[Kimchi-devel] Rethink the Relationship of Template and VM

[Sheldon]

On 04/28/2014 01:45 PM, Mark Wu wrote:
> On 04/27/2014 10:38 PM, Zhou Zheng Sheng wrote:
>> Hi all,
>>
>> I'm working on host device passthrough. A a problem troubles me: I see
>> in current Kimchi code, when adding a specific SCSI or iSCSI LUN, it is
>> added to the template but not the VM. This is counter-intuitive, because
>> a template is to store the common information for lots of VMs, while a
>> specific LUN should only be used by just one VM. It's OK for DIR, NFS
>> and Logical storage pool being managed by the template, because actually
>> the template allocates a new specific volume for a new VM, so the
>> specific volume goes with the specific VM but not the template. Since we
>> don't define a specific DIR storage volume in the template, why we
>> define a concrete LUN in it?
>>
>> The first problem in the current design is that we can not attach a new
>> LUN to a VM after the VM is created.
>>
>> Another problem is that we mix the "things in common" and "things
>> special" in template, thus we make its responsibility complex. Static
>> and dynamic validations are also mixed in template.
>>
>> The third problem is that if we get 10 LUNs for 10 VMs, the user has to
>> create 10 templates at first, then create 10 VMs from the 10 templates
>> respectively. It's a bit tedious.
>>
>> The fourth problem is that if a LUN is used by a VM, usually it should
>> not be used by other VMs, so it implies that by specifying a LUN in a
>> template, the template should only create just one VM. What's the point
>> to make a template that only produces one VM?
>>
>> It seems a cleaner way is putting SCSI LUN handling code in VM. Firstly,
>> we can assign a SCSI/iSCSI storage pool to the template. When it's time
>> to create a VM from the template, Kimchi lists all the available LUNs in
>> the storage pool and the user can just pick some LUNs. The VM override
>> parameters are suitable to store the LUNs information. It also makes
>> possible to implement some mechanisms to add/remove LUNs after a VM is
>> created, which is a very typical user requirement.
>>
>> The same problem exists in host device passthrough. For a specific
>> device, it should be passthrough to a specific VM but not a template.
>> I'd like to collect some thoughts before my device passthrough patch V2.
>> In which place you'd suggest me to put device passthrough information,
>> template or VM?
> Template should NOT include any vm specific information. As I mentioned
> in the comments of your pci passthrough patch, we need allow user have
> chance to customize the configuration when creating vm based on
> template.
ACK
>> Thanks for sharing your ideas!
>>
>
>


-- 
Thanks and best regards!

Sheldon Feng(冯少合)<shaohef at linux.vnet.ibm.com>
IBM Linux Technology Center