3 files changed, 37 insertions, 2 deletions
diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
index 0ce045c0b3..91f44d01b9 100644
--- a/docs/qapi-code-gen.txt
+++ b/docs/qapi-code-gen.txt
@@ -53,6 +53,23 @@ The use of '*' as a prefix to the name means the member is optional.  Optional
 members should always be added to the end of the dictionary to preserve
 backwards compatibility.
 
+
+A complex type definition can specify another complex type as its base.
+In this case, the fields of the base type are included as top-level fields
+of the new complex type's dictionary in the QMP wire format. An example
+definition is:
+
+ { 'type': 'BlockdevOptionsGenericFormat', 'data': { 'file': 'str' } }
+ { 'type': 'BlockdevOptionsGenericCOWFormat',
+   'base': 'BlockdevOptionsGenericFormat',
+   'data': { '*backing': 'str' } }
+
+An example BlockdevOptionsGenericCOWFormat object on the wire could use
+both fields like this:
+
+ { "file": "/some/place/my-image",
+   "backing": "/some/place/my-backing-file" }
+
 === Enumeration types ===
 
 An enumeration type is a dictionary containing a single key whose value is a
diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index 566fe5e4d9..4a1652b56f 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -86,6 +86,7 @@ def generate_struct(expr):
     structname = expr.get('type', "")
     fieldname = expr.get('field', "")
     members = expr['data']
+    base = expr.get('base')
 
     ret = mcgen('''
 struct %(name)s
@@ -93,6 +94,9 @@ struct %(name)s
 ''',
           name=structname)
 
+    if base:
+        ret += generate_struct_fields({'base': base})
+
     ret += generate_struct_fields(members)
 
     if len(fieldname):
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 1e44004a1e..c39e6284b8 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -17,7 +17,7 @@ import os
 import getopt
 import errno
 
-def generate_visit_struct_fields(name, field_prefix, fn_prefix, members):
+def generate_visit_struct_fields(name, field_prefix, fn_prefix, members, base = None):
     substructs = []
     ret = ''
     full_name = name if not fn_prefix else "%s_%s" % (name, fn_prefix)
@@ -42,6 +42,19 @@ static void visit_type_%(full_name)s_fields(Visitor *m, %(name)s ** obj, Error *
         name=name, full_name=full_name)
     push_indent()
 
+    if base:
+        ret += mcgen('''
+visit_start_implicit_struct(m, obj ? (void**) &(*obj)->%(c_name)s : NULL, sizeof(%(type)s), &err);
+if (!err) {
+    visit_type_%(type)s_fields(m, obj ? &(*obj)->%(c_prefix)s%(c_name)s : NULL, &err);
+    error_propagate(errp, err);
+    err = NULL;
+    visit_end_implicit_struct(m, &err);
+}
+''',
+                     c_prefix=c_var(field_prefix),
+                     type=type_name(base), c_name=c_var('base'))
+
     for argname, argentry, optional, structured in parse_args(members):
         if optional:
             ret += mcgen('''
@@ -124,8 +137,9 @@ def generate_visit_struct(expr):
 
     name = expr['type']
     members = expr['data']
+    base = expr.get('base')
 
-    ret = generate_visit_struct_fields(name, "", "", members)
+    ret = generate_visit_struct_fields(name, "", "", members, base)
 
     ret += mcgen('''