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

[Fabio Fantoni <fabio.fantoni@xxxxxxx>]

Il 05/09/2013 15:00, Stefano Stabellini ha scritto:
> 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.
Exact.

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

> 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)?
Yes.
xl cd-insert command works with cdrom devices already present on domU 
defined on xl file configuration.
The cdrom can be empty or not, the only exception is the empty cdrom 
added default by qemu that is not usable with cd-insert because not 
defined on xl file configuration.
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