[libvirt] [PATCH] RFC: Support QEMU live uprgade

[Daniel P. Berrange]

On Tue, Nov 12, 2013 at 08:14:11PM +0800, Zheng Sheng ZS Zhou wrote:
> Hi all,
> 
> Recently QEMU developers are working on a feature to allow upgrading
> a live QEMU instance to a new version without restarting the VM. This
> is implemented as live migration between the old and new QEMU process
> on the same host [1]. Here is the the use case:
> 
> 1) Guests are running QEMU release 1.6.1.
> 2) Admin installs QEMU release 1.6.2 via RPM or deb.
> 3) Admin starts a new VM using the updated QEMU binary, and asks the old
> QEMU process to migrate the VM to the newly started VM.
> 
> I think it will be very useful to support QEMU live upgrade in libvirt.
> After some investigations, I found migrating to the same host breaks
> the current migration code. I'd like to propose a new work flow for
> QEMU live migration. It is to implement the above step 3).

How does it break migration code ? Your patch below is effectively
re-implementing the multistep migration workflow, leaving out many
important features (seemless reconnect to SPICE clients for example)
which is really bad for our ongoing code support burden, so not
something I want to see.

Daniel
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