[v3,1/4] doc: separate versioning.rst into version and policy
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Message ID 1565864619-17206-2-git-send-email-mdr@ashroe.eu
State Superseded
Delegated to: Thomas Monjalon
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  • doc: changes to abi policy introducing major abi versions
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Commit Message

Ray Kinsella Aug. 15, 2019, 10:23 a.m. UTC
Separate versioning.rst into abi versioning and abi policy guidance, in
preparation for adding more detail to the abi policy.

Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
---
 doc/guides/contributing/abi_policy.rst     | 169 +++++++++
 doc/guides/contributing/abi_versioning.rst | 427 +++++++++++++++++++++
 doc/guides/contributing/index.rst          |   3 +-
 doc/guides/contributing/versioning.rst     | 591 -----------------------------
 4 files changed, 598 insertions(+), 592 deletions(-)
 create mode 100644 doc/guides/contributing/abi_policy.rst
 create mode 100644 doc/guides/contributing/abi_versioning.rst
 delete mode 100644 doc/guides/contributing/versioning.rst

Patch
diff mbox series

diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
new file mode 100644
index 0000000..55bacb4
--- /dev/null
+++ b/doc/guides/contributing/abi_policy.rst
@@ -0,0 +1,169 @@ 
+..  SPDX-License-Identifier: BSD-3-Clause
+    Copyright 2018 The DPDK contributors
+
+.. abi_api_policy:
+
+DPDK ABI/API policy
+===================
+
+Description
+-----------
+
+This document details some methods for handling ABI management in the DPDK.
+
+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
+~~~~~~~~~~~~~~
+
+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
+is the result of compilation.  It is also effectively cloned when applications
+link to dynamic libraries.  That is to say when an application is compiled to
+link against dynamic libraries, it is assumed that the ABI remains constant
+between the time the application is compiled/linked, and the time that it runs.
+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.
+
+
+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.
+
+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 may be deprecated in whole or in part as needed by a given
+update.
+
+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:
+
+#. At least 3 acknowledgments of the need to do so must be made on the
+   dpdk.org mailing list.
+
+   - 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.
+
+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::
+
+   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:
+
+* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
+  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
+
+* The members of ``struct rte_foo`` have been reorganized in release 2.0 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
+  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,
+  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
+  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
+-----------------
+
+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 prototypes of those exported functions (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.
diff --git a/doc/guides/contributing/abi_versioning.rst b/doc/guides/contributing/abi_versioning.rst
new file mode 100644
index 0000000..53e6ac0
--- /dev/null
+++ b/doc/guides/contributing/abi_versioning.rst
@@ -0,0 +1,427 @@ 
+..  SPDX-License-Identifier: BSD-3-Clause
+    Copyright 2018 The DPDK contributors
+
+.. library_versioning:
+
+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
+functionality or behavior. When that occurs, it is desirable to allow for
+backward compatibility for a time with older binaries that are dynamically
+linked to the DPDK.
+
+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
+library so that older binaries need not be immediately recompiled.
+
+The macros exported are:
+
+* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
+  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
+
+* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
+  the linker to bind references to symbol ``b`` to the internal symbol
+  ``b_e``.
+
+* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
+  fully qualified function ``p``, so that if a symbol becomes versioned, it
+  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
+
+.. code-block:: c
+
+ /*
+  * Create an acl context object for apps to
+  * manipulate
+  */
+ struct rte_acl_ctx *
+ rte_acl_create(const struct rte_acl_param *param)
+ {
+        ...
+ }
+
+
+Assume that struct rte_acl_ctx is a private structure, and that a developer
+wishes to enhance the acl api so that a debugging flag can be enabled on a
+per-context basis.  This requires an addition to the structure (which, being
+private, is safe), but it also requires modifying the code as follows
+
+.. code-block:: c
+
+ /*
+  * Create an acl context object for apps to
+  * manipulate
+  */
+ struct rte_acl_ctx *
+ rte_acl_create(const struct rte_acl_param *param, int debug)
+ {
+        ...
