%poky; ] > This chapter describes fundamental procedures such as creating layers, adding new software packages, extending or customizing images, porting work to new hardware (adding a new machine), and so forth. You will find the procedures documented here occur often in the develop cycle using the Yocto Project.

The OpenEmbedded build system supports organizing Metadata into multiple layers. Layers allow you to isolate different types of customizations from each other. You might find it tempting to keep everything in one layer when working on a single project. However, the more modular you organize your Metadata, the easier it is to cope with future changes. To illustrate how layers are used to keep things modular, consider machine customizations. These types of customizations typically reside in a special layer, rather than a general layer, called a Board Specific Package (BSP) Layer. Furthermore, the machine customizations should be isolated from recipes and Metadata that support a new GUI environment, for example. This situation gives you a couple of layers: one for the machine configurations, and one for the GUI environment. It is important to understand, however, that the BSP layer can still make machine-specific additions to recipes within the GUI environment layer without polluting the GUI layer itself with those machine-specific changes. You can accomplish this through a recipe that is a BitBake append (.bbappend) file, which is described later in this section.

The Source Directory contains both general layers and BSP layers right out of the box. You can easily identify layers that ship with a Yocto Project release in the Source Directory by their folder names. Folders that are layers begin with the string meta. It is not a requirement that a layer begins with the string meta. For example, when you set up the Source Directory structure, you will see several layers: meta, meta-hob, meta-skeleton, meta-yocto, and meta-yocto-bsp. Each of these folders is a layer. Furthermore, if you set up a local copy of the meta-intel Git repository and then explore the folder of that general layer, you will discover many BSP layers inside. For more information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

It is very easy to create your own layers to use with the OpenEmbedded build system. The Yocto Project ships with scripts that speed up creating general layers and BSP layers. This section describes the steps you perform by hand to create a layer so that you can better understand them. For information about the layer-creation scripts, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide and the "Creating a General Layer Using the yocto-layer Script" section further down in this manual. Follow these general steps to create your layer: Check Existing Layers: Before creating a new layer, you should be sure someone has not already created a layer containing the Metadata you need. You can see the OpenEmbedded Metadata Index for a list of layers from the OpenEmbedded community that can be used in the Yocto Project. Create a Directory: Create the directory for your layer. While not strictly required, prepend the name of the folder with the string meta-. For example: meta-mylayer meta-GUI_xyz meta-mymachine Create a Layer Configuration File: Inside your new layer folder, you need to create a conf/layer.conf file. It is easiest to take an existing layer configuration file and copy that to your layer's conf directory and then modify the file as needed. The meta-yocto-bsp/conf/layer.conf file demonstrates the required syntax: # We have a conf and classes directory, add to BBPATH BBPATH .= ":${LAYERDIR}" # We have recipes-* directories, add to BBFILES BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \ ${LAYERDIR}/recipes-*/*/*.bbappend" BBFILE_COLLECTIONS += "yoctobsp" BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/" BBFILE_PRIORITY_yoctobsp = "5" Here is an explanation of the example: The configuration and classes directory is appended to BBPATH. All non-distro layers, which include all BSP layers, are expected to append the layer directory to the BBPATH. On the other hand, distro layers, such as meta-yocto, can choose to enforce their own precedence over BBPATH. For an example of that syntax, see the layer.conf file for the meta-yocto layer. The recipes for the layers are appended to BBFILES. The BBFILE_COLLECTIONS variable is then appended with the layer name. The BBFILE_PATTERN variable is set to a regular expression and is used to match files from BBFILES into a particular layer. In this case, LAYERDIR is used to make BBFILE_PATTERN match within the layer's path. The BBFILE_PRIORITY variable then assigns a priority to the layer. Applying priorities is useful in situations where the same package might appear in multiple layers and allows you to choose what layer should take precedence. Note the use of the LAYERDIR variable, which expands to the directory of the current layer. Through the use of the BBPATH variable, BitBake locates .bbclass files, configuration files, and files that are included with include and require statements. For these cases, BitBake uses the first file that matches the name found in BBPATH. This is similar to the way the PATH variable is used for binaries. We recommend, therefore, that you use unique .bbclass and configuration filenames in your custom layer. Add Content: Depending on the type of layer, add the content. If the layer adds support for a machine, add the machine configuration in a conf/machine/ file within the layer. If the layer adds distro policy, add the distro configuration in a conf/distro/ file with the layer. If the layer introduces new recipes, put the recipes you need in recipes-* subdirectories within the layer. In order to be compliant with the Yocto Project, a layer must contain a README file. To create layers that are easier to maintain, you should consider the following: Avoid "overlaying" entire recipes from other layers in your configuration. In other words, don't copy an entire recipe into your layer and then modify it. Use .bbappend files to override the parts of the recipe you need to modify. Avoid duplicating include files. Use .bbappend files for each recipe that uses an include file. Or, if you are introducing a new recipe that requires the included file, use the path relative to the original layer directory to refer to the file. For example, use require recipes-core/somepackage/somefile.inc instead of require somefile.inc. If you're finding you have to overlay the include file, it could indicate a deficiency in the include file in the layer to which it originally belongs. If this is the case, you need to address that deficiency instead of overlaying the include file. For example, consider how Qt 4 database support plug-ins are configured. The Source Directory does not have MySQL or PostgreSQL, however OpenEmbedded's layer meta-oe does. Consequently, meta-oe uses .bbappend files to modify the QT_SQL_DRIVER_FLAGS variable to enable the appropriate plugins. This variable was added to the qt4.inc include file in the Source Directory specifically to allow the meta-oe layer to be able to control which plugins are built. We also recommend the following: Store custom layers in a Git repository that uses the meta-<layer_name> format. Clone the repository alongside other meta directories in the Source Directory. Following these recommendations keeps your Source Directory and its configuration entirely inside the Yocto Project's core base.

Before the OpenEmbedded build system can use your new layer, you need to enable it. To enable your layer, simply add your layer's path to the BBLAYERS variable in your conf/bblayers.conf file, which is found in the Build Directory. The following example shows how to enable a layer named meta-mylayer: LCONF_VERSION = "6" BBPATH = "${TOPDIR}" BBFILES ?= "" BBLAYERS ?= " \ $HOME/poky/meta \ $HOME/poky/meta-yocto \ $HOME/poky/meta-yocto-bsp \ $HOME/poky/meta-mylayer \ " BBLAYERS_NON_REMOVABLE ?= " \ $HOME/poky/meta \ $HOME/poky/meta-yocto \ " BitBake parses each conf/layer.conf file as specified in the BBLAYERS variable within the conf/bblayers.conf file. During the processing of each conf/layer.conf file, BitBake adds the recipes, classes and configurations contained within the particular layer to the source directory.

Recipes used to append Metadata to other recipes are called BitBake append files. BitBake append files use the .bbappend file type suffix, while the corresponding recipes to which Metadata is being appended use the .bb file type suffix. A .bbappend file allows your layer to make additions or changes to the content of another layer's recipe without having to copy the other recipe into your layer. Your .bbappend file resides in your layer, while the main .bb recipe file to which you are appending Metadata resides in a different layer. Append files must have the same root name as the corresponding recipe. For example, the append file someapp_&DISTRO;.bbappend must apply to someapp_&DISTRO;.bb. This means the original recipe and append file names are version number-specific. If the corresponding recipe is renamed to update to a newer version, the underlying .bbappend file must be renamed as well. During the build process, BitBake displays an error on starting if it detects a .bbappend file that does not have a corresponding recipe with a matching name. See the BB_DANGLINGAPPENDS_WARNONLY variable for information on how to handle this error. Being able to append information to an existing recipe not only avoids duplication, but also automatically applies recipe changes in a different layer to your layer. If you were copying recipes, you would have to manually merge changes as they occur. As an example, consider the main formfactor recipe and a corresponding formfactor append file both from the Source Directory. Here is the main formfactor recipe, which is named formfactor_0.0.bb and located in the "meta" layer at meta/recipes-bsp/formfactor: DESCRIPTION = "Device formfactor information" SECTION = "base" LICENSE = "MIT" LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \ file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420" PR = "r20" SRC_URI = "file://config file://machconfig" S = "${WORKDIR}" PACKAGE_ARCH = "${MACHINE_ARCH}" INHIBIT_DEFAULT_DEPS = "1" do_install() { # Only install file if it has a contents install -d ${D}${sysconfdir}/formfactor/ install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/ if [ -s "${S}/machconfig" ]; then install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/ fi } Here is the append file, which is named formfactor_0.0.bbappend and is from the Crown Bay BSP Layer named meta-intel/meta-crownbay. The file is in recipes-bsp/formfactor: FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:" PRINC := "${@int(PRINC) + 2}" This example adds or overrides files in SRC_URI within a .bbappend by extending the path BitBake uses to search for files. The most reliable way to do this is by prepending the FILESEXTRAPATHS variable. For example, if you have your files in a directory that is named the same as your package (PN), you can add this directory by adding the following to your .bbappend file: FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:" Using the immediate expansion assignment operator := is important because of the reference to THISDIR. The trailing colon character is important as it ensures that items in the list remain colon-separated. BitBake automatically defines the THISDIR variable. You should never set this variable yourself. Using _prepend ensures your path will be searched prior to other paths in the final list. Also, not all append files add extra files. Many append files simply exist to add build options (e.g. systemd). For these cases, it is not necessary to use the "_prepend" part of the statement.

Each layer is assigned a priority value. Priority values control which layer takes precedence if there are recipe files with the same name in multiple layers. For these cases, the recipe file from the layer with a higher priority number takes precedence. Priority values also affect the order in which multiple .bbappend files for the same recipe are applied. You can either specify the priority manually, or allow the build system to calculate it based on the layer's dependencies. To specify the layer's priority manually, use the BBFILE_PRIORITY variable. For example: BBFILE_PRIORITY_mylayer = "1" It is possible for a recipe with a lower version number PV in a layer that has a higher priority to take precedence. Also, the layer priority does not currently affect the precedence order of .conf or .bbclass files. Future versions of BitBake might address this.

You can use the BitBake layer management tool to provide a view into the structure of recipes across a multi-layer project. Being able to generate output that reports on configured layers with their paths and priorities and on .bbappend files and their applicable recipes can help to reveal potential problems. Use the following form when running the layer management tool. $ bitbake-layers <command> [arguments] The following list describes the available commands: help: Displays general help or help on a specified command. show-layers: Show the current configured layers. show-recipes: Lists available recipes and the layers that provide them. show-overlayed: Lists overlayed recipes. A recipe is overlayed when a recipe with the same name exists in another layer that has a higher layer priority. show-appends: Lists .bbappend files and the recipe files to which they apply. show-cross-depends: Lists dependency relationships between recipes that cross layer boundaries. flatten: Flattens the layer configuration into a separate output directory. Flattening your layer configuration builds a "flattened" directory that contains the contents of all layers, with any overlayed recipes removed and any .bbappend files appended to the corresponding recipes. You might have to perform some manual cleanup of the flattened layer as follows: Non-recipe files (such as patches) are overwritten. The flatten command shows a warning for these files. Anything beyond the normal layer setup has been added to the layer.conf file. Only the lowest priority layer's layer.conf is used. Overridden and appended items from .bbappend files need to be cleaned up. The contents of each .bbappend end up in the flattened recipe. However, if there are appended or changed variable values, you need to tidy these up yourself. Consider the following example. Here, the bitbake-layers command adds the line #### bbappended ... so that you know where the following lines originate: ... DESCRIPTION = "A useful utility" ... EXTRA_OECONF = "--enable-something" ... #### bbappended from meta-anotherlayer #### DESCRIPTION = "Customized utility" EXTRA_OECONF += "--enable-somethingelse" Ideally, you would tidy up these utilities as follows: ... DESCRIPTION = "Customized utility" ... EXTRA_OECONF = "--enable-something --enable-somethingelse" ...

