Re: [PATCH v2 1/5] qdev: add user_creatable_requires_machine_allowance class flag

[Damien Hedde]

On 4/21/22 17:59, Peter Maydell wrote:
> On Thu, 31 Mar 2022 at 13:19, Damien Hedde <damien.hedde@greensocs.com> wrote:
> > This flag will be used in device_add to check if
> > the device needs special allowance from the machine
> > model.
> >
> > It will replace the current check based only on the
> > device being a TYPE_SYB_BUS_DEVICE.
> >
> > Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
> > ---
> >
> > v2:
> >   + change the flag name and put it just below user_creatable
> > ---
> >   include/hw/qdev-core.h | 9 +++++++++
> >   hw/core/qdev.c         | 1 +
> >   hw/core/sysbus.c       | 1 +
> >   3 files changed, 11 insertions(+)
> >
> > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> > index 92c3d65208..6a040fcd3b 100644
> > --- a/include/hw/qdev-core.h
> > +++ b/include/hw/qdev-core.h
> > @@ -122,6 +122,15 @@ struct DeviceClass {
> >        * TODO remove once we're there
> >        */
> >       bool user_creatable;
> > +    /*
> > +     * Some devices can be user created under certain conditions (eg:
> > +     * specific machine support for sysbus devices), but it is
> > +     * preferable to prevent global allowance for the reasons
> > +     * described above.
> > +     * This flag is an additional constraint over user_creatable:
> > +     * user_creatable still needs to be set to true.
> > +     */
> > +    bool user_creatable_requires_machine_allowance;
>
> "allowance" doesn't have the meaning you seem to be trying to give it here.
> (It means "the amount of something you're allowed to have", like
> a baggage allowance, or "an amount of money you're given for something",
> like a travel allowance.)

> Do you mean "user creatable only if the machine permits it" ?
Yes.

> More generally, the pluggable-sysbus stuff is an awful hack
> that I wish we didn't have to have. I'm not sure I want to see
> us expanding the use of it to other device types...

I not really trying to trigger code when adding devices. I'm just trying 
to use the related per-machine allow-list as a way to prevent the user 
to add such devices (specifically cpu group/cluster) on any random 
machine which would most probably not "work".

Thanks,
Damien