Re: [Xen-devel] Many same managed domain

[Mats Petersson <mats@xxxxxxxxxxxxxxxxx>]

At 15:46 22/07/2007, Daniel P. Berrange wrote:
> 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.
With live migration/save&restore, you shouldn't need to worry about 
the name [1], but obviously, the UUID should be the same for the new 
and old migrated domain, and live migration should be allowed to "localhost".
[1] Part of "xm save/migrate" is to prepend "migrating" to the name 
of the domain, so there should be no name conflict with live 
migration when the new domain is created.
--
Mats


> Regards,
> Dan.
> --
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