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+.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
+
+Working With Licenses
+*********************
+
+As mentioned in the ":ref:`overview-manual/development-environment:licensing`"
+section in the Yocto Project Overview and Concepts Manual, open source
+projects are open to the public and they consequently have different
+licensing structures in place. This section describes the mechanism by
+which the :term:`OpenEmbedded Build System`
+tracks changes to
+licensing text and covers how to maintain open source license compliance
+during your project's lifecycle. The section also describes how to
+enable commercially licensed recipes, which by default are disabled.
+
+Tracking License Changes
+========================
+
+The license of an upstream project might change in the future. In order
+to prevent these changes going unnoticed, the
+:term:`LIC_FILES_CHKSUM`
+variable tracks changes to the license text. The checksums are validated
+at the end of the configure step, and if the checksums do not match, the
+build will fail.
+
+Specifying the ``LIC_FILES_CHKSUM`` Variable
+--------------------------------------------
+
+The :term:`LIC_FILES_CHKSUM` variable contains checksums of the license text
+in the source code for the recipe. Following is an example of how to
+specify :term:`LIC_FILES_CHKSUM`::
+
+   LIC_FILES_CHKSUM = "file://COPYING;md5=xxxx \
+                       file://licfile1.txt;beginline=5;endline=29;md5=yyyy \
+                       file://licfile2.txt;endline=50;md5=zzzz \
+                       ..."
+
+.. note::
+
+   -  When using "beginline" and "endline", realize that line numbering
+      begins with one and not zero. Also, the included lines are
+      inclusive (i.e. lines five through and including 29 in the
+      previous example for ``licfile1.txt``).
+
+   -  When a license check fails, the selected license text is included
+      as part of the QA message. Using this output, you can determine
+      the exact start and finish for the needed license text.
+
+The build system uses the :term:`S`
+variable as the default directory when searching files listed in
+:term:`LIC_FILES_CHKSUM`. The previous example employs the default
+directory.
+
+Consider this next example::
+
+   LIC_FILES_CHKSUM = "file://src/ls.c;beginline=5;endline=16;\
+                                       md5=bb14ed3c4cda583abc85401304b5cd4e"
+   LIC_FILES_CHKSUM = "file://${WORKDIR}/license.html;md5=5c94767cedb5d6987c902ac850ded2c6"
+
+The first line locates a file in ``${S}/src/ls.c`` and isolates lines
+five through 16 as license text. The second line refers to a file in
+:term:`WORKDIR`.
+
+Note that :term:`LIC_FILES_CHKSUM` variable is mandatory for all recipes,
+unless the :term:`LICENSE` variable is set to "CLOSED".
+
+Explanation of Syntax
+---------------------
+
+As mentioned in the previous section, the :term:`LIC_FILES_CHKSUM` variable
+lists all the important files that contain the license text for the
+source code. It is possible to specify a checksum for an entire file, or
+a specific section of a file (specified by beginning and ending line
+numbers with the "beginline" and "endline" parameters, respectively).
+The latter is useful for source files with a license notice header,
+README documents, and so forth. If you do not use the "beginline"
+parameter, then it is assumed that the text begins on the first line of
+the file. Similarly, if you do not use the "endline" parameter, it is
+assumed that the license text ends with the last line of the file.
+
+The "md5" parameter stores the md5 checksum of the license text. If the
+license text changes in any way as compared to this parameter then a
+mismatch occurs. This mismatch triggers a build failure and notifies the
+developer. Notification allows the developer to review and address the
+license text changes. Also note that if a mismatch occurs during the
+build, the correct md5 checksum is placed in the build log and can be
+easily copied to the recipe.
+
+There is no limit to how many files you can specify using the
+:term:`LIC_FILES_CHKSUM` variable. Generally, however, every project
+requires a few specifications for license tracking. Many projects have a
+"COPYING" file that stores the license information for all the source
+code files. This practice allows you to just track the "COPYING" file as
+long as it is kept up to date.
+
+.. note::
+
+   -  If you specify an empty or invalid "md5" parameter,
+      :term:`BitBake` returns an md5
+      mis-match error and displays the correct "md5" parameter value
+      during the build. The correct parameter is also captured in the
+      build log.
+
+   -  If the whole file contains only license text, you do not need to
+      use the "beginline" and "endline" parameters.
