com/rpm-software-management/mock/issues/894. The two remaining items on that issue are "optional" items that are not blocking this proposed change.

Feedback

Benefit to Fedora

With the switch to DNF 5 as the default package manager on the horizon, the build infrastructure offers an opportunity to subject a crucial subset of DNF 5's features to heavy testing. This change will let us verify that every build dependency in the distribution is installable by DNF 5.

In addition, we expect a substantial performance improvement for package builds that spend a significant portion of their time installing build dependencies. Larger, compilation-heavy packages likely won't see much improvement; the difference will be most apparent when building many smaller packages. Switching the build system over to DNF 5 will let us measure the performance improvement over DNF across a wide variety of install transactions.

Scope

  • Proposal owners:

The work to support DNF 5 in Mock is done already. This change should be as simple as setting the Mock option config_opts['package_manager'] = 'dnf5' in Mock, Koji, and Copr for F40+ builds (Koji config option exists from the yum -> dnf4 era). The dnf5 doesn't necessarily have to be installed on building hosts - in such a case, Mock will automatically use /bin/dnf-3 (DNF4) from the host to install DNF5 into the bootstrap chroot, to further use *that* DNF5 for build chroot installation.

  • Other developers:
  • Policies and guidelines: N/A (not needed for this Change)
  • Trademark approval: N/A (not needed for this Change)
  • Alignment with Community Initiatives:

Upgrade/compatibility impact

None expected.


How To Test

There are no special steps needed to test the change after it happens (updated mock-core-configs package is installed on your host), just enjoy the installation speedup.

There's a way to test this on Fedora 37+ or EPEL8+ host (builder) in advance. Considering you want to build SRCRPM like mock -r fedora-40-x86_64 your.src.rpm, you can do this instead:

1. mock -r fedora-40-x86_64 --scrub=all (mandatory step to cleanup DNF4 from all caches)

2. mock -r fedora-40-x86_64 --config-opts=package_manager=dnf5 your.src.rpm (DNF5 is installed and cached in bootstrap)

3. mock -r fedora-40-x86_64 --scrub=all (to invalidate caches again)


User Experience

This change will mostly be invisible to users. The builds, namely the buildroot preparation, will be much faster.

Dependencies

None, both DNF4 and DNF5 are already part of the distribution and nothing is changing for them.


Contingency Plan

  • Contingency mechanism: (What to do? Who will do it?)

Revert the F40 Mock configuration in Koji and Copr back to using dnf (5-minute work).

  • Contingency deadline:

F40 Beta freeze

We plan to implement the change at least a month before the F40 Mass Rebuild event starts, ideally as soon as possible. The builds conducted prior to the mass rebuild will offer us added assurance that the mass rebuild won't be affected, and will provide us with time to address any potential issues in advance.

  • Blocks release? Yes

Documentation

Mock bootstrap, aka why DNF5 is not necessary on host

Package manager support in Mock


Release Notes

The build system has now transitioned to using the DNF5 package manager for preparing Fedora 40 package building environment, replacing the DNF4 utilized for earlier Fedora releases. The introduction of DNF5 makes the build environment preparation faster. This is also the initial phase of migrating towards DNF5 as the default package manager in forthcoming Fedora releases.

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