%poky; ] > This appendix presents customizations you can apply to both the standard and extensible SDK. Each subsection identifies the type of SDK to which the section applies.

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.

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.

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.

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: Arrange to be created a directory that can be shared over HTTP or HTTPS. 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. Build the extensible SDK normally (i.e., use the bitbake -c populate_sdk_ext imagename command). 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.

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

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.

The devtool add command automatically creates a recipe based on the source tree with which you provide it. Currently, the command has support for the following: Autotools (autoconf and automake) CMake Scons qmake Plain Makefile Out-of-tree kernel module Binary package (i.e. "-b" option) Node.js module through npm Python modules that use setuptools or distutils Apart from binary packages, the determination of how a source tree should be treated is automatic based on the files present within that source tree. For example, if a CMakeLists.txt file is found, then the source tree is assumed to be using CMake and is treated accordingly. In most cases, you need to edit the automatically generated recipe in order to make it build properly. Typically, you would go through several edit and build cycles until you can build the recipe. Once the recipe can be built, you could use possible further iterations to test the recipe on the target device. The remainder of this section covers specifics regarding how parts of the recipe are generated.

If you do not specify a name and version on the command line, devtool add attempts to determine the name and version of the software being built from various metadata within the source tree. Furthermore, the command sets the name of the created recipe file accordingly. If the name or version cannot be determined, the devtool add command prints an error and you must re-run the command with both the name and version or just the name or version specified. Sometimes the name or version determined from the source tree might be incorrect. For such a case, you must run the following commands: $ devtool reset -n recipename After running the devtool reset command, you need to run devtool add again and provide the name or the version.

The devtool add command attempts to detect build-time dependencies and map them to other recipes in the system. During this mapping, the command fills in the names of those recipes in the DEPENDS value within the recipe. If a dependency cannot be mapped, then a comment is placed in the recipe indicating such. The inability to map a dependency might be caused because the naming is not recognized or because the dependency simply is not available. For cases where the dependency is not available, you must use the devtool add command to add an additional recipe to satisfy the dependency and then come back to the first recipe and add its name to DEPENDS. If you need to add runtime dependencies, you can do so by adding the following to your recipe: RDEPENDS_${PN} += "dependency1 dependency2 ..." The devtool add command often cannot distinguish between mandatory and optional dependencies. Consequently, some of the detected dependencies might in fact be optional. When in doubt, consult the documentation or the configure script for the software the recipe is building for further details. In some cases, you might find you can substitute the dependency for an option to disable the associated functionality passed to the configure script.

The devtool add command attempts to determine if the software you are adding is able to be distributed under a common open-source license and sets the LICENSE value accordingly. You should double-check this value against the documentation or source files for the software you are building and update that LICENSE value if necessary. The devtool add command also sets the LIC_FILES_CHKSUM value to point to all files that appear to be license-related. However, license statements often appear in comments at the top of source files or within documentation. Consequently, you might need to amend the LIC_FILES_CHKSUM variable to point to one or more of those comments if present. Setting LIC_FILES_CHKSUM is particularly important for third-party software. The command attempts to ensure correct licensing should you upgrade the recipe to a newer upstream version in future. Any change in licensing is detected and you receive an error prompting you to check the license text again. If the devtool add command cannot determine licensing information, the LICENSE value is set to "CLOSED" and the LIC_FILES_CHKSUM vaule remains unset. This behavior allows you to continue with development but is unlikely to be correct in all cases. Consequently, you should check the documentation or source files for the software you are building to determine the actual license.

