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>

1 files changed, 28 insertions, 0 deletions

diff --git a/qapi/qobject-input-visitor.c b/qapi/qobject-input-visitor.c
index 23843b242e..bd94cf187a 100644
--- a/qapi/qobject-input-visitor.c
+++ b/qapi/qobject-input-visitor.c
@@ -14,6 +14,7 @@
 
 #include "qemu/osdep.h"
 #include <math.h>
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qobject-input-visitor.h"
 #include "qapi/visitor-impl.h"
@@ -43,6 +44,7 @@ typedef struct StackObject {
 
 struct QObjectInputVisitor {
     Visitor visitor;
+    CompatPolicyInput deprecated_policy;
 
     /* Root of visit at visitor creation. */
     QObject *root;
@@ -662,6 +664,23 @@ static void qobject_input_optional(Visitor *v, const char *name, bool *present)
     *present = true;
 }
 
+static bool qobject_input_deprecated_accept(Visitor *v, const char *name,
+                                            Error **errp)
+{
+    QObjectInputVisitor *qiv = to_qiv(v);
+
+    switch (qiv->deprecated_policy) {
+    case COMPAT_POLICY_INPUT_ACCEPT:
+        return true;
+    case COMPAT_POLICY_INPUT_REJECT:
+        error_setg(errp, "Deprecated parameter '%s' disabled by policy",
+                   name);
+        return false;
+    default:
+        abort();
+    }
+}
+
 static void qobject_input_free(Visitor *v)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
@@ -696,6 +715,7 @@ static QObjectInputVisitor *qobject_input_visitor_base_new(QObject *obj)
     v->visitor.end_list = qobject_input_end_list;
     v->visitor.start_alternate = qobject_input_start_alternate;
     v->visitor.optional = qobject_input_optional;
+    v->visitor.deprecated_accept = qobject_input_deprecated_accept;
     v->visitor.free = qobject_input_free;
 
     v->root = qobject_ref(obj);
@@ -718,6 +738,14 @@ Visitor *qobject_input_visitor_new(QObject *obj)
     return &v->visitor;
 }
 
+void qobject_input_visitor_set_policy(Visitor *v,
+                                       CompatPolicyInput deprecated)
+{
+    QObjectInputVisitor *qiv = to_qiv(v);
+
+    qiv->deprecated_policy = deprecated;
+}
+
 Visitor *qobject_input_visitor_new_keyval(QObject *obj)
 {
     QObjectInputVisitor *v = qobject_input_visitor_base_new(obj);