@@ -1,33 +1,46 @@
.. SPDX-License-Identifier: BSD-3-Clause
- Copyright 2018 The DPDK contributors
+ Copyright 2019 The DPDK contributors
-.. abi_api_policy:
+.. _abi_policy:
-DPDK ABI/API policy
-===================
+ABI Policy
+==========
Description
-----------
-This document details some methods for handling ABI management in the DPDK.
+This document details the management policy that ensures the long-term stability
+of the DPDK ABI and API.
General Guidelines
------------------
-#. Whenever possible, ABI should be preserved
-#. ABI/API may be changed with a deprecation process
-#. The modification of symbols can generally be managed with versioning
-#. Libraries or APIs marked in ``experimental`` state may change without constraint
-#. New APIs will be marked as ``experimental`` for at least one release to allow
- any issues found by users of the new API to be fixed quickly
-#. The addition of symbols is generally not problematic
-#. The removal of symbols generally is an ABI break and requires bumping of the
- LIBABIVER macro
-#. Updates to the minimum hardware requirements, which drop support for hardware which
- was previously supported, should be treated as an ABI change.
-
-What is an ABI
-~~~~~~~~~~~~~~
+#. Major ABI versions are declared every **year** and are then supported for one
+ year, typically aligned with the :ref:`LTS release <stable_lts_releases>`.
+#. The ABI version is managed at a project level in DPDK, with the ABI version
+ reflected in all :ref:`library's soname <what_is_soname>`.
+#. The ABI should be preserved and not changed lightly. ABI changes must follow
+ the outlined :ref:`deprecation process <abi_changes>`.
+#. The addition of symbols is generally not problematic. The modification of
+ symbols is managed with :ref:`ABI Versioning <abi_versioning>`.
+#. The removal of symbols is considered an :ref:`ABI breakage <abi_breakages>`,
+ once approved these will form part of the next ABI version.
+#. Libraries or APIs marked as :ref:`Experimental <experimental_apis>` are not
+ considered part of an ABI version and may change without constraint.
+#. Updates to the :ref:`minimum hardware requirements <hw_rqmts>`, which drop
+ support for hardware which was previously supported, should be treated as an
+ ABI change.
+
+.. note::
+
+ In 2019, the DPDK community stated it's intention to move to ABI stable
+ releases, over a number of release cycles. Beginning with maintaining ABI
+ stability through one year of DPDK releases starting from DPDK 19.11. This
+ policy will be reviewed in 2020, with intention of lengthening the stability
+ period.
+
+What is an ABI?
+~~~~~~~~~~~~~~~
An ABI (Application Binary Interface) is the set of runtime interfaces exposed
by a library. It is similar to an API (Application Programming Interface) but
@@ -39,30 +52,66 @@ Therefore, in the case of dynamic linking, it is critical that an ABI is
preserved, or (when modified), done in such a way that the application is unable
to behave improperly or in an unexpected fashion.
+What is an ABI version?
+~~~~~~~~~~~~~~~~~~~~~~~
-ABI/API Deprecation
--------------------
+An ABI version is an instance of a library's ABI at a specific release. Certain
+releases are considered by the community to be milestone releases, the yearly
+LTS for example. Supporting those milestone release's ABI for some number of
+subsequent releases is desirable to facilitate application upgrade. Those ABI
+version's aligned with milestones release are therefore called 'ABI major
+versions' and are supported for some number of releases.
+
+More details on major ABI version can be found in the :ref:`ABI versioning
+<major_abi_versions>` guide.
The DPDK ABI policy
-~~~~~~~~~~~~~~~~~~~
+-------------------
+
+A major ABI version is declared every year, aligned with that year's LTS
+release, e.g. v19.11. This ABI version is then supported for one year by all
+subsequent releases within that time period, until the next LTS release, e.g.
+v20.11.
+
+At the declaration of a major ABI version, major version numbers encoded in
+libraries soname's are bumped to indicate the new version, with the minor
+version reset to ``0``. An example would be ``librte_eal.so.20.3`` would become
+``librte_eal.so.21.0``.
+
+The ABI may then change multiple times, without warning, between the last major
+ABI version increment and the HEAD label of the git tree, with the condition
+that ABI compatibility with the major ABI version is preserved and therefore
+soname's do not change.
