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authorBjorn Helgaas <bhelgaas@google.com>2021-06-02 00:31:43 +0300
committerMasahiro Yamada <masahiroy@kernel.org>2021-06-05 17:49:46 +0300
commitc7c90e121e992eefdf07945e5a6e9cf097b29463 (patch)
treeecf6d93c6f42294695b874c2d78e3d058dc52380 /include/linux/kconfig.h
parent43ac711053fc6d94a3f16141c4efe20059a9d918 (diff)
downloadlinux-c7c90e121e992eefdf07945e5a6e9cf097b29463.tar.xz
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 <bhelgaas@google.com> Acked-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Diffstat (limited to 'include/linux/kconfig.h')
-rw-r--r--include/linux/kconfig.h6
1 files 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))