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Re: [libvirt] [PATCH] qemu: Transition domain to PAUSED after 'stop' command



On 19.09.2012 14:59, Martin Kletzander wrote:
> On 09/19/2012 12:16 PM, Michal Privoznik wrote:
>> On 19.09.2012 11:43, Michal Privoznik wrote:
>>> Currently, we mark domain PAUSED (but not emit an event)
>>> just before we issue 'stop' on monitor; This command can
>>> take ages to finish, esp. when domain's doing a lot of
>>> IO - users can enforce qemu to open files with O_DIRECT
>>> which doesn't return from write() until data reaches the
>>> block device. Having said that, we report PAUSED even if
>>> domain is not paused yet.
>>> ---
>>>
>>> The event is emitted correctly after all operations returns though.
>>> But if mgmt app would 'virsh domstate $dom' as we are issuing 'stop'
>>> monitor command it could get spurious results.
>>
>> Just for the record, qemu 'stop' command is guaranteed to NOT return
>> until after all disks are synced. It is not that kind of command which
>> just requests an operation an returns immediately (like 'shutdown' or
>> something).
>>
>> This bug really confuses the enemy - esp. when mgmt application asks
>> from another thread, it may get PAUSED domain state even though qemu is
>> still syncing the disks or monitor command hasn't been issued at all or
>> is about to fail.
>>
> 
> That sounds reasonable. Reporting PAUSED when the domain is _being_
> stopped and even if the operation might still fail is less sensible to
> me as well. It would be nice to have a STOPPING state, but that's idea
> for a longer period of time and more places in the code consequently
> heading towards more problems etc.
> 
> So ACK for this version.
> 
> Martin
> 

Thanks, pushed now.

Michal


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