Re: [Qemu-devel] [RFC PATCH v2 1/3] s390x/ccs: add ccw-testdev emulated device

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 7 Dec 2017 13:38:22 +0100
Halil Pasic <pasic@linux.vnet.ibm.com> wrote:

> On 12/07/2017 12:59 PM, Cornelia Huck wrote:
> > On Thu, 7 Dec 2017 07:33:19 +0100
> > Thomas Huth <thuth@redhat.com> wrote:
> >   
> >> On 08.11.2017 17:54, Halil Pasic wrote:  
> >   
> >>> +static ccw_cb_t get_ccw_cb(CcwTestDevOpMode op_mode)
> >>> +{
> >>> +    switch (op_mode) {
> >>> +    case OP_MODE_FIB:
> >>> +        return ccw_testdev_ccw_cb_mode_fib;
> >>> +    case OP_MODE_NOP:
> >>> +    default:
> >>> +        return ccw_testdev_ccw_cb_mode_nop;    
> >>
> >> Do we really want to use "nop" for unknown modes? Or should there rather
> >> be a ccw_testdev_ccw_cb_mode_error instead, too?  
> > 
> > I like the idea of an error mode.  
> 
> What would be the benefit of the error mode? The idea is that
> the tester in the guest has a certain set of tests implemented
> each requiring certain behavior from the device. This behavior
> is represented by the mode.
> 
> If the device does not support the mode, the set of tests can't
> be executed meaningfully. The only option is either ignore them
> (and preferably report them as ignored), or fail them (not soo
> good in my opinion).

Failing it sounds superior to me: You really want to know if something
does not work as expected.

> 
> The in guest tester should simply iterate over it test sets
> and try to select the mode the test set (or suite in other
> terminology) requires. If selecting the mode fails, than
> means you are working with an old ccw-testdev.
> 
> > 
> > Related: Should the device have a mechanism to report the supported
> > modes?
> >   
> 
> I don't see the value. See above. I think the set mode operation
> reporting failure is sufficient.
> 
> But if you have something in mind, please do tell. I'm open.

If we keep guest/host in lockstep, we probably don't need this. But if
not, self-reporting looks like a reasonable feature as it gives more
flexibility.