CodingStyle recommends IS_ENABLED(CONFIG_FOO) over #ifdef. Add an example of the #ifdef, since it's not completely obvious that in many cases the #ifdef needs to test both CONFIG_FOO and CONFIG_FOO_MODULE. Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> --- Documentation/CodingStyle | 15 +++++++++++++-- include/linux/kconfig.h | 3 ++- 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index a096836..b3e9743 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -911,8 +911,19 @@ The compiler will constant-fold the conditional away, and include or exclude the block of code just as with an #ifdef, so this will not add any runtime overhead. However, this approach still allows the C compiler to see the code inside the block, and check it for correctness (syntax, types, symbol -references, etc). Thus, you still have to use an #ifdef if the code inside the -block references symbols that will not exist if the condition is not met. +references, etc). + +Because the compiler processes the block, you have to use an #ifdef instead +of IS_ENABLED() when code inside the block references symbols that will not +exist if the condition is not met. Different CONFIG_FOO autoconf.h symbols +are generated for modular Kconfig options than for builtin ones, so you +need "#if defined(CONFIG_FOO) || defined(CONFIG_FOO_MODULE)" if FOO can be +a module: + + .config include/generated/autoconf.h + ------------ ---------------------------- + CONFIG_FOO=y #define CONFIG_FOO 1 + CONFIG_FOO=m #define CONFIG_FOO_MODULE 1 At the end of any non-trivial #if or #ifdef block (more than a few lines), place a comment after the #endif on the same line, noting the conditional diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h index 15ec117..51a5f66 100644 --- a/include/linux/kconfig.h +++ b/include/linux/kconfig.h @@ -60,7 +60,8 @@ /* * 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)) -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
