qapi: output def_value_str when query command line options

Change qapi interfaces to output the newly added def_value_str when querying
command line options.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Leandro Dorileo <l@dorileo.org>
Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
Signed-off-by: Chunyan Liu <cyliu@suse.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

qapi-schema.json

@@ -2855,12 +2855,15 @@
 #
 # @help: #optional human readable text string, not suitable for parsing.
 #
+# @default: #optional default value string (since 2.1)
+#
 # Since 1.5
 ##
 { 'type': 'CommandLineParameterInfo',
   'data': { 'name': 'str',
             'type': 'CommandLineParameterType',
-            '*help': 'str' } }
+            '*help': 'str',
+            '*default': 'str' } }
 
 ##
 # @CommandLineOptionInfo:

qmp-commands.hx

@@ -2898,6 +2898,8 @@ Each array entry contains the following:
               or 'size')
     - "help": human readable description of the parameter
               (json-string, optional)
+    - "default": default value string for the parameter
+                 (json-string, optional)
 
 Example:
 

util/qemu-config.c

@@ -82,6 +82,10 @@ static CommandLineParameterInfoList *query_option_descs(const QemuOptDesc *desc)
             info->has_help = true;
             info->help = g_strdup(desc[i].help);
         }
+        if (desc[i].def_value_str) {
+            info->has_q_default = true;
+            info->q_default = g_strdup(desc[i].def_value_str);
+        }
 
         entry = g_malloc0(sizeof(*entry));
         entry->value = info;