[libvirt] Google Summer of Code 2013 ideas wiki open

[Michal Privoznik]

On 15.04.2013 04:43, harryxiyou wrote:
> On Fri, Apr 12, 2013 at 11:29 PM, Stefan Hajnoczi <stefanha at gmail.com> wrote:
>> On Fri, Apr 12, 2013 at 10:58 AM, Daniel P. Berrange
>> <berrange at redhat.com> wrote:
>>> On Fri, Apr 12, 2013 at 08:34:18AM +0200, Michal Privoznik wrote:
>>>> On 10.04.2013 15:13, harryxiyou wrote:
>>>>>
>>>>> Hi all,
>>>>>
>>>>> I've also got some ideas like following for GSOC 2013.
>>>>>
>>>>> Storage driver jobs.
>>>>>
>>>>> Currently, there is no Libvirt storage API to rename storage volume,
>>>>> storage pool, snapshot, etc. There is also no Libvirt API to move
>>>>> volume from one pool to another using libvirt API. Possibly those
>>>>> pools could have different backend (lvm, dir, ...). So i wanna finish
>>>>> these jobs for Libvirt during GSOC 2013. See following in details.
>>>>>
>>>>>
>>>>> 1, Rename storage volume. I will develop ' virsh vol-rename xxx'
>>>>> option for virsh tool.
>>>>>
>>>>> 2, Rename storage pool. I will develop 'virsh pool-rename xxx'
>>>>> option for virsh tool.
>>>>>
>>>>> 3, Rename snapshot. I will develop 'virsh snapshot-rename xxx'
>>>>> option for virsh tool.
>>>>
>>>> I am not sure we want *rename virsh commands. Not only for storage, but
>>>> in general. And even if we do want these, they don't require a new API.
>>>> They can be implemented with simple vir*GetXML(); vir*Define();
>>>> vir*Undefine();
>>>
>>> Actually I disagree - I think you want explicit APIs for renames, so that
>>> it can be done atomically / with minimal risk of failure halfway.
>>>
>>>>>
>>>>> 4, Move volume from one pool to another. I will develop 'virsh vol-move xxx'
>>>>> option for virsh tool.
>>>>
>>>> This one makes more sense, however I am worried about difficulty a bit.
>>>> A GSoC project should take 3 months for a student to complete. This is
>>>> something that even unexperienced user can accomplish in less than a month.
>>>
>>> Isn't all the libvirt functionality for this already existing? it it
>>> is basically just  virStorageVolCreateFrom(...original vol) and then
>>> delete the original volume.
>>
>> Michal said earlier that virsh vol-move seemed too small a task.
>>
>> Do you think that these 4 tasks together merit a 12-week project?
>>
> 
> Let me give a summary about my ideas for Libvirt of GSOC 2013.
> 
> Libvirt storage jobs.
> 
> This project includes renaming storage volume(storage pool, snapshot,etc),
> moving volume from one pool to another, the capability support for storage
> driver (like virsh capabilities for the hypervisor drivers, e.g. what pool types
> it supports, what volume types each pool type supports, even may what
> operations/APIs the pool type support, ...etc).
> 
> If these ones(or portions of them) are deserved to do, we should add them
> to our wiki of GSOC 2013. Students will submit their applications for these
> ideas at April 22nd. Could anyone please review these ideas(or portions
> of them)? Thanks very much in advance.
> 

Makes sense. However, I would drop renaming limitation just for volumes.
At least not specifically say in description it's just a 'volume
renaming'. This as advantage that we are more flexible and if student is
doing good, he/she can introduce renaming to other libvirt objects as
well. If he/she doesn't have so much time, doing renaming just for
volumes is fine.

Just a side note, I am still not huge fan of introducing a special API
for this renaming. Doing it in virsh makes sense, however introducing a
new API seems like overkill to me. I mean, if mgmt application has 2
threads fighting over one domain, it has to already have a mutual
exclusion procedure. If there are no such threads, then we are safe per se.

But if we are ever going to have a rename API, it's gonna be hard time
for everyone. We would have to move files (e.g. associated snapshots,
monitor socket, logs, etc) and what if we fail somewhere in the middle
of the process. We would have to perform a rollback.

Michal