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[libvirt] [PATCH v2] qemu: Report the offset from host UTC for RTC_CHANGE event



https://bugzilla.redhat.com/show_bug.cgi?id=964177

Though both libvirt and QEMU's document say RTC_CHANGE returns
the offset from the host UTC, qemu actually returns the offset
from the specified date instead when specific date is provided
(-rtc base=$date).

It's not safe for qemu to fix it in code, it worked like that
for 3 years, changing it now may break other QEMU use cases.
What qemu tries to do is to fix the document:

http://lists.gnu.org/archive/html/qemu-devel/2013-05/msg04782.html

And in libvirt side, instead of reply on the qemu, this convert
the offset returned from qemu to the offset from host UTC, by:

  /*
   * a: the offset from qemu RTC_CHANGE event
   * b: The specified date (-rtc base=$date)
   * c: the host date when libvirt gets the RTC_CHANGE event
   * offset: What libvirt will report
   */

  offset = a + (b - c);

The specified date (-rtc base=$date) is recorded in clock's def as
an internal only member (may be useful to exposed outside?).

Internal only XML tag "starttime" is introduced to not lose the
domain process's starttime after libvirt restarting/reloading:

<clock offset='variable' adjustment='304' basis='utc' starttime='1370423588'/>
---
 src/conf/domain_conf.c  | 27 +++++++++++++++++++++++----
 src/conf/domain_conf.h  |  3 +++
 src/qemu/qemu_command.c |  3 +++
 src/qemu/qemu_process.c | 13 +++++++++++++
 4 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index a16ebd1..7773abf 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -96,6 +96,7 @@ typedef enum {
    VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES = (1<<18),
    VIR_DOMAIN_XML_INTERNAL_ALLOW_ROM = (1<<19),
    VIR_DOMAIN_XML_INTERNAL_ALLOW_BOOT = (1<<20),
+   VIR_DOMAIN_XML_INTERNAL_STARTTIME = (1 << 21)
 } virDomainXMLInternalFlags;
 
 VIR_ENUM_IMPL(virDomainTaint, VIR_DOMAIN_TAINT_LAST,
@@ -11193,6 +11194,16 @@ virDomainDefParseXML(xmlDocPtr xml,
         break;
     }
 
+    if (def->clock.offset == VIR_DOMAIN_CLOCK_OFFSET_VARIABLE &&
+        flags & VIR_DOMAIN_XML_INTERNAL_STARTTIME) {
+        if (virXPathULongLong("number(./clock/@starttime)", ctxt,
+                              &def->clock.data.variable.starttime) < 0) {
+            virReportError(VIR_ERR_XML_ERROR, "%s",
+                           _("invalid starttime"));
+            goto error;
+        }
+    }
+
     if ((n = virXPathNodeSet("./clock/timer", ctxt, &nodes)) < 0)
         goto error;
 
@@ -15788,7 +15799,8 @@ virDomainResourceDefFormat(virBufferPtr buf,
 
 verify(((VIR_DOMAIN_XML_INTERNAL_STATUS |
          VIR_DOMAIN_XML_INTERNAL_ACTUAL_NET |
-         VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES)
+         VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES |
+         VIR_DOMAIN_XML_INTERNAL_STARTTIME)
         & DUMPXML_FLAGS) == 0);
 
 /* This internal version can accept VIR_DOMAIN_XML_INTERNAL_*,
@@ -15810,7 +15822,8 @@ virDomainDefFormatInternal(virDomainDefPtr def,
     virCheckFlags(DUMPXML_FLAGS |
                   VIR_DOMAIN_XML_INTERNAL_STATUS |
                   VIR_DOMAIN_XML_INTERNAL_ACTUAL_NET |
-                  VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES,
+                  VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES |
+                  VIR_DOMAIN_XML_INTERNAL_STARTTIME,
                   -1);
 
     if (!(type = virDomainVirtTypeToString(def->virtType))) {
@@ -16208,6 +16221,10 @@ virDomainDefFormatInternal(virDomainDefPtr def,
         virBufferAsprintf(buf, " adjustment='%lld' basis='%s'",
                           def->clock.data.variable.adjustment,
                           virDomainClockBasisTypeToString(def->clock.data.variable.basis));
+
+        if (flags & VIR_DOMAIN_XML_INTERNAL_STARTTIME)
+            virBufferAsprintf(buf, " starttime='%llu'",
+                              def->clock.data.variable.starttime);
         break;
     case VIR_DOMAIN_CLOCK_OFFSET_TIMEZONE:
         virBufferEscapeString(buf, " timezone='%s'", def->clock.data.timezone);
@@ -16586,7 +16603,8 @@ virDomainSaveStatus(virDomainXMLOptionPtr xmlopt,
     unsigned int flags = (VIR_DOMAIN_XML_SECURE |
                           VIR_DOMAIN_XML_INTERNAL_STATUS |
                           VIR_DOMAIN_XML_INTERNAL_ACTUAL_NET |
-                          VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES);
+                          VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES |
+                          VIR_DOMAIN_XML_INTERNAL_STARTTIME);
 
     int ret = -1;
     char *xml;
@@ -16674,7 +16692,8 @@ virDomainObjListLoadStatus(virDomainObjListPtr doms,
     if (!(obj = virDomainObjParseFile(statusFile, caps, xmlopt, expectedVirtTypes,
                                       VIR_DOMAIN_XML_INTERNAL_STATUS |
                                       VIR_DOMAIN_XML_INTERNAL_ACTUAL_NET |
-                                      VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES)))
+                                      VIR_DOMAIN_XML_INTERNAL_PCI_ORIG_STATES |
+                                      VIR_DOMAIN_XML_INTERNAL_STARTTIME)))
         goto error;
 
     virUUIDFormat(obj->def->uuid, uuidstr);
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 3a71d6c..cca92b4 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1767,6 +1767,9 @@ struct _virDomainClockDef {
         struct {
             long long adjustment;
             int basis;
+
+            /* Store the start time of guest process, internal only */
+            unsigned long long starttime;
         } variable;
 
         /* Timezone name, when
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index c4a162a..9254525 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -5518,6 +5518,9 @@ qemuBuildClockArgStr(virDomainClockDefPtr def)
         now += def->data.variable.adjustment;
         gmtime_r(&now, &nowbits);
 
+        /* Store the starttime of qemu process */
+        def->data.variable.starttime = now;
+
         virBufferAsprintf(&buf, "base=%d-%02d-%02dT%02d:%02d:%02d",
                           nowbits.tm_year + 1900,
                           nowbits.tm_mon + 1,
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index d4fd4fb..39c62b3 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -796,6 +796,19 @@ qemuProcessHandleRTCChange(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
 
     virObjectLock(vm);
+
+    /* QEMU's RTC_CHANGE event returns the offset from the specified
+     * date instead of the host UTC if a specific date is provided
+     * (-rtc base=$date). We need to convert it to be offset from
+     * host UTC.
+     */
+    if (vm->def->clock.offset == VIR_DOMAIN_CLOCK_OFFSET_VARIABLE) {
+        time_t now = time(NULL);
+
+        offset += vm->def->clock.data.variable.starttime -
+                  (unsigned long long)now;
+    }
+
     event = virDomainEventRTCChangeNewFromObj(vm, offset);
 
     if (vm->def->clock.offset == VIR_DOMAIN_CLOCK_OFFSET_VARIABLE)
-- 
1.8.1.4


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