qmp: switch to the new error format on the wire

IMPORTANT: this 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 Almost all error classes have been replaced by GenericError.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 <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>

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
 -------------------

monitor.c

@@ -353,16 +353,26 @@ 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);
@@ -372,9 +382,7 @@ 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;
     }

qapi-schema.json

@@ -658,7 +658,6 @@
 # Returns information about the current VNC server
 #
 # Returns: @VncInfo
-#          If VNC support is not compiled in, FeatureDisabled
 #
 # Since: 0.14.0
 ##
@@ -1042,9 +1041,6 @@
 #                       virtual address (defaults to CPU 0)
 #
 # Returns: Nothing on success
-#          If @cpu is not a valid VCPU, InvalidParameterValue
-#          If @filename cannot be opened, OpenFileFailed
-#          If an I/O error occurs while writing the file, IOError
 #
 # Since: 0.14.0
 #
@@ -1065,8 +1061,6 @@
 # @filename: the file to save the memory to as binary data
 #
 # Returns: Nothing on success
-#          If @filename cannot be opened, OpenFileFailed
-#          If an I/O error occurs while writing the file, IOError
 #
 # Since: 0.14.0
 #
@@ -1108,7 +1102,6 @@
 # Injects an Non-Maskable Interrupt into all guest's VCPUs.
 #
 # Returns:  If successful, nothing
-#           If the Virtual Machine doesn't support NMI injection, Unsupported
 #
 # Since:  0.14.0
 #
@@ -1159,7 +1152,6 @@
 # Returns: nothing on success
 #          If @device is not a valid block device, DeviceNotFound
 #          If @device is not encrypted, DeviceNotEncrypted
-#          If @password is not valid for this device, InvalidPassword
 #
 # Notes:  Not all block formats support encryption and some that do are not
 #         able to validate that a password is correct.  Disk corruption may
@@ -1200,11 +1192,6 @@
 #
 # Returns: nothing on success
 #          If @device is not a valid block device, DeviceNotFound
-#          If @size is negative, InvalidParameterValue
-#          If the block device has no medium inserted, DeviceHasNoMedium
-#          If the block device does not support resize, Unsupported
-#          If the block device is read-only, DeviceIsReadOnly
-#          If a long-running operation is using the device, DeviceInUse
 #
 # Since: 0.14.0
 ##
@@ -1266,10 +1253,6 @@
 #
 # Returns: nothing on success
 #          If @device is not a valid block device, DeviceNotFound
-#          If @device is busy, DeviceInUse will be returned
-#          If @snapshot-file can't be created, OpenFileFailed
-#          If @snapshot-file can't be opened, OpenFileFailed
-#          If @format is invalid, InvalidBlockFormat
 #
 # Note: The transaction aborts on the first failure.  Therefore, there will
 # be only one device or snapshot file returned in an error condition, and
@@ -1298,8 +1281,6 @@
 #
 # Returns: nothing on success
 #          If @device is not a valid block device, DeviceNotFound
-#          If @snapshot-file can't be opened, OpenFileFailed
-#          If @format is invalid, InvalidBlockFormat
 #
 # Since 0.14.0
 ##
@@ -1501,11 +1482,6 @@
 #
 # Returns: Nothing on success
 #          If Spice is not enabled, DeviceNotFound
-#          If @protocol does not support connected, InvalidParameter
-#          If @protocol is invalid, InvalidParameter
-#          If any other error occurs, SetPasswdFailed
-#
-# Notes: If VNC is not enabled, SetPasswdFailed is returned.
 #
 # Since: 0.14.0
 ##
@@ -1527,8 +1503,6 @@
 #
 # Returns: Nothing on success
 #          If @protocol is `spice' and Spice is not active, DeviceNotFound
-#          If an error occurs setting password expiration, SetPasswdFailed
-#          If @protocol is not `spice' or 'vnc', InvalidParameter
 #
 # Since: 0.14.0
 #
@@ -1551,8 +1525,6 @@
 #
 # Returns:  Nothing on success
 #           If @device is not a valid block device, DeviceNotFound
-#           If @device is not removable and @force is false, DeviceNotRemovable
