Re: [Qemu-devel] [Xen-devel] RFC: configuring QEMU virtfs for Xen PV(H) guests

[Juergen Gross <jgross@suse.com>]

On 07/03/16 11:51, Wei Liu wrote:
> On Mon, Mar 07, 2016 at 08:21:46AM +0100, Juergen Gross wrote:
>> Hi Wei,
>>
>> On 15/02/16 14:44, Wei Liu wrote:
>>> On Mon, Feb 15, 2016 at 02:33:05PM +0100, Juergen Gross wrote:
>>>> On 15/02/16 14:16, Wei Liu wrote:
>>>>> On Mon, Feb 15, 2016 at 09:07:13AM +0000, Paul Durrant wrote:
>>>>>>>
>>>>> [...]
>>>>>>> # Option 2: Invent a xen-9p device
>>>>>>>
>>>>>>> Another way of doing it is to expose a dummy xen-9p device, so that we
>>>>>>> can use -fsdev XXX -device xen-9p,YYY.  This simple device should be
>>>>>>> used to capture the parameters like mount_tag and fsdev_id, and then
>>>>>>> chained itself to a known location.  Later Xen transport can traverse
>>>>>>> this known location. This xen-9p device doesn't seem to fit well into
>>>>>>> the hierarchy. The best I can think of its parent should be
>>>>>>> TYPE_DEVICE.  In this case:
>>>>>>>
>>>>>>> 1. Toolstack arranges some xenstore entries.
>>>>>>> 2. Toolstack arranges command line options for QEMU:
>>>>>>>       -fsdev XXX -device xen-9p,XXX
>>>>>>> 3. QEMU starts up in xen-attach mode, scans xenstore for relevant
>>>>>>>    entries, then traverses the known location.
>>>>>>>
>>>>>>> Downside: Inventing a dummy device looks suboptimal to me.
>>>>
>>>> Sorry, didn't notice this thread before.
>>>>
>>>
>>> No need to be sorry. I posted this last Friday night. I wouldn't expect
>>> many replies on Monady.
>>>
>>>> For Xen pvUSB backend in qemu I need a Xen system device acting as
>>>> parent for being able to attach/detach virtual USB busses.
>>>>
>>>> I haven't had time to update my patches for some time, but the patch
>>>> for this system device is rather easy. It could be used as a parent
>>>> of the xen-9p devices, too.
>>>>
>>>> I've attached the patch for reference.
>>>>
>>>
>>> Thanks. I will have a look at your patch.
>>
>> Did you have some time to look at the patch? I'm asking because I
>> finally found some time to start working on V2 of my qemu based pvUSB
>> backend. Stefano asked me to hide the system device in my backend and
>> I want to avoid that in case you are needing it, too.
>>
> 
> Yes. I need this device. I'm not sure what "hiding this device in
> backend" means though.

Stefano wanted it to be pvusb backend private: instead of adding it to
hw/xenpv/xen_machine_pv.c he wanted me to add it to hw/usb/xen-usb.c
where it would be usable by the pvUSB backend only.

With you needing that device I can leave the patch more or less
unmodified (some rebasing to the actual qemu version is needed).

Thanks for looking into the patch,

Juergen