From 0b70161692e437740e480b89ab2c253b6a72dfc5 Mon Sep 17 00:00:00 2001 From: Scott Rifenbark Date: Tue, 30 Jan 2018 15:46:53 -0800 Subject: concepts-manual: Added new manual tree Tree added only. (From yocto-docs rev: bacfd8c9103489c9b5a3459855d0804531ef3a75) Signed-off-by: Scott Rifenbark Signed-off-by: Richard Purdie --- .../concepts-manual/concepts-manual-concepts.xml | 1929 +++++++++++++ .../concepts-manual-customization.xsl | 27 + .../concepts-manual-development-environment.xml | 2890 ++++++++++++++++++++ .../concepts-manual-eclipse-customization.xsl | 35 + .../concepts-manual/concepts-manual-intro.xml | 103 + .../concepts-manual/concepts-manual-style.css | 988 +++++++ documentation/concepts-manual/concepts-manual.xml | 94 + .../concepts-manual/figures/YP-flow-diagram.png | Bin 0 -> 190715 bytes .../figures/analysis-for-package-splitting.png | Bin 0 -> 63291 bytes .../figures/configuration-compile-autoreconf.png | Bin 0 -> 46080 bytes .../figures/cross-development-toolchains.png | Bin 0 -> 59275 bytes .../figures/getting-started-title.png | Bin 0 -> 13472 bytes .../concepts-manual/figures/git-workflow.png | Bin 0 -> 26586 bytes .../concepts-manual/figures/image-generation.png | Bin 0 -> 112991 bytes documentation/concepts-manual/figures/images.png | Bin 0 -> 22926 bytes .../concepts-manual/figures/index-downloads.png | Bin 0 -> 36362 bytes .../concepts-manual/figures/layer-input.png | Bin 0 -> 45856 bytes .../concepts-manual/figures/package-feeds.png | Bin 0 -> 30112 bytes documentation/concepts-manual/figures/patching.png | Bin 0 -> 42523 bytes .../concepts-manual/figures/sdk-generation.png | Bin 0 -> 115643 bytes documentation/concepts-manual/figures/sdk.png | Bin 0 -> 67478 bytes .../concepts-manual/figures/source-fetching.png | Bin 0 -> 38860 bytes .../concepts-manual/figures/source-input.png | Bin 0 -> 39872 bytes .../concepts-manual/figures/source-repos.png | Bin 0 -> 298757 bytes .../concepts-manual/figures/user-configuration.png | Bin 0 -> 74109 bytes .../figures/yocto-environment-ref.png | Bin 0 -> 83206 bytes .../concepts-manual/figures/yp-download.png | Bin 0 -> 230971 bytes 27 files changed, 6066 insertions(+) create mode 100644 documentation/concepts-manual/concepts-manual-concepts.xml create mode 100644 documentation/concepts-manual/concepts-manual-customization.xsl create mode 100644 documentation/concepts-manual/concepts-manual-development-environment.xml create mode 100644 documentation/concepts-manual/concepts-manual-eclipse-customization.xsl create mode 100644 documentation/concepts-manual/concepts-manual-intro.xml create mode 100644 documentation/concepts-manual/concepts-manual-style.css create mode 100644 documentation/concepts-manual/concepts-manual.xml create mode 100644 documentation/concepts-manual/figures/YP-flow-diagram.png create mode 100644 documentation/concepts-manual/figures/analysis-for-package-splitting.png create mode 100644 documentation/concepts-manual/figures/configuration-compile-autoreconf.png create mode 100644 documentation/concepts-manual/figures/cross-development-toolchains.png create mode 100644 documentation/concepts-manual/figures/getting-started-title.png create mode 100644 documentation/concepts-manual/figures/git-workflow.png create mode 100644 documentation/concepts-manual/figures/image-generation.png create mode 100644 documentation/concepts-manual/figures/images.png create mode 100644 documentation/concepts-manual/figures/index-downloads.png create mode 100644 documentation/concepts-manual/figures/layer-input.png create mode 100644 documentation/concepts-manual/figures/package-feeds.png create mode 100644 documentation/concepts-manual/figures/patching.png create mode 100755 documentation/concepts-manual/figures/sdk-generation.png create mode 100644 documentation/concepts-manual/figures/sdk.png create mode 100644 documentation/concepts-manual/figures/source-fetching.png create mode 100644 documentation/concepts-manual/figures/source-input.png create mode 100644 documentation/concepts-manual/figures/source-repos.png create mode 100644 documentation/concepts-manual/figures/user-configuration.png create mode 100644 documentation/concepts-manual/figures/yocto-environment-ref.png create mode 100644 documentation/concepts-manual/figures/yp-download.png (limited to 'documentation') diff --git a/documentation/concepts-manual/concepts-manual-concepts.xml b/documentation/concepts-manual/concepts-manual-concepts.xml new file mode 100644 index 0000000000..e4d6026b70 --- /dev/null +++ b/documentation/concepts-manual/concepts-manual-concepts.xml @@ -0,0 +1,1929 @@ + %poky; ] > + + +Yocto Project Concepts + + + This chapter describes concepts for various areas of the Yocto Project. + Currently, topics include Yocto Project components, cross-development + generation, shared state (sstate) cache, runtime dependencies, + Pseudo and Fakeroot, x32 psABI, Wayland support, and Licenses. + + +
+ Yocto Project Components + + + The + BitBake + task executor together with various types of configuration files + form the OpenEmbedded Core. + This section overviews these components by describing their use and + how they interact. + + + + BitBake handles the parsing and execution of the data files. + The data itself is of various types: + + + Recipes: + Provides details about particular pieces of software. + + + Class Data: + Abstracts common build information (e.g. how to build a + Linux kernel). + + + Configuration Data: + Defines machine-specific settings, policy decisions, and + so forth. + Configuration data acts as the glue to bind everything + together. + + + + + + BitBake knows how to combine multiple data sources together and + refers to each data source as a layer. + For information on layers, see the + "Understanding and Creating Layers" + section of the Yocto Project Development Tasks Manual. + + + + Following are some brief details on these core components. + For additional information on how these components interact during + a build, see the + "Development Concepts" + section. + + +
+ BitBake + + + BitBake is the tool at the heart of the OpenEmbedded build + system and is responsible for parsing the + Metadata, + generating a list of tasks from it, and then executing those + tasks. + + + + This section briefly introduces BitBake. + If you want more information on BitBake, see the + BitBake User Manual. + + + + To see a list of the options BitBake supports, use either of + the following commands: + + $ bitbake -h + $ bitbake --help + + + + + The most common usage for BitBake is + bitbake packagename, + where packagename is the name of the + package you want to build (referred to as the "target" in this + manual). + The target often equates to the first part of a recipe's + filename (e.g. "foo" for a recipe named + foo_1.3.0-r0.bb). + So, to process the + matchbox-desktop_1.2.3.bb recipe file, you + might type the following: + + $ bitbake matchbox-desktop + + Several different versions of + matchbox-desktop might exist. + BitBake chooses the one selected by the distribution + configuration. + You can get more details about how BitBake chooses between + different target versions and providers in the + "Preferences" + section of the BitBake User Manual. + + + + BitBake also tries to execute any dependent tasks first. + So for example, before building + matchbox-desktop, BitBake would build a + cross compiler and glibc if they had not + already been built. + + + + A useful BitBake option to consider is the + -k or --continue + option. + This option instructs BitBake to try and continue processing + the job as long as possible even after encountering an error. + When an error occurs, the target that failed and those that + depend on it cannot be remade. + However, when you use this option other dependencies can + still be processed. + +
+ +
+ Metadata (Recipes) + + + Files that have the .bb suffix are + "recipes" files. + In general, a recipe contains information about a single piece + of software. + This information includes the location from which to download + the unaltered source, any source patches to be applied to that + source (if needed), which special configuration options to + apply, how to compile the source files, and how to package the + compiled output. + + + + The term "package" is sometimes used to refer to recipes. + However, since the word "package" is used for the packaged + output from the OpenEmbedded build system (i.e. + .ipk or .deb files), + this document avoids using the term "package" when referring + to recipes. + +
+ +
+ Metadata (Virtual Providers) + + + Prior to the build, if you know that several different recipes + provide the same functionality, you can use a virtual provider + (i.e. virtual/*) as a placeholder for the + actual provider. + The actual provider would be determined at build time. + In this case, you should add virtual/* + to + DEPENDS, + rather than listing the specified provider. + You would select the actual provider by setting the + PREFERRED_PROVIDER + variable (i.e. + PREFERRED_PROVIDER_virtual/*) + in the build's configuration file (e.g. + poky/build/conf/local.conf). + + Any recipe that PROVIDES a virtual/* + item that is ultimately not selected through + PREFERRED_PROVIDER does not get built. + Preventing these recipes from building is usually the + desired behavior since this mechanism's purpose is to + select between mutually exclusive alternative providers. + + + + + The following lists specific examples of virtual providers: + + + virtual/mesa: + Provides gbm.pc. + + + virtual/egl: + Provides egl.pc and possibly + wayland-egl.pc. + + + virtual/libgl: + Provides gl.pc (i.e. libGL). + + + virtual/libgles1: + Provides glesv1_cm.pc + (i.e. libGLESv1_CM). + + + virtual/libgles2: + Provides glesv2.pc + (i.e. libGLESv2). + + + +
+ +
+ Classes + + + Class files (.bbclass) contain information + that is useful to share between + Metadata + files. + An example is the + autotools + class, which contains common settings for any application that + Autotools uses. + The + "Classes" + chapter in the Yocto Project Reference Manual provides + details about classes and how to use them. + +
+ +
+ Configuration + + + The configuration files (.conf) define + various configuration variables that govern the OpenEmbedded + build process. + These files fall into several areas that define machine + configuration options, distribution configuration options, + compiler tuning options, general common configuration options, + and user configuration options in + local.conf, which is found in the + Build Directory. + +
+
+ +
+ Cross-Development Toolchain Generation + + + The Yocto Project does most of the work for you when it comes to + creating + cross-development toolchains. + This section provides some technical background on how + cross-development toolchains are created and used. + For more information on toolchains, you can also see the + Yocto Project Application Development and the Extensible Software Development Kit (eSDK) + manual. + + + + In the Yocto Project development environment, cross-development + toolchains are used to build the image and applications that run + on the target hardware. + With just a few commands, the OpenEmbedded build system creates + these necessary toolchains for you. + + + + The following figure shows a high-level build environment regarding + toolchain construction and use. + + + + + + + + Most of the work occurs on the Build Host. + This is the machine used to build images and generally work within the + the Yocto Project environment. + When you run BitBake to create an image, the OpenEmbedded build system + uses the host gcc compiler to bootstrap a + cross-compiler named gcc-cross. + The gcc-cross compiler is what BitBake uses to + compile source files when creating the target image. + You can think of gcc-cross simply as an + automatically generated cross-compiler that is used internally within + BitBake only. + + The extensible SDK does not use + gcc-cross-canadian since this SDK + ships a copy of the OpenEmbedded build system and the sysroot + within it contains gcc-cross. + + + + + The chain of events that occurs when gcc-cross is + bootstrapped is as follows: + + gcc -> binutils-cross -> gcc-cross-initial -> linux-libc-headers -> glibc-initial -> glibc -> gcc-cross -> gcc-runtime + + + + gcc: + The build host's GNU Compiler Collection (GCC). + + + binutils-cross: + The bare minimum binary utilities needed in order to run + the gcc-cross-initial phase of the + bootstrap operation. + + + gcc-cross-initial: + An early stage of the bootstrap process for creating + the cross-compiler. + This stage builds enough of the gcc-cross, + the C library, and other pieces needed to finish building the + final cross-compiler in later stages. + This tool is a "native" package (i.e. it is designed to run on + the build host). + + + linux-libc-headers: + Headers needed for the cross-compiler. + + + glibc-initial: + An initial version of the Embedded GLIBC needed to bootstrap + glibc. + + + gcc-cross: + The final stage of the bootstrap process for the + cross-compiler. + This stage results in the actual cross-compiler that + BitBake uses when it builds an image for a targeted + device. + + If you are replacing this cross compiler toolchain + with a custom version, you must replace + gcc-cross. + + This tool is also a "native" package (i.e. it is + designed to run on the build host). + + + gcc-runtime: + Runtime libraries resulting from the toolchain bootstrapping + process. + This tool produces a binary that consists of the + runtime libraries need for the targeted device. + + + + + + You can use the OpenEmbedded build system to build an installer for + the relocatable SDK used to develop applications. + When you run the installer, it installs the toolchain, which contains + the development tools (e.g., the + gcc-cross-canadian), + binutils-cross-canadian, and other + nativesdk-* tools, + which are tools native to the SDK (i.e. native to + SDK_ARCH), + you need to cross-compile and test your software. + The figure shows the commands you use to easily build out this + toolchain. + This cross-development toolchain is built to execute on the + SDKMACHINE, + which might or might not be the same + machine as the Build Host. + + If your target architecture is supported by the Yocto Project, + you can take advantage of pre-built images that ship with the + Yocto Project and already contain cross-development toolchain + installers. + + + + + Here is the bootstrap process for the relocatable toolchain: + + gcc -> binutils-crosssdk -> gcc-crosssdk-initial -> linux-libc-headers -> + glibc-initial -> nativesdk-glibc -> gcc-crosssdk -> gcc-cross-canadian + + + + gcc: + The build host's GNU Compiler Collection (GCC). + + + binutils-crosssdk: + The bare minimum binary utilities needed in order to run + the gcc-crosssdk-initial phase of the + bootstrap operation. + + + gcc-crosssdk-initial: + An early stage of the bootstrap process for creating + the cross-compiler. + This stage builds enough of the + gcc-crosssdk and supporting pieces so that + the final stage of the bootstrap process can produce the + finished cross-compiler. + This tool is a "native" binary that runs on the build host. + + + linux-libc-headers: + Headers needed for the cross-compiler. + + + glibc-initial: + An initial version of the Embedded GLIBC needed to bootstrap + nativesdk-glibc. + + + nativesdk-glibc: + The Embedded GLIBC needed to bootstrap the + gcc-crosssdk. + + + gcc-crosssdk: + The final stage of the bootstrap process for the + relocatable cross-compiler. + The gcc-crosssdk is a transitory compiler + and never leaves the build host. + Its purpose is to help in the bootstrap process to create the + eventual relocatable gcc-cross-canadian + compiler, which is relocatable. + This tool is also a "native" package (i.e. it is + designed to run on the build host). + + + gcc-cross-canadian: + The final relocatable cross-compiler. + When run on the + SDKMACHINE, + this tool + produces executable code that runs on the target device. + Only one cross-canadian compiler is produced per architecture + since they can be targeted at different processor optimizations + using configurations passed to the compiler through the + compile commands. + This circumvents the need for multiple compilers and thus + reduces the size of the toolchains. + + + + + + For information on advantages gained when building a + cross-development toolchain installer, see the + "Building an SDK Installer" + section in the Yocto Project Application Development and the + Extensible Software Development Kit (eSDK) manual. + +
+ + + + +
+ Shared State Cache + + + By design, the OpenEmbedded build system builds everything from + scratch unless BitBake can determine that parts do not need to be + rebuilt. + Fundamentally, building from scratch is attractive as it means all + parts are built fresh and there is no possibility of stale data + causing problems. + When developers hit problems, they typically default back to + building from scratch so they know the state of things from the + start. + + + + Building an image from scratch is both an advantage and a + disadvantage to the process. + As mentioned in the previous paragraph, building from scratch + ensures that everything is current and starts from a known state. + However, building from scratch also takes much longer as it + generally means rebuilding things that do not necessarily need + to be rebuilt. + + + + The Yocto Project implements shared state code that supports + incremental builds. + The implementation of the shared state code answers the following + questions that were fundamental roadblocks within the OpenEmbedded + incremental build support system: + + + What pieces of the system have changed and what pieces have + not changed? + + + How are changed pieces of software removed and replaced? + + + How are pre-built components that do not need to be rebuilt + from scratch used when they are available? + + + + + + For the first question, the build system detects changes in the + "inputs" to a given task by creating a checksum (or signature) of + the task's inputs. + If the checksum changes, the system assumes the inputs have changed + and the task needs to be rerun. + For the second question, the shared state (sstate) code tracks + which tasks add which output to the build process. + This means the output from a given task can be removed, upgraded + or otherwise manipulated. + The third question is partly addressed by the solution for the + second question assuming the build system can fetch the sstate + objects from remote locations and install them if they are deemed + to be valid. + + The OpenEmbedded build system does not maintain + PR + information as part of the shared state packages. + Consequently, considerations exist that affect maintaining + shared state feeds. + For information on how the OpenEmbedded build system + works with packages and can track incrementing + PR information, see the + "Automatically Incrementing a Binary Package Revision Number" + section in the Yocto Project Development Tasks Manual. + + + + + The rest of this section goes into detail about the overall + incremental build architecture, the checksums (signatures), shared + state, and some tips and tricks. + + +
