From b245d469c61cb853b83cbf3b538ee8a20c194cf0 Mon Sep 17 00:00:00 2001 From: "Yann E. MORIN" Date: Sat, 5 Apr 2014 17:21:47 +0200 Subject: [PATCH] manual: add notes about depending on a virtual package Signed-off-by: "Yann E. MORIN" Signed-off-by: Thomas Petazzoni --- docs/manual/adding-packages-virtual.txt | 49 +++++++++++++++++++++++++ 1 file changed, 49 insertions(+) diff --git a/docs/manual/adding-packages-virtual.txt b/docs/manual/adding-packages-virtual.txt index e8820a09a..c1b5a0a4a 100644 --- a/docs/manual/adding-packages-virtual.txt +++ b/docs/manual/adding-packages-virtual.txt @@ -91,3 +91,52 @@ provider, but only if it is selected. Of course, do not forget to add the proper build and runtime dependencies for this package! + +Notes on depending on a virtual package +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +When adding a package that requires a certain +FEATURE+ provided by a virtual +package, you have to use +depends on BR2_PACKAGE_HAS_FEATURE+, like so: + +--------------------------- +config BR2_PACKAGE_HAS_FEATURE + bool + +config BR2_PACKAGE_FOO + bool "foo" + depends on BR2_PACKAGE_HAS_FEATURE +--------------------------- + +Notes on depending on a specific provider +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +If your package really requires a specific provider, then you'll have to +make your package +depends on+ this provider; you can _not_ +select+ a +provider. + +Let's take an example with two providers for a +FEATURE+: + +--------------------------- +config BR2_PACKAGE_HAS_FEATURE + bool + +config BR2_PACKAGE_FOO + bool "foo" + select BR2_PACKAGE_HAS_FEATURE + +config BR2_PACKAGE_BAR + bool "bar" + select BR2_PACKAGE_HAS_FEATURE +--------------------------- + +And you are adding a package that needs +FEATURE+ as provided by +foo+, +but not as provided by +bar+. + +If you were to use +select BR2_PACKAGE_FOO+, then the user would still +be able to select +BR2_PACKAGE_BAR+ in the menuconfig. This would create +a configuration inconsistency, whereby two providers of the same +FEATURE+ +would be enabled at once, one explicitly set by the user, the other +implicitly by your +select+. + +Instead, you have to use +depends on BR2_PACKAGE_FOO+, which avoids any +implicit configuration inconsistency.