Messages in this thread | | | Subject | Re: [PATCH 1/2] linux/kconfig.h: generalize IS_ENABLED logic | From | Michal Marek <> | Date | Wed, 7 Oct 2015 10:15:27 +0200 |
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On 2015-10-06 23:05, Rasmus Villemoes wrote: > It's not hard to generalize the macro magic used to build the > IS_ENABLED macro and friends to produce a few other potentially useful > macros: > > CHOOSE_EXPR(CONFIG_FOO, expr): if CONFIG_FOO is set expands to > expr, otherwise expands to nothing. > > CHOOSE_EXPR(CONFIG_FOO, expr1, expr2): if CONFIG_FOO is set, > expands to expr1, otherwise expands to expr2.
FWIW, I agree with Ingo that the CHOOSE_EXPR name is not really obvious. IF_CONFIG is a better alternative IMO, since the average programmer probably does not know __builtin_choose_expr() to see the analogy.
> Similarly, we can define helpers for conditional struct members and > their associated initializers. It would probably take some time to get > used to reading, to pick another random example, > > struct task_struct { > ... > COND_DECLARATION(CONFIG_KASAN, unsigned int kasan_depth) > ... > }
While the C standard syntax requires struct-declaration to actually declare a member, the compiler will happily ignore the extra semicolon if you write
truct task_struct { ... CHOOSE_EXPR(CONFIG_KASAN, unsigned int kasan_depth); ... }
So I think that the COND_DECLARATION macro is not necessary.
> #define INIT_KASAN(tsk) COND_INITIALIZER(CONFIG_KASAN, .kasan_depth = 1)
COND_INITIALIZER on the other hand is useful (CHOOSE_EXPR(CONFIG_KASAN, .kasan_depth = 1 _COMMA) does does not work, unfortunately).
> [and I'm certainly not proposing any mass conversion], but I think it > might be nice to avoid lots of short #ifdef/#else/#endif sections.
It should be accompanied by a patch to scripts/tags.sh teaching ctags/etags about the new macros.
Michal
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