+ Overall Architecture + + + When determining what parts of the system need to be built, + BitBake works on a per-task basis rather than a per-recipe + basis. + You might wonder why using a per-task basis is preferred over + a per-recipe basis. + To help explain, consider having the IPK packaging backend + enabled and then switching to DEB. + In this case, the + do_install + and + do_package + task outputs are still valid. + However, with a per-recipe approach, the build would not + include the .deb files. + Consequently, you would have to invalidate the whole build and + rerun it. + Rerunning everything is not the best solution. + Also, in this case, the core must be "taught" much about + specific tasks. + This methodology does not scale well and does not allow users + to easily add new tasks in layers or as external recipes + without touching the packaged-staging core. + +
+ +
+ Checksums (Signatures) + + + The shared state code uses a checksum, which is a unique + signature of a task's inputs, to determine if a task needs to + be run again. + Because it is a change in a task's inputs that triggers a + rerun, the process needs to detect all the inputs to a given + task. + For shell tasks, this turns out to be fairly easy because + the build process generates a "run" shell script for each task + and it is possible to create a checksum that gives you a good + idea of when the task's data changes. + + + + To complicate the problem, there are things that should not be + included in the checksum. + First, there is the actual specific build path of a given + task - the + WORKDIR. + It does not matter if the work directory changes because it + should not affect the output for target packages. + Also, the build process has the objective of making native + or cross packages relocatable. + + Both native and cross packages run on the build host. + However, cross packages generate output for the target + architecture. + + The checksum therefore needs to exclude + WORKDIR. + The simplistic approach for excluding the work directory is to + set WORKDIR to some fixed value and + create the checksum for the "run" script. + + + + Another problem results from the "run" scripts containing + functions that might or might not get called. + The incremental build solution contains code that figures out + dependencies between shell functions. + This code is used to prune the "run" scripts down to the + minimum set, thereby alleviating this problem and making the + "run" scripts much more readable as a bonus. + + + + So far we have solutions for shell scripts. + What about Python tasks? + The same approach applies even though these tasks are more + difficult. + The process needs to figure out what variables a Python + function accesses and what functions it calls. + Again, the incremental build solution contains code that first + figures out the variable and function dependencies, and then + creates a checksum for the data used as the input to the task. + + + + Like the WORKDIR case, situations exist + where dependencies should be ignored. + For these cases, you can instruct the build process to + ignore a dependency by using a line like the following: + + PACKAGE_ARCHS[vardepsexclude] = "MACHINE" + + This example ensures that the + PACKAGE_ARCHS + variable does not depend on the value of + MACHINE, + even if it does reference it. + + + + Equally, there are cases where we need to add dependencies + BitBake is not able to find. + You can accomplish this by using a line like the following: + + PACKAGE_ARCHS[vardeps] = "MACHINE" + + This example explicitly adds the MACHINE + variable as a dependency for + PACKAGE_ARCHS. + + + + Consider a case with in-line Python, for example, where + BitBake is not able to figure out dependencies. + When running in debug mode (i.e. using + -DDD), BitBake produces output when it + discovers something for which it cannot figure out dependencies. + The Yocto Project team has currently not managed to cover + those dependencies in detail and is aware of the need to fix + this situation. + + + + Thus far, this section has limited discussion to the direct + inputs into a task. + Information based on direct inputs is referred to as the + "basehash" in the code. + However, there is still the question of a task's indirect + inputs - the things that were already built and present in the + Build Directory. + The checksum (or signature) for a particular task needs to add + the hashes of all the tasks on which the particular task + depends. + Choosing which dependencies to add is a policy decision. + However, the effect is to generate a master checksum that + combines the basehash and the hashes of the task's + dependencies. + + + + At the code level, there are a variety of ways both the + basehash and the dependent task hashes can be influenced. + Within the BitBake configuration file, we can give BitBake + some extra information to help it construct the basehash. + The following statement effectively results in a list of + global variable dependency excludes - variables never + included in any checksum: + + BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \ + SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \ + USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \ + PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \ + CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX" + + The previous example excludes + WORKDIR + since that variable is actually constructed as a path within + TMPDIR, + which is on the whitelist. + + + + The rules for deciding which hashes of dependent tasks to + include through dependency chains are more complex and are + generally accomplished with a Python function. + The code in meta/lib/oe/sstatesig.py shows + two examples of this and also illustrates how you can insert + your own policy into the system if so desired. + This file defines the two basic signature generators + OE-Core + uses: "OEBasic" and "OEBasicHash". + By default, there is a dummy "noop" signature handler enabled + in BitBake. + This means that behavior is unchanged from previous versions. + OE-Core uses the "OEBasicHash" signature handler by default + through this setting in the bitbake.conf + file: + + BB_SIGNATURE_HANDLER ?= "OEBasicHash" + + The "OEBasicHash" BB_SIGNATURE_HANDLER + is the same as the "OEBasic" version but adds the task hash to + the stamp files. + This results in any + Metadata + change that changes the task hash, automatically + causing the task to be run again. + This removes the need to bump + PR + values, and changes to Metadata automatically ripple across + the build. + + + + It is also worth noting that the end result of these + signature generators is to make some dependency and hash + information available to the build. + This information includes: + + + BB_BASEHASH_task-taskname: + The base hashes for each task in the recipe. + + + BB_BASEHASH_filename:taskname: + The base hashes for each dependent task. + + + BBHASHDEPS_filename:taskname: + The task dependencies for each task. + + + BB_TASKHASH: + The hash of the currently running task. + + + +
+ +
+ Shared State + + + Checksums and dependencies, as discussed in the previous + section, solve half the problem of supporting a shared state. + The other part of the problem is being able to use checksum + information during the build and being able to reuse or rebuild + specific components. + + + + The + sstate + class is a relatively generic implementation of how to + "capture" a snapshot of a given task. + The idea is that the build process does not care about the + source of a task's output. + Output could be freshly built or it could be downloaded and + unpacked from somewhere - the build process does not need to + worry about its origin. + + + + There are two types of output, one is just about creating a + directory in + WORKDIR. + A good example is the output of either + do_install + or + do_package. + The other type of output occurs when a set of data is merged + into a shared directory tree such as the sysroot. + + + + The Yocto Project team has tried to keep the details of the + implementation hidden in sstate class. + From a user's perspective, adding shared state wrapping to a task + is as simple as this + do_deploy + example taken from the + deploy + class: + + DEPLOYDIR = "${WORKDIR}/deploy-${PN}" + SSTATETASKS += "do_deploy" + do_deploy[sstate-inputdirs] = "${DEPLOYDIR}" + do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}" + + python do_deploy_setscene () { + sstate_setscene(d) + } + addtask do_deploy_setscene + do_deploy[dirs] = "${DEPLOYDIR} ${B}" + + The following list explains the previous example: + + + Adding "do_deploy" to SSTATETASKS + adds some required sstate-related processing, which is + implemented in the + sstate + class, to before and after the + do_deploy + task. + + + The + do_deploy[sstate-inputdirs] = "${DEPLOYDIR}" + declares that do_deploy places its + output in ${DEPLOYDIR} when run + normally (i.e. when not using the sstate cache). + This output becomes the input to the shared state cache. + + + The + do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}" + line causes the contents of the shared state cache to be + copied to ${DEPLOY_DIR_IMAGE}. + + If do_deploy is not already in + the shared state cache or if its input checksum + (signature) has changed from when the output was + cached, the task will be run to populate the shared + state cache, after which the contents of the shared + state cache is copied to + ${DEPLOY_DIR_IMAGE}. + If do_deploy is in the shared + state cache and its signature indicates that the + cached output is still valid (i.e. if no + relevant task inputs have changed), then the + contents of the shared state cache will be copied + directly to + ${DEPLOY_DIR_IMAGE} by the + do_deploy_setscene task + instead, skipping the + do_deploy task. + + + + The following task definition is glue logic needed to + make the previous settings effective: + + python do_deploy_setscene () { + sstate_setscene(d) + } + addtask do_deploy_setscene + + sstate_setscene() takes the flags + above as input and accelerates the + do_deploy task through the + shared state cache if possible. + If the task was accelerated, + sstate_setscene() returns True. + Otherwise, it returns False, and the normal + do_deploy task runs. + For more information, see the + "setscene" + section in the BitBake User Manual. + + + The do_deploy[dirs] = "${DEPLOYDIR} ${B}" + line creates ${DEPLOYDIR} and + ${B} before the + do_deploy task runs, and also sets + the current working directory of + do_deploy to + ${B}. + For more information, see the + "Variable Flags" + section in the BitBake User Manual. + + In cases where + sstate-inputdirs and + sstate-outputdirs would be the + same, you can use + sstate-plaindirs. + For example, to preserve the + ${PKGD} and + ${PKGDEST} output from the + do_package + task, use the following: + + do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}" + + + + + sstate-inputdirs and + sstate-outputdirs can also be used + with multiple directories. + For example, the following declares + PKGDESTWORK and + SHLIBWORK as shared state + input directories, which populates the shared state + cache, and PKGDATA_DIR and + SHLIBSDIR as the corresponding + shared state output directories: + + do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}" + do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}" + + + + These methods also include the ability to take a + lockfile when manipulating shared state directory + structures, for cases where file additions or removals + are sensitive: + + do_package[sstate-lockfile] = "${PACKAGELOCK}" + + + + + + + Behind the scenes, the shared state code works by looking in + SSTATE_DIR + and + SSTATE_MIRRORS + for shared state files. + Here is an example: + + SSTATE_MIRRORS ?= "\ + file://.* http://someserver.tld/share/sstate/PATH;downloadfilename=PATH \n \ + file://.* file:///some/local/dir/sstate/PATH" + + + The shared state directory + (SSTATE_DIR) is organized into + two-character subdirectories, where the subdirectory + names are based on the first two characters of the hash. + If the shared state directory structure for a mirror has the + same structure as SSTATE_DIR, you must + specify "PATH" as part of the URI to enable the build system + to map to the appropriate subdirectory. + + + + + The shared state package validity can be detected just by + looking at the filename since the filename contains the task + checksum (or signature) as described earlier in this section. + If a valid shared state package is found, the build process + downloads it and uses it to accelerate the task. + + + + The build processes use the *_setscene + tasks for the task acceleration phase. + BitBake goes through this phase before the main execution + code and tries to accelerate any tasks for which it can find + shared state packages. + If a shared state package for a task is available, the + shared state package is used. + This means the task and any tasks on which it is dependent + are not executed. + + + + As a real world example, the aim is when building an IPK-based + image, only the + do_package_write_ipk + tasks would have their shared state packages fetched and + extracted. + Since the sysroot is not used, it would never get extracted. + This is another reason why a task-based approach is preferred + over a recipe-based approach, which would have to install the + output from every task. + +
+ +
+ Tips and Tricks + + + The code in the build system that supports incremental builds + is not simple code. + This section presents some tips and tricks that help you work + around issues related to shared state code. + + +
+ Debugging + + + Seeing what metadata went into creating the input signature + of a shared state (sstate) task can be a useful debugging + aid. + This information is available in signature information + (siginfo) files in + SSTATE_DIR. + For information on how to view and interpret information in + siginfo files, see the + "Viewing Task Variable Dependencies" + section in the Yocto Project Development Tasks Manual. + +
+ +
+ Invalidating Shared State + + + The OpenEmbedded build system uses checksums and shared + state cache to avoid unnecessarily rebuilding tasks. + Collectively, this scheme is known as "shared state code." + + + + As with all schemes, this one has some drawbacks. + It is possible that you could make implicit changes to your + code that the checksum calculations do not take into + account. + These implicit changes affect a task's output but do not + trigger the shared state code into rebuilding a recipe. + Consider an example during which a tool changes its output. + Assume that the output of rpmdeps + changes. + The result of the change should be that all the + package and + package_write_rpm shared state cache + items become invalid. + However, because the change to the output is + external to the code and therefore implicit, + the associated shared state cache items do not become + invalidated. + In this case, the build process uses the cached items + rather than running the task again. + Obviously, these types of implicit changes can cause + problems. + + + + To avoid these problems during the build, you need to + understand the effects of any changes you make. + Realize that changes you make directly to a function + are automatically factored into the checksum calculation. + Thus, these explicit changes invalidate the associated + area of shared state cache. + However, you need to be aware of any implicit changes that + are not obvious changes to the code and could affect + the output of a given task. + + + + When you identify an implicit change, you can easily + take steps to invalidate the cache and force the tasks + to run. + The steps you can take are as simple as changing a + function's comments in the source code. + For example, to invalidate package shared state files, + change the comment statements of + do_package + or the comments of one of the functions it calls. + Even though the change is purely cosmetic, it causes the + checksum to be recalculated and forces the OpenEmbedded + build system to run the task again. + + For an example of a commit that makes a cosmetic + change to invalidate shared state, see this + commit. + + +
+
+
+ +
