</para>
</section>
+<section id='sdk-a-closer-look-at-devtool-add'>
+ <title>A Closer Look at <filename>devtool add</filename></title>
+
+ <para>
+ The <filename>devtool add</filename> command automatically creates a
+ recipe based on the source tree with which you provide it.
+ Currently, the command has support for the following:
+ <itemizedlist>
+ <listitem><para>
+ Autotools (<filename>autoconf</filename> and
+ <filename>automake</filename>)
+ </para></listitem>
+ <listitem><para>
+ <filename>CMake</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>Scons</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>qmake</filename>
+ </para></listitem>
+ <listitem><para>
+ Plain <filename>Makefile</filename>
+ </para></listitem>
+ <listitem><para>
+ Out-of-tree kernel module
+ </para></listitem>
+ <listitem><para>
+ Binary package (i.e. "-b" option)
+ </para></listitem>
+ <listitem><para>
+ <filename>Node.js</filename> module through
+ <filename>npm</filename>
+ </para></listitem>
+ <listitem><para>
+ Python modules that use <filename>setuptools</filename>
+ or <filename>distutils</filename>
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ 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 <filename>CMakeLists.txt</filename> file is found,
+ then the source tree is assumed to be using
+ <filename>CMake</filename> and is treated accordingly.
+ <note>
+ 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.
+ </note>
+ </para>
+
+ <para>
+ The remainder of this section covers specifics regarding how parts
+ of the recipe are generated.
+ </para>
+
+ <section id='sdk-name-and-version'>
+ <title>Name and Version</title>
+
+ <para>
+ If you do not specify a name and version on the command
+ line, <filename>devtool add</filename> 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
+ <filename>devtool add</filename> command prints an error and
+ you must re-run the command with both the name and version
+ or just the name or version specified.
+ </para>
+
+ <para>
+ Sometimes the name or version determined from the source tree
+ might be incorrect.
+ For such a case, you must run the following commands:
+ <literallayout class='monospaced'>
+ $ devtool reset -n <replaceable>recipename</replaceable>
+ </literallayout>
+ After running the <filename>devtool reset</filename> command,
+ you need to run <filename>devtool add</filename> again and
+ provide the name or the version.
+ </para>
+ </section>
+
+ <section id='sdk-dependency-detection-and-mapping'>
+ <title>Dependency Detection and Mapping</title>
+
+ <para>
+ The <filename>devtool add</filename> 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
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
+ 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 <filename>devtool add</filename> command to add an
+ additional recipe to satisfy the dependency and then come
+ back to the first recipe and add its name to
+ <filename>DEPENDS</filename>.
+ </para>
+
+ <para>
+ If you need to add runtime dependencies, you can do so by
+ adding the following to your recipe:
+ <literallayout class='monospaced'>
+ RDEPENDS_${PN} += "dependency1 dependency2 ..."
+ </literallayout>
+ <note>
+ The <filename>devtool add</filename> 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.
+ </note>
+ </para>
+ </section>
+
+ <section id='sdk-license-detection'>
+ <title>License Detection</title>
+
+ <para>
+ The <filename>devtool add</filename> command attempts to
+ determine if the software you are adding is able to be
+ distributed under a common open-source license and sets the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
+ value accordingly.
+ You should double-check this value against the documentation
+ or source files for the software you are building and update
+ that <filename>LICENSE</filename> value if necessary.
+ </para>
+
+ <para>
+ The <filename>devtool add</filename> command also sets the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
+ 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
+ <filename>LIC_FILES_CHKSUM</filename> variable to point to one
+ or more of those comments if present.
+ Setting <filename>LIC_FILES_CHKSUM</filename> 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.
+ </para>
+
+ <para>
+ If the <filename>devtool add</filename> command cannot
+ determine licensing information, the
+ <filename>LICENSE</filename> value is set to "CLOSED" and the
+ <filename>LIC_FILES_CHKSUM</filename> 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.
+ </para>
+ </section>
+
+ <section id='sdk-adding-makefile-only-software'>
+ <title>Adding Makefile-Only Software</title>
+
+ <para>
+ The use of <filename>make</filename> by itself is very common
+ in both proprietary and open source software.
+ Unfortunately, Makefiles are often not written with
+ cross-compilation in mind.
+ Thus, <filename>devtool add</filename> often cannot do very
+ much to ensure that these Makefiles build correctly.
+ It is very common, for example, to explicitly call
+ <filename>gcc</filename> instead of using the
+ <filename>CC</filename> variable.
+ Usually, in a cross-compilation environment,
+ <filename>gcc</filename> is the compiler for the build host
+ and the cross-compiler is named something similar to
+ <filename>arm-poky-linux-gnueabi-gcc</filename> and might
+ require some arguments (e.g. to point to the associated sysroot
+ for the target machine).
