qapi: Implement deprecated-output=hide for QMP command results

This policy suppresses deprecated bits in output, and thus permits
"testing the future".  Implement it for QMP command results.  Example:
when QEMU is run with -compat deprecated-output=hide, then

    {"execute": "query-cpus-fast"}

yields

    {"return": [{"thread-id": 9805, "props": {"core-id": 0, "thread-id": 0, "socket-id": 0}, "qom-path": "/machine/unattached/device[0]", "cpu-index": 0, "target": "x86_64"}]}

instead of

    {"return": [{"arch": "x86", "thread-id": 22436, "props": {"core-id": 0, "thread-id": 0, "socket-id": 0}, "qom-path": "/machine/unattached/device[0]", "cpu-index": 0, "target": "x86_64"}]}

Note the suppression of deprecated member "arch".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-4-armbru@redhat.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/qapi/qobject-output-visitor.c b/qapi/qobject-output-visitor.c
index ba6f6ac..e487330 100644
--- a/qapi/qobject-output-visitor.c
+++ b/qapi/qobject-output-visitor.c
@@ -13,6 +13,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qapi/compat-policy.h"
 #include "qapi/qobject-output-visitor.h"
 #include "qapi/visitor-impl.h"
 #include "qemu/queue.h"
@@ -31,6 +32,8 @@ typedef struct QStackEntry {
 
 struct QObjectOutputVisitor {
     Visitor visitor;
+    CompatPolicyOutput deprecated_policy;
+
     QSLIST_HEAD(, QStackEntry) stack; /* Stack of unfinished containers */
     QObject *root; /* Root of the output visit */
     QObject **result; /* User's storage location for result */
@@ -207,6 +210,13 @@ static bool qobject_output_type_null(Visitor *v, const char *name,
     return true;
 }
 
+static bool qobject_output_deprecated(Visitor *v, const char *name)
+{
+    QObjectOutputVisitor *qov = to_qov(v);
+
+    return qov->deprecated_policy != COMPAT_POLICY_OUTPUT_HIDE;
+}
+
 /* Finish building, and return the root object.
  * The root object is never null. The caller becomes the object's
  * owner, and should use qobject_unref() when done with it.  */
@@ -256,6 +266,7 @@ Visitor *qobject_output_visitor_new(QObject **result)
     v->visitor.type_number = qobject_output_type_number;
     v->visitor.type_any = qobject_output_type_any;
     v->visitor.type_null = qobject_output_type_null;
+    v->visitor.deprecated = qobject_output_deprecated;
     v->visitor.complete = qobject_output_complete;
     v->visitor.free = qobject_output_free;
 
@@ -264,3 +275,11 @@ Visitor *qobject_output_visitor_new(QObject **result)
 
     return &v->visitor;
 }
+
+void qobject_output_visitor_set_policy(Visitor *v,
+                                       CompatPolicyOutput deprecated)
+{
+    QObjectOutputVisitor *qov = to_qov(v);
+
+    qov->deprecated_policy = deprecated;
+}