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From "Mice Xia" <mice_...@tcloudcomputing.com>
Subject RE: [MERGE] Support VM Snapshot
Date Mon, 11 Mar 2013 02:33:57 GMT
Nitin,

Could you give an example for this?
I'm not aware of how many operations that do not involve state change but need lock VM, if
there are many of them, perhaps we need a more generic way to handle this, like adding lockVM()/unlockVM()/checkVMLock()
methods and use them in these non-state-change operations. But I'm worrying the complexity,
VM full/delta sync is already very complicated, not sure if it's a good idea to handle lock
sync in them.

Regards
Mice

-----Original Message-----
From: Nitin Mehta [mailto:Nitin.Mehta@citrix.com] 
Sent: Saturday, March 09, 2013 12:59 AM
To: cloudstack-dev@incubator.apache.org; Alex Huang
Cc: Anthony Xu
Subject: Re: [MERGE] Support VM Snapshot

Not to nitpick but for better understanding of what Alex's comment on the vm lifecycle. 
I went through the commit and saw the code change below. This change successfully avoids other
vm state changes when the vm is in snapshotting operation but what about the case when the
user triggers "vm snapshot" operation when there is some other state transition is happening
or say another vm operation which doesn't involve State change but requires the resource to
be locked during the operation is executing ?  


     @Override
     public boolean stateTransitTo(VMInstanceVO vm, VirtualMachine.Event e, Long hostId) throws
NoTransitionException {
+        // if there are active vm snapshots task, state change is not
allowed
+        if(_vmSnapshotMgr.hasActiveVMSnapshotTasks(vm.getId())){
+            s_logger.error("State transit with event: " + e + " failed
due to: " + vm.getInstanceName() + " has active VM snapshots tasks");
+            return false;
+        }



Thanks,
-Nitin


On 01/02/13 10:23 PM, "Mice Xia" <weiran.xia1@gmail.com> wrote:

