qapi: Add alias for ErrorClass

The qapi enum ErrorClass is unusual that it uses 'CamelCase' names,
contrary to our documented convention of preferring 'lower-case'.
However, this enum is entrenched in the API; we cannot change
what strings QMP outputs.  Meanwhile, we want to simplify how
c_enum_const() is used to generate enum constants, by moving away
from the heuristics of camel_to_upper() to a more straightforward
c_name(N).upper() - but doing so will rename all of the ErrorClass
constants and cause churn to all client files, where the new names
are aesthetically less pleasing (ERROR_CLASS_DEVICENOTFOUND looks
like we can't make up our minds on whether to break between words).

So as always in computer science, solve the problem by some more
indirection: rename the qapi type to QapiErrorClass, and add a
new enum ErrorClass in error.h whose members are aliases of the
qapi type, but with the spelling expected elsewhere in the tree.
Then, when c_enum_const() changes the munging, we only have to
adjust the one alias spot.

Suggested by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1447836791-369-26-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

include/qapi/error.h

@@ -90,6 +90,20 @@
  */
 typedef struct Error Error;
 
+/*
+ * Overall category of an error.
+ * Based on the qapi type QapiErrorClass, but reproduced here for nicer
+ * enum names.
+ */
+typedef enum ErrorClass {
+    ERROR_CLASS_GENERIC_ERROR = QAPI_ERROR_CLASS_GENERIC_ERROR,
+    ERROR_CLASS_COMMAND_NOT_FOUND = QAPI_ERROR_CLASS_COMMAND_NOT_FOUND,
+    ERROR_CLASS_DEVICE_ENCRYPTED = QAPI_ERROR_CLASS_DEVICE_ENCRYPTED,
+    ERROR_CLASS_DEVICE_NOT_ACTIVE = QAPI_ERROR_CLASS_DEVICE_NOT_ACTIVE,
+    ERROR_CLASS_DEVICE_NOT_FOUND = QAPI_ERROR_CLASS_DEVICE_NOT_FOUND,
+    ERROR_CLASS_KVM_MISSING_CAP = QAPI_ERROR_CLASS_KVM_MISSING_CAP,
+} ErrorClass;
+
 /*
  * Get @err's human-readable error message.
  */

monitor.c

@@ -403,7 +403,7 @@ static QDict *build_qmp_error_dict(Error *err)
     QObject *obj;
 
     obj = qobject_from_jsonf("{ 'error': { 'class': %s, 'desc': %s } }",
-                             ErrorClass_lookup[error_get_class(err)],
+                             QapiErrorClass_lookup[error_get_class(err)],
                              error_get_pretty(err));
 
     return qobject_to_qdict(obj);

qapi/common.json

@@ -3,7 +3,7 @@
 # QAPI common definitions
 
 ##
-# @ErrorClass
+# @QapiErrorClass
 #
 # QEMU error classes
 #
@@ -24,7 +24,8 @@
 #
 # Since: 1.2
 ##
-{ 'enum': 'ErrorClass',
+{ 'enum': 'QapiErrorClass',
+  # Keep this in sync with ErrorClass in error.h
   'data': [ 'GenericError', 'CommandNotFound', 'DeviceEncrypted',
             'DeviceNotActive', 'DeviceNotFound', 'KVMMissingCap' ] }
 

qapi/qmp-dispatch.c

@@ -114,7 +114,7 @@ static QObject *do_qmp_dispatch(QObject *request, Error **errp)
 QObject *qmp_build_error_object(Error *err)
 {
     return qobject_from_jsonf("{ 'class': %s, 'desc': %s }",
-                              ErrorClass_lookup[error_get_class(err)],
+                              QapiErrorClass_lookup[error_get_class(err)],
                               error_get_pretty(err));
 }