+
+Enabling Commercially Licensed Recipes
+======================================
+
+By default, the OpenEmbedded build system disables components that have
+commercial or other special licensing requirements. Such requirements
+are defined on a recipe-by-recipe basis through the
+:term:`LICENSE_FLAGS` variable
+definition in the affected recipe. For instance, the
+``poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly`` recipe
+contains the following statement::
+
+   LICENSE_FLAGS = "commercial"
+
+Here is a
+slightly more complicated example that contains both an explicit recipe
+name and version (after variable expansion)::
+
+   LICENSE_FLAGS = "license_${PN}_${PV}"
+
+In order for a component restricted by a
+:term:`LICENSE_FLAGS` definition to be enabled and included in an image, it
+needs to have a matching entry in the global
+:term:`LICENSE_FLAGS_ACCEPTED`
+variable, which is a variable typically defined in your ``local.conf``
+file. For example, to enable the
+``poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly`` package, you
+could add either the string "commercial_gst-plugins-ugly" or the more
+general string "commercial" to :term:`LICENSE_FLAGS_ACCEPTED`. See the
+":ref:`dev-manual/licenses:license flag matching`" section for a full
+explanation of how :term:`LICENSE_FLAGS` matching works. Here is the
+example::
+
+   LICENSE_FLAGS_ACCEPTED = "commercial_gst-plugins-ugly"
+
+Likewise, to additionally enable the package built from the recipe
+containing ``LICENSE_FLAGS = "license_${PN}_${PV}"``, and assuming that
+the actual recipe name was ``emgd_1.10.bb``, the following string would
+enable that package as well as the original ``gst-plugins-ugly``
+package::
+
+   LICENSE_FLAGS_ACCEPTED = "commercial_gst-plugins-ugly license_emgd_1.10"
+
+As a convenience, you do not need to specify the
+complete license string for every package. You can use
+an abbreviated form, which consists of just the first portion or
+portions of the license string before the initial underscore character
+or characters. A partial string will match any license that contains the
+given string as the first portion of its license. For example, the
+following value will also match both of the packages
+previously mentioned as well as any other packages that have licenses
+starting with "commercial" or "license".
+::
+
+   LICENSE_FLAGS_ACCEPTED = "commercial license"
+
+License Flag Matching
+---------------------
+
+License flag matching allows you to control what recipes the
+OpenEmbedded build system includes in the build. Fundamentally, the
+build system attempts to match :term:`LICENSE_FLAGS` strings found in
+recipes against strings found in :term:`LICENSE_FLAGS_ACCEPTED`.
+A match causes the build system to include a recipe in the
+build, while failure to find a match causes the build system to exclude
+a recipe.
+
+In general, license flag matching is simple. However, understanding some
+concepts will help you correctly and effectively use matching.
+
+Before a flag defined by a particular recipe is tested against the
+entries of :term:`LICENSE_FLAGS_ACCEPTED`, the expanded
+string ``_${PN}`` is appended to the flag. This expansion makes each
+:term:`LICENSE_FLAGS` value recipe-specific. After expansion, the
+string is then matched against the entries. Thus, specifying
+``LICENSE_FLAGS = "commercial"`` in recipe "foo", for example, results
+in the string ``"commercial_foo"``. And, to create a match, that string
+must appear among the entries of :term:`LICENSE_FLAGS_ACCEPTED`.
+
+Judicious use of the :term:`LICENSE_FLAGS` strings and the contents of the
+:term:`LICENSE_FLAGS_ACCEPTED` variable allows you a lot of flexibility for
+including or excluding recipes based on licensing. For example, you can
+broaden the matching capabilities by using license flags string subsets
+in :term:`LICENSE_FLAGS_ACCEPTED`.
+
+.. note::
+
+   When using a string subset, be sure to use the part of the expanded
+   string that precedes the appended underscore character (e.g.
+   ``usethispart_1.3``, ``usethispart_1.4``, and so forth).
+
+For example, simply specifying the string "commercial" in the
+:term:`LICENSE_FLAGS_ACCEPTED` variable matches any expanded
+:term:`LICENSE_FLAGS` definition that starts with the string
+"commercial" such as "commercial_foo" and "commercial_bar", which
+are the strings the build system automatically generates for
+hypothetical recipes named "foo" and "bar" assuming those recipes simply
+specify the following::
+
+   LICENSE_FLAGS = "commercial"
+
+Thus, you can choose to exhaustively enumerate each license flag in the
+list and allow only specific recipes into the image, or you can use a
+string subset that causes a broader range of matches to allow a range of
+recipes into the image.
