.. SPDX-License-Identifier: BSD-3-Clause
- Copyright 2018 The DPDK contributors
+ Copyright 2019 The DPDK contributors
-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 no more frequently than yearly. Compatibility
+ with the major ABI version is mandatory in subsequent releases until a new
+ major ABI version is declared.
+#. Major ABI versions are usually but not always declared aligned with a
+ :ref:`LTS release <stable_lts_releases>`.
+#. The ABI version is managed at a project level in DPDK, and is reflected in
+ all non-experimental :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>` may
+ change without constraint, as they are not considered part of an ABI version.
+#. 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 its intention to move to ABI stable
+ releases, over a number of release cycles. This change begins 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. Additional implementation detail can be
+ found in the :ref:`release notes <20_02_abi_changes>`.
+
+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
preserved, or (when modified), done in such a way that the application is unable
to behave improperly or in an unexpected fashion.
+.. _figure_what_is_an_abi:
+
+.. figure:: img/what_is_an_abi.*
+
+ Illustration of DPDK API and ABI.
-ABI/API Deprecation
--------------------
+
+What is an ABI version?
+~~~~~~~~~~~~~~~~~~~~~~~
+
+An ABI version is an instance of a library's ABI at a specific release. Certain
+releases are considered to be milestone releases, the yearly LTS release for
+example. The ABI of a milestone release may be declared as a 'major ABI
+version', where this ABI version is then supported for some number of subsequent
+releases and is annotated in the library's :ref:`soname<what_is_soname>`.
+
+ABI version support in subsequent releases facilitates application upgrades, by
+enabling applications built against the milestone release to upgrade to
+subsequent releases of a library without a rebuild.
+
+More details on major ABI version can be found in the :ref:`ABI versioning
+<major_abi_versions>` guide.
The DPDK ABI policy
-~~~~~~~~~~~~~~~~~~~
+-------------------
+
+A new major ABI version is declared no more frequently than yearly, with
+declarations usually aligning with a LTS release, e.g. ABI 20 for DPDK 19.11.
+Compatibility with the major ABI version is then mandatory in subsequent
+releases until the next major ABI version is declared, e.g. ABI 21 for DPDK
+20.11.
+
+At the declaration of a major ABI version, major version numbers encoded in
+libraries' sonames 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``.
-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.
+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
+sonames do not change.
-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.
+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 may be deprecated in whole or in part as needed by a given
-update.
+An ABI version is supported in all new releases until the next major ABI version
+is declared. When changing the major ABI version, the release notes will detail
+all 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:
+.. _figure_abi_stability_policy:
+
+.. figure:: img/abi_stability_policy.*
+
+ Mapping of new ABI versions and ABI version compatibility to DPDK
+ releases.
+
+.. _abi_changes:
+
+ABI Changes
+~~~~~~~~~~~
+
+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 deprecation
+ notices. This process however should not be undertaken lightly, as a general
+ rule ABI stability is extremely important for downstream consumers of DPDK.
+ The API should only be changed for significant reasons, such as performance
+ enhancements. API 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.
no maintainer is available for the component, the tree/sub-tree maintainer
for that component must acknowledge the ABI change instead.
+ - The acknowledgment of three members of the technical board, as delegates
+ 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::
+ - In situations in which an ``experimental`` symbol has been stable for some
+ time. When promoting the symbol to become part of the next ABI version, the
+ maintainer may choose to provide an alias to the ``experimental`` tag, so
+ as not to break consuming applications.
+
+#. 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 its 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 deprecation 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()`` ; ``rte_foo()``
+ is part of the major ABI version ``20``.
+
+* DPDK 20.02 release defines a new function ``rte_foo(uint8_t bar)``.
+ 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
+ declared as ``__rte_deprecated`` and an deprecation notice is 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 ABI version. The application can only
+ ensure its runtime dependencies are met by specifying ``DPDK (>= 20.2)`` as
+ an explicit package dependency, as the soname can 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`` and ``rte_foo()`` may be
+ removed.
+
+.. _deprecation_notices:
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
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.
+
+After the experimental tag has been formally removed, a tree/sub-tree maintainer
+may choose to offer an alias to the experimental tag so as not to break
+applications using the symbol. The alias is then dropped at the declaration of
+next major ABI version.
+
+Libraries
+~~~~~~~~~
+
+Libraries marked as ``experimental`` are entirely not considered part of an ABI
+version, and may change without warning at any time.
git.droids-corp.org / dpdk.git / blobdiff