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Re: [libvirt] [PATCH] qemu: Only issue the rtc-reset-reinjection QMP command on x86.



On Mon, May 25, 2015 at 17:43:05 +0200, Martin Kletzander wrote:
> On Mon, May 25, 2015 at 05:26:01PM +0200, Peter Krempa wrote:
> >On Mon, May 25, 2015 at 16:59:08 +0200, Andrea Bolognani wrote:
> >> The command is only defined in QEMU for TARGET_I386, so issuing it on
> >> any other architecture can't possibly work.
> >>
> >> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1211938
> >> ---
> >>  src/qemu/qemu_driver.c | 20 +++++++++++++-------
> >>  1 file changed, 13 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> >> index aa0acde..743ca6e 100644
> >> --- a/src/qemu/qemu_driver.c
> >> +++ b/src/qemu/qemu_driver.c
> >> @@ -18945,7 +18945,10 @@ qemuDomainSetTime(virDomainPtr dom,
> >>          goto endjob;
> >>      }
> >>
> >> -    if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_RTC_RESET_REINJECTION)) {
> >> +    /* The rtc-reset-reinjection QMP command is only available on x86 */
> >
> >Since we properly track support for this command via the capabilities
> >and qemu does not expose it:
> >
> >> +    if (ARCH_IS_X86(vm->def->os.arch) &&
> >> +        !virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_RTC_RESET_REINJECTION))
> >> +    {
> >>          virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
> >>                         _("cannot set time: qemu doesn't support "
> >>                           "rtc-reset-reinjection command"));
> >
> >I'd simply remove this error message since it is semantically wrong once
> >PPC does not require to reset the RTC reinjection.
> >
> >> @@ -18968,13 +18971,16 @@ qemuDomainSetTime(virDomainPtr dom,
> >>          goto endjob;
> >>      }
> >>
> >> -    qemuDomainObjEnterMonitor(driver, vm);
> >> -    rv = qemuMonitorRTCResetReinjection(priv->mon);
> >> -    if (qemuDomainObjExitMonitor(driver, vm) < 0)
> >> -        goto endjob;
> >> +    /* The rtc-reset-reinjection QMP command is only available on x86 */
> >> +    if (ARCH_IS_X86(vm->def->os.arch)) {
> >> +        qemuDomainObjEnterMonitor(driver, vm);
> >> +        rv = qemuMonitorRTCResetReinjection(priv->mon);
> >
> >And just conditionally call this when the
> >QEMU_CAPS_RTC_RESET_REINJECTION is present and not in an architecture
> >specific way.
> >
> >By this you get rid of the arch specific hackery.
> >
> 
> But on x86 we don't even want to call the SetTime command when we
> cannot reset the rtc reinjection.  On ppc there is no reinjection
> being done, hence nothing to reset.

Well I don't think that the missing reinjection request should be a hard
requirement on x86 since the guest can modify time independently and in
that case the reinjection command won't be even issued. The guest agent
command is technically a guest issued time change too, so there's only
the added bonus that we'd reset the interrupt backlog. One slight issue
is that libvirt does not allow to reset the interrupt backlog while not
setting the time though.

Even if we decide that the check for the existance of the command should
be arch-specific and should report error, the actual place where the
command is called should be made dependant on the presence of the
command rather than the ARCH check, so that it does not need to be
modified once it's implemented somewhere else.

Peter

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