| # Simple Kconfig recursive issue |
| # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| # |
| # Test with: |
| # |
| # make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig |
| # |
| # This Kconfig file has a simple recursive dependency issue. In order to |
| # understand why this recursive dependency issue occurs lets consider what |
| # Kconfig needs to address. We iterate over what Kconfig needs to address |
| # by stepping through the questions it needs to address sequentially. |
| # |
| # * What values are possible for CORE? |
| # |
| # CORE_BELL_A_ADVANCED selects CORE, which means that it influences the values |
| # that are possible for CORE. So for example if CORE_BELL_A_ADVANCED is 'y', |
| # CORE must be 'y' too. |
| # |
| # * What influences CORE_BELL_A_ADVANCED ? |
| # |
| # As the name implies CORE_BELL_A_ADVANCED is an advanced feature of |
| # CORE_BELL_A so naturally it depends on CORE_BELL_A. So if CORE_BELL_A is 'y' |
| # we know CORE_BELL_A_ADVANCED can be 'y' too. |
| # |
| # * What influences CORE_BELL_A ? |
| # |
| # CORE_BELL_A depends on CORE, so CORE influences CORE_BELL_A. |
| # |
| # But that is a problem, because this means that in order to determine |
| # what values are possible for CORE we ended up needing to address questions |
| # regarding possible values of CORE itself again. Answering the original |
| # question of what are the possible values of CORE would make the kconfig |
| # tools run in a loop. When this happens Kconfig exits and complains about |
| # the "recursive dependency detected" error. |
| # |
| # Reading the Documentation/kbuild/Kconfig.recursion-issue-01 file it may be |
| # obvious that an easy to solution to this problem should just be the removal |
| # of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already |
| # since CORE_BELL_A depends on CORE. Recursive dependency issues are not always |
| # so trivial to resolve, we provide another example below of practical |
| # implications of this recursive issue where the solution is perhaps not so |
| # easy to understand. Note that matching semantics on the dependency on |
| # CORE also consist of a solution to this recursive problem. |
| |
| mainmenu "Simple example to demo kconfig recursive dependency issue" |
| |
| config CORE |
| tristate |
| |
| config CORE_BELL_A |
| tristate |
| depends on CORE |
| |
| config CORE_BELL_A_ADVANCED |
| tristate |
| depends on CORE_BELL_A |
| select CORE |