bitbake: bitbake-user-manual: Enhance environment variable discussion.
Fixes [YOCTO #8567] Updated the variable list describing the variables that affect how environment variables are handled. Also updated the section on how those variables are passed. (Bitbake rev: 91cb52b1e77bba9d046239933b5c0513d01e6824) Signed-off-by: Scott Rifenbark <srifenbark@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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@ -42,9 +42,9 @@
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<literallayout class='monospaced'>
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$ grep processor /proc/cpuinfo
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</literallayout>
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This command returns the number of processors, which takes into
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account hyper-threading.
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Thus, a quad-core build host with hyper-threading most likely
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This command returns the number of processors, which takes into
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account hyper-threading.
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Thus, a quad-core build host with hyper-threading most likely
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shows eight processors, which is the value you would then assign to
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<filename>BB_NUMBER_THREADS</filename>.
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</para>
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@ -116,16 +116,35 @@
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Prior to parsing configuration files, Bitbake looks
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at certain variables, including:
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<itemizedlist>
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<listitem><para><link linkend='var-BB_ENV_WHITELIST'><filename>BB_ENV_WHITELIST</filename></link></para></listitem>
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<listitem><para><link linkend='var-BB_PRESERVE_ENV'><filename>BB_PRESERVE_ENV</filename></link></para></listitem>
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<listitem><para><link linkend='var-BB_ENV_EXTRAWHITE'><filename>BB_ENV_EXTRAWHITE</filename></link></para></listitem>
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<listitem><para>
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<link linkend='var-BB_ENV_WHITELIST'><filename>BB_ENV_WHITELIST</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_ENV_EXTRAWHITE'><filename>BB_ENV_EXTRAWHITE</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_PRESERVE_ENV'><filename>BB_PRESERVE_ENV</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_ORIGENV'><filename>BB_ORIGENV</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BITBAKE_UI'><filename>BITBAKE_UI</filename></link>
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</para></listitem>
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</itemizedlist>
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You can find information on how to pass environment variables into the BitBake
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execution environment in the
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"<link linkend='passing-information-into-the-build-task-environment'>Passing Information Into the Build Task Environment</link>" section.
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The first four variables in this list relate to how BitBake treats shell
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environment variables during task execution.
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By default, BitBake cleans the environment variables and provides tight
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control over the shell execution environment.
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However, through the use of these first four variables, you can
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apply your control regarding the
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environment variables allowed to be used by BitBake in the shell
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during execution of tasks.
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See the
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"<link linkend='passing-information-into-the-build-task-environment'>Passing Information Into the Build Task Environment</link>"
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section and the information about these variables in the
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variable glossary for more information on how they work and
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on how to use them.
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</para>
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<para>
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@ -1107,10 +1107,18 @@
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<title>Passing Information Into the Build Task Environment</title>
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<para>
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When running a task, BitBake tightly controls the execution
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When running a task, BitBake tightly controls the shell execution
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environment of the build tasks to make
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sure unwanted contamination from the build machine cannot
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influence the build.
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<note>
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By default, BitBake cleans the environment to include only those
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things exported or listed in its whitelist to ensure that the build
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environment is reproducible and consistent.
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You can prevent this "cleaning" by setting the
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<link linkend='var-BB_PRESERVE_ENV'><filename>BB_PRESERVE_ENV</filename></link>
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variable.
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</note>
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Consequently, if you do want something to get passed into the
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build task environment, you must take these two steps:
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<orderedlist>
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@ -1118,14 +1126,16 @@
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Tell BitBake to load what you want from the environment
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into the datastore.
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You can do so through the
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<link linkend='var-BB_ENV_WHITELIST'><filename>BB_ENV_WHITELIST</filename></link>
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and
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<link linkend='var-BB_ENV_EXTRAWHITE'><filename>BB_ENV_EXTRAWHITE</filename></link>
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variable.
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variables.
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For example, assume you want to prevent the build system from
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accessing your <filename>$HOME/.ccache</filename>
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directory.
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The following command tells BitBake to load
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<filename>CCACHE_DIR</filename> from the environment into
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the datastore:
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The following command "whitelists" the environment variable
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<filename>CCACHE_DIR</filename> causing BitBack to allow that
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variable into the datastore:
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<literallayout class='monospaced'>
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export BB_ENV_EXTRAWHITE="$BB_ENV_EXTRAWHITE CCACHE_DIR"
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</literallayout></para></listitem>
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@ -1174,12 +1184,6 @@
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The previous example returns <filename>BAR</filename> from the original
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execution environment.
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</para>
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<para>
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By default, BitBake cleans the environment to include only those
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things exported or listed in its whitelist to ensure that the build
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environment is reproducible and consistent.
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</para>
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</section>
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</section>
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