+ Automatically Added Runtime Dependencies + + + The OpenEmbedded build system automatically adds common types of + runtime dependencies between packages, which means that you do not + need to explicitly declare the packages using + RDEPENDS. + Three automatic mechanisms exist (shlibdeps, + pcdeps, and depchains) + that handle shared libraries, package configuration (pkg-config) + modules, and -dev and + -dbg packages, respectively. + For other types of runtime dependencies, you must manually declare + the dependencies. + + + shlibdeps: + During the + do_package + task of each recipe, all shared libraries installed by the + recipe are located. + For each shared library, the package that contains the + shared library is registered as providing the shared + library. + More specifically, the package is registered as providing + the + soname + of the library. + The resulting shared-library-to-package mapping + is saved globally in + PKGDATA_DIR + by the + do_packagedata + task. + + Simultaneously, all executables and shared libraries + installed by the recipe are inspected to see what shared + libraries they link against. + For each shared library dependency that is found, + PKGDATA_DIR is queried to + see if some package (likely from a different recipe) + contains the shared library. + If such a package is found, a runtime dependency is added + from the package that depends on the shared library to the + package that contains the library. + + The automatically added runtime dependency also + includes a version restriction. + This version restriction specifies that at least the + current version of the package that provides the shared + library must be used, as if + "package (>= version)" + had been added to + RDEPENDS. + This forces an upgrade of the package containing the shared + library when installing the package that depends on the + library, if needed. + + If you want to avoid a package being registered as + providing a particular shared library (e.g. because the library + is for internal use only), then add the library to + PRIVATE_LIBS + inside the package's recipe. + + + pcdeps: + During the + do_package + task of each recipe, all pkg-config modules + (*.pc files) installed by the recipe + are located. + For each module, the package that contains the module is + registered as providing the module. + The resulting module-to-package mapping is saved globally in + PKGDATA_DIR + by the + do_packagedata + task. + + Simultaneously, all pkg-config modules installed by + the recipe are inspected to see what other pkg-config + modules they depend on. + A module is seen as depending on another module if it + contains a "Requires:" line that specifies the other module. + For each module dependency, + PKGDATA_DIR is queried to see if some + package contains the module. + If such a package is found, a runtime dependency is added + from the package that depends on the module to the package + that contains the module. + + The pcdeps mechanism most often + infers dependencies between -dev + packages. + + + + depchains: + If a package foo depends on a package + bar, then foo-dev + and foo-dbg are also made to depend on + bar-dev and + bar-dbg, respectively. + Taking the -dev packages as an + example, the bar-dev package might + provide headers and shared library symlinks needed by + foo-dev, which shows the need + for a dependency between the packages. + + The dependencies added by + depchains are in the form of + RRECOMMENDS. + + By default, foo-dev also has an + RDEPENDS-style dependency on + foo, because the default value of + RDEPENDS_${PN}-dev (set in + bitbake.conf) includes + "${PN}". + + + To ensure that the dependency chain is never broken, + -dev and -dbg + packages are always generated by default, even if the + packages turn out to be empty. + See the + ALLOW_EMPTY + variable for more information. + + + + + + The do_package task depends on the + do_packagedata + task of each recipe in + DEPENDS + through use of a + [deptask] + declaration, which guarantees that the required + shared-library/module-to-package mapping information will be available + when needed as long as DEPENDS has been + correctly set. + +
+ +
+ Fakeroot and Pseudo + + + Some tasks are easier to implement when allowed to perform certain + operations that are normally reserved for the root user (e.g. + do_install, + do_package_write*, + do_rootfs, + and + do_image*). + For example, the do_install task benefits + from being able to set the UID and GID of installed files to + arbitrary values. + + + + One approach to allowing tasks to perform root-only operations + would be to require BitBake to run as root. + However, this method is cumbersome and has security issues. + The approach that is actually used is to run tasks that benefit + from root privileges in a "fake" root environment. + Within this environment, the task and its child processes believe + that they are running as the root user, and see an internally + consistent view of the filesystem. + As long as generating the final output (e.g. a package or an image) + does not require root privileges, the fact that some earlier + steps ran in a fake root environment does not cause problems. + + + + The capability to run tasks in a fake root environment is known as + "fakeroot", + which is derived from the BitBake keyword/variable + flag that requests a fake root environment for a task. + + + + In the OpenEmbedded build system, the program that implements + fakeroot is known as Pseudo. + Pseudo overrides system calls by using the environment variable + LD_PRELOAD, which results in the illusion + of running as root. + To keep track of "fake" file ownership and permissions resulting + from operations that require root permissions, Pseudo uses + an SQLite 3 database. + This database is stored in + ${WORKDIR}/pseudo/files.db + for individual recipes. + Storing the database in a file as opposed to in memory + gives persistence between tasks and builds, which is not + accomplished using fakeroot. + Caution + If you add your own task that manipulates the same files or + directories as a fakeroot task, then that task also needs to + run under fakeroot. + Otherwise, the task cannot run root-only operations, and + cannot see the fake file ownership and permissions set by the + other task. + You need to also add a dependency on + virtual/fakeroot-native:do_populate_sysroot, + giving the following: + + fakeroot do_mytask () { + ... + } + do_mytask[depends] += "virtual/fakeroot-native:do_populate_sysroot" + + + For more information, see the + FAKEROOT* + variables in the BitBake User Manual. + You can also reference the + "Pseudo" + and + "Why Not Fakeroot?" + articles for background information on Pseudo. + +
+ +
+ Wayland + + + Wayland + is a computer display server protocol that + provides a method for compositing window managers to communicate + directly with applications and video hardware and expects them to + communicate with input hardware using other libraries. + Using Wayland with supporting targets can result in better control + over graphics frame rendering than an application might otherwise + achieve. + + + + The Yocto Project provides the Wayland protocol libraries and the + reference + Weston + compositor as part of its release. + This section describes what you need to do to implement Wayland and + use the compositor when building an image for a supporting target. + + +
+ Support + + + The Wayland protocol libraries and the reference Weston + compositor ship as integrated packages in the + meta layer of the + Source Directory. + Specifically, you can find the recipes that build both Wayland + and Weston at + meta/recipes-graphics/wayland. + + + + You can build both the Wayland and Weston packages for use only + with targets that accept the + Mesa 3D and Direct Rendering Infrastructure, + which is also known as Mesa DRI. + This implies that you cannot build and use the packages if your + target uses, for example, the + Intel Embedded Media + and Graphics Driver + (Intel EMGD) that + overrides Mesa DRI. + + Due to lack of EGL support, Weston 1.0.3 will not run + directly on the emulated QEMU hardware. + However, this version of Weston will run under X emulation + without issues. + + +
+ +
+ Enabling Wayland in an Image + + + To enable Wayland, you need to enable it to be built and enable + it to be included in the image. + + +
+ Building + + + To cause Mesa to build the wayland-egl + platform and Weston to build Wayland with Kernel Mode + Setting + (KMS) + support, include the "wayland" flag in the + DISTRO_FEATURES + statement in your local.conf file: + + DISTRO_FEATURES_append = " wayland" + + + If X11 has been enabled elsewhere, Weston will build + Wayland with X11 support + + +
+ +
+ Installing + + + To install the Wayland feature into an image, you must + include the following + CORE_IMAGE_EXTRA_INSTALL + statement in your local.conf file: + + CORE_IMAGE_EXTRA_INSTALL += "wayland weston" + + +
+
+ +
+ Running Weston + + + To run Weston inside X11, enabling it as described earlier and + building a Sato image is sufficient. + If you are running your image under Sato, a Weston Launcher + appears in the "Utility" category. + + + + Alternatively, you can run Weston through the command-line + interpretor (CLI), which is better suited for development work. + To run Weston under the CLI, you need to do the following after + your image is built: + + + Run these commands to export + XDG_RUNTIME_DIR: + + mkdir -p /tmp/$USER-weston + chmod 0700 /tmp/$USER-weston + export XDG_RUNTIME_DIR=/tmp/$USER-weston + + + + Launch Weston in the shell: + + weston + + + +
+
+ +
+ Licenses + + + This section describes the mechanism by which the OpenEmbedded + build system tracks changes to licensing text. + The section also describes how to enable commercially licensed + recipes, which by default are disabled. + + + + For information that can help you maintain compliance with + various open source licensing during the lifecycle of the product, + see the + "Maintaining Open Source License Compliance During Your Project's Lifecycle" + section in the Yocto Project Development Tasks Manual. + + +
+ Tracking License Changes + + + The license of an upstream project might change in the future. + In order to prevent these changes going unnoticed, the + LIC_FILES_CHKSUM + variable tracks changes to the license text. The checksums are + validated at the end of the configure step, and if the + checksums do not match, the build will fail. + + +
+ Specifying the <filename>LIC_FILES_CHKSUM</filename> Variable + + + The LIC_FILES_CHKSUM + variable contains checksums of the license text in the + source code for the recipe. + Following is an example of how to specify + LIC_FILES_CHKSUM: + + LIC_FILES_CHKSUM = "file://COPYING;md5=xxxx \ + file://licfile1.txt;beginline=5;endline=29;md5=yyyy \ + file://licfile2.txt;endline=50;md5=zzzz \ + ..." + + Notes + + + When using "beginline" and "endline", realize + that line numbering begins with one and not + zero. + Also, the included lines are inclusive (i.e. + lines five through and including 29 in the + previous example for + licfile1.txt). + + + When a license check fails, the selected license + text is included as part of the QA message. + Using this output, you can determine the exact + start and finish for the needed license text. + + + + + + + The build system uses the + S + variable as the default directory when searching files + listed in LIC_FILES_CHKSUM. + The previous example employs the default directory. + + + + Consider this next example: + + LIC_FILES_CHKSUM = "file://src/ls.c;beginline=5;endline=16;\ + md5=bb14ed3c4cda583abc85401304b5cd4e" + LIC_FILES_CHKSUM = "file://${WORKDIR}/license.html;md5=5c94767cedb5d6987c902ac850ded2c6" + + + + + The first line locates a file in + ${S}/src/ls.c and isolates lines five + through 16 as license text. + The second line refers to a file in + WORKDIR. + + + + Note that LIC_FILES_CHKSUM variable is + mandatory for all recipes, unless the + LICENSE variable is set to "CLOSED". + +
+ +
+ Explanation of Syntax + + + As mentioned in the previous section, the + LIC_FILES_CHKSUM variable lists all + the important files that contain the license text for the + source code. + It is possible to specify a checksum for an entire file, + or a specific section of a file (specified by beginning and + ending line numbers with the "beginline" and "endline" + parameters, respectively). + The latter is useful for source files with a license + notice header, README documents, and so forth. + If you do not use the "beginline" parameter, then it is + assumed that the text begins on the first line of the file. + Similarly, if you do not use the "endline" parameter, + it is assumed that the license text ends with the last + line of the file. + + + + The "md5" parameter stores the md5 checksum of the license + text. + If the license text changes in any way as compared to + this parameter then a mismatch occurs. + This mismatch triggers a build failure and notifies + the developer. + Notification allows the developer to review and address + the license text changes. + Also note that if a mismatch occurs during the build, + the correct md5 checksum is placed in the build log and + can be easily copied to the recipe. + + + + There is no limit to how many files you can specify using + the LIC_FILES_CHKSUM variable. + Generally, however, every project requires a few + specifications for license tracking. + Many projects have a "COPYING" file that stores the + license information for all the source code files. + This practice allows you to just track the "COPYING" + file as long as it is kept up to date. + Tips + + + If you specify an empty or invalid "md5" + parameter, BitBake returns an md5 mis-match + error and displays the correct "md5" parameter + value during the build. + The correct parameter is also captured in + the build log. + + + If the whole file contains only license text, + you do not need to use the "beginline" and + "endline" parameters. + + + + +
+
+ +
+ Enabling Commercially Licensed Recipes + + + By default, the OpenEmbedded build system disables + components that have commercial or other special licensing + requirements. + Such requirements are defined on a + recipe-by-recipe basis through the + LICENSE_FLAGS + variable definition in the affected recipe. + For instance, the + poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly + recipe contains the following statement: + + LICENSE_FLAGS = "commercial" + + Here is a slightly more complicated example that contains both + an explicit recipe name and version (after variable expansion): + + LICENSE_FLAGS = "license_${PN}_${PV}" + + In order for a component restricted by a + LICENSE_FLAGS definition to be enabled and + included in an image, it needs to have a matching entry in the + global + LICENSE_FLAGS_WHITELIST + variable, which is a variable typically defined in your + local.conf file. + For example, to enable the + poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly + package, you could add either the string + "commercial_gst-plugins-ugly" or the more general string + "commercial" to LICENSE_FLAGS_WHITELIST. + See the + "License Flag Matching" + section for a full + explanation of how LICENSE_FLAGS matching + works. + Here is the example: + + LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly" + + Likewise, to additionally enable the package built from the + recipe containing + LICENSE_FLAGS = "license_${PN}_${PV}", + and assuming that the actual recipe name was + emgd_1.10.bb, the following string would + enable that package as well as the original + gst-plugins-ugly package: + + LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly license_emgd_1.10" + + As a convenience, you do not need to specify the complete + license string in the whitelist for every package. + You can use an abbreviated form, which consists + of just the first portion or portions of the license + string before the initial underscore character or characters. + A partial string will match any license that contains the + given string as the first portion of its license. + For example, the following whitelist string will also match + both of the packages previously mentioned as well as any other + packages that have licenses starting with "commercial" or + "license". + + LICENSE_FLAGS_WHITELIST = "commercial license" + + + +
+ License Flag Matching + + + License flag matching allows you to control what recipes + the OpenEmbedded build system includes in the build. + Fundamentally, the build system attempts to match + LICENSE_FLAGS + strings found in recipes against + LICENSE_FLAGS_WHITELIST + strings found in the whitelist. + A match causes the build system to include a recipe in the + build, while failure to find a match causes the build + system to exclude a recipe. + + + + In general, license flag matching is simple. + However, understanding some concepts will help you + correctly and effectively use matching. + + + + Before a flag + defined by a particular recipe is tested against the + contents of the whitelist, the expanded string + _${PN} is appended to the flag. + This expansion makes each + LICENSE_FLAGS value recipe-specific. + After expansion, the string is then matched against the + whitelist. + Thus, specifying + LICENSE_FLAGS = "commercial" + in recipe "foo", for example, results in the string + "commercial_foo". + And, to create a match, that string must appear in the + whitelist. + + + + Judicious use of the LICENSE_FLAGS + strings and the contents of the + LICENSE_FLAGS_WHITELIST variable + allows you a lot of flexibility for including or excluding + recipes based on licensing. + For example, you can broaden the matching capabilities by + using license flags string subsets in the whitelist. + + When using a string subset, be sure to use the part of + the expanded string that precedes the appended + underscore character (e.g. + usethispart_1.3, + usethispart_1.4, and so forth). + + For example, simply specifying the string "commercial" in + the whitelist matches any expanded + LICENSE_FLAGS definition that starts + with the string "commercial" such as "commercial_foo" and + "commercial_bar", which are the strings the build system + automatically generates for hypothetical recipes named + "foo" and "bar" assuming those recipes simply specify the + following: + + LICENSE_FLAGS = "commercial" + + Thus, you can choose to exhaustively + enumerate each license flag in the whitelist and + allow only specific recipes into the image, or + you can use a string subset that causes a broader range of + matches to allow a range of recipes into the image. + + + + This scheme works even if the + LICENSE_FLAGS string already + has _${PN} appended. + For example, the build system turns the license flag + "commercial_1.2_foo" into "commercial_1.2_foo_foo" and + would match both the general "commercial" and the specific + "commercial_1.2_foo" strings found in the whitelist, as + expected. + + + + Here are some other scenarios: + + + You can specify a versioned string in the recipe + such as "commercial_foo_1.2" in a "foo" recipe. + The build system expands this string to + "commercial_foo_1.2_foo". + Combine this license flag with a whitelist that has + the string "commercial" and you match the flag + along with any other flag that starts with the + string "commercial". + + + Under the same circumstances, you can use + "commercial_foo" in the whitelist and the build + system not only matches "commercial_foo_1.2" but + also matches any license flag with the string + "commercial_foo", regardless of the version. + + + You can be very specific and use both the + package and version parts in the whitelist (e.g. + "commercial_foo_1.2") to specifically match a + versioned recipe. + + + +
+ + +
+
+ +
