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

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.

> Thanks for sharing your ideas! >