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, 19 insertions, 0 deletions

diff --git a/src/tests/sbus_codegen_tests_generated.h b/src/tests/sbus_codegen_tests_generated.h
index c3a23c870..3f7621588 100644
--- a/src/tests/sbus_codegen_tests_generated.h
+++ b/src/tests/sbus_codegen_tests_generated.h
@@ -6,6 +6,25 @@
 #include "sbus/sssd_dbus.h"
 
 /* ------------------------------------------------------------------------
+ * DBus Vtable handler structures
+ *
+ * These structures are filled in by implementors of the different
+ * dbus interfaces to handle method calls.
+ *
+ * Handler functions of type sbus_msg_handler_fn accept raw messages,
+ * other handlers will be typed appropriately. If a handler that is
+ * set to NULL is invoked it will result in a
+ * org.freedesktop.DBus.Error.NotSupported error for the caller.
+ */
+
+/* vtable for com.planetexpress.Ship */
+struct com_planetexpress_Ship {
+    struct sbus_vtable vtable; /* derive from sbus_vtable */
+    sbus_msg_handler_fn MoveUniverse;
+    sbus_msg_handler_fn crash_now;
+};
+
+/* ------------------------------------------------------------------------
  * DBus Interface Metadata
  *
  * These structure definitions are filled in with the information about