-#           If @force is false and @device is locked, DeviceLocked
 #
 # Notes:    Ejecting a device will no media results in success
 #
@@ -1595,7 +1567,6 @@
 #
 # Returns: Nothing on success.
 #          If @device is not a valid block device, DeviceNotFound
-#          If @format is not a valid block format, InvalidBlockFormat
 #          If the new block device is encrypted, DeviceEncrypted.  Note that
 #          if this error is returned, the device has been opened successfully
 #          and an additional call to @block_passwd is required to set the
@@ -1631,7 +1602,6 @@
 #
 # Returns: Nothing on success
 #          If @device is not a valid block device, DeviceNotFound
-#          If the argument combination is invalid, InvalidParameterCombination
 #
 # Since: 1.1
 ##
@@ -1665,11 +1635,7 @@
 # @speed:  #optional the maximum speed, in bytes per second
 #
 # Returns: Nothing on success
-#          If streaming is already active on this device, DeviceInUse
 #          If @device does not exist, DeviceNotFound
-#          If image streaming is not supported by this device, NotSupported
-#          If @base does not exist, BaseNotFound
-#          If @speed is invalid, InvalidParameter
 #
 # Since: 1.1
 ##
@@ -1691,8 +1657,6 @@
 #          Defaults to 0.
 #
 # Returns: Nothing on success
-#          If the job type does not support throttling, NotSupported
-#          If the speed value is invalid, InvalidParameter
 #          If no background operation is active on this device, DeviceNotActive
 #
 # Since: 1.1
@@ -1722,7 +1686,6 @@
 #
 # Returns: Nothing on success
 #          If no background operation is active on this device, DeviceNotActive
-#          If cancellation already in progress, DeviceInUse
 #
 # Since: 1.1
 ##
@@ -1792,8 +1755,6 @@
 # format.
 #
 # Returns: Nothing on success
-#          If @filename cannot be opened, OpenFileFailed
-#          If an I/O error occurs while writing the file, IOError
 #
 # Since: 1.1
 ##
@@ -1808,7 +1769,6 @@
 #
 # Returns: Nothing on success
 #          If @id is not a valid device, DeviceNotFound
-#          If the device does not support unplug, BusNoHotplug
 #
 # Notes: When this command completes, the device may not be removed from the
 #        guest.  Hot removal is an operation that requires guest cooperation.
@@ -1849,14 +1809,6 @@
 # want to dump all guest's memory, please specify the start @begin and @length
 #
 # Returns: nothing on success
-#          If @begin contains an invalid address, InvalidParameter
-#          If only one of @begin and @length is specified, MissingParameter
-#          If @protocol stats with "fd:", and the fd cannot be found, FdNotFound
-#          If @protocol starts with "file:", and the file cannot be
-#             opened, OpenFileFailed
-#          If @protocol does not start with "fd:" or "file:", InvalidParameter
-#          If an I/O error occurs while writing the file, IOError
-#          If the target does not support this command, Unsupported
 #
 # Since: 1.2
 ##
@@ -1883,10 +1835,6 @@
 #
 # Returns: Nothing on success
 #          If @type is not a valid network backend, DeviceNotFound
-#          If @id is not a valid identifier, InvalidParameterValue
-#          if @id already exists, DuplicateId
-#          If @props contains an invalid parameter for this backend,
-#            InvalidParameter
 ##
 { 'command': 'netdev_add',
   'data': {'type': 'str', 'id': 'str', '*props': '**'},
@@ -2206,8 +2154,6 @@
 # @fdname: file descriptor name
 #
 # Returns: Nothing on success
-#          If file descriptor was not received, FdNotSupplied
-#          If @fdname is not valid, InvalidParameterType
 #
 # Since: 0.14.0
 #
@@ -2227,7 +2173,6 @@
 # @fdname: file descriptor name
 #
 # Returns: Nothing on success
-#          If @fdname is not found, FdNotFound
 #
 # Since: 0.14.0
 ##

qmp-commands.hx

@@ -435,8 +435,8 @@ 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 fails when the guest doesn't support injecting.
+      Currently, only x86 guests do.
 
 EQMP