diff --git a/qapi/introspect.json b/qapi/introspect.json
index 3d22166b2b..3cb6c1aca4 100644
--- a/qapi/introspect.json
+++ b/qapi/introspect.json
@@ -174,6 +174,11 @@
 #            and may even differ from the order of the values of the
 #            enum type of the @tag.
 #
+# @features: names of features that are supported by this version and build and
+#            aren't othervise visible through schema introspection (e.g. change
+#            of behaviour related to an object type that didn't come with a
+#            syntactic change in the schema of the object type) (since: 4.1)
+#
 # Values of this type are JSON object on the wire.
 #
 # Since: 2.5
@@ -181,7 +186,8 @@
 { 'struct': 'SchemaInfoObject',
   'data': { 'members': [ 'SchemaInfoObjectMember' ],
             '*tag': 'str',
-            '*variants': [ 'SchemaInfoObjectVariant' ] } }
+            '*variants': [ 'SchemaInfoObjectVariant' ],
+            '*features': [ 'str' ] } }
 
 ##
 # @SchemaInfoObjectMember:
diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt
index b517b0cfbf..e8ec8ac1de 100644
--- a/docs/devel/qapi-code-gen.txt
+++ b/docs/devel/qapi-code-gen.txt
@@ -719,6 +719,34 @@ any non-empty complex type (struct, union, or alternate), and a
 pointer to that QAPI type is passed as a single argument.
 
 
+=== Features ===
+
+Sometimes, the behaviour of QEMU changes compatibly, but without a
+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.
+
+In the schema, features can be specified as simple strings, for example:
+
+{ 'struct': 'TestType',
+  'data': { 'number': 'int' },
+  'features': [ 'allow-negative-numbers' ] }
+
+Another option is to specify features as dictionaries, where the key
+'name' specifies the feature string to be exposed to clients:
+
+{ 'struct': 'TestType',
+  'data': { 'number': 'int' },
+  'features': [ { 'name': 'allow-negative-numbers' } ] }
+
+This expanded form is necessary if you want to make the feature
+conditional (see below in "Configuring the schema").
+
+
 === Downstream extensions ===
 
 QAPI schema names that are externally visible, say in the Client JSON
@@ -771,6 +799,16 @@ Example: a conditional 'bar' enum member.
   [ 'foo',
     { 'name' : 'bar', 'if': 'defined(IFCOND)' } ] }
 
+Similarly, features can be specified as a dictionary with a 'name' and
+an 'if' key.
+
+Example: a conditional 'allow-negative-numbers' feature
+
+{ 'struct': 'TestType',
+  'data': { 'number': 'int' },
+  'features': [ { 'name': 'allow-negative-numbers',
+                  'if' 'defined(IFCOND)' } ] }
+
 Please note that you are responsible to ensure that the C code will
 compile with an arbitrary combination of conditions, since the
 generators are unable to check it at this point.
diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
index f07869ec73..692d787f04 100644
--- a/scripts/qapi/common.py
+++ b/scripts/qapi/common.py
@@ -886,12 +886,29 @@ def check_enum(expr, info):
 def check_struct(expr, info):
     name = expr['struct']
     members = expr['data']
+    features = expr.get('features')
 
     check_type(info, "'data' for struct '%s'" % name, members,
                allow_dict=True, allow_optional=True)
     check_type(info, "'base' for struct '%s'" % name, expr.get('base'),
                allow_metas=['struct'])
 
+    if features:
+        if not isinstance(features, list):
+            raise QAPISemError(info,
+                               "Struct '%s' requires an array for 'features'" %
+                               name)
+        for f in features:
+            assert isinstance(f, dict)
+            check_known_keys(info, "feature of struct %s" % (name), f,
+                             ['name'], ['if'])
+
+            check_if(f, info)
+            f['if'] = listify_cond(f.get('if'))
+
+            if not isinstance(f['name'], str):
+                raise QAPISemError(info, "Feature names for struct '%s' must "
+                                         "be strings" % name)
 
 def check_known_keys(info, source, keys, required, optional):
 
@@ -947,6 +964,10 @@ def normalize_members(members):
                 continue
             members[key] = {'type': arg}
 
+def normalize_features(features):
+    if isinstance(features, list):
+        features[:] = [f if isinstance(f, dict) else {'name': f}
+                       for f in features]
 
 def check_exprs(exprs):
     global all_names
@@ -986,8 +1007,10 @@ def check_exprs(exprs):
             normalize_members(expr['data'])
         elif 'struct' in expr:
             meta = 'struct'
-            check_keys(expr_elem, 'struct', ['data'], ['base', 'if'])
+            check_keys(expr_elem, 'struct', ['data'],
+                       ['base', 'if', 'features'])
             normalize_members(expr['data'])
+            normalize_features(expr.get('features'))
             struct_types[expr[meta]] = expr
         elif 'command' in expr:
             meta = 'command'
@@ -1126,10 +1149,12 @@ class QAPISchemaVisitor(object):
     def visit_array_type(self, name, info, ifcond, element_type):
         pass
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         pass
 
-    def visit_object_type_flat(self, name, info, ifcond, members, variants):
+    def visit_object_type_flat(self, name, info, ifcond, members, variants,
+                               features):
         pass
 
     def visit_alternate_type(self, name, info, ifcond, variants):
@@ -1290,7 +1315,7 @@ class QAPISchemaArrayType(QAPISchemaType):
 
 class QAPISchemaObjectType(QAPISchemaType):
     def __init__(self, name, info, doc, ifcond,
-                 base, local_members, variants):
+                 base, local_members, variants, features):
         # struct has local_members, optional base, and no variants
         # flat union has base, variants, and no local_members
         # simple union has local_members, variants, and no base
@@ -1307,6 +1332,7 @@ class QAPISchemaObjectType(QAPISchemaType):
         self.local_members = local_members
         self.variants = variants
         self.members = None
+        self.features = features
 
     def check(self, schema):
         QAPISchemaType.check(self, schema)
@@ -1368,9 +1394,11 @@ class QAPISchemaObjectType(QAPISchemaType):
 
     def visit(self, visitor):
         visitor.visit_object_type(self.name, self.info, self.ifcond,
-                                  self.base, self.local_members, self.variants)
+                                  self.base, self.local_members, self.variants,
+                                  self.features)
         visitor.visit_object_type_flat(self.name, self.info, self.ifcond,
-                                       self.members, self.variants)
+                                       self.members, self.variants,
+                                       self.features)
 
 
 class QAPISchemaMember(object):
@@ -1675,7 +1703,7 @@ class QAPISchema(object):
                   ('null',   'null',    'QNull' + pointer_suffix)]:
             self._def_builtin_type(*t)
         self.the_empty_object_type = QAPISchemaObjectType(
-            'q_empty', None, None, None, None, [], None)
+            'q_empty', None, None, None, None, [], None, [])
         self._def_entity(self.the_empty_object_type)
 
         qtypes = ['none', 'qnull', 'qnum', 'qstring', 'qdict', 'qlist',
@@ -1721,7 +1749,7 @@ class QAPISchema(object):
             assert ifcond == typ._ifcond # pylint: disable=protected-access
         else:
             self._def_entity(QAPISchemaObjectType(name, info, doc, ifcond,
-                                                  None, members, None))
+                                                  None, members, None, []))
         return name
 
     def _def_enum_type(self, expr, info, doc):
@@ -1752,9 +1780,10 @@ class QAPISchema(object):
         base = expr.get('base')
         data = expr['data']
         ifcond = expr.get('if')
+        features = expr.get('features')
         self._def_entity(QAPISchemaObjectType(name, info, doc, ifcond, base,
                                               self._make_members(data, info),
-                                              None))
+                                              None, features))
 
     def _make_variant(self, case, typ, ifcond):
         return QAPISchemaObjectTypeVariant(case, typ, ifcond)
@@ -1795,7 +1824,7 @@ class QAPISchema(object):
             QAPISchemaObjectType(name, info, doc, ifcond, base, members,
                                  QAPISchemaObjectTypeVariants(tag_name,
                                                               tag_member,
-                                                              variants)))
+                                                              variants), []))
 
