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>

4 files changed, 65 insertions, 0 deletions

diff --git a/src/tests/sbus_codegen_tests.c b/src/tests/sbus_codegen_tests.c
index 6b2abf8bc..39856fac7 100644
--- a/src/tests/sbus_codegen_tests.c
+++ b/src/tests/sbus_codegen_tests.c
@@ -112,6 +112,38 @@ START_TEST(test_signals)
 }
 END_TEST
 
+static int
+mock_move_universe(DBusMessage *msg, struct sbus_connection *conn)
+{
+    /* not called */
+    return 0;
+}
+
+static int
+mock_crash_now(DBusMessage *msg, struct sbus_connection *conn)
+{
+    /* not called */
+    return 0;
+}
+
+START_TEST(test_vtable)
+{
+    struct com_planetexpress_Ship vtable = {
+        { &com_planetexpress_Ship_meta, 0 },
+        mock_move_universe,
+        mock_crash_now,
+    };
+
+    /*
+     * These are not silly tests:
+     * - Will fail compilation if c-symbol name was not respected
+     * - Will fail if method order was not respected
+     */
+    ck_assert(vtable.crash_now == mock_crash_now);
+    ck_assert(vtable.MoveUniverse == mock_move_universe);
+}
+END_TEST
+
 Suite *create_suite(void)
 {
     Suite *s = suite_create("sbus_codegen");
@@ -123,6 +155,7 @@ Suite *create_suite(void)
     tcase_add_test(tc, test_methods);
     tcase_add_test(tc, test_properties);
     tcase_add_test(tc, test_signals);
+    tcase_add_test(tc, test_vtable);
 
     /* Add all test cases to the test suite */
     suite_add_tcase(s, tc);
diff --git a/src/tests/sbus_codegen_tests.xml b/src/tests/sbus_codegen_tests.xml
index 0def3585a..e571dbc17 100755
--- a/src/tests/sbus_codegen_tests.xml
+++ b/src/tests/sbus_codegen_tests.xml
@@ -29,6 +29,11 @@
         <signal name="BecameSentient">
             <arg name="gender" type="s"/>
         </signal>
+
+        <!-- A method with a specific c name -->
+        <method name="Crash">
+            <annotation value="crash_now" name="org.freedesktop.DBus.GLib.CSymbol"/>
+        </method>
     </interface>
 
     <!--
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, }
 };
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