From c527fd1f14c27855a37f2e8ac5346ce8d940ced2 Mon Sep 17 00:00:00 2001 From: Tudor Florea Date: Thu, 16 Oct 2014 03:05:19 +0200 Subject: initial commit for Enea Linux 4.0-140929 Migrated from the internal git server on the daisy-enea-point-release branch Signed-off-by: Tudor Florea --- .../bitbake-user-manual-execution.xml | 850 +++++++++++++++++++++ 1 file changed, 850 insertions(+) create mode 100644 bitbake/doc/bitbake-user-manual/bitbake-user-manual-execution.xml (limited to 'bitbake/doc/bitbake-user-manual/bitbake-user-manual-execution.xml') diff --git a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-execution.xml b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-execution.xml new file mode 100644 index 0000000000..8514f23f25 --- /dev/null +++ b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-execution.xml @@ -0,0 +1,850 @@ + + + + Execution + + + The primary purpose for running BitBake is to produce some kind + of output such as an image, a kernel, or a software development + kit. + Of course, you can execute the bitbake + command with options that cause it to execute single tasks, + compile single recipe files, capture or clear data, or simply + return information about the execution environment. + + + + This chapter describes BitBake's execution process from start + to finish when you use it to create an image. + The execution process is launched using the following command + form: + + $ bitbake <target> + + For information on the BitBake command and its options, + see + "The BitBake Command" + section. + + + + Prior to executing BitBake, you should take advantage of parallel + thread execution by setting the + BB_NUMBER_THREADS + variable in your local.conf + configuration file. + + +
+ Parsing the Base Configuration Metadata + + + The first thing BitBake does is parse base configuration + metadata. + Base configuration metadata consists of the + bblayers.conf file to determine what + layers BitBake needs to recognize, all necessary + layer.conf files (one from each layer), + and bitbake.conf. + The data itself is of various types: + + Recipes: + Details about particular pieces of software. + + Class Data: + An abstraction of common build information + (e.g. how to build a Linux kernel). + + Configuration Data: + Machine-specific settings, policy decisions, + and so forth. + Configuration data acts as the glue to bind everything + together. + + + + + The layer.conf files are used to + construct key variables such as + BBPATH + and + BBFILES. + BBPATH is used to search for + configuration and class files under + conf/ and class/ + directories, respectively. + BBFILES is used to find recipe files + (.bb and .bbappend). + If there is no bblayers.conf file, + it is assumed the user has set the BBPATH + and BBFILES directly in the environment. + + + + Next, the bitbake.conf file is searched + using the BBPATH variable that was + just constructed. + The bitbake.conf file may also include other + configuration files using the + include or + require directives. + + + + Prior to parsing configuration files, Bitbake looks + at certain variables, including: + + BB_ENV_WHITELIST + BB_PRESERVE_ENV + BB_ENV_EXTRAWHITE + + BITBAKE_UI + + + You can find information on how to pass environment variables into the BitBake + execution environment in the + "Passing Information Into the Build Task Environment" section. + + + + The base configuration metadata is global + and therefore affects all recipes and tasks that are executed. + + + + BitBake first searches the current working directory for an + optional conf/bblayers.conf configuration file. + This file is expected to contain a + BBLAYERS + variable that is a space delimited list of 'layer' directories. + Recall that if BitBake cannot find a bblayers.conf + file then it is assumed the user has set the BBPATH + and BBFILES directly in the environment. + + + + For each directory (layer) in this list, a conf/layer.conf + file is searched for and parsed with the + LAYERDIR + variable being set to the directory where the layer was found. + The idea is these files automatically setup + BBPATH + and other variables correctly for a given build directory. + + + + BitBake then expects to find the conf/bitbake.conf + file somewhere in the user-specified BBPATH. + That configuration file generally has include directives to pull + in any other metadata such as files specific to the architecture, + the machine, the local environment, and so forth. + + + + Only variable definitions and include directives are allowed + in .conf files. + Some variables directly influence BitBake's behavior. + These variables might have been set from the environment + depending on the environment variables previously + mentioned or set in the configuration files. + The + "Variables Glossary" + chapter presents a full list of variables. + + + + After parsing configuration files, BitBake uses its rudimentary + inheritance mechanism, which is through class files, to inherit + some standard classes. + BitBake parses a class when the inherit directive responsible + for getting that class is encountered. + + + + The base.bbclass file is always included. + Other classes that are specified in the configuration using the + INHERIT + variable are also included. + BitBake searches for class files in a "classes" subdirectory under + the paths in BBPATH in the same way as + configuration files. + + + + A good way to get an idea of the configuration files and + the class files used in your execution environment is to + run the following BitBake command: + + $ bitbake -e > mybb.log + + Examining the top of