+ x32 psABI + + + x32 processor-specific Application Binary Interface + (x32 psABI) + is a native 32-bit processor-specific ABI for + Intel 64 (x86-64) + architectures. + An ABI defines the calling conventions between functions in a + processing environment. + The interface determines what registers are used and what the sizes are + for various C data types. + + + + Some processing environments prefer using 32-bit applications even + when running on Intel 64-bit platforms. + Consider the i386 psABI, which is a very old 32-bit ABI for Intel + 64-bit platforms. + The i386 psABI does not provide efficient use and access of the + Intel 64-bit processor resources, leaving the system underutilized. + Now consider the x86_64 psABI. + This ABI is newer and uses 64-bits for data sizes and program + pointers. + The extra bits increase the footprint size of the programs, + libraries, and also increases the memory and file system size + requirements. + Executing under the x32 psABI enables user programs to utilize CPU + and system resources more efficiently while keeping the memory + footprint of the applications low. + Extra bits are used for registers but not for addressing mechanisms. + + + + The Yocto Project supports the final specifications of x32 psABI + as follows: + + + You can create packages and images in x32 psABI format on + x86_64 architecture targets. + + + You can successfully build recipes with the x32 toolchain. + + + You can create and boot + core-image-minimal and + core-image-sato images. + + + RPM Package Manager (RPM) support exists for x32 binaries. + + + Support for large images exists. + + + + + + For steps on how to use x32 psABI, see the + "Using x32 psABI" + section in the Yocto Project Development Tasks Manual. + +
+ + diff --git a/documentation/concepts-manual/concepts-manual-customization.xsl b/documentation/concepts-manual/concepts-manual-customization.xsl new file mode 100644 index 0000000000..9733bf87b2 --- /dev/null +++ b/documentation/concepts-manual/concepts-manual-customization.xsl @@ -0,0 +1,27 @@ + + + + + + + + + + + + + + + + + + + + + diff --git a/documentation/concepts-manual/concepts-manual-development-environment.xml b/documentation/concepts-manual/concepts-manual-development-environment.xml new file mode 100644 index 0000000000..7d177cecca --- /dev/null +++ b/documentation/concepts-manual/concepts-manual-development-environment.xml @@ -0,0 +1,2890 @@ + %poky; ] > + + +The Yocto Project Development Environment + + + This chapter takes a look at the Yocto Project development + environment and also provides a detailed look at what goes on during + development in that environment. + The chapter provides Yocto Project Development environment concepts that + help you understand how work is accomplished in an open source environment, + which is very different as compared to work accomplished in a closed, + proprietary environment. + + + + Specifically, this chapter addresses open source philosophy, workflows, + Git, source repositories, licensing, recipe syntax, and development + syntax. + + +
+ Introduction + + + The Yocto Project is an open-source collaboration project whose + focus is for developers of embedded Linux systems. + Among other things, the Yocto Project uses an + OpenEmbedded build system. + The build system, which is based on the OpenEmbedded (OE) project and + uses the + BitBake tool, + constructs complete Linux images for architectures based on ARM, MIPS, + PowerPC, x86 and x86-64. + + Historically, the OpenEmbedded build system, which is the + combination of BitBake and OE components, formed a reference + build host that was known as + "Poky" + (Pah-kee). + The term "Poky", as used throughout the Yocto Project Documentation + set, can have different meanings. + + The Yocto Project provides various ancillary tools for the embedded + developer and also features the Sato reference User Interface, which + is optimized for stylus-driven, low-resolution screens. + + + + + + + + + + Here are some highlights for the Yocto Project: + + + + + Provides a recent Linux kernel along with a set of system + commands and libraries suitable for the embedded + environment. + + + Makes available system components such as X11, GTK+, Qt, + Clutter, and SDL (among others) so you can create a rich user + experience on devices that have display hardware. + For devices that do not have a display or where you wish to + use alternative UI frameworks, these components need not be + installed. + + + Creates a focused and stable core compatible with the + OpenEmbedded project with which you can easily and reliably + build and develop. + + + Fully supports a wide range of hardware and device emulation + through the Quick EMUlator (QEMU). + + + Provides a layer mechanism that allows you to easily extend + the system, make customizations, and keep them organized. + + + + + You can use the Yocto Project to generate images for many kinds + of devices. + As mentioned earlier, the Yocto Project supports creation of + reference images that you can boot within and emulate using QEMU. + The standard example machines target QEMU full-system + emulation for 32-bit and 64-bit variants of x86, ARM, MIPS, and + PowerPC architectures. + Beyond emulation, you can use the layer mechanism to extend + support to just about any platform that Linux can run on and that + a toolchain can target. + + + + Another Yocto Project feature is the Sato reference User + Interface. + This optional UI that is based on GTK+ is intended for devices with + restricted screen sizes and is included as part of the + OpenEmbedded Core layer so that developers can test parts of the + software stack. + + + + While the Yocto Project does not provide a strict testing framework, + it does provide or generate for you artifacts that let you perform + target-level and emulated testing and debugging. + Additionally, if you are an + Eclipse IDE user, you can + install an Eclipse Yocto Plug-in to allow you to develop within that + familiar environment. + + + + By default, using the Yocto Project to build an image creates a Poky + distribution. + However, you can create your own distribution by providing key + Metadata. + A good example is Angstrom, which has had a distribution + based on the Yocto Project since its inception. + Other examples include commercial distributions like + Wind River Linux, + Mentor Embedded Linux, + ENEA Linux + and others. + See the "Creating Your Own Distribution" + section in the Yocto Project Development Tasks Manual for more + information. + +
+ +
+ Open Source Philosophy + + + Open source philosophy is characterized by software development + directed by peer production and collaboration through an active + community of developers. + Contrast this to the more standard centralized development models + used by commercial software companies where a finite set of developers + produces a product for sale using a defined set of procedures that + ultimately result in an end product whose architecture and source + material are closed to the public. + + + + Open source projects conceptually have differing concurrent agendas, + approaches, and production. + These facets of the development process can come from anyone in the + public (community) that has a stake in the software project. + The open source environment contains new copyright, licensing, domain, + and consumer issues that differ from the more traditional development + environment. + In an open source environment, the end product, source material, + and documentation are all available to the public at no cost. + + + + A benchmark example of an open source project is the Linux kernel, + which was initially conceived and created by Finnish computer science + student Linus Torvalds in 1991. + Conversely, a good example of a non-open source project is the + Windows family of operating + systems developed by + Microsoft Corporation. + + + + Wikipedia has a good historical description of the Open Source + Philosophy + here. + You can also find helpful information on how to participate in the + Linux Community + here. + +
+ +
+ Workflows + + + This section provides workflow concepts using the Yocto Project and + Git. + In particular, the information covers basic practices that describe + roles and actions in a collaborative development environment. + + If you are familiar with this type of development environment, you + might not want to read this section. + + + + + The Yocto Project files are maintained using Git in "master" + branches whose Git histories track every change and whose structures + provides branches for all diverging functionality. + Although there is no need to use Git, many open source projects do so. + + + + For the Yocto Project, a key individual called the "maintainer" is + responsible for the "master" branch of a given Git repository. + The "master" branch is the “upstream” repository from which final or + most recent builds of the project occur. + The maintainer is responsible for accepting changes from other + developers and for organizing the underlying branch structure to + reflect release strategies and so forth. + For information on finding out who is responsible for (maintains) + a particular area of code, see the + "Submitting a Change to the Yocto Project" + section of the Yocto Project Development Tasks Manual. + + + + + The Yocto Project poky Git repository also has an + upstream contribution Git repository named + poky-contrib. + You can see all the branches in this repository using the web interface + of the + Source Repositories organized + within the "Poky Support" area. + These branches temporarily hold changes to the project that have been + submitted or committed by the Yocto Project development team and by + community members who contribute to the project. + The maintainer determines if the changes are qualified to be moved + from the "contrib" branches into the "master" branch of the Git + repository. + + + + Developers (including contributing community members) create and + maintain cloned repositories of the upstream "master" branch. + The cloned repositories are local to their development platforms and + are used to develop changes. + When a developer is satisfied with a particular feature or change, + they "push" the changes to the appropriate "contrib" repository. + + + + Developers are responsible for keeping their local repository + up-to-date with "master". + They are also responsible for straightening out any conflicts that + might arise within files that are being worked on simultaneously by + more than one person. + All this work is done locally on the developer’s machine before + anything is pushed to a "contrib" area and examined at the maintainer’s + level. + + + + A somewhat formal method exists by which developers commit changes + and push them into the "contrib" area and subsequently request that + the maintainer include them into "master". + This process is called “submitting a patch” or "submitting a change." + For information on submitting patches and changes, see the + "Submitting a Change to the Yocto Project" + section in the Yocto Project Development Tasks Manual. + + + + To summarize the development workflow: a single point of entry + exists for changes into the project’s "master" branch of the + Git repository, which is controlled by the project’s maintainer. + And, a set of developers exist who independently develop, test, and + submit changes to "contrib" areas for the maintainer to examine. + The maintainer then chooses which changes are going to become a + permanent part of the project. + + + + + + + + While each development environment is unique, there are some best + practices or methods that help development run smoothly. + The following list describes some of these practices. + For more information about Git workflows, see the workflow topics in + the + Git Community Book. + + + Make Small Changes: + It is best to keep the changes you commit small as compared to + bundling many disparate changes into a single commit. + This practice not only keeps things manageable but also allows + the maintainer to more easily include or refuse changes. + + It is also good practice to leave the repository in a + state that allows you to still successfully build your project. + In other words, do not commit half of a feature, + then add the other half as a separate, later commit. + Each commit should take you from one buildable project state + to another buildable state. + + + Use Branches Liberally: + It is very easy to create, use, and delete local branches in + your working Git repository. + You can name these branches anything you like. + It is helpful to give them names associated with the particular + feature or change on which you are working. + Once you are done with a feature or change and have merged it + into your local master branch, simply discard the temporary + branch. + + + Merge Changes: + The git merge command allows you to take + the changes from one branch and fold them into another branch. + This process is especially helpful when more than a single + developer might be working on different parts of the same + feature. + Merging changes also automatically identifies any collisions + or "conflicts" that might happen as a result of the same lines + of code being altered by two different developers. + + + Manage Branches: + Because branches are easy to use, you should use a system + where branches indicate varying levels of code readiness. + For example, you can have a "work" branch to develop in, a + "test" branch where the code or change is tested, a "stage" + branch where changes are ready to be committed, and so forth. + As your project develops, you can merge code across the + branches to reflect ever-increasing stable states of the + development. + + + Use Push and Pull: + The push-pull workflow is based on the concept of developers + "pushing" local commits to a remote repository, which is + usually a contribution repository. + This workflow is also based on developers "pulling" known + states of the project down into their local development + repositories. + The workflow easily allows you to pull changes submitted by + other developers from the upstream repository into your + work area ensuring that you have the most recent software + on which to develop. + The Yocto Project has two scripts named + create-pull-request and + send-pull-request that ship with the + release to facilitate this workflow. + You can find these scripts in the scripts + folder of the + Source Directory. + For information on how to use these scripts, see the + "Using Scripts to Push a Change Upstream and Request a Pull" + section in the Yocto Project Development Tasks Manual. + + + Patch Workflow: + This workflow allows you to notify the maintainer through an + email that you have a change (or patch) you would like + considered for the "master" branch of the Git repository. + To send this type of change, you format the patch and then + send the email using the Git commands + git format-patch and + git send-email. + For information on how to use these scripts, see the + "Submitting a Change to the Yocto Project" + section in the Yocto Project Development Tasks Manual. + + + +
+ +
+ Git + + + The Yocto Project makes extensive use of Git, which is a + free, open source distributed version control system. + Git supports distributed development, non-linear development, + and can handle large projects. + It is best that you have some fundamental understanding + of how Git tracks projects and how to work with Git if + you are going to use the Yocto Project for development. + This section provides a quick overview of how Git works and + provides you with a summary of some essential Git commands. + Notes + + + For more information on Git, see + . + + + If you need to download Git, it is recommended that you add + Git to your system through your distribution's "software + store" (e.g. for Ubuntu, use the Ubuntu Software feature). + For the Git download page, see + . + + + For examples beyond the limited few in this section on how + to use Git with the Yocto Project, see the + "Working With Yocto Project Source Files" + section in the Yocto Project Development Tasks Manual. + + + + + +
