Re: [PATCH 04/10] vfio: ccw: replace IO_REQ event with SSCH_REQ event

[Pierre Morel]

On 22/05/2018 17:41, Cornelia Huck wrote:
> On Fri, 4 May 2018 13:02:36 +0200
> Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx> wrote:
>
> > On 04/05/2018 03:19, Dong Jia Shi wrote:
> > > * Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx> [2018-05-03 16:26:29 +0200]:
> > >   
> > > > On 02/05/2018 09:46, Dong Jia Shi wrote:
> > > > > * Cornelia Huck <cohuck@xxxxxxxxxx> [2018-04-30 17:33:05 +0200]:
> > > > >   
> > > > > > On Thu, 26 Apr 2018 15:48:06 +0800
> > > > > > Dong Jia Shi <bjsdjshi@xxxxxxxxxxxxxxxxxx> wrote:
> > > > > >   
> > > > > > > * Dong Jia Shi <bjsdjshi@xxxxxxxxxxxxxxxxxx> [2018-04-26 15:30:54 +0800]:
> > > > > > >
> > > > > > > [...]
> > > > > > >   
> > > > > > > > > @@ -179,7 +160,7 @@ static int fsm_irq(struct vfio_ccw_private *private,
> > > > > > > > >    	if (private->io_trigger)
> > > > > > > > >    		eventfd_signal(private->io_trigger, 1);
> > > > > > > > >
> > > > > > > > > -	return private->state;
> > > > > > > > > +	return VFIO_CCW_STATE_IDLE;
> > > > > > > > This is not right. For example, if we are in STANDBY state (subch driver
> > > > > > > > is probed, but mdev device is not created), we can not jump to IDLE
> > > > > > > > state.
> > > > > > > I see my problem, for STANDBY state, we should introduce another event
> > > > > > > callback for VFIO_CCW_EVENT_INTERRUPT. It doesn't make sense to call
> > > > > > > fsm_irq() which tries to signal userspace with interrupt notification
> > > > > > > when mdev is not created yet... So we'd need a separated fix for this
> > > > > > > issue too.
> > > > > > But how do we even get into that situation when we don't have an mdev
> > > > > > yet?
> > > > > >   
> > > > > We cann't... So let's assign fsm_nop() as the interrupt callback for
> > > > > STANDBY state?
> > > > >   
> > > > :) Isn't it exactly what my patch series handle?
> > > As far as I see, that's not true. ;)
> > >
> > > After this series applied,
> > > vfio_ccw_jumptable[VFIO_CCW_STATE_STANDBY][VFIO_CCW_EVENT_INTERRUPT] is
> > > still fsm_irq().
> > >   
> >
> > What I mean is, this code tries to handle design problems
> > without changing too much of the original code at first.
> >
> > The problem here is not that the fsm_irq function is called on interrupt,
> > if we have an interrupt it must be signaled to user land.
> > The problem is that this state is entered at the wrong moment.
> >
> > STANDBY should be entered, during the mdev_open when we realize the QEMU
> > device,
> > and not during the probe, in which we should stay in NOT_OPER until we
> > get the QEMU device.
> >
> > The probe() and mdev_open() function should be modified, not the state
> > table.
> So, the takeaway is that we should handle starting via the init
> callbacks and not via the state machine?
hum, sorry, I think that my previous answer was not completely right,
and did not really answer to Dong Jia comment, yes fsm_irq was not
at its place, thinking again about the comments of both of you
I think that we can suppress the INIT event.

I would like to rebase the patch to include the comments you both did.


--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany