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

[Shannon Zhao <zhaoshenglong@xxxxxxxxxx>]

On 2016/1/24 2:42, Andrew Cooper wrote:
> On 23/01/16 17:14, Jonathan Creekmore wrote:
>> 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.
> 
> I would like to be able to convert some of our "#ifdef CONFIG_FOO" code
> into "if ( IS_ENABLED(CONFIG_FOO) )" to reduce the quantity of code-rot
> in often-disabled options.
> 
> However, I agree that we don't want all the module complexity.  i.e.
> IS_ENABLED() is the only one of these we need.
> 
Oh, yes. Will drop other macros.

Thanks,
-- 
Shannon


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