qemu_domain: add timestamp in tainting of guests log

We lacked of timestamp in tainting of guests log,
which bring troubles for finding guest issues:
such as whether a guest powerdown caused by qemu-monitor-command
or others issues inside guests.
If we had timestamp in tainting of guests log,
it would be helpful when checking guest's /var/log/messages.
Signed-off-by: NChen Hanxiao <chenhanxiao@gmail.com>

src/qemu/qemu_domain.c

@@ -4008,9 +4008,12 @@ void qemuDomainObjTaint(virQEMUDriverPtr driver,
 {
     virErrorPtr orig_err = NULL;
     bool closeLog = false;
-
-    if (virDomainObjTaint(obj, taint)) {
+    char *timestamp = NULL;
     char uuidstr[VIR_UUID_STRING_BUFLEN];
+
+    if (!virDomainObjTaint(obj, taint))
+        return;
+
     virUUIDFormat(obj->def->uuid, uuidstr);
 
     VIR_WARN("Domain id=%d name='%s' uuid=%s is tainted: %s",
@@ -4023,32 +4026,35 @@ void qemuDomainObjTaint(virQEMUDriverPtr driver,
      * preserve original error, and clear any error that
      * is raised */
     orig_err = virSaveLastError();
+
+    if (!(timestamp = virTimeStringNow()))
+        goto cleanup;
+
     if (logCtxt == NULL) {
         logCtxt = qemuDomainLogContextNew(driver, obj,
                                           QEMU_DOMAIN_LOG_CONTEXT_MODE_ATTACH);
         if (!logCtxt) {
-                if (orig_err) {
-                    virSetError(orig_err);
-                    virFreeError(orig_err);
-                }
             VIR_WARN("Unable to open domainlog");
-                return;
+            goto cleanup;
         }
         closeLog = true;
     }
 
     if (qemuDomainLogContextWrite(logCtxt,
-                                      "Domain id=%d is tainted: %s\n",
+                                  "%s: Domain id=%d is tainted: %s\n",
+                                  timestamp,
                                   obj->def->id,
                                   virDomainTaintTypeToString(taint)) < 0)
         virResetLastError();
+
+ cleanup:
+    VIR_FREE(timestamp);
     if (closeLog)
         qemuDomainLogContextFree(logCtxt);
     if (orig_err) {
         virSetError(orig_err);
         virFreeError(orig_err);
     }
-    }
 }