Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure control domains

[Halil Pasic]

On 08/27/2018 03:51 PM, Cornelia Huck wrote:
> On Mon, 27 Aug 2018 09:47:58 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > On 08/27/2018 04:33 AM, Cornelia Huck wrote:
> > > On Thu, 23 Aug 2018 10:16:59 -0400
> > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
> > >   
> > > > On 08/23/2018 06:25 AM, Cornelia Huck wrote:
> > > > > On Wed, 22 Aug 2018 15:16:19 -0400
> > > > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
> > > > >      
> > > > > > One of the things I suggested in a private conversation with Christian
> > > > > > earlier
> > > > > > today was to provide an additional rw sysfs attribute - a boolean - that
> > > > > > indicates
> > > > > > whether all usage domains should also be control domains. The default
> > > > > > could be
> > > > > > true. This would allow one to configure guests with usage-only domains
> > > > > > as well
> > > > > > as satisfy the convention.
> > > > > Would this additional attribute then control "add usage domains to the
> > > > > list of control domains automatically", or "don't allow to add a usage
> > > > > domain if it has not already been added as a control domain"?
> > > > It was just a proposal that wasn't really discussed at all, but this
> > > > attribute would add usage domains to the list of control domains
> > > > automatically if set to one. That would be the default behavior which
> > > > would be turned off by manually setting it to zero.
> > > If we want to do something like that, having it add the usage domains
> > > automatically sounds like the more workable alternative. What I like
> > > about this is that we make it explicit that we change the masks beyond
> > > what the admin explicitly configured, and provide a knob to turn off
> > > that behaviour.
> >
> > So, are you saying I should go ahead and implement this?
>
> I'm just saying that it does not sound like a bad idea :)
>
> If you agree that it's a good idea and if others also like it... I'd
> certainly not mind you going ahead :)

I can live with it. What I don't like about it is that it adds
more context dependent semantics. The same sequence of actions
results in a different result (depending on the mode of operation).

Regards,
Halil