Re: [Xen-devel] Many same managed domain

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Sun, Jul 22, 2007 at 02:09:01PM +0900, Masaki Kanno wrote:
> Hi,
> 
> When I tested xm new command without uuid parameter repeatedly, 
> I saw many same managed domain as follows. 
> 
> # xm list
> Name                                        ID   Mem VCPUs      State   
> Time(s)
> Domain-0                                     0   941     2     r-----     51.9
> # xm new /xen/vm1.conf 
> Using config file "/xen/vm1.conf".
> # xm new /xen/vm1.conf 
> Using config file "/xen/vm1.conf".
> # xm new /xen/vm1.conf 
> Using config file "/xen/vm1.conf".
> # xm list
> Name                                        ID   Mem VCPUs      State   
> Time(s)
> Domain-0                                     0   941     2     r-----     56.3
> vm1                                              256     1                 0.0
> vm1                                              256     1                 0.0
> vm1                                              256     1                 0.0
> 
> 
> But, when I tested xm new command with uuid parameter repeatedly, 
> I did not see same managed domain as follows. 
> 
> # xm list
> Name                                        ID   Mem VCPUs      State   
> Time(s)
> Domain-0                                     0   941     2     r-----     69.9
> # xm new /xen/vm1.conf uuid="aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee"
> Using config file "/xen/vm1.conf".
> # xm new /xen/vm1.conf uuid="aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee"
> Using config file "/xen/vm1.conf".
> # xm new /xen/vm1.conf uuid="aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee"
> Using config file "/xen/vm1.conf".
> # xm list
> Name                                        ID   Mem VCPUs      State   
> Time(s)
> Domain-0                                     0   941     2     r-----     74.4
> vm1                                              256     1                 0.0
> 
> 
> I think that xm new command should cause a command error if without 
> uuid parameter.  What do you think?

No that would break backwards compatability for user who rely on Xen 
autogenerating the UUID. 

In order to maintain back-compatability with existing use cases, the user
needs to be able to update the existing VM config with 'xm new' if the name
or UUID match, while preventing multiple VMs with same name. So the the rules 
when defining a new VM need to follow this logic

  - If the UUID is not specified
        - If a VM with same name exists
            => Update the config for that existing VM
        - Else no vm with same name exists
            => Define a brand new VM with auto-generated UUID
  - Else UUID is specified
        - If a VM with same UUID exists
              - If name is different
                    => Error
              - Else if name is same
                    => Update the config for that existing VM
       - Else no VM with same UUID exists
            => Define a branch new VM with that name

Depending on where in the XenD code you put this error checking you may need
some extra special case rules handle stuff like localhost migration.

Regards,
Dan.
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