+ Repositories, Tags, and Branches + + + As mentioned briefly in the previous section and also in the + "Workflows" section, + the Yocto Project maintains source repositories at + . + If you look at this web-interface of the repositories, each item + is a separate Git repository. + + + + Git repositories use branching techniques that track content + change (not files) within a project (e.g. a new feature or updated + documentation). + Creating a tree-like structure based on project divergence allows + for excellent historical information over the life of a project. + This methodology also allows for an environment from which you can + do lots of local experimentation on projects as you develop + changes or new features. + + + + A Git repository represents all development efforts for a given + project. + For example, the Git repository poky contains + all changes and developments for Poky over the course of its + entire life. + That means that all changes that make up all releases are captured. + The repository maintains a complete history of changes. + + + + You can create a local copy of any repository by "cloning" it + with the git clone command. + When you clone a Git repository, you end up with an identical + copy of the repository on your development system. + Once you have a local copy of a repository, you can take steps to + develop locally. + For examples on how to clone Git repositories, see the + "Working With Yocto Project Source Files" + section in the Yocto Project Development Tasks Manual. + + + + It is important to understand that Git tracks content change and + not files. + Git uses "branches" to organize different development efforts. + For example, the poky repository has + several branches that include the current "&DISTRO_NAME_NO_CAP;" + branch, the "master" branch, and many branches for past + Yocto Project releases. + You can see all the branches by going to + and + clicking on the + [...] + link beneath the "Branch" heading. + + + + Each of these branches represents a specific area of development. + The "master" branch represents the current or most recent + development. + All other branches represent offshoots of the "master" branch. + + + + When you create a local copy of a Git repository, the copy has + the same set of branches as the original. + This means you can use Git to create a local working area + (also called a branch) that tracks a specific development branch + from the upstream source Git repository. + in other words, you can define your local Git environment to + work on any development branch in the repository. + To help illustrate, consider the following example Git commands: + + $ cd ~ + $ git clone git://git.yoctoproject.org/poky + $ cd poky + $ git checkout -b &DISTRO_NAME_NO_CAP; origin/&DISTRO_NAME_NO_CAP; + + In the previous example after moving to the home directory, the + git clone command creates a + local copy of the upstream poky Git repository. + By default, Git checks out the "master" branch for your work. + After changing the working directory to the new local repository + (i.e. poky), the + git checkout command creates + and checks out a local branch named "&DISTRO_NAME_NO_CAP;", which + tracks the upstream "origin/&DISTRO_NAME_NO_CAP;" branch. + Changes you make while in this branch would ultimately affect + the upstream "&DISTRO_NAME_NO_CAP;" branch of the + poky repository. + + + + It is important to understand that when you create and checkout a + local working branch based on a branch name, + your local environment matches the "tip" of that particular + development branch at the time you created your local branch, + which could be different from the files in the "master" branch + of the upstream repository. + In other words, creating and checking out a local branch based on + the "&DISTRO_NAME_NO_CAP;" branch name is not the same as + cloning and checking out the "master" branch if the repository. + Keep reading to see how you create a local snapshot of a Yocto + Project Release. + + + + Git uses "tags" to mark specific changes in a repository. + Typically, a tag is used to mark a special point such as the final + change before a project is released. + You can see the tags used with the poky Git + repository by going to + and + clicking on the + [...] + link beneath the "Tag" heading. + + + + Some key tags for the poky are + jethro-14.0.3, + morty-16.0.1, + pyro-17.0.0, and + &DISTRO_NAME_NO_CAP;-&POKYVERSION;. + These tags represent Yocto Project releases. + + + + When you create a local copy of the Git repository, you also + have access to all the tags in the upstream repository. + Similar to branches, you can create and checkout a local working + Git branch based on a tag name. + When you do this, you get a snapshot of the Git repository that + reflects the state of the files when the change was made associated + with that tag. + The most common use is to checkout a working branch that matches + a specific Yocto Project release. + Here is an example: + + $ cd ~ + $ git clone git://git.yoctoproject.org/poky + $ cd poky + $ git fetch --all --tags --prune + $ git checkout tags/pyro-17.0.0 -b my-pyro-17.0.0 + + In this example, the name of the top-level directory of your + local Yocto Project repository is poky. + After moving to the poky directory, the + git fetch command makes all the upstream + tags available locally in your repository. + Finally, the git checkout command + creates and checks out a branch named "my-pyro-17.0.0" that is + based on the specific change upstream in the repository + associated with the "pyro-17.0.0" tag. + The files in your repository now exactly match that particular + Yocto Project release as it is tagged in the upstream Git + repository. + It is important to understand that when you create and + checkout a local working branch based on a tag, your environment + matches a specific point in time and not the entire development + branch (i.e. the "tip" of the branch). + +
+ +
+ Basic Commands + + + Git has an extensive set of commands that lets you manage changes + and perform collaboration over the life of a project. + Conveniently though, you can manage with a small set of basic + operations and workflows once you understand the basic + philosophy behind Git. + You do not have to be an expert in Git to be functional. + A good place to look for instruction on a minimal set of Git + commands is + here. + + + + If you do not know much about Git, you should educate + yourself by visiting the links previously mentioned. + + + + The following list of Git commands briefly describes some basic + Git operations as a way to get started. + As with any set of commands, this list (in most cases) simply shows + the base command and omits the many arguments they support. + See the Git documentation for complete descriptions and strategies + on how to use these commands: + + + git init: + Initializes an empty Git repository. + You cannot use Git commands unless you have a + .git repository. + + + git clone: + Creates a local clone of a Git repository that is on + equal footing with a fellow developer’s Git repository + or an upstream repository. + + + git add: + Locally stages updated file contents to the index that + Git uses to track changes. + You must stage all files that have changed before you + can commit them. + + + git commit: + Creates a local "commit" that documents the changes you + made. + Only changes that have been staged can be committed. + Commits are used for historical purposes, for determining + if a maintainer of a project will allow the change, + and for ultimately pushing the change from your local + Git repository into the project’s upstream repository. + + + git status: + Reports any modified files that possibly need to be + staged and gives you a status of where you stand regarding + local commits as compared to the upstream repository. + + + git checkout branch-name: + Changes your working branch. + This command is analogous to "cd". + + git checkout –b working-branch: + Creates and checks out a working branch on your local + machine that you can use to isolate your work. + It is a good idea to use local branches when adding + specific features or changes. + Using isolated branches facilitates easy removal of + changes if they do not work out. + + git branch: + Displays the existing local branches associated with your + local repository. + The branch that you have currently checked out is noted + with an asterisk character. + + + git branch -D branch-name: + Deletes an existing local branch. + You need to be in a local branch other than the one you + are deleting in order to delete + branch-name. + + + git pull: + Retrieves information from an upstream Git repository + and places it in your local Git repository. + You use this command to make sure you are synchronized with + the repository from which you are basing changes + (.e.g. the "master" branch). + + + git push: + Sends all your committed local changes to the upstream Git + repository that your local repository is tracking + (e.g. a contribution repository). + The maintainer of the project draws from these repositories + to merge changes (commits) into the appropriate branch + of project's upstream repository. + + + git merge: + Combines or adds changes from one + local branch of your repository with another branch. + When you create a local Git repository, the default branch + is named "master". + A typical workflow is to create a temporary branch that is + based off "master" that you would use for isolated work. + You would make your changes in that isolated branch, + stage and commit them locally, switch to the "master" + branch, and then use the git merge + command to apply the changes from your isolated branch + into the currently checked out branch (e.g. "master"). + After the merge is complete and if you are done with + working in that isolated branch, you can safely delete + the isolated branch. + + + git cherry-pick: + Choose and apply specific commits from one branch + into another branch. + There are times when you might not be able to merge + all the changes in one branch with + another but need to pick out certain ones. + + + gitk: + Provides a GUI view of the branches and changes in your + local Git repository. + This command is a good way to graphically see where things + have diverged in your local repository. + + You need to install the gitk + package on your development system to use this + command. + + + + git log: + Reports a history of your commits to the repository. + This report lists all commits regardless of whether you + have pushed them upstream or not. + + + git diff: + Displays line-by-line differences between a local + working file and the same file as understood by Git. + This command is useful to see what you have changed + in any given file. + + + +
+
+ +
+ Yocto Project Source Repositories + + + The Yocto Project team maintains complete source repositories for all + Yocto Project files at + . + This web-based source code browser is organized into categories by + function such as IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and + so forth. + From the interface, you can click on any particular item in the "Name" + column and see the URL at the bottom of the page that you need to clone + a Git repository for that particular item. + Having a local Git repository of the + Source Directory, + which is usually named "poky", allows + you to make changes, contribute to the history, and ultimately enhance + the Yocto Project's tools, Board Support Packages, and so forth. + + + + For any supported release of Yocto Project, you can also go to the + Yocto Project Website and + select the "Downloads" tab and get a released tarball of the + poky repository or any supported BSP tarballs. + Unpacking these tarballs gives you a snapshot of the released + files. + Notes + + + The recommended method for setting up the Yocto Project + Source Directory + and the files for supported BSPs + (e.g., meta-intel) is to use + Git to create a local copy of + the upstream repositories. + + + Be sure to always work in matching branches for both + the selected BSP repository and the + Source Directory + (i.e. poky) repository. + For example, if you have checked out the "master" branch + of poky and you are going to use + meta-intel, be sure to checkout the + "master" branch of meta-intel. + + + + + + + In summary, here is where you can get the project files needed for + development: + + + + Source Repositories: + + This area contains IDE Plugins, Matchbox, Poky, Poky Support, + Tools, Yocto Linux Kernel, and Yocto Metadata Layers. + You can create local copies of Git repositories for each of + these areas. + + + + For steps on how to view and access these upstream Git + repositories, see the + "Accessing Source Repositories" + Section in the Yocto Project Development Tasks Manual. + + + + Index of /releases: + + This is an index of releases such as + the Eclipse + Yocto Plug-in, miscellaneous support, Poky, Pseudo, installers + for cross-development toolchains, and all released versions of + Yocto Project in the form of images or tarballs. + Downloading and extracting these files does not produce a local + copy of the Git repository but rather a snapshot of a + particular release or image. + + + + For steps on how to view and access these files, see the + "Accessing Index of Releases" + section in the Yocto Project Development Tasks Manual. + + + "Downloads" page for the + Yocto Project Website: + + + This section will change due to + reworking of the YP Website. + + The Yocto Project website includes a "Downloads" tab + that allows you to download any Yocto Project + release and Board Support Package (BSP) in tarball form. + The tarballs are similar to those found in the + Index of /releases: area. + + + + For steps on how to use the "Downloads" page, see the + "Using the Downloads Page" + section in the Yocto Project Development Tasks Manual. + + + +
+ +
+ Licensing + + + Because open source projects are open to the public, they have + different licensing structures in place. + License evolution for both Open Source and Free Software has an + interesting history. + If you are interested in this history, you can find basic information + here: + + + Open source license history + + + Free software license history + + + + + + In general, the Yocto Project is broadly licensed under the + Massachusetts Institute of Technology (MIT) License. + MIT licensing permits the reuse of software within proprietary + software as long as the license is distributed with that software. + MIT is also compatible with the GNU General Public License (GPL). + Patches to the Yocto Project follow the upstream licensing scheme. + You can find information on the MIT license + here. + You can find information on the GNU GPL + here. + + + + When you build an image using the Yocto Project, the build process + uses a known list of licenses to ensure compliance. + You can find this list in the + Source Directory + at meta/files/common-licenses. + Once the build completes, the list of all licenses found and used + during that build are kept in the + Build Directory + at tmp/deploy/licenses. + + + + If a module requires a license that is not in the base list, the + build process generates a warning during the build. + These tools make it easier for a developer to be certain of the + licenses with which their shipped products must comply. + However, even with these tools it is still up to the developer to + resolve potential licensing issues. + + + + The base list of licenses used by the build process is a combination + of the Software Package Data Exchange (SPDX) list and the Open + Source Initiative (OSI) projects. + SPDX Group is a working group of + the Linux Foundation that maintains a specification for a standard + format for communicating the components, licenses, and copyrights + associated with a software package. + OSI is a corporation + dedicated to the Open Source Definition and the effort for reviewing + and approving licenses that conform to the Open Source Definition + (OSD). + + + + You can find a list of the combined SPDX and OSI licenses that the + Yocto Project uses in the + meta/files/common-licenses directory in your + Source Directory. + + + + For information that can help you maintain compliance with various + open source licensing during the lifecycle of a product created using + the Yocto Project, see the + "Maintaining Open Source License Compliance During Your Product's Lifecycle" + section in the Yocto Project Development Tasks Manual. + +
+ +
+ Recipe Syntax + + + Understanding recipe file syntax is important for + writing recipes. + The following list overviews the basic items that make up a + BitBake recipe file. + For more complete BitBake syntax descriptions, see the + "Syntax and Operators" + chapter of the BitBake User Manual. + + Variable Assignments and Manipulations: + Variable assignments allow a value to be assigned to a + variable. + The assignment can be static text or might include + the contents of other variables. + In addition to the assignment, appending and prepending + operations are also supported. + The following example shows some of the ways + you can use variables in recipes: + + S = "${WORKDIR}/postfix-${PV}" + CFLAGS += "-DNO_ASM" + SRC_URI_append = " file://fixup.patch" + + + Functions: + Functions provide a series of actions to be performed. + You usually use functions to override the default + implementation of a task function or to complement + a default function (i.e. append or prepend to an + existing function). + Standard functions use sh shell + syntax, although access to OpenEmbedded variables and + internal methods are also available. + The following is an example function from the + sed recipe: + + do_install () { + autotools_do_install + install -d ${D}${base_bindir} + mv ${D}${bindir}/sed ${D}${base_bindir}/sed + rmdir ${D}${bindir}/ + } + + It is also possible to implement new functions that + are called between existing tasks as long as the + new functions are not replacing or complementing the + default functions. + You can implement functions in Python + instead of shell. + Both of these options are not seen in the majority of + recipes. + Keywords: + BitBake recipes use only a few keywords. + You use keywords to include common + functions (inherit), load parts + of a recipe from other files + (include and + require) and export variables + to the environment (export). + The following example shows the use of some of + these keywords: + + export POSTCONF = "${STAGING_BINDIR}/postconf" + inherit autoconf + require otherfile.inc + + + Comments: + Any lines that begin with the hash character + (#) are treated as comment lines + and are ignored: + + # This is a comment + + + + + + + This next list summarizes the most important and most commonly + used parts of the recipe syntax. + For more information on these parts of the syntax, you can + reference the + Syntax and Operators + chapter in the BitBake User Manual. + + Line Continuation: \ - + Use the backward slash (\) + character to split a statement over multiple lines. + Place the slash character at the end of the line that + is to be continued on the next line: + + VAR = "A really long \ + line" + + + You cannot have any characters including spaces + or tabs after the slash character. + + + + Using Variables: ${...} - + Use the ${VARNAME} syntax to + access the contents of a variable: + + SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz" + + + It is important to understand that the value of a + variable expressed in this form does not get + substituted automatically. + The expansion of these expressions happens + on-demand later (e.g. usually when a function that + makes reference to the variable executes). + This behavior ensures that the values are most + appropriate for the context in which they are + finally used. + On the rare occasion that you do need the variable + expression to be expanded immediately, you can use + the := operator instead of + = when you make the + assignment, but this is not generally needed. + + + Quote All Assignments: "value" - + Use double quotes around the value in all variable + assignments. + + VAR1 = "${OTHERVAR}" + VAR2 = "The version is ${PV}" + + + Conditional Assignment: ?= - + Conditional assignment is used to assign a value to + a variable, but only when the variable is currently + unset. + Use the question mark followed by the equal sign + (?=) to make a "soft" assignment + used for conditional assignment. + Typically, "soft" assignments are used in the + local.conf file for variables + that are allowed to come through from the external + environment. + + Here is an example where + VAR1 is set to "New value" if + it is currently empty. + However, if VAR1 has already been + set, it remains unchanged: + + VAR1 ?= "New value" + + In this next example, VAR1 + is left with the value "Original value": + + VAR1 = "Original value" + VAR1 ?