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

[Christian Borntraeger]

On 17.10.19 16:21, Thomas Huth 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 <address@hidden>
> ---
>  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.

I think a warn message is ok, but we should never make  this a hard
error.

I am pretty sure that there are some tools in the wild that create xmls
or qemu commands lines cross-platform and deploy those  dynamically.
These tools have probably been fixed to work good enough with s390x
but nobody with qemu clue has ever looked at these command lines. And
I am pretty sure that no user will actually see the command like nor
the error message.

So this warning will stay unnoticed until we make this a hard error. And
then we have broken a previously working setup.

In other words, I appreciate the willingness to detect mis-uses but I 
fear that we will never be able to assume that everything is fixed.



> 
>  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");
> +    }
> +
>      s390_sclp_init();
>      /* init memory + setup max page size. Required for the CPU model */
>      s390_memory_init(machine->ram_size);
>