[libvirt] pvpanic plans?
Paolo Bonzini
pbonzini at redhat.com
Thu Oct 31 15:26:13 UTC 2013
Il 31/10/2013 16:09, Michael S. Tsirkin ha scritto:
> On Thu, Oct 31, 2013 at 03:56:42PM +0100, Paolo Bonzini wrote:
>> Il 31/10/2013 15:52, Michael S. Tsirkin ha scritto:
>>>>> Yes, it does.
>>> What does it break exactly?
>>
>> The point of a panicked event is to examine the guest at a particular
>> moment in time (e.g. host-initiated crash dump). If you let the guest
>> run, it may reboot and prevent you from getting a meaningful dump.
>
> Well we trust guest anyway, so I think we can trust it to call halt.
No, we cannot. Reboot-in-guest-after-dump-on-host is a perfectly fine
configuration.
>>>>> But I think that, once we make the pvpanic device is
>>>>> optional, to a large extent there is no bug. Adding the pvpanic
>>>>> device to the VM will make libvirt obey <oncrash> instead of the
>>>>> in-guest setting, and that's it.
>>>>>
>>>>> Two months have passed and no casualties have been reported due to
>>>>> pvpanic. Let's just remove the auto-pvpanic from all machine types in
>>>>> 1.7 (yes, that's backwards incompatible in a strict sense), document
>>>>> it in the release notes, and hope that the old QEMU versions with
>>>>> mandatory pvpanic die of old age.
>>>
>>> Nod. I'm fine with that.
>>>
>>> I think we still need to do get rid of the PANICKED state somehow.
>>> If we can't replace it with RUNNING state, let's replace it with PAUSED.
>>>
>>> For example, you can't continue from panicked for some reason.
>>> You can't do a reset. But you can pause and then continue.
>>
>> We need to keep the PANICKED state, but we can make it a normal
>> "resumable" state.
>
> If it's resumable how is it different from PAUSED?
If the guest panics while for some reason libvirtd went down, libvirt
can see what happened. It is similar to the "I/O error" state in this
respect.
> Looks like all transitions from paused state should be allowed from panicked
> state. So why keep it separate?
Because you can poll for the state instead of watching an event.
Paolo
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