[dpdk-dev] [PATCH v2 2/3] doc: changes to abi policy introducing major abi versions
mdr at ashroe.eu
Fri Aug 2 17:38:57 CEST 2019
This policy change introduces major ABI versions, these are
declared every year, typically aligned with the LTS release
and are supported by subsequent releases in the following year.
This change is intended to improve ABI stabilty for those projects
Signed-off-by: Ray Kinsella <mdr at ashroe.eu>
doc/guides/contributing/abi_policy.rst | 272 +++++++++++++++++++++++----------
doc/guides/contributing/stable.rst | 36 +++--
2 files changed, 213 insertions(+), 95 deletions(-)
diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
index 55bacb4..fa78622 100644
@@ -1,5 +1,5 @@
.. SPDX-License-Identifier: BSD-3-Clause
- Copyright 2018 The DPDK contributors
+ Copyright 2019 The DPDK contributors
@@ -9,25 +9,37 @@ DPDK ABI/API policy
-This document details some methods for handling ABI management in the DPDK.
+This document details the DPDK ABI/API management policy, to ensure the
+long-term stability of the DPDK ABI/API.
-#. 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 LTS release.
+#. ABI versioning is managed at a project level in DPDK, with the supported ABI
+ version reflected in all library's soname.
+#. The ABI should be preserved and not changed lightly. The ABI may still be
+ changed, by following the outlined deprecation process.
+#. The addition of symbols is generally not problematic. The modification of
+ symbols should be managed with ABI versioning.
+#. The removal of symbols is considered an ABI breakage, once approved these
+ will form part of the next ABI version.
+#. Libraries or APIs marked as ``experimental`` are not considered part of the
+ major ABI version and may change without constraint.
+#. Updates to the minimum hardware requirements, which drop support for hardware
+ which was previously supported, should be treated as an ABI change.
+ Note that in 2019 the DPDK community stated it's intention to move to ABI
+ stable releases over a number of releases. 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
+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 +51,40 @@ 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.
+The DPDK ABI policy
-The DPDK ABI policy
+A major ABI version is declared every years, aligned with that years 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.
+At the declaration of a major ABI version, major version numbers encoded in
+libraries soname's are bumped to indicate the new version, with minor version
+reset to 0. An example would be ``librte_eal.so.20.3`` would become
+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.
-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.
+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 20.0.
-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 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 may be deprecated in whole or in part as needed by a given
-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. The requirements
+for doing so are:
#. At least 3 acknowledgments of the need to do so must be made on the
dpdk.org mailing list.
@@ -71,81 +93,165 @@ 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 compatibly with the major ABI version must be maintained through
+ `<ABI versioning>`_, with forward-only compatibility offered for any ABI
+ changes that are indicated to be part of the next ABI version.
+ - In situations were backward compatibility is not possible, read the
+ section `<ABI Breakages>`_.
-#. A full deprecation cycle, as explained above, must be made to offer
- downstream consumers sufficient warning of the change.
+ - No backward or forward compatibility is offered for API changes marked as
+ ``experimental``, as described in the section `<Experimental APIs>`_.
-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.
+#. If a newly proposed API functionally replaces an existing one, when the new
+ API becomes non-experimental, then the old one is marked with
+ - The depreciated API should follow the notification process to be removed,
+ see `<Examples of 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 ABI compatibility preserving code rests
+ with the original contributor of the ABI changes, then with the
+ contributor's company and then finally with the maintainer.
+ 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.
+ Note that forward-only compatibility is offered for those changes made
+ between major ABI versions. As a library's soname however only describes
+ 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.
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.
+For those ABI changes that may be too significant to reasonably maintain
+multiple versions. In those cases, ABIs may be updated without backward
+compatibility being provided.
+The additional requirements to approve an ABI breakage, on top of those
+that described in the section `<ABI Changes>`_ are:
+#. 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 DPDK 20.0.
+* 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 at DPDK20.0`` is
+ preserved through `<ABI versioning>`_.
+ - The new function may be marked with the ``__rte_experimental`` tag for a
+ number of releases, as described in the section `<Experimental APIs>`_;
+ - Once ``rte_foo(uint8_t bar)`` becomes non-experimental ``rte_foo()`` is then
+ declared as ``__rte_depreciated``, with an associated deprecation notice
+* 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
+ note on `forward-only`_ compatibility.
+* 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 21.0 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
+ supporting 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
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
+ 21.0, 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 21.0, in DPDK version
-* 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.
-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
@@ -167,3 +273,11 @@ 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.
+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 ABI
+versioning, with minor version incremented with each ABI change to library.
diff --git a/doc/guides/contributing/stable.rst b/doc/guides/contributing/stable.rst
index 6a5eee9..db783c7 100644
@@ -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 `<DPDK ABI/API 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
@@ -68,10 +71,13 @@ 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 master
-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.
+Backporting is a naturally conservative activity, and therefore should only
+include bug fixes and support for new hardware, were adding support does not
+necessitate DPDK ABI/API changes.
+All patches accepted on the master 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 at dpdk.org`` tag in the
commit message body as follows::
@@ -86,13 +92,18 @@ commit message body as follows::
Signed-off-by: Alex Smith <alex.smith at example.com>
-Fixes not suitable for backport should not include the ``Cc: stable at dpdk.org`` tag.
+Fixes not suitable for backport should not include the ``Cc: stable at dpdk.org``
-Features should not be backported to stable releases. It may be acceptable, in
-limited cases, to back port features for the LTS release where:
+New features, with the exception of new hardware support, should not be
+backported to stable releases. In the case of new hardware support or any other
+exceptional circumstances limited backporting maybe permitted to the LTS release
-* There is a justifiable use case (for example a new PMD).
-* The change is non-invasive.
+* There is a justifiable use case, for example the change is required to support
+ a new platform or device (for example a new PMD).
+* The change is ABI/API preserving, it does not present an obvious "new feature"
+ to end consumer.
* The work of preparing the backport is done by the proposer.
* There is support within the community.
@@ -119,10 +130,3 @@ A Stable Release will be released by:
Stable releases are available on the `dpdk.org download page <http://core.dpdk.org/download/>`_.
-The Stable Release should not be seen as a way of breaking or circumventing
-the DPDK ABI policy.
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