= "New value" + + + Appending: += - + Use the plus character followed by the equals sign + (+=) to append values to existing + variables. + + This operator adds a space between the existing + content of the variable and the new content. + + Here is an example: + + SRC_URI += "file://fix-makefile.patch" + + + Prepending: =+ - + Use the equals sign followed by the plus character + (=+) to prepend values to existing + variables. + + This operator adds a space between the new content + and the existing content of the variable. + + Here is an example: + + VAR =+ "Starts" + + + Appending: _append - + Use the _append operator to + append values to existing variables. + This operator does not add any additional space. + Also, the operator is applied after all the + +=, and + =+ operators have been applied and + after all = assignments have + occurred. + + The following example shows the space being + explicitly added to the start to ensure the appended + value is not merged with the existing value: + + SRC_URI_append = " file://fix-makefile.patch" + + You can also use the _append + operator with overrides, which results in the actions + only being performed for the specified target or + machine: + + SRC_URI_append_sh4 = " file://fix-makefile.patch" + + + Prepending: _prepend - + Use the _prepend operator to + prepend values to existing variables. + This operator does not add any additional space. + Also, the operator is applied after all the + +=, and + =+ operators have been applied and + after all = assignments have + occurred. + + The following example shows the space being + explicitly added to the end to ensure the prepended + value is not merged with the existing value: + + CFLAGS_prepend = "-I${S}/myincludes " + + You can also use the _prepend + operator with overrides, which results in the actions + only being performed for the specified target or + machine: + + CFLAGS_prepend_sh4 = "-I${S}/myincludes " + + + Overrides: - + You can use overrides to set a value conditionally, + typically based on how the recipe is being built. + For example, to set the + KBRANCH + variable's value to "standard/base" for any target + MACHINE, + except for qemuarm where it should be set to + "standard/arm-versatile-926ejs", you would do the + following: + + KBRANCH = "standard/base" + KBRANCH_qemuarm = "standard/arm-versatile-926ejs" + + Overrides are also used to separate alternate values + of a variable in other situations. + For example, when setting variables such as + FILES + and + RDEPENDS + that are specific to individual packages produced by + a recipe, you should always use an override that + specifies the name of the package. + + Indentation: + Use spaces for indentation rather than than tabs. + For shell functions, both currently work. + However, it is a policy decision of the Yocto Project + to use tabs in shell functions. + Realize that some layers have a policy to use spaces + for all indentation. + + Using Python for Complex Operations: ${@python_code} - + For more advanced processing, it is possible to use + Python code during variable assignments (e.g. + search and replacement on a variable). + You indicate Python code using the + ${@python_code} + syntax for the variable assignment: + + SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz + + + Shell Function Syntax: + Write shell functions as if you were writing a shell + script when you describe a list of actions to take. + You should ensure that your script works with a generic + sh and that it does not require + any bash or other shell-specific + functionality. + The same considerations apply to various system + utilities (e.g. sed, + grep, awk, + and so forth) that you might wish to use. + If in doubt, you should check with multiple + implementations - including those from BusyBox. + + + +
+ +
+ Development Concepts + + + This section takes a more detailed look inside the development + process. + The following diagram represents development at a high level. + The remainder of this chapter expands on the fundamental input, output, + process, and + Metadata) blocks + that make up development in the Yocto Project environment. + + + + + + + + In general, development consists of several functional areas: + + User Configuration: + Metadata you can use to control the build process. + + Metadata Layers: + Various layers that provide software, machine, and + distro Metadata. + Source Files: + Upstream releases, local projects, and SCMs. + Build System: + Processes under the control of + BitBake. + This block expands on how BitBake fetches source, applies + patches, completes compilation, analyzes output for package + generation, creates and tests packages, generates images, and + generates cross-development tools. + Package Feeds: + Directories containing output packages (RPM, DEB or IPK), + which are subsequently used in the construction of an image or + SDK, produced by the build system. + These feeds can also be copied and shared using a web server or + other means to facilitate extending or updating existing + images on devices at runtime if runtime package management is + enabled. + Images: + Images produced by the development process. + + Application Development SDK: + Cross-development tools that are produced along with an image + or separately with BitBake. + + + +
+ User Configuration + + + User configuration helps define the build. + Through user configuration, you can tell BitBake the + target architecture for which you are building the image, + where to store downloaded source, and other build properties. + + + + The following figure shows an expanded representation of the + "User Configuration" box of the + general Yocto Project Development Environment figure: + + + + + + + + BitBake needs some basic configuration files in order to complete + a build. + These files are *.conf files. + The minimally necessary ones reside as example files in the + Source Directory. + For simplicity, this section refers to the Source Directory as + the "Poky Directory." + + + + When you clone the poky Git repository or you + download and unpack a Yocto Project release, you can set up the + Source Directory to be named anything you want. + For this discussion, the cloned repository uses the default + name poky. + + The Poky repository is primarily an aggregation of existing + repositories. + It is not a canonical upstream source. + + + + + The meta-poky layer inside Poky contains + a conf directory that has example + configuration files. + These example files are used as a basis for creating actual + configuration files when you source the build environment + script + (i.e. + &OE_INIT_FILE;). + + + + Sourcing the build environment script creates a + Build Directory + if one does not already exist. + BitBake uses the Build Directory for all its work during builds. + The Build Directory has a conf directory that + contains default versions of your local.conf + and bblayers.conf configuration files. + These default configuration files are created only if versions + do not already exist in the Build Directory at the time you + source the build environment setup script. + + + + Because the Poky repository is fundamentally an aggregation of + existing repositories, some users might be familiar with running + the &OE_INIT_FILE; script in the context + of separate OpenEmbedded-Core and BitBake repositories rather than a + single Poky repository. + This discussion assumes the script is executed from within a cloned + or unpacked version of Poky. + + + + Depending on where the script is sourced, different sub-scripts + are called to set up the Build Directory (Yocto or OpenEmbedded). + Specifically, the script + scripts/oe-setup-builddir inside the + poky directory sets up the Build Directory and seeds the directory + (if necessary) with configuration files appropriate for the + Yocto Project development environment. + + The scripts/oe-setup-builddir script + uses the $TEMPLATECONF variable to + determine which sample configuration files to locate. + + + + + The local.conf file provides many + basic variables that define a build environment. + Here is a list of a few. + To see the default configurations in a local.conf + file created by the build environment script, see the + local.conf.sample in the + meta-poky layer: + + Parallelism Options: + Controlled by the + BB_NUMBER_THREADS, + PARALLEL_MAKE, + and + BB_NUMBER_PARSE_THREADS + variables. + Target Machine Selection: + Controlled by the + MACHINE + variable. + Download Directory: + Controlled by the + DL_DIR + variable. + Shared State Directory: + Controlled by the + SSTATE_DIR + variable. + Build Output: + Controlled by the + TMPDIR + variable. + + + Configurations set in the conf/local.conf + file can also be set in the + conf/site.conf and + conf/auto.conf configuration files. + + + + + The bblayers.conf file tells BitBake what + layers you want considered during the build. + By default, the layers listed in this file include layers + minimally needed by the build system. + However, you must manually add any custom layers you have created. + You can find more information on working with the + bblayers.conf file in the + "Enabling Your Layer" + section in the Yocto Project Development Tasks Manual. + + + + The files site.conf and + auto.conf are not created by the environment + initialization script. + If you want the site.conf file, you need to + create that yourself. + The auto.conf file is typically created by + an autobuilder: + + site.conf: + You can use the conf/site.conf + configuration file to configure multiple build directories. + For example, suppose you had several build environments and + they shared some common features. + You can set these default build properties here. + A good example is perhaps the packaging format to use + through the + PACKAGE_CLASSES + variable. + One useful scenario for using the + conf/site.conf file is to extend your + BBPATH + variable to include the path to a + conf/site.conf. + Then, when BitBake looks for Metadata using + BBPATH, it finds the + conf/site.conf file and applies your + common configurations found in the file. + To override configurations in a particular build directory, + alter the similar configurations within that build + directory's conf/local.conf file. + + auto.conf: + The file is usually created and written to by + an autobuilder. + The settings put into the file are typically the same as + you would find in the conf/local.conf + or the conf/site.conf files. + + + + + + You can edit all configuration files to further define + any particular build environment. + This process is represented by the "User Configuration Edits" + box in the figure. + + + + When you launch your build with the + bitbake target + command, BitBake sorts out the configurations to ultimately + define your build environment. + It is important to understand that the OpenEmbedded build system + reads the configuration files in a specific order: + site.conf, auto.conf, + and local.conf. + And, the build system applies the normal assignment statement + rules. + Because the files are parsed in a specific order, variable + assignments for the same variable could be affected. + For example, if the auto.conf file and + the local.conf set + variable1 to different values, because + the build system parses local.conf after + auto.conf, + variable1 is assigned the value from + the local.conf file. + +
+ +
+ Metadata, Machine Configuration, and Policy Configuration + + + The previous section described the user configurations that + define BitBake's global behavior. + This section takes a closer look at the layers the build system + uses to further control the build. + These layers provide Metadata for the software, machine, and + policy. + + + + In general, three types of layer input exist: + + Policy Configuration: + Distribution Layers provide top-level or general + policies for the image or SDK being built. + For example, this layer would dictate whether BitBake + produces RPM or IPK packages. + Machine Configuration: + Board Support Package (BSP) layers provide machine + configurations. + This type of information is specific to a particular + target architecture. + Metadata: + Software layers contain user-supplied recipe files, + patches, and append files. + + + + + + The following figure shows an expanded representation of the + Metadata, Machine Configuration, and Policy Configuration input + (layers) boxes of the + general Yocto Project Development Environment figure: + + + + + + + + In general, all layers have a similar structure. + They all contain a licensing file + (e.g. COPYING) if the layer is to be + distributed, a README file as good practice + and especially if the layer is to be distributed, a + configuration directory, and recipe directories. + + + + The Yocto Project has many layers that can be used. + You can see a web-interface listing of them on the + Source Repositories + page. + The layers are shown at the bottom categorized under + "Yocto Metadata Layers." + These layers are fundamentally a subset of the + OpenEmbedded Metadata Index, + which lists all layers provided by the OpenEmbedded community. + + Layers exist in the Yocto Project Source Repositories that + cannot be found in the OpenEmbedded Metadata Index. + These layers are either deprecated or experimental in nature. + + + + + BitBake uses the conf/bblayers.conf file, + which is part of the user configuration, to find what layers it + should be using as part of the build. + + + + For more information on layers, see the + "Understanding and Creating Layers" + section in the Yocto Project Development Tasks Manual. + + +
+ Distro Layer + + + The distribution layer provides policy configurations for your + distribution. + Best practices dictate that you isolate these types of + configurations into their own layer. + Settings you provide in + conf/distro/distro.conf override + similar + settings that BitBake finds in your + conf/local.conf file in the Build + Directory. + + + + The following list provides some explanation and references + for what you typically find in the distribution layer: + + classes: + Class files (.bbclass) hold + common functionality that can be shared among + recipes in the distribution. + When your recipes inherit a class, they take on the + settings and functions for that class. + You can read more about class files in the + "Classes" + section of the Yocto Reference Manual. + + conf: + This area holds configuration files for the + layer (conf/layer.conf), + the distribution + (conf/distro/distro.conf), + and any distribution-wide include files. + + recipes-*: + Recipes and append files that affect common + functionality across the distribution. + This area could include recipes and append files + to add distribution-specific configuration, + initialization scripts, custom image recipes, + and so forth. + + +
+ +
+ BSP Layer + + + The BSP Layer provides machine configurations. + Everything in this layer is specific to the machine for which + you are building the image or the SDK. + A common structure or form is defined for BSP layers. + You can learn more about this structure in the + Yocto Project Board Support Package (BSP) Developer's Guide. + + In order for a BSP layer to be considered compliant with the + Yocto Project, it must meet some structural requirements. + + + + + The BSP Layer's configuration directory contains + configuration files for the machine + (conf/machine/machine.conf) and, + of course, the layer (conf/layer.conf). + + + + The remainder of the layer is dedicated to specific recipes + by function: recipes-bsp, + recipes-core, + recipes-graphics, and + recipes-kernel. + Metadata can exist for multiple formfactors, graphics + support systems, and so forth. + + While the figure shows several recipes-* + directories, not all these directories appear in all + BSP layers. + + +
+ +
+ Software Layer + + + The software layer provides the Metadata for additional + software packages used during the build. + This layer does not include Metadata that is specific to the + distribution or the machine, which are found in their + respective layers. + + + + This layer contains any new recipes that your project needs + in the form of recipe files. + +
+
+ +
+ Sources + + + In order for the OpenEmbedded build system to create an image or + any target, it must be able to access source files. + The + general Yocto Project Development Environment figure + represents source files using the "Upstream Project Releases", + "Local Projects", and "SCMs (optional)" boxes. + The figure represents mirrors, which also play a role in locating + source files, with the "Source Mirror(s)" box. + + + + The method by which source files are ultimately organized is + a function of the project. + For example, for released software, projects tend to use tarballs + or other archived files that can capture the state of a release + guaranteeing that it is statically represented. + On the other hand, for a project that is more dynamic or + experimental in nature, a project might keep source files in a + repository controlled by a Source Control Manager (SCM) such as + Git. + Pulling source from a repository allows you to control + the point in the repository (the revision) from which you want to + build software. + Finally, a combination of the two might exist, which would give the + consumer a choice when deciding where to get source files. + + + + BitBake uses the + SRC_URI + variable to point to source files regardless of their location. + Each recipe must have a SRC_URI variable + that points to the source. + + + + Another area that plays a significant role in where source files + come from is pointed to by the + DL_DIR + variable. + This area is a cache that can hold previously downloaded source. + You can also instruct the OpenEmbedded build system to create + tarballs from Git repositories, which is not the default behavior, + and store them in the DL_DIR by using the + BB_GENERATE_MIRROR_TARBALLS + variable. + + + + Judicious use of a DL_DIR directory can + save the build system a trip across the Internet when looking + for files. + A good method for using a download directory is to have + DL_DIR point to an area outside of your + Build Directory. + Doing so allows you to safely delete the Build Directory + if needed without fear of removing any downloaded source file. + + + + The remainder of this section provides a deeper look into the + source files and the mirrors. + Here is a more detailed look at the source file area of the + base figure: + + + +