+ }
+
+
+Note also that, being a public function, the header file prototype must also be
+changed, as must all the call sites, to reflect the new ABI footprint.  We will
+maintain previous ABI versions that are accessible only to previously compiled
+binaries
+
+The addition of a parameter to the function is ABI breaking as the function is
+public, and existing application may use it in its current form.  However, the
+compatibility macros in DPDK allow a developer to use symbol versioning so that
+multiple functions can be mapped to the same public symbol based on when an
+application was linked to it.  To see how this is done, we start with the
+requisite libraries version map file.  Initially the version map file for the
+acl library looks like this
+
+.. code-block:: none
+
+   DPDK_2.0 {
+        global:
+
+        rte_acl_add_rules;
+        rte_acl_build;
+        rte_acl_classify;
+        rte_acl_classify_alg;
+        rte_acl_classify_scalar;
+        rte_acl_create;
+        rte_acl_dump;
+        rte_acl_find_existing;
+        rte_acl_free;
+        rte_acl_ipv4vlan_add_rules;
+        rte_acl_ipv4vlan_build;
+        rte_acl_list_dump;
+        rte_acl_reset;
+        rte_acl_reset_rules;
+        rte_acl_set_ctx_classify;
+
+        local: *;
+   };
+
+This file needs to be modified as follows
+
+.. code-block:: none
+
+   DPDK_2.0 {
+        global:
+
+        rte_acl_add_rules;
+        rte_acl_build;
+        rte_acl_classify;
+        rte_acl_classify_alg;
+        rte_acl_classify_scalar;
+        rte_acl_create;
+        rte_acl_dump;
+        rte_acl_find_existing;
+        rte_acl_free;
+        rte_acl_ipv4vlan_add_rules;
+        rte_acl_ipv4vlan_build;
+        rte_acl_list_dump;
+        rte_acl_reset;
+        rte_acl_reset_rules;
+        rte_acl_set_ctx_classify;
+
+        local: *;
+   };
+
+   DPDK_2.1 {
+        global:
+        rte_acl_create;
+
+   } DPDK_2.0;
+
+The addition of the new block tells the linker that a new version node is
+available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
+symbols from the DPDK_2.0 node.  This list is directly translated into a list of
+exported symbols when DPDK is compiled as a shared library
+
+Next, we need to specify in the code which function map to the rte_acl_create
+symbol at which versions.  First, at the site of the initial symbol definition,
+we need to update the function so that it is uniquely named, and not in conflict
+with the public symbol name
+
+.. code-block:: c
+
+  struct rte_acl_ctx *
+ -rte_acl_create(const struct rte_acl_param *param)
+ +rte_acl_create_v20(const struct rte_acl_param *param)
+ {
+        size_t sz;
+        struct rte_acl_ctx *ctx;
+        ...
+
+Note that the base name of the symbol was kept intact, as this is conducive to
+the macros used for versioning symbols.  That is our next step, mapping this new
+symbol name to the initial symbol name at version node 2.0.  Immediately after
+the function, we add this line of code
+
+.. code-block:: c
+
+   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
+
+Remembering to also add the rte_compat.h header to the requisite c file where
+these changes are being made.  The above macro instructs the linker to create a
+new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
+builds, but now points to the above newly named function.  We have now mapped
+the original rte_acl_create symbol to the original function (but with a new
+name)
+
+Next, we need to create the 2.1 version of the symbol.  We create a new function
+name, with a different suffix, and  implement it appropriately
+
+.. code-block:: c
+
+   struct rte_acl_ctx *
+   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
+   {
+        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
+
+        ctx->debug = debug;
+
+        return ctx;
+   }
+
+This code serves as our new API call.  Its the same as our old call, but adds
+the new parameter in place.  Next we need to map this function to the symbol
+``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
+in the header file, adding the macro there to inform all including applications,
+that on re-link, the default rte_acl_create symbol should point to this
+function.  Note that we could do this by simply naming the function above
+rte_acl_create, and the linker would chose the most recent version tag to apply
+in the version script, but we can also do this in the header file
+
+.. code-block:: c
+
+   struct rte_acl_ctx *
+   -rte_acl_create(const struct rte_acl_param *param);
+   +rte_acl_create(const struct rte_acl_param *param, int debug);
+   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
+
+The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
+header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
+version node to it.  This method is more explicit and flexible than just
+re-implementing the exact symbol name, and allows for other features (such as
+linking to the old symbol version by default, when the new ABI is to be opt-in
+for a period.
