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Date: Tue, 8 Feb 2011 12:37:14 +0530
From: Amit Shah <amit.shah@redhat.com>
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Subject: [Qemu-devel] Re: new->old version migration
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>, qemu list <qemu-devel@nongnu.org>, Juan Quintela <quintela@redhat.com>

On (Tue) 08 Feb 2011 [08:42:14], Michael S. Tsirkin wrote:
> I see. I'm unhappy with the facts that
> 1. if (feature) is spread all over the code instead
>    of just in migration
> 2. it is also obfuscated with if (flow_control)
>    instead of plain if (migrate to qemu < 0.14)
>    so removing it will be much harder
> 3. this forces anyone who wants
>    a VM compatible with qemu 0.13 to also lose data,
>    even if migration to 0.13 is never attempted.

If a machine is started with -M pc-0.13 then we can safely assume the
user will want to migrate to another 0.13 machine.

Also, flow control is not part of qemu yet.  This code ensures that when
flow control lands, we'll be ready to use it.

So there's 0 difference with this code to a user that runs with -M
pc-0.13.  But this code will ensure a user running with 0.15 and 0.14
can migrate among the two machine types with and without flow control
being available (assuming chardev flow control lands in 0.15).

		Amit