The yocto-layer script simplifies creating a new general layer. For information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Specific (BSP) Developer's Guide. The default mode of the script's operation is to prompt you for information needed to generate the layer: The layer priority Whether or not to create a sample recipe. Whether or not to create a sample append file. You use the yocto-layer create sub-command to create a new general layer. In its simplest form, you can create a layer as follows: $ yocto-layer create mylayer The previous example creates a layer named meta-mylayer in the current directory. As the yocto-layer create command runs, default values for the prompts appear in brackets. Pressing enter without supplying anything on the command line or pressing enter and providing an invalid response causes the script to accept the default value. Once the script completes, the new layer is created in the current working directory. The script names the layer according to the string you provide and the prepended meta- string. If you choose to not generate a sample recipe or append file, the script creates the following within the layer: The conf directory: This directory contains the layers .conf. The root name for the file is the same as the root name your provided for the layer. The COPYING.MIT: The copyright and use notice for the software. The README file: A file describing the contents of your new layer. If you choose to generate a sample recipe file, the script prompts you for the name for the recipe and then creates it in <layer>/recipes-example/example/. in a directory named recipes-example. The script creates a .bb file and a directory, which contains a sample helloworld.csource file and along with a sample patch file. If you do not provide a recipe name, the script uses "example". If you choose to generate a sample append file, the script prompts you for the name for the file and then creates it in <layer>/recipes-example-bbappend/example-bbappend/. The script creates a .bbappend file and a directory, which contains a sample patch file. If you do not provide a recipe name, the script uses "example". The script also prompts you for the version of the append file. The version should match the recipe to which the append file is associated. The easiest way to see how the yocto-layer script works is to experiment with the script. You can also read the usage information by entering the following: $ yocto-layer help Once you create your general layer, you must add it to your bblayers.conf file. Here is an example: BBLAYERS = ?" \ /usr/local/src/yocto/meta \ /usr/local/src/yocto/meta-yocto \ /usr/local/src/yocto/meta-yocto-bsp \ /usr/local/src/yocto/meta-mylayer \ " BBLAYERS_NON_REMOVABLE ?= " \ /usr/local/src/yocto/meta \ /usr/local/src/yocto/meta-yocto \ " Adding the layer to this file enables the build system to the layer during the build.

You can customize images to satisfy particular requirements. This section describes several methods and provides guidelines for each.

One way to get additional software into an image is to create a custom image. The following example shows the form for the two lines you need: IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2" inherit core-image By creating a custom image, a developer has total control over the contents of the image. It is important to use the correct names of packages in the IMAGE_INSTALL variable. You must use the OpenEmbedded notation and not the Debian notation for the names (e.g. eglibc-dev instead of libc6-dev). The other method for creating a custom image is to base it on an existing image. For example, if you want to create an image based on core-image-sato but add the additional package strace to the image, copy the meta/recipes-sato/images/core-image-sato.bb to a new .bb and add the following line to the end of the copy: IMAGE_INSTALL += "strace"

For complex custom images, the best approach is to create a custom package group recipe that is used to build the image or images. A good example of a package group recipe is meta/recipes-core/packagegroups/packagegroup-core-boot.bb. The PACKAGES variable lists the package group packages you wish to produce. inherit packagegroup sets appropriate default values and automatically adds -dev and -dbg complementary packages for every package specified in PACKAGES. Note that the inherit line should be towards the top of the recipe, certainly before you set PACKAGES. For each package you specify in PACKAGES, you can use RDEPENDS and RRECOMMENDS entries to provide a list of packages the parent task package should contain. Following is an example: DESCRIPTION = "My Custom Package Groups" inherit packagegroup PACKAGES = "\ packagegroup-custom-apps \ packagegroup-custom-tools \ " RDEPENDS_packagegroup-custom-apps = "\ dropbear \ portmap \ psplash" RDEPENDS_packagegroup-custom-tools = "\ oprofile \ oprofileui-server \ lttng-control \ lttng-viewer" RRECOMMENDS_packagegroup-custom-tools = "\ kernel-module-oprofile" In the previous example, two package group packages are created with their dependencies and their recommended package dependencies listed: packagegroup-custom-apps, and packagegroup-custom-tools. To build an image using these package group packages, you need to add packagegroup-custom-apps and/or packagegroup-custom-tools to IMAGE_INSTALL. For other forms of image dependencies see the other areas of this section.

You might want to customize your image by enabling or disabling high-level image features by using the IMAGE_FEATURES and EXTRA_IMAGE_FEATURES variables. Although the functions for both variables are nearly equivalent, best practices dictate using IMAGE_FEATURES from within a recipe and using EXTRA_IMAGE_FEATURES from within your local.conf file, which is found in the Build Directory. To understand how these features work, the best reference is meta/classes/core-image.bbclass. In summary, the file looks at the contents of the IMAGE_FEATURES variable and then maps those contents into a set of package groups. Based on this information, the build system automatically adds the appropriate packages to the IMAGE_INSTALL variable. Effectively, you are enabling extra features by extending the class or creating a custom class for use with specialized image .bb files. Use the EXTRA_IMAGE_FEATURES variable from within your local configuration file. Using a separate area from which to enable features with this variable helps you avoid overwriting the features in the image recipe that are enabled with IMAGE_FEATURES. The value of EXTRA_IMAGE_FEATURES is added to IMAGE_FEATURES within meta/conf/bitbake.conf. To illustrate how you can use these variables to modify your image, consider an example that selects the SSH server. The Yocto Project ships with two SSH servers you can use with your images: Dropbear and OpenSSH. Dropbear is a minimal SSH server appropriate for resource-constrained environments, while OpenSSH is a well-known standard SSH server implementation. By default, the core-image-sato image is configured to use Dropbear. The core-image-basic and core-image-lsb images both include OpenSSH. The core-image-minimal image does not contain an SSH server. You can customize your image and change these defaults. Edit the IMAGE_FEATURES variable in your recipe or use the EXTRA_IMAGE_FEATURES in your local.conf file so that it configures the image you are working with to include ssh-server-dropbear or ssh-server-openssh. See the "Images" section in the Yocto Project Reference Manual for a complete list of image features that ship with the Yocto Project.

It is possible to customize image contents by using variables from your local configuration in your conf/local.conf file. Because it is limited to local use, this method generally only allows you to add packages and is not as flexible as creating your own customized image. When you add packages using local variables this way, you need to realize that these variable changes affect all images at the same time and might not be what you require. The simplest way to add extra packages to all images is by using the IMAGE_INSTALL variable with the _append operator: IMAGE_INSTALL_append = " strace" Use of the syntax is important. Specifically, the space between the quote and the package name, which is strace in this example. This space is required since the _append operator does not add the space. Furthermore, you must use _append instead of the += operator if you want to avoid ordering issues. The reason for this is because doing so unconditionally appends to the variable and avoids ordering problems due to the variable being set in image recipes and .bbclass files with operators like ?=. Using _append ensures the operation takes affect. As shown in its simplest use, IMAGE_INSTALL_append affects all images. It is possible to extend the syntax so that the variable applies to a specific image only. Here is an example: IMAGE_INSTALL_append_pn-core-image-minimal = " strace" This example adds strace to core-image-minimal only. You can add packages using a similar approach through the CORE_IMAGE_EXTRA_INSTALL variable. If you use this variable, only core-image-* images are affected.

Recipes add packages to your image. Writing a recipe means creating a .bb file that sets some variables. For information on variables that are useful for recipes and for information about recipe naming issues, see the "Required" section of the Yocto Project Reference Manual. Before writing a recipe from scratch, it is often useful to check whether someone else has written one already. OpenEmbedded is a good place to look as it has a wider scope and range of packages. Because the Yocto Project aims to be compatible with OpenEmbedded, most recipes you find there should work for you. For new packages, the simplest way to add a recipe is to base it on a similar pre-existing recipe. The sections that follow provide some examples that show how to add standard types of packages. When writing shell functions, you need to be aware of BitBake's curly brace parsing. If a recipe uses a closing curly brace within the function and the character has no leading spaces, BitBake produces a parsing error. If you use a pair of curly brace in a shell function, the closing curly brace must not be located at the start of the line without leading spaces. Here is an example that causes BitBake to produce a parsing error: fakeroot create_shar() { cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh usage() { echo "test" ###### The following "}" at the start of the line causes a parsing error ###### } EOF } Writing the recipe this way avoids the error: fakeroot create_shar() { cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh usage() { echo "test" ######The following "}" with a leading space at the start of the line avoids the error ###### } EOF }

Building an application from a single file that is stored locally (e.g. under files/) requires a recipe that has the file listed in the SRC_URI variable. Additionally, you need to manually write the do_compile and do_install tasks. The S variable defines the directory containing the source code, which is set to WORKDIR in this case - the directory BitBake uses for the build. DESCRIPTION = "Simple helloworld application" SECTION = "examples" LICENSE = "MIT" LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302" PR = "r0" SRC_URI = "file://helloworld.c" S = "${WORKDIR}" do_compile() { ${CC} helloworld.c -o helloworld } do_install() { install -d ${D}${bindir} install -m 0755 helloworld ${D}${bindir} } By default, the helloworld, helloworld-dbg, and helloworld-dev packages are built. For information on how to customize the packaging process, see the "Splitting an Application into Multiple Packages" section.

Applications that use Autotools such as autoconf and automake require a recipe that has a source archive listed in SRC_URI and also inherits Autotools, which instructs BitBake to use the autotools.bbclass file, which contains the definitions of all the steps needed to build an Autotool-based application. The result of the build is automatically packaged. And, if the application uses NLS for localization, packages with local information are generated (one package per language). Following is one example: (hello_2.3.bb) DESCRIPTION = "GNU Helloworld application" SECTION = "examples" LICENSE = "GPLv2+" LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe" PR = "r0" SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz" inherit autotools gettext The variable LIC_FILES_CHKSUM is used to track source license changes as described in the "Track License Changes" section. You can quickly create Autotool-based recipes in a manner similar to the previous example.