+
+One last thing we need to do.  Note that we've taken what was a public symbol,
+and duplicated it into two uniquely and differently named symbols.  We've then
+mapped each of those back to the public symbol ``rte_acl_create`` with different
+version tags.  This only applies to dynamic linking, as static linking has no
+notion of versioning.  That leaves this code in a position of no longer having a
+symbol simply named ``rte_acl_create`` and a static build will fail on that
+missing symbol.
+
+To correct this, we can simply map a function of our choosing back to the public
+symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
+assumption is that the most recent version of the symbol is the one you want to
+map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
+defined, we add this
+
+.. code-block:: c
+
+   struct rte_acl_ctx *
+   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
+   {
+        ...
+   }
+   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
+
+That tells the compiler that, when building a static library, any calls to the
+symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
+
+That's it, on the next shared library rebuild, there will be two versions of
+rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
+and a new DPDK_2.1 version, used by future built applications.
+
+
+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.
+After having gone through the ABI deprecation announcement process, removal is
+easy.  Start by removing the symbol from the requisite version map file:
+
+.. code-block:: none
+
+   DPDK_2.0 {
+        global:
+
+        rte_acl_add_rules;
+        rte_acl_build;
+        rte_acl_classify;
+        rte_acl_classify_alg;
+        rte_acl_classify_scalar;
+        rte_acl_dump;
+ -      rte_acl_create
+        rte_acl_find_existing;
+        rte_acl_free;
+        rte_acl_ipv4vlan_add_rules;
+        rte_acl_ipv4vlan_build;
+        rte_acl_list_dump;
+        rte_acl_reset;
+        rte_acl_reset_rules;
+        rte_acl_set_ctx_classify;
+
+        local: *;
+   };
+
+   DPDK_2.1 {
+        global:
+        rte_acl_create;
+   } DPDK_2.0;
+
+
+Next remove the corresponding versioned export.
+
+.. code-block:: c
+
+ -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
+
+
+Note that the internal function definition could also be removed, but its used
+in our example by the newer version _v21, so we leave it in place.  This is a
+coding style choice.
+
+Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
+indicate to applications doing dynamic linking that this is a later, and
+possibly incompatible library version:
+
+.. code-block:: c
+
+   -LIBABIVER := 1
+   +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
+specifies an API, then removing part of it, typically makes it incomplete.  In
+those cases it is better to remove the entire node
+
+To do this, start by modifying the version map file, such that all symbols from
+the node to be removed are merged into the next node in the map
+
+In the case of our map above, it would transform to look as follows
+
+.. code-block:: none
+
+   DPDK_2.1 {
+        global:
+
+        rte_acl_add_rules;
+        rte_acl_build;
+        rte_acl_classify;
+        rte_acl_classify_alg;
+        rte_acl_classify_scalar;
+        rte_acl_dump;
+        rte_acl_create
+        rte_acl_find_existing;
+        rte_acl_free;
+        rte_acl_ipv4vlan_add_rules;
+        rte_acl_ipv4vlan_build;
+        rte_acl_list_dump;
+        rte_acl_reset;
+        rte_acl_reset_rules;
+        rte_acl_set_ctx_classify;
+
+        local: *;
+ };
+
+Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
+updated to point to the new version node in any header files for all affected
+symbols.
+
+.. code-block:: c
+
+ -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
+ +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
+
+Lastly, any VERSION_SYMBOL macros that point to the old version node should be
+removed, taking care to keep, where need old code in place to support newer
+versions of the symbol.
+
+
+Running the ABI Validator
+-------------------------
+
+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>`_.
+
+This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
+utilities which can be installed via a package manager. For example::
+
+   sudo yum install abi-compliance-checker
+   sudo yum install abi-dumper
+
+The syntax of the ``validate-abi.sh`` utility is::
+
+   ./devtools/validate-abi.sh <REV1> <REV2>
+
+Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
+https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
+on the local repo.
