[libvirt] [PATCHv2 02/26] snapshot: better event when reverting qemu to paused snapshot

[Eric Blake]

On 08/24/2011 08:21 AM, Daniel P. Berrange wrote:
>> +++ b/src/qemu/qemu_driver.c
>> @@ -8804,14 +8804,16 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>>                                        QEMU_ASYNC_JOB_NONE);
>>               if (rc<  0)
>>                   goto endjob;
>> +            event = virDomainEventNewFromObj(vm,
>> +                                             VIR_DOMAIN_EVENT_SUSPENDED,
>> +                                             VIR_DOMAIN_EVENT_SUSPENDED_FROM_SNAPSHOT);
>>           } else {
>>               virDomainObjSetState(vm, VIR_DOMAIN_RUNNING,
>>                                    VIR_DOMAIN_RUNNING_FROM_SNAPSHOT);
>> +            event = virDomainEventNewFromObj(vm,
>> +                                             VIR_DOMAIN_EVENT_STARTED,
>> +                                             VIR_DOMAIN_EVENT_STARTED_FROM_SNAPSHOT);
>>           }
>> -
>> -        event = virDomainEventNewFromObj(vm,
>> -                                         VIR_DOMAIN_EVENT_STARTED,
>> -                                         VIR_DOMAIN_EVENT_STARTED_FROM_SNAPSHOT);
>>       } else {
>
> This isn't so nice. The lifecycle model for VMs is
>
>      shutoff<---->  running<------>paused

Even when you use virDomainCreateWithFlags(, VIR_DOMAIN_START_PAUSED)?

>
> This change creates a direct transition from shutoff to paused, missing
> out the running state, which will break any apps which are just looking
> to find out when guests stop/start and don't care about pause/resume.
> Also
>
>      virsh start --paused $GUEST
>
> will only emit a 'VIR_DOMAIN_EVENT_STARTED', so the current beahviour for
> reverting to a paused snapshot matches that.
>
> Arguably we could *also* emit an VIR_DOMAIN_EVENT_SUSPENDED, immediately
> *after* the VIR_DOMAIN_EVENT_STARTED, in both cases though.

This may have bigger cleanup impact, then, if we want to guarantee both 
STARTED and SUSPENDED events on all code paths where we can start life 
paused.

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org