Re: [Qemu-devel] [PATCH RFC v3 30/32] qapi: New QMP command query-schema for QMP schema introspection

[Eric Blake]

On 08/04/2015 09:58 AM, Markus Armbruster wrote:
> Caution, rough edges.
> 

> 
>   The empty object type is used when a command takes no arguments or
>   produces no results.


> +++ b/scripts/qapi.py

> @@ -1050,6 +1054,9 @@ class QAPISchema(object):
>                    ('bool',   'boolean', 'bool',     'false'),
>                    ('any',    'value',   'QObject' + pointer_suffix , 
> 'NULL')]:
>              self._def_builtin_type(*t)
> +        self.the_empty_object_type = QAPISchemaObjectType(':empty', None, 
> None,
> +                                                          [], None)
> +        self._def_entity(self.the_empty_object_type)

We mentioned moving this into its own patch.  In particular, I looked at
what it would take to allow anonymous structs for flat union types:

{ 'union': 'Flat', 'base': 'Base',
  'discriminator': 'type',
  'data': { 'branch1': {},
            'branch2': { 'integer': 'int' } } }

but having _make_implicit_object_type() return None caused subsequent
failures.  Normalizing to always use the special ':empty' might be worth
doing if you hoist this work earlier; here's the diff I was playing with.

And while at it, should types like 'Abort' and 'ChardevDummy' (which are
both intentionally empty) normalize to the same ':empty' type during
introspection, or is it okay if two separate types with the same (lack
of) member contents can result in separate type numbers in the
introspection?

diff --git i/scripts/qapi-commands.py w/scripts/qapi-commands.py
index 7ff7c31..06e6a1e 100644
--- i/scripts/qapi-commands.py
+++ w/scripts/qapi-commands.py
@@ -76,7 +76,7 @@ def gen_marshal_vars(arg_type, ret_type):
 ''',
                      c_type=ret_type.c_type())

-    if arg_type:
+    if arg_type and arg_type.members:
         ret += mcgen('''
 QmpInputVisitor *mi = qmp_input_visitor_new_strict(QOBJECT(args));
 QapiDeallocVisitor *md;
@@ -108,7 +108,7 @@ bool has_%(c_name)s = false;
 def gen_marshal_input_visit(arg_type, dealloc=False):
     ret = ''

-    if not arg_type:
+    if not arg_type or not arg_type.members:
         return ret

     push_indent()
diff --git i/scripts/qapi.py w/scripts/qapi.py
index 34c2884..133b859 100644
--- i/scripts/qapi.py
+++ w/scripts/qapi.py
@@ -1071,7 +1071,7 @@ class QAPISchema(object):

     def _make_implicit_object_type(self, name, role, members):
         if not members:
-            return None
+            return ':empty'
         name = ':obj-%s-%s' % (name, role)
         if not self.lookup_entity(name, QAPISchemaObjectType):
             self._def_entity(QAPISchemaObjectType(name, None, None,
@@ -1155,17 +1155,17 @@ class QAPISchema(object):

     def _def_command(self, expr, info):
         name = expr['command']
-        data = expr.get('data')
+        data = expr.get('data', {})
         rets = expr.get('returns')
         gen = expr.get('gen', True)
         success_response = expr.get('success-response', True)
-        if isinstance(data, OrderedDict):
+        if isinstance(data, dict):
             data = self._make_implicit_object_type(name, 'arg',

self._make_members(data))
         if isinstance(rets, list):
             assert len(rets) == 1
             rets = self._make_array_type(rets[0])
-        elif isinstance(rets, OrderedDict):
+        elif isinstance(rets, dict):
             rets = self._make_implicit_object_type(name, 'ret',

self._make_members(rets))
         self._def_entity(QAPISchemaCommand(name, info, data, rets, gen,
@@ -1173,8 +1173,8 @@ class QAPISchema(object):

     def _def_event(self, expr, info):
         name = expr['event']
-        data = expr.get('data')
-        if isinstance(data, OrderedDict):
+        data = expr.get('data', {})
+        if isinstance(data, dict):
             data = self._make_implicit_object_type(name, 'arg',

self._make_members(data))
         self._def_entity(QAPISchemaEvent(name, info, data))
diff --git i/tests/qapi-schema/event-case.out
w/tests/qapi-schema/event-case.out
index cdfd264..6a84fdd 100644
--- i/tests/qapi-schema/event-case.out
+++ w/tests/qapi-schema/event-case.out
@@ -1,2 +1,2 @@
 object :empty
-event oops None
+event oops :empty
diff --git i/tests/qapi-schema/indented-expr.out
w/tests/qapi-schema/indented-expr.out
index 226d300..8999a6d 100644
--- i/tests/qapi-schema/indented-expr.out
+++ w/tests/qapi-schema/indented-expr.out
@@ -1,5 +1,5 @@
 object :empty
-command eins None -> None
+command eins :empty -> None
    gen=True success_response=True
-command zwei None -> None
+command zwei :empty -> None
    gen=True success_response=True
diff --git i/tests/qapi-schema/qapi-schema-test.out
w/tests/qapi-schema/qapi-schema-test.out
index 386b057..57cae76 100644
--- i/tests/qapi-schema/qapi-schema-test.out
+++ w/tests/qapi-schema/qapi-schema-test.out
@@ -51,8 +51,8 @@ object :obj-user_def_cmd2-arg
 object :obj-user_def_cmd3-arg
     member a: int optional=False
     member b: int optional=True
-event EVENT_A None
-event EVENT_B None
+event EVENT_A :empty
+event EVENT_B :empty
 event EVENT_C :obj-EVENT_C-arg
 event EVENT_D :obj-EVENT_D-arg
 enum EnumOne ['value1', 'value2', 'value3']
@@ -154,7 +154,7 @@ command __org.qemu_x-command
:obj-__org.qemu_x-command-arg -> __org.qemu_x-Union
    gen=True success_response=True
 command guest-sync :obj-guest-sync-arg -> any
    gen=True success_response=True
-command user_def_cmd None -> None
+command user_def_cmd :empty -> None
    gen=True success_response=True
 command user_def_cmd1 :obj-user_def_cmd1-arg -> None
    gen=True success_response=True
diff --git i/tests/qapi-schema/returns-int.out
w/tests/qapi-schema/returns-int.out
index a2da259..29825e8 100644
--- i/tests/qapi-schema/returns-int.out
+++ w/tests/qapi-schema/returns-int.out
@@ -1,3 +1,3 @@
 object :empty
-command guest-get-time None -> int
+command guest-get-time :empty -> int
    gen=True success_response=True


-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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