The use of make by itself is very common in both proprietary and open source software. Unfortunately, Makefiles are often not written with cross-compilation in mind. Thus, devtool add often cannot do very much to ensure that these Makefiles build correctly. It is very common, for example, to explicitly call gcc instead of using the CC variable. Usually, in a cross-compilation environment, gcc is the compiler for the build host and the cross-compiler is named something similar to arm-poky-linux-gnueabi-gcc and might require some arguments (e.g. to point to the associated sysroot for the target machine). When writing a recipe for Makefile-only software, keep the following in mind: You probably need to patch the Makefile to use variables instead of hardcoding tools within the toolchain such as gcc and g++. The environment in which make runs is set up with various standard variables for compilation (e.g. CC, CXX, and so forth) in a similar manner to the environment set up by the SDK's environment setup script. One easy way to see these variables is to run the devtool build command on the recipe and then look in oe-logs/run.do_compile. Towards the top of this file you will see a list of environment variables that are being set. You can take advantage of these variables within the Makefile. If the Makefile sets a default for a variable, that default overrides the value set in the environment, which is usually not desirable. In this situation, you can either patch the Makefile so it sets the default using the "?=" operator, or you can alternatively force the value on the make command line. To force the value on the command line, add the variable setting to EXTRA_OEMAKE within the recipe as follows: EXTRA_OEMAKE += "'CC=${CC}' 'CXX=${CXX}'" In the above example, single quotes are used around the variable settings as the values are likely to contain spaces because required default options are passed to the compiler. Hardcoding paths inside Makefiles is often problematic in a cross-compilation environment. This is particularly true because those hardcoded paths often point to locations on the build host and thus will either be read-only or will introduce contamination into the cross-compilation by virtue of being specific to the build host rather than the target. Patching the Makefile to use prefix variables or other path variables is usually the way to handle this. Sometimes a Makefile runs target-specific commands such as ldconfig. For such cases, you might be able to simply apply patches that remove these commands from the Makefile.

Often, you need to build additional tools that run on the build host system as opposed to the target. You should indicate this using one of the following methods when you run devtool add: Specify the name of the recipe such that it ends with "-native". Specifying the name like this produces a recipe that only builds for the build host. Specify the "‐‐also-native" option with the devtool add command. Specifying this option creates a recipe file that still builds for the target but also creates a variant with a "-native" suffix that builds for the build host. If you need to add a tool that is shipped as part of a source tree that builds code for the target, you can typically accomplish this by building the native and target parts separately rather than within the same compilation process. Realize though that with the "‐‐also-native" option, you can add the tool using just one recipe file.

You can use the devtool add command in the following form to add Node.js modules: $ devtool add "npm://registry.npmjs.org;name=forever;version=0.15.1" The name and version parameters are mandatory. Lockdown and shrinkwrap files are generated and pointed to by the recipe in order to freeze the version that is fetched for the dependencies according to the first time. This also saves checksums that are verified on future fetches. Together, these behaviors ensure the reproducibility and integrity of the build. You must use quotes around the URL. The devtool add does not require the quotes, but the shell considers ";" as a splitter between multiple commands. Thus, devtool add does not receive the other parts resulting in several "command not found" errors. In order to support adding Node.js modules, a nodejs recipe must be part of your SDK in order to provide Node.js itself.

When building a recipe with devtool build the typical workflow is as follows: Fetch the source Unpack the source Configure the source Compiling the source Install the build output Package the installed output For recipes in the workspace, fetching and unpacking is disabled as the source tree has already been prepared and is persistent. Each of these build steps is defined as a function, usually with a "do_" prefix. These functions are typically shell scripts but can instead be written in Python. If you look at the contents of a recipe, you will see that the recipe does not include complete instructions for building the software. Instead, common functionality is encapsulated in classes inherited with the inherit directive, leaving the recipe to describe just the things that are specific to the software to be built. A base class exists that is implicitly inherited by all recipes and provides the functionality that most typical recipes need. The remainder of this section presents information useful when working with recipes.

When you are debugging a recipe that you previously created using devtool add or whose source you are modifying by using the devtool modify command, after the first run of devtool build, you will find some symbolic links created within the source tree: oe-logs, which points to the directory in which log files and run scripts for each build step are created and oe-workdir, which points to the temporary work area for the recipe. You can use these links to get more information on what is happening at each build step. These locations under oe-workdir are particularly useful: image/: Contains all of the files installed at the do_install stage. Within a recipe, this directory is referred to by the expression ${D}. sysroot-destdir/: Contains a subset of files installed within do_install that have been put into the shared sysroot. For more information, see the "Sharing Files Between Recipes" section. packages-split/: Contains subdirectories for each package produced by the recipe. (more on "Packaging" below) For more information, see the "Packaging" section.

