mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-25 05:34:00 +08:00
58 lines
2.2 KiB
Plaintext
58 lines
2.2 KiB
Plaintext
|
# 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
|