sbus: Add sbus_vtable and update codegen to support it

Each interface is a vtable structure derived from
sbus_vtable, in the sense that it has an sbus_vtable
struct as its first argument. This lets us upcast the
interface vtable structure to an sbus_vtable and dispatch
to it dynamically and cleanly.

The interface metadata contains information about which
vtable offset in the interface metadata should be dispatched
to for a given function. This is a common scheme, not only
among dbus implementations, but also compiled languages.

Currently all the vtable functions are of type
sbus_msg_handler_fn. These are the handlers we are familiar
with and perform raw processing of the message. Later commits
will introduce type safe handlers that levelage compile checking
and automatic argument packing/unpacking.

Although this may seem contrived now, the remainder of the
dbus infrastructure work will build on this, including
ofd.Properties, ofd.ObjectManager, ofd.Introspect, compiler
checked type safe unpacking/packing, etc.

The codegen now generates vtable structures for each interface
along-side the metadata, and fills in vtable offsets
appropriately.

It is obviously still possible to hand-craft such vtables and
metadata if needed for a special case.

Once again examples output can be found at:

  src/tests/sbus_codegen_tests_generated.h

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
Reviewed-by: Sumit Bose <sbose@redhat.com>
Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/tests/sbus_codegen_tests_generated.c b/src/tests/sbus_codegen_tests_generated.c
index 556eea12c..ccf612996 100644
--- a/src/tests/sbus_codegen_tests_generated.c
+++ b/src/tests/sbus_codegen_tests_generated.c
@@ -3,6 +3,7 @@
 #include "util/util.h"
 #include "sbus/sssd_dbus.h"
 #include "sbus/sssd_dbus_meta.h"
+#include "sbus_codegen_tests_generated.h"
 
 /* arguments for com.planetexpress.Ship.MoveUniverse */
 const struct sbus_arg_meta com_planetexpress_Ship_MoveUniverse__in[] = {
@@ -23,6 +24,13 @@ const struct sbus_method_meta com_planetexpress_Ship__methods[] = {
         "MoveUniverse", /* name */
         com_planetexpress_Ship_MoveUniverse__in,
         com_planetexpress_Ship_MoveUniverse__out,
+        offsetof(struct com_planetexpress_Ship, MoveUniverse),
+    },
+    {
+        "Crash", /* name */
+        NULL, /* no in_args */
+        NULL, /* no out_args */
+        offsetof(struct com_planetexpress_Ship, crash_now),
     },
     { NULL, }
 };