+
+This scheme works even if the :term:`LICENSE_FLAGS` string already has
+``_${PN}`` appended. For example, the build system turns the license
+flag "commercial_1.2_foo" into "commercial_1.2_foo_foo" and would match
+both the general "commercial" and the specific "commercial_1.2_foo"
+strings found in the :term:`LICENSE_FLAGS_ACCEPTED` variable, as expected.
+
+Here are some other scenarios:
+
+-  You can specify a versioned string in the recipe such as
+   "commercial_foo_1.2" in a "foo" recipe. The build system expands this
+   string to "commercial_foo_1.2_foo". Combine this license flag with a
+   :term:`LICENSE_FLAGS_ACCEPTED` variable that has the string
+   "commercial" and you match the flag along with any other flag that
+   starts with the string "commercial".
+
+-  Under the same circumstances, you can add "commercial_foo" in the
+   :term:`LICENSE_FLAGS_ACCEPTED` variable and the build system not only
+   matches "commercial_foo_1.2" but also matches any license flag with
+   the string "commercial_foo", regardless of the version.
+
+-  You can be very specific and use both the package and version parts
+   in the :term:`LICENSE_FLAGS_ACCEPTED` list (e.g.
+   "commercial_foo_1.2") to specifically match a versioned recipe.
+
+Other Variables Related to Commercial Licenses
+----------------------------------------------
+
+There are other helpful variables related to commercial license handling,
+defined in the
+``poky/meta/conf/distro/include/default-distrovars.inc`` file::
+
+   COMMERCIAL_AUDIO_PLUGINS ?= ""
+   COMMERCIAL_VIDEO_PLUGINS ?= ""
+
+If you
+want to enable these components, you can do so by making sure you have
+statements similar to the following in your ``local.conf`` configuration
+file::
+
+   COMMERCIAL_AUDIO_PLUGINS = "gst-plugins-ugly-mad \
+       gst-plugins-ugly-mpegaudioparse"
+   COMMERCIAL_VIDEO_PLUGINS = "gst-plugins-ugly-mpeg2dec \
+       gst-plugins-ugly-mpegstream gst-plugins-bad-mpegvideoparse"
+   LICENSE_FLAGS_ACCEPTED = "commercial_gst-plugins-ugly commercial_gst-plugins-bad commercial_qmmp"
+
+
+Of course, you could also create a matching list for those
+components using the more general "commercial" in the
+:term:`LICENSE_FLAGS_ACCEPTED` variable, but that would also enable all
+the other packages with :term:`LICENSE_FLAGS`
+containing "commercial", which you may or may not want::
+
+   LICENSE_FLAGS_ACCEPTED = "commercial"
+
+Specifying audio and video plugins as part of the
+``COMMERCIAL_AUDIO_PLUGINS`` and ``COMMERCIAL_VIDEO_PLUGINS`` statements
+(along with the enabling :term:`LICENSE_FLAGS_ACCEPTED`) includes the
+plugins or components into built images, thus adding support for media
+formats or components.
+
+Maintaining Open Source License Compliance During Your Product's Lifecycle
+==========================================================================
+
+One of the concerns for a development organization using open source
+software is how to maintain compliance with various open source
+licensing during the lifecycle of the product. While this section does
+not provide legal advice or comprehensively cover all scenarios, it does
+present methods that you can use to assist you in meeting the compliance
+requirements during a software release.
+
+With hundreds of different open source licenses that the Yocto Project
+tracks, it is difficult to know the requirements of each and every
+license. However, the requirements of the major FLOSS licenses can begin
+to be covered by assuming that there are three main areas of concern:
+
+-  Source code must be provided.
+
+-  License text for the software must be provided.
+
+-  Compilation scripts and modifications to the source code must be
+   provided.
+
+There are other requirements beyond the scope of these three and the
+methods described in this section (e.g. the mechanism through which
+source code is distributed).
+
+As different organizations have different methods of complying with open
+source licensing, this section is not meant to imply that there is only
+one single way to meet your compliance obligations, but rather to
+describe one method of achieving compliance. The remainder of this
+section describes methods supported to meet the previously mentioned
+three requirements. Once you take steps to meet these requirements, and
+prior to releasing images, sources, and the build system, you should
+audit all artifacts to ensure completeness.
