KernelGitGuide

Git is the source code management tool used by the Linux kernel developer community. Ubuntu has adopted this tool for our own Linux kernel source code so that we can interact better with the community and the other kernel developers.

Installing GIT

To use git you must have the git package installed on your system, which you can install like this: 

  • sudo apt install git

Obtaining the kernel sources for an Ubuntu release using git

The source for each release is maintained in its own git repository on Launchpad.

The git repository is listed in the Vcs-Git: header in the source package and is of the following form: 

  • git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/<source package>/+git/<series>

For example, the standard Jammy kernel is available at: 

  • git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy

There is a tree for each of the currently supported releases as well as any open development and upcoming releases. For example:

  • focal

    git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal

    jammy

    git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy

    noble

    git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble

Replace your intended Ubuntu series in the above URL, and pull the source for the kernels you need.

The distro kernel is always on the master branch in these repositories. Each release also has a master-next branch containing the commits that will go into the master branch and become the next SRU release for that series.

A number of releases also have other source packages which represent other related but divergent kernels for other purposes. For example, there is a specialized AWS kernel available in the linux-aws source package. (Previously these sorts of things were done in Topic Branches and some older kernels and projects still use them.)

If you cannot use the git protocol (perhaps because of a firewall), you can use the slower https protocol. For example:

Obtaining a copy

To obtain a local copy you can simply git clone the repository for the release you are interested in. The git command is part of the git package.

For example to obtain the Jammy tree: 

  • git clone git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy

This will download several hundred megabytes of data. If you plan on working on more than one kernel release you can save space and time by downloading the upstream kernel tree, and use it as a reference. Note that once these two trees are tied together you cannot simply delete or move the virgin Linus tree without manually updating .git/objects/info/alternates in your Ubuntu kernel tree: 

  • git clone git://kernel.ubuntu.com/ubuntu/linux.git
git clone --reference linux git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy
git clone --reference linux git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble

In each case you will end up with a new directory <ubuntu-release> containing the source and the full history which can be manipulated using the git command from within each directory.

If you are an advanced git user, you can also add each Ubuntu series as a remote so that you can have all kernel series you need in a single directory. For example, 

  • git remote add jammy git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy
git fetch jammy
git checkout -b jammy --track jammy/master
git checkout -b jammy-next --track jammy/master-next

By default you will have the latest version of the kernel tree, the master tree. You can switch to any previously released kernel version using the release tags. To obtain a full list of the tagged versions in the release, use the git tag command below: 

  • $ git tag -l Ubuntu-*
Ubuntu-5.4.0-47.51
Ubuntu-5.4.0-48.52
Ubuntu-5.4.0-49.53
Ubuntu-5.4.0-51.56
Ubuntu-5.4.0-52.57
...

To look at the Ubuntu-5.4.0-52.57 version you can simply checkout a new branch pointing to that version: 

  • git checkout -b temp Ubuntu-5.4.0-52.57

You may then manipulate the release - for example, by adding new commits.

Maintaining local changes

During development, the kernel git repository is being constantly rebased against Linus' tree. In other words, Ubuntu specific changes are not being merged, but rather popped off, the tree updated to mainline, and then the Ubuntu specific changes reapplied. There are two ways to track the kernel git tree, depending on whether you have local changes or not:

No Local Changes 

  • git fetch
git reset --hard origin/master

Preserve Local Changes 

  • git fetch
git rebase --onto origin/master origin/master@{1}

Pushing changes to the main repo

Since the main repo is not publicly writable, the primary means for sending patches to the kernel team is using git format-patch. The output from this command can then be sent to the kernel-team mailing list.

Alternatively, if you have a publicly available git repository for which changes can be pulled from, you can use git request-pull to generate an email message to send to the kernel-team mailing list.

