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

[Eric Blake <eblake@redhat.com>]

On 10/17/19 9:45 AM, Christian Borntraeger wrote:
> 
> 
> 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 <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.
> 
> 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.

That's what the deprecation process is for. This patch is incomplete 
unless it also touches qemu-deprecated.texi.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org