qapi: Implement deprecated-input=reject for QMP commands

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

    {"execute": "query-cpus"}

fails like this

    {"error": {"class": "CommandNotFound", "desc": "Deprecated command query-cpus disabled by policy"}}

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

    {"error": {"class": "CommandNotFound", "desc": "The command query-cpus has not been found"}}

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-10-armbru@redhat.com>

include/qapi/qmp/dispatch.h

@@ -26,6 +26,7 @@ typedef enum QmpCommandOptions
     QCO_ALLOW_OOB             =  (1U << 1),
     QCO_ALLOW_PRECONFIG       =  (1U << 2),
     QCO_COROUTINE             =  (1U << 3),
+    QCO_DEPRECATED            =  (1U << 4),
 } QmpCommandOptions;
 
 typedef struct QmpCommand

qapi/qmp-dispatch.c

@@ -167,6 +167,19 @@ QDict *qmp_dispatch(const QmpCommandList *cmds, QObject *request,
                   "The command %s has not been found", command);
         goto out;
     }
+    if (cmd->options & QCO_DEPRECATED) {
+        switch (compat_policy.deprecated_input) {
+        case COMPAT_POLICY_INPUT_ACCEPT:
+            break;
+        case COMPAT_POLICY_INPUT_REJECT:
+            error_set(&err, ERROR_CLASS_COMMAND_NOT_FOUND,
+                      "Deprecated command %s disabled by policy",
+                      command);
+            goto out;
+        default:
+            abort();
+        }
+    }
     if (!cmd->enabled) {
         error_set(&err, ERROR_CLASS_COMMAND_NOT_FOUND,
                   "Command %s has been disabled%s%s",

scripts/qapi/commands.py

@@ -210,12 +210,16 @@ def gen_marshal(name: str,
 
 
 def gen_register_command(name: str,
+                         features: List[QAPISchemaFeature],
                          success_response: bool,
                          allow_oob: bool,
                          allow_preconfig: bool,
                          coroutine: bool) -> str:
     options = []
 
+    if 'deprecated' in [f.name for f in features]:
+        options += ['QCO_DEPRECATED']
+
     if not success_response:
         options += ['QCO_NO_SUCCESS_RESP']
     if allow_oob:
@@ -326,9 +330,9 @@ def visit_command(self,
             self._genc.add(gen_marshal(name, arg_type, boxed, ret_type))
         with self._temp_module('./init'):
             with ifcontext(ifcond, self._genh, self._genc):
-                self._genc.add(gen_register_command(name, success_response,
-                                                    allow_oob, allow_preconfig,
-                                                    coroutine))
+                self._genc.add(gen_register_command(
+                    name, features, success_response, allow_oob,
+                    allow_preconfig, coroutine))
 
 
 def gen_commands(schema: QAPISchema,

tests/unit/test-qmp-cmds.c

@@ -281,6 +281,28 @@ static void test_dispatch_cmd_io(void)
     qobject_unref(ret3);
 }
 
+static void test_dispatch_cmd_deprecated(void)
+{
+    const char *cmd = "{ 'execute': 'test-command-features1' }";
+    QDict *ret;
+
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    /* accept */
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 0);
+    qobject_unref(ret);
+
+    compat_policy.has_deprecated_input = true;
+    compat_policy.deprecated_input = COMPAT_POLICY_INPUT_ACCEPT;
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 0);
+    qobject_unref(ret);
+
+    compat_policy.deprecated_input = COMPAT_POLICY_INPUT_REJECT;
+    do_qmp_dispatch_error(false, ERROR_CLASS_COMMAND_NOT_FOUND, cmd);
+}
+
 static void test_dispatch_cmd_ret_deprecated(void)
 {
     const char *cmd = "{ 'execute': 'test-features0' }";
@@ -379,6 +401,8 @@ 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_deprecated",
+                    test_dispatch_cmd_deprecated);
     g_test_add_func("/qmp/dispatch_cmd_ret_deprecated",
                     test_dispatch_cmd_ret_deprecated);
     g_test_add_func("/qmp/dealloc_types", test_dealloc_types);