+ </para>
+
+ <para>
+ When writing a recipe for Makefile-only software, keep the
+ following in mind:
+ <itemizedlist>
+ <listitem><para>
+ You probably need to patch the Makefile to use
+ variables instead of hardcoding tools within the
+ toolchain such as <filename>gcc</filename> and
+ <filename>g++</filename>.
+ </para></listitem>
+ <listitem><para>
+ The environment in which <filename>make</filename> runs
+ is set up with various standard variables for
+ compilation (e.g. <filename>CC</filename>,
+ <filename>CXX</filename>, 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
+ <filename>devtool build</filename> command on the
+ recipe and then look in
+ <filename>oe-logs/run.do_compile</filename>.
+ 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.
+ </para></listitem>
+ <listitem><para>
+ 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
+ <filename>make</filename> command line.
+ To force the value on the command line, add the
+ variable setting to
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'><filename>EXTRA_OEMAKE</filename></ulink>
+ within the recipe as follows:
+ <literallayout class='monospaced'>
+ EXTRA_OEMAKE += "'CC=${CC}' 'CXX=${CXX}'"
+ </literallayout>
+ 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.
+ </para></listitem>
+ <listitem><para>
+ 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.
+ </para></listitem>
+ <listitem><para>
+ Sometimes a Makefile runs target-specific commands such
+ as <filename>ldconfig</filename>.
+ For such cases, you might be able to simply apply
+ patches that remove these commands from the Makefile.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='sdk-adding-native-tools'>
+ <title>Adding Native Tools</title>
+
+ <para>
+ 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 <filename>devtool add</filename>:
+ <itemizedlist>
+ <listitem><para>
+ 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.
+ </para></listitem>
+ <listitem><para>
+ Specify the "‐‐also-native" option with the
+ <filename>devtool add</filename> 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.
+ </para></listitem>
+ </itemizedlist>
+ <note>
+ 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.
+ </note>
+ </para>
+ </section>
+
+ <section id='sdk-adding-node-js-modules'>
+ <title>Adding <filename>Node.js</filename> Modules</title>
+
+ <para>
+ You can use the <filename>devtool add</filename> command in the
+ following form to add <filename>Node.js</filename> modules:
+ <literallayout class='monospaced'>
+ $ devtool add "npm://registry.npmjs.org;name=forever;version=0.15.1"
+ </literallayout>
+ 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.
+ <note><title>Notes</title>
+ <itemizedlist>
+ <listitem><para>
+ You must use quotes around the URL.
+ The <filename>devtool add</filename> does not require
+ the quotes, but the shell considers ";" as a splitter
+ between multiple commands.
+ Thus, <filename>devtool add</filename> does not receive
+ the other parts resulting in several "command not found"
+ errors.
+ </para></listitem>
+ <listitem><para>
+ In order to support adding
+ <filename>Node.js</filename> modules, a
+ <filename>nodejs</filename> recipe must be part of your
+ SDK in order to provide <filename>Node.js</filename>
+ itself.
+ </para></listitem>
+ </itemizedlist>
+ </note>
+ </para>
+ </section>
+</section>
+
+<section id='sdk-working-with-recipes'>
+ <title>Working With Recipes</title>
+
+ <para>
+ When building a recipe with <filename>devtool build</filename> the
+ typical workflow is as follows:
+ <orderedlist>
+ <listitem><para>
+ Fetch the source
+ </para></listitem>
+ <listitem><para>
+ Unpack the source
+ </para></listitem>
+ <listitem><para>
+ Configure the source
+ </para></listitem>
+ <listitem><para>
+ Compiling the source
+ </para></listitem>
+ <listitem><para>
+ Install the build output
+ </para></listitem>
+ <listitem><para>
+ Package the installed output
+ </para></listitem>
+ </orderedlist>
+ 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.
+ </para>
+
+ <para>
+ 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 <filename>inherit</filename> directive, leaving the recipe
+ to describe just the things that are specific to the software to be
+ built.
+ A <ulink url='ref-classes-base'><filename>base</filename></ulink>
+ class exists that is implicitly inherited by all recipes and provides
+ the functionality that most typical recipes need.
+ </para>
+
+ <para>
+ The remainder of this section presents information useful when
+ working with recipes.
+ </para>
+
+ <section id='sdk-finding-logs-and-work-files'>
+ <title>Finding Logs and Work Files</title>
+
+ <para>
+ When you are debugging a recipe that you previously created using
+ <filename>devtool add</filename> or whose source you are modifying
+ by using the <filename>devtool modify</filename> command, after
+ the first run of <filename>devtool build</filename>, you will
+ find some symbolic links created within the source tree:
+ <filename>oe-logs</filename>, which points to the directory in
+ which log files and run scripts for each build step are created
+ and <filename>oe-workdir</filename>, 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.