>as Alex suggested
>updated vm-snapshot branch, commit ebca6890fd
>
>1. remove snapshotting/revertting state from VM state machine
>2  prevent VM state change if there are active vm snapshot tasks
>3  change VMSnapshotService interface, except for ListVMSnapshotCmd, 
>need some time to replace it in QueryService, maybe after merging to 
>master
>4  remove unused methods and fix some typos
>
>Regards
>Mice
>
>2013/2/1 Mice Xia <mice_xia@tcloudcomputing.com>:
>> Hi, Alex,
>>
>> Thanks for your feedbacks, please see my comments inline.
>>
>> - VM states is designed for VM lifecycle.  Snapshot is not part of VM 
>>life cycle so therefore the state should not be there.  I think it 
>>make sense to add attributes to VM that says "Do Not Change State" and  
>>who changed the VM to that state.  Then virtualmachinemanager must 
>>obey that until the external caller changes the attribute to now you 
>>can change state.  The would make more sense and decouples 
>>snapshotting from vm lifecycle management.  Snapshotting then has it's 
>>own state (which I see it does already).  If we want to reflect that a 
>>vm snapshot is being taken of a VM, that's a function of the 
>>apiresponse module that gathers up everything about a vm but it shouldn't be changed
in the vm states.
>>
>> [mice] the reason that I added snapshotting/reverting state is that 
>>VM could be in suspend/pause state during snapshoting/reverting, which 
>>is difficult to be categorized into existing states; and during the 
>>process, VM should not be allowed to take any operations; and by 
>>adding new states to VM, the implementation seems more 'natural' and 
>>only minimum codes are changed to virtualmachinemanager.
>> Of course there are some other ways to prevent operations, such as 
>>check if associated snapshots are in snapshotting/reverting states 
>>either in each method (start/stop/migrate/delete...) or hook 
>>stateTransitTo(), but in this way, it does not reflect VM's real state 
>>in hypervisor and more existing codes will be touched.
>>
>> -  Does VM Revert operation work in the following way: Stop VM, 
>>restore to snapshot, and run VM?  Shouldn't this be orchestration 
>>inside snapshot manager?
>>
>> [mice] if a running VM is reverted to a memory enabled snapshot, 
>>current implementation is running--> reverting-->running  If a stopped 
>>VM is reverted to memory disabled snapshot:
>>stopped-->reverting->stopped
>> If a running VM is reverted to a memory disabled snapshot:
>>running--(Stop VM)-->stopped-->reverting--> stopped  If a stopped VM 
>>is reverted to a memory enabled snapshot:
>>stopped--(Start VM)-->running->reverting-->running
>>
>> These logics are implemented in snapshot manager.
>>
>> - Does VM snapshot interfere with volume snapshot?  Volume snapshot 
>>today makes the assumption that it is the only code that's making 
>>snapshots and can break if there are additional snapshots in between.
>>This is bad design in volume snapshot but unfortunately that's how 
>>it's design.
>>
>> [mice] about volume snapshot, for xensever, if parent VHD cannot be 
>>found, it will take a full volume snapshot (this indeed break current 
>>semantics but it still works)  For vmware, the volume snapshot is 
>>always a full one.
>>
>> - VMSnapshotService follows the other services in passing the cmds to 
>>the service.  That's really a bad practice that we should stop.  Cmds 
>>are really translations between over-the-wire api and java interface.
>>They shouldn't have been passed to down to the java interface.
>> [
>> mice] I'll change it
>>
>> A small note: Would it be better to call it VM restore than VM revert?
>>Revert really should be RevertTo which I think is in the code but is 
>>not consistent.  Some places it's just REVERT (for example, the event 
>>is just revert).
>>
>> [mice] there is already RESTORE, which is restoring a destroyed VM to 
>>stopped. RevertTo is fine with me.
>>
>> -Mice
>>
>>
>> -----Original Message-----
>> From: Alex Huang [mailto:Alex.Huang@citrix.com]
>> Sent: Friday, February 01, 2013 9:24 AM
>> To: CloudStack DeveloperList
>> Cc: Mice Xia
>> Subject: RE: [MERGE] Support VM Snapshot
>>
>> Hi Mice,
>>
>> Sorry it took so long to review this.  Wanted to as soon as I saw it 
>>on the list but was sick and didn't get a chance.  In general, I think 
>>the code is excellent.  I'm impressed how much Cloudstack internal 
>>code in touch and how comfortable the changes look.  Nicely done!
>>
>> I have a few comments:
>> - VM states is designed for VM lifecycle.  Snapshot is not part of VM 
>>life cycle so therefore the state should not be there.  I think it 
>>make sense to add attributes to VM that says "Do Not Change State" and  
>>who changed the VM to that state.  Then virtualmachinemanager must 
>>obey that until the external caller changes the attribute to now you 
>>can change state.  The would make more sense and decouples 
>>snapshotting from vm lifecycle management.  Snapshotting then has it's 
>>own state (which I see it does already).  If we want to reflect that a 
>>vm snapshot is being taken of a VM, that's a function of the 
>>apiresponse module that gathers up everything about a vm but it shouldn't be changed
in the vm states.
>> -  Does VM Revert operation work in the following way: Stop VM, 
>>restore to snapshot, and run VM?  Shouldn't this be orchestration 
>>inside snapshot manager?
>> - Does VM snapshot interfere with volume snapshot?  Volume snapshot 
>>today makes the assumption that it is the only code that's making 
>>snapshots and can break if there are additional snapshots in between.
>>This is bad design in volume snapshot but unfortunately that's how 
>>it's design.
>> - VMSnapshotService follows the other services in passing the cmds to 
>>the service.  That's really a bad practice that we should stop.  Cmds 
>>are really translations between over-the-wire api and java interface.
>>They shouldn't have been passed to down to the java interface.
>>
>> A small note: Would it be better to call it VM restore than VM revert?
>>Revert really should be RevertTo which I think is in the code but is 
>>not consistent.  Some places it's just REVERT (for example, the event 
>>is just revert).
>>
>> --Alex
>>
>>> -----Original Message-----
>>> From: Chiradeep Vittal
>>> Sent: Wednesday, January 30, 2013 4:44 PM
>>> To: CloudStack DeveloperList
>>> Cc: Alex Huang
>>> Subject: Re: [MERGE] Support VM Snapshot
>>>
>>> Can we get Alex to review this? He is the designer of the state 
>>>machine.
>>>
>>> On 1/30/13 5:26 AM, "Murali Reddy" <Murali.Reddy@citrix.com> wrote:
>>>
>>> >On 30/01/13 2:24 PM, "Mice Xia" <mice_xia@tcloudcomputing.com> wrote:
>>> >
>>> >>Agreed.
>>> >>Adding VM states are likely to have some side-effects, but for 
>>> >>moveVMToUser case, does it explicitly reject other transient 
>>> >>states such as stating/stopping/migrating?
>>> >>
>>> >>-Mice
>>> >
>>> >No, it just accepts any state other than 'Running' (though it 
>>> >should have checked for the valid states in which VM can move to other user).
>>> >
>>> >I am just saying, there could such VM state based assumptions, you 
>>> >might want to check.
>>> >
>>

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