[PATCH 3/3] migration-5.1.rst: preliminary description of UNPACKDIR changes

[michael.opdenacker@bootlin.com]

From: Michael Opdenacker <michael.opdenacker@bootlin.com>

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
---
 .../migration-guides/migration-5.1.rst        | 55 +++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/documentation/migration-guides/migration-5.1.rst b/documentation/migration-guides/migration-5.1.rst
index b4db04bcee..84ef35e28a 100644
--- a/documentation/migration-guides/migration-5.1.rst
+++ b/documentation/migration-guides/migration-5.1.rst
@@ -11,6 +11,61 @@ Project 5.1 Release (codename "styhead") from the prior release.
 
 .. _migration-5.1-supported-kernel-versions:
 
+:term:`WORKDIR` changes
+~~~~~~~~~~~~~~~~~~~~~~~
+
+S = ${WORKDIR} no longer supported
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If a recipe has :term:`S` set to be :term:`WORKDIR`, this is no longer
+supported, and an error will be issued. The recipe should be changed to::
+
+    S = "${WORKDIR}/sources"
+    UNPACKDIR = "${S}"
+
+Any :term:`WORKDIR` references where files from :term:`SRC_URI` are referenced
+should be changed to :term:`S`. These are commonly in :ref:`ref-tasks-compile`,
+:ref:`ref-tasks-compile`, :ref:`ref-tasks-install` and :term:`LIC_FILES_CHKSUM`.
+
+:term:`WORKDIR` references in recipes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+:term:`WORKDIR` references in other recipes need auditing. If they reference
+files from :term:`SRC_URI`, they likely need changing to :term:`UNPACKDIR`.
+These are commonly in :ref:`ref-tasks-compile` and :ref:`ref-tasks-install`
+for things like service or configuration files. One unusual case is
+``${WORKDIR}/${BP}`` which should probably be set to ``${S}``.
+
+References to ``../`` in :term:`LIC_FILES_CHKSUM` or elsewhere may need changing
+to :term:`UNPACKDIR`. References to :term:`WORKDIR` in ``sed`` commands are
+usually left as they are.
+
+General notes
+^^^^^^^^^^^^^
+
+Files from :ref:`ref-tasks-unpack` now unpack to ``WORKDIR/sources-unpack/``
+rather than ``WORKDIR/``.
+
+If :term:`S` is set to a subdirectory under :term:`WORKDIR` and that
+subdirectory exists in ``sources-unpack`` after :ref:`ref-tasks-unpack` runs,
+it is moved to :term:`WORKDIR`. This means that ``S = "${WORKDIR}/${BP}"``,
+``S = "${WORKDIR}/git"`` and also deeper paths continue to work as expected
+without changes. We cannot use symlinks to do this as it breaks autotools
+based recipes. Keeping all sources under ``sources-unpack`` wasn't considered
+as it meant more invasive recipes changes. The key objective was separating the
+:ref:`ref-tasks-unpack` task output from :term:`WORKDIR`.
+
+Previously, :term:`S` was always created but after the recent changes it is no
+longer the case. This means the check in ``do_unpack_qa`` triggers where
+:term:`S` is not created by a recipe while it didn't happen before. This can
+require to add an :term:`S` definition to a recipe that only uses
+``file://`` :term:`SRC_URI` entries. Building C files from :term:`UNPACKDIR`
+without setting :term:`S` to point at it does not work as the debug prefix
+mapping doesn't handle that.
+
+``devtool``  and ``recipetool`` have been updated to handle this and their
+support for ``S = WORKDIR`` and ``oe-local-files`` has been removed.
+
 Supported kernel versions
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.34.1