qapi: add query-cpu-definitions command (v2)

This command attempts to map to the behavior of -cpu ?.  Unfortunately, the
output of this command differs wildly across targets.

To accommodate this, we use a weak symbol to implement a default version of the
command that fails with a QERR_NOT_SUPPORTED error code.  Targets can then
override and implement this command if it makes sense for them.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

qapi-schema.json

@@ -2222,3 +2222,26 @@
 # Since: 1.2.0
 ##
 { 'command': 'query-machines', 'returns': ['MachineInfo'] }
+
+##
+# @CpuDefinitionInfo:
+#
+# Virtual CPU definition.
+#
+# @name: the name of the CPU definition
+#
+# Since: 1.2.0
+##
+{ 'type': 'CpuDefinitionInfo',
+  'data': { 'name': 'str' } }
+
+##
+# @query-cpu-definitions:
+#
+# Return a list of supported virtual CPU definitions
+#
+# Returns: a list of CpuDefInfo
+#
+# Since: 1.2.0
+##
+{ 'command': 'query-cpu-definitions', 'returns': ['CpuDefinitionInfo'] }

qmp-commands.hx

@@ -2230,3 +2230,9 @@ EQMP
         .mhandler.cmd_new = qmp_marshal_input_query_machines,
     },
 
+    {
+        .name       = "query-cpu-definitions",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_query_cpu_definitions,
+    },
+

qmp.c

@@ -467,3 +467,9 @@ DevicePropertyInfoList *qmp_device_list_properties(const char *typename,
 
     return prop_list;
 }
+
+CpuDefinitionInfoList GCC_WEAK *qmp_query_cpu_definitions(Error **errp)
+{
+    error_set(errp, QERR_NOT_SUPPORTED);
+    return NULL;
+}