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+<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
+[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
+<!--SPDX-License-Identifier: CC-BY-2.0-UK-->
+
+<appendix id='sdk-appendix-customizing'>
+
+<title>Customizing the Extensible SDK</title>
+
+<para>
+    This appendix describes customizations you can apply to the extensible SDK.
+</para>
+
+<section id='sdk-configuring-the-extensible-sdk'>
+    <title>Configuring the Extensible SDK</title>
+
+    <para>
+        The extensible SDK primarily consists of a pre-configured copy of
+        the OpenEmbedded build system from which it was produced.
+        Thus, the SDK's configuration is derived using that build system and
+        the filters shown in the following list.
+        When these filters are present, the OpenEmbedded build system applies
+        them against <filename>local.conf</filename> and
+        <filename>auto.conf</filename>:
+        <itemizedlist>
+            <listitem><para>
+                Variables whose values start with "/" are excluded since the
+                assumption is that those values are paths that are likely to
+                be specific to the
+                <ulink url='&YOCTO_DOCS_REF_URL;#hardware-build-system-term'>build host</ulink>.
+                </para></listitem>
+            <listitem><para>
+                Variables listed in
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_LOCAL_CONF_BLACKLIST'><filename>SDK_LOCAL_CONF_BLACKLIST</filename></ulink>
+                are excluded.
+                These variables are not allowed through from the OpenEmbedded
+                build system configuration into the extensible SDK
+                configuration.
+                Typically, these variables are specific to the machine on
+                which the build system is running and could be problematic
+                as part of the extensible SDK configuration.</para>
+
+                <para>For a list of the variables excluded by default, see the
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_LOCAL_CONF_BLACKLIST'><filename>SDK_LOCAL_CONF_BLACKLIST</filename></ulink>
+                in the glossary of the Yocto Project Reference Manual.
+                </para></listitem>
+            <listitem><para>
+                Variables listed in
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_LOCAL_CONF_WHITELIST'><filename>SDK_LOCAL_CONF_WHITELIST</filename></ulink>
+                are included.
+                Including a variable in the value of
+                <filename>SDK_LOCAL_CONF_WHITELIST</filename> overrides either
+                of the previous two filters.
+                The default value is blank.
+                </para></listitem>
+            <listitem><para>
+                Classes inherited globally with
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-INHERIT'><filename>INHERIT</filename></ulink>
+                that are listed in
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_INHERIT_BLACKLIST'><filename>SDK_INHERIT_BLACKLIST</filename></ulink>
+                are disabled.
+                Using <filename>SDK_INHERIT_BLACKLIST</filename> to disable
+                these classes is the typical method to disable classes that
+                are problematic or unnecessary in the SDK context.
+                The default value blacklists the
+                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-buildhistory'><filename>buildhistory</filename></ulink>
+                and
+                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-icecc'><filename>icecc</filename></ulink>
+                classes.
+                </para></listitem>
+        </itemizedlist>
+        Additionally, the contents of <filename>conf/sdk-extra.conf</filename>,
+        when present, are appended to the end of
+        <filename>conf/local.conf</filename> within the produced SDK, without
+        any filtering.
+        The <filename>sdk-extra.conf</filename> file is particularly useful
+        if you want to set a variable value just for the SDK and not the
+        OpenEmbedded build system used to create the SDK.
+    </para>
+</section>
+
+<section id='adjusting-the-extensible-sdk-to-suit-your-build-hosts-setup'>
+    <title>Adjusting the Extensible SDK to Suit Your Build Host's Setup</title>
+
+    <para>
+        In most cases, the extensible SDK defaults should work with your
+        <ulink url='&YOCTO_DOCS_REF_URL;#hardware-build-system-term'>build host's</ulink>
+        setup.
+        However, some cases exist for which you might consider making
+        adjustments:
+        <itemizedlist>
+            <listitem><para>
+                If your SDK configuration inherits additional classes
+                using the
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-INHERIT'><filename>INHERIT</filename></ulink>
+                variable and you do not need or want those classes enabled in
+                the SDK, you can blacklist them by adding them to the
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_INHERIT_BLACKLIST'><filename>SDK_INHERIT_BLACKLIST</filename></ulink>
+                variable as described in the fourth bullet of the previous
+                section.
