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Subject: Re: [PATCH] kconfig.h: explain IS_MODULE(), IS_ENABLED()
To:     Bjorn Helgaas <helgaas@kernel.org>, linux-kernel@vger.kernel.org
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Paul Cercueil <paul@crapouillou.net>,
        =?UTF-8?Q?Krzysztof_Wilczy=c5=84ski?= <kw@linux.com>,
        Bjorn Helgaas <bhelgaas@google.com>
References: <20210601213143.1973770-1-helgaas@kernel.org>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <819816a2-be1a-8d63-a26b-31f8caa8c944@infradead.org>
Date:   Tue, 1 Jun 2021 14:53:45 -0700
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On 6/1/21 2:31 PM, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> 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>


Thanks.

> ---
>  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))
>  
> 


-- 
~Randy