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

[Wei Liu <wei.liu2@citrix.com>]

On Mon, Mar 07, 2016 at 11:56:15AM +0100, Juergen Gross wrote:
> 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).
> 

Yes, please make it available to other PV backends. Someone might want
to graft every device we have to that hierarchy some day later. ;-)

> Thanks for looking into the patch,
> 

Thanks for posting this patch and sorry for the long delay.

Wei.

> Juergen
>