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Date: Fri, 08 Jul 2011 12:17:45 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 0/3] non-migratable devices
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: qemu-devel@nongnu.org

On 07/08/2011 11:59 AM, Gerd Hoffmann wrote:
>
>
>> For scsi-cd and other empty-but-generally-migratable devices we should
>> probably add an empty vmstate, so that any further addition can be done
>> as subsections.
>
> That will break migration to older versions which don't know about the
> new sections, even if they are empty ...

scsi-cd is new in 0.15, older versions have scsi-disk only.  That's why 
we should take the occasion to add the empty vmstate at least to it.

For other devices, it's better to make the breakage in a single version. 
  It also allows to make 0.15 the "flag day" where each device shall 
have a VMState or the entire VM will not be migratable.  If desired, in 
the future we can revert this behavior for pc-0.14 and earlier machines.

Paolo