Applications that use GNU make also require a recipe that has the source archive listed in SRC_URI. You do not need to add a do_compile step since by default BitBake starts the make command to compile the application. If you need additional make options you should store them in the EXTRA_OEMAKE variable. BitBake passes these options into the make GNU invocation. Note that a do_install task is still required. Otherwise, BitBake runs an empty do_install task by default. Some applications might require extra parameters to be passed to the compiler. For example, the application might need an additional header path. You can accomplish this by adding to the CFLAGS variable. The following example shows this: CFLAGS_prepend = "-I ${S}/include " In the following example, mtd-utils is a makefile-based package: DESCRIPTION = "Tools for managing memory technology devices." SECTION = "base" DEPENDS = "zlib lzo e2fsprogs util-linux" HOMEPAGE = "http://www.linux-mtd.infradead.org/" LICENSE = "GPLv2+" LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \ file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c" SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=995cfe51b0a3cf32f381c140bf72b21bf91cef1b \ file://add-exclusion-to-mkfs-jffs2-git-2.patch" S = "${WORKDIR}/git/" PR = "r1" EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' \ 'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'" do_install () { oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} \ INCLUDEDIR=${includedir} install -d ${D}${includedir}/mtd/ for f in ${S}/include/mtd/*.h; do install -m 0644 $f ${D}${includedir}/mtd/ done } PARALLEL_MAKE = "" BBCLASSEXTEND = "native" If your sources are available as a tarball instead of a Git repository, you will need to provide the URL to the tarball as well as an md5 or sha256 sum of the download. Here is an example: SRC_URI="ftp://ftp.infradead.org/pub/mtd-utils/mtd-utils-1.4.9.tar.bz2" SRC_URI[md5sum]="82b8e714b90674896570968f70ca778b" You can generate the md5 or sha256 sums by using the md5sum or sha256sum commands with the target file as the only argument. Here is an example: $ md5sum mtd-utils-1.4.9.tar.bz2 82b8e714b90674896570968f70ca778b mtd-utils-1.4.9.tar.bz2

You can use the variables PACKAGES and FILES to split an application into multiple packages. Following is an example that uses the libXpm recipe. By default, this recipe generates a single package that contains the library along with a few binaries. You can modify the recipe to split the binaries into separate packages: require xorg-lib-common.inc DESCRIPTION = "X11 Pixmap library" LICENSE = "X-BSD" LIC_FILES_CHKSUM = "file://COPYING;md5=3e07763d16963c3af12db271a31abaa5" DEPENDS += "libxext libsm libxt" PR = "r3" PE = "1" XORG_PN = "libXpm" PACKAGES =+ "sxpm cxpm" FILES_cxpm = "${bindir}/cxpm" FILES_sxpm = "${bindir}/sxpm" In the previous example, we want to ship the sxpm and cxpm binaries in separate packages. Since bindir would be packaged into the main PN package by default, we prepend the PACKAGES variable so additional package names are added to the start of list. This results in the extra FILES_* variables then containing information that define which files and directories go into which packages. Files included by earlier packages are skipped by latter packages. Thus, the main PN package does not include the above listed files.

To add a post-installation script to a package, add a pkg_postinst_PACKAGENAME() function to the .bb file and use PACKAGENAME as the name of the package you want to attach to the postinst script. Normally PN can be used, which automatically expands to PACKAGENAME. A post-installation function has the following structure: pkg_postinst_PACKAGENAME () { #!/bin/sh -e # Commands to carry out } The script defined in the post-installation function is called when the root filesystem is created. If the script succeeds, the package is marked as installed. If the script fails, the package is marked as unpacked and the script is executed when the image boots again. Sometimes it is necessary for the execution of a post-installation script to be delayed until the first boot. For example, the script might need to be executed on the device itself. To delay script execution until boot time, use the following structure in the post-installation script: pkg_postinst_PACKAGENAME () { #!/bin/sh -e if [ x"$D" = "x" ]; then # Actions to carry out on the device go here else exit 1 fi } The previous example delays execution until the image boots again because the D variable points to the directory containing the image when the root filesystem is created at build time but is unset when executed on the first boot.

Adding a new machine to the Yocto Project is a straightforward process. This section provides information that gives you an idea of the changes you must make. The information covers adding machines similar to those the Yocto Project already supports. Although well within the capabilities of the Yocto Project, adding a totally new architecture might require changes to gcc/eglibc and to the site information, which is beyond the scope of this manual. For a complete example that shows how to add a new machine, see the "Creating a New BSP Layer Using the yocto-bsp Script" in the Yocto Project Board Support Package (BSP) Developer's Guide.

To add a machine configuration you need to add a .conf file with details of the device being added to the conf/machine/ file. The name of the file determines the name the OpenEmbedded build system uses to reference the new machine. The most important variables to set in this file are as follows: TARGET_ARCH (e.g. "arm") PREFERRED_PROVIDER_virtual/kernel (see below) MACHINE_FEATURES (e.g. "apm screen wifi") You might also need these variables: SERIAL_CONSOLE (e.g. "115200 ttyS0") KERNEL_IMAGETYPE (e.g. "zImage") IMAGE_FSTYPES (e.g. "tar.gz jffs2") You can find full details on these variables in the reference section. You can leverage many existing machine .conf files from meta/conf/machine/.

The OpenEmbedded build system needs to be able to build a kernel for the machine. You need to either create a new kernel recipe for this machine, or extend an existing recipe. You can find several kernel examples in the Source Directory at meta/recipes-kernel/linux that you can use as references. If you are creating a new recipe, normal recipe-writing rules apply for setting up a SRC_URI. Thus, you need to specify any necessary patches and set S to point at the source code. You need to create a configure task that configures the unpacked kernel with a defconfig. You can do this by using a make defconfig command or, more commonly, by copying in a suitable defconfig file and and then running make oldconfig. By making use of inherit kernel and potentially some of the linux-*.inc files, most other functionality is centralized and the the defaults of the class normally work well. If you are extending an existing kernel, it is usually a matter of adding a suitable defconfig file. The file needs to be added into a location similar to defconfig files used for other machines in a given kernel. A possible way to do this is by listing the file in the SRC_URI and adding the machine to the expression in COMPATIBLE_MACHINE: COMPATIBLE_MACHINE = '(qemux86|qemumips)'

A formfactor configuration file provides information about the target hardware for which the image is being built and information that the build system cannot obtain from other sources such as the kernel. Some examples of information contained in a formfactor configuration file include framebuffer orientation, whether or not the system has a keyboard, the positioning of the keyboard in relation to the screen, and the screen resolution. The build system uses reasonable defaults in most cases, but if customization is necessary you need to create a machconfig file in the meta/recipes-bsp/formfactor/files directory. This directory contains directories for specific machines such as qemuarm and qemux86. For information about the settings available and the defaults, see the meta/recipes-bsp/formfactor/files/config file found in the same area. Following is an example for qemuarm: HAVE_TOUCHSCREEN=1 HAVE_KEYBOARD=1 DISPLAY_CAN_ROTATE=0 DISPLAY_ORIENTATION=0 #DISPLAY_WIDTH_PIXELS=640 #DISPLAY_HEIGHT_PIXELS=480 #DISPLAY_BPP=16 DISPLAY_DPI=150 DISPLAY_SUBPIXEL_ORDER=vrgb

Libraries are an integral part of your system. This section describes some common practices you might find helpful when working with libraries to build your system: How to include static library files How to use the Multilib feature to combine multiple versions of library files into a single image How to install multiple versions of the same library in parallel on the same system

If you are building a library and the library offers static linking, you can control which static library files (*.a files) get included in the built library. The PACKAGES and FILES_* variables in the meta/conf/bitbake.conf configuration file define how files installed by the do_install task are packaged. By default, the PACKAGES variable contains ${PN}-staticdev, which includes all static library files. Previously released versions of the Yocto Project defined the static library files through ${PN}-dev. Following, is part of the BitBake configuration file. You can see where the static library files are defined: PACKAGES = "${PN}-dbg ${PN} ${PN}-doc ${PN}-dev ${PN}-staticdev ${PN}-locale" PACKAGES_DYNAMIC = "${PN}-locale-*" FILES = "" FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \ ${sysconfdir} ${sharedstatedir} ${localstatedir} \ ${base_bindir}/* ${base_sbindir}/* \ ${base_libdir}/*${SOLIBS} \ ${datadir}/${BPN} ${libdir}/${BPN}/* \ ${datadir}/pixmaps ${datadir}/applications \ ${datadir}/idl ${datadir}/omf ${datadir}/sounds \ ${libdir}/bonobo/servers" FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \ ${datadir}/gnome/help" SECTION_${PN}-doc = "doc" FILES_${PN}-dev = "${includedir} ${libdir}/lib*${SOLIBSDEV} ${libdir}/*.la \ ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \ ${datadir}/aclocal ${base_libdir}/*.o" SECTION_${PN}-dev = "devel" ALLOW_EMPTY_${PN}-dev = "1" RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})" FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a" SECTION_${PN}-staticdev = "devel" RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"

The build system offers the ability to build libraries with different target optimizations or architecture formats and combine these together into one system image. You can link different binaries in the image against the different libraries as needed for specific use cases. This feature is called "Multilib." An example would be where you have most of a system compiled in 32-bit mode using 32-bit libraries, but you have something large, like a database engine, that needs to be a 64-bit application and uses 64-bit libraries. Multilib allows you to get the best of both 32-bit and 64-bit libraries. While the Multilib feature is most commonly used for 32 and 64-bit differences, the approach the build system uses facilitates different target optimizations. You could compile some binaries to use one set of libraries and other binaries to use other different sets of libraries. The libraries could differ in architecture, compiler options, or other optimizations. This section overviews the Multilib process only. For more details on how to implement Multilib, see the Multilib wiki page. Aside from this wiki page, several examples exist in the meta-skeleton layer found in the Source Directory: multilib-example.conf configuration file multilib-example2.conf configuration file recipes-multilib/images/core-image-multilib-example.bb recipe

User-specific requirements drive the Multilib feature, Consequently, there is no one "out-of-the-box" configuration that likely exists to meet your needs. In order to enable Multilib, you first need to ensure your recipe is extended to support multiple libraries. Many standard recipes are already extended and support multiple libraries. You can check in the meta/conf/multilib.conf configuration file in the Source Directory to see how this is done using the BBCLASSEXTEND variable. Eventually, all recipes will be covered and this list will be unneeded. For the most part, the Multilib class extension works automatically to extend the package name from ${PN} to ${MLPREFIX}${PN}, where MLPREFIX is the particular multilib (e.g. "lib32-" or "lib64-"). Standard variables such as DEPENDS, RDEPENDS, RPROVIDES, RRECOMMENDS, PACKAGES, and PACKAGES_DYNAMIC are automatically extended by the system. If you are extending any manual code in the recipe, you can use the ${MLPREFIX} variable to ensure those names are extended correctly. This automatic extension code resides in multilib.bbclass.

