[Qemu-devel] [PATCH 24/27] qmp: switch to the new error format on the wire

[Luiz Capitulino]

IMPORTANT: this commit BREAKS QMP's compatibility for the error response.

This commit changes QMP's wire protocol to make use of the simpler
error format introduced by previous commits.

There are two important (and mostly incompatible) changes:

 1. Almost all error classes have been replaced by GenericError. The
    only classes that are still supported for compatibility with
    libvirt are: CommandNotFound, DeviceNotActive, KVMMissingCap,
    DeviceNotFound and MigrationExpected

 2. The 'data' field of the error dictionary is gone

As an example, an error response like:

  { "error": { "class": "DeviceNotRemovable",
               "data": { "device": "virtio0" },
               "desc": "Device 'virtio0' is not removable" } }

Will now be emitted as:

  { "error": { "class": "GenericError",
               "desc": "Device 'virtio0' is not removable" } }

Signed-off-by: Luiz Capitulino <address@hidden>
---
 QMP/qmp-spec.txt | 10 +++-------
 monitor.c        | 18 +++++++++++++-----
 qmp-commands.hx  |  3 +--
 3 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/QMP/qmp-spec.txt b/QMP/qmp-spec.txt
index 1ba916c..a277896 100644
--- a/QMP/qmp-spec.txt
+++ b/QMP/qmp-spec.txt
@@ -106,14 +106,11 @@ completed because of an error condition.
 
 The format is:
 
-{ "error": { "class": json-string, "data": json-object, "desc": json-string },
-  "id": json-value }
+{ "error": { "class": json-string, "desc": json-string }, "id": json-value }
 
  Where,
 
-- The "class" member contains the error class name (eg. "ServiceUnavailable")
-- The "data" member contains specific error data and is defined in a
-  per-command basis, it will be an empty json-object if the error has no data
+- The "class" member contains the error class name (eg. "GenericError")
 - The "desc" member is a human-readable error message. Clients should
   not attempt to parse this message.
 - The "id" member contains the transaction identification associated with
@@ -173,8 +170,7 @@ S: {"return": {"enabled": true, "present": true}, "id": 
"example"}
 ------------------
 
 C: { "execute": }
-S: {"error": {"class": "JSONParsing", "desc": "Invalid JSON syntax", "data":
-{}}}
+S: {"error": {"class": "GenericError", "desc": "Invalid JSON syntax" } }
 
 3.5 Powerdown event
 -------------------
diff --git a/monitor.c b/monitor.c
index 4eeb0c5..8b00b3b 100644
--- a/monitor.c
+++ b/monitor.c
@@ -356,16 +356,26 @@ static void monitor_json_emitter(Monitor *mon, const 
QObject *data)
     QDECREF(json);
 }
 
+static QDict *build_qmp_error_dict(const QError *err)
+{
+    QObject *obj;
+
+    obj = qobject_from_jsonf("{ 'error': { 'class': %s, 'desc': %p } }",
+                             ErrorClass_lookup[err->err_class],
+                             qerror_human(err));
+
+    return qobject_to_qdict(obj);
+}
+
 static void monitor_protocol_emitter(Monitor *mon, QObject *data)
 {
     QDict *qmp;
 
     trace_monitor_protocol_emitter(mon);
 
-    qmp = qdict_new();
-
     if (!monitor_has_error(mon)) {
         /* success response */
+        qmp = qdict_new();
         if (data) {
             qobject_incref(data);
             qdict_put_obj(qmp, "return", data);
@@ -375,9 +385,7 @@ static void monitor_protocol_emitter(Monitor *mon, QObject 
*data)
         }
     } else {
         /* error response */
-        qdict_put(mon->error->error, "desc", qerror_human(mon->error));
-        qdict_put(qmp, "error", mon->error->error);
-        QINCREF(mon->error->error);
+        qmp = build_qmp_error_dict(mon->error);
         QDECREF(mon->error);
         mon->error = NULL;
     }
diff --git a/qmp-commands.hx b/qmp-commands.hx
index e3cf3c5..e520b51 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -435,8 +435,7 @@ Example:
 -> { "execute": "inject-nmi" }
 <- { "return": {} }
 
-Note: inject-nmi is only supported for x86 guest currently, it will
-      returns "Unsupported" error for non-x86 guest.
+Note: inject-nmi is only supported for x86 guests.
 
 EQMP
 
-- 
1.7.11.2.249.g31c7954.dirty