Re: sparse using insane amounts of memory

[Sam Ravnborg <sam-uyr5N9Q2VtJg9hUCZPvPmw@public.gmane.org>]

> 
> You can then make it a compile-time failure with something like
> 
> 	extern unsigned int this_doesnt_exist_and_wont_link;
> 
> 	is_contiguous_mask(x) ? (x) : this_doesnt_exist_and_wont_link;
> 
> which returns "x" if it's ok, and an unlinkable expression if it isn't.

Or you can use the already defined macros in kernel.h for this:

/* Force a compilation error if condition is true */
#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))

/* Force a compilation error if condition is true, but also produce a
   result (of value 0 and type size_t), so the expression can be used
   e.g. in a structure initializer (or where-ever else comma expressions
   aren't permitted). */
#define BUILD_BUG_ON_ZERO(e) (sizeof(char[1 - 2 * !!(e)]) - 1)

	Sam