..  SPDX-License-Identifier: BSD-3-Clause
    Copyright 2018 The DPDK contributors

.. _stable_lts_releases:

DPDK Stable Releases and Long Term Support
==========================================

This section sets out the guidelines for the DPDK Stable Releases and the DPDK
Long Term Support releases (LTS).


Introduction
------------

The purpose of the DPDK Stable Releases is to maintain releases of DPDK with
backported fixes over an extended period of time. This provides downstream
consumers of DPDK with a stable target on which to base applications or
packages.

The primary characteristics of stable releases is that they attempt to
fix issues and not introduce any new regressions while keeping backwards
compatibility with the initial release of the stable version.

The Long Term Support release (LTS) is a designation applied to a Stable
Release to indicate longer term support.


Stable Releases
---------------

Any release of DPDK can be designated as a Stable Release if a
maintainer volunteers to maintain it and there is a commitment from major
contributors to validate it before releases.
If a version is to be a "Stable Release", it should be designated as such
within one month of that version being initially released.

A Stable Release is used to backport fixes from an ``N`` release back to an
``N-1`` release, for example, from 16.11 to 16.07.

The duration of a stable is one complete release cycle (4 months). It can be
longer, up to 1 year, if a maintainer continues to support the stable branch,
or if users supply backported fixes, however the explicit commitment should be
for one release cycle.

The release cadence is determined by the maintainer based on the number of
bugfixes and the criticality of the bugs. Releases should be coordinated with
the validation engineers to ensure that a tagged release has been tested.


LTS Release
-----------

A stable release can be designated as an LTS release based on community
agreement and a commitment from a maintainer. The current policy is that each
year's November (X.11) release will be maintained as an LTS for 3 years,
however that is dependent on continued community support for validation.

After the X.11 release, an LTS branch will be created for it at
https://git.dpdk.org/dpdk-stable where bugfixes will be backported to.

A LTS release may align with the declaration of a new major ABI version,
please read the :doc:`abi_policy` for more information.

It is anticipated that there will be at least 3 releases per year of the LTS
or approximately 1 every 4 months. This is done to align with the DPDK main
branch releases so that fixes have already gone through validation as part of
the DPDK main branch release validation. However, the cadence can be shorter or
longer depending on the number and criticality of the backported
fixes. Releases should be coordinated with the validation engineers to ensure
that a tagged release has been tested.

For a list of the currently maintained stable/LTS branches please see
the latest `stable roadmap <https://core.dpdk.org/roadmap/#stable>`_.

At the end of the 3 years, a final X.11.N release will be made and at that
point the LTS branch will no longer be maintained with no further releases.


What changes should be backported
---------------------------------

Backporting should be limited to bug fixes. All patches accepted on the main
branch with a Fixes: tag should be backported to the relevant stable/LTS
branches, unless the submitter indicates otherwise. If there are exceptions,
they will be discussed on the mailing lists.

Fixes suitable for backport should have a ``Cc: stable@dpdk.org`` tag in the
commit message body as follows::

     doc: fix some parameter description

     Update the docs, fixing description of some parameter.

     Fixes: abcdefgh1234 ("doc: add some parameter")
     Cc: stable@dpdk.org

     Signed-off-by: Alex Smith <alex.smith@example.com>


Fixes not suitable for backport should not include the ``Cc: stable@dpdk.org`` tag.

To support the goal of stability and not introducing regressions,
new code being introduced is limited to bug fixes.
New features should not be backported to stable releases.

In some limited cases, it may be acceptable to backport a new feature
to a stable release. Some of the factors which impact the decision by
stable maintainers are as follows:

* Does the feature break API/ABI?
* Does the feature break backwards compatibility?
* Is it for the latest LTS release (to avoid LTS upgrade issues)?
* Is there a commitment from the proposer or affiliation to validate the feature
  and check for regressions in related functionality?
* Is there a track record of the proposer or affiliation validating stable releases?
* Is it obvious that the feature will not impact existing functionality?
* How intrusive is the code change?
* What is the scope of the code change?
* Does it impact common components or vendor specific?
* Is there a justifiable use case (a clear user need)?
* Is there a community consensus about the backport?

Performance improvements are generally not considered to be fixes,
but may be considered in some cases where:

* It is fixing a performance regression that occurred previously.
* An existing feature in LTS is not usable as intended without it.

APIs marked as ``experimental`` are not considered part of the ABI version
and can be changed without prior notice. This is necessary for the API to be
improved and stabilized and become part of the ABI version in the future.

However, in LTS releases ``experimental`` API should not be changed as there
will not be a future ABI version on the branch and compatibility with previous
release of an LTS version is of the highest importance.

The Stable Mailing List
-----------------------

The Stable and LTS release are coordinated on the stable@dpdk.org mailing
list.

All fix patches to the main branch that are candidates for backporting
should also be CCed to the `stable@dpdk.org <https://mails.dpdk.org/listinfo/stable>`_
mailing list.


Releasing
---------

A Stable Release will be released by:

* Tagging the release with YY.MM.n (year, month, number).
* Uploading a tarball of the release to dpdk.org.
* Sending an announcement to the `announce@dpdk.org <https://mails.dpdk.org/listinfo/announce>`_
  list.

Stable releases are available on the `dpdk.org download page <https://core.dpdk.org/download/>`_.