+
+.. note::
+
+   The Yocto Project generates a license manifest during image creation
+   that is located in ``${DEPLOY_DIR}/licenses/``\ `image_name`\ ``-``\ `datestamp`
+   to assist with any audits.
+
+Providing the Source Code
+-------------------------
+
+Compliance activities should begin before you generate the final image.
+The first thing you should look at is the requirement that tops the list
+for most compliance groups --- providing the source. The Yocto Project has
+a few ways of meeting this requirement.
+
+One of the easiest ways to meet this requirement is to provide the
+entire :term:`DL_DIR` used by the
+build. This method, however, has a few issues. The most obvious is the
+size of the directory since it includes all sources used in the build
+and not just the source used in the released image. It will include
+toolchain source, and other artifacts, which you would not generally
+release. However, the more serious issue for most companies is
+accidental release of proprietary software. The Yocto Project provides
+an :ref:`archiver <ref-classes-archiver>` class to
+help avoid some of these concerns.
+
+Before you employ :term:`DL_DIR` or the :ref:`archiver <ref-classes-archiver>` class, you need to
+decide how you choose to provide source. The source :ref:`archiver <ref-classes-archiver>` class
+can generate tarballs and SRPMs and can create them with various levels
+of compliance in mind.
+
+One way of doing this (but certainly not the only way) is to release
+just the source as a tarball. You can do this by adding the following to
+the ``local.conf`` file found in the :term:`Build Directory`::
+
+   INHERIT += "archiver"
+   ARCHIVER_MODE[src] = "original"
+
+During the creation of your
+image, the source from all recipes that deploy packages to the image is
+placed within subdirectories of ``DEPLOY_DIR/sources`` based on the
+:term:`LICENSE` for each recipe.
+Releasing the entire directory enables you to comply with requirements
+concerning providing the unmodified source. It is important to note that
+the size of the directory can get large.
+
+A way to help mitigate the size issue is to only release tarballs for
+licenses that require the release of source. Let us assume you are only
+concerned with GPL code as identified by running the following script:
+
+.. code-block:: shell
+
+   # Script to archive a subset of packages matching specific license(s)
+   # Source and license files are copied into sub folders of package folder
+   # Must be run from build folder
+   #!/bin/bash
+   src_release_dir="source-release"
+   mkdir -p $src_release_dir
+   for a in tmp/deploy/sources/*; do
+      for d in $a/*; do
+         # Get package name from path
+         p=`basename $d`
+         p=${p%-*}
+         p=${p%-*}
+         # Only archive GPL packages (update *GPL* regex for your license check)
+         numfiles=`ls tmp/deploy/licenses/$p/*GPL* 2> /dev/null | wc -l`
+         if [ $numfiles -ge 1 ]; then
+            echo Archiving $p
+            mkdir -p $src_release_dir/$p/source
+            cp $d/* $src_release_dir/$p/source 2> /dev/null
+            mkdir -p $src_release_dir/$p/license
+            cp tmp/deploy/licenses/$p/* $src_release_dir/$p/license 2> /dev/null
+         fi
+      done
+   done
+
+At this point, you
+could create a tarball from the ``gpl_source_release`` directory and
+provide that to the end user. This method would be a step toward
+achieving compliance with section 3a of GPLv2 and with section 6 of
+GPLv3.
+
+Providing License Text
+----------------------
+
+One requirement that is often overlooked is inclusion of license text.
+This requirement also needs to be dealt with prior to generating the
+final image. Some licenses require the license text to accompany the
+binary. You can achieve this by adding the following to your
+``local.conf`` file::
+
+   COPY_LIC_MANIFEST = "1"
+   COPY_LIC_DIRS = "1"
+   LICENSE_CREATE_PACKAGE = "1"
+
+Adding these statements to the
+configuration file ensures that the licenses collected during package
+generation are included on your image.
+
+.. note::
+
+   Setting all three variables to "1" results in the image having two
+   copies of the same license file. One copy resides in
+   ``/usr/share/common-licenses`` and the other resides in
+   ``/usr/share/license``.
+
+   The reason for this behavior is because
+   :term:`COPY_LIC_DIRS` and
+   :term:`COPY_LIC_MANIFEST`
+   add a copy of the license when the image is built but do not offer a
+   path for adding licenses for newly installed packages to an image.
