[Qemu-devel] Re: [RFC PATCH 0/5] Save state error handling (kill off no_migrate)

[Anthony Liguori <anthony@codemonkey.ws>]

On 10/05/2010 09:29 PM, Alex Williamson wrote:
> On Tue, 2010-10-05 at 14:58 -0600, Alex Williamson wrote:
>    
>> On Tue, 2010-10-05 at 15:49 -0500, Anthony Liguori wrote:
>>      
>>> On 10/05/2010 03:46 PM, Alex Williamson wrote:
>>>        
>>>> On Tue, 2010-10-05 at 15:41 -0500, Anthony Liguori wrote:
>>>>
>>>>          
>>>>> On 10/05/2010 03:35 PM, Alex Williamson wrote:
>>>>>
>>>>>            
>>>>>> I was thinking of making KVM VMs with assigned PCI devices
>>>>>> unsavable/unmigratable, but I wasn't thrilled with the
>>>>>> no_migrate solutions.  The more generic solutions seems to be
>>>>>> simply letting save handlers return an error if the device can't
>>>>>> be migrated.  This is also much more generic than a one-way
>>>>>> bit flip of the no_migrate flag.  For a vmsd based registration,
>>>>>> the pre_save() routine seems to be the right place to allow
>>>>>> devices to abort.  The series also carries the error back through
>>>>>> all the vmstate callers.  If this looks good, I'll give it some
>>>>>> more testing and submit as non-RFC.  Thanks,
>>>>>>
>>>>>>
>>>>>>              
>>>>> Doesn't this mean that we don't fail the migration until after
>>>>> transferring all of the memory contents?
>>>>>
>>>>>            
>>>> That's the case with the current no_migrate implementation too, it
>>>> doesn't get called until qemu_savevm_state_complete().  Thanks,
>>>>
>>>>          
>>> Ouch, that's unfortunate but also should be easily fixable.
>>>
>>> But making a save handler fail seems would make it impossible to get
>>> instant failure semantics.
>>>        
>> True.  Ok, so maybe we do still need a separate no migrate registration.
>> In any case, I think it's a good idea to allow the save routines to have
>> a failure path, but I'll work on a way to disable migration that's not
>> quite so coupled with the savevm entry (it seems silly for device
>> assignment to register a savevm only for the purpose of then registering
>> as non-migratable).  Thanks,
>>      
> On second thought, I think we should take the same approach with the
> live handlers.  We just need to make SaveSetParamsHandler return an int
> and check it and the SaveLiveStateHandler return for<  0.  Then we have
> a full spectrum of points at which a savevm handler can abort a
> migration.  If that sounds reasonable, I'll send a new series tomorrow.
>    

Yes, makes sense to me.

Regards,

Anthony Liguori

> Thanks,
>
> Alex
>
>