Re: [PATCH] hw/s390x: Emit a warning if user tried to enable USB

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 17 Oct 2019 16:40:56 +0200
Thomas Huth <thuth@redhat.com> wrote:

> On 17/10/2019 16.34, Cornelia Huck wrote:
> > On Thu, 17 Oct 2019 16:21:23 +0200
> > Thomas Huth <thuth@redhat.com> wrote:
> >   
> >> There is no USB on s390x, so running qemu-system-s390x with
> >> "-machine ...,usb=on" is certainly wrong. Emit a warning to make
> >> the users aware of their misconfiguration.
> >>
> >> Signed-off-by: Thomas Huth <thuth@redhat.com>
> >> ---
> >>  After a year or two, we could finally turn this into a hard error,
> >>  but I think we should give the users some time to fix their command
> >>  lines first, so I'm initially only emitting a warning here.
> >>
> >>  hw/s390x/s390-virtio-ccw.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> >> index d3edeef0ad..af8c4c0daf 100644
> >> --- a/hw/s390x/s390-virtio-ccw.c
> >> +++ b/hw/s390x/s390-virtio-ccw.c
> >> @@ -243,6 +243,10 @@ static void ccw_init(MachineState *machine)
> >>      VirtualCssBus *css_bus;
> >>      DeviceState *dev;
> >>  
> >> +    if (machine->usb) {
> >> +        warn_report("This machine does not support USB");  
> > 
> > I'm wondering if this is the only machine type not supporting usb...
> > if not, how are others handling it?  
> 
> I think most machines are silently ignoring it, like we did on s390x
> until now, too.

I'm wondering how many options we have that do nothing when configured
:)

> 
> > The usb parsing code in machine.c does not care if usb is even
> > configured (CONFIG_USB).  
> 
> machine.c is common code, so you can not use CONFIG_USB there.

Hm, yes.

> 
> > There's other stuff in there like
> > igd-passthru, which seems to be x86 specific; probably historical
> > reasons?  
> 
> IMHO igd-passthru should be moved to the xen machine, which seems to be
> the only user.

OTOH, I can currently specify igd-passthru=on on any machine, which
would break if we moved it. Not that it makes any sense...