[libvirt] RFC: libvirt support for QEMU live patching

Peter Krempa pkrempa at redhat.com
Mon Sep 18 08:26:40 UTC 2017


On Mon, Sep 18, 2017 at 09:37:14 +0200, Martin Kletzander wrote:
> On Fri, Sep 15, 2017 at 09:18:18AM +0100, Daniel P. Berrange wrote:
> > On Fri, Sep 15, 2017 at 01:27:31PM +0530, Madhu Pavan wrote:

[...]

> > It isn't possible to make it work correctly in the general case, because
> > both QEMU processes want to own the same files on disk. eg both might want
> > to listen on a UNIX socket /foo/bar, but only one can do this. If you let
> > the new QEMU delete the original QEMU's sockets, then you either break or
> > delay incoming connections during the migration time, and you make it
> > impossible to roll back on failure, or both. This kind of thing is not
> > something that's acceptable for the usage scenerio described, which would
> > need to be bulletproof to be usable in production.
> > 
> 
> Can't we utilize namespaces for this?  Lot of the things could be
> separated, so we could fire up a new VM that's "containerized" like
> this, migrate to it and then fire up a new one and migrate back.  If the
> first migration fails then we can still fallback.  If it does not, then
> the second one "should" not either.

If you are willing to accept this kind of slow-down/overhead you can
as well as save the VM to file and restore it. This works as the upgrade
path even now.
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