Moving to the Yocto Project 2.4 Release
=======================================

This section provides migration information for moving to the Yocto
Project 2.4 Release from the prior release.

.. _migration-2.4-memory-resident-mode:

Memory Resident Mode
--------------------

A persistent mode is now available in BitBake's default operation,
replacing its previous "memory resident mode" (i.e.
``oe-init-build-env-memres``). Now you only need to set
:term:`BB_SERVER_TIMEOUT` to a timeout (in
seconds) and BitBake's server stays resident for that amount of time
between invocations. The ``oe-init-build-env-memres`` script has been
removed since a separate environment setup script is no longer needed.

.. _migration-2.4-packaging-changes:

Packaging Changes
-----------------

This section provides information about packaging changes that have
occurred:

-  ``python3`` Changes:

   -  The main "python3" package now brings in all of the standard
      Python 3 distribution rather than a subset. This behavior matches
      what is expected based on traditional Linux distributions. If you
      wish to install a subset of Python 3, specify ``python-core`` plus
      one or more of the individual packages that are still produced.

   -  ``python3``: The ``bz2.py``, ``lzma.py``, and
      ``_compression.py`` scripts have been moved from the
      ``python3-misc`` package to the ``python3-compression`` package.

-  ``binutils``: The ``libbfd`` library is now packaged in a separate
   "libbfd" package. This packaging saves space when certain tools (e.g.
   ``perf``) are installed. In such cases, the tools only need
   ``libbfd`` rather than all the packages in ``binutils``.

-  ``util-linux`` Changes:

   -  The ``su`` program is now packaged in a separate "util-linux-su"
      package, which is only built when "pam" is listed in the
      :term:`DISTRO_FEATURES` variable.
      ``util-linux`` should not be installed unless it is needed because
      ``su`` is normally provided through the shadow file format. The
      main ``util-linux`` package has runtime dependencies (i.e.
      :term:`RDEPENDS`) on the ``util-linux-su`` package
      when "pam" is in ``DISTRO_FEATURES``.

   -  The ``switch_root`` program is now packaged in a separate
      "util-linux-switch-root" package for small initramfs images that
      do not need the whole ``util-linux`` package or the busybox
      binary, which are both much larger than ``switch_root``. The main
      ``util-linux`` package has a recommended runtime dependency (i.e.
      :term:`RRECOMMENDS`) on the
      ``util-linux-switch-root`` package.

   -  The ``ionice`` program is now packaged in a separate
      "util-linux-ionice" package. The main ``util-linux`` package has a
      recommended runtime dependency (i.e. ``RRECOMMENDS``) on the
      ``util-linux-ionice`` package.

-  ``initscripts``: The ``sushell`` program is now packaged in a
   separate "initscripts-sushell" package. This packaging change allows
   systems to pull ``sushell`` in when ``selinux`` is enabled. The
   change also eliminates needing to pull in the entire ``initscripts``
   package. The main ``initscripts`` package has a runtime dependency
   (i.e. ``RDEPENDS``) on the ``sushell`` package when "selinux" is in
   ``DISTRO_FEATURES``.

-  ``glib-2.0``: The ``glib-2.0`` package now has a recommended
   runtime dependency (i.e. ``RRECOMMENDS``) on the ``shared-mime-info``
   package, since large portions of GIO are not useful without the MIME
   database. You can remove the dependency by using the
   :term:`BAD_RECOMMENDATIONS` variable if
   ``shared-mime-info`` is too large and is not required.

-  *Go Standard Runtime:* The Go standard runtime has been split out
   from the main ``go`` recipe into a separate ``go-runtime`` recipe.

.. _migration-2.4-removed-recipes:

Removed Recipes
---------------

The following recipes have been removed:

-  ``acpitests``: This recipe is not maintained.

-  ``autogen-native``: No longer required by Grub, oe-core, or
   meta-oe.

-  ``bdwgc``: Nothing in OpenEmbedded-Core requires this recipe. It
   has moved to meta-oe.

-  ``byacc``: This recipe was only needed by rpm 5.x and has moved to
   meta-oe.

-  ``gcc (5.4)``: The 5.4 series dropped the recipe in favor of 6.3 /
   7.2.