+
+Minor versions are incremented to indicate the release of a new ABI compatible
+DPDK release, typically the DPDK quarterly releases. An example of this, might
+be that ``librte_eal.so.20.1`` would indicate the first ABI compatible DPDK
+release, following the declaration of the new major ABI version ``20``.
-ABI versions are set at the time of major release labeling, and the ABI may
-change multiple times, without warning, between the last release label and the
-HEAD label of the git tree.
+ABI versions, are supported by each release until such time as the next major
+ABI version is declared. At that time, the deprecation of the previous major ABI
+version will be noted in the Release Notes with guidance on individual symbol
+depreciation and upgrade notes provided.
-ABI versions, once released, are available until such time as their
-deprecation has been noted in the Release Notes for at least one major release
-cycle. For example consider the case where the ABI for DPDK 2.0 has been
-shipped and then a decision is made to modify it during the development of
-DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
-release and the modification will be made available in the DPDK 2.2 release.
+.. _abi_changes:
-ABI versions may be deprecated in whole or in part as needed by a given
-update.
+ABI Changes
+~~~~~~~~~~~
-Some ABI changes may be too significant to reasonably maintain multiple
-versions. In those cases ABI's may be updated without backward compatibility
-being provided. The requirements for doing so are:
+The ABI may still change after the declaration of a major ABI version, that is
+new APIs may be still added or existing APIs may be modified.
+
+.. Warning::
+
+ Note that, this policy details the method by which the ABI may be changed,
+ with due regard to preserving compatibility and observing depreciation
+ notices. This process however should not be undertaken lightly, as a general
+ rule ABI stability is extremely important for downstream consumers of DPDK.
+ The ABI should only be changed for significant reasons, such as performance
+ enhancements. ABI breakages due to changes such as reorganizing public
+ structure fields for aesthetic or readability purposes should be avoided.
+
+The requirements for changing the ABI are:
#. At least 3 acknowledgments of the need to do so must be made on the
dpdk.org mailing list.
@@ -71,34 +120,119 @@ being provided. The requirements for doing so are:
no maintainer is available for the component, the tree/sub-tree maintainer
for that component must acknowledge the ABI change instead.
+ - The acknowledgment of a member of the technical board, as a delegate of the
+ `technical board <https://core.dpdk.org/techboard/>`_ acknowledging the
+ need for the ABI change, is also mandatory.
+
- It is also recommended that acknowledgments from different "areas of
interest" be sought for each deprecation, for example: from NIC vendors,
CPU vendors, end-users, etc.
-#. The changes (including an alternative map file) can be included with
- deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
- to provide more details about oncoming changes.
- ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
- More preferred way to provide this information is sending the feature
- as a separate patch and reference it in deprecation notice.
+#. Backward compatibility with the major ABI version must be maintained through
+ :ref:`abi_versioning`, with :ref:`forward-only <forward-only>` compatibility
+ offered for any ABI changes that are indicated to be part of the next ABI
+ version.
-#. A full deprecation cycle, as explained above, must be made to offer
- downstream consumers sufficient warning of the change.
+ - In situations where backward compatibility is not possible, read the
+ section on :ref:`abi_breakages`.
-Note that the above process for ABI deprecation should not be undertaken
-lightly. ABI stability is extremely important for downstream consumers of the
-DPDK, especially when distributed in shared object form. Every effort should
-be made to preserve the ABI whenever possible. The ABI should only be changed
-for significant reasons, such as performance enhancements. ABI breakage due to
-changes such as reorganizing public structure fields for aesthetic or
-readability purposes should be avoided.
+ - No backward or forward compatibility is offered for API changes marked as
+ ``experimental``, as described in the section on :ref:`Experimental APIs
+ and Libraries <experimental_apis>`.
-.. note::
+#. If a newly proposed API functionally replaces an existing one, when the new
+ API becomes non-experimental, then the old one is marked with
+ ``__rte_deprecated``.
+
+ - The depreciated API should follow the notification process to be removed,
+ see :ref:`deprecation_notices`.
+
+ - At the declaration of the next major ABI version, those ABI changes then
+ become a formal part of the new ABI and the requirement to preserve ABI
+ compatibility with the last major ABI version is then dropped.
