qemu: monitor: Extract handling of JSON block job error codes

My intention is to split qemuMonitorJSONBlockJob() into simpler separate
functions for every block job type. Since the error handling code is the
same for all block jobs, this patch extracts the code into a separate
function that will later be reused in more places.

With the new helper qemuMonitorJSONErrorIsClass we can save a few
function calls as we can extract the error object once.

src/qemu/qemu_monitor_json.c

@@ -4247,6 +4247,39 @@ qemuMonitorJSONBlockJobInfo(qemuMonitorPtr mon,
 }
 
 
+static int
+qemuMonitorJSONBlockJobError(virJSONValuePtr reply,
+                             const char *cmd_name,
+                             const char *device)
+{
+    virJSONValuePtr error;
+
+    if (!(error = virJSONValueObjectGet(reply, "error")))
+        return 0;
+
+    if (qemuMonitorJSONErrorIsClass(error, "DeviceNotActive")) {
+        virReportError(VIR_ERR_OPERATION_INVALID,
+                       _("No active operation on device: %s"), device);
+    } else if (qemuMonitorJSONErrorIsClass(error, "DeviceInUse")) {
+        virReportError(VIR_ERR_OPERATION_FAILED,
+                       _("Device %s in use"), device);
+    } else if (qemuMonitorJSONErrorIsClass(error, "NotSupported")) {
+        virReportError(VIR_ERR_OPERATION_INVALID,
+                       _("Operation is not supported for device: %s"), device);
+    } else if (qemuMonitorJSONErrorIsClass(error, "CommandNotFound")) {
+        virReportError(VIR_ERR_OPERATION_INVALID,
+                       _("Command '%s' is not found"), cmd_name);
+    } else {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("Unexpected error: (%s) '%s'"),
+                       NULLSTR(virJSONValueObjectGetString(error, "class")),
+                       NULLSTR(virJSONValueObjectGetString(error, "desc")));
+    }
+
+    return -1;
+}
+
+
 /* speed is in bytes/sec */
 int
 qemuMonitorJSONBlockJob(qemuMonitorPtr mon,
@@ -4317,34 +4350,15 @@ qemuMonitorJSONBlockJob(qemuMonitorPtr mon,
     if (!cmd)
         return -1;
 
-    ret = qemuMonitorJSONCommand(mon, cmd, &reply);
+    if (qemuMonitorJSONCommand(mon, cmd, &reply) < 0)
+        goto cleanup;
 
-    if (ret == 0 && virJSONValueObjectHasKey(reply, "error")) {
-        ret = -1;
-        if (qemuMonitorJSONHasError(reply, "DeviceNotActive")) {
-            virReportError(VIR_ERR_OPERATION_INVALID,
-                           _("No active operation on device: %s"),
-                           device);
-        } else if (qemuMonitorJSONHasError(reply, "DeviceInUse")) {
-            virReportError(VIR_ERR_OPERATION_FAILED,
-                           _("Device %s in use"), device);
-        } else if (qemuMonitorJSONHasError(reply, "NotSupported")) {
-            virReportError(VIR_ERR_OPERATION_INVALID,
-                           _("Operation is not supported for device: %s"),
-                           device);
-        } else if (qemuMonitorJSONHasError(reply, "CommandNotFound")) {
-            virReportError(VIR_ERR_OPERATION_INVALID,
-                           _("Command '%s' is not found"), cmd_name);
-        } else {
-            virJSONValuePtr error = virJSONValueObjectGet(reply, "error");
+    if (qemuMonitorJSONBlockJobError(reply, cmd_name, device) < 0)
+        goto cleanup;
 
-            virReportError(VIR_ERR_INTERNAL_ERROR,
-                           _("Unexpected error: (%s) '%s'"),
-                           NULLSTR(virJSONValueObjectGetString(error, "class")),
-                           NULLSTR(virJSONValueObjectGetString(error, "desc")));
-        }
-    }
+    ret = 0;
 
+ cleanup:
     virJSONValueFree(cmd);
     virJSONValueFree(reply);
     return ret;