Re: [PATCH 1/2] mm: convert k{un}map_atomic(p, KM_type) to k{un}map_atomic(p)

Peter Zijlstra
2011-08-29T12:33:12Z

On Fri, 2011-08-26 at 16:40 -0400, Nick Bowler wrote:
> > Extra marks will be awarded for
> > working out how to make unconverted code generate a compile warning ;)
>
> It's possible to (ab)use the C preprocessor to accomplish this sort of
> thing. For instance, consider the following:
>
> #include <stdio.h>
>
> int foo(int x)
> {
> return x;
> }
>
> /* Deprecated; call foo instead. */
> static inline int __attribute__((deprecated)) foo_unconverted(int x, int unused)
> {
> return foo(x);
> }
>
> #define PASTE(a, b) a ## b
> #define PASTE2(a, b) PASTE(a, b)
>
> #define NARG_(_9, _8, _7, _6, _5, _4, _3, _2, _1, n, ...) n
> #define NARG(...) NARG_(__VA_ARGS__, 9, 8, 7, 6, 5, 4, 3, 2, 1, :)
>
> #define foo1(...) foo(__VA_ARGS__)
> #define foo2(...) foo_unconverted(__VA_ARGS__)
> #define foo(...) PASTE2(foo, NARG(__VA_ARGS__)(__VA_ARGS__))

Very neat ;-)