+ </para>
+
+ <para>
+ These locations under <filename>oe-workdir</filename> are
+ particularly useful:
+ <itemizedlist>
+ <listitem><para><filename>image/</filename>:
+ Contains all of the files installed at the
+ <ulink url='&YOCTO_DOCS_REF_URL;ref-tasks-install'><filename>do_install</filename></ulink>
+ stage.
+ Within a recipe, this directory is referred to by the
+ expression
+ <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>.
+ </para></listitem>
+ <listitem><para><filename>sysroot-destdir/</filename>:
+ Contains a subset of files installed within
+ <filename>do_install</filename> that have been put into the
+ shared sysroot.
+ For more information, see the
+ "<link linkend='sdk-sharing-files-between-recipes'>Sharing Files Between Recipes</link>"
+ section.
+ </para></listitem>
+ <listitem><para><filename>packages-split/</filename>:
+ Contains subdirectories for each package produced by the
+ recipe. (more on "Packaging" below)
+ For more information, see the
+ "<link linkend='sdk-packaging'>Packaging</link>" section.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='sdk-setting-configure-arguments'>
+ <title>Setting Configure Arguments</title>
+
+ <para>
+ 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
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></ulink>
+ set within the recipe.
+ If you wish to pass additional options, add them to
+ <filename>EXTRA_OECONF</filename>.
+ Other supported build tools have similar variables
+ (e.g.
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></ulink>
+ for CMake,
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OESCONS'><filename>EXTRA_OESCONS</filename></ulink>
+ for <filename>Scons</filename>, and so forth).
+ If you need to pass anything on the <filename>make</filename>
+ command line, you can use <filename>EXTRA_OEMAKE</filename> to do
+ so.
+ </para>
+
+ <para>
+ You can use the <filename>devtool configure-help</filename> 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
+ <filename>EXTRA_OECONF</filename>.
+ If applicable, the command also shows you the output of the
+ configure script's "‐‐help" option as a reference.
+ </para>
+ </section>
+
+ <section id='sdk-sharing-files-between-recipes'>
+ <title>Sharing Files Between Recipes</title>
+
+ <para>
+ 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.
+ </para>
+
+ <para>
+ Recipes should never write files directly into the sysroot.
+ Instead, files should be installed into standard locations
+ during the
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
+ task within the
+ <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>
+ 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.
+ </para>
+ </section>
+
+ <section id='sdk-packaging'>
+ <title>Packaging</title>
+
+ <para>
+ 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.
+ </para>
+
+ <para>
+ During the
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>
+ task, files installed during the
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
+ 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 <filename>-doc</filename> package.
+ Recipes that package software that has optional modules or
+ plugins might do additional package splitting as well.
+ </para>
+
+ <para>
+ After building a recipe you can see where files have gone by
+ looking in the <filename>oe-workdir/packages-split</filename>
+ directory, which contains a subdirectory for each package.
+ Apart from some advanced cases, the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
+ and
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>
+ variables controls splitting.
+ The <filename>PACKAGES</filename> variable lists all of the
+ packages to be produced, while the <filename>FILES</filename>
+ variable specifies which files to include in each package,
+ using an override to specify the package.
+ For example, <filename>FILES_${PN}</filename> specifies the files
+ to go into the main package (i.e. the main package is named the
+ same as the recipe and
+ <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
+ evaluates to the recipe name).
+ The order of the <filename>PACKAGES</filename> value is significant.
+ For each installed file, the first package whose
+ <filename>FILES</filename> value matches the file is the package
+ into which the file goes.
+ Defaults exist for both the <filename>PACKAGES</filename> and
+ <filename>FILES</filename> 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.
+ </para>
+ </section>
+
+ <section id='sdk-restoring-the-target-device-to-its-original-state'>
+ <title>Restoring the Target Device to its Original State</title>
+
+ <para>
+ If you use the <filename>devtool deploy-target</filename>
+ 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
+ <filename>devtool deploy-target</filename> command.
+ Because the <filename>devtool deploy-target</filename> command
+ backs up any files it overwrites, you can use the
+ <filename>devtool undeploy-target</filename> to restore those files
+ and remove any other files the recipe deployed.
+ Consider the following example:
+ <literallayout class='monospaced'>
+ $ devtool undeploy-target lighttpd root@192.168.7.2
+ </literallayout>
+ If you have deployed multiple applications, you can remove them
+ all at once thus restoring the target device back to its
+ original state:
+ <literallayout class='monospaced'>
+ $ devtool undeploy-target -a root@192.168.7.2
+ </literallayout>
+ 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.
+ <note>
+ The <filename>devtool deploy-target</filename> and
+ <filename>devtool undeploy-target</filename> 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
+ <filename>devtool deploy-target</filename> and the package
+ manager operations on the target device.
+ Doing so could result in a conflicting set of files.
+ </note>
+ </para>
+ </section>
+</section>
+
</appendix>
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