After you have set up the recipes, you need to define the actual combination of multiple libraries you want to build. You accomplish this through your local.conf configuration file in the Build Directory. An example configuration would be as follows: MACHINE = "qemux86-64" require conf/multilib.conf MULTILIBS = "multilib:lib32" DEFAULTTUNE_virtclass-multilib-lib32 = "x86" IMAGE_INSTALL = "lib32-connman" This example enables an additional library named lib32 alongside the normal target packages. When combining these "lib32" alternatives, the example uses "x86" for tuning. For information on this particular tuning, see meta/conf/machine/include/ia32/arch-ia32.inc. The example then includes lib32-connman in all the images, which illustrates one method of including a multiple library dependency. You can use a normal image build to include this dependency, for example: $ bitbake core-image-sato You can also build Multilib packages specifically with a command like this: $ bitbake lib32-connman

Different packaging systems have different levels of native Multilib support. For the RPM Package Management System, the following implementation details exist: A unique architecture is defined for the Multilib packages, along with creating a unique deploy folder under tmp/deploy/rpm in the Build Directory. For example, consider lib32 in a qemux86-64 image. The possible architectures in the system are "all", "qemux86_64", "lib32_qemux86_64", and "lib32_x86". The ${MLPREFIX} variable is stripped from ${PN} during RPM packaging. The naming for a normal RPM package and a Multilib RPM package in a qemux86-64 system resolves to something similar to bash-4.1-r2.x86_64.rpm and bash-4.1.r2.lib32_x86.rpm, respectively. When installing a Multilib image, the RPM backend first installs the base image and then installs the Multilib libraries. The build system relies on RPM to resolve the identical files in the two (or more) Multilib packages. For the IPK Package Management System, the following implementation details exist: The ${MLPREFIX} is not stripped from ${PN} during IPK packaging. The naming for a normal RPM package and a Multilib IPK package in a qemux86-64 system resolves to something like bash_4.1-r2.x86_64.ipk and lib32-bash_4.1-rw_x86.ipk, respectively. The IPK deploy folder is not modified with ${MLPREFIX} because packages with and without the Multilib feature can exist in the same folder due to the ${PN} differences. IPK defines a sanity check for Multilib installation using certain rules for file comparison, overridden, etc.

Situations can exist where you need to install and use multiple versions of the same library on the same system at the same time. These situations almost always exist when a library API changes and you have multiple pieces of software that depend on the separate versions of the library. To accommodate these situations, you can install multiple versions of the same library in parallel on the same system. The process is straight forward as long as the libraries use proper versioning. With properly versioned libraries, all you need to do to individually specify the libraries is create separate, appropriately named recipes where the PN part of the name includes a portion that differentiates each library version (e.g.the major part of the version number). Thus, instead of having a single recipe that loads one version of a library (e.g. clutter), you provide multiple recipes that result in different versions of the libraries you want. As an example, the following two recipes would allow the two separate versions of the clutter library to co-exist on the same system: clutter-1.6_1.6.20.bb clutter-1.8_1.8.4.bb Additionally, if you have other recipes that depend on a given library, you need to use the DEPENDS variable to create the dependency. Continuing with the same example, if you want to have a recipe depend on the 1.8 version of the clutter library, use the following in your recipe: DEPENDS = "clutter-1.8"

Configuring the Yocto Project kernel consists of making sure the .config file has all the right information in it for the image you are building. You can use the menuconfig tool and configuration fragments to make sure your .config file is just how you need it. This section describes how to use menuconfig, create and use configuration fragments, and how to interactively tweak your .config file to create the leanest kernel configuration file possible. For more information on kernel configuration, see the "Changing the Configuration" section in the Yocto Project Linux Kernel Development Manual.

The easiest way to define kernel configurations is to set them through the menuconfig tool. This tool provides an interactive method with which to set kernel configurations. For general information on menuconfig, see . To use the menuconfig tool in the Yocto Project development environment, you must build the tool using BitBake. Thus, the environment must be set up using the &OE_INIT_FILE; script found in the Build Directory. The following commands build and invoke menuconfig assuming the Source Directory top-level folder is ~/poky: $ cd ~/poky $ source oe-init-build-env $ bitbake linux-yocto -c menuconfig Once menuconfig comes up, its standard interface allows you to interactively examine and configure all the kernel configuration parameters. After making your changes, simply exit the tool and save your changes to create an updated version of the .config configuration file. Consider an example that configures the linux-yocto-3.4 kernel. The OpenEmbedded build system recognizes this kernel as linux-yocto. Thus, the following commands from the shell in which you previously sourced the environment initialization script cleans the shared state cache and the WORKDIR directory and then builds and launches menuconfig: $ bitbake linux-yocto -c menuconfig Once menuconfig launches, you use the interface to navigate through the selections to find the configuration settings in which you are interested. For example, consider the CONFIG_SMP configuration setting. You can find it at Processor Type and Features under the configuration selection Symmetric Multi-processing Support. After highlighting the selection, you can use the arrow keys to select or deselect the setting. When you are finished with all your selections, exit out and save them. Saving the selections updates the .config configuration file. This is the file that the OpenEmbedded build system uses to configure the kernel during the build. You can find and examine this file in the Build Directory in tmp/work/. The actual .config is located in the area where the specific kernel is built. For example, if you were building a Linux Yocto kernel based on the Linux 3.4 kernel and you were building a QEMU image targeted for x86 architecture, the .config file would be located here: ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.4.11+git1+84f... ...656ed30-r1/linux-qemux86-standard-build The previous example directory is artificially split and many of the characters in the actual filename are omitted in order to make it more readable. Also, depending on the kernel you are using, the exact pathname for linux-yocto-3.4... might differ. Within the .config file, you can see the kernel settings. For example, the following entry shows that symmetric multi-processor support is not set: # CONFIG_SMP is not set A good method to isolate changed configurations is to use a combination of the menuconfig tool and simple shell commands. Before changing configurations with menuconfig, copy the existing .config and rename it to something else, use menuconfig to make as many changes an you want and save them, then compare the renamed configuration file against the newly created file. You can use the resulting differences as your base to create configuration fragments to permanently save in your kernel layer. Be sure to make a copy of the .config and don't just rename it. The build system needs an existing .config from which to work.

Configuration fragments are simply kernel options that appear in a file placed where the OpenEmbedded build system can find and apply them. Syntactically, the configuration statement is identical to what would appear in the .config file, which is in the Build Directory in tmp/work/<arch>-poky-linux/linux-yocto-<release-specific-string>/linux-<arch>-<build-type>. It is simple to create a configuration fragment. For example, issuing the following from the shell creates a configuration fragment file named my_smp.cfg that enables multi-processor support within the kernel: $ echo "CONFIG_SMP=y" >> my_smp.cfg All configuration files must use the .cfg extension in order for the OpenEmbedded build system to recognize them as a configuration fragment. Where do you put your configuration files? You can place these configuration files in the same area pointed to by SRC_URI. The OpenEmbedded build system will pick up the configuration and add it to the kernel's configuration. For example, suppose you had a set of configuration options in a file called myconfig.cfg. If you put that file inside a directory named /linux-yocto that resides in the same directory as the kernel's append file and then add a SRC_URI statement such as the following to the kernel's append file, those configuration options will be picked up and applied when the kernel is built. SRC_URI += "file://myconfig.cfg" As mentioned earlier, you can group related configurations into multiple files and name them all in the SRC_URI statement as well. For example, you could group separate configurations specifically for Ethernet and graphics into their own files and add those by using a SRC_URI statement like the following in your append file: SRC_URI += "file://myconfig.cfg \ file://eth.cfg \ file://gfx.cfg"

You can make sure the .config is as lean or efficient as possible by reading the output of the kernel configuration fragment audit, noting any issues, making changes to correct the issues, and then repeating. As part of the kernel build process, the kernel_configcheck task runs. This task validates the kernel configuration by checking the final .config file against the input files. During the check, the task produces warning messages for the following issues: Requested options that did not make the final .config file. Configuration items that appear twice in the same configuration fragment. Configuration items tagged as 'required' were overridden. A board overrides a non-board specific option. Listed options not valid for the kernel being processed. In other words, the option does not appear anywhere. The kernel_configcheck task can also optionally report if an option is overridden during processing. For each output warning, a message points to the file that contains a list of the options and a pointer to the config fragment that defines them. Collectively, the files are the key to streamlining the configuration. To streamline the configuration, do the following: Start with a full configuration that you know works - it builds and boots successfully. This configuration file will be your baseline. Separately run the configme and kernel_configcheck tasks. Take the resulting list of files from the kernel_configcheck task warnings and do the following: Drop values that are redefined in the fragment but do not change the final .config file. Analyze and potentially drop values from the .config file that override required configurations. Analyze and potentially remove non-board specific options. Remove repeated and invalid options. After you have worked through the output of the kernel configuration audit, you can re-run the configme and kernel_configcheck tasks to see the results of your changes. If you have more issues, you can deal with them as described in the previous step. Iteratively working through steps two through four eventually yields a minimal, streamlined configuration file. Once you have the best .config, you can build the Linux Yocto kernel.

Patching the kernel involves changing or adding configurations to an existing kernel, changing or adding recipes to the kernel that are needed to support specific hardware features, or even altering the source code itself. You can use the yocto-kernel script found in the Source Directory under scripts to manage kernel patches and configuration. See the "Managing kernel Patches and Config Items with yocto-kernel" section in the Yocto Project Board Support Packages (BSP) Developer's Guide for more information. This example creates a simple patch by adding some QEMU emulator console output at boot time through printk statements in the kernel's calibrate.c source code file. Applying the patch and booting the modified image causes the added messages to appear on the emulator's console. The example assumes a clean build exists for the qemux86 machine in a Source Directory named poky. Furthermore, the Build Directory is build and is located in poky and the kernel is based on the Linux 3.4 kernel. For general information on how to configure the most efficient build, see the "Building an Image" section in the Yocto Project Quick Start. Also, for more information on patching the kernel, see the "Applying Patches" section in the Yocto Project Linux Kernel Development Manual.

The first step is to create a layer so you can isolate your changes: $cd ~/poky $mkdir meta-mylayer Creating a directory that follows the Yocto Project layer naming conventions sets up the layer for your changes. The layer is where you place your configuration files, append files, and patch files. To learn more about creating a layer and filling it with the files you need, see the "Understanding and Creating Layers" section.

Each time you build a kernel image, the kernel source code is fetched and unpacked into the following directory: ${S}/linux See the "Finding the Temporary Source Code" section and the S variable for more information about where source is kept during a build. For this example, we are going to patch the init/calibrate.c file by adding some simple console printk statements that we can see when we boot the image using QEMU.

