[libvirt] [Xen-devel] [PATCH] libxl: allow an <emulator> to be selected in the domain config XML

[Jim Fehlig]

Marek Marczykowski wrote:
> On 31.05.2013 10:25, Ian Campbell wrote:
>   
>> On Thu, 2013-05-30 at 11:53 -0600, Jim Fehlig wrote:
>>     
>>> Marek Marczykowski wrote:
>>>       
>>>> On 01.05.2013 16:11, Daniel P. Berrange wrote:
>>>>   
>>>>         
>>>>> On Wed, May 01, 2013 at 02:44:11PM +0100, David Scott wrote:
>>>>>     
>>>>>           
>>>>>> On 01/05/13 09:46, Ian Campbell wrote:
>>>>>>       
>>>>>>             
>>>>>>> I would suggest that libvirt+libxl expose the version as the "emulator"
>>>>>>> option and not the path. Just leave the path as the default in the
>>>>>>> normal case. You may also want to provide an extra
>>>>>>> emulator-path-override tag/attribute/XML for advanced users, but that's
>>>>>>> up to you.
>>>>>>>
>>>>>>> If you need to support upgrade from xend then you could perhaps treat
>>>>>>> <emulator> values not in the set of valid LIBXL_DEVICE_MODEL_VERSION
>>>>>>> string (currently "qemu-xen" and "qemu-xen-traditional") as a path to a
>>>>>>> qemu-xen-traditional device model -- no xend user can possibly have been
>>>>>>> using the new device model with xend. Or you could take the approach
>>>>>>> that xl does and just warn.
>>>>>>>         
>>>>>>>               
>>>>>> This would work for me: it doesn't seem too bad to consider
>>>>>> "qemu-xen" and "qemu-xen-traditional" as special virtual paths. It's
>>>>>> a useful observation that xend never supported the new device model.
>>>>>> Jim: should I cook up patch v3? :-)
>>>>>>       
>>>>>>             
>>>>> No, that really doesn't fly. The <emlator> element must always point
>>>>> to a qualfied binary path.
>>>>>
>>>>> IMHO, libvirt should just default to the new QEMU binary and if people
>>>>> want to use the old one, they can configure the emulator path for it.
>>>>>     
>>>>>           
>>>> What about stubdom? Any idea how to do it better than special paths? Even if
>>>> given path will point to stubdom binary, I don't know how libvirt shoud
>>>> distinguish it from standalone qemu and set b_info->device_model_stubdomain
>>>> accordingly.
>>>>   
>>>>         
>>> As mentioned in my reply to your stubdom patch, this should be handled
>>> in libxl IMO.
>>>       
>> The default is handled in libxl, so you don't need to do anything if you
>> don't want to. It's up to you if you want to provide an override
>> facility in libvirt. Personally I'd do it with a specific XML
>> property/key/whatever rather than magic emulator paths...
>>     
>
> Optional attribute for <emulator> tag? Maybe sth like:
> <emulator type="stubdom">/usr/lib/xen/boot/ioemu-stubdom.gz</emulator>
> ?
>   

That sounds like a reasonable compromise to me.

Regards,
Jim