Add support for @virtual markup in spice protocol

This means the member is not sent on the network at all.
Instead its initialized to the attribute argument when demarshalled.

This is useful for backwards compatibility support.

python_modules/demarshal.py

@@ -400,6 +400,9 @@ def write_validate_item(writer, container, item, scope, parent_scope, start,
 
 def write_validate_member(writer, container, member, parent_scope, start,
                           want_nw_size, want_mem_size, want_extra_size):
+    if member.has_attr("virtual"):
+        return
+
     if member.has_minor_attr():
         prefix = "if (minor >= %s)" % (member.get_minor_attr())
         newline = False
@@ -740,6 +743,10 @@ def write_parse_pointer(writer, t, at_end, dest, member_name, is_64bit, scope):
         writer.statement("n_ptr++")
 
 def write_member_parser(writer, container, member, dest, scope):
+    if member.has_attr("virtual"):
+        writer.assign(dest.get_ref(member.name), member.attributes["virtual"][0])
+        return
+
     if member.is_switch():
         write_switch_parser(writer, container, member, dest, scope)
         return

python_modules/marshal.py

@@ -266,6 +266,9 @@ def write_switch_marshaller(writer, container, switch, src, scope):
 def write_member_marshaller(writer, container, member, src, scope):
     if member.has_attr("outvar"):
         writer.out_prefix = "%s_%s" % (member.attributes["outvar"][0], writer.out_prefix)
+    if member.has_attr("virtual"):
+        writer.comment("Don't marshall @virtual %s" % member.name).newline()
+        return
     if member.has_attr("nomarshal"):
         writer.comment("Don't marshall @nomarshal %s" % member.name).newline()
         return

python_modules/ptypes.py

@@ -518,9 +518,13 @@ class Member(Containee):
         return self.has_end_attr()
 
     def is_fixed_nw_size(self):
+        if self.has_attr("virtual"):
+            return True
         return self.member_type.is_fixed_nw_size()
 
     def get_fixed_nw_size(self):
+        if self.has_attr("virtual"):
+            return 0
         size = self.member_type.get_fixed_nw_size()
         if self.has_minor_attr():
             minor = self.get_minor_attr()