Two methods exist by which you can create the patch: Git workflow and Quilt workflow. For kernel patches, the Git workflow is more appropriate. This section assumes the Git workflow and shows the steps specific to this example. Change the working directory: Change to where the kernel source code is before making your edits to the calibrate.c file: $ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux Because you are working in an established Git repository, you must be in this directory in order to commit your changes and create the patch file. The PV and PR variables represent the version and revision for the linux-yocto recipe. The PV variable includes the Git meta and machine hashes, which make the directory name longer than you might expect. Edit the source file: Edit the init/calibrate.c file to have the following changes: void __cpuinit calibrate_delay(void) { unsigned long lpj; static bool printed; int this_cpu = smp_processor_id(); printk("*************************************\n"); printk("* *\n"); printk("* HELLO YOCTO KERNEL *\n"); printk("* *\n"); printk("*************************************\n"); if (per_cpu(cpu_loops_per_jiffy, this_cpu)) { . . . Stage and commit your changes: These Git commands list out the changed file, stage it, and then commit the file: $ git status $ git add init/calibrate.c $ git commit -m "calibrate: Add printk example" Generate the patch file: This Git command creates the a patch file named 0001-calibrate-Add-printk-example.patch in the current directory. $ git format-patch -1

These steps get your layer set up for the build: Create additional structure: Create the additional layer structure: $ cd ~/poky/meta-mylayer $ mkdir conf $ mkdir recipes-kernel $ mkdir recipes-kernel/linux $ mkdir recipes-kernel/linux/linux-yocto The conf directory holds your configuration files, while the recipes-kernel directory holds your append file and your patch file. Create the layer configuration file: Move to the meta-mylayer/conf directory and create the layer.conf file as follows: # We have a conf and classes directory, add to BBPATH BBPATH .= ":${LAYERDIR}" # We have recipes-* directories, add to BBFILES BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \ ${LAYERDIR}/recipes-*/*/*.bbappend" BBFILE_COLLECTIONS += "mylayer" BBFILE_PATTERN_mylayer = "^${LAYERDIR}/" BBFILE_PRIORITY_mylayer = "5" Notice mylayer as part of the last three statements. Create the kernel recipe append file: Move to the meta-mylayer/recipes-kernel/linux directory and create the linux-yocto_3.4.bbappend file as follows: FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:" SRC_URI += "file://0001-calibrate-Add-printk-example.patch" PRINC := "${@int(PRINC) + 1}" The FILESEXTRAPATHS and SRC_URI statements enable the OpenEmbedded build system to find the patch file. Put the patch file in your layer: Move the 0001-calibrate-Add-printk-example.patch file to the meta-mylayer/recipes-kernel/linux/linux-yocto directory.

Do the following to make sure the build parameters are set up for the example. Once you set up these build parameters, they do not have to change unless you change the target architecture of the machine you are building: Build for the Correct Target Architecture: Your selected MACHINE definition within the local.conf file in the Build Directory specifies the target architecture used when building the Linux kernel. By default, MACHINE is set to qemux86, which specifies a 32-bit Intel Architecture target machine suitable for the QEMU emulator. Identify Your meta-mylayer Layer: The BBLAYERS variable in the bblayers.conf file found in the poky/build/conf directory needs to have the path to your local meta-mylayer layer. By default, the BBLAYERS variable contains paths to meta, meta-yocto, and meta-yocto-bsp in the poky Git repository. Add the path to your meta-mylayer location: BBLAYERS ?= " \ $HOME/poky/meta \ $HOME/poky/meta-yocto \ $HOME/poky/meta-yocto-bsp \ $HOME/poky/meta-mylayer \ " BBLAYERS_NON_REMOVABLE ?= " \ $HOME/poky/meta \ $HOME/poky/meta-yocto \ "

The following steps build and boot your modified kernel image: Be sure your build environment is initialized: Your environment should be set up since you previously sourced the &OE_INIT_FILE; script. If it is not, source the script again from poky. $ cd ~/poky $ source &OE_INIT_FILE; Clean up: Be sure to clean the shared state out by running the cleansstate BitBake task as follows from your Build Directory: $ bitbake -c cleansstate linux-yocto Never remove any files by hand from the tmp/deploy directory inside the Build Directory. Always use the various BitBake clean tasks to clear out previous build artifacts. Build the image: Next, build the kernel image using this command: $ bitbake -k linux-yocto

These steps boot the image and allow you to see the changes Boot the image: Boot the modified image in the QEMU emulator using this command: $ runqemu qemux86 Verify the changes: Log into the machine using root with no password and then use the following shell command to scroll through the console's boot output. # dmesg | less You should see the results of your printk statements as part of the output.

When you build an image using the Yocto Project and do not alter any distribution Metadata, you are creating a Poky distribution. If you wish to gain more control over package alternative selections, compile-time options, and other low-level configuration, you can create your own distribution. To create your own distribution, the basic steps consist of creating your own distribution layer, creating your own distribution configuration file, and then adding any needed code and Metadata to the layer. The following steps provide some more detail: Create a layer for your new distro: Create your distribution layer so that you can keep your Metadata and code for the distribution separate. It is strongly recommended that you create and use your own layer for configuration and code. Using your own layer as compared to just placing configurations in a local.conf configuration file makes it easier to reproduce the same build configuration when using multiple build machines. Create the Distribution Configuration File: The distribution configuration file needs to be created in the conf/distro directory of your layer. You need to name it using your distribution name (e.g. mydistro.conf). You can split out parts of your configuration file into include files and then "require" them from within your distribution configuration file. Be sure to place the include files in the conf/distro/include directory of your layer. A common example usage of include files would be to separate out the selection of desired version and revisions for individual recipes. If you want to base your distribution configuration file on the very basic configuration from OE-Core, you can "require" conf/distro/defaultsetup.conf. Alternatively, you can create a distribution configuration file from scratch using the defaultsetup.conf file or configuration files from other distributions such as Poky or Angstrom as references. Your configuration file needs to set the following variables: DISTRO_NAME [required] DISTRO_VERSION [required] DISTRO_FEATURES [required if creating from scratch] DISTRO_EXTRA_RDEPENDS [optional] DISTRO_EXTRA_RRECOMMENDS [optional] TCLIBC [required if creating from scratch] Provide Miscellaneous Variables: Be sure to define any other variable for which you want to create a default or enforce as part of the distribution configuration. You can include nearly any variable from the local.conf file. The variables you use are not limited to the list in the previous bulleted item. Point to Your Distribution Configuration File: In your local.conf file in the Build Directory, set your DISTRO variable to point to your distribution's configuration file. For example, if your distribution's configuration file is named mydistro.conf, then you point to it as follows: DISTRO = "mydistro" Add More to the Layer if Necessary: Use your layer to hold other information needed for the distribution: Add recipes for installing distro-specific configuration files that are not already installed by another recipe. If you have distro-specific configuration files that are included by an existing recipe, you should add a .bbappend for those. For general information on how to add recipes to your layer, see the "Creating Your Own Layer" section. Add any image recipes that are specific to your distribution. Add a psplash append file for a branded splash screen. For information on append files, see the "Using .bbappend Files" section. Add any other append files to make custom changes that are specific to individual recipes.

Very small distributions have some significant advantages such as requiring less on-die or in-package memory (cheaper), better performance through efficient cache usage, lower power requirements due to less memory, faster boot times, and reduced development overhead. Some real-world examples where a very small distribution gives you distinct advantages are digital cameras, medical devices, and small headless systems. This section presents information that shows you how you can trim your distribution to even smaller sizes than the poky-tiny distribution, which is around 5 Mbytes, that can be built out-of-the-box using the Yocto Project.

The following list presents the overall steps you need to consider and perform to create distributions with smaller root filesystems, faster boot times, maintain your critical functionality, and avoid initial RAM disks: Determine your goals and guiding principles. Understand what gives your image size. Reduce the size of the root filesystem. Reduce the size of the kernel. Look for other ways to minimize size. Iterate on the process.

Before you can reach your destination, you need to know where you are going. Here is an example list that you can use as a guide when creating very small distributions: Determine how much space you need (e.g. a kernel that is 1 Mbyte or less and a root filesystem that is 3 Mbytes or less). Find the areas that are currently taking 90% of the space and concentrate on reducing those areas. Do not create any difficult "hacks" to achieve your goals. Leverage the device-specific options. Work in a separate layer so that you keep changes isolated. For information on how to create layers, see the "Understanding and Creating Layers" section.

It is easiest to have something to start with when creating your own distribution. You can use the Yocto Project out-of-the-box to create the poky-tiny distribution. Ultimately, you will want to make changes in your own distribution that are likely modeled after poky-tiny. To use poky-tiny in your build, set the DISTRO variable in your local.conf file to "poky-tiny" as described in the "Creating Your Own Distribution" section. Understanding some memory concepts will help you reduce the system size. Memory consists of static, dynamic, and temporary memory. Static memory is the TEXT (the code), DATA (initialized data in the code), and BSS (uninitialized data) sections. Dynamic memory contains memory that is allocated at runtime, stacks, hash tables, and so forth. Temporary memory is recovered after the boot process. This memory consists of memory used for decompressing the kernel and for the __init__ functions. To help you see where you currently are with kernel and root filesystem sizes, you can use two tools found in the Source Directory in the scripts directory: ksize.py: Reports component sizes for the kernel build objects. dirsize.py: Reports component sizes for the root filesystem. This next tool and command helps you organize configuration fragments and view file dependencies in a human-readable form: merge_config.sh: Helps you manage configuration files and fragments within the kernel. With this tool, you can merge individual configuration fragments together. The tool allows you to make overrides and warns you of any missing configuration options. The tool is ideal for allowing you to iterate on configurations, create minimal configurations, and create a configuration files for different machines without having to duplicate your process. The merge_config.sh script is part of the Linux Yocto kernel Git repository in the scripts/kconfig directory. For more information on configuration fragments, see the "Generating Configuration Files" section of the Yocto Project Linux Kernel Development Manual and the "Creating Configuration Fragments" section, which is in this manual. bitbake -u depexp -g <bitbake_target>: Using the BitBake command with these options brings up a Dependency Explorer from which you can view file dependencies. Understanding these dependencies allows you to make informed decisions when cutting out various pieces of the kernel and root filesystem.

The root filesystem is made up of packages for booting, libraries, and applications. To change things you can configure how the packaging happens, which changes the way you build them. You can also tweak the filesystem itself or select a different filesystem. First, check out what is hogging your root filesystem running the dirsize.py script from your root directory: $ cd <root-directory-of-image> $ dirsize.py 100000 > dirsize-100k.log $ cat dirsize-100k.log You can apply a filter to the script to ignore files under a certain size. This example filters out anything below 100 Kbytes. The sizes reported by the tool are uncompressed and thus, will be smaller by a relatively constant factor in a compressed root filesystem. When you examine your log file, you can focus on areas of the root filesystem that take up large amounts of memory. You need to be sure that what you eliminate does not cripple the functionality you need. One way to see how packages relate to each other is by using the Dependency Explorer UI with the BitBake command: $ cd <image-directory> $ bitbake -u depexp -g <image> Use the interface to select potential packages you wish to eliminate and see their dependency relationships. When deciding how to reduce the size, get rid of packages that result in minimal impact on the feature set. For example, you might not need a VGA display. Or, you might be able to get by with devtmpfs and mdev instead of udev. Use the local.conf file to make changes. For example, to eliminate udev and glib, set the following in the local configuration file: VIRTUAL-RUNTIME_dev_manager = "" Finally, you should consider exactly the type of root filesystem you need to meet your needs while also reducing its size. For example, consider cramfs, squashfs, ubifs, ext2, or an initramfs using initramfs. Be aware that ext3 requires a 1 Mbyte journal. If you are okay with running read-only you don't need this journal. After each round of elimination, you need to rebuild your system and then use the tools to see the effects of your reductions.

