[libvirt] [PATCH] qemu: fix command line building for iommu devices

[Daniel P. Berrange]

On Mon, Oct 03, 2016 at 03:08:39PM +0200, Peter Krempa wrote:
> On Mon, Oct 03, 2016 at 14:04:02 +0100, Daniel Berrange wrote:
> > On Mon, Oct 03, 2016 at 03:02:38PM +0200, Peter Krempa wrote:
> > > On Mon, Oct 03, 2016 at 13:41:13 +0100, Daniel Berrange wrote:
> > > > The intel-iommu device has existed since QEMU 2.2.0, but
> > > > it was only possible to create it with -device since
> > > > QEMU 2.7.0, thanks to:
> > > > 
> > > >   commit 621d983a1f9051f4cfc3f402569b46b77d8449fc
> > > >   Author: Marcel Apfelbaum <marcel at redhat.com>
> > > >   Date:   Mon Jun 27 18:38:34 2016 +0300
> > > > 
> > > >     hw/iommu: enable iommu with -device
> > > > 
> > > >     Use the standard '-device intel-iommu' to create the IOMMU device.
> > > >     The legacy '-machine,iommu=on' can still be used.
> > > > 
> > > > The libvirt capability check & command line formatting code
> > > > is thus broken for all QEMU versions 2.2.0 -> 2.6.0 inclusive.
> > > > 
> > > > This fixes it to use iommu=on instead.
> > > > 
> > > > Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
> > > > ---
> > > 
> > > Is there any value to make it work with older versions rather than just
> > > clearing it completely on the versions that don't support it with
> > > -device?
> > 
> > Err that's what this change does
> 
> I asked incorrectly. I see that this adds support to enabling the iommu
> via -machine, but I want to know whether that is of any value.
> 
> I'd just drop the capability and allow it to work since 2.7.0 only as
> it's a new feature anyways.

It is only new from libvirt's POV - its been around since 2014 in QEMU
and IMHO we should support that in libvirt, not least because no distro
even ships 2.7.0 yet

Regards,
Daniel
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