From c7c90e121e992eefdf07945e5a6e9cf097b29463 Mon Sep 17 00:00:00 2001 From: Bjorn Helgaas Date: Tue, 1 Jun 2021 16:31:43 -0500 Subject: [PATCH] kconfig.h: explain IS_MODULE(), IS_ENABLED() Extend IS_MODULE() and IS_ENABLED comments to explain why one might use "#if IS_ENABLED(CONFIG_FOO)" instead of "#ifdef CONFIG_FOO". To wit, "#ifdef CONFIG_FOO" is true only for CONFIG_FOO=y, while "#if IS_ENABLED(CONFIG_FOO)" is true for both CONFIG_FOO=y and CONFIG_FOO=m. This is because "CONFIG_FOO=m" in .config does not result in "CONFIG_FOO" being defined. The actual definitions are in autoconf.h, where: CONFIG_FOO=y results in #define CONFIG_FOO 1 CONFIG_FOO=m results in #define CONFIG_FOO_MODULE 1 Signed-off-by: Bjorn Helgaas Acked-by: Randy Dunlap Signed-off-by: Masahiro Yamada --- include/linux/kconfig.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h index cc8fa109cfa3..20d1079e92b4 100644 --- a/include/linux/kconfig.h +++ b/include/linux/kconfig.h @@ -51,7 +51,8 @@ /* * IS_MODULE(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'm', 0 - * otherwise. + * otherwise. CONFIG_FOO=m results in "#define CONFIG_FOO_MODULE 1" in + * autoconf.h. */ #define IS_MODULE(option) __is_defined(option##_MODULE) @@ -66,7 +67,8 @@ /* * IS_ENABLED(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y' or 'm', - * 0 otherwise. + * 0 otherwise. Note that CONFIG_FOO=y results in "#define CONFIG_FOO 1" in + * autoconf.h, while CONFIG_FOO=m results in "#define CONFIG_FOO_MODULE 1". */ #define IS_ENABLED(option) __or(IS_BUILTIN(option), IS_MODULE(option))