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

On 06/04/2013 05:49 AM, Osier Yang wrote: > 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 privided s/privided/provided/ > (-rtc base=$date). > > It's not safe for qemu to fix it in code, it worked like that > for 3 years, changing it now may break other QEMU use cases. > What qemu tries to do is to fix the document: > > http://lists.gnu.org/archive/html/qemu-devel/2013-05/msg04782.html > > And in libvirt side, instead of reply on the qemu, this covert s/covert/convert/ > the offset returned from qemu to the offset from host UTC, by: > > /* > * a: the offset from qemu RTC_CHANGE event > * b: The specified date (-rtc base=$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?). > --- > src/conf/domain_conf.h | 3 +++ > src/qemu/qemu_command.c | 3 +++ > src/qemu/qemu_process.c | 12 ++++++++++++ > 3 files changed, 18 insertions(+) Incomplete. You need to track the start time across libvirtd restarts (in internal XML) for this to reliably work for an event received after a restart; you also have to cope with a libvirtd restart not finding the field in internal XML (because the libvirtd restart was due to upgrading libvirt in the meantime). > > diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h > index 3a71d6c..3947a56 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, internaly only */ Spelling; either 'internal' or 'internally' > + time_t 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; Is there anything we can read out of /proc/nnn for the qemu process that would give us a more accurate start time? In fact, why not use virProcessGetStartTime()? And if virProcessGetStartTime is reliable across libvirtd restarts, then you might not need to store a time_t starttime in _virDomainClockDef.