[v9,0/4] doc: changes to abi policy introducing major abi versions
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Kinsella, Ray Nov. 8, 2019, 12:46 p.m. UTC
TL;DR abbreviation:
A major ABI version that all DPDK releases during an agreed period support. ABI
versioning is managed at a project-level, in place of library-level management.
ABI changes to add new features are permitted, as long as ABI compatibility with
the major ABI version is maintained.

Detail:
This patch introduces major ABI versions, initally released aligned with the LTS
release and maintained for one year through subsequent releases. The intention
is that the one year abi support period, will then be reviewed after the initial
year with the intention of lengthening the period for the next ABI version and
declaring new major ABI versions less frequently.

ABI changes that preserve ABI compatibility with the major ABI version are
permitted in subsequent releases. ABI changes, follow similar approval rules as
before with the additional gate of now requiring technical board approval. The
merging and release of ABI breaking changes would now be pushed to the
declaration of the next major ABI version.

This change encourages developers to maintain ABI compatibility with the major
ABI version, by promoting a permissive culture around those changes that
preserve ABI compatibility. This approach begins to align DPDK with those
projects that declare major ABI versions (e.g. version 2.x, 3.x) and support
those versions for some period, typically two years or more.

To provide an example of how this might work in practice:

 * DPDK v20 is declared as the supported ABI version for one year, aligned with
   the DPDK v19.11 (LTS) release. All library sonames are updated to reflect the
   new ABI version, e.g. librte_eal.so.20, librte_acl.so.20...
 * DPDK v20.02 .. v20.08 releases are ABI compatible with the DPDK v20 ABI. ABI
   changes are permitted from DPDK v20.02 onwards, with the condition that ABI
   compatibility with DPDK v20 is preserved.
 * DPDK v21 is declared as the new supported ABI version for two years, aligned
   with the DPDK v20.11 (LTS) release. The DPDK v20 ABI is now depreciated,
   library sonames are updated to v21 and ABI compatibility breaking changes may
   be introduced.

v9
 * Loosened up word around when new major ABI's are declared.
   (as suggested by Thomas Monjalon and agreed at the Techboard)

v8
 * Fixed intermediate build warnings, figure annotations and typo's.
   (as suggested by John McNamara).

v7
 * PNGs are now SVG. Some additional clarifications. Fixed typos and grammatical
   errors. (as suggested by Thomas Monjalon and David Marchand)

v6
 * Added figure to abi_policy.rst, comparing and contrasting the DPDK abi and
   api. (as suggested by Aaron Conole)

v5
 * Added figure to abi_policy.rst, mapping abi versions and abi compatibility to
   DPDK releases. (as suggested by Neil Horman)

v4
 * Removed changes to stable.rst, fixed typos and clarified the ABI policy
   "warning".

v3
 * Added myself as the maintainer of the ABI policy.
 * Updated the policy and versioning guides to use the year of the LTS+1 (e.g.
   v20), as the abi major version number.

v2
 * Restructured the patch into 3 patches:
   1. Splits the original versioning document into an ABI policy document
     and ABI versioning document.
   2. Add changes to the policy document introducing major ABI versions.
   3. Fixes up the versioning document in light of major ABI versioning. 
 * Reduces the initial ABI stability from two years to one year, with a review
   after the first year.
 * Adds detail around ABI version handling for experimental libraries.
 * Adds detail around chain of responsility for removing deprecated symbols.

Ray Kinsella (4):
  doc: separate versioning.rst into version and policy
  doc: changes to abi policy introducing major abi versions
  doc: updates to versioning guide for abi versions
  doc: add maintainer for abi policy

 MAINTAINERS                                        |    4 +
 doc/guides/contributing/abi_policy.rst             |  326 ++++++
 doc/guides/contributing/abi_versioning.rst         |  515 ++++++++++
 .../contributing/img/abi_stability_policy.svg      | 1059 ++++++++++++++++++++
 doc/guides/contributing/img/what_is_an_abi.svg     |  382 +++++++
 doc/guides/contributing/index.rst                  |    3 +-
 doc/guides/contributing/patches.rst                |    6 +-
 doc/guides/contributing/stable.rst                 |   12 +-
 doc/guides/contributing/versioning.rst             |  591 -----------
 doc/guides/rel_notes/deprecation.rst               |    6 +-
 10 files changed, 2298 insertions(+), 606 deletions(-)
 create mode 100644 doc/guides/contributing/abi_policy.rst
 create mode 100644 doc/guides/contributing/abi_versioning.rst
 create mode 100644 doc/guides/contributing/img/abi_stability_policy.svg
 create mode 100644 doc/guides/contributing/img/what_is_an_abi.svg
 delete mode 100644 doc/guides/contributing/versioning.rst