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>

include/qapi/compat-policy.h

@@ -17,4 +17,13 @@
 
 extern CompatPolicy compat_policy;
 
+/*
+ * Create a QObject output visitor for @obj for use with QMP
+ *
+ * This is like qobject_output_visitor_new(), except it obeys the
+ * policy for handling deprecated management interfaces set with
+ * -compat.
+ */
+Visitor *qobject_output_visitor_new_qmp(QObject **result);
+
 #endif

include/qapi/qobject-output-visitor.h

@@ -15,6 +15,7 @@
 #define QOBJECT_OUTPUT_VISITOR_H
 
 #include "qapi/visitor.h"
+#include "qapi/qapi-types-compat.h"
 
 typedef struct QObjectOutputVisitor QObjectOutputVisitor;
 
@@ -53,4 +54,7 @@ typedef struct QObjectOutputVisitor QObjectOutputVisitor;
  */
 Visitor *qobject_output_visitor_new(QObject **result);
 
+void qobject_output_visitor_set_policy(Visitor *v,
+                                       CompatPolicyOutput deprecated);
+
 #endif

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)(Visitor *v, const char *name);
+
     /* Must be set */
     VisitorType type;
 

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 visit 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(Visitor *v, const char *name);
+
 /*
  * Visit an enum value.
  *

qapi/qapi-visit-core.c

@@ -135,6 +135,15 @@ bool visit_optional(Visitor *v, const char *name, bool *present)
     return *present;
 }
 
+bool visit_deprecated(Visitor *v, const char *name)
+{
+    trace_visit_deprecated(v, name);
+    if (v->deprecated) {
+        return v->deprecated(v, name);
+    }
+    return true;
+}
+
 bool visit_is_input(Visitor *v)
 {
     return v->type == VISITOR_INPUT;

qapi/qmp-dispatch.c

@@ -19,6 +19,7 @@
 #include "qapi/qmp/dispatch.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qjson.h"
+#include "qapi/qobject-output-visitor.h"
 #include "sysemu/runstate.h"
 #include "qapi/qmp/qbool.h"
 #include "qemu/coroutine.h"
@@ -26,6 +27,14 @@
 
 CompatPolicy compat_policy;
 
+Visitor *qobject_output_visitor_new_qmp(QObject **result)
+{
+    Visitor *v = qobject_output_visitor_new(result);
+
+    qobject_output_visitor_set_policy(v, compat_policy.deprecated_output);
+    return v;
+}
+
 static QDict *qmp_dispatch_check_obj(QDict *dict, bool allow_oob,
                                      Error **errp)
 {

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;
+}

qapi/trace-events

@@ -17,6 +17,7 @@ visit_start_alternate(void *v, const char *name, void *obj, size_t size) "v=%p n
 visit_end_alternate(void *v, void *obj) "v=%p obj=%p"
 
 visit_optional(void *v, const char *name, bool *present) "v=%p name=%s present=%p"
+visit_deprecated(void *v, const char *name) "v=%p name=%s"
 
 visit_type_enum(void *v, const char *name, int *obj) "v=%p name=%s obj=%p"
 visit_type_int(void *v, const char *name, int64_t *obj) "v=%p name=%s obj=%p"

scripts/qapi/commands.py

@@ -96,7 +96,7 @@ static void qmp_marshal_output_%(c_name)s(%(c_type)s ret_in,
 {
     Visitor *v;
 
-    v = qobject_output_visitor_new(ret_out);
+    v = qobject_output_visitor_new_qmp(ret_out);
     if (visit_type_%(c_name)s(v, "unused", &ret_in, errp)) {
         visit_complete(v, ret_out);
     }
@@ -251,9 +251,9 @@ class QAPISchemaGenCommandVisitor(QAPISchemaModularCVisitor):
         visit = self._module_basename('qapi-visit', name)
         self._genc.add(mcgen('''
 #include "qemu/osdep.h"
+#include "qapi/compat-policy.h"
 #include "qapi/visitor.h"
 #include "qapi/qmp/qdict.h"
-#include "qapi/qobject-output-visitor.h"
 #include "qapi/qobject-input-visitor.h"
 #include "qapi/dealloc-visitor.h"
 #include "qapi/error.h"

scripts/qapi/visit.py

@@ -77,6 +77,7 @@ bool visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
                      c_type=base.c_name())
 
     for memb in members:
+        deprecated = 'deprecated' in [f.name for f in memb.features]
         ret += gen_if(memb.ifcond)
         if memb.optional:
             ret += mcgen('''
@@ -84,6 +85,12 @@ bool visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
 ''',
                          name=memb.name, c_name=c_name(memb.name))
             indent.increase()
+        if deprecated:
+            ret += mcgen('''
+    if (visit_deprecated(v, "%(name)s")) {
+''',
+                         name=memb.name)
+            indent.increase()
         ret += mcgen('''
     if (!visit_type_%(c_type)s(v, "%(name)s", &obj->%(c_name)s, errp)) {
         return false;
@@ -91,6 +98,11 @@ bool visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
 ''',
                      c_type=memb.type.c_name(), name=memb.name,
                      c_name=c_name(memb.name))
+        if deprecated:
+            indent.decrease()
+            ret += mcgen('''
+    }
+''')
         if memb.optional:
             indent.decrease()
             ret += mcgen('''

