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Re: [libvirt] [PATCH 1/2] libxl: Report connect type as Xen



On Tue, Jun 11, 2013 at 10:27:37AM -0600, Jim Fehlig wrote:
> Michal Privoznik wrote:
> > On 11.06.2013 16:12, Jim Fehlig wrote:
> >   
> >> Michal Privoznik wrote:
> >>     
> >>> On 10.06.2013 22:21, Jim Fehlig wrote:
> >>>   
> >>>       
> >>>> Currently, the libxl driver reports a connection type of "xenlight".
> >>>> To be compatible with the legacy Xen driver, it should return "Xen".
> >>>>
> >>>> Note: I noticed this while testing the libxl driver on OpenStack.
> >>>> After switching my Xen compute nodes to use the libxl stack, I
> >>>> could no longer launch instances on those nodes since
> >>>> hypervisor_type was reported as "xenlight" instead of "xen".
> >>>> ---
> >>>>  src/libxl/libxl_driver.c |    2 +-
> >>>>  1 files changed, 1 insertions(+), 1 deletions(-)
> >>>>
> >>>> diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
> >>>> index 3990354..935919b 100644
> >>>> --- a/src/libxl/libxl_driver.c
> >>>> +++ b/src/libxl/libxl_driver.c
> >>>> @@ -1405,7 +1405,7 @@ libxlConnectClose(virConnectPtr conn ATTRIBUTE_UNUSED)
> >>>>  static const char *
> >>>>  libxlConnectGetType(virConnectPtr conn ATTRIBUTE_UNUSED)
> >>>>  {
> >>>> -    return "xenlight";
> >>>> +    return "Xen";
> >>>>  }
> >>>>  
> >>>>  static int
> >>>>
> >>>>     
> >>>>         
> >>> I am not so convinced about this one. I think there exist some
> >>> applications which want to distinguish between "Xen" and "xenlight".
> >>>       
> >> If that was the case, we would have went with a libxl:// URI.  In fact,
> >> the original libxl driver patch introduced a libxl:// URI, but Daniel V.
> >> pointed out that approach conflicted with libvirt's goal of minimizing
> >> the impact on application stacks as the lower layers churn
> >>
> >> https://www.redhat.com/archives/libvir-list/2011-March/msg00449.html
> >>     
> >
> > Right, you certainly got a point there. But I'd like to see DV's input
> > in here then.

  Yes, the main service that libvirt provide for a given hypervisor
stack is hide the inevitable changes that the evolution of the
underlying technology implies. When the libxl driver was introduced
it was then normal to try to minimize the impact on existing Xen users,
and I still think that's the right approach, especially if there have
been report of breakages in the field.
  If we really want to expose a way to differenciate a xen from libxl
(or future) then virConnectGetSysinfo which is a structured kind of
reply is a better way to carry this. virConnectGetType is better left
undifferencied in those cases.

  So to me ACK to the patch. Jim if you have the evironment to test
both it might be interesting to compare the 2 outputs returned from
virConnectGetSysinfo and see if infrastructure code can still make a
difference from both environment with it.

Daniel

-- 
Daniel Veillard      | Open Source and Standards, Red Hat
veillard redhat com  | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | virtualization library  http://libvirt.org/


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