Kernel is built by including policies for hardware-independent aspects. What subsystems do you enable? What architecture are you building for? Which drivers do you build by default. You can modify the kernel source if you want to help with boot time. Run the ksize.py script from the top-level Linux build directory to get an idea of what is making up the kernel: $ cd <top-level-linux-build-directory> $ ksize.py > ksize.log $ cat ksize.log When you examine the log, you will see how much space is taken up with the built-in .o files for drivers, networking, core kernel files, filesystem, sound, and so forth. The sizes reported by the tool are uncompressed and thus, will be smaller by a relatively constant factor in a compressed kernel image. Look to reduce the areas that are large and taking up around the "90% rule". To examine, or drill down, into any particular area, use the -d option with the script: $ ksize.py -d > ksize.log Using this option breaks out the individual file information for each area of the kernel (e.g. drivers, networking, and so forth). Use your log file to see what you can eliminate from the kernel based on features you can let go. For example, if you are not going to need sound, you do not need any drivers that support sound. After figuring out what to eliminate, you need to reconfigure kernel to reflect those changes during the next build. You could run menuconfig and make all your changes at once. However, that makes it difficult to see the effects of your individual eliminations and also makes it difficult to replicate the changes for perhaps another target device. A better method is to start with no configurations using allnoconfig, create configuration fragments for individual changes, and then manage the fragments into a single configuration file using merge_config.sh. The tool makes it easy for you to iterate using the configuration change/build cycle. Each time you make configuration changes, you need to rebuild the kernel and check to see what impact your changes had on the overall size.

Depending on your particular circumstances, other areas that you can trim likely exist. The key to finding these areas is through tools and methods described here combined with experimentation and iteration. Here are a couple of areas to experiment with: eglibc: In general, follow this process: Remove eglibc features from DISTRO_FEATURES that you think you don't need. Build your distribution. If the build fails due to missing symbols in a package, determine if you can reconfigure the package to not need those features. For example, change the configuration to not support wide character support as is done for ncurses. Or, if support for those characters is needed, determine what eglibc features provide the support and restore the configuration. Rebuild and repeat the process. busybox: For BusyBox, use a process similar as described for eglibc. A difference is you will need to boot the resulting system to see if you are able to do everything you expect from the running system. You need to be sure to integrate configuration fragments into Busybox because BusyBox handles its own core features and then allows you to add configuration fragments on top.

If you have not reached your goals on system size, you need to iterate on the process. The process is the same. Use the tools and see just what is taking up 90% of the root filesystem and the kernel. Decide what you can eliminate without limiting your device beyond what you need. Depending on your system, a good place to look might be Busybox, which provides a stripped down version of Unix tools in a single, executable file. You might be able to drop virtual terminal services or perhaps ipv6.

This section describes a few tasks that involve packages: Incrementing a package revision number Handling a package name alias Handling optional module packaging Setting up Runtime Package Management

If a committed change results in changing the package output, then the value of the PR variable needs to be increased (or "bumped"). Increasing PR occurs one of two ways: Automatically using a Package Revision Service (PR Service). Manually incrementing the PR variable. Given that one of the challenges any build system and its users face is how to maintain a package feed that is compatible with existing package manager applications such as RPM, APT, and OPKG, using an automated system is much preferred over a manual system. In either system, the main requirement is that version numbering increases in a linear fashion and that a number of version components exist that support that linear progression. The following two sections provide information on the PR Service and on manual PR bumping.

As mentioned, attempting to maintain revision numbers in the Metadata is error prone, inaccurate and causes problems for people submitting recipes. Conversely, the PR Service automatically generates increasing numbers, particularly the revision field, which removes the human element. For additional information on using a PR Service, you can see the PR Service wiki page. The Yocto Project uses variables in order of decreasing priority to facilitate revision numbering (i.e. PE, PV, and PR for epoch, version and revision, respectively). The values are highly dependent on the policies and procedures of a given distribution and package feed. Because the OpenEmbedded build system uses "signatures", which are unique to a given build, the build system knows when to rebuild packages. All the inputs into a given task are represented by a signature, which can trigger a rebuild when different. Thus, the build system itself does not rely on the PR numbers to trigger a rebuild. The signatures, however, can be used to generate PR values. The PR Service works with both OEBasic and OEBasicHash generators. The value of PR bumps when the checksum changes and the different generator mechanisms change signatures under different circumstances. As implemented, the build system includes values from the PR Service into the PR field as an addition using the form ".x" so r0 becomes r0.1, r0.2 and so forth. This scheme allows existing PR values to be used for whatever reasons, which include manual PR bumps should it be necessary. By default, the PR Service is not enabled or running. Thus, the packages generated are just "self consistent". The build system adds and removes packages and there are no guarantees about upgrade paths but images will be consistent and correct with the latest changes. The simplest form for a PR Service is for it to exist for a single host development system that builds the package feed (building system). For this scenario, you can enable the PR Service by adding the following to your local.conf file in the Build Directory: PRSERV_HOST = "localhost:0" Once the service is started, packages will automatically get increasing PR values and BitBake will take care of starting and stopping the server. If you have a more complex setup where multiple host development systems work against a common, shared package feed, you have a single PR Service running and it is connected to each building system. For this scenario, you need to start the PR Service using the bitbake-prserv command: bitbake-prserv ‐‐host <ip> ‐‐port <port> ‐‐start In addition to hand-starting the service, you need to update the local.conf file of each building system as described earlier so each system points to the server and port. It is also recommended you use build history, which adds some sanity checks to package versions, in conjunction with the server that is running the PR Service. To enable build history, add the following to each building system's local.conf file: # It is recommended to activate "buildhistory" for testing the PR service INHERIT += "buildhistory" BUILDHISTORY_COMMIT = "1" For information on build history, see the "Maintaining Build Output Quality" section in the Yocto Project Reference Manual. The OpenEmbedded build system does not maintain PR information as part of the shared state (sstate) packages. If you maintain an sstate feed, its expected that either all your building systems that contribute to the sstate feed use a shared PR Service, or you do not run a PR Service on any of your building systems. Having some systems use a PR Service while others do not leads to obvious problems. For more information on shared state, see the "Shared State Cache" section in the Yocto Project Reference Manual.

If a committed change results in changing the package output, then the value of the PR variable needs to be increased (or "bumped") as part of that commit. For new recipes you should add the PR variable and set its initial value equal to "r0", which is the default. Even though the default value is "r0", the practice of adding it to a new recipe makes it harder to forget to bump the variable when you make changes to the recipe in future. If you are sharing a common .inc file with multiple recipes, you can also use the INC_PR variable to ensure that the recipes sharing the .inc file are rebuilt when the .inc file itself is changed. The .inc file must set INC_PR (initially to "r0"), and all recipes referring to it should set PR to "$(INC_PR).0" initially, incrementing the last number when the recipe is changed. If the .inc file is changed then its INC_PR should be incremented. When upgrading the version of a package, assuming the PV changes, the PR variable should be reset to "r0" (or "$(INC_PR).0" if you are using INC_PR). Usually, version increases occur only to packages. However, if for some reason PV changes but does not increase, you can increase the PE variable (Package Epoch). The PE variable defaults to "0". Version numbering strives to follow the Debian Version Field Policy Guidelines. These guidelines define how versions are compared and what "increasing" a version means.

Sometimes a package name you are using might exist under an alias or as a similarly named package in a different distribution. The OpenEmbedded build system implements a distro_check task that automatically connects to major distributions and checks for these situations. If the package exists under a different name in a different distribution, you get a distro_check mismatch. You can resolve this problem by defining a per-distro recipe name alias using the DISTRO_PN_ALIAS variable. Following is an example that shows how you specify the DISTRO_PN_ALIAS variable: DISTRO_PN_ALIAS_pn-PACKAGENAME = "distro1=package_name_alias1 \ distro2=package_name_alias2 \ distro3=package_name_alias3 \ ..." If you have more than one distribution alias, separate them with a space. Note that the build system currently automatically checks the Fedora, OpenSUSE, Debian, Ubuntu, and Mandriva distributions for source package recipes without having to specify them using the DISTRO_PN_ALIAS variable. For example, the following command generates a report that lists the Linux distributions that include the sources for each of the recipes. $ bitbake world -f -c distro_check The results are stored in the build/tmp/log/distro_check-${DATETIME}.results file found in the Source Directory.

Many pieces of software split functionality into optional modules (or plugins) and the plugins that are built might depend on configuration options. To avoid having to duplicate the logic that determines what modules are available in your recipe or to avoid having to package each module by hand, the OpenEmbedded build system provides functionality to handle module packaging dynamically. To handle optional module packaging, you need to do two things: Ensure the module packaging is actually done Ensure that any dependencies on optional modules from other recipes are satisfied by your recipe

To ensure the module packaging actually gets done, you use the do_split_packages function within the populate_packages python function in your recipe. The do_split_packages function searches for a pattern of files or directories under a specified path and creates a package for each one it finds by appending to the PACKAGES variable and setting the appropriate values for FILES_packagename, RDEPENDS_packagename, DESCRIPTION_packagename, and so forth. Here is an example from the lighttpd recipe: python populate_packages_prepend () { lighttpd_libdir = d.expand('${libdir}') do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$', 'lighttpd-module-%s', 'Lighttpd module for %s', extra_depends='') } The previous example specifies a number of things in the call to do_split_packages. A directory within the files installed by your recipe through do_install in which to search. A regular expression to match module files in that directory. In the example, note the parentheses () that mark the part of the expression from which the module name should be derived. A pattern to use for the package names. A description for each package. An empty string for extra_depends, which disables the default dependency on the main lighttpd package. Thus, if a file in ${libdir} called mod_alias.so is found, a package called lighttpd-module-alias is created for it and the DESCRIPTION is set to "Lighttpd module for alias". Often, packaging modules is as simple as the previous example. However, more advanced options exist that you can employ to do_split_packages to modify its behavior. And, if you need to, you can add more logic by specifying a hook function that is called for each package. It is also perfectly acceptable to call do_split_packages multiple times if you have more than one set of modules to package. For more examples that show how to use do_split_packages, see the connman.inc file in the meta/recipes-connectivity/connman/ directory of the poky source repository. You can also find examples in meta/classes/kernel.bbclass. Following is a reference that shows do_split_packages mandatory and optional arguments: Mandatory arguments root The path in which to search file_regex Regular expression to match searched files. Use parentheses () to mark the part of this expression that should be used to derive the module name (to be substituted where %s is used in other function arguments as noted below) output_pattern Pattern to use for the package names. Must include %s. description Description to set for each package. Must include %s. Optional arguments postinst Postinstall script to use for all packages (as a string) recursive True to perform a recursive search - default False hook A hook function to be called for every match. The function will be called with the following arguments (in the order listed): f Full path to the file/directory match pkg The package name file_regex As above output_pattern As above modulename The module name derived using file_regex extra_depends Extra runtime dependencies (RDEPENDS) to be set for all packages. The default value of None causes a dependency on the main package (${PN}) - if you do not want this, pass empty string '' for this parameter. aux_files_pattern Extra item(s) to be added to FILES for each package. Can be a single string item or a list of strings for multiple items. Must include %s. postrm postrm script to use for all packages (as a string) allow_dirs True to allow directories to be matched - default False prepend If True, prepend created packages to PACKAGES instead of the default False which appends them match_path match file_regex on the whole relative path to the root rather than just the file name aux_files_pattern_verbatim Extra item(s) to be added to FILES for each package, using the actual derived module name rather than converting it to something legal for a package name. Can be a single string item or a list of strings for multiple items. Must include %s. allow_links True to allow symlinks to be matched - default False

The second part for handling optional module packaging is to ensure that any dependencies on optional modules from other recipes are satisfied by your recipe. You can be sure these dependencies are satisfied by using the PACKAGES_DYNAMIC variable. Here is an example that continues with the lighttpd recipe shown earlier: PACKAGES_DYNAMIC = "lighttpd-module-.*" The name specified in the regular expression can of course be anything. In this example, it is lighttpd-module- and is specified as the prefix to ensure that any RDEPENDS and RRECOMMENDS on a package name starting with the prefix are satisfied during build time. If you are using do_split_packages as described in the previous section, the value you put in PACKAGES_DYNAMIC should correspond to the name pattern specified in the call to do_split_packages.

