# Customizing the Extensible SDK

This appendix presents customizations you can apply to the extensible SDK.

## Configuring the Extensible SDK

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 following filters, which the OpenEmbedded build system applies against `local.conf` and `auto.conf` if they are present:

- Variables whose values start with "/" are excluded since the assumption is that those values are paths that are likely to be specific to the build host.

- Variables listed in `SDK_LOCAL_CONF_BLACKLIST` are excluded. The default value blacklists `CONF_VERSION`, `BB_NUMBER_THREADS`, `PARALLEL_MAKE`, `PRSERV_HOST`, and `SSTATE_MIRRORS`.

- Variables listed in `SDK_LOCAL_CONF_WHITELIST` are included. Including a variable in the value of `SDK_LOCAL_CONF_WHITELIST` overrides either of the above two conditions. The default value is blank.

- Classes inherited globally with `INHERIT` that are listed in `SDK_INHERIT_BLACKLIST` are disabled. Using `SDK_INHERIT_BLACKLIST` to disable these classes is is the typical method to disable classes that are problematic or unnecessary in the SDK context. The default value blacklists the `buildhistory` and `icecc` classes.

Additionally, the contents of `conf/sdk-extra.conf`, when present, are appended to the end of `conf/local.conf` within the produced SDK, without any filtering. The `sdk-extra.conf` 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.

## Adjusting the Extensible SDK to Suit Your Build System Setup

In most cases, the extensible SDK defaults should work. However, some cases exist for which you might consider making adjustments:

- If your SDK configuration inherits additional classes using the `INHERIT` variable and you do not need or want those classes enabled in the SDK, you can blacklist them by adding them to the `SDK_INHERIT_BLACKLIST` variable. The default value of `SDK_INHERIT_BLACKLIST` is set using the "?=" operator. Consequently, you will need to either set the complete value using "=" or append the value using "_append".

- If you have classes or recipes that add additional tasks to the standard build flow (i.e. that execute as part of building the recipe as opposed to needing to be called explicitly), then you need to do one of the following:

  - Ensure the tasks are shared state tasks (i.e. their output is saved to and can be restored from the shared state cache), or that the tasks are able to be produced quickly from a task that is a shared state task and add the task name to the value of `SDK_RECRDEP_TASKS`.

  - 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 `SDK_INHERIT_BLACKLIST` as previously described.

- 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 "Providing Additional Installable Extensible SDK Content" section for information.

- If you want users of the SDK to be able to easily update the SDK, you need to set the `SDK_UPDATE_URL` variable. For more information, see the "Providing Updates After Installing the Extensible SDK" section.

- If you have adjusted the list of files and directories that appear in `COREBASE` (other than layers that are enabled through `bblayers.conf`), then you must list these files in `COREBASE_FILES` so that the files are copied into the SDK.

- If your OpenEmbedded build system setup uses a different environment setup script other than `&OE_INIT_FILE;` or `oe-init-build-env-memres`, then you must set `OE_INIT_ENV_SCRIPT` to point to the environment setup script you use.

  You must also reflect this change in the value used for the `COREBASE_FILES` variable as previously described.

## Changing the Appearance of the Extensible SDK

You can change the title shown by the SDK installer by setting the `SDK_TITLE` variable. By default, this title is derived from `DISTRO_NAME` when it is set. If the `DISTRO_NAME` variable is not set, the title is derived from the `DISTRO` variable.

## Providing Updates After Installing the Extensible SDK

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 to make it possible for those that use the SDK to update their installations with the `devtool sdk-update` command:

1. Arrange to be created a directory that can be shared over HTTP or HTTPS.

2. Set the `SDK_UPDATE_URL` 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 `devtool sdk-update` command.

3. Build the extensible SDK normally (i.e., use the `bitbake -c populate_sdk_ext` imagename command).

4. Publish the SDK using the following command:

            $ oe-publish-sdk some_path/sdk-installer.sh path_to_shared/http_directory

   You must repeat this step each time you rebuild the SDK with changes that you want to make available through the update mechanism.

Completing the above steps allows users of the existing SDKs to simply run `devtool sdk-update` to retrieve the latest updates. See the "Updating the Extensible SDK" section for further information.

## Providing Additional Installable Extensible SDK Content

If you want the users of the extensible SDK you are building to be able to add items to the SDK without needing to build the items from source, you need to do a number of things:

1. Ensure the additional items you want the user to be able to install are actually built. You can ensure these items are built a number of different ways: 1) Build them explicitly, perhaps using one or more "meta" recipes that depend on lists of other recipes to keep things tidy, or 2) Build the "world" target and set `EXCLUDE_FROM_WORLD_pn-`recipename for the recipes you do not want built. See the `EXCLUDE_FROM_WORLD` variable for additional information.

2. Expose the `sstate-cache` directory produced by the build. Typically, you expose this directory over HTTP or HTTPS.

3. Set the appropriate configuration so that the produced SDK knows how to find the configuration. The variable you need to set is `SSTATE_MIRRORS`:

            SSTATE_MIRRORS = "file://.*  http://example.com/some_path/sstate-cache/PATH"

   You can set the `SSTATE_MIRRORS` variable in two different places:

   - 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 `local.conf` or custom distro configuration file. You can then "whitelist" the variable through to the SDK by adding the following:

              SDK_LOCAL_CONF_WHITELIST = "SSTATE_MIRRORS"

   - Alternatively, if you just want to set the `SSTATE_MIRRORS` variable's value for the SDK alone, create a `conf/sdk-extra.conf` either in your Build Directory or within any layer and put your `SSTATE_MIRRORS` setting within that file.

     This second option is the safest option should you have any doubts as to which method to use when setting `SSTATE_MIRRORS`.

## Minimizing the Size of the Extensible SDK Installer Download

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 `devtool command` by setting the following in your configuration:

         SDK_EXT_TYPE = "minimal"

Setting `SDK_EXT_TYPE` 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 must be installed either "on the fly" or through actions you perform using `devtool` or explicitly with the `devtool sdk-install` command.

In most cases, when building a minimal SDK you will need to also enable bringing in the information on a wider range of packages produced by the system. This is particularly true so that `devtool add` is able to effectively map dependencies it discovers in a source tree to the appropriate recipes. Also so that the `devtool search` command is able to return useful results.

To facilitate this wider range of information, you would additionally set the following:

         SDK_INCLUDE_PKGDATA = "1"

See the `SDK_INCLUDE_PKGDATA` variable for additional information.

Setting the `SDK_INCLUDE_PKGDATA` 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.

You can use `EXCLUDE_FROM_WORLD_pn-`recipename 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.

If you set `SDK_EXT_TYPE` to "minimal", then providing a shared state mirror is mandatory so that items can be installed as needed. See the "Providing Additional Installable Extensible SDK Content" section for more information.

You can explicitly control whether or not to include the toolchain when you build an SDK by setting the `SDK_INCLUDE_TOOLCHAIN` variable to "1". In particular, it is useful to include the toolchain when you have set `SDK_EXT_TYPE` to "minimal", which by default, excludes the toolchain. Also, it is helpful if you are building a small SDK for use with an IDE, such as Eclipse, or some other tool where you do not want to take extra steps to install a toolchain.