Re: [PATCH v3 1/9] s390: vfio_ap: link the vfio_ap devices to the vfio_ap bus subsystem

[Pierre Morel]

On 14/02/2019 17:57, Cornelia Huck wrote:
> On Thu, 14 Feb 2019 16:47:30