+
+For example::
+
+   # Check between the previous and latest commit:
+   ./devtools/validate-abi.sh HEAD~1 HEAD
+
+   # Check on a specific compilation target:
+   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
+
+   # Check between two tags:
+   ./devtools/validate-abi.sh v2.0.0 v2.1.0
+
+   # Check between git master and local topic-branch "vhost-hacking":
+   ./devtools/validate-abi.sh master vhost-hacking
+
+After the validation script completes (it can take a while since it need to
+compile both tags) it will create compatibility reports in the
+``./abi-check/compat_report`` directory. Listed incompatibilities can be found
+as follows::
+
+  grep -lr Incompatible abi-check/compat_reports/
diff --git a/doc/guides/contributing/index.rst b/doc/guides/contributing/index.rst
index e2608d3..2fefd91 100644
--- a/doc/guides/contributing/index.rst
+++ b/doc/guides/contributing/index.rst
@@ -10,7 +10,8 @@  Contributor's Guidelines
 
     coding_style
     design
-    versioning
+    abi_policy
+    abi_versioning
     documentation
     patches
     vulnerability
diff --git a/doc/guides/contributing/versioning.rst b/doc/guides/contributing/versioning.rst
deleted file mode 100644
index 3ab2c43..0000000
--- a/doc/guides/contributing/versioning.rst
+++ /dev/null
@@ -1,591 +0,0 @@ 
-..  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.
-
-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
-~~~~~~~~~~~~~~
-
-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
-is the result of compilation.  It is also effectively cloned when applications
-link to dynamic libraries.  That is to say when an application is compiled to
-link against dynamic libraries, it is assumed that the ABI remains constant
-between the time the application is compiled/linked, and the time that it runs.
-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.
-
-
-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.
-
-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 may be deprecated in whole or in part as needed by a given
-update.
-
-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:
-
-#. At least 3 acknowledgments of the need to do so must be made on the
-   dpdk.org mailing list.
-
-   - 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.
-
-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::
-
-   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:
-
-* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
-  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
-
-* The members of ``struct rte_foo`` have been reorganized in release 2.0 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
-  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,
-  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
-  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
------------------
-
-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 prototypes of those exported functions (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
-functionality or behavior. When that occurs, it is desirable to allow for
-backward compatibility for a time with older binaries that are dynamically
-linked to the DPDK.
-
-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
-library so that older binaries need not be immediately recompiled.
-
-The macros exported are:
-
-* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
-  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
-
-* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
-  the linker to bind references to symbol ``b`` to the internal symbol
-  ``b_e``.
-
-* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
-  fully qualified function ``p``, so that if a symbol becomes versioned, it
-  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
-
-.. code-block:: c
-
- /*
-  * Create an acl context object for apps to
-  * manipulate
-  */
- struct rte_acl_ctx *
- rte_acl_create(const struct rte_acl_param *param)
- {
-        ...
- }
-
-
-Assume that struct rte_acl_ctx is a private structure, and that a developer
-wishes to enhance the acl api so that a debugging flag can be enabled on a
-per-context basis.  This requires an addition to the structure (which, being
-private, is safe), but it also requires modifying the code as follows
-
-.. code-block:: c
-
- /*
-  * Create an acl context object for apps to
-  * manipulate
-  */
- struct rte_acl_ctx *
- rte_acl_create(const struct rte_acl_param *param, int debug)
- {
-        ...