Using Commit templates

In debian/commit-templates/ in the source tree there are several templates that should be used when committing changes that you expect to be integrated with the Ubuntu kernel repo. The commit templates contain comments for how to fill out the required information. Also note that all commits must have a Signed-off-by line (the "-s" option to git commit). A typical git commit command will look like: 

  • git commit -s -F debian/commit-templates/patch -e

Note that the -e (edit) option must follow the -F option, else git will not let you edit the commit-template before committing. The primary one you will use is the patch template. It is commented heavily, so should be self explanatory. Some templates do not require editing such as the bumpabi and updateconfigs templates. An example commit log will look like this: 

  • UBUNTU: scsi: My cool change to the scsi subsystem

UpstreamStatus: Merged with 2.6.15-rc3

My cool change to the scsi subsystem makes scsi transfers increase
magically to 124GiB/sec.

Signed-off-by: Joe Cool Hacker <jch@ubuntu.com>

The first line is critical and should summarise the change. The prefix for the line defines the type of the commit (see below). The last line should contain your sign-off for the patch and any acks it has received. The remainder of the text should concisely describe the change.

  • Prefix

    Meaning

    UBUNTU: SAUCE:

    a kernel source modification which is specific to Ubuntu

    UBUNTU: [Config]

    a change to the kernel configuration

    UBUNTU:

    any other change to the debian packaging for the kernel

    <none>

    upstream kernel patches

Patch acceptance criteria

In general, Ubuntu will apply the same criteria applicable to upstream kernel. Here is a checklist of reading and tools related to posting kernel patches:

  • <kernel-directory>/Documentation/SubmittingPatches

  • <kernel-directory>/scripts/checkpatch.pl

  • <kernel-directory>/scripts/cleanpatch

  • <kernel-directory>/scripts/cleanfile

  • <kernel-directory>/scripts/Lindent

If you are creating a new file, it is helpful to run it through cleanfile and/or Lindent before creating a patch
If you have generated a patch, it helps running it through checkpatch.pl and cleanpatch if necessary
Also, using the commit template described above is a good idea for Ubuntu-specific patches

[old] Developers with access to kernel.ubuntu.com

The kernel team has a git repo located on kernel.ubuntu.com (AKA zinc.ubuntu.com) in /srv/kernel.ubuntu.com/git/ubuntu.

You can, if you want, create a clone for yourself in your directory, and just have your changes pulled when ready.

Suggested way to do this: 

  • git clone -l -n -s --bare /srv/kernel.ubuntu.com/git/ubuntu/ubuntu-jaunty.git
vi ubuntu-jaunty.git/description
( give it a descriptive name )
mv ubuntu-jaunty.git/ /srv/kernel.ubuntu.com/git/<user>/my-git-tree.git

You can now push your changes to this tree via ssh. Note the -l -n -s options do a few special things, mainly making your repo share objects with ours (saves space).

Now you need to run git update-server-info in your tree so that it is available over http transport 

  • cd /srv/kernel.ubuntu.com/git/<user>/my-git-tree.git
git update-server-info
mv hooks/post-update.sample hooks/post-update
chmod +x hooks/post-update

For older versions of git instead of using the post-update hook use 

  • chmod +x /srv/kernel.ubuntu.com/git/<user>/my-git-tree.git/hooks/post-commit

To work on your branch, now clone to your local machine from the same origin tree (not the tree you just created on zinc -- this is only for pushing to): 

  • git clone git://kernel.ubuntu.com/ubuntu/ubuntu-jaunty.git my-tree
git remote add zinc ssh://kernel.ubuntu.com/srv/kernel.ubuntu.com/git/<user>/my-git-tree.git
<do work>
git push zinc master

Suggested method for keeping this tree synced with the ubuntu tree, instead of git pull, is to do: 

  • cd my-tree
git fetch origin
git rebase origin

This will keep your changes on top of the original tree (as opposed to being merged). This is also a good idea because during development (e.g. while following the upstream git repo), we frequently rebase to linux-2.6.git upstream, so the HEAD is not always suitable for pull/merge.

Kernel/Dev/KernelGitGuide (last edited 2024-01-23 08:27:33 by anthonywong)