+ Upstream Project Releases + + + Upstream project releases exist anywhere in the form of an + archived file (e.g. tarball or zip file). + These files correspond to individual recipes. + For example, the figure uses specific releases each for + BusyBox, Qt, and Dbus. + An archive file can be for any released product that can be + built using a recipe. + +
+ +
+ Local Projects + + + Local projects are custom bits of software the user provides. + These bits reside somewhere local to a project - perhaps + a directory into which the user checks in items (e.g. + a local directory containing a development source tree + used by the group). + + + + The canonical method through which to include a local project + is to use the + externalsrc + class to include that local project. + You use either the local.conf or a + recipe's append file to override or set the + recipe to point to the local directory on your disk to pull + in the whole source tree. + + + + For information on how to use the + externalsrc class, see the + "externalsrc.bbclass" + section. + +
+ +
+ Source Control Managers (Optional) + + + Another place the build system can get source files from is + through an SCM such as Git or Subversion. + In this case, a repository is cloned or checked out. + The + do_fetch + task inside BitBake uses + the SRC_URI + variable and the argument's prefix to determine the correct + fetcher module. + + + + For information on how to have the OpenEmbedded build system + generate tarballs for Git repositories and place them in the + DL_DIR + directory, see the + BB_GENERATE_MIRROR_TARBALLS + variable. + + + + When fetching a repository, BitBake uses the + SRCREV + variable to determine the specific revision from which to + build. + +
+ +
+ Source Mirror(s) + + + Two kinds of mirrors exist: pre-mirrors and regular mirrors. + The + PREMIRRORS + and + MIRRORS + variables point to these, respectively. + BitBake checks pre-mirrors before looking upstream for any + source files. + Pre-mirrors are appropriate when you have a shared directory + that is not a directory defined by the + DL_DIR + variable. + A Pre-mirror typically points to a shared directory that is + local to your organization. + + + + Regular mirrors can be any site across the Internet that is + used as an alternative location for source code should the + primary site not be functioning for some reason or another. + +
+
+ +
+ Package Feeds + + + When the OpenEmbedded build system generates an image or an SDK, + it gets the packages from a package feed area located in the + Build Directory. + The + general Yocto Project Development Environment figure + shows this package feeds area in the upper-right corner. + + + + This section looks a little closer into the package feeds area used + by the build system. + Here is a more detailed look at the area: + + + + + Package feeds are an intermediary step in the build process. + The OpenEmbedded build system provides classes to generate + different package types, and you specify which classes to enable + through the + PACKAGE_CLASSES + variable. + Before placing the packages into package feeds, + the build process validates them with generated output quality + assurance checks through the + insane + class. + + + + The package feed area resides in the Build Directory. + The directory the build system uses to temporarily store packages + is determined by a combination of variables and the particular + package manager in use. + See the "Package Feeds" box in the illustration and note the + information to the right of that area. + In particular, the following defines where package files are + kept: + + DEPLOY_DIR: + Defined as tmp/deploy in the Build + Directory. + + DEPLOY_DIR_*: + Depending on the package manager used, the package type + sub-folder. + Given RPM, IPK, or DEB packaging and tarball creation, the + DEPLOY_DIR_RPM, + DEPLOY_DIR_IPK, + DEPLOY_DIR_DEB, + or + DEPLOY_DIR_TAR, + variables are used, respectively. + + PACKAGE_ARCH: + Defines architecture-specific sub-folders. + For example, packages could exist for the i586 or qemux86 + architectures. + + + + + + BitBake uses the do_package_write_* tasks to + generate packages and place them into the package holding area (e.g. + do_package_write_ipk for IPK packages). + See the + "do_package_write_deb", + "do_package_write_ipk", + "do_package_write_rpm", + and + "do_package_write_tar" + sections for additional information. + As an example, consider a scenario where an IPK packaging manager + is being used and package architecture support for both i586 + and qemux86 exist. + Packages for the i586 architecture are placed in + build/tmp/deploy/ipk/i586, while packages for + the qemux86 architecture are placed in + build/tmp/deploy/ipk/qemux86. + +
+ +
+ BitBake + + + The OpenEmbedded build system uses + BitBake + to produce images. + You can see from the + general Yocto Project Development Environment figure, + the BitBake area consists of several functional areas. + This section takes a closer look at each of those areas. + + + + Separate documentation exists for the BitBake tool. + See the + BitBake User Manual + for reference material on BitBake. + + +
+ Source Fetching + + + The first stages of building a recipe are to fetch and unpack + the source code: + + + + + The + do_fetch + and + do_unpack + tasks fetch the source files and unpack them into the work + directory. + + For every local file (e.g. file://) + that is part of a recipe's + SRC_URI + statement, the OpenEmbedded build system takes a checksum + of the file for the recipe and inserts the checksum into + the signature for the do_fetch. + If any local file has been modified, the + do_fetch task and all tasks that + depend on it are re-executed. + + By default, everything is accomplished in the + Build Directory, + which has a defined structure. + For additional general information on the Build Directory, + see the + "build/" + section in the Yocto Project Reference Manual. + + + + Unpacked source files are pointed to by the + S + variable. + Each recipe has an area in the Build Directory where the + unpacked source code resides. + The name of that directory for any given recipe is defined from + several different variables. + You can see the variables that define these directories + by looking at the figure: + + TMPDIR - + The base directory where the OpenEmbedded build system + performs all its work during the build. + + PACKAGE_ARCH - + The architecture of the built package or packages. + + TARGET_OS - + The operating system of the target device. + + PN - + The name of the built package. + + PV - + The version of the recipe used to build the package. + + PR - + The revision of the recipe used to build the package. + + WORKDIR - + The location within TMPDIR where + a specific package is built. + + S - + Contains the unpacked source files for a given recipe. + + + +
+ +
+ Patching + + + Once source code is fetched and unpacked, BitBake locates + patch files and applies them to the source files: + + + + + The + do_patch + task processes recipes by + using the + SRC_URI + variable to locate applicable patch files, which by default + are *.patch or + *.diff files, or any file if + "apply=yes" is specified for the file in + SRC_URI. + + + + BitBake finds and applies multiple patches for a single recipe + in the order in which it finds the patches. + Patches are applied to the recipe's source files located in the + S + directory. + + + + For more information on how the source directories are + created, see the + "Source Fetching" + section. + +
+ +
+ Configuration and Compilation + + + After source code is patched, BitBake executes tasks that + configure and compile the source code: + + + + + This step in the build process consists of three tasks: + + + do_prepare_recipe_sysroot: + This task sets up the two sysroots in + ${WORKDIR} + (i.e. recipe-sysroot and + recipe-sysroot-native) so that + the sysroots contain the contents of the + do_populate_sysroot + tasks of the recipes on which the recipe + containing the tasks depends. + A sysroot exists for both the target and for the native + binaries, which run on the host system. + + do_configure: + This task configures the source by enabling and + disabling any build-time and configuration options for + the software being built. + Configurations can come from the recipe itself as well + as from an inherited class. + Additionally, the software itself might configure itself + depending on the target for which it is being built. + + + The configurations handled by the + do_configure + task are specific + to source code configuration for the source code + being built by the recipe. + + If you are using the + autotools + class, + you can add additional configuration options by using + the + EXTRA_OECONF + or + PACKAGECONFIG_CONFARGS + variables. + For information on how this variable works within + that class, see the + meta/classes/autotools.bbclass file. + + do_compile: + Once a configuration task has been satisfied, BitBake + compiles the source using the + do_compile + task. + Compilation occurs in the directory pointed to by the + B + variable. + Realize that the B directory is, by + default, the same as the + S + directory. + do_install: + Once compilation is done, BitBake executes the + do_install + task. + This task copies files from the B + directory and places them in a holding area pointed to + by the + D + variable. + + +
+ +
+ Package Splitting + + + After source code is configured and compiled, the + OpenEmbedded build system analyzes + the results and splits the output into packages: + + + + + The + do_package + and + do_packagedata + tasks combine to analyze + the files found in the + D directory + and split them into subsets based on available packages and + files. + The analyzing process involves the following as well as other + items: splitting out debugging symbols, + looking at shared library dependencies between packages, + and looking at package relationships. + The do_packagedata task creates package + metadata based on the analysis such that the + OpenEmbedded build system can generate the final packages. + Working, staged, and intermediate results of the analysis + and package splitting process use these areas: + + PKGD - + The destination directory for packages before they are + split. + + PKGDATA_DIR - + A shared, global-state directory that holds data + generated during the packaging process. + + PKGDESTWORK - + A temporary work area used by the + do_package task. + + PKGDEST - + The parent directory for packages after they have + been split. + + + The FILES + variable defines the files that go into each package in + PACKAGES. + If you want details on how this is accomplished, you can + look at the + package + class. + + + + Depending on the type of packages being created (RPM, DEB, or + IPK), the do_package_write_* task + creates the actual packages and places them in the + Package Feed area, which is + ${TMPDIR}/deploy. + You can see the + "Package Feeds" + section for more detail on that part of the build process. + + Support for creating feeds directly from the + deploy/* directories does not exist. + Creating such feeds usually requires some kind of feed + maintenance mechanism that would upload the new packages + into an official package feed (e.g. the + Ångström distribution). + This functionality is highly distribution-specific + and thus is not provided out of the box. + + +
+ +
+ Image Generation + + + Once packages are split and stored in the Package Feeds area, + the OpenEmbedded build system uses BitBake to generate the + root filesystem image: + + + + + The image generation process consists of several stages and + depends on several tasks and variables. + The + do_rootfs + task creates the root filesystem (file and directory structure) + for an image. + This task uses several key variables to help create the list + of packages to actually install: + + IMAGE_INSTALL: + Lists out the base set of packages to install from + the Package Feeds area. + PACKAGE_EXCLUDE: + Specifies packages that should not be installed. + + IMAGE_FEATURES: + Specifies features to include in the image. + Most of these features map to additional packages for + installation. + PACKAGE_CLASSES: + Specifies the package backend to use and consequently + helps determine where to locate packages within the + Package Feeds area. + IMAGE_LINGUAS: + Determines the language(s) for which additional + language support packages are installed. + + PACKAGE_INSTALL: + The final list of packages passed to the package manager + for installation into the image. + + + + + + With + IMAGE_ROOTFS + pointing to the location of the filesystem under construction and + the PACKAGE_INSTALL variable providing the + final list of packages to install, the root file system is + created. + + + + Package installation is under control of the package manager + (e.g. dnf/rpm, opkg, or apt/dpkg) regardless of whether or + not package management is enabled for the target. + At the end of the process, if package management is not + enabled for the target, the package manager's data files + are deleted from the root filesystem. + As part of the final stage of package installation, postinstall + scripts that are part of the packages are run. + Any scripts that fail to run + on the build host are run on the target when the target system + is first booted. + If you are using a + read-only root filesystem, + all the post installation scripts must succeed during the + package installation phase since the root filesystem is + read-only. + + + + The final stages of the do_rootfs task + handle post processing. + Post processing includes creation of a manifest file and + optimizations. + + + + The manifest file (.manifest) resides + in the same directory as the root filesystem image. + This file lists out, line-by-line, the installed packages. + The manifest file is useful for the + testimage + class, for example, to determine whether or not to run + specific tests. + See the + IMAGE_MANIFEST + variable for additional information. + + + + Optimizing processes run across the image include + mklibs, prelink, + and any other post-processing commands as defined by the + ROOTFS_POSTPROCESS_COMMAND + variable. + The mklibs process optimizes the size + of the libraries, while the + prelink process optimizes the dynamic + linking of shared libraries to reduce start up time of + executables. + + + + After the root filesystem is built, processing begins on + the image through the + do_image + task. + The build system runs any pre-processing commands as defined + by the + IMAGE_PREPROCESS_COMMAND + variable. + This variable specifies a list of functions to call before + the OpenEmbedded build system creates the final image output + files. + + + + The OpenEmbedded build system dynamically creates + do_image_* tasks as needed, based + on the image types specified in the + IMAGE_FSTYPES + variable. + The process turns everything into an image file or a set of + image files and compresses the root filesystem image to reduce + the overall size of the image. + The formats used for the root filesystem depend on the + IMAGE_FSTYPES variable. + + + + As an example, a dynamically created task when creating a + particular image type would take the + following form: + + do_image_type[depends] + + So, if the type as specified by the + IMAGE_FSTYPES were + ext4, the dynamically generated task + would be as follows: + + do_image_ext4[depends] + + + + + The final task involved in image creation is the + do_image_complete + task. + This task completes the image by applying any image + post processing as defined through the + IMAGE_POSTPROCESS_COMMAND + variable. + The variable specifies a list of functions to call once the + OpenEmbedded build system has created the final image output + files. + + + + The entire image generation process is run under Pseudo. + Running under Pseudo ensures that the files in the root + filesystem have correct ownership. + +
+ +
+ SDK Generation + + + The OpenEmbedded build system uses BitBake to generate the + Software Development Kit (SDK) installer script for both the + standard and extensible SDKs: + + + + + For more information on the cross-development toolchain + generation, see the + "Cross-Development Toolchain Generation" + section. + For information on advantages gained when building a + cross-development toolchain using the + do_populate_sdk + task, see the + "Building an SDK Installer" + section in the Yocto Project Application Development and the + Extensible Software Development Kit (SDK) manual. + + + + Like image generation, the SDK script process consists of + several stages and depends on many variables. + The do_populate_sdk and + do_populate_sdk_ext tasks use these + key variables to help create the list of packages to actually + install. + For information on the variables listed in the figure, see the + "Application Development SDK" + section. + + + + The do_populate_sdk task helps create + the standard SDK and handles two parts: a target part and a + host part. + The target part is the part built for the target hardware and + includes libraries and headers. + The host part is the part of the SDK that runs on the + SDKMACHINE. + + + + The do_populate_sdk_ext task helps create + the extensible SDK and handles host and target parts + differently than its counter part does for the standard SDK. + For the extensible SDK, the task encapsulates the build system, + which includes everything needed (host and target) for the SDK. + + + + Regardless of the type of SDK being constructed, the + tasks perform some cleanup after which a cross-development + environment setup script and any needed configuration files + are created. + The final output is the Cross-development + toolchain installation script (.sh file), + which includes the environment setup script. + +
+ +
