[libvirt] [PATCH V6] support offline migration

[Eric Blake]

On 09/11/2012 08:35 AM, Daniel P. Berrange wrote:
>>
>> Do we really need a new user-visible flag, or can we make this work
>> automatically without having to involve the user?
>> On the other hand, what happens if we do keep this as a user-visible
>> flag?  Should 'virsh migrate --offline' silently ignore the flag if the
>> guest is online, or should it error out stating that the guest is
>> running and not offline?
>>
>> Also, I think we NEED to error out if the guest is offline but the
>> --persistent flag is not set; that is, an offline migration only makes
>> sense if the persistent flag has been requested, but I think that 'virsh
>> migrate --persistent' should automatically be smart enough to do an
>> offline migration.
> 
> No we must not do that. If a guest has shutoff we cannot assume that
> the user / app wants to copy it across to the other host. eg consider
> this scenario
> 
>   admin a: check if guestfoo is running
>   admin b: check if guestfoo is running
>   admin a: migrate guestfoo barhost
>   admin b: migrate guestfoo wizzhost
> 
> IMHO step 4 should fail unless the admin explicitly requested
> that they want to copy across the offline config

Good point - the new flag is necessary, and must be user-visible.  At
which point, do we argue that use of the MIGRATE_OFFLINE flag
automatically implies MIGRATE_PERSISTENT, or should it be an error
unless the user explicitly requests both flags?

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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