Wait to receive QMP greeting before sending any monitor commands

Technically speaking we should wait until we receive the QMP
greeting message before attempting to send any QMP monitor
commands. Mostly we've got away with this, but there is a race
in some QEMU which cause it to SEGV if you sent it data too
soon after startup. Waiting for the QMP greeting avoids the
race
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/qemu/qemu_monitor.c

@@ -79,6 +79,7 @@ struct _qemuMonitor {
 
     unsigned json: 1;
     unsigned json_hmp: 1;
+    unsigned wait_greeting: 1;
 };
 
 static virClassPtr qemuMonitorClass;
@@ -365,6 +366,9 @@ qemuMonitorIOProcess(qemuMonitorPtr mon)
     if (len < 0)
         return -1;
 
+    if (len && mon->wait_greeting)
+        mon->wait_greeting = 0;
+
     if (len < mon->bufferOffset) {
         memmove(mon->buffer, mon->buffer + len, mon->bufferOffset - len);
         mon->bufferOffset -= len;
@@ -538,7 +542,8 @@ static void qemuMonitorUpdateWatch(qemuMonitorPtr mon)
     if (mon->lastError.code == VIR_ERR_OK) {
         events |= VIR_EVENT_HANDLE_READABLE;
 
-        if (mon->msg && mon->msg->txOffset < mon->msg->txLength)
+        if ((mon->msg && mon->msg->txOffset < mon->msg->txLength) &&
+            !mon->wait_greeting)
             events |= VIR_EVENT_HANDLE_WRITABLE;
     }
 
@@ -718,6 +723,8 @@ qemuMonitorOpenInternal(virDomainObjPtr vm,
     mon->hasSendFD = hasSendFD;
     mon->vm = vm;
     mon->json = json;
+    if (json)
+        mon->wait_greeting = 1;
     mon->cb = cb;
     qemuMonitorLock(mon);
 

tests/qemumonitortestutils.c

@@ -418,6 +418,9 @@ static qemuMonitorCallbacks qemuCallbacks = {
     .errorNotify = qemuMonitorTestErrorNotify,
 };
 
+#define QEMU_JSON_GREETING "{\"QMP\": {\"version\": {\"qemu\": {\"micro\": 1, \"minor\": 0, \"major\": 1}, \"package\": \" (qemu-kvm-1.0.1)\"}, \"capabilities\": []}}"
+#define QEMU_TEXT_GREETING "QEMU 1.0,1 monitor - type 'help' for more information"
+
 qemuMonitorTestPtr qemuMonitorTestNew(bool json, virCapsPtr caps)
 {
     qemuMonitorTestPtr test;
@@ -458,7 +461,7 @@ qemuMonitorTestPtr qemuMonitorTestNew(bool json, virCapsPtr caps)
 
     if (!(test->mon = qemuMonitorOpen(test->vm,
                                       &src,
-                                      true,
+                                      json ? 1 : 0,
                                       &qemuCallbacks)))
         goto error;
     qemuMonitorLock(test->mon);
@@ -468,8 +471,13 @@ qemuMonitorTestPtr qemuMonitorTestNew(bool json, virCapsPtr caps)
     if (!test->client)
         goto error;
 
+    if (qemuMonitorTestAddReponse(test, json ?
+                                  QEMU_JSON_GREETING :
+                                  QEMU_TEXT_GREETING) < 0)
+        goto error;
+
     if (virNetSocketAddIOCallback(test->client,
-                                  VIR_EVENT_HANDLE_READABLE,
+                                  VIR_EVENT_HANDLE_WRITABLE,
                                   qemuMonitorTestIO,
                                   test,
                                   NULL) < 0)