[Spice-devel] migration and qemu/spice versions

[Yonit Halperin]

On 09/06/2011 01:03 PM, Gerd Hoffmann wrote:
> On 09/06/11 11:54, Yonit Halperin wrote:
>> Hi,
>> I'm working on the changes discussed in the thread "changing the timing
>> of spice client linking in migration (RHBZ #725009)".
>> In order to be backward compatible with respect to spice-server and qemu
>> we need
>> (1) new qemu calling the old switch_host if the server is old (instead
>> of spice_server_migrate_end)
>
> New qemu can just call spice_server_migrate_start() and check the return
> value. If it succeeds just go on with seamless migration, otherwise
> (return value < 0) fallback to switch-host.
>
>> (2) new spice-server using the old switch host (and not the new
>> migration mechanism) if qemu is old.
>
> Old qemu which can't handle seamless migration will never ever call
> spice_server_migrate_start().
>
> cheers,
> Gerd
>
This would work, but IMHO it is less readable:
1) I don't plan to use spice_server_migrate_start. We will tell the 
client to connect to the target upon client_migrate_info.
2) Maybe the interface for migration will have more changes in the 
future. Actually, maybe also for this feature, if libvirt will support 
an async client_migrate_info, and we will need an interface for calling 
the appropriate callback.

Cheers,
Yonit.