+                <note>
+                    The default value of
+                    <filename>SDK_INHERIT_BLACKLIST</filename> is set using
+                    the "?=" operator.
+                    Consequently, you will need to either define the entire
+                    list by using the "=" operator, or you will need to append
+                    a value using either "_append" or the "+=" operator.
+                    You can learn more about these operators in the
+                    "<ulink url='&YOCTO_DOCS_BB_URL;#basic-syntax'>Basic Syntax</ulink>"
+                    section of the BitBake User Manual.
+                </note>.
+                </para></listitem>
+            <listitem><para>
+                If you have classes or recipes that add additional tasks to
+                the standard build flow (i.e. the tasks execute as the recipe
+                builds as opposed to being called explicitly), then you need
+                to do one of the following:
+                <itemizedlist>
+                    <listitem><para>
+                        After ensuring the tasks are
+                        <ulink url='&YOCTO_DOCS_OM_URL;#shared-state-cache'>shared state</ulink>
+                        tasks (i.e. the output of the task is saved to and
+                        can be restored from the shared state cache) or
+                        ensuring the tasks are able to be produced quickly from
+                        a task that is a shared state task, add the task name
+                        to the value of
+                        <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_RECRDEP_TASKS'><filename>SDK_RECRDEP_TASKS</filename></ulink>.
+                        </para></listitem>
+                    <listitem><para>
+                        Disable the tasks if they are added by a class and
+                        you do not need the functionality the class provides
+                        in the extensible SDK.
+                        To disable the tasks, add the class to the
+                        <filename>SDK_INHERIT_BLACKLIST</filename> variable
+                        as described in the previous section.
+                        </para></listitem>
+                </itemizedlist>
+                </para></listitem>
+            <listitem><para>
+                Generally, you want to have a shared state mirror set up so
+                users of the SDK can add additional items to the SDK after
+                installation without needing to build the items from source.
+                See the
+                "<link linkend='sdk-providing-additional-installable-extensible-sdk-content'>Providing Additional Installable Extensible SDK Content</link>"
+                section for information.
+                </para></listitem>
+            <listitem><para>
+                If you want users of the SDK to be able to easily update the
+                SDK, you need to set the
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_UPDATE_URL'><filename>SDK_UPDATE_URL</filename></ulink>
+                variable.
+                For more information, see the
+                "<link linkend='sdk-providing-updates-to-the-extensible-sdk-after-installation'>Providing Updates to the Extensible SDK After Installation</link>"
+                section.
+                </para></listitem>
+            <listitem><para>
+                If you have adjusted the list of files and directories that
+                appear in
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-COREBASE'><filename>COREBASE</filename></ulink>
+                (other than layers that are enabled through
+                <filename>bblayers.conf</filename>), then you must list these
+                files in
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-COREBASE_FILES'><filename>COREBASE_FILES</filename></ulink>
+                so that the files are copied into the SDK.
+                </para></listitem>
+            <listitem><para>
+                If your OpenEmbedded build system setup uses a different
+                environment setup script other than
+                <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>,
+                then you must set
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-OE_INIT_ENV_SCRIPT'><filename>OE_INIT_ENV_SCRIPT</filename></ulink>
+                to point to the environment setup script you use.
+                <note>
+                    You must also reflect this change in the value used for the
+                    <filename>COREBASE_FILES</filename> variable as previously
+                    described.
+                </note>
+                </para></listitem>
+        </itemizedlist>
+    </para>
+</section>
+
+<section id='sdk-changing-the-sdk-installer-title'>
+    <title>Changing the Extensible SDK Installer Title</title>
+
+    <para>
+        You can change the displayed title for the SDK installer by setting
+        the
+        <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_TITLE'><filename>SDK_TITLE</filename></ulink>
+        variable and then rebuilding the the SDK installer.
+        For information on how to build an SDK installer, see the
+        "<link linkend='sdk-building-an-sdk-installer'>Building an SDK Installer</link>"
+        section.
+    </para>
+
+    <para>
+        By default, this title is derived from
+        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_NAME'><filename>DISTRO_NAME</filename></ulink>
+        when it is set.
+        If the <filename>DISTRO_NAME</filename> variable is not set, the title
+        is derived from the
+        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
+        variable.
