Re: [Xen-devel] [PATCH v5 1/8] Kconfig: import kconfig.h from Linux 4.3

[Jonathan Creekmore <jonathan.creekmore@xxxxxxxxx>]

Shannon Zhao writes:

> From: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
>
> To support using CONFIG_ options in C/CPP expressions, import kconfig.h
> from the Linux v4.3 tag (commit id
> 6a13feb9c82803e2b815eca72fa7a9f5561d7861).
>
> CC: Doug Goldstein <cardoe@xxxxxxxxxx>
> Signed-off-by: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> ---
>  xen/include/xen/config.h  |  2 +-
>  xen/include/xen/kconfig.h | 54 
> +++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 55 insertions(+), 1 deletion(-)
>  create mode 100644 xen/include/xen/kconfig.h
>
> diff --git a/xen/include/xen/config.h b/xen/include/xen/config.h
> index 7595599..eeb49db 100644
> --- a/xen/include/xen/config.h
> +++ b/xen/include/xen/config.h
> @@ -7,7 +7,7 @@
>  #ifndef __XEN_CONFIG_H__
>  #define __XEN_CONFIG_H__
>
> -#include <generated/autoconf.h>
> +#include <xen/kconfig.h>
>
>  #ifndef __ASSEMBLY__
>  #include <xen/compiler.h>
> diff --git a/xen/include/xen/kconfig.h b/xen/include/xen/kconfig.h
> new file mode 100644
> index 0000000..d68a7ed
> --- /dev/null
> +++ b/xen/include/xen/kconfig.h
> @@ -0,0 +1,54 @@
> +#ifndef __XEN_KCONFIG_H
> +#define __XEN_KCONFIG_H
> +
> +#include <generated/autoconf.h>
> +
> +/*
> + * Helper macros to use CONFIG_ options in C/CPP expressions. Note that
> + * these only work with boolean and tristate options.
> + */
> +
> +/*
> + * Getting something that works in C and CPP for an arg that may or may
> + * not be defined is tricky.  Here, if we have "#define CONFIG_BOOGER 1"
> + * we match on the placeholder define, insert the "0," for arg1 and generate
> + * the triplet (0, 1, 0).  Then the last step cherry picks the 2nd arg (a 
> one).
> + * When CONFIG_BOOGER is not defined, we generate a (... 1, 0) pair, and when
> + * the last step cherry picks the 2nd arg, we get a zero.
> + */
> +#define __ARG_PLACEHOLDER_1 0,
> +#define config_enabled(cfg) _config_enabled(cfg)
> +#define _config_enabled(value) __config_enabled(__ARG_PLACEHOLDER_##value)
> +#define __config_enabled(arg1_or_junk) ___config_enabled(arg1_or_junk 1, 0)
> +#define ___config_enabled(__ignored, val, ...) val
> +
> +/*
> + * IS_BUILTIN(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y', 0
> + * otherwise. For boolean options, this is equivalent to
> + * IS_ENABLED(CONFIG_FOO).
> + */
> +#define IS_BUILTIN(option) config_enabled(option)
> +
> +/*
> + * IS_MODULE(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'm', 0
> + * otherwise.
> + */
> +#define IS_MODULE(option) config_enabled(option##_MODULE)
> +
> +/*
> + * IS_REACHABLE(CONFIG_FOO) evaluates to 1 if the currently compiled
> + * code can call a function defined in code compiled based on CONFIG_FOO.
> + * This is similar to IS_ENABLED(), but returns false when invoked from
> + * built-in code when CONFIG_FOO is set to 'm'.
> + */
> +#define IS_REACHABLE(option) (config_enabled(option) || \
> +              (config_enabled(option##_MODULE) && config_enabled(MODULE)))
> +
> +/*
> + * IS_ENABLED(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y' or 'm',
> + * 0 otherwise.
> + */
> +#define IS_ENABLED(option) \
> +     (IS_BUILTIN(option) || IS_MODULE(option))
> +
> +#endif /* __XEN_KCONFIG_H */

I am not sure that the complexity of this file is necessary since Xen
does not support loadable modules. Essentially, IS_ENABLED(CONFIG_FOO)
is as simple as #ifdef CONFIG_FOO.

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