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

[Markus Armbruster <armbru@redhat.com>]

Cornelia Huck <cohuck@redhat.com> writes:

> 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
> :)

Plenty.

-machine usb=on (and its sugared form -usb) are just one of many options
that deposit configuration for the board to pick up.  Some boards do,
some don't.  Some boards pick up and reject some configuration they
can't use.  Some don't.  It's a big family of hack jobs.

For -drive (and its sugared forms), we have generic code to turn "not
picked up" into an error: drive_check_orphaned().
a66c9dc734 "blockdev: Orphaned drive search", 2014-10-03
720b8dc052 "blockdev: Make orphaned -drive fatal", 2017-02-21

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