If the software your recipe is building uses GNU autoconf, then a fixed set of arguments is passed to it to enable cross-compilation plus any extras specified by EXTRA_OECONF set within the recipe. If you wish to pass additional options, add them to EXTRA_OECONF. Other supported build tools have similar variables (e.g. EXTRA_OECMAKE for CMake, EXTRA_OESCONS for Scons, and so forth). If you need to pass anything on the make command line, you can use EXTRA_OEMAKE to do so. You can use the devtool configure-help command to help you set the arguments listed in the previous paragraph. The command determines the exact options being passed, and shows them to you along with any custom arguments specified through EXTRA_OECONF. If applicable, the command also shows you the output of the configure script's "‐‐help" option as a reference.

Recipes often need to use files provided by other recipes on the build host. For example, an application linking to a common library needs access to the library itself and its associated headers. The way this access is accomplished within the extensible SDK is through the sysroot. One sysroot exists per "machine" for which the SDK is being built. In practical terms, this means a sysroot exists for the target machine, and a sysroot exists for the build host. Recipes should never write files directly into the sysroot. Instead, files should be installed into standard locations during the do_install task within the ${D} directory. A subset of these files automatically go into the sysroot. The reason for this limitation is that almost all files that go into the sysroot are cataloged in manifests in order to ensure they can be removed later when a a recipe is modified or removed. Thus, the sysroot is able to remain free from stale files.

Packaging is not always particularly relevant within the extensible SDK. However, if you examine build output gets into the final image on the target device, it is important to understand packaging because the contents of the image are expressed in terms of packages ... not recipes. During the do_package task, files installed during the do_install task are split into one main package, which is almost always named the same as the recipe, and several other packages. This separation is done because not all of those installed files are always useful in every image. For example, you probably do not need any of the documentation installed in a production image. Consequently, for each recipe the documentation files are separated into a -doc package. Recipes that package software that has optional modules or plugins might do additional package splitting as well. After building a recipe you can see where files have gone by looking in the oe-workdir/packages-split directory, which contains a subdirectory for each package. Apart from some advanced cases, the PACKAGES and FILES variables controls splitting. The PACKAGES variable lists all of the packages to be produced, while the FILES variable specifies which files to include in each package, using an override to specify the package. For example, FILES_${PN} specifies the files to go into the main package (i.e. the main package is named the same as the recipe and ${PN} evaluates to the recipe name). The order of the PACKAGES value is significant. For each installed file, the first package whose FILES value matches the file is the package into which the file goes. Defaults exist for both the PACKAGES and FILES variables. Consequently, you might find you do not even need to set these variables in your recipe unless the software the recipe is building installs files into non-standard locations.

If you use the devtool deploy-target command to write a recipe's build output to the target, and you are working on an existing component of the system, then you might find yourself in a situation where you need to restore the original files that existed prior to running the devtool deploy-target command. Because the devtool deploy-target command backs up any files it overwrites, you can use the devtool undeploy-target to restore those files and remove any other files the recipe deployed. Consider the following example: $ devtool undeploy-target lighttpd root@192.168.7.2 If you have deployed multiple applications, you can remove them all at once thus restoring the target device back to its original state: $ devtool undeploy-target -a root@192.168.7.2 Information about files deployed to the target as well as any backed up files are stored on the target itself. This storage of course requires some additional space on the target machine. The devtool deploy-target and devtool undeploy-target command do not currently interact with any package management system on the target device (e.g. RPM or OPKG). Consequently, you should not intermingle operations devtool deploy-target and the package manager operations on the target device. Doing so could result in a conflicting set of files.