Re: [Xen-devel] [PATCH 10/11] libxl: Allow migration with qemu-xen.

[Alex Bligh <alex@xxxxxxxxxxx>]

Ian,

Firstly, thanks for the review. I think the issue of JSON_ERROR's removal
you thought was OK in the end because it was from the _internal file

--On 12 February 2013 15:44:52 +0000 Ian Jackson 
<Ian.Jackson@xxxxxxxxxxxxx> wrote:
> Alex Bligh writes ("[Xen-devel] [PATCH 10/11] libxl: Allow migration with 
qemu-xen."):
> > Backport of xen-unstable patch:
> > : HG changeset patch
> > : User Anthony PERARD <anthony.perard@xxxxxxxxxx>
> > : Date 1349693136 -3600
> > : Node ID 0995890022391682a2499a202c3c8608e1d3780a
> > : Parent  08fac5c2bf3dcbc493ce45091383f6ce1938f369
>
> This backport is fine but needs to come at the end of the series, I
> think ?
I can reorder patch 11 so it precedes patch 10 if you want. It's only
there as I found the bug in patch 11 later. Tell me if you want me to
do this.

If I'm right re JSON_ERROR, the only substantive issue is the following:

> I've had another thought: what if this series is applied, including
> this final patch, but the result is used with an older qemu which
> hasn't had the relevant features added ?
Does that ever happen? By which I mean does that ever happen in a manner
that is permitted?

I thought if you were using Xen 4.2 you pretty much had to be using either
a qemu upstream compiled specifically for Xen and thus distributed with
it, so you'd expect to upgrade it, or you'd be using one of the newer
upstream releases which has all this stuff in anyway. Was there some
window where true upstream qemu (as opposed to the one carried by Xen) had
a release version which carried Xen 4.2 support and qemu DM, but not
live migrate?

> AFAICT the result would probably be a failure to execute the logdirty
> switch.  Is that error sufficiently clean ?
This might depend on our policy of using mixed versions of qemu and
xen. If a policy of "either use the version of qemu included in Xen
or use a version greater than N.N.N" is ok, then I think the answer is
yes.

If not, then I'm not sure. Does Xen currently check the version of
qemu somehow?

--
Alex Bligh

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