- }
-
-
-Note also that, being a public function, the header file prototype must also be
-changed, as must all the call sites, to reflect the new ABI footprint.  We will
-maintain previous ABI versions that are accessible only to previously compiled
-binaries
-
-The addition of a parameter to the function is ABI breaking as the function is
-public, and existing application may use it in its current form.  However, the
-compatibility macros in DPDK allow a developer to use symbol versioning so that
-multiple functions can be mapped to the same public symbol based on when an
-application was linked to it.  To see how this is done, we start with the
-requisite libraries version map file.  Initially the version map file for the
-acl library looks like this
-
-.. code-block:: none
-
-   DPDK_2.0 {
-        global:
-
-        rte_acl_add_rules;
-        rte_acl_build;
-        rte_acl_classify;
-        rte_acl_classify_alg;
-        rte_acl_classify_scalar;
-        rte_acl_create;
-        rte_acl_dump;
-        rte_acl_find_existing;
-        rte_acl_free;
-        rte_acl_ipv4vlan_add_rules;
-        rte_acl_ipv4vlan_build;
-        rte_acl_list_dump;
-        rte_acl_reset;
-        rte_acl_reset_rules;
-        rte_acl_set_ctx_classify;
-
-        local: *;
-   };
-
-This file needs to be modified as follows
-
-.. code-block:: none
-
-   DPDK_2.0 {
-        global:
-
-        rte_acl_add_rules;
-        rte_acl_build;
-        rte_acl_classify;
-        rte_acl_classify_alg;
-        rte_acl_classify_scalar;
-        rte_acl_create;
-        rte_acl_dump;
-        rte_acl_find_existing;
-        rte_acl_free;
-        rte_acl_ipv4vlan_add_rules;
-        rte_acl_ipv4vlan_build;
-        rte_acl_list_dump;
-        rte_acl_reset;
-        rte_acl_reset_rules;
-        rte_acl_set_ctx_classify;
-
-        local: *;
-   };
-
-   DPDK_2.1 {
-        global:
-        rte_acl_create;
-
-   } DPDK_2.0;
-
-The addition of the new block tells the linker that a new version node is
-available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
-symbols from the DPDK_2.0 node.  This list is directly translated into a list of
-exported symbols when DPDK is compiled as a shared library
-
-Next, we need to specify in the code which function map to the rte_acl_create
-symbol at which versions.  First, at the site of the initial symbol definition,
-we need to update the function so that it is uniquely named, and not in conflict
-with the public symbol name
-
-.. code-block:: c
-
-  struct rte_acl_ctx *
- -rte_acl_create(const struct rte_acl_param *param)
- +rte_acl_create_v20(const struct rte_acl_param *param)
- {
-        size_t sz;
-        struct rte_acl_ctx *ctx;
-        ...
-
-Note that the base name of the symbol was kept intact, as this is conducive to
-the macros used for versioning symbols.  That is our next step, mapping this new
-symbol name to the initial symbol name at version node 2.0.  Immediately after
-the function, we add this line of code
-
-.. code-block:: c
-
-   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
-
-Remembering to also add the rte_compat.h header to the requisite c file where
-these changes are being made.  The above macro instructs the linker to create a
-new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
-builds, but now points to the above newly named function.  We have now mapped
-the original rte_acl_create symbol to the original function (but with a new
-name)
-
-Next, we need to create the 2.1 version of the symbol.  We create a new function
-name, with a different suffix, and  implement it appropriately
-
-.. code-block:: c
-
-   struct rte_acl_ctx *
-   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
-   {
-        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
-
-        ctx->debug = debug;
-
-        return ctx;
-   }
-
-This code serves as our new API call.  Its the same as our old call, but adds
-the new parameter in place.  Next we need to map this function to the symbol
-``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
-in the header file, adding the macro there to inform all including applications,
-that on re-link, the default rte_acl_create symbol should point to this
-function.  Note that we could do this by simply naming the function above
-rte_acl_create, and the linker would chose the most recent version tag to apply
-in the version script, but we can also do this in the header file
-
-.. code-block:: c
-
-   struct rte_acl_ctx *
-   -rte_acl_create(const struct rte_acl_param *param);
-   +rte_acl_create(const struct rte_acl_param *param, int debug);
-   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
-
-The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
-header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
-version node to it.  This method is more explicit and flexible than just
-re-implementing the exact symbol name, and allows for other features (such as
-linking to the old symbol version by default, when the new ABI is to be opt-in
-for a period.
-
-One last thing we need to do.  Note that we've taken what was a public symbol,
-and duplicated it into two uniquely and differently named symbols.  We've then
-mapped each of those back to the public symbol ``rte_acl_create`` with different
-version tags.  This only applies to dynamic linking, as static linking has no
-notion of versioning.  That leaves this code in a position of no longer having a
-symbol simply named ``rte_acl_create`` and a static build will fail on that
-missing symbol.
