vl.c: add HMP help to machine

The help is based on the actual machine properties
exposing only the relevant options.

Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Greg Bellows <greg.bellows@linaro.org>
Message-id: 1418217570-15517-4-git-send-email-marcel.a@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

vl.c

@@ -1423,6 +1423,31 @@ MachineInfoList *qmp_query_machines(Error **errp)
     return mach_list;
 }
 
+static int machine_help_func(QemuOpts *opts, MachineState *machine)
+{
+    ObjectProperty *prop;
+
+    if (!qemu_opt_has_help_opt(opts)) {
+        return 0;
+    }
+
+    QTAILQ_FOREACH(prop, &OBJECT(machine)->properties, node) {
+        if (!prop->set) {
+            continue;
+        }
+
+        error_printf("%s.%s=%s", MACHINE_GET_CLASS(machine)->name,
+                     prop->name, prop->type);
+        if (prop->description) {
+            error_printf(" (%s)\n", prop->description);
+        } else {
+            error_printf("\n");
+        }
+    }
+
+    return 1;
+}
+
 /***********************************************************/
 /* main execution loop */
 
@@ -3758,6 +3783,9 @@ int main(int argc, char **argv, char **envp)
 
     current_machine = MACHINE(object_new(object_class_get_name(
                           OBJECT_CLASS(machine_class))));
+    if (machine_help_func(qemu_get_machine_opts(), current_machine)) {
+        exit(0);
+    }
     object_property_add_child(object_get_root(), "machine",
                               OBJECT(current_machine), &error_abort);
     cpu_exec_init_all();