It is necessary to reset RTC interrupt reinjection backlog if
guest time is synchronized via a different mechanism, such as 
QGA's guest-set-time command.

Failing to do so causes both corrections to be applied (summed),
resulting in an incorrect guest time.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

---
 hw/timer/mc146818rtc.c |   22 ++++++++++++++++++++++
 qapi-schema.json       |   12 ++++++++++++
 qmp-commands.hx        |   23 +++++++++++++++++++++++
 3 files changed, 57 insertions(+)

Index: qemu/hw/timer/mc146818rtc.c
===================================================================
--- qemu.orig/hw/timer/mc146818rtc.c	2014-06-02 23:14:09.570443599 -0300
+++ qemu/hw/timer/mc146818rtc.c	2014-06-02 23:14:11.707436729 -0300
@@ -26,6 +26,7 @@
 #include "sysemu/sysemu.h"
 #include "hw/timer/mc146818rtc.h"
 #include "qapi/visitor.h"
+#include "qmp-commands.h"
 
 #ifdef TARGET_I386
 #include "hw/i386/apic.h"
@@ -84,6 +85,9 @@
     Notifier clock_reset_notifier;
     LostTickPolicy lost_tick_policy;
     Notifier suspend_notifier;
+#ifdef TARGET_I386
+    QLIST_ENTRY(RTCState) link;
+#endif
 } RTCState;
 
 static void rtc_set_time(RTCState *s);
@@ -522,6 +526,20 @@
         rtc_from_bcd(s, s->cmos_data[RTC_CENTURY]) * 100 - 1900;
 }
 
+#ifdef TARGET_I386
+static QLIST_HEAD(, RTCState) rtc_devices =
+    QLIST_HEAD_INITIALIZER(rtc_devices);
+
+void qmp_rtc_reset_reinjection(Error **errp)
+{
+    RTCState *s;
+
+    QLIST_FOREACH(s, &rtc_devices, link) {
+        s->irq_coalesced = 0;
+    }
+}
+#endif
+
 static void rtc_set_time(RTCState *s)
 {
     struct tm tm;
@@ -911,6 +929,10 @@
     } else {
         isa_init_irq(isadev, &s->irq, RTC_ISA_IRQ);
     }
+#ifdef TARGET_I386
+    QLIST_INSERT_HEAD(&rtc_devices, s, link);
+#endif
+
     return isadev;
 }
 
Index: qemu/qapi-schema.json
===================================================================
--- qemu.orig/qapi-schema.json	2014-06-02 23:14:09.570443599 -0300
+++ qemu/qapi-schema.json	2014-06-02 23:14:11.709436722 -0300
@@ -4722,3 +4722,15 @@
               'btn'     : 'InputBtnEvent',
               'rel'     : 'InputMoveEvent',
               'abs'     : 'InputMoveEvent' } }
+
+##
+# @rtc-reset-reinjection
+#
+# This command will reset the RTC interrupt reinjection backlog.
+# Can be used if another mechanism to synchronize guest time
+# is in effect, for example QEMU guest agent's guest-set-time
+# command.
+#
+# Since: 2.1
+##
+{ 'command': 'rtc-reset-reinjection' }
Index: qemu/qmp-commands.hx
===================================================================
--- qemu.orig/qmp-commands.hx	2014-06-02 23:14:09.570443599 -0300
+++ qemu/qmp-commands.hx	2014-06-02 23:14:11.710436719 -0300
@@ -3572,3 +3572,26 @@
                    } } ] }
 
 EQMP
+
+#if defined (TARGET_I386)
+    {
+        .name       = "rtc-reset-reinjection",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_rtc_reset_reinjection,
+    },
+#endif
+
+SQMP
+rtc-reset-reinjection
+---------------------
+
+Reset the RTC interrupt reinjection backlog.
+
+Arguments: None.
+
+Example:
+
+-> { "execute": "rtc-reset-reinjection" }
+<- { "return": {} }
+
+EQMP