[win-pv-devel] [PATCH] Check WinTime and XenTime for drift

[Owen Smith <owen.smith@xxxxxxxxxx>]

Windows 10/Server 2016 changed how Windows maintains the accuracy of its clock
This can allow reported time to drift away from host time, and Windows time
will need to be updated regularly in order to minimise the drift.

* Add a wrapper for SetXenTime to manage the critical section
* Remove SetXenTime from CheckSuspend and call it from the calling function
* Add a timeout to the WaitForMultipleObjectsEx, which calls SetXenTime
* Prevent SetXenTime from updating the time if its not changed (and avoid
  outputting the log lines)

Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
---
 src/xenagent/service.cpp | 20 +++++++++++++++++---
 src/xenagent/service.h   |  1 +
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/xenagent/service.cpp b/src/xenagent/service.cpp
index a8d45fc..427faee 100644
--- a/src/xenagent/service.cpp
+++ b/src/xenagent/service.cpp
@@ -239,6 +239,15 @@ bool CXenIfaceCreator::CheckShutdown()
     return false;
 }
 
+void CXenIfaceCreator::CheckXenTime()
+{
+    CCritSec crit(&m_crit);
+    if (m_device == NULL)
+        return;
+
+    SetXenTime();
+}
+
 void CXenIfaceCreator::CheckSuspend()
 {
     CCritSec crit(&m_crit);
@@ -268,7 +277,6 @@ void CXenIfaceCreator::CheckSuspend()
     if (m_agent.ConvDevicePresent())
         StartSlateModeWatch();
 
-    SetXenTime();
     m_count = count;
 }
 
@@ -473,6 +481,9 @@ void CXenIfaceCreator::SetXenTime()
     SYSTEMTIME cur = { 0 };
     GetLocalTime(&cur);
 
+    if (memcmp(&cur, &sys, sizeof(SYSTEMTIME)) == 0)
+        return;
+
     CXenAgent::Log("Time Now = %d/%d/%d %d:%02d:%02d.%d\n",
                    cur.wYear, cur.wMonth, cur.wDay,
                    cur.wHour, cur.wMinute, cur.wSecond, cur.wMilliseconds);
@@ -732,11 +743,12 @@ void CXenAgent::OnPowerEvent(DWORD evt, LPVOID data)
 
 bool CXenAgent::ServiceMainLoop()
 {
+    DWORD   timeout = 30 * 60 * 1000;
     HANDLE  events[] = { m_svc_stop,
                          m_xeniface.m_evt_shutdown,
                          m_xeniface.m_evt_suspend,
                          m_xeniface.m_evt_slate_mode };
-    DWORD   wait = WaitForMultipleObjectsEx(4, events, FALSE, INFINITE, TRUE);
+    DWORD   wait = WaitForMultipleObjectsEx(4, events, FALSE, timeout, TRUE);
 
     switch (wait) {
     case WAIT_OBJECT_0:
@@ -749,6 +761,7 @@ bool CXenAgent::ServiceMainLoop()
 
     case WAIT_OBJECT_0+2:
         ResetEvent(m_xeniface.m_evt_suspend);
+        m_xeniface.CheckXenTime();
         m_xeniface.CheckSuspend();
         return true; // continue loop
 
@@ -761,8 +774,9 @@ bool CXenAgent::ServiceMainLoop()
 
         return true; // continue loop
     }
-    case WAIT_IO_COMPLETION:
     case WAIT_TIMEOUT:
+        m_xeniface.CheckXenTime();
+    case WAIT_IO_COMPLETION:
         m_xeniface.CheckSuspend();
         return !m_xeniface.CheckShutdown();
 
diff --git a/src/xenagent/service.h b/src/xenagent/service.h
index 47b7352..4126841 100644
--- a/src/xenagent/service.h
+++ b/src/xenagent/service.h
@@ -69,6 +69,7 @@ public: // IDeviceCreator
 
 public:
     bool CheckShutdown();
+    void CheckXenTime();
     void CheckSuspend();
     bool CheckSlateMode(std::string *mode);
 
-- 
2.16.2.windows.1


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