Repository Layout¶

The repository is based on the upstream Linux kernel tree. All branches except master, though, are downstream-only.

Branches¶

os-build, a.k.a “the development branch”¶

Frequency: Merges ‘master’ branch daily

The os-build branch is the development branch of the tree. The os-build branch tracks the latest version of the kernel patches for RHEL and Fedora, as well as the kernel configuration and build scripts. This is the branch to send merge request to. When a new release is made, this branch is merged into the release branch. Configuration and build scripts can be found in the redhat/ directory. Refer to the Configuration section below for more details.

If this branch does not compile or boot, then please see ark-latest branch below.

master¶

Frequency: Mirrors Linus’s tree

The master branch tracks Linus’s master branch (i.e. “mainline”).

ark-latest¶

Frequency: Reset daily after os-build branch merges ‘master’

This branch points to the latest release branch. This branch may differ slightly from os-build and contain critical patches that resolve compile or boot issues. This is not a development branch, do not base merge requests off this branch.

Release branches¶

Each time the kernel is rebased, a set of branches is created to track that release.

ark/patches/vX.Y[-rcN]¶

Branches in this format (e.g. ark/patches/v5.4-rc1 or ark/patches/v5.3) contain the kernel patches ARK carries for that particular kernel release. These are merged into the ark/vX.Y release branches.

ark/vX.Y[-rcN]¶

Branches in this format (e.g. ark/v5.4-rc1 or ark/v5.3) contain the set of patches that were added on top of the upstream kernel release along with the configuration and build scripts. They can be checked out and built into RPMs. The master branch points to the latest version of these branches.

Tags¶

vX.Y[-rcN]¶

Tags in this format (e.g. v5.4-rc1 or v5.3) are the upstream Linux kernel tags from Linus’s tree.

kernel-X.Y.Z-N.<dist> and kernel-X.Y.Z-0.rcN.YYYYMMDDgit<short-hash>.<dist>¶

Tags in this format (e.g. kernel-5.4.0-1.elrdy, kernel-5.6.0-1.fc33, or kernel-5.6.0-0.rc5.20200314gitabcd1234.fc33) map to the RPM name-version-release tuple in the build system. These can be used to check out the source tree used to build that RPM. Tags with the elrdy dist are Always Ready kernel releases and tags with the fcNN dist are Fedora kernels.

The tags come in two varieties. The first is kernel builds based off an upstream tag. kernel-5.4.0-1.elrdy and kernel-5.6.0-0.rc6.fc33 fall into this category. The second variety, which includes a date and commit hash, is based off a snapshot of Linus’s master branch for that particular day. The git commit hash included in the release is the commit in Linus’s tree the build is based on, not the commit in the Fedora source tree.

Fedora RPM tagging in the ARK kernel began in May 2020 for fc33. Previous RPM tags are not available in the ARK kernel tree.

Configuration¶

The configuration layout is somewhat complicated. All configuration is located on the os-build branch in redhat/configs/. Inside this directory there are a number of scripts used to automatically generate complete configurations, along with a number of directories that contain configuration snippets. At this time, there are three main configuration directories: rhel, common, and fedora. rhel and fedora are configuration “flavors”, while common is shared configuration across flavors.

A flavor is defined by:

Adding the flavor name to redhat/configs/flavors on its own line.
Create a directory using your flavor name in redhat/configs/ that matches the layout of other flavors.
Defining a configuration priority by creating a file called redhat/configs/priority.$flavorname. This file needs to define a number of bash variables that describe the priority of the various configuration directories and should include the directory you defined in step 2.

common and pending-rhel¶

The common directory contains configuration values that are shared across all configuration “flavors”. For a configuration to be in common, it MUST be reviewed and approved by one or more Red Hat subsystem maintainers since it affects RHEL. A flavor’s configurations can override settings in common, so it’s not guaranteed settings in common are the same across all flavors. It’s simply a good place to set common values across the flavors and use as a base for new flavors.

pending-rhel is where configuration options that have not been reviewed are placed. Automation creates snippets for all new configuration options exposed during a rebase of ARK in the pending-rhel directory, at which point subsystem maintainers review the options and set them as appropriate before moving them into common.

New RHEL configurations are placed in pending-rhel because it is assumed that RHEL generally has the most conservative settings, whereas other flavors like Fedora will be (for the most part) a superset of the RHEL configuration.

fedora and pending-fedora¶

The fedora directory contains settings that have been reviewed by Fedora kernel maintainers for the Fedora Rawhide kernel.

Since Fedora tends to turn on more things than RHEL, it’s common for a rebase to expose new configuration options that only apply to Fedora. For this reason, Fedora has a pending-fedora directory as well. pending-fedora contains settings that are not exposed by the common configuration set and only apply to Fedora. It is, like pending-rhel, populated automatically during a rebase. A Fedora kernel maintain can review the settings at their leisure and move them over to fedora as they do so.