-Managing ABI updates
-====================
+.. SPDX-License-Identifier: BSD-3-Clause
+ Copyright 2018 The DPDK contributors
+
+DPDK ABI/API policy
+===================
Description
-----------
This document details some methods for handling ABI management in the DPDK.
-Note this document is not exhaustive, in that C library versioning is flexible
-allowing multiple methods to achieve various goals, but it will provide the user
-with some introductory methods
General Guidelines
------------------
#. Whenever possible, ABI should be preserved
-#. The libraries marked in experimental state may change without constraint.
-#. The addition of symbols is generally not problematic
+#. 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
---------------
+~~~~~~~~~~~~~~
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.
-The DPDK ABI policy
+
+ABI/API Deprecation
-------------------
+The DPDK ABI policy
+~~~~~~~~~~~~~~~~~~~
+
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.
#. At least 3 acknowledgments of the need to do so must be made on the
dpdk.org mailing list.
-#. The changes (including an alternative map file) must be gated with
- the ``RTE_NEXT_ABI`` option, and provided with a deprecation notice at the
- same time.
- It will become the default ABI in the next release.
+ - The acknowledgment of the maintainer of the component is mandatory, or if
+ no maintainer is available for the component, the tree/sub-tree maintainer
+ for that component must acknowledge the ABI change instead.
+
+ - 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.
#. A full deprecation cycle, as explained above, must be made to offer
downstream consumers sufficient warning of the change.
-#. At the beginning of the next release cycle, every ``RTE_NEXT_ABI``
- conditions will be removed, the ``LIBABIVER`` variable in the makefile(s)
- where the ABI is changed will be incremented, and the map files will
- be updated.
-
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
changes such as reorganizing public structure fields for aesthetic or
readability purposes should be avoided.
+.. 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.
+
Examples of Deprecation Notices
--------------------------------
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The following are some examples of ABI deprecation notices which would be
added to the Release Notes:
these changes. Binaries using this library built prior to version 2.1 will
require updating and recompilation.
-Versioning Macros
+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
-----------------
+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.
+
+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
+must be placed in an EXPERIMENTAL version block in the corresponding libraries'
+version map script.
+Secondly, the corresponding definitions of those exported functions, and
+their forward declarations (in the development header files), must be marked
+with the ``__rte_experimental`` tag (see ``rte_compat.h``).
+The DPDK build makefiles perform a check to ensure that the map file and the
+C code reflect the same list of symbols.
+This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
+during compilation in the corresponding library Makefile.
+
+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.
+
+
+Library versioning
+------------------
+
+Downstreams might want to provide different DPDK releases at the same time to
+support multiple consumers of DPDK linked against older and newer sonames.
+
+Also due to the interdependencies that DPDK libraries can have applications
+might end up with an executable space in which multiple versions of a library
+are mapped by ld.so.
+
+Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
+depending on LibA.
+
+.. note::
+
+ Application
+ \-> LibA.old
+ \-> LibB.new -> LibA.new
+
+That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
+If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
+library - versions defined in the libraries ``LIBABIVER``.
+An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
+``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
+
+
+ABI versioning
+--------------
+
+Versioning Macros
+~~~~~~~~~~~~~~~~~
+
When a symbol is exported from a library to provide an API, it also provides a
calling convention (ABI) that is embodied in its name, return type and
arguments. Occasionally that function may need to change to accommodate new
backward compatibility for a time with older binaries that are dynamically
linked to the DPDK.
-To support backward compatibility the ``lib/librte_compat/rte_compat.h``
+To support backward compatibility the ``rte_compat.h``
header file provides macros to use when updating exported functions. These
macros are used in conjunction with the ``rte_<library>_version.map`` file for
a given library to allow multiple versions of a symbol to exist in a shared
can still be mapped back to the public symbol name.
Examples of ABI Macro use
--------------------------
+^^^^^^^^^^^^^^^^^^^^^^^^^
Updating a public API
-~~~~~~~~~~~~~~~~~~~~~
+_____________________
Assume we have a function as follows
Deprecating part of a public API
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+________________________________
Lets assume that you've done the above update, and after a few releases have
passed you decide you would like to retire the old version of the function.
+LIBABIVER := 2
Deprecating an entire ABI version
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+_________________________________
While removing a symbol from and ABI may be useful, it is often more practical
to remove an entire version node at once. If a version node completely
removed, taking care to keep, where need old code in place to support newer
versions of the symbol.
+
Running the ABI Validator
-------------------------
-The ``scripts`` directory in the DPDK source tree contains a utility program,
+The ``devtools`` directory in the DPDK source tree contains a utility program,
``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
Compliance Checker
<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
The syntax of the ``validate-abi.sh`` utility is::
- ./scripts/validate-abi.sh <REV1> <REV2> <TARGET>
+ ./devtools/validate-abi.sh <REV1> <REV2> <TARGET>
Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
For example::
# Check between the previous and latest commit:
- ./scripts/validate-abi.sh HEAD~1 HEAD x86_64-native-linuxapp-gcc
+ ./devtools/validate-abi.sh HEAD~1 HEAD x86_64-native-linux-gcc
# Check between two tags:
- ./scripts/validate-abi.sh v2.0.0 v2.1.0 x86_64-native-linuxapp-gcc
+ ./devtools/validate-abi.sh v2.0.0 v2.1.0 x86_64-native-linux-gcc
# Check between git master and local topic-branch "vhost-hacking":
- ./scripts/validate-abi.sh master vhost-hacking x86_64-native-linuxapp-gcc
+ ./devtools/validate-abi.sh master vhost-hacking x86_64-native-linux-gcc
After the validation script completes (it can take a while since it need to
compile both tags) it will create compatibility reports in the
git.droids-corp.org / dpdk.git / blobdiff