the mybb.log + shows you the many configuration files and class files + used in your execution environment. + + + + + You need to be aware of how BitBake parses curly braces. + If a recipe uses a closing curly brace within the function and + the character has no leading spaces, BitBake produces a parsing + error. + If you use a pair of curly brace in a shell function, the + closing curly brace must not be located at the start of the line + without leading spaces. + + + + Here is an example that causes BitBake to produce a parsing + error: + + fakeroot create_shar() { + cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh + usage() + { + echo "test" + ###### The following "}" at the start of the line causes a parsing error ###### + } + EOF + } + + Writing the recipe this way avoids the error: + + fakeroot create_shar() { + cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh + usage() + { + echo "test" + ######The following "}" with a leading space at the start of the line avoids the error ###### + } + EOF + } + + + +
+ +
+ Locating and Parsing Recipes + + + During the configuration phase, BitBake will have set + BBFILES. + BitBake now uses it to construct a list of recipes to parse, + along with any append files (.bbappend) + to apply. + BBFILES is a space-separated list of + available files and supports wildcards. + An example would be: + + BBFILES = "/path/to/bbfiles/*.bb /path/to/appends/*.bbappend" + + BitBake parses each recipe and append file located + with BBFILES and stores the values of + various variables into the datastore. + + Append files are applied in the order they are encountered in + BBFILES. + + For each file, a fresh copy of the base configuration is + made, then the recipe is parsed line by line. + Any inherit statements cause BitBake to find and + then parse class files (.bbclass) + using + BBPATH + as the search path. + Finally, BitBake parses in order any append files found in + BBFILES. + + + + One common convention is to use the recipe filename to define + pieces of metadata. + For example, in bitbake.conf the recipe + name and version set + PN and + PV: + + PV = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE'),d)[1] or '1.0'}" + PN = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE'),d)[0] or 'defaultpkgname'}" + + In this example, a recipe called "something_1.2.3.bb" sets + PN to "something" and + PV to "1.2.3". + + + + By the time parsing is complete for a recipe, BitBake + has a list of tasks that the recipe defines and a set of + data consisting of keys and values as well as + dependency information about the tasks. + + + + BitBake does not need all of this information. + It only needs a small subset of the information to make + decisions about the recipe. + Consequently, BitBake caches the values in which it is + interested and does not store the rest of the information. + Experience has shown it is faster to re-parse the metadata than to + try and write it out to the disk and then reload it. + + + + Where possible, subsequent BitBake commands reuse this cache of + recipe information. + The validity of this cache is determined by first computing a + checksum of the base configuration data (see + BB_HASHCONFIG_WHITELIST) + and then checking if the checksum matches. + If that checksum matches what is in the cache and the recipe + and class files have not changed, Bitbake is able to use + the cache. + BitBake then reloads the cached information about the recipe + instead of reparsing it from scratch. + + + + Recipe file collections exist to allow the user to + have multiple repositories of + .bb files that contain the same + exact package. + For example, one could easily use them to make one's + own local copy of an upstream repository, but with + custom modifications that one does not want upstream. + Here is an example: + + BBFILES = "/stuff/openembedded/*/*.bb /stuff/openembedded.modified/*/*.bb" + BBFILE_COLLECTIONS = "upstream local" + BBFILE_PATTERN_upstream = "^/stuff/openembedded/" + BBFILE_PATTERN_local = "^/stuff/openembedded.modified/" + BBFILE_PRIORITY_upstream = "5" + BBFILE_PRIORITY_local = "10" + + + The layers mechanism is now the preferred method of collecting + code. + While the collections code remains, its main use is to set layer + priorities and to deal with overlap (conflicts) between layers. + + +
+ +
+ Preferences and Providers + + + Assuming BitBake has been instructed to execute a target + and that all the recipe files have been parsed, BitBake + starts to figure out how to build the target. + BitBake starts by looking through the + PROVIDES + set in recipe files. + The default PROVIDES for a recipe is its name + (PN), + however, a recipe can provide multiple things. + + + + As an example of adding an extra provider, suppose a recipe named + foo_1.0.bb contained the following: + + PROVIDES += "virtual/bar_1.0" + + The recipe now provides both "foo_1.0" and "virtual/bar_1.0". + The "virtual/" namespace is often used to denote cases where + multiple providers are expected with the user choosing between + them. + Kernels and toolchain components are common cases of this in + OpenEmbedded. + + + + Sometimes a target might have multiple providers. + A common example is "virtual/kernel", which is provided by each + kernel recipe. + Each machine often selects the best kernel provider by using a + line similar to the following in the machine configuration file: + + PREFERRED_PROVIDER_virtual/kernel = "linux-yocto" + + The default + PREFERRED_PROVIDER + is the provider with the same name as the target. + Bitbake iterates through each target it needs