qapi: Implement deprecated-input=reject for QMP command arguments

This policy rejects deprecated input, and thus permits "testing the
future".  Implement it for QMP command arguments: reject commands with
deprecated ones.  Example: when QEMU is run with -compat
deprecated-input=reject, then

    {"execute": "eject", "arguments": {"device": "cd"}}

fails like this

    {"error": {"class": "GenericError", "desc": "Deprecated parameter 'device' disabled by policy"}}

When the deprecated parameter is removed, the error will change to

    {"error": {"class": "GenericError", "desc": "Parameter 'device' is unexpected"}}

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-11-armbru@redhat.com>

include/qapi/compat-policy.h

@@ -17,6 +17,15 @@
 
 extern CompatPolicy compat_policy;
 
+/*
+ * Create a QObject input visitor for @obj for use with QMP
+ *
+ * This is like qobject_input_visitor_new(), except it obeys the
+ * policy for handling deprecated management interfaces set with
+ * -compat.
+ */
+Visitor *qobject_input_visitor_new_qmp(QObject *obj);
+
 /*
  * Create a QObject output visitor for @obj for use with QMP
  *

include/qapi/qobject-input-visitor.h

@@ -15,6 +15,7 @@
 #ifndef QOBJECT_INPUT_VISITOR_H
 #define QOBJECT_INPUT_VISITOR_H
 
+#include "qapi/qapi-types-compat.h"
 #include "qapi/visitor.h"
 
 typedef struct QObjectInputVisitor QObjectInputVisitor;
@@ -58,6 +59,9 @@ typedef struct QObjectInputVisitor QObjectInputVisitor;
  */
 Visitor *qobject_input_visitor_new(QObject *obj);
 
+void qobject_input_visitor_set_policy(Visitor *v,
+                                      CompatPolicyInput deprecated);
+
 /*
  * Create a QObject input visitor for @obj for use with keyval_parse()
  *

include/qapi/visitor-impl.h

@@ -113,6 +113,9 @@ struct Visitor
        The core takes care of the return type in the public interface. */
     void (*optional)(Visitor *v, const char *name, bool *present);
 
+    /* Optional */
+    bool (*deprecated_accept)(Visitor *v, const char *name, Error **errp);
+
     /* Optional */
     bool (*deprecated)(Visitor *v, const char *name);
 

include/qapi/visitor.h

@@ -459,6 +459,15 @@ void visit_end_alternate(Visitor *v, void **obj);
  */
 bool visit_optional(Visitor *v, const char *name, bool *present);
 
+/*
+ * Should we reject deprecated member @name?
+ *
+ * @name must not be NULL.  This function is only useful between
+ * visit_start_struct() and visit_end_struct(), since only objects
+ * have deprecated members.
+ */
+bool visit_deprecated_accept(Visitor *v, const char *name, Error **errp);
+
 /*
  * Should we visit deprecated member @name?
  *