tests/qapi-schema/qapi-schema-test.json

@@ -299,14 +299,15 @@
   'features': [ 'feature1' ] }
 
 { 'command': 'test-features0',
-  'data': { 'fs0': 'FeatureStruct0',
+  'data': { '*fs0': 'FeatureStruct0',
-            'fs1': 'FeatureStruct1',
+            '*fs1': 'FeatureStruct1',
-            'fs2': 'FeatureStruct2',
+            '*fs2': 'FeatureStruct2',
-            'fs3': 'FeatureStruct3',
+            '*fs3': 'FeatureStruct3',
-            'fs4': 'FeatureStruct4',
+            '*fs4': 'FeatureStruct4',
-            'cfs1': 'CondFeatureStruct1',
+            '*cfs1': 'CondFeatureStruct1',
-            'cfs2': 'CondFeatureStruct2',
+            '*cfs2': 'CondFeatureStruct2',
-            'cfs3': 'CondFeatureStruct3' },
+            '*cfs3': 'CondFeatureStruct3' },
+  'returns': 'FeatureStruct1',
   'features': [] }
 
 { 'command': 'test-command-features1',

tests/qapi-schema/qapi-schema-test.out

@@ -409,15 +409,15 @@ alternate FeatureAlternate1
     case eins: FeatureStruct1
     feature feature1
 object q_obj_test-features0-arg
-    member fs0: FeatureStruct0 optional=False
+    member fs0: FeatureStruct0 optional=True
-    member fs1: FeatureStruct1 optional=False
+    member fs1: FeatureStruct1 optional=True
-    member fs2: FeatureStruct2 optional=False
+    member fs2: FeatureStruct2 optional=True
-    member fs3: FeatureStruct3 optional=False
+    member fs3: FeatureStruct3 optional=True
-    member fs4: FeatureStruct4 optional=False
+    member fs4: FeatureStruct4 optional=True
-    member cfs1: CondFeatureStruct1 optional=False
+    member cfs1: CondFeatureStruct1 optional=True
-    member cfs2: CondFeatureStruct2 optional=False
+    member cfs2: CondFeatureStruct2 optional=True
-    member cfs3: CondFeatureStruct3 optional=False
+    member cfs3: CondFeatureStruct3 optional=True
-command test-features0 q_obj_test-features0-arg -> None
+command test-features0 q_obj_test-features0-arg -> FeatureStruct1
     gen=True success_response=True boxed=False oob=False preconfig=False
 command test-command-features1 None -> None
     gen=True success_response=True boxed=False oob=False preconfig=False

tests/unit/test-qmp-cmds.c

@@ -1,4 +1,5 @@
 #include "qemu/osdep.h"
+#include "qapi/compat-policy.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qjson.h"
 #include "qapi/qmp/qnum.h"
@@ -49,12 +50,17 @@ void qmp_user_def_cmd1(UserDefOne * ud1, Error **errp)
 {
 }
 
-void qmp_test_features0(FeatureStruct0 *fs0, FeatureStruct1 *fs1,
+FeatureStruct1 *qmp_test_features0(bool has_fs0, FeatureStruct0 *fs0,
-                       FeatureStruct2 *fs2, FeatureStruct3 *fs3,
+                                   bool has_fs1, FeatureStruct1 *fs1,
-                       FeatureStruct4 *fs4, CondFeatureStruct1 *cfs1,
+                                   bool has_fs2, FeatureStruct2 *fs2,
-                       CondFeatureStruct2 *cfs2, CondFeatureStruct3 *cfs3,
+                                   bool has_fs3, FeatureStruct3 *fs3,
-                       Error **errp)
+                                   bool has_fs4, FeatureStruct4 *fs4,
+                                   bool has_cfs1, CondFeatureStruct1 *cfs1,
+                                   bool has_cfs2, CondFeatureStruct2 *cfs2,
+                                   bool has_cfs3, CondFeatureStruct3 *cfs3,
+                                   Error **errp)
 {
+    return g_new0(FeatureStruct1, 1);
 }
 
 void qmp_test_command_features1(Error **errp)
@@ -275,6 +281,30 @@ static void test_dispatch_cmd_io(void)
     qobject_unref(ret3);
 }
 
+static void test_dispatch_cmd_ret_deprecated(void)
+{
+    const char *cmd = "{ 'execute': 'test-features0' }";
+    QDict *ret;
+
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    /* default accept */
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 1);
+    qobject_unref(ret);
+
+    compat_policy.has_deprecated_output = true;
+    compat_policy.deprecated_output = COMPAT_POLICY_OUTPUT_ACCEPT;
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 1);
+    qobject_unref(ret);
+
+    compat_policy.deprecated_output = COMPAT_POLICY_OUTPUT_HIDE;
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 0);
+    qobject_unref(ret);
+}
+
 /* test generated dealloc functions for generated types */
 static void test_dealloc_types(void)
 {
@@ -349,6 +379,8 @@ int main(int argc, char **argv)
     g_test_add_func("/qmp/dispatch_cmd_io", test_dispatch_cmd_io);
     g_test_add_func("/qmp/dispatch_cmd_success_response",
                     test_dispatch_cmd_success_response);
+    g_test_add_func("/qmp/dispatch_cmd_ret_deprecated",
+                    test_dispatch_cmd_ret_deprecated);
     g_test_add_func("/qmp/dealloc_types", test_dealloc_types);
     g_test_add_func("/qmp/dealloc_partial", test_dealloc_partial);