to build and + resolves them and their dependencies using this process. + + + + Understanding how providers are chosen is made complicated by the fact + that multiple versions might exist. + BitBake defaults to the highest version of a provider. + Version comparisons are made using the same method as Debian. + You can use the + PREFERRED_VERSION + variable to specify a particular version. + You can influence the order by using the + DEFAULT_PREFERENCE + variable. + By default, files have a preference of "0". + Setting the DEFAULT_PREFERENCE to "-1" makes the + recipe unlikely to be used unless it is explicitly referenced. + Setting the DEFAULT_PREFERENCE to "1" makes it likely the recipe is used. + PREFERRED_VERSION overrides any DEFAULT_PREFERENCE setting. + DEFAULT_PREFERENCE is often used to mark newer and more experimental recipe + versions until they have undergone sufficient testing to be considered stable. + + + + When there are multiple “versions” of a given recipe, + BitBake defaults to selecting the most recent + version, unless otherwise specified. + If the recipe in question has a + DEFAULT_PREFERENCE + set lower than + the other recipes (default is 0), then it will not be + selected. + This allows the person or persons maintaining + the repository of recipe files to specify + their preference for the default selected version. + In addition, the user can specify their preferred version. + + + + If the first recipe is named a_1.1.bb, + then the + PN variable + will be set to “a”, and the + PV + variable will be set to 1.1. + + + + If we then have a recipe named a_1.2.bb, BitBake + will choose 1.2 by default. + However, if we define the following variable in a + .conf file that BitBake parses, we + can change that. + + PREFERRED_VERSION_a = "1.1" + + + + + In summary, BitBake has created a list of providers, which is prioritized, for each target. + +
+ +
+ Dependencies + + + Each target BitBake builds consists of multiple tasks such as + fetch, unpack, + patch, configure, + and compile. + For best performance on multi-core systems, BitBake considers each + task as an independent + entity with its own set of dependencies. + + + + Dependencies are defined through several variables. + You can find information about variables BitBake uses in + the Variables Glossary + near the end of this manual. + At a basic level, it is sufficient to know that BitBake uses the + DEPENDS and + RDEPENDS variables when + calculating dependencies. + + + + For more information on how BitBake handles dependencies, see the + "Dependencies" section. + +
+ +
+ The Task List + + + Based on the generated list of providers and the dependency information, + BitBake can now calculate exactly what tasks it needs to run and in what + order it needs to run them. + The + "Executing Tasks" section has more + information on how BitBake chooses which task to execute next. + + + + The build now starts with BitBake forking off threads up to the limit set in the + BB_NUMBER_THREADS + variable. + BitBake continues to fork threads as long as there are tasks ready to run, + those tasks have all their dependencies met, and the thread threshold has not been + exceeded. + + + + It is worth noting that you can greatly speed up the build time by properly setting + the BB_NUMBER_THREADS variable. + + + + As each task completes, a timestamp is written to the directory specified by the + STAMP variable. + On subsequent runs, BitBake looks in the build directory within + tmp/stampsand does not rerun + tasks that are already completed unless a timestamp is found to be invalid. + Currently, invalid timestamps are only considered on a per + recipe file basis. + So, for example, if the configure stamp has a timestamp greater than the + compile timestamp for a given target, then the compile task would rerun. + Running the compile task again, however, has no effect on other providers + that depend on that target. + + + + The exact format of the stamps is partly configurable. + In modern versions of BitBake, a hash is appended to the + stamp so that if the configuration changes, the stamp becomes + invalid and the task is automatically rerun. + This hash, or signature used, is governed by the signature policy + that is configured (see the + "Checksums (Signatures)" + section for information). + It is also possible to append extra metadata to the stamp using + the "stamp-extra-info" task flag. + For example, OpenEmbedded uses this flag to make some tasks machine-specific. + + + + Some tasks are marked as "nostamp" tasks. + No timestamp file is created when these tasks are run. + Consequently, "nostamp" tasks are always rerun. + + + + For more information on tasks, see the + "Tasks" section. + +
+ +
+ Executing Tasks + + + Tasks can either be a shell task or a Python task. + For shell tasks, BitBake writes a shell script to + ${T}/run.do_taskname.pid + and then executes the script. + The generated shell script contains all the exported variables, + and the shell functions with all variables expanded. + Output from the shell script goes to the file + ${T}/log.do_taskname.pid. + Looking at the expanded shell functions in the run file and + the output in the log files is a useful debugging technique. + + + + For Python tasks, BitBake executes the task internally and logs + information to the controlling terminal. + Future versions of BitBake will write the functions to files + similar to the way shell tasks are handled. + Logging will be handled in a way similar to shell tasks as well. + + + + The order in which BitBake runs the tasks is controlled by its + task scheduler. + It is possible to configure the scheduler and define custom + implementations for specific use cases. + For more information, see these variables that control the + behavior: + + + BB_SCHEDULER + + + BB_SCHEDULERS + + + It is possible to have functions run before and after a task's main + function. + This is done using the "prefuncs" and "postfuncs" flags of the task + that lists the functions to run. + +
