[libvirt] [PATCH] Don't log an internal error when the guest hasn't updated balloon stats

[Ján Tomko]

If virDomainMemoryStats is called too soon after domain startup,
QEMU returns:
"error":{"class":"GenericError","desc":"guest hasn't updated any stats yet"}
when we try to query balloon stats.

Check for this reply and log it as OPERATION_INVALID instead of
INTERNAL_ERROR. This means the daemon only logs it at the debug level,
without polluting system logs.

Reported by Laszlo Pal:
https://www.redhat.com/archives/libvirt-users/2014-May/msg00023.html
---
 src/qemu/qemu_monitor_json.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index f8ab975..88f6b6c 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -1460,26 +1460,38 @@ int qemuMonitorJSONGetMemoryStats(qemuMonitorPtr mon,
         goto cleanup;
 
     if (!(cmd = qemuMonitorJSONMakeCommand("qom-get",
                                            "s:path", balloonpath,
                                            "s:property", "guest-stats",
                                            NULL)))
         goto cleanup;
 
     ret = qemuMonitorJSONCommand(mon, cmd, &reply);
 
-    if (ret == 0)
-        ret = qemuMonitorJSONCheckError(cmd, reply);
-
     if (ret < 0)
         goto cleanup;
 
+    if ((data = virJSONValueObjectGet(reply, "error"))) {
+        const char *klass = virJSONValueObjectGetString(data, "class");
+        const char *desc = virJSONValueObjectGetString(data, "desc");
+
+        if (STREQ_NULLABLE(klass, "GenericError") &&
+            STREQ_NULLABLE(desc, "guest hasn't updated any stats yet")) {
+            virReportError(VIR_ERR_OPERATION_INVALID, "%s",
+                           _("the guest hasn't updated any stats yet"));
+            ret = -1;
+            goto cleanup;
+        }
+    }
+
+    ret = qemuMonitorJSONCheckError(cmd, reply);
+
     if (!(data = virJSONValueObjectGet(reply, "return"))) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("qom-get reply was missing return data"));
         goto cleanup;
     }
 
     if (!(statsdata = virJSONValueObjectGet(data, "stats"))) {
         VIR_DEBUG("data does not include 'stats'");
         goto cleanup;
     }
-- 
1.8.3.2