qapi: Add feature flags to commands

Similarly to features for struct types introduce the feature flags also
for commands. This will allow notifying management layers of fixes and
compatible changes in the behaviour of a command which may not be
detectable any other way.

The changes were heavily inspired by commit 6a8c0b5.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20191018081454.21369-3-armbru@redhat.com>

docs/devel/qapi-code-gen.txt

@@ -457,7 +457,8 @@ Syntax:
                 '*gen': false,
                 '*allow-oob': true,
                 '*allow-preconfig': true,
-                '*if': COND }
+                '*if': COND,
+                '*features': FEATURES }
 
 Member 'command' names the command.
 
@@ -640,9 +641,10 @@ change in the QMP syntax (usually by allowing values or operations
 that previously resulted in an error).  QMP clients may still need to
 know whether the extension is available.
 
-For this purpose, a list of features can be specified for a struct type.
-This is exposed to the client as a list of string, where each string
-signals that this build of QEMU shows a certain behaviour.
+For this purpose, a list of features can be specified for a command or
+struct type.  This is exposed to the client as a list of strings,
+where each string signals that this build of QEMU shows a certain
+behaviour.
 
 Each member of the 'features' array defines a feature.  It can either
 be { 'name': STRING, '*if': COND }, or STRING, which is shorthand for

qapi/introspect.json

@@ -266,13 +266,17 @@
 # @allow-oob: whether the command allows out-of-band execution,
 #             defaults to false (Since: 2.12)
 #
+# @features: names of features associated with the command, in no particular
+#            order. (since 4.2)
+#
 # TODO: @success-response (currently irrelevant, because it's QGA, not QMP)
 #
 # Since: 2.5
 ##
 { 'struct': 'SchemaInfoCommand',
   'data': { 'arg-type': 'str', 'ret-type': 'str',
-            '*allow-oob': 'bool' } }
+            '*allow-oob': 'bool',
+            '*features': [ 'str' ] } }
 
 ##
 # @SchemaInfoEvent:

scripts/qapi/commands.py

@@ -277,7 +277,8 @@ def visit_end(self):
         genc.add(gen_registry(self._regy.get_content(), self._prefix))
 
     def visit_command(self, name, info, ifcond, arg_type, ret_type, gen,
-                      success_response, boxed, allow_oob, allow_preconfig):
+                      success_response, boxed, allow_oob, allow_preconfig,
+                      features):
         if not gen:
             return
         # FIXME: If T is a user-defined type, the user is responsible

scripts/qapi/doc.py

@@ -249,12 +249,14 @@ def visit_alternate_type(self, name, info, ifcond, variants):
                                body=texi_entity(doc, 'Members', ifcond)))
 
     def visit_command(self, name, info, ifcond, arg_type, ret_type, gen,
-                      success_response, boxed, allow_oob, allow_preconfig):
+                      success_response, boxed, allow_oob, allow_preconfig,
+                      features):
         doc = self.cur_doc
         if boxed:
             body = texi_body(doc)
             body += ('\n@b{Arguments:} the members of @code{%s}\n'
                      % arg_type.name)
+            body += texi_features(doc)
             body += texi_sections(doc, ifcond)
         else:
             body = texi_entity(doc, 'Arguments', ifcond)

scripts/qapi/expr.py

@@ -185,6 +185,22 @@ def normalize_features(features):
                        for f in features]
 
 
+def check_features(features, info):
+    if features is None:
+        return
+    if not isinstance(features, list):
+        raise QAPISemError(info, "'features' must be an array")
+    for f in features:
+        source = "'features' member"
+        assert isinstance(f, dict)
+        check_keys(f, info, source, ['name'], ['if'])
+        check_name_is_str(f['name'], info, source)
+        source = "%s '%s'" % (source, f['name'])
+        check_name_str(f['name'], info, source)
+        check_if(f, info, source)
+        normalize_if(f)
+
+
 def normalize_enum(expr):
     if isinstance(expr['data'], list):
         expr['data'] = [m if isinstance(m, dict) else {'name': m}
@@ -217,23 +233,10 @@ def check_enum(expr, info):
 def check_struct(expr, info):
     name = expr['struct']
     members = expr['data']
-    features = expr.get('features')
 
     check_type(members, info, "'data'", allow_dict=name)
     check_type(expr.get('base'), info, "'base'")
-
-    if features:
-        if not isinstance(features, list):
-            raise QAPISemError(info, "'features' must be an array")
-        for f in features:
-            source = "'features' member"
-            assert isinstance(f, dict)
-            check_keys(f, info, source, ['name'], ['if'])
-            check_name_is_str(f['name'], info, source)
-            source = "%s '%s'" % (source, f['name'])
-            check_name_str(f['name'], info, source)
-            check_if(f, info, source)
-            normalize_if(f)
+    check_features(expr.get('features'), info)
 
 
 def check_union(expr, info):
@@ -283,6 +286,7 @@ def check_command(expr, info):
         raise QAPISemError(info, "'boxed': true requires 'data'")
     check_type(args, info, "'data'", allow_dict=not boxed)
     check_type(rets, info, "'returns'", allow_array=True)
+    check_features(expr.get('features'), info)
 
 
 def check_event(expr, info):
@@ -358,10 +362,11 @@ def check_exprs(exprs):
         elif meta == 'command':
             check_keys(expr, info, meta,
                        ['command'],
-                       ['data', 'returns', 'boxed', 'if',
+                       ['data', 'returns', 'boxed', 'if', 'features',
                         'gen', 'success-response', 'allow-oob',
                         'allow-preconfig'])
             normalize_members(expr.get('data'))
+            normalize_features(expr.get('features'))
             check_command(expr, info)
         elif meta == 'event':
             check_keys(expr, info, meta,

scripts/qapi/introspect.py

@@ -211,13 +211,18 @@ def visit_alternate_type(self, name, info, ifcond, variants):
                            for m in variants.variants]}, ifcond)
 
     def visit_command(self, name, info, ifcond, arg_type, ret_type, gen,
-                      success_response, boxed, allow_oob, allow_preconfig):
+                      success_response, boxed, allow_oob, allow_preconfig,
+                      features):
         arg_type = arg_type or self._schema.the_empty_object_type
         ret_type = ret_type or self._schema.the_empty_object_type
         obj = {'arg-type': self._use_type(arg_type),
                'ret-type': self._use_type(ret_type)}
         if allow_oob:
             obj['allow-oob'] = allow_oob
+
+        if features:
+            obj['features'] = [(f.name, {'if': f.ifcond}) for f in features]
+
         self._gen_qlit(name, 'command', obj, ifcond)
 
     def visit_event(self, name, info, ifcond, arg_type, boxed):

scripts/qapi/schema.py

@@ -110,7 +110,8 @@ def visit_alternate_type(self, name, info, ifcond, variants):
         pass
 
     def visit_command(self, name, info, ifcond, arg_type, ret_type, gen,
-                      success_response, boxed, allow_oob, allow_preconfig):
+                      success_response, boxed, allow_oob, allow_preconfig,
+                      features):
         pass
 
     def visit_event(self, name, info, ifcond, arg_type, boxed):
@@ -659,10 +660,14 @@ class QAPISchemaCommand(QAPISchemaEntity):
     meta = 'command'
 
     def __init__(self, name, info, doc, ifcond, arg_type, ret_type,
-                 gen, success_response, boxed, allow_oob, allow_preconfig):
+                 gen, success_response, boxed, allow_oob, allow_preconfig,
+                 features):
         QAPISchemaEntity.__init__(self, name, info, doc, ifcond)
         assert not arg_type or isinstance(arg_type, str)
         assert not ret_type or isinstance(ret_type, str)
+        for f in features:
+            assert isinstance(f, QAPISchemaFeature)
+            f.set_defined_in(name)
         self._arg_type_name = arg_type
         self.arg_type = None
         self._ret_type_name = ret_type
@@ -672,6 +677,7 @@ def __init__(self, name, info, doc, ifcond, arg_type, ret_type,
         self.boxed = boxed
         self.allow_oob = allow_oob
         self.allow_preconfig = allow_preconfig
+        self.features = features
 
     def check(self, schema):
         QAPISchemaEntity.check(self, schema)
@@ -701,13 +707,19 @@ def check(self, schema):
                         "command's 'returns' cannot take %s"
                         % self.ret_type.describe())
 
+        # Features are in a name space separate from members
+        seen = {}
+        for f in self.features:
+            f.check_clash(self.info, seen)
+
     def visit(self, visitor):
         QAPISchemaEntity.visit(self, visitor)
         visitor.visit_command(self.name, self.info, self.ifcond,
                               self.arg_type, self.ret_type,
                               self.gen, self.success_response,
                               self.boxed, self.allow_oob,
-                              self.allow_preconfig)
+                              self.allow_preconfig,
+                              self.features)
 
 
 class QAPISchemaEvent(QAPISchemaEntity):
@@ -984,6 +996,7 @@ def _def_command(self, expr, info, doc):
         allow_oob = expr.get('allow-oob', False)
         allow_preconfig = expr.get('allow-preconfig', False)
         ifcond = expr.get('if')
+        features = expr.get('features', [])
         if isinstance(data, OrderedDict):
             data = self._make_implicit_object_type(
                 name, info, doc, ifcond, 'arg', self._make_members(data, info))
@@ -992,7 +1005,8 @@ def _def_command(self, expr, info, doc):
             rets = self._make_array_type(rets[0], info)
         self._def_entity(QAPISchemaCommand(name, info, doc, ifcond, data, rets,
                                            gen, success_response,
-                                           boxed, allow_oob, allow_preconfig))
+                                           boxed, allow_oob, allow_preconfig,
+                                           self._make_features(features, info)))
 
     def _def_event(self, expr, info, doc):
         name = expr['event']

tests/qapi-schema/test-qapi.py

@@ -72,7 +72,8 @@ def visit_alternate_type(self, name, info, ifcond, variants):
         self._print_if(ifcond)
 
     def visit_command(self, name, info, ifcond, arg_type, ret_type, gen,
-                      success_response, boxed, allow_oob, allow_preconfig):
+                      success_response, boxed, allow_oob, allow_preconfig,
+                      features):
         print('command %s %s -> %s'
               % (name, arg_type and arg_type.name,
                  ret_type and ret_type.name))