[RFC] Saner typechecking for closures

[Matthew Wilcox <willy@infradead.org>]

What would you think to this?

+++ b/include/linux/delayed_call.h
@@ -14,13 +14,12 @@ struct delayed_call {

 #define DEFINE_DELAYED_CALL(name) struct delayed_call name = {NULL, NULL}

-/* I really wish we had closures with sane typechecking... */
-static inline void set_delayed_call(struct delayed_call *call,
-               void (*fn)(void *), void *arg)
-{
-       call->fn = fn;
-       call->arg = arg;
-}
+/* Typecheck the arg is appropriate for the function */
+#define set_delayed_call(call, _fn, _arg) do {                         \
+       (void)sizeof(_fn(_arg));                                        \
+       (call)->fn = (void (*)(void *))(_fn);                           \
+       (call)->arg = (_arg);                                           \
+} while (0)

 static inline void do_delayed_call(struct delayed_call *call)
 {


That should give us the possibility of passing any pointer
to the function, but gets us away from void pointers.  I did this as a
followup:

-extern void page_put_link(void *);
+extern void page_put_link(struct folio *);

...

-void page_put_link(void *arg)
+void page_put_link(struct folio *folio)
 {
-       put_page(arg);
+       folio_put(folio);
 }
 EXPORT_SYMBOL(page_put_link);

and similar changes to the three callers.

Or is there something newer and shinier we should be using instead of
delayed_call?