Re: [Qemu-devel] [PATCH] -machine vmport=off: Allow disabling of VMWare ioport emulation

["Richard W.M. Jones" <rjones@redhat.com>]

On Tue, May 20, 2014 at 09:47:26AM +0100, Dr. David Alan Gilbert wrote:
> * Gerd Hoffmann (kraxel@redhat.com) wrote:
> > >      /* init basic PC hardware */
> > > -    pc_basic_device_init(isa_bus, gsi, &rtc_state, &floppy, xen_enabled(),
> > > -        0x4);
> > > +    pc_basic_device_init(isa_bus, gsi, &rtc_state, &floppy,
> > > +                         !qemu_opt_get_bool(qemu_get_machine_opts(), "vmport",
> > > +                                            true) || xen_enabled(), 0x4);
> > 
> > pc_basic_device_init
> >   (isa_bus, gsi, &rtc_state, &floppy,
> >    !qemu_opt_get_bool(qemu_get_machine_opts(),"vmport",!xen_enabled()),
> >    0x4);
> > 
> > ?
> > 
> > This makes vmport switchable on xen too, with traditional behavior being
> > the default (off on xen, on otherwise).
> 
> Yes I guess that would work (although documenting it would be a little hairy);
> however, does anyone understand the reasons it's disabled in the Xen world?

It was disabled in this patch.  The commit message is saying that
vmport cannot work in Xen, but I'm not exactly clear why.

  commit 1611977c3d8fdbdac6090cbd1f5555cee4aed6d9
  Author: Anthony PERARD <anthony.perard@citrix.com>
  Date:   Tue May 3 17:06:54 2011 +0100

    pc, Disable vmport initialisation with Xen.
    
    This is because there is not synchronisation of the vcpu register
    between Xen and QEMU, so vmport can't work properly.
    
    This patch introduces no_vmport parameter to pc_basic_device_init.
    
    Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
    Signed-off-by: Alexander Graf <agraf@suse.de>

Rich.

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