Re: [Qemu-devel] [RFC] Introduce vm_stop_permanent()

[Jan Kiszka]

On 2011-07-28 20:00, Luiz Capitulino wrote:
> On Thu, 28 Jul 2011 19:52:31 +0200
> Jan Kiszka <address@hidden> wrote:
> 
>> On 2011-07-28 19:48, Luiz Capitulino wrote:
>>> On Thu, 28 Jul 2011 14:39:23 -0300
>>> Luiz Capitulino <address@hidden> wrote:
>>>
>>>> On Thu, 28 Jul 2011 17:20:41 +0200
>>>> Jan Kiszka <address@hidden> wrote:
>>>>
>>>>> On 2011-07-28 17:18, Luiz Capitulino wrote:
>>>>>> On Thu, 28 Jul 2011 16:19:19 +0200
>>>>>> Jan Kiszka <address@hidden> wrote:
>>>>>>
>>>>>>> On 2011-07-28 15:37, Avi Kivity wrote:
>>>>>>>> On 07/28/2011 04:31 PM, Luiz Capitulino wrote:
>>>>>>>>> On Thu, 28 Jul 2011 10:23:22 +0300
>>>>>>>>> Avi Kivity<address@hidden>  wrote:
>>>>>>>>>
>>>>>>>>>>  On 07/28/2011 12:44 AM, Blue Swirl wrote:
>>>>>>>>>>  >  On Wed, Jul 27, 2011 at 9:42 PM, Luiz
>>>>>>>>> Capitulino<address@hidden>   wrote:
>>>>>>>>>>  >  >   This function should be used when the VM is not supposed to
>>>>>>>>> resume
>>>>>>>>>>  >  >   execution (eg. by issuing 'cont' monitor command).
>>>>>>>>>>  >  >
>>>>>>>>>>  >  >   Today, we allow the user to resume execution even when:
>>>>>>>>>>  >  >
>>>>>>>>>>  >  >     o the guest shuts down and -no-shutdown is used
>>>>>>>>>>  >  >     o there's a kvm internal error
>>>>>>>>>>  >  >     o loading the VM state with -loadvm or "loadvm" in the
>>>>>>>>> monitor fails
>>>>>>>>>>  >  >
>>>>>>>>>>  >  >   I think only badness can happen from the cases above.
>>>>>>>>>>  >
>>>>>>>>>>  >  I'd suppose a system_reset should bring the system back to
>>>>>>>>> sanity and
>>>>>>>>>>  >  then clear vm_permanent_stopped (where's -ly?)
>>>>>>>>>
>>>>>>>>> What's -ly?
>>>>>>>>>
>>>>>>>>
>>>>>>>> permanent-ly.
>>>>>>>>
>>>>>>>>>>  >  except maybe for KVM
>>>>>>>>>>  >  internal error if that can't be recovered. Then it would not very
>>>>>>>>>>  >  permanent anymore, so the name would need adjusting.
>>>>>>>>>>
>>>>>>>>>>  Currently, all kvm internal errors are recoverable by reset (and
>>>>>>>>>>  possibly by fiddling with memory/registers).
>>>>>>>>>
>>>>>>>>> Ok, but a poweroff in the guest isn't recoverable with system_reset
>>>>>>>>> right? Or does it depend on the guest?
>>>>>>>>
>>>>>>>> Right, it's not recoverable if you shut the power down where the 
>>>>>>>> tractor
>>>>>>>> beam is coupled to the main reactor.
>>>>>>>
>>>>>>> system_reset will bring all emulated devices back into their power-on
>>>>>>> state - unless we have remaining bugs to fix. Actually, one may consider
>>>>>>> issuing this reset automatically on vm_start after "permant" vm_stop.
>>>>
>>>> The only permanent vm_stop we'd have is poweroff when -no-shutdown is used.
>>>>
>>>> Are you saying that system_reset should be able to recover from that too?
>>>
>>> It already does, so we don't have permanent stops.
>>
>> Exactly. We just have stops over inconsistent states that require a
>> reset to continue with anything useful.
> 
> Yes. If I got you right, you suggest that we do the reset automatically.
> 
> I think it's better to let the user do it, because s/he might want to
> do something else before resetting. For example, for the kvm error the
> user might want to save the vm state.

Associating the reset with a cont means requesting an explicit action
from the user. I'm not suggesting to do the reset when the stop state is
entered.

> 
> For the poweroff case with -no-shutdown it's probably fine, but I don't
> want to hard code special cases. It's better and easier to treat them all
> as "require system_reset to recover".

In any case, we need to tag the current state as stopped-and-invalid or
so vs. a normal stop. That remains a valuable first step. How to deal
with that information is the second one.

Jan

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