如何将Go函数作为参数传递给C函数？

I'm trying to pass a Go function to a C function.

Something like:

stm := C.struct_tray_menu{
    ....
    fn: // definition of method
    ....
}
C.menu_cb(stm);

and pass that into a C function:

static void menu_cb(struct tray_menu *item) {
  (void)item;
  printf("menu: clicked on %s
", item->text);
}

I'd just like to know how to define something like C.function.

the main problem is misunderstanding of definition of go in c. so final code is look like

//export callOnMeGo
func callOnMeGo(in int) int {
    fmt.Printf("Go.callOnMeGo(): called with arg = %d
", in)
    return  in+ 1
}

func main() {

    C.some_c_func((C.callback_fcn)(unsafe.Pointer(C.callOnMeGo_cgo)))
    //dont forget to use (funcDefinedInGO_cgo) for with postfix _cgo

...