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Recursive dependency issues with kconfig are unavoidable due to some limitations with kconfig, since these issues are recurring provide a hint to the user how they can resolve these dependency issues and also document why such limitation exists. While at it also document a bit of future prospects of ways to enhance Kconfig, including providing formal semantics and evaluation of use of a SAT solver. If you're interested in this work or prospects of it check out the kconfig-sat project wiki [0] and mailing list [1]. [0] http://kernelnewbies.org/KernelProjects/kconfig-sat [1] https://groups.google.com/d/forum/kconfig-sat Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: James Bottomley <jbottomley@odin.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Paul Bolle <pebolle@tiscali.nl> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Takashi Iwai <tiwai@suse.de> Cc: "Yann E. MORIN" <yann.morin.1998@free.fr> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Mate Soos <soos.mate@gmail.com> Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com> Signed-off-by: Michal Marek <mmarek@suse.com>
57 lines
2.2 KiB
Text
57 lines
2.2 KiB
Text
# Simple Kconfig recursive issue
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# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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#
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# Test with:
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#
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# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
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#
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# This Kconfig file has a simple recursive dependency issue. In order to
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# understand why this recursive dependency issue occurs lets consider what
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# Kconfig needs to address. We iterate over what Kconfig needs to address
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# by stepping through the questions it needs to address sequentially.
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#
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# * What values are possible for CORE?
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#
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# CORE_BELL_A_ADVANCED selects CORE, which means that it influences the values
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# that are possible for CORE. So for example if CORE_BELL_A_ADVANCED is 'y',
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# CORE must be 'y' too.
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#
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# * What influences CORE_BELL_A_ADVANCED ?
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#
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# As the name implies CORE_BELL_A_ADVANCED is an advanced feature of
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# CORE_BELL_A so naturally it depends on CORE_BELL_A. So if CORE_BELL_A is 'y'
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# we know CORE_BELL_A_ADVANCED can be 'y' too.
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#
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# * What influences CORE_BELL_A ?
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#
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# CORE_BELL_A depends on CORE, so CORE influences CORE_BELL_A.
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#
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# But that is a problem, because this means that in order to determine
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# what values are possible for CORE we ended up needing to address questions
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# regarding possible values of CORE itself again. Answering the original
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# question of what are the possible values of CORE would make the kconfig
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# tools run in a loop. When this happens Kconfig exits and complains about
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# the "recursive dependency detected" error.
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#
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# Reading the Documentation/kbuild/Kconfig.recursion-issue-01 file it may be
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# obvious that an easy to solution to this problem should just be the removal
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# of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already
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# since CORE_BELL_A depends on CORE. Recursive dependency issues are not always
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# so trivial to resolve, we provide another example below of practical
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# implications of this recursive issue where the solution is perhaps not so
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# easy to understand. Note that matching semantics on the dependency on
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# CORE also consist of a solution to this recursive problem.
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mainmenu "Simple example to demo kconfig recursive dependency issue"
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config CORE
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tristate
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config CORE_BELL_A
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tristate
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depends on CORE
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config CORE_BELL_A_ADVANCED
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tristate
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depends on CORE_BELL_A
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select CORE
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