+
+ - The responsibility for removing redundant ABI compatibility code rests
+ with the original contributor of the ABI changes, failing that, then with
+ the contributor's company and then finally with the maintainer.
+
+.. _forward-only:
+
+.. Note::
+
+ Note that forward-only compatibility is offered for those changes made
+ between major ABI versions. As a library's soname can only describe
+ compatibility with the last major ABI version, until the next major ABI
+ version is declared, these changes therefore cannot be resolved as a runtime
+ dependency through the soname. Therefore any application wishing to make use
+ of these ABI changes can only ensure that it's runtime dependencies are met
+ through Operating System package versioning.
+
+.. _hw_rqmts:
+
+.. Note::
Updates to the minimum hardware requirements, which drop support for hardware
which was previously supported, should be treated as an ABI change, and
- follow the relevant deprecation policy procedures as above: 3 acks and
- announcement at least one release in advance.
+ follow the relevant deprecation policy procedures as above: 3 acks, technical
+ board approval and announcement at least one release in advance.
+
+.. _abi_breakages:
+
+ABI Breakages
+~~~~~~~~~~~~~
+
+For those ABI changes that are too significant to reasonably maintain multiple
+symbol versions, there is an amended process. In these cases, ABIs may be
+updated without the requirement of backward compatibility being provided. These
+changes must follow the `same process :ref:`described above <abi_changes>` as non-breaking
+changes, however with the following additional requirements:
+
+#. ABI breaking changes (including an alternative map file) can be included with
+ deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option, to provide
+ more details about oncoming changes. ``RTE_NEXT_ABI`` wrapper will be removed
+ at the declaration of the next major ABI version.
+
+#. Once approved, and after the depreciation notice has been observed these
+ changes will form part of the next declared major ABI version.
+
+Examples of ABI Changes
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The following are examples of allowable ABI changes occurring between
+declarations of major ABI versions.
+
+* DPDK 19.11 release, defines the function ``rte_foo()``, and ``rte_foo()``
+ as part of the major ABI version ``20``.
+
+* DPDK 20.02 release defines a new function ``rte_foo(uint8_t bar)``, and
+ this is not a problem as long as the symbol ``rte_foo@DPDK20`` is
+ preserved through :ref:`abi_versioning`.
+
+ - The new function may be marked with the ``__rte_experimental`` tag for a
+ number of releases, as described in the section :ref:`experimental_apis`.
+
+ - Once ``rte_foo(uint8_t bar)`` becomes non-experimental ``rte_foo()`` is then
+ declared as ``__rte_depreciated``, with an associated deprecation notice
+ provided.
+
+* DPDK 19.11 is not re-released to include ``rte_foo(uint8_t bar)``, the new
+ version of ``rte_foo`` only exists from DPDK 20.02 onwards as described in the
+ :ref:`note on forward-only compatibility<forward-only>`.
+
+* DPDK 20.02 release defines the experimental function ``__rte_experimental
+ rte_baz()``. This function may or may not exist in the DPDK 20.05 release.
+
+* An application ``dPacket`` wishes to use ``rte_foo(uint8_t bar)``, before the
+ declaration of the DPDK ``21`` major API version. The application can only
+ ensure it's runtime dependencies are met by specifying ``DPDK (>= 20.2)`` as
+ an explicit package dependency, as the soname only may only indicate the
+ supported major ABI version.
+
+* At the release of DPDK 20.11, the function ``rte_foo(uint8_t bar)`` becomes
+ formally part of then new major ABI version DPDK 21.0 and ``rte_foo()`` may be
+ removed.
+
+.. _deprecation_notices:
Examples of Deprecation Notices
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -106,46 +240,42 @@ Examples of Deprecation Notices
The following are some examples of ABI deprecation notices which would be
added to the Release Notes:
-* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
- to be replaced with the inline function ``rte_foo()``.
+* The Macro ``#RTE_FOO`` is deprecated and will be removed with ABI version
+ 21, to be replaced with the inline function ``rte_foo()``.
* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
- in version 2.0. Backwards compatibility will be maintained for this function
- until the release of version 2.1
+ in version 20.2. Backwards compatibility will be maintained for this function
+ until the release of the new DPDK major ABI version 21, in DPDK version
+ 20.11.
-* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
+* The members of ``struct rte_foo`` have been reorganized in DPDK 20.02 for
performance reasons. Existing binary applications will have backwards
- compatibility in release 2.0, while newly built binaries will need to
- reference the new structure variant ``struct rte_foo2``. Compatibility will
- be removed in release 2.2, and all applications will require updating and
+ compatibility in release 20.02, while newly built binaries will need to
+ reference the new structure variant ``struct rte_foo2``. Compatibility will be
+ removed in release 20.11, and all applications will require updating and
rebuilding to the new structure at that time, which will be renamed to the
original ``struct rte_foo``.
* Significant ABI changes are planned for the ``librte_dostuff`` library. The
- upcoming release 2.0 will not contain these changes, but release 2.1 will,
+ upcoming release 20.02 will not contain these changes, but release 20.11 will,
and no backwards compatibility is planned due to the extensive nature of
- these changes. Binaries using this library built prior to version 2.1 will
+ these changes. Binaries using this library built prior to ABI version 21 will
require updating and recompilation.
-New API replacing previous one
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-If a new API proposed functionally replaces an existing one, when the new API
-becomes non-experimental then the old one is marked with ``__rte_deprecated``.
-Deprecated APIs are removed completely just after the next LTS.
-
-Reminder that old API should follow deprecation process to be removed.
+.. _experimental_apis:
+Experimental
+------------
-Experimental APIs
------------------
+APIs
+~~~~
-APIs marked as ``experimental`` are not considered part of the ABI and may
-change without warning at any time. Since changes to APIs are most likely
-immediately after their introduction, as users begin to take advantage of
-those new APIs and start finding issues with them, new DPDK APIs will be
-automatically marked as ``experimental`` to allow for a period of stabilization
-before they become part of a tracked ABI.
+APIs marked as ``experimental`` are not considered part of an ABI version and
+may change without warning at any time. Since changes to APIs are most likely
+immediately after their introduction, as users begin to take advantage of those
+new APIs and start finding issues with them, new DPDK APIs will be automatically
+marked as ``experimental`` to allow for a period of stabilization before they
+become part of a tracked ABI version.
Note that marking an API as experimental is a multi step process.
To mark an API as experimental, the symbols which are desired to be exported
@@ -163,7 +293,16 @@ In addition to tagging the code with ``__rte_experimental``,
the doxygen markup must also contain the EXPERIMENTAL string,
and the MAINTAINERS file should note the EXPERIMENTAL libraries.
-For removing the experimental tag associated with an API, deprecation notice
-is not required. Though, an API should remain in experimental state for at least
-one release. Thereafter, normal process of posting patch for review to mailing
-list can be followed.
+For removing the experimental tag associated with an API, deprecation notice is
+not required. Though, an API should remain in experimental state for at least
+one release. Thereafter, the normal process of posting patch for review to
+mailing list can be followed.
+
+Libraries
+~~~~~~~~~
+
+Libraries marked as ``experimental`` are entirely not considered part of an ABI
+version, and may change without warning at any time. Experimental libraries
+always have a major version of ``0`` to indicate they exist outside of
+:ref:`abi_versioning` , with the minor version incremented with each ABI change
+to library.
@@ -1,7 +1,7 @@
.. SPDX-License-Identifier: BSD-3-Clause
Copyright 2018 The DPDK contributors
-.. stable_lts_releases:
+.. _stable_lts_releases:
DPDK Stable Releases and Long Term Support
==========================================
@@ -53,6 +53,9 @@ year's November (X.11) release will be maintained as an LTS for 2 years.
After the X.11 release, an LTS branch will be created for it at
http://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 :ref:`abi_policy` for more information.
+
It is anticipated that there will be at least 4 releases per year of the LTS
or approximately 1 every 3 months. However, the cadence can be shorter or
longer depending on the number and criticality of the backported
@@ -119,10 +122,3 @@ A Stable Release will be released by:
list.
Stable releases are available on the `dpdk.org download page <http://core.dpdk.org/download/>`_.
-
-
-ABI
----
-
-The Stable Release should not be seen as a way of breaking or circumventing
-the DPDK ABI policy.