Re: [Xen-devel] xen4.2 + qemu-upstream domain rename partial failure (& migration)

[Alex Bligh <alex@xxxxxxxxxxx>]

Ian,

--On 16 January 2013 09:56:28 +0000 Ian Campbell <Ian.Campbell@xxxxxxxxxx> 
wrote:
> On Sat, 2013-01-12 at 10:26 +0000, Alex Bligh wrote:
> > So, to be clear, it's renaming in xenstore (and xl list) but not the
> > rename is not being transmitted to qemu to affect (e.g.) the vnc name.
> > Hence after a migration, "--incoming" gets stuck on the end of the VNC
> > name even when a migration is successful.
> Yes, this is a known issue unfortunately.
>
> > I don't really understand how this is meant to work. Should something
> > be setting a watch on the xenstore "name" element? Or should libxl be
> > issuing QMP command on the name change?
> Assuming such a QMP command exists this would be the right thing to do I
> think.
No such QMP command exists currently. Adding one to fix VNC would be
reasonably trivial. The 'change' command currently exists to change
the password, and we could add a 'hostname' option. This would have
the biproduct of allowing you to name your machine 'Foo' rather than
'QEMU (Foo)' on VNC - I for one find the latter annoying. I'd be
happy to provide a patch for that if the QEMU folks would take it.

However, this won't solve the entire issue as the machine name seems
to be used for several things in QEMU - to pick a random example, some
SPICE stuff that I have no idea about. I don't know whether for all of
those things it's going to be safe to rename them when the domain
is created. Certainly changing the 'ps' line for qemu is not going
to be trivial.

> > Or is this just doomed to fail? In which case the name passed as -name
> > to the QEMU command line should probably be the original name, not the
> > name with "--incoming" on on a migration, and 'xl rename' is just going
> > to fail to change it.
> Yes, this approach has a couple of problems, firstly the "xl rename" one
> you've identified but secondly the renaming is all contained within xl
> and the libxl API has to way to express a different name to pass to the
> device model. The QMP renaming approach is probably best.
I count only one problem there :-)

A 'nasty hack' approach would simply be to delete '--incoming' from the
end of string before it is passed to QEMU.

A marginally less nasty hack might be to create the domain to start off
with without the '--incoming', then rename it to '--incoming', then
rename it back. Of course this has the risk of death between creation
and first rename.

--
Alex Bligh

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel