Messages in this thread | | | From | Rasmus Villemoes <> | Subject | Re: [PATCHSET v2] ->follow_link() without dropping from RCU mode | Date | Fri, 11 Dec 2015 08:49:24 +0100 |
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On Fri, Dec 11 2015, Al Viro <viro@ZenIV.linux.org.uk> wrote:
> I would really love to be able to say > set_delayed_call(done, kfree, p); > but as it is I had to keep a wrapper - void kfree_link(void *). The problem > is, you can't assign void f(const void *) to void (*p)(void *) - mismatch of > qualifiers in the arguments makes the latter not assignment-compatible with > the former. If there's a clever trick allowing to sidestep that, I'd be > very happy; I don't know one. Any ideas not starting with "use C11" (or, > worse yet, "use such and such C++ misfeature with arseloads of RTL required > in order to implement it") would be welcome...
I _think_ this satisfies these very reasonable criteria. What you're looking for is presumably __attribute__((__transparent_union__)). At least this compiles without warnings at -Wall -Wextra and gives the expected disassembly, and the gcc docs mention transparent_union at least back to 4.0.4.
#include <stddef.h>
struct delayed_call { void (*fn)(void *); void *arg; }; union delayed_call_fn { void (*fn)(void *); void (*kfree_like)(const void *); } __attribute__((__transparent_union__));
void set_delayed_call(struct delayed_call *call, union delayed_call_fn u, void *arg) { call->fn = u.fn; call->arg = arg; }
void some_cb(void *); void kfree(const void *); extern struct delayed_call done;
void test(void) { set_delayed_call(&done, some_cb, NULL); set_delayed_call(&done, kfree, NULL); }
Rasmus
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