-
-To correct this, we can simply map a function of our choosing back to the public
-symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
-assumption is that the most recent version of the symbol is the one you want to
-map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
-defined, we add this
-
-.. code-block:: c
-
-   struct rte_acl_ctx *
-   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
-   {
-        ...
-   }
-   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
-
-That tells the compiler that, when building a static library, any calls to the
-symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
-
-That's it, on the next shared library rebuild, there will be two versions of
-rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
-and a new DPDK_2.1 version, used by future built applications.
-
-
-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.
-After having gone through the ABI deprecation announcement process, removal is
-easy.  Start by removing the symbol from the requisite version map file:
-
-.. code-block:: none
-
-   DPDK_2.0 {
-        global:
-
-        rte_acl_add_rules;
-        rte_acl_build;
-        rte_acl_classify;
-        rte_acl_classify_alg;
-        rte_acl_classify_scalar;
-        rte_acl_dump;
- -      rte_acl_create
-        rte_acl_find_existing;
-        rte_acl_free;
-        rte_acl_ipv4vlan_add_rules;
-        rte_acl_ipv4vlan_build;
-        rte_acl_list_dump;
-        rte_acl_reset;
-        rte_acl_reset_rules;
-        rte_acl_set_ctx_classify;
-
-        local: *;
-   };
-
-   DPDK_2.1 {
-        global:
-        rte_acl_create;
-   } DPDK_2.0;
-
-
-Next remove the corresponding versioned export.
-
-.. code-block:: c
-
- -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
-
-
-Note that the internal function definition could also be removed, but its used
-in our example by the newer version _v21, so we leave it in place.  This is a
-coding style choice.
-
-Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
-indicate to applications doing dynamic linking that this is a later, and
-possibly incompatible library version:
-
-.. code-block:: c
-
-   -LIBABIVER := 1
-   +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
-specifies an API, then removing part of it, typically makes it incomplete.  In
-those cases it is better to remove the entire node
-
-To do this, start by modifying the version map file, such that all symbols from
-the node to be removed are merged into the next node in the map
-
-In the case of our map above, it would transform to look as follows
-
-.. code-block:: none
-
-   DPDK_2.1 {
-        global:
-
-        rte_acl_add_rules;
-        rte_acl_build;
-        rte_acl_classify;
-        rte_acl_classify_alg;
-        rte_acl_classify_scalar;
-        rte_acl_dump;
-        rte_acl_create
-        rte_acl_find_existing;
-        rte_acl_free;
-        rte_acl_ipv4vlan_add_rules;
-        rte_acl_ipv4vlan_build;
-        rte_acl_list_dump;
-        rte_acl_reset;
-        rte_acl_reset_rules;
-        rte_acl_set_ctx_classify;
-
-        local: *;
- };
-
-Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
-updated to point to the new version node in any header files for all affected
-symbols.
-
-.. code-block:: c
-
- -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
- +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
-
-Lastly, any VERSION_SYMBOL macros that point to the old version node should be
-removed, taking care to keep, where need old code in place to support newer
-versions of the symbol.
-
-
-Running the ABI Validator
--------------------------
-
-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>`_.
-
-This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
-utilities which can be installed via a package manager. For example::
-
-   sudo yum install abi-compliance-checker
-   sudo yum install abi-dumper
-
-The syntax of the ``validate-abi.sh`` utility is::
-
-   ./devtools/validate-abi.sh <REV1> <REV2>
-
-Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
-https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
-on the local repo.
-
-For example::
-
-   # Check between the previous and latest commit:
-   ./devtools/validate-abi.sh HEAD~1 HEAD
-
-   # Check on a specific compilation target:
-   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
-
-   # Check between two tags:
-   ./devtools/validate-abi.sh v2.0.0 v2.1.0
-
-   # Check between git master and local topic-branch "vhost-hacking":
-   ./devtools/validate-abi.sh master vhost-hacking
-
-After the validation script completes (it can take a while since it need to
-compile both tags) it will create compatibility reports in the
-``./abi-check/compat_report`` directory. Listed incompatibilities can be found
-as follows::
-
-  grep -lr Incompatible abi-check/compat_reports/