For RPM, IPK, and DEB package formats, it is possible to set up a repository that is a host-based package feed from which you can install packages on the target system during runtime. Doing so is optional and depends on the following: You take specific steps to set up the feed. When you build your image, you select to use the appropriate package manager by setting the PACKAGE_CLASSES variable. You have a web server, such as Apache 2, installed and configured on the development host. You have createrepo installed on the development host. You enable package management on the target by listing "package-management" in the IMAGE_FEATURES variable. Following are the steps to set up the optional repository. This examples assumes you are using RPM and the Apache 2 server: Add the directory to your Apache configuration, which you can find at /etc/httpd/conf/httpd.conf. Use commands similar to these on the development system. These example commands assume a top-level Source Directory named poky in your home directory: <VirtualHost *:80> .... Alias /rpm ~/poky/build/tmp/deploy/rpm <Directory "~/poky/build/tmp/deploy/rpm"> Options +Indexes </Directory> </VirtualHost> Reload the Apache configuration as follows. For all commands, be sure you have root privileges. If your development system is using Fedora or CentOS, use the following: service httpd reload For Ubuntu, use the following: /etc/init.d/apache2 reload For OpenSUSE, use the following: /etc/init.d/apache2 reload Change your working directory to tmp/deploy/rpm in the Build Directory. Create the repository data on the host using this command: createrepo . If you're updating, add ‐‐update to save some time. If you are using Security-Enhanced Linux (SELinux), you need to label the files as being accessible through Apache. Use the following command from the development host: chcon -R -h -t httpd_sys_content_t . On the target machine, add the repository to Smart. For somealias, provide a local alias for the repository: smart channel ‐‐add <somealias> type=rpm-md baseurl=http://server.name/rpm Also from the target machine, fetch the repository information using this command: smart update After taking these steps and making sure that the other requirements mentioned at the beginning of the section are met, reboot the target device to take advantage of runtime package installations. If your packages are IPK, you can install packages onto an existing running system by first sharing the tmp/deploy/ipk/ directory through a web server and then by changing /etc/opkg/base-feeds.conf to point at the shared server. Following is an example: $ src/gz all http://www.mysite.com/somedir/deploy/ipk/all $ src/gz armv7a http://www.mysite.com/somedir/deploy/ipk/armv7a $ src/gz beagleboard http://www.mysite.com/somedir/deploy/ipk/beagleboard

By default, the OpenEmbedded build system does its work from within the Build Directory. The build process involves fetching the source files, unpacking them, and then patching them if necessary before the build takes place. Situations exist where you might want to build software from source files that are external to and thus outside of the Source Directory. For example, suppose you have a project that includes a new BSP with a heavily customized kernel, a very minimal image, and some new user-space recipes. And, you want to minimize exposing the build system to the development team so that they can focus on their project and maintain everyone's workflow as much as possible. In this case, you want a kernel source directory on the development machine where the development occurs. You want the recipe's SRC_URI variable to point to the external directory and use it as is, not copy it. To build from software that comes from an external source, all you need to do is change your recipe so that it inherits the externalsrc.bbclass class and then sets the S variable to point to your external source code. Here are the statements to put in your recipe: inherit externalsrc S = "/some/path/to/your/package/source" It is important to know that the externalsrc.bbclass assumes that the source directory S and the Build Directory B are different even though by default these directories are the same. This assumption is important because it supports building different variants of the recipe by using the BBCLASSEXTEND variable. You could allow the Build Directory to be the same as the source directory but you would not be able to build more than one variant of the recipe. Consequently, if you are building multiple variants of the recipe, you need to establish a Build Directory that is different than the source directory.

By default, the Yocto Project uses SysVinit as the initialization manager. However, support also exists for systemd, which is a full replacement for init with parallel starting of services, reduced shell overhead and other features, used by many distributions. If you want to use SysVinit, you do not have to do anything. But, if you want to use systemd, you must take some steps as described in the following sections. NOTES TO SELF: systemd is a full replacement of for init with parallel starting of services, reduced shell overhead and other features, used by many distributions. I think you set the VIRTUAL-RUNTIME in a recipe. I found a recipe called packagegroup-core-boot.bb, which is an OE-Core recipe, that has a bunch of them. The comment refers to the group as "VIRTUAL-RUNTIME providers". The list includes VIRTUAL-RUNTIME_dev_manager, VIRTUAL-RUNTIME_init_manager, VIRTUAL-RUNTIME_login_manager, VIRTUAL-RUNTIME_initscripts, and VIRTUAL-RUNTIME_keymaps.

Set the following variables in your local.conf file as follows: DISTRO_FEATURES = "systemd" VIRTUAL-RUNTIME_init_manager = "systemd" You can save some disk space by adding sysvinit to the distribution features considered for backfill as follows: DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit" Doing so removes any redundant sysvinit scripts.

Set the following variables in your local.conf file as follows: DISTRO_FEATURES = "systemd" VIRTUAL-RUNTIME_init_manager = "systemd" Doing so causes your main image to use the packagegroup-core-boot.bb recipe and systemd. The rescue/minimal image cannot use this group. However, it can install sysvinit and the appropriate packages with have both systemd and sysvinit.

You might find that there are groups of recipes or append files that you want to filter out of the build process. Usually, this is not necessary. However, on rare occasions where you might want to use a layer but exclude parts that are causing problems, such as introducing a different version of a recipe, you can use BBMASK to exclude the recipe. It is possible to filter or mask out .bb and .bbappend files. You can do this by providing an expression with the BBMASK variable. Here is an example: BBMASK = "/meta-mymachine/recipes-maybe/" Here, all .bb and .bbappend files in the directory that matches the expression are ignored during the build process. See the glossary entry for the BBMASK variable for more information. The value you provide is passed to python's regular expression compiler. The expression is compared against the full paths to the files. For complete syntax information, see python's documentation at .

If you're working on a recipe that pulls from an external Source Code Manager (SCM), it is possible to have the OpenEmbedded build system notice new recipe changes added to the SCM and then build the resulting package that depends on the new recipes by using the latest versions. This only works for SCMs from which it is possible to get a sensible revision number for changes. Currently, you can do this with Apache Subversion (SVN), Git, and Bazaar (BZR) repositories. To enable this behavior, simply add the following to the local.conf configuration file found in the Build Directory: SRCREV_pn-<PN> = "${AUTOREV}" where PN is the name of the recipe for which you want to enable automatic source revision updating.

Suppose, for security reasons, you need to disable your target device's root filesystem's write permissions (i.e. you need a read-only root filesystem). Or, perhaps you are running the device's operating system from a read-only storage device. For either case, you can customize your image for that behavior. Supporting a read-only root filesystem requires that the system and applications do not try to write to the root filesystem. You must configure all parts of the target system to write elsewhere, or gracefully fail in the event of failing to write to the root filesystem.

To create the read-only root filesystem, simply add the read-only-rootfs feature to your image. Using either of the following statements in your image recipe or from within the local.conf file found in the Build Directory causes the build system to create a read-only root filesystem: IMAGE_FEATURES = "read-only-rootfs" or EXTRA_IMAGE_FEATURES = "read-only-rootfs" For more information on how to use these variables, see the "Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES" section. For information on the variables, see IMAGE_FEATURES and EXTRA_IMAGE_FEATURES.

It is very important that you make sure all post-Installation (pkg_postinst) scripts for packages that are installed into the image can be run at the time when the root filesystem is created during the build on the host system. These scripts cannot attempt to run during first-boot on the target device. With the read-only-rootfs feature enabled, the build system checks during root filesystem creation to make sure all post-installation scripts succeed. If any of these scripts still need to be run after the root filesystem is created, the build immediately fails. These checks during build time ensure that the build fails rather than the target device fails later during its initial boot operation. Most of the common post-installation scripts generated by the build system for the out-of-the-box Yocto Project are engineered so that they can run during root filesystem creation (e.g. post-installation scripts for caching fonts). However, if you create and add custom scripts, you need to be sure they can be run during file system creation. Here are some common problems that prevent post-installation scripts from running during root filesystem creation: Not using $D in front of absolute paths: The build system defines $D at root filesystem creation time, and it is blank when run on the target device. This implies two purposes for $D: ensuring paths are valid in both the host and target environments, and checking to determine which environment is being used as a method for taking appropriate actions. Attempting to run processes that are specific to or dependent on the target architecture: You can work around these attempts by using native tools to accomplish the same tasks, or by alternatively running the processes under QEMU, which has the qemu_run_binary function. For more information, see the meta/classes/qemu.bbclass class in the Source Directory.

With the read-only-rootfs feature enabled, any attempt by the target to write to the root filesystem at runtime fails. Consequently, you must make sure that you configure processes and applications that attempt these types of writes do so to directories with write access (e.g. /tmp or /var/run).

GDB allows you to examine running programs, which in turn helps you to understand and fix problems. It also allows you to perform post-mortem style analysis of program crashes. GDB is available as a package within the Yocto Project and by default is installed in SDK images. See the "Images" chapter in the Yocto Project Reference Manual for a description of these images. You can find information on GDB at . For best results, install -dbg packages for the applications you are going to debug. Doing so makes available extra debug symbols that give you more meaningful output. Sometimes, due to memory or disk space constraints, it is not possible to use GDB directly on the remote target to debug applications. These constraints arise because GDB needs to load the debugging information and the binaries of the process being debugged. Additionally, GDB needs to perform many computations to locate information such as function names, variable names and values, stack traces and so forth - even before starting the debugging process. These extra computations place more load on the target system and can alter the characteristics of the program being debugged. To help get past the previously mentioned constraints, you can use Gdbserver. Gdbserver runs on the remote target and does not load any debugging information from the debugged process. Instead, a GDB instance processes the debugging information that is run on a remote computer - the host GDB. The host GDB then sends control commands to Gdbserver to make it stop or start the debugged program, as well as read or write memory regions of that debugged program. All the debugging information loaded and processed as well as all the heavy debugging is done by the host GDB. Offloading these processes gives the Gdbserver running on the target a chance to remain small and fast. Because the host GDB is responsible for loading the debugging information and for doing the necessary processing to make actual debugging happen, the user has to make sure the host can access the unstripped binaries complete with their debugging information and also be sure the target is compiled with no optimizations. The host GDB must also have local access to all the libraries used by the debugged program. Because Gdbserver does not need any local debugging information, the binaries on the remote target can remain stripped. However, the binaries must also be compiled without optimization so they match the host's binaries. To remain consistent with GDB documentation and terminology, the binary being debugged on the remote target machine is referred to as the "inferior" binary. For documentation on GDB see the GDB site. The remainder of this section describes the steps you need to take to debug using the GNU project debugger.

Before you can initiate a remote debugging session, you need to be sure you have set up the cross-development environment, toolchain, and sysroot. The "Preparing for Application Development" chapter of the Yocto Project Application Developer's Guide describes this process. Be sure you have read that chapter and have your environment set up.

Make sure Gdbserver is installed on the target. If it is not, install the package gdbserver, which needs the libthread-db1 package. As an example, to launch Gdbserver on the target and make it ready to "debug" a binary named helloworld, from the host you need to enter a command like the following. This command connects to the target and launches Gdbserver on the target: $ gdbserver localhost:2345 /usr/bin/helloworld Gdbserver should now be listening on port 2345 for debugging commands coming from a remote GDB process that is running on the host computer. Communication between Gdbserver and the host GDB are done using TCP. To use other communication protocols, please refer to the Gdbserver documentation.

Running GDB on the host computer takes a number of stages. This section describes those stages.

A suitable GDB cross-binary is required that runs on your host computer but also knows about the the ABI of the remote target. You can get this binary from the Cross-Development Toolchain. Here is an example where the toolchain has been installed in the default directory /opt/poky/&DISTRO;: /opt/poky/1.4/sysroots/i686-pokysdk-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gdb where arm is the target architecture and linux-gnueabi the target ABI. Alternatively, you can use BitBake to build the gdb-cross binary. Here is an example: $ bitbake gdb-cross Once the binary is built, you can find it here: tmp/sysroots/<host-arch>/usr/bin/<target-platform>/<target-abi>-gdb

Aside from the GDB cross-binary, you also need a GDB initialization file in the same top directory in which your binary resides. When you start GDB on your host development system, GDB finds this initialization file and executes all the commands within. For information on the .gdbinit, see "Debugging with GDB" by maintained by sourceware.org. You need to add a statement in the .gdbinit file that points to your root filesystem. Here is an example that points to the root filesystem for an ARM-based target device: set sysroot /home/jzhang/sysroot_arm

Before launching the host GDB, you need to be sure you have sourced the cross-debugging environment script, which if you installed the root filesystem in the default location is at /opt/poky/&DISTRO; and begins with the string "environment-setup". For more information, see the "Setting Up the Cross-Development Environment" section in the Yocto Project Application Developer's Guide. Finally, switch to the directory where the binary resides and run the cross-gdb binary. Provide the binary file you are going to debug. For example, the following command continues with the example used in the previous section by loading the helloworld binary as well as the debugging information: $ arm-poky-linux-gnuabi-gdb helloworld The commands in your .gdbinit execute and the GDB prompt appears.

From the target, you need to connect to the remote GDB server that is running on the host. You need to specify the remote host and port. Here is the command continuing with the example: target remote 192.168.7.2:2345

You can now proceed with debugging as normal - as if you were debugging on the local machine. For example, to instruct GDB to break in the "main" function and then continue with execution of the inferior binary use the following commands from within GDB: (gdb) break main (gdb) continue For more information about using GDB, see the project's online documentation at .

OProfile is a statistical profiler well suited for finding performance bottlenecks in both userspace software and in the kernel. This profiler provides answers to questions like "Which functions does my application spend the most time in when doing X?" Because the OpenEmbedded build system is well integrated with OProfile, it makes profiling applications on target hardware straightforward. For more information on how to set up and run OProfile, see the "OProfile" section in the Yocto Project Profiling and Tracing Manual. To use OProfile, you need an image that has OProfile installed. The easiest way to do this is with tools-profile in the IMAGE_FEATURES variable. You also need debugging symbols to be available on the system where the analysis takes place. You can gain access to the symbols by using dbg-pkgs in the IMAGE_FEATURES variable or by installing the appropriate -dbg packages. For successful call graph analysis, the binaries must preserve the frame pointer register and should also be compiled with the -fno-omit-framepointer flag. You can achieve this by setting the SELECTED_OPTIMIZATION variable with the following options: -fexpensive-optimizations -fno-omit-framepointer -frename-registers -O2 You can also achieve it by setting the DEBUG_BUILD variable to "1" in the local.conf configuration file. If you use the DEBUG_BUILD variable, you will also add extra debug information that can make the debug packages large.

Using OProfile you can perform all the profiling work on the target device. A simple OProfile session might look like the following: # opcontrol --reset # opcontrol --start --separate=lib --no-vmlinux -c 5 . . [do whatever is being profiled] . . # opcontrol --stop $ opreport -cl In this example, the reset command clears any previously profiled data. The next command starts OProfile. The options used when starting the profiler separate dynamic library data within applications, disable kernel profiling, and enable callgraphing up to five levels deep. To profile the kernel, you would specify the --vmlinux=/path/to/vmlinux option. The vmlinux file is usually in the source directory in the /boot/ directory and must match the running kernel. After you perform your profiling tasks, the next command stops the profiler. After that, you can view results with the opreport command with options to see the separate library symbols and callgraph information. Callgraphing logs information about time spent in functions and about a function's calling function (parent) and called functions (children). The higher the callgraphing depth, the more accurate the results. However, higher depths also increase the logging overhead. Consequently, you should take care when setting the callgraphing depth. On ARM, binaries need to have the frame pointer enabled for callgraphing to work. To accomplish this use the -fno-omit-framepointer option with gcc. For more information on using OProfile, see the OProfile online documentation at .

A graphical user interface for OProfile is also available. You can download and build this interface from the Yocto Project at . If the "tools-profile" image feature is selected, all necessary binaries are installed onto the target device for OProfileUI interaction. Even though the source directory usually includes all needed patches on the target device, you might find you need other OProfile patches for recent OProfileUI features. If so, see the OProfileUI README for the most recent information.

Using OProfile in online mode assumes a working network connection with the target hardware. With this connection, you just need to run "oprofile-server" on the device. By default, OProfile listens on port 4224. You can change the port using the --port command-line option. The client program is called oprofile-viewer and its UI is relatively straightforward. You access key functionality through the buttons on the toolbar, which are duplicated in the menus. Here are the buttons: Connect: Connects to the remote host. You can also supply the IP address or hostname. Disconnect: Disconnects from the target. Start: Starts profiling on the device. Stop: Stops profiling on the device and downloads the data to the local host. Stopping the profiler generates the profile and displays it in the viewer. Download: Downloads the data from the target and generates the profile, which appears in the viewer. Reset: Resets the sample data on the device. Resetting the data removes sample information collected from previous sampling runs. Be sure you reset the data if you do not want to include old sample information. Save: Saves the data downloaded from the target to another directory for later examination. Open: Loads previously saved data. The client downloads the complete 'profile archive' from the target to the host for processing. This archive is a directory that contains the sample data, the object files, and the debug information for the object files. The archive is then converted using the oparchconv script, which is included in this distribution. The script uses opimport to convert the archive from the target to something that can be processed on the host. Downloaded archives reside in the Build Directory in /tmp and are cleared up when they are no longer in use. If you wish to perform kernel profiling, you need to be sure a vmlinux file that matches the running kernel is available. In the source directory, that file is usually located in /boot/vmlinux-KERNELVERSION, where KERNEL-version is the version of the kernel. The OpenEmbedded build system generates separate vmlinux packages for each kernel it builds. Thus, it should just be a question of making sure a matching package is installed (e.g. opkg install kernel-vmlinux. The files are automatically installed into development and profiling images alongside OProfile. A configuration option exists within the OProfileUI settings page that you can use to enter the location of the vmlinux file. Waiting for debug symbols to transfer from the device can be slow, and it is not always necessary to actually have them on the device for OProfile use. All that is needed is a copy of the filesystem with the debug symbols present on the viewer system. The "Launching GDB on the Host Computer" section covers how to create such a directory with the source directory and how to use the OProfileUI Settings dialog to specify the location. If you specify the directory, it will be used when the file checksums match those on the system you are profiling.

If network access to the target is unavailable, you can generate an archive for processing in oprofile-viewer as follows: # opcontrol --reset # opcontrol --start --separate=lib --no-vmlinux -c 5 . . [do whatever is being profiled] . . # opcontrol --stop # oparchive -o my_archive In the above example, my_archive is the name of the archive directory where you would like the profile archive to be kept. After the directory is created, you can copy it to another host and load it using oprofile-viewer open functionality. If necessary, the archive is converted.

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, we can begin to cover the requirements of the major FLOSS licenses, 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. 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.

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 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. But, the more serious issue for most companies is accidental release of proprietary software. The Yocto Project provides an archiver class to help avoid some of these concerns. Before you employ DL_DIR or the archiver class, you need to decide how you choose to provide source. The source 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 original source as a tarball. You can do this by adding the following to the local.conf file found in the Build Directory: ARCHIVER_MODE ?= "original" ARCHIVER_CLASS = "${@'archive-${ARCHIVER_MODE}-source' if ARCHIVER_MODE != 'none' else ''}" INHERIT += "${ARCHIVER_CLASS}" SOURCE_ARCHIVE_PACKAGE_TYPE = "tar" 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 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's assume you are only concerned with GPL code as identified with the following: $ cd poky/build/tmp/deploy/sources $ mkdir ~/gpl_source_release $ for dir in */*GPL*; do cp -r $dir ~/gpl_source_release; 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.

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" Adding these statements to the configuration file ensures that the licenses collected during package generation are included on your image. As the source archiver has already archived the original unmodified source which would contain 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.

At this point, we have addressed all we need to address 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 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 may be required to 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: # We built using the &DISTRO_NAME; branch of the poky repo $ git clone -b &DISTRO_NAME; 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-yocto/conf/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: # LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf # changes incompatibly LCONF_VERSION = "6" BBPATH = "${TOPDIR}" BBFILES ?= "" BBLAYERS ?= " \ ##COREBASE##/meta \ ##COREBASE##/meta-yocto \ ##COREBASE##/meta-yocto-bsp \ ##COREBASE##/meta-mylayer \ " BBLAYERS_NON_REMOVABLE ?= " \ ##COREBASE##/meta \ ##COREBASE##/meta-yocto \ " Creating and providing an archive of the 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.