# Backporting patches

Note

This is an advanced topic for developers and maintainers. Readers should familiarize themselves with building and running Open vSwitch, with the git tool, and with the Open vSwitch patch submission process.

The backporting of patches from one git tree to another takes multiple forms within Open vSwitch, but is broadly applied in the following fashion:

- Contributors submit their proposed changes to the latest development branch

- Contributors and maintainers provide feedback on the patches

- When the change is satisfactory, maintainers apply the patch to the development branch.

- Maintainers backport changes from a development branch to release branches.

With regards to Open vSwitch user space code and code that does not comprise the Linux datapath and compat code, the development branch is main in the Open vSwitch repository. Patches are applied first to this branch, then to the most recent branch-X.Y, then earlier branch-X.Z, and so on. The most common kind of patch in this category is a bugfix which affects main and other branches.

## Changes to userspace components

Patches which are fixing bugs should be considered for backporting from main to release branches. Open vSwitch contributors submit their patches targeted to the main branch, using the `Fixes` tag described in Submitting Patches. The maintainer first applies the patch to main, then backports the patch to each older affected tree, as far back as it goes or at least to all currently supported branches. This is usually each branch back to the oldest maintained LTS release branch or the last 4 release branches if the oldest LTS is newer.

If the fix only affects a particular branch and not main, contributors should submit the change with the target branch listed in the subject line of the patch. Contributors should list all versions that the bug affects. The `git format-patch` argument `--subject-prefix` may be used when posting the patch, for example:

    $ git format-patch HEAD --subject-prefix="PATCH branch-2.7"

If a maintainer is backporting a change to older branches and the backport is not a trivial cherry-pick, then the maintainer may opt to submit the backport for the older branch on the mailing list for further review. This should be done in the same manner as described above.

## Changes to Linux kernel components

Changes to the Linux kernel components in Open vSwitch go through review in the upstream Linux Netdev community. The Netdev Maintainer Handbook describes the general process for merging patches to the upstream Linux kernel networking subsystem.

Backports to older kernel versions are handled via the Stable tree mechanism.

Backports for Linux datapath code are no longer accepted into the Open vSwitch tree as that code is not present in the Open vSwitch distribution since Open vSwitch 3.0.