Re: [Xen-devel] Questions about hvm domU default devices with upstream qemu

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 5 Sep 2013, Fabio Fantoni wrote:
> Il 05/09/2013 13:23, Stefano Stabellini ha scritto:
> > On Wed, 4 Sep 2013, Fabio Fantoni wrote:
> > > Il 04/09/2013 15:17, Stefano Stabellini ha scritto:
> > > > On Wed, 4 Sep 2013, Fabio Fantoni wrote:
> > > > > Il 04/07/2013 15:51, Fabio Fantoni ha scritto:
> > > > > > Last year I posted a question about default devices of upstream qemu
> > > > > > that
> > > > > > differ from qemu traditional, like empty floppy and cdrom in
> > > > > > particular.
> > > > > > About empty floppy now is disabled as workaround.
> > > > > > About empty cdrom Stabellini tells that is useful, so I tried to use
> > > > > > it
> > > > > > but
> > > > > > cd-insert was failing,and I must define other empty cdrom on xl
> > > > > > configuration file, for example with: ',raw,hdb,ro,cdrom'.
> > > > > > It seem that there isn't default devices usable without define them
> > > > > > in
> > > > > > xen,
> > > > > > and I think that probably need to revise the definition of the
> > > > > > devices
> > > > > > to
> > > > > > avoid empty and unusable ones and to do everything as best as
> > > > > > possible
> > > > > > (also
> > > > > > with possibly reviewing qemu side).
> > > > > > Another good thing is also consider pv domU case and possible future
> > > > > > support
> > > > > > of spice and/or other useful features.
> > > > > > Thanks for any reply.
> > > > > I seen no replies about this, I think is important improve upstream
> > > > > qemu
> > > > > support and remove the traditional ASA upstream will be equivalent or
> > > > > superior
> > > > > in all features.
> > > > > 
> > > > > I also think is good idea add q35 support on xen.
> > > > > Seem that hvm domUs have performance limits, in particular on windows
> > > > > domUs
> > > > > (also with pv drivers) caused probably by old hardware emulation by
> > > > > qemu
> > > > > and/or xen support limited on some instruction sets.
> > > > > I don't know how to add essential q35 support on hvmloader to do some
> > > > > tests
> > > > > and have effective data about improvements.
> > > > > Anyone on this?
> > > > I agree that this is important and thanks for raising the issue.
> > > > It would be nice if somebody stepped up to do the q35 work.
> > > Thanks for reply, can you reply also on questions about default devices
> > > with
> > > upstream qemu please?
> > I think it might be a good idea to keep the same set of default devices
> > between qemu-traditional and qemu-xen.
> > 
> > We always had an empty cdrom and I don't see why we should remove it. If
> > cd-insert doesn't work, it's a bug and should be fixed.
> > 
> > Supporting spice in PV guests would be hard, because spice needs QXL
> > that is a PCI device. PV guests don't have a PCI bus. Of course if
> > somebody did the work to make QXL and spice work with PV guests I would
> > be happy to accept it.
> > 
> > I agree that we should keep improving upstream QEMU, however removing
> > qemu-traditional is not going to be easy because it's needed for
> > compatibility when a guest started with qemu-traditional is
> > live-migrated to a new system. But we can make sure that this remains
> > the only use case for it.
> 
> Thanks for reply.
> 
> About qemu default empty and unusable floppy and cdrom I have already reply at
> start of year that qemu traditional does not have them.
> The tests were with xl only if I remember good, now I checked also on old
> production server with xend and qemu traditional. I confirm that hvm domUs is
> without empty floppy and cdrom also in that case.
>
> cd-insert works (tested with xl and upstream qemu). cd-insert does not works
> only with qemu default empty cdrom because is undefined on xen side.

So HVM domUs do NOT have a cdrom drive by default with qemu-traditional.

Do they have an empty cdrom drive by default with qemu-xen?

Is the lack of a cdrom drive the reason why cd-insert doesn't work by
default (unless you specify an empty cdrom drive in the VM config file)?

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