Re: [RFC PATCH v2 10/16] qdev-monitor: allow adding any sysbus device before machine is ready

[Damien Hedde]

On 9/23/21 13:55, Ani Sinha wrote:
> On Thu, 23 Sep 2021, Ani Sinha wrote:
>
> > On Wed, 22 Sep 2021, Damien Hedde wrote:
> >
> > > Skip the sysbus device type per-machine allow-list check before the
> > > MACHINE_INIT_PHASE_READY phase.
> > >
> > > This patch permits adding any sysbus device (it still needs to be
> > > user_creatable) when using the -preconfig experimental option.
> > >
> > > Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
> > > ---
> > >
> > > This commit is RFC. Depending on the condition to allow a device
> > > to be added, it may change.
> > > ---
> > >   softmmu/qdev-monitor.c | 9 +++++++--
> > >   1 file changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
> > > index f1c9242855..73b991adda 100644
> > > --- a/softmmu/qdev-monitor.c
> > > +++ b/softmmu/qdev-monitor.c
> > > @@ -269,8 +269,13 @@ static DeviceClass *qdev_get_device_class(const char 
> > > **driver, Error **errp)
> > >           return NULL;
> > >       }
> > >
> > > -    if (object_class_dynamic_cast(oc, TYPE_SYS_BUS_DEVICE)) {
> > > -        /* sysbus devices need to be allowed by the machine */
> > > +    if (object_class_dynamic_cast(oc, TYPE_SYS_BUS_DEVICE) &&
> > > +        phase_check(MACHINE_INIT_PHASE_READY)) {
> > > +        /*
> > > +         * Sysbus devices need to be allowed by the machine.
> > > +         * We only check that after the machine is ready in order to let
> > > +         * us add any user_creatable sysbus device during machine creation.
> > > +         */
> > >           MachineClass *mc = 
> > > MACHINE_CLASS(object_get_class(qdev_get_machine()));
> > >           if (!machine_class_is_dynamic_sysbus_dev_allowed(mc, *driver)) {
> > >               error_setg(errp, "'%s' is not an allowed pluggable sysbus device "
> >
> > Since now you are adding the state of the machine creation in the
> > valiation condition, the failure error message becomes misleading.
> > Better to do this I think :
> >
> > if (object class is TYPE_SYS_BUS_DEVICE)
> > {
> >    if (!phase_check(MACHINE_INIT_PHASE_READY))
> >      {
> >        // error out here saying the state of the machine creation is too
> > early
> >      }
> >
> >      // do the other check on dynamic sysbus
> >
> > }
>
> The other thing to consider is whether we should put the machine phaze
> check at a higher level, at qdev_device_add() perhaps. One might envison
> that different device types may be allowed to be added at different
> stages of machine creation. So this check needs be more generalized for
> the future.

Hi Ani,

I think moving out the allowance check from qdev_get_device_class is a 
good idea. The code will be more clear even if the check is not generalized.

Thanks,
--
Damien