+    </para>
+
+    <para>
+        The
+        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-populate-sdk-*'><filename>populate_sdk_base</filename></ulink>
+        class defines the default value of the <filename>SDK_TITLE</filename>
+        variable as follows:
+        <literallayout class='monospaced'>
+     SDK_TITLE ??= "${@d.getVar('DISTRO_NAME') or d.getVar('DISTRO')} SDK"
+        </literallayout>
+    </para>
+
+    <para>
+        While several ways exist to change this variable, an efficient method
+        is to set the variable in your distribution's configuration file.
+        Doing so creates an SDK installer title that applies across your
+        distribution.
+        As an example, assume you have your own layer for your distribution
+        named "meta-mydistro" and you are using the same type of file
+        hierarchy as does the default "poky" distribution.
+        If so, you could update the <filename>SDK_TITLE</filename> variable
+        in the
+        <filename>~/meta-mydistro/conf/distro/mydistro.conf</filename> file
+        using the following form:
+        <literallayout class='monospaced'>
+     SDK_TITLE = "<replaceable>your_title</replaceable>"
+        </literallayout>
+    </para>
+</section>
+
+<section id='sdk-providing-updates-to-the-extensible-sdk-after-installation'>
+    <title>Providing Updates to the Extensible SDK After Installation</title>
+
+    <para>
+        When you make changes to your configuration or to the metadata and
+        if you want those changes to be reflected in installed SDKs, you need
+        to perform additional steps.
+        These steps make it possible for anyone using the installed SDKs to
+        update the installed SDKs by using the
+        <filename>devtool sdk-update</filename> command:
+        <orderedlist>
+            <listitem><para>
+                Create a directory that can be shared over HTTP or HTTPS.
+                You can do this by setting up a web server such as an
+                <ulink url='https://en.wikipedia.org/wiki/Apache_HTTP_Server'>Apache HTTP Server</ulink>
+                or
+                <ulink url='https://en.wikipedia.org/wiki/Nginx'>Nginx</ulink>
+                server in the cloud to host the directory.
+                This directory must contain the published SDK.
+                </para></listitem>
+            <listitem><para>
+                Set the
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_UPDATE_URL'><filename>SDK_UPDATE_URL</filename></ulink>
+                variable to point to the corresponding HTTP or HTTPS URL.
+                Setting this variable causes any SDK built to default to that
+                URL and thus, the user does not have to pass the URL to the
+                <filename>devtool sdk-update</filename> command as described
+                in the
+                "<link linkend='sdk-applying-updates-to-an-installed-extensible-sdk'>Applying Updates to an Installed Extensible SDK</link>"
+                section.
+                </para></listitem>
+            <listitem><para>
+                Build the extensible SDK normally (i.e., use the
+                <filename>bitbake -c populate_sdk_ext</filename> <replaceable>imagename</replaceable>
+                command).
+                </para></listitem>
+            <listitem><para>
+                Publish the SDK using the following command:
+                <literallayout class='monospaced'>
+     $ oe-publish-sdk <replaceable>some_path</replaceable>/sdk-installer.sh <replaceable>path_to_shared_http_directory</replaceable>
+                </literallayout>
+                You must repeat this step each time you rebuild the SDK
+                with changes that you want to make available through the
+                update mechanism.
+                </para></listitem>
+        </orderedlist>
+    </para>
+
+    <para>
+        Completing the above steps allows users of the existing installed
+        SDKs to simply run <filename>devtool sdk-update</filename> to
+        retrieve and apply the latest updates.
+        See the
+        "<link linkend='sdk-applying-updates-to-an-installed-extensible-sdk'>Applying Updates to an Installed Extensible SDK</link>"
+        section for further information.
+    </para>
+</section>
+
+<section id='sdk-changing-the-default-sdk-installation-directory'>
+    <title>Changing the Default SDK Installation Directory</title>
+
+    <para>
+        When you build the installer for the Extensible SDK, the default
+        installation directory for the SDK is based on the
+        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
+        and
+        <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKEXTPATH'><filename>SDKEXTPATH</filename></ulink>
+        variables from within the
+        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-populate-sdk-*'><filename>populate_sdk_base</filename></ulink>
+        class as follows:
+        <literallayout class='monospaced'>
+     SDKEXTPATH ??= "~/${@d.getVar('DISTRO')}_sdk"
+        </literallayout>
+        You can change this default installation directory by specifically
+        setting the <filename>SDKEXTPATH</filename> variable.
