qapi: add support for command options

Options allow for changes in commands behavior. This commit introduces
the QCO_NO_SUCCESS_RESP option, which causes a command to not emit a
success response.

This is needed by commands such as qemu-ga's guest-shutdown, which
may not be able to complete before the VM vanishes. In this case, it's
useful and simpler not to bother sending a success response.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qapi/qmp-core.h

@@ -25,16 +25,24 @@ typedef enum QmpCommandType
     QCT_NORMAL,
 } QmpCommandType;
 
+typedef enum QmpCommandOptions
+{
+    QCO_NO_OPTIONS = 0x0,
+    QCO_NO_SUCCESS_RESP = 0x1,
+} QmpCommandOptions;
+
 typedef struct QmpCommand
 {
     const char *name;
     QmpCommandType type;
     QmpCommandFunc *fn;
+    QmpCommandOptions options;
     QTAILQ_ENTRY(QmpCommand) node;
     bool enabled;
 } QmpCommand;
 
-void qmp_register_command(const char *name, QmpCommandFunc *fn);
+void qmp_register_command(const char *name, QmpCommandFunc *fn,
+                          QmpCommandOptions options);
 QmpCommand *qmp_find_command(const char *name);
 QObject *qmp_dispatch(QObject *request);
 void qmp_disable_command(const char *name);

qapi/qmp-dispatch.c

@@ -94,8 +94,12 @@ static QObject *do_qmp_dispatch(QObject *request, Error **errp)
     switch (cmd->type) {
     case QCT_NORMAL:
         cmd->fn(args, &ret, errp);
-        if (!error_is_set(errp) && ret == NULL) {
-            ret = QOBJECT(qdict_new());
+        if (!error_is_set(errp)) {
+            if (cmd->options & QCO_NO_SUCCESS_RESP) {
+                g_assert(!ret);
+            } else if (!ret) {
+                ret = QOBJECT(qdict_new());
+            }
         }
         break;
     }

qapi/qmp-registry.c

@@ -17,7 +17,8 @@
 static QTAILQ_HEAD(QmpCommandList, QmpCommand) qmp_commands =
     QTAILQ_HEAD_INITIALIZER(qmp_commands);
 
-void qmp_register_command(const char *name, QmpCommandFunc *fn)
+void qmp_register_command(const char *name, QmpCommandFunc *fn,
+                          QmpCommandOptions options)
 {
     QmpCommand *cmd = g_malloc0(sizeof(*cmd));
 
@@ -25,6 +26,7 @@ void qmp_register_command(const char *name, QmpCommandFunc *fn)
     cmd->type = QCT_NORMAL;
     cmd->fn = fn;
     cmd->enabled = true;
+    cmd->options = options;
     QTAILQ_INSERT_TAIL(&qmp_commands, cmd, node);
 }
 

scripts/qapi-commands.py

@@ -291,14 +291,24 @@ def gen_marshal_input(name, args, ret_type, middle_mode):
 
     return ret
 
+def option_value_matches(opt, val, cmd):
+    if opt in cmd and cmd[opt] == val:
+        return True
+    return False
+
 def gen_registry(commands):
     registry=""
     push_indent()
     for cmd in commands:
+        options = 'QCO_NO_OPTIONS'
+        if option_value_matches('success-response', 'no', cmd):
+            options = 'QCO_NO_SUCCESS_RESP'
+
         registry += mcgen('''
-qmp_register_command("%(name)s", qmp_marshal_input_%(c_name)s);
+qmp_register_command("%(name)s", qmp_marshal_input_%(c_name)s, %(opts)s);
 ''',
-                     name=cmd['command'], c_name=c_fun(cmd['command']))
+                     name=cmd['command'], c_name=c_fun(cmd['command']),
+                     opts=options)
     pop_indent()
     ret = mcgen('''
 static void qmp_init_marshal(void)