bitbake: user-manual-metadata.xml: WIP - Some edits in the checksum area.
(Bitbake rev: f74045d9ac88aece1d6f8d6a95389d01971ffdac) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark
Richard Purdie
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@ -1735,36 +1735,77 @@
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<title>Task Checksums and Setscene</title>
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<para>
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This list is a place holder of content that needs explanation here.
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Items should be moved to appropriate sections below as completed.
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BitBake uses checksums (or signatures) along with the setscene
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to determine if a task needs to be run.
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This section describes the process.
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To help understand how BitBake does this, the section assumes an
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OpenEmbedded metadata-based example.
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</para>
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<para>
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This list is a place holder of content existed from previous work
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on the manual.
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Some or all of it probably needs integrated into the subsections
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that make up this section.
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For now, I have just provided a short glossary-like description
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for each variable.
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Ultimately, this list goes away.
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<itemizedlist>
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<listitem><para><filename>STAMP</filename></para></listitem>
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<listitem><para><filename>STAMPCLEAN</filename></para></listitem>
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<listitem><para><filename>BB_STAMP_WHITELIST</filename></para></listitem>
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<listitem><para><filename>BB_STAMP_POLICY</filename></para></listitem>
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<listitem><para><filename>BB_HASHCHECK_FUNCTION</filename></para></listitem>
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<listitem><para><filename>BB_SETSCENE_VERIFY_FUNCTION</filename></para></listitem>
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<listitem><para><filename>BB_SETSCENE_DEPVALID</filename></para></listitem>
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<listitem><para><filename>BB_TASKHASH</filename></para></listitem>
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<listitem><para><filename>STAMP</filename>:
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The base path to create stamp files.</para></listitem>
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<listitem><para><filename>STAMPCLEAN</filename>
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Again, the base path to create stamp files but can use wildcards
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for matching a range of files for clean operations.
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</para></listitem>
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<listitem><para><filename>BB_STAMP_WHITELIST</filename>
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Lists stamp files that are looked at when the stamp policy
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is "whitelist".
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</para></listitem>
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<listitem><para><filename>BB_STAMP_POLICY</filename>
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Defines the mode for comparing timestamps of stamp files.
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</para></listitem>
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<listitem><para><filename>BB_HASHCHECK_FUNCTION</filename>
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Specifies the name of the function to call during
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the "setscene" part of the task's execution in order
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to validate the list of task hashes.
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</para></listitem>
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<listitem><para><filename>BB_SETSCENE_VERIFY_FUNCTION</filename>
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Specifies a function to call that verifies the list of
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planned task execution before the main task execution
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happens.
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</para></listitem>
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<listitem><para><filename>BB_SETSCENE_DEPVALID</filename>
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Specifies a function BitBake calls that determines
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whether BitBake requires a setscene dependency to
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be met.
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</para></listitem>
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<listitem><para><filename>BB_TASKHASH</filename>
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Within an executing task, this variable holds the hash
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of the task as returned by the currently enabled
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signature generator.
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</para></listitem>
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</itemizedlist>
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</para>
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<section id='setscene'>
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<title>Setscene</title>
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<para>
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This section needs to get the concept of the setscene across.
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The reader needs to know what it is and what it is used for during
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the build process.
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</para>
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</section>
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<section id='checksums'>
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<title>Checksums (Signatures)</title>
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<para>
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BitBake uses checksums (or signatures) along with the setscene
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to determine if a task needs to be run.
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This section describes the process.
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To help understand how BitBake does this, the section assumes an
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OpenEmbedded metadata-based example.
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</para>
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<para>
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The setscene code uses a checksum, which is a unique signature of a task's
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inputs, to determine if a task needs to be run again.
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Because it is a change in a task's inputs that triggers a rerun, the process
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needs to detect all the inputs to a given task.
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A checksum is a unique signature of a task's inputs.
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The setscene code uses a checksum to determine if a task needs
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to be run.
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Because it is a change in a task's inputs that triggers running
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the task, the process needs to detect all the inputs to a given task.
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For shell tasks, this turns out to be fairly easy because
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BitBake generates a "run" shell script for each task and
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it is possible to create a checksum that gives you a good idea of when
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@ -1776,9 +1817,9 @@
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the checksum.
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First, there is the actual specific build path of a given task -
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the working directory.
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It does not matter if the work directory changes because it should not
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It does not matter if the working directory changes because it should not
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affect the output for target packages.
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The simplistic approach for excluding the work directory is to set
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The simplistic approach for excluding the working directory is to set
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it to some fixed value and create the checksum for the "run" script.
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</para>
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