Summary

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.

Current GIT Trees

All of the current live Ubuntu kernel repositories are at the URL below:

• http://kernel.ubuntu.com/git/

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

• karmic	git://kernel.ubuntu.com/ubuntu/ubuntu-karmic.git
  jaunty	git://kernel.ubuntu.com/ubuntu/ubuntu-jaunty.git
  intrepid	git://kernel.ubuntu.com/ubuntu/ubuntu-intrepid.git
  hardy	git://kernel.ubuntu.com/ubuntu/ubuntu-hardy.git
  gutsy	git://kernel.ubuntu.com/ubuntu/ubuntu-gutsy.git
  feisty	git://kernel.ubuntu.com/ubuntu/ubuntu-feisty.git
  edgy	git://kernel.ubuntu.com/ubuntu/ubuntu-edgy.git
  dapper	git://kernel.ubuntu.com/ubuntu/ubuntu-dapper.git

To find out what else is available try browsing http://kernel.ubuntu.com/git and searching for ubuntu).

Installing GIT

To obtain the git binaries, simply install the git-core package:

• sudo apt-get install git-core

Use apt-get because other tools such as aptitude will autoremove packages that have no install links.

Note that the git package is an entirely different tool which will not do what you want.

Getting the Ubuntu Linux kernel repo

The Ubuntu Linux kernel git repository is located at git://kernel.ubuntu.com/ubuntu/ubuntu-<release>.git. To download a local copy of the repo, use this command:

• git clone git://kernel.ubuntu.com/ubuntu/ubuntu-jaunty.git

This will take some time depending on your connection. There is several hundred megabytes of data to download. If you already have an upstream kernel tree, you can use the --reference option to avoid downloading redundant objects:

• git clone --reference linux-2.6/ git://kernel.ubuntu.com/ubuntu/ubuntu-jaunty.git

This will reduce the amount of data to download to around 6 MiB.

Change into the directory:

• cd ubuntu-jaunty

By default your will have the latest version of the kernel tree, the master tree. You can get a copy of the kernel version you want to work on. To determine which the latest official release is:

• git tag | grep Ubuntu*

This results in something like this:

• Ubuntu-2.6.27-7.10
  Ubuntu-2.6.27-7.11
  Ubuntu-2.6.27-7.12
  Ubuntu-2.6.27-7.13
  Ubuntu-2.6.27-7.14

For example, with the exact above output you could checkout the latest released version of the kernel:

• git checkout Ubuntu-2.6.27-7.14

Once this is complete, you can keep your tree up-to-date by running this command:

• git fetch

** Warning ** During development, the kernel git repository is being constantly rebased against Linus' tree. IOW, Ubuntu specific changes are not being merged, but rather popped off, the tree updated to mainline, and then the Ubuntu specific changes reapplied; they are rebased. 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.

Commit templates

In debian/commit-templates/ there are several templates that must be used when commiting 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.

An example commit log will look like such:

  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>

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 Linent 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

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 /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
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
*do work*
git send-pack kernel.ubuntu.com:/srv/kernel.ubuntu.com/git/<user>/my-git-tree.git 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.

Git tips and tricks

Reordering patches

git rebase -i HEAD~10

allows you to interactively reorder the last 10 patches in your branch. You can also squash some patches together. Just follow the directions at the bottom of the file opened up on typing the command.

More information

Please read the documentation included with the git-core package for more details on git commands. A tutorial is also available at http://www.kernel.org/pub/software/scm/git/docs/gittutorial.html.

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