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Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/> |
Date: |
Fri, 23 May 2014 15:35:19 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) |
Luiz Capitulino <address@hidden> writes:
> On Fri, 23 May 2014 00:50:38 -0300
> Marcelo Tosatti <address@hidden> wrote:
>
>> > Then the guest triggers an RTC update, so qemu sends an event, but the
>> > event is lost. Then libvirtd starts again, and doesn't realize the
>> > event is lost.
>>
>> Yes, but that case is also true for any other QMP asynchronous event,
>> and therefore should be handled generically i suppose (QMP channel data
>> should be maintained across libvirtd shutdown). Luiz?
>
> Maintaining QMP channel data doesn't solve this problem, because all sorts
> of race conditions are still possible. For example, libvirt could crash
> after having received the event but before handling it.
>
> The most reliable way we found to solve this problem, and that's what we
> do for other events, is to allow libvirt to query the information the event
> is reporting. An event is nothing more than a state change in QEMU, and QEMU
> state is persistent during the life time of the VM, so we allow libvirt to
> query the state of anything that may send an event.
In fact, this is a general rule: when libvirt tracks an event, it also
needs a way to poll for the information in the event.
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Eric Blake, 2014/05/22
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Marcelo Tosatti, 2014/05/22
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Laine Stump, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Laine Stump, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Eric Blake, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Marcelo Tosatti, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Eric Blake, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Laine Stump, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Luiz Capitulino, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>,
Markus Armbruster <=
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Marcelo Tosatti, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Marcelo Tosatti, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Luiz Capitulino, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Daniel P. Berrange, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Eric Blake, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Paolo Bonzini, 2014/05/23
- Re: [Qemu-devel] [libvirt] [PATCHv2 3/4] qemu: fix RTC_CHANGE event for <clock offset='variable' basis='utc'/>, Marcelo Tosatti, 2014/05/29