+ Stamp Files and the Rerunning of Tasks + + + For each task that completes successfully, BitBake writes a + stamp file into the + STAMPS_DIR + directory. + The beginning of the stamp file's filename is determined by the + STAMP + variable, and the end of the name consists of the task's name + and current + input checksum. + + This naming scheme assumes that + BB_SIGNATURE_HANDLER + is "OEBasicHash", which is almost always the case in + current OpenEmbedded. + + To determine if a task needs to be rerun, BitBake checks if a + stamp file with a matching input checksum exists for the task. + If such a stamp file exists, the task's output is assumed to + exist and still be valid. + If the file does not exist, the task is rerun. + + The stamp mechanism is more general than the shared + state (sstate) cache mechanism described in the + "Setscene Tasks and Shared State" + section. + BitBake avoids rerunning any task that has a valid + stamp file, not just tasks that can be accelerated through + the sstate cache. + However, you should realize that stamp files only + serve as a marker that some work has been done and that + these files do not record task output. + The actual task output would usually be somewhere in + TMPDIR + (e.g. in some recipe's + WORKDIR.) + What the sstate cache mechanism adds is a way to cache task + output that can then be shared between build machines. + + + Since STAMPS_DIR is usually a subdirectory + of TMPDIR, removing + TMPDIR will also remove + STAMPS_DIR, which means tasks will + properly be rerun to repopulate TMPDIR. + + + + If you want some task to always be considered "out of date", + you can mark it with the + nostamp + varflag. + If some other task depends on such a task, then that task will + also always be considered out of date, which might not be what + you want. + + + + For details on how to view information about a task's + signature, see the + "Viewing Task Variable Dependencies" + section in the Yocto Project Development Tasks Manual. + +
+ +
+ Setscene Tasks and Shared State + + + The description of tasks so far assumes that BitBake needs to + build everything and there are no prebuilt objects available. + BitBake does support skipping tasks if prebuilt objects are + available. + These objects are usually made available in the form of a + shared state (sstate) cache. + + For information on variables affecting sstate, see the + SSTATE_DIR + and + SSTATE_MIRRORS + variables. + + + + + The idea of a setscene task (i.e + do_taskname_setscene) + is a version of the task where + instead of building something, BitBake can skip to the end + result and simply place a set of files into specific locations + as needed. + In some cases, it makes sense to have a setscene task variant + (e.g. generating package files in the + do_package_write_* task). + In other cases, it does not make sense, (e.g. a + do_patch + task or + do_unpack + task) since the work involved would be equal to or greater than + the underlying task. + + + + In the OpenEmbedded build system, the common tasks that have + setscene variants are + do_package, + do_package_write_*, + do_deploy, + do_packagedata, + and + do_populate_sysroot. + Notice that these are most of the tasks whose output is an + end result. + + + + The OpenEmbedded build system has knowledge of the relationship + between these tasks and other tasks that precede them. + For example, if BitBake runs + do_populate_sysroot_setscene for + something, there is little point in running any of the + do_fetch, do_unpack, + do_patch, + do_configure, + do_compile, and + do_install tasks. + However, if do_package needs to be run, + BitBake would need to run those other tasks. + + + + It becomes more complicated if everything can come from an + sstate cache because some objects are simply not required at + all. + For example, you do not need a compiler or native tools, such + as quilt, if there is nothing to compile or patch. + If the do_package_write_* packages are + available from sstate, BitBake does not need the + do_package task data. + + + + To handle all these complexities, BitBake runs in two phases. + The first is the "setscene" stage. + During this stage, BitBake first checks the sstate cache for + any targets it is planning to build. + BitBake does a fast check to see if the object exists rather + than a complete download. + If nothing exists, the second phase, which is the setscene + stage, completes and the main build proceeds. + + + + If objects are found in the sstate cache, the OpenEmbedded + build system works backwards from the end targets specified + by the user. + For example, if an image is being built, the OpenEmbedded build + system first looks for the packages needed for that image and + the tools needed to construct an image. + If those are available, the compiler is not needed. + Thus, the compiler is not even downloaded. + If something was found to be unavailable, or the download or + setscene task fails, the OpenEmbedded build system then tries + to install dependencies, such as the compiler, from the cache. + + + + The availability of objects in the sstate cache is handled by + the function specified by the + BB_HASHCHECK_FUNCTION + variable and returns a list of the objects that are available. + The function specified by the + BB_SETSCENE_DEPVALID + variable is the function that determines whether a given + dependency needs to be followed, and whether for any given + relationship the function needs to be passed. + The function returns a True or False value. + +
+
+ +
+ Images + + + The images produced by the OpenEmbedded build system + are compressed forms of the + root filesystem that are ready to boot on a target device. + You can see from the + general Yocto Project Development Environment figure + that BitBake output, in part, consists of images. + This section is going to look more closely at this output: + + + + + For a list of example images that the Yocto Project provides, + see the + "Images" + chapter in the Yocto Project Reference Manual. + + + + Images are written out to the + Build Directory + inside the + tmp/deploy/images/machine/ + folder as shown in the figure. + This folder contains any files expected to be loaded on the + target device. + The + DEPLOY_DIR + variable points to the deploy directory, + while the + DEPLOY_DIR_IMAGE + variable points to the appropriate directory containing images for + the current configuration. + + kernel-image: + A kernel binary file. + The + KERNEL_IMAGETYPE + variable setting determines the naming scheme for the + kernel image file. + Depending on that variable, the file could begin with + a variety of naming strings. + The deploy/images/machine + directory can contain multiple image files for the + machine. + root-filesystem-image: + Root filesystems for the target device (e.g. + *.ext3 or *.bz2 + files). + The + IMAGE_FSTYPES + variable setting determines the root filesystem image + type. + The deploy/images/machine + directory can contain multiple root filesystems for the + machine. + kernel-modules: + Tarballs that contain all the modules built for the kernel. + Kernel module tarballs exist for legacy purposes and + can be suppressed by setting the + MODULE_TARBALL_DEPLOY + variable to "0". + The deploy/images/machine + directory can contain multiple kernel module tarballs + for the machine. + bootloaders: + Bootloaders supporting the image, if applicable to the + target machine. + The deploy/images/machine + directory can contain multiple bootloaders for the + machine. + symlinks: + The deploy/images/machine + folder contains + a symbolic link that points to the most recently built file + for each machine. + These links might be useful for external scripts that + need to obtain the latest version of each file. + + + +
+ +
+ Application Development SDK + + + In the + general Yocto Project Development Environment figure, + the output labeled "Application Development SDK" represents an + SDK. + The SDK generation process differs depending on whether you build + a standard SDK + (e.g. bitbake -c populate_sdk imagename) + or an extensible SDK + (e.g. bitbake -c populate_sdk_ext imagename). + This section is going to take a closer look at this output: + + + + + The specific form of this output is a self-extracting + SDK installer (*.sh) that, when run, + installs the SDK, which consists of a cross-development + toolchain, a set of libraries and headers, and an SDK + environment setup script. + Running this installer essentially sets up your + cross-development environment. + You can think of the cross-toolchain as the "host" + part because it runs on the SDK machine. + You can think of the libraries and headers as the "target" + part because they are built for the target hardware. + The environment setup script is added so that you can initialize + the environment before using the tools. + + + Notes + + + The Yocto Project supports several methods by which you can + set up this cross-development environment. + These methods include downloading pre-built SDK installers + or building and installing your own SDK installer. + + + For background information on cross-development toolchains + in the Yocto Project development environment, see the + "Cross-Development Toolchain Generation" + section. + + + For information on setting up a cross-development + environment, see the + Yocto Project Application Development and the Extensible Software Development Kit (eSDK) + manual. + + + + + + Once built, the SDK installers are written out to the + deploy/sdk folder inside the + Build Directory + as shown in the figure at the beginning of this section. + Depending on the type of SDK, several variables exist that help + configure these files. + The following list shows the variables associated with a standard + SDK: + + DEPLOY_DIR: + Points to the deploy + directory. + SDKMACHINE: + Specifies the architecture of the machine + on which the cross-development tools are run to + create packages for the target hardware. + + SDKIMAGE_FEATURES: + Lists the features to include in the "target" part + of the SDK. + + TOOLCHAIN_HOST_TASK: + Lists packages that make up the host + part of the SDK (i.e. the part that runs on + the SDKMACHINE). + When you use + bitbake -c populate_sdk imagename + to create the SDK, a set of default packages + apply. + This variable allows you to add more packages. + + TOOLCHAIN_TARGET_TASK: + Lists packages that make up the target part + of the SDK (i.e. the part built for the + target hardware). + + SDKPATH: + Defines the default SDK installation path offered by the + installation script. + + + This next list, shows the variables associated with an extensible + SDK: + + DEPLOY_DIR: + Points to the deploy directory. + + SDK_EXT_TYPE: + Controls whether or not shared state artifacts are copied + into the extensible SDK. + By default, all required shared state artifacts are copied + into the SDK. + + SDK_INCLUDE_PKGDATA: + Specifies whether or not packagedata will be included in + the extensible SDK for all recipes in the "world" target. + + SDK_INCLUDE_TOOLCHAIN: + Specifies whether or not the toolchain will be included + when building the extensible SDK. + + SDK_LOCAL_CONF_WHITELIST: + A list of variables allowed through from the build system + configuration into the extensible SDK configuration. + + SDK_LOCAL_CONF_BLACKLIST: + A list of variables not allowed through from the build + system configuration into the extensible SDK configuration. + + SDK_INHERIT_BLACKLIST: + A list of classes to remove from the + INHERIT + value globally within the extensible SDK configuration. + + + +
+
+ + + diff --git a/documentation/concepts-manual/concepts-manual-eclipse-customization.xsl b/documentation/concepts-manual/concepts-manual-eclipse-customization.xsl new file mode 100644 index 0000000000..17fff727f9 --- /dev/null +++ b/documentation/concepts-manual/concepts-manual-eclipse-customization.xsl @@ -0,0 +1,35 @@ + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/documentation/concepts-manual/concepts-manual-intro.xml b/documentation/concepts-manual/concepts-manual-intro.xml new file mode 100644 index 0000000000..51a21b6e23 --- /dev/null +++ b/documentation/concepts-manual/concepts-manual-intro.xml @@ -0,0 +1,103 @@ + %poky; ] > + + + +The Yocto Project Overview Manual +
+ Welcome + + + Welcome to the Yocto Project Overview Manual! + This manual introduces the Yocto Project by providing concepts, + software overviews, best-known-methods (BKMs), and any other + high-level introductory information suitable for a new Yocto + Project user. + + + + The following list describes what you can get from this manual: + + + Major Topic: + Provide a high-level description of this major topic. + + + Major Topic: + Provide a high-level description of this major topic. + + + Major Topic: + Provide a high-level description of this major topic. + + + Major Topic: + Provide a high-level description of this major topic. + + + + + + This manual does not give you the following: + + + Step-by-step Instructions for Development Tasks: + Instructional procedures reside in other manuals within + the Yocto Project documentation set. + For example, the + Yocto Project Development Tasks Manual + provides examples on how to perform various development + tasks. + As another example, the + Yocto Project Application Development and the Extensible Software Development Kit (eSDK) + manual contains detailed instructions on how to install an + SDK, which is used to develop applications for target + hardware. + + + Reference Material: + This type of material resides in an appropriate reference + manual. + For example, system variables are documented in the + Yocto Project Reference Manual. + As another example, the + Yocto Project Board Support Package (BSP) Developer's Guide + contains reference information on BSPs. + + + Detailed Public Information Not Specific to the + Yocto Project: + For example, exhaustive information on how to use the + Source Control Manager Git is better covered with Internet + searches and official Git Documentation than through the + Yocto Project documentation. + + + +
+ +
+ Other Information + + + Because this manual presents information for many different + topics, supplemental information is recommended for full + comprehension. + For additional introductory information on the Yocto Project, see + the Yocto Project Website. + You can find an introductory to using the Yocto Project by working + through the + Yocto Project Quick Start. + + + + For a comprehensive list of links and other documentation, see the + "Links and Related Documentation" + section in the Yocto Project Reference Manual. + +
+ + diff --git a/documentation/concepts-manual/concepts-manual-style.css b/documentation/concepts-manual/concepts-manual-style.css new file mode 100644 index 0000000000..a03f7dc0c1 --- /dev/null +++ b/documentation/concepts-manual/concepts-manual-style.css @@ -0,0 +1,988 @@ +/* + Generic XHTML / DocBook XHTML CSS Stylesheet. + + Browser wrangling and typographic design by + Oyvind Kolas / pippin@gimp.org + + Customised for Poky by + Matthew Allum / mallum@o-hand.com + + Thanks to: + Liam R. E. 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padding-top: 10px; + position: absolute; + bottom: 0px; + left: 0px; + + background: url('/gfx/footing_bg.png') transparent; +} +*/ + + + + /****************** / + / nasty ie tweaks / +/ ******************/ + +/* +div.heading, div.navheader { + width:expression(document.body.clientWidth + "px"); +} + +div.footing, div.navfooter { + width:expression(document.body.clientWidth + "px"); + margin-left:expression("-5em"); +} +body { + padding:expression("4em 5em 0em 5em"); +} +*/ + + /**************************************** / + / mozilla vendor specific css extensions / +/ ****************************************/ +/* +div.navfooter, div.footing{ + -moz-opacity: 0.8em; +} + +div.figure, +div.table, +div.informalfigure, +div.informaltable, +div.informalexample, +div.example, +.tip, +.warning, +.caution, +.note { + -moz-border-radius: 0.5em; +} + +b.keycap, +.keycap { + -moz-border-radius: 0.3em; +} +*/ + +table tr td table tr td { + display: none; +} + + +hr { + display: none; +} + +table { + border: 0em; +} + + .photo { + float: right; + margin-left: 1.5em; + margin-bottom: 1.5em; + margin-top: 0em; + max-width: 17em; + border: 1px solid gray; + padding: 3px; + background: white; +} + .seperator { + padding-top: 2em; + clear: both; + } + + #validators { + margin-top: 5em; + text-align: right; + color: #777; + } + @media print { + body { + font-size: 8pt; + } + .noprint { + display: none; + } + } + + +.tip, +.note { + background: #f0f0f2; + color: #333; + padding: 20px; + margin: 20px; +} + +.tip h3, +.note h3 { + padding: 0em; + margin: 0em; + font-size: 2em; + font-weight: bold; + color: #333; +} + +.tip a, +.note a { + color: #333; + text-decoration: underline; +} + +.footnote { + font-size: small; + color: #333; +} + +/* Changes the announcement text */ +.tip h3, +.warning h3, +.caution h3, +.note h3 { + font-size:large; + color: #00557D; +} diff --git a/documentation/concepts-manual/concepts-manual.xml b/documentation/concepts-manual/concepts-manual.xml new file mode 100644 index 0000000000..930a202e1a --- /dev/null +++ b/documentation/concepts-manual/concepts-manual.xml @@ -0,0 +1,94 @@ + %poky; ] > + + + + + + + + + + + + Getting Started With Yocto Project + + + + + Scott Rifenbark + + Scotty's Documentation Services, INC + + srifenbark@gmail.com + + + + + + 2.5 + April 2018 + The initial document released with the Yocto Project 2.5 Release. + + + + + ©RIGHT_YEAR; + Linux Foundation + + + + + Permission is granted to copy, distribute and/or modify this document under + the terms of the + Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by + Creative Commons. + + Manual Notes + + + This version of the + Yocto Project Overview Manual + is for the &YOCTO_DOC_VERSION; release of the + Yocto Project. + To be sure you have the latest version of the manual + for this release, use the manual from the + Yocto Project documentation page. + + + For manuals associated with other releases of the Yocto + Project, go to the + Yocto Project documentation page + and use the drop-down "Active Releases" button + and choose the manual associated with the desired + Yocto Project. + + + To report any inaccuracies or problems with this + manual, send an email to the Yocto Project + discussion group at + yocto@yoctoproject.com or log into + the freenode #yocto channel. + + + + + + + + + + + + + + + diff --git a/documentation/concepts-manual/figures/YP-flow-diagram.png b/documentation/concepts-manual/figures/YP-flow-diagram.png new file mode 100644 index 0000000000..8264410504 Binary files /dev/null and b/documentation/concepts-manual/figures/YP-flow-diagram.png differ diff --git a/documentation/concepts-manual/figures/analysis-for-package-splitting.png b/documentation/concepts-manual/figures/analysis-for-package-splitting.png new file mode 100644 index 0000000000..04f2794ea9 Binary files /dev/null and b/documentation/concepts-manual/figures/analysis-for-package-splitting.png differ diff --git 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