+ +
+ Checksums (Signatures) + + + A checksum is a unique signature of a task's inputs. + The signature of a task can be used to determine if a task + needs to be run. + Because it is a change in a task's inputs that triggers running + the task, BitBake needs to detect all the inputs to a given task. + For shell tasks, this turns out to be fairly easy because + BitBake 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, some things should not be included in + the checksum. + First, there is the actual specific build path of a given task - + the working directory. + It does not matter if the working directory changes because it should not + affect the output for target packages. + The simplistic approach for excluding the working directory is to set + it to some fixed value and create the checksum for the "run" script. + BitBake goes one step better and uses the + BB_HASHBASE_WHITELIST + variable to define a list of variables that should never be included + when generating the signatures. + + + + 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 working directory 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. + + + + 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. + This example uses variables from OpenEmbedded to help illustrate + the concept: + + 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 the work directory, which is part of + TMPDIR. + + + + 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 OpenEmbedded 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. + + + + + + It is worth noting that BitBake's "-S" option lets you + debug Bitbake's processing of signatures. + The options passed to -S allow different debugging modes + to be used, either using BitBake's own debug functions + or possibly those defined in the metadata/signature handler + itself. + The simplest parameter to pass is "none", which causes a + set of signature information to be written out into + STAMP_DIR + corresponding to the targets specified. + The other currently available parameter is "printdiff", + which causes BitBake to try to establish the closest + signature match it can (e.g. in the sstate cache) and then + run bitbake-diffsigs over the matches + to determine the stamps and delta where these two + stamp trees diverge. + + It is likely that future versions of BitBake with + provide other signature handlers triggered through + additional "-S" paramters. + + + + + You can find more information on checksum metadata in the + "Task Checksums and Setscene" + section. + +
+ +
+ Setscene + + + The setscene process enables BitBake to handle "pre-built" artifacts. + The ability to handle and reuse these artifacts allows BitBake + the luxury of not having to build something from scratch every time. + Instead, BitBake can use, when possible, existing build artifacts. + + + + BitBake needs to have reliable data indicating whether or not an + artifact is compatible. + Signatures, described in the previous section, provide an ideal + way of representing whether an artifact is compatible. + If a signature is the same, an object can be reused. + + + + If an object can be reused, the problem then becomes how to + replace a given task or set of tasks with the pre-built artifact. + BitBake solves the problem with the "setscene" process. + + + + When BitBake is asked to build a given target, before building anything, + it first asks whether cached information is available for any of the + targets it's building, or any of the intermediate targets. + If cached information is available, BitBake uses this information instead of + running the main tasks. + + + + BitBake first calls the function defined by the + BB_HASHCHECK_FUNCTION + variable with a list of tasks and corresponding + hashes it wants to build. + This function is designed to be fast and returns a list + of the tasks for which it believes in can obtain artifacts. + + + + Next, for each of the tasks that were returned as possibilities, + BitBake executes a setscene version of the task that the possible + artifact covers. + Setscene versions of a task have the string "_setscene" appended to the + task name. + So, for example, the task with the name xxx has + a setscene task named xxx_setscene. + The setscene version of the task executes and provides the necessary + artifacts returning either success or failure. + + + + As previously mentioned, an artifact can cover more than one task. + For example, it is pointless to obtain a compiler if you + already have the compiled binary. + To handle this, BitBake calls the + BB_SETSCENE_DEPVALID + function for each successful setscene task to know whether or not it needs + to obtain the dependencies of that task. + + + + Finally, after all the setscene tasks have executed, BitBake calls the + function listed in + BB_SETSCENE_VERIFY_FUNCTION + with the list of tasks BitBake thinks has been "covered". + The metadata can then ensure that this list is correct and can + inform BitBake that it wants specific tasks to be run regardless + of the setscene result. + + + + You can find more information on setscene metadata in the + "Task Checksums and Setscene" + section. + +
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