[libvirt] [PATCH] qemu: Issue rtc_reset_reinjection command after guest-set-time

[Michal Privoznik]

On 13.08.2014 18:30, Eric Blake wrote:
> On 08/13/2014 06:51 AM, Michal Privoznik wrote:
>
> s/_/-/2 in the subject line
>
>> An advice appeared there on the qemu-devel list [1]. When a domain is
>> suspended and then resumed guest kernel is not aware of this. So we've
>> introduced virDomainSetTime API that resets the time within guest
>> using qemu-ga. On the other hand, qemu itself is trying to make RTC
>> beat faster to catch the difference. But if we don't tell qemu that
>> guest's time was reset via the other method, both mechanisms are
>> applied resulting in again wrong guest time. In order to avoid summing
>> both corrections we need to tell qemu that it should not use the RTC
>> injection if the guest time is set via guest agent.
>>
>> 1: http://www.mail-archive.com/qemu-devel@nongnu.org/msg236435.html
>>
>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>> ---
>
>> +++ b/src/qemu/qemu_driver.c
>> @@ -16879,6 +16879,16 @@ qemuDomainSetTime(virDomainPtr dom,
>>       rv = qemuAgentSetTime(priv->agent, seconds, nseconds, rtcSync);
>>       qemuDomainObjExitAgent(vm);
>>
>> +    if (!virDomainObjIsActive(vm)) {
>> +        virReportError(VIR_ERR_OPERATION_INVALID,
>> +                       "%s", _("domain is not running"));
>> +        goto endjob;
>> +    }
>> +
>> +    qemuDomainObjEnterMonitor(driver, vm);
>> +    rv = qemuMonitorRTCResetReinjection(priv->mon);
>> +    qemuDomainObjExitMonitor(driver, vm);
>
> This forces the command to fail if qemu is too old to have
> rtc-reset-reinjection but the agent is new enough to set time.  Should
> you make this code conditional on whether qemu supports the QMP command?

I'm not sure. If that's the case, both corrections will apply so guest 
ends up with incorrect time anyway. And if the API is to guarantee 
correctly set time, it must fail if such guarantees can't be made IMO.

>
>
>>   }
>> +
>> +int
>> +qemuMonitorJSONRTCResetReinjection(qemuMonitorPtr mon)
>> +{
>> +    int ret = -1;
>> +    virJSONValuePtr cmd;
>> +    virJSONValuePtr reply = NULL;
>> +
>> +    if (!(cmd = qemuMonitorJSONMakeCommand("rtc-reset-reinjection",
>> +                                           NULL)))
>> +        return ret;
>> +
>> +    ret = qemuMonitorJSONCommand(mon, cmd, &reply);
>> +
>> +    if (ret == 0)
>> +        ret = qemuMonitorJSONCheckError(cmd, reply);
>> +
>> +    virJSONValueFree(cmd);
>> +    virJSONValueFree(reply);
>> +    return ret;
>> +}
>
> Is it worth enhancing the testsuite to add coverage for this command and
> expected response?

Yeah. I'll post v2.

Michal