Re: [Xen-devel] [PATCH v3 5/5] libxl: add domain config parameter to force start of qemu

[Juergen Gross <jgross@xxxxxxxx>]

On 24/03/16 21:28, Wei Liu wrote:
> On Wed, Mar 23, 2016 at 01:24:07PM +0100, Juergen Gross 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 impossible 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>
> 
> I can't say I like this.
> 
> Libxl can be made smart enough to detect whether starting a device model
> is required (as you already did in previous patch) then start qemu on
> demand.
> 
> There is a xen-attach mode in qemu, and libxl already has machinery for
> starting qemu. I suspect what you need to do is refactoring existing
> code and expose the right parameter for qemu. Then you wouldn't need
> this user visible option at all. You would also save the resources for
> always having an idle qemu in toolstack domain.
> 
> Let me know if this is to vague.

No, that's okay. I think I'll drop this patch for now and start a clean
attempt after 4.7 is out.

Juergen


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