     def _def_alternate_type(self, expr, info, doc):
         name = expr['alternate']
diff --git a/scripts/qapi/doc.py b/scripts/qapi/doc.py
index 5c8c136899..433e9fcbfb 100755
--- a/scripts/qapi/doc.py
+++ b/scripts/qapi/doc.py
@@ -220,7 +220,8 @@ class QAPISchemaGenDocVisitor(qapi.common.QAPISchemaVisitor):
                                body=texi_entity(doc, 'Values', ifcond,
                                                 member_func=texi_enum_value)))
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         doc = self.cur_doc
         if base and base.is_implicit():
             base = None
diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
index f7f2ca07e4..8909cecde4 100644
--- a/scripts/qapi/introspect.py
+++ b/scripts/qapi/introspect.py
@@ -188,11 +188,15 @@ const QLitObject %(c_name)s = %(c_string)s;
         self._gen_qlit('[' + element + ']', 'array', {'element-type': element},
                        ifcond)
 
-    def visit_object_type_flat(self, name, info, ifcond, members, variants):
+    def visit_object_type_flat(self, name, info, ifcond, members, variants,
+                               features):
         obj = {'members': [self._gen_member(m) for m in members]}
         if variants:
             obj.update(self._gen_variants(variants.tag_member.name,
                                           variants.variants))
+        if features:
+            obj['features'] = [ (f['name'], f) for f in features ]
+
         self._gen_qlit(name, 'object', obj, ifcond)
 
     def visit_alternate_type(self, name, info, ifcond, variants):
diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py
index 2bd6fcd44f..3edd9374aa 100644
--- a/scripts/qapi/types.py
+++ b/scripts/qapi/types.py
@@ -227,7 +227,8 @@ class QAPISchemaGenTypeVisitor(QAPISchemaModularCVisitor):
             self._genh.add(gen_array(name, element_type))
             self._gen_type_cleanup(name)
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         # Nothing to do for the special empty builtin
         if name == 'q_empty':
             return
diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
index 826b8066e1..c1cd675c95 100644
--- a/scripts/qapi/visit.py
+++ b/scripts/qapi/visit.py
@@ -326,7 +326,8 @@ class QAPISchemaGenVisitVisitor(QAPISchemaModularCVisitor):
             self._genh.add(gen_visit_decl(name))
             self._genc.add(gen_visit_list(name, element_type))
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         # Nothing to do for the special empty builtin
         if name == 'q_empty':
             return
diff --git a/tests/qapi-schema/double-type.err b/tests/qapi-schema/double-type.err
index 799193dba1..69457173a7 100644
--- a/tests/qapi-schema/double-type.err
+++ b/tests/qapi-schema/double-type.err
@@ -1,2 +1,2 @@
 tests/qapi-schema/double-type.json:2: Unknown key 'command' in struct 'bar'
-Valid keys are 'base', 'data', 'if', 'struct'.
+Valid keys are 'base', 'data', 'features', 'if', 'struct'.
diff --git a/tests/qapi-schema/test-qapi.py b/tests/qapi-schema/test-qapi.py
index d21fca01fc..f2d6815c86 100644
--- a/tests/qapi-schema/test-qapi.py
+++ b/tests/qapi-schema/test-qapi.py
@@ -38,7 +38,8 @@ class QAPISchemaTestVisitor(QAPISchemaVisitor):
         print('array %s %s' % (name, element_type.name))
         self._print_if(ifcond)
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         print('object %s' % name)
         if base:
             print('    base %s' % base.name)
diff --git a/tests/qapi-schema/unknown-expr-key.err b/tests/qapi-schema/unknown-expr-key.err
index 6ff8bb99c5..4340eaf894 100644
--- a/tests/qapi-schema/unknown-expr-key.err
+++ b/tests/qapi-schema/unknown-expr-key.err
@@ -1,2 +1,2 @@
 tests/qapi-schema/unknown-expr-key.json:2: Unknown keys 'bogus', 'phony' in struct 'bar'
-Valid keys are 'base', 'data', 'if', 'struct'.
+Valid keys are 'base', 'data', 'features', 'if', 'struct'.