-  ``gnome-common``: Deprecated upstream and no longer needed.

-  ``go-bootstrap-native``: Go 1.9 does its own bootstrapping so this
   recipe has been removed.

-  ``guile``: This recipe was only needed by ``autogen-native`` and
   ``remake``. The recipe is no longer needed by either of these
   programs.

-  ``libclass-isa-perl``: This recipe was previously needed for LSB 4,
   no longer needed.

-  ``libdumpvalue-perl``: This recipe was previously needed for LSB 4,
   no longer needed.

-  ``libenv-perl``: This recipe was previously needed for LSB 4, no
   longer needed.

-  ``libfile-checktree-perl``: This recipe was previously needed for
   LSB 4, no longer needed.

-  ``libi18n-collate-perl``: This recipe was previously needed for LSB
   4, no longer needed.

-  ``libiconv``: This recipe was only needed for ``uclibc``, which was
   removed in the previous release. ``glibc`` and ``musl`` have their
   own implementations. ``meta-mingw`` still needs ``libiconv``, so it
   has been moved to ``meta-mingw``.

-  ``libpng12``: This recipe was previously needed for LSB. The
   current ``libpng`` is 1.6.x.

-  ``libpod-plainer-perl``: This recipe was previously needed for LSB
   4, no longer needed.

-  ``linux-yocto (4.1)``: This recipe was removed in favor of 4.4,
   4.9, 4.10 and 4.12.

-  ``mailx``: This recipe was previously only needed for LSB
   compatibility, and upstream is defunct.

-  ``mesa (git version only)``: The git version recipe was stale with
   respect to the release version.

-  ``ofono (git version only)``: The git version recipe was stale with
   respect to the release version.

-  ``portmap``: This recipe is obsolete and is superseded by
   ``rpcbind``.

-  ``python3-pygpgme``: This recipe is old and unmaintained. It was
   previously required by ``dnf``, which has switched to official
   ``gpgme`` Python bindings.

-  ``python-async``: This recipe has been removed in favor of the
   Python 3 version.

-  ``python-gitdb``: This recipe has been removed in favor of the
   Python 3 version.

-  ``python-git``: This recipe was removed in favor of the Python 3
   version.

-  ``python-mako``: This recipe was removed in favor of the Python 3
   version.

-  ``python-pexpect``: This recipe was removed in favor of the Python
   3 version.

-  ``python-ptyprocess``: This recipe was removed in favor of Python
   the 3 version.

-  ``python-pycurl``: Nothing is using this recipe in
   OpenEmbedded-Core (i.e. ``meta-oe``).

-  ``python-six``: This recipe was removed in favor of the Python 3
   version.

-  ``python-smmap``: This recipe was removed in favor of the Python 3
   version.

-  ``remake``: Using ``remake`` as the provider of ``virtual/make`` is
   broken. Consequently, this recipe is not needed in OpenEmbedded-Core.

.. _migration-2.4-kernel-device-tree-move:

Kernel Device Tree Move
-----------------------

Kernel Device Tree support is now easier to enable in a kernel recipe.
The Device Tree code has moved to a
:ref:`kernel-devicetree <ref-classes-kernel-devicetree>` class.
Functionality is automatically enabled for any recipe that inherits the
:ref:`kernel <ref-classes-kernel>` class and sets the
:term:`KERNEL_DEVICETREE` variable. The
previous mechanism for doing this,
``meta/recipes-kernel/linux/linux-dtb.inc``, is still available to avoid
breakage, but triggers a deprecation warning. Future releases of the
Yocto Project will remove ``meta/recipes-kernel/linux/linux-dtb.inc``.
It is advisable to remove any ``require`` statements that request
``meta/recipes-kernel/linux/linux-dtb.inc`` from any custom kernel
recipes you might have. This will avoid breakage in post 2.4 releases.

.. _migration-2.4-package-qa-changes:

Package QA Changes
------------------

The following package QA changes took place:

-  The "unsafe-references-in-scripts" QA check has been removed.

-  If you refer to ``${COREBASE}/LICENSE`` within
   :term:`LIC_FILES_CHKSUM` you receive a
   warning because this file is a description of the license for
   OE-Core. Use ``${COMMON_LICENSE_DIR}/MIT`` if your recipe is
   MIT-licensed and you cannot use the preferred method of referring to
   a file within the source tree.

.. _migration-2.4-readme-changes:

``README`` File Changes
-----------------------

The following are changes to ``README`` files:

-  The main Poky ``README`` file has been moved to the ``meta-poky``
   layer and has been renamed ``README.poky``. A symlink has been
   created so that references to the old location work.

-  The ``README.hardware`` file has been moved to ``meta-yocto-bsp``. A
   symlink has been created so that references to the old location work.

-  A ``README.qemu`` file has been created with coverage of the
   ``qemu*`` machines.

.. _migration-2.4-miscellaneous-changes:

Miscellaneous Changes
---------------------

The following are additional changes:

-  The ``ROOTFS_PKGMANAGE_BOOTSTRAP`` variable and any references to it
   have been removed. You should remove this variable from any custom
   recipes.

-  The ``meta-yocto`` directory has been removed.

   .. note::

      In the Yocto Project 2.1 release
      meta-yocto
      was renamed to
      meta-poky
      and the
      meta-yocto
      subdirectory remained to avoid breaking existing configurations.

-  The ``maintainers.inc`` file, which tracks maintainers by listing a
   primary person responsible for each recipe in OE-Core, has been moved
   from ``meta-poky`` to OE-Core (i.e. from
   ``meta-poky/conf/distro/include`` to ``meta/conf/distro/include``).

-  The :ref:`buildhistory <ref-classes-buildhistory>` class now makes
   a single commit per build rather than one commit per subdirectory in
   the repository. This behavior assumes the commits are enabled with
   :term:`BUILDHISTORY_COMMIT` = "1", which
   is typical. Previously, the ``buildhistory`` class made one commit
   per subdirectory in the repository in order to make it easier to see
   the changes for a particular subdirectory. To view a particular
   change, specify that subdirectory as the last parameter on the
   ``git show`` or ``git diff`` commands.

-  The ``x86-base.inc`` file, which is included by all x86-based machine
   configurations, now sets :term:`IMAGE_FSTYPES`
   using ``?=`` to "live" rather than appending with ``+=``. This change
   makes the default easier to override.

-  BitBake fires multiple "BuildStarted" events when multiconfig is
   enabled (one per configuration). For more information, see the
   ":ref:`Events <bitbake:bitbake-user-manual/bitbake-user-manual-metadata:events>`" section in the BitBake User
   Manual.

-  By default, the ``security_flags.inc`` file sets a
   :term:`GCCPIE` variable with an option to enable
   Position Independent Executables (PIE) within ``gcc``. Enabling PIE
   in the GNU C Compiler (GCC), makes Return Oriented Programming (ROP)
   attacks much more difficult to execute.

-  OE-Core now provides a ``bitbake-layers`` plugin that implements a
   "create-layer" subcommand. The implementation of this subcommand has
   resulted in the ``yocto-layer`` script being deprecated and will
   likely be removed in the next Yocto Project release.

-  The ``vmdk``, ``vdi``, and ``qcow2`` image file types are now used in
   conjunction with the "wic" image type through ``CONVERSION_CMD``.
   Consequently, the equivalent image types are now ``wic.vmdk``,
   ``wic.vdi``, and ``wic.qcow2``, respectively.

-  ``do_image_<type>[depends]`` has replaced ``IMAGE_DEPENDS_<type>``.
   If you have your own classes that implement custom image types, then
   you need to update them.

-  OpenSSL 1.1 has been introduced. However, the default is still 1.0.x
   through the :term:`PREFERRED_VERSION`
   variable. This preference is set is due to the remaining
   compatibility issues with other software. The
   :term:`PROVIDES` variable in the openssl 1.0 recipe
   now includes "openssl10" as a marker that can be used in
   :term:`DEPENDS` within recipes that build software
   that still depend on OpenSSL 1.0.

-  To ensure consistent behavior, BitBake's "-r" and "-R" options (i.e.
   prefile and postfile), which are used to read or post-read additional
   configuration files from the command line, now only affect the
   current BitBake command. Before these BitBake changes, these options
   would "stick" for future executions.