+   :term:`LICENSE_CREATE_PACKAGE`
+   adds a separate package and an upgrade path for adding licenses to an
+   image.
+
+As the source :ref:`archiver <ref-classes-archiver>` class has already archived the original
+unmodified source that contains the license files, you would have
+already met the requirements for inclusion of the license information
+with source as defined by the GPL and other open source licenses.
+
+Providing Compilation Scripts and Source Code Modifications
+-----------------------------------------------------------
+
+At this point, we have addressed all we need to prior to generating the
+image. The next two requirements are addressed during the final
+packaging of the release.
+
+By releasing the version of the OpenEmbedded build system and the layers
+used during the build, you will be providing both compilation scripts
+and the source code modifications in one step.
+
+If the deployment team has a :ref:`overview-manual/concepts:bsp layer`
+and a distro layer, and those
+those layers are used to patch, compile, package, or modify (in any way)
+any open source software included in your released images, you might be
+required to release those layers under section 3 of GPLv2 or section 1
+of GPLv3. One way of doing that is with a clean checkout of the version
+of the Yocto Project and layers used during your build. Here is an
+example:
+
+.. code-block:: shell
+
+   # We built using the dunfell branch of the poky repo
+   $ git clone -b dunfell git://git.yoctoproject.org/poky
+   $ cd poky
+   # We built using the release_branch for our layers
+   $ git clone -b release_branch git://git.mycompany.com/meta-my-bsp-layer
+   $ git clone -b release_branch git://git.mycompany.com/meta-my-software-layer
+   # clean up the .git repos
+   $ find . -name ".git" -type d -exec rm -rf {} \;
+
+One thing a development organization might want to consider for end-user
+convenience is to modify
+``meta-poky/conf/templates/default/bblayers.conf.sample`` to ensure that when
+the end user utilizes the released build system to build an image, the
+development organization's layers are included in the ``bblayers.conf`` file
+automatically::
+
+   # POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf
+   # changes incompatibly
+   POKY_BBLAYERS_CONF_VERSION = "2"
+
+   BBPATH = "${TOPDIR}"
+   BBFILES ?= ""
+
+   BBLAYERS ?= " \
+     ##OEROOT##/meta \
+     ##OEROOT##/meta-poky \
+     ##OEROOT##/meta-yocto-bsp \
+     ##OEROOT##/meta-mylayer \
+     "
+
+Creating and
+providing an archive of the :term:`Metadata`
+layers (recipes, configuration files, and so forth) enables you to meet
+your requirements to include the scripts to control compilation as well
+as any modifications to the original source.
+
+Compliance Limitations with Executables Built from Static Libraries
+-------------------------------------------------------------------
+
+When package A is added to an image via the :term:`RDEPENDS` or :term:`RRECOMMENDS`
+mechanisms as well as explicitly included in the image recipe with
+:term:`IMAGE_INSTALL`, and depends on a static linked library recipe B
+(``DEPENDS += "B"``), package B will neither appear in the generated license
+manifest nor in the generated source tarballs.  This occurs as the
+:ref:`license <ref-classes-license>` and :ref:`archiver <ref-classes-archiver>`
+classes assume that only packages included via :term:`RDEPENDS` or :term:`RRECOMMENDS`
+end up in the image.
+
+As a result, potential obligations regarding license compliance for package B
+may not be met.
+
+The Yocto Project doesn't enable static libraries by default, in part because
+of this issue. Before a solution to this limitation is found, you need to
+keep in mind that if your root filesystem is built from static libraries,
+you will need to manually ensure that your deliveries are compliant
+with the licenses of these libraries.
+
+Copying Non Standard Licenses
+=============================
+
+Some packages, such as the linux-firmware package, have many licenses
+that are not in any way common. You can avoid adding a lot of these
+types of common license files, which are only applicable to a specific
+package, by using the
+:term:`NO_GENERIC_LICENSE`
+variable. Using this variable also avoids QA errors when you use a
+non-common, non-CLOSED license in a recipe.
+
+Here is an example that uses the ``LICENSE.Abilis.txt`` file as
+the license from the fetched source::
+
+   NO_GENERIC_LICENSE[Firmware-Abilis] = "LICENSE.Abilis.txt"
+