+    </para>
+
+    <para>
+        While a number of ways exist through which you can set this variable,
+        the method that makes the most sense is to set the variable in your
+        distribution's configuration file.
+        Doing so creates an SDK installer default directory that applies
+        across your distribution.
+        As an example, assume you have your own layer for your distribution
+        named "meta-mydistro" and you are using the same type of file
+        hierarchy as does the default "poky" distribution.
+        If so, you could update the <filename>SDKEXTPATH</filename> variable
+        in the
+        <filename>~/meta-mydistro/conf/distro/mydistro.conf</filename> file
+        using the following form:
+        <literallayout class='monospaced'>
+     SDKEXTPATH = "<replaceable>some_path_for_your_installed_sdk</replaceable>"
+        </literallayout>
+    </para>
+
+    <para>
+        After building your installer, running it prompts the user for
+        acceptance of the
+        <replaceable>some_path_for_your_installed_sdk</replaceable> directory
+        as the default location to install the Extensible SDK.
+    </para>
+</section>
+
+<section id='sdk-providing-additional-installable-extensible-sdk-content'>
+    <title>Providing Additional Installable Extensible SDK Content</title>
+
+    <para>
+        If you want the users of an extensible SDK you build to be
+        able to add items to the SDK without requiring the users to build
+        the items from source, you need to do a number of things:
+        <orderedlist>
+            <listitem><para>
+                Ensure the additional items you want the user to be able to
+                install are already built:
+                <itemizedlist>
+                    <listitem><para>
+                        Build the items explicitly.
+                        You could use one or more "meta" recipes that depend
+                        on lists of other recipes.
+                        </para></listitem>
+                    <listitem><para>
+                        Build the "world" target and set
+                        <filename>EXCLUDE_FROM_WORLD_pn-</filename><replaceable>recipename</replaceable>
+                        for the recipes you do not want built.
+                        See the
+                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXCLUDE_FROM_WORLD'><filename>EXCLUDE_FROM_WORLD</filename></ulink>
+                        variable for additional information.
+                        </para></listitem>
+                </itemizedlist>
+                </para></listitem>
+            <listitem><para>
+                Expose the <filename>sstate-cache</filename> directory
+                produced by the build.
+                Typically, you expose this directory by making it available
+                through an
+                <ulink url='https://en.wikipedia.org/wiki/Apache_HTTP_Server'>Apache HTTP Server</ulink>
+                or
+                <ulink url='https://en.wikipedia.org/wiki/Nginx'>Nginx</ulink>
+                server.
+                </para></listitem>
+            <listitem><para>
+                Set the appropriate configuration so that the produced SDK
+                knows how to find the configuration.
+                The variable you need to set is
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_MIRRORS'><filename>SSTATE_MIRRORS</filename></ulink>:
+                <literallayout class='monospaced'>
+     SSTATE_MIRRORS = "file://.*  http://<replaceable>example</replaceable>.com/<replaceable>some_path</replaceable>/sstate-cache/PATH"
+                </literallayout>
+                You can set the <filename>SSTATE_MIRRORS</filename> variable
+                in two different places:
+                <itemizedlist>
+                    <listitem><para>
+                        If the mirror value you are setting is appropriate to
+                        be set for both the OpenEmbedded build system that is
+                        actually building the SDK and the SDK itself (i.e. the
+                        mirror is accessible in both places or it will fail
+                        quickly on the OpenEmbedded build system side, and its
+                        contents will not interfere with the build), then you
+                        can set the variable in your
+                        <filename>local.conf</filename> or custom distro
+                        configuration file.
+                        You can then "whitelist" the variable through
+                        to the SDK by adding the following:
+                        <literallayout class='monospaced'>
+     SDK_LOCAL_CONF_WHITELIST = "SSTATE_MIRRORS"
+                        </literallayout>
+                        </para></listitem>
+                    <listitem><para>
+                        Alternatively, if you just want to set the
+                        <filename>SSTATE_MIRRORS</filename> variable's value
+                        for the SDK alone, create a
+                        <filename>conf/sdk-extra.conf</filename> file either in
+                        your
+                        <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
+                        or within any layer and put your
+                        <filename>SSTATE_MIRRORS</filename> setting within
+                        that file.
+                        <note>
+                            This second option is the safest option should
+                            you have any doubts as to which method to use when
+                            setting <filename>SSTATE_MIRRORS</filename>.
+                        </note>
+                        </para></listitem>
+                </itemizedlist>
+                </para></listitem>
+        </orderedlist>
+    </para>
+</section>
+
+<section id='sdk-minimizing-the-size-of-the-extensible-sdk-installer-download'>
+    <title>Minimizing the Size of the Extensible SDK Installer Download</title>
+
+    <para>
+        By default, the extensible SDK bundles the shared state artifacts for
+        everything needed to reconstruct the image for which the SDK was built.
+        This bundling can lead to an SDK installer file that is a Gigabyte or
+        more in size.
+        If the size of this file causes a problem, you can build an SDK that
+        has just enough in it to install and provide access to the
+        <filename>devtool command</filename> by setting the following in your
+        configuration:
+        <literallayout class='monospaced'>
+     SDK_EXT_TYPE = "minimal"
+        </literallayout>
+        Setting
+        <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_EXT_TYPE'><filename>SDK_EXT_TYPE</filename></ulink>
+        to "minimal" produces an SDK installer that is around 35 Mbytes in
+        size, which downloads and installs quickly.
+        You need to realize, though, that the minimal installer does not
+        install any libraries or tools out of the box.
+        These libraries and tools must be installed either "on the fly" or
+        through actions you perform using <filename>devtool</filename> or
+        explicitly with the <filename>devtool sdk-install</filename> command.
+    </para>
+
+    <para>
+        In most cases, when building a minimal SDK you need to also enable
+        bringing in the information on a wider range of packages produced by
+        the system.
+        Requiring this wider range of information is particularly true
+        so that <filename>devtool add</filename> is able to effectively map
+        dependencies it discovers in a source tree to the appropriate recipes.
+        Additionally, the information enables the
+        <filename>devtool search</filename> command to return useful results.
+    </para>
+
+    <para>
+        To facilitate this wider range of information, you would need to
+        set the following:
+        <literallayout class='monospaced'>
+     SDK_INCLUDE_PKGDATA = "1"
+        </literallayout>
+        See the
+        <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_INCLUDE_PKGDATA'><filename>SDK_INCLUDE_PKGDATA</filename></ulink>
+        variable for additional information.
+    </para>
+
+    <para>
+        Setting the <filename>SDK_INCLUDE_PKGDATA</filename> variable as
+        shown causes the "world" target to be built so that information
+        for all of the recipes included within it are available.
+        Having these recipes available increases build time significantly and
+        increases the size of the SDK installer by 30-80 Mbytes depending on
+        how many recipes are included in your configuration.
+    </para>
+
+    <para>
+        You can use
+        <filename>EXCLUDE_FROM_WORLD_pn-</filename><replaceable>recipename</replaceable>
+        for recipes you want to exclude.
+        However, it is assumed that you would need to be building the "world"
+        target if you want to provide additional items to the SDK.
+        Consequently, building for "world" should not represent undue
+        overhead in most cases.
+        <note>
+            If you set <filename>SDK_EXT_TYPE</filename> to "minimal",
+            then providing a shared state mirror is mandatory so that items
+            can be installed as needed.
+            See the
+            "<link linkend='sdk-providing-additional-installable-extensible-sdk-content'>Providing Additional Installable Extensible SDK Content</link>"
+            section for more information.
+        </note>
+    </para>
+
+    <para>
+        You can explicitly control whether or not to include the toolchain
+        when you build an SDK by setting the
+        <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_INCLUDE_TOOLCHAIN'><filename>SDK_INCLUDE_TOOLCHAIN</filename></ulink>
+        variable to "1".
+        In particular, it is useful to include the toolchain when you
+        have set <filename>SDK_EXT_TYPE</filename> to "minimal", which by
+        default, excludes the toolchain.
+        Also, it is helpful if you are building a small SDK for use with
+        an IDE or some
+        other tool where you do not want to take extra steps to install a
+        toolchain.
+    </para>
+</section>
+</appendix>
+<!--
+vim: expandtab tw=80 ts=4
+-->