Re: [Xen-devel] [PATCH 2/3] libxl: add domain config parameter to force start of qemu

[Juergen Gross <jgross@xxxxxxxx>]

On 17/03/16 17:06, George Dunlap wrote:
> On Thu, Mar 10, 2016 at 3:00 PM, Juergen Gross <jgross@xxxxxxxx> wrote:
>> Today the device model (qemu) is started for a pv domain only in case
>> a device requiring qemu is specified in the domain configuration
>> (qdisk, vfb, channel). If there is no such device the device model
>> isn't started and hence it is possible to add such a device to the
>> domain later.
>>
>> Add a domain configuration parameter to specify the device model is
>> to be started in any case. This will enable adding devices with a
>> qemu based backend later.
>>
>> While the optimal solution would be to start the device model
>> automatically when needed this would require some major rework of
>> libxl at multiple places.
>>
>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> 
> So wait -- what happens now if you try to attach a disk with a qdisk
> backend to a PV guest that didn't start with qemu running?

It won't work (that was my test case for the patch).

> I'd really like to see patch 3 get in, but I'm not really in favor of
> this sort of a user-visible hack, particularly as we have to support
> it in libxl more or less indefinitely.

Hmm, really? We can add a smarter variant later which will start the
device model in case it isn't started yet. Then the new config parameter
could be just ignored.

I didn't do the smart variant as I'm not sure I could set it up in time
for 4.7. I'd be happy to do it with some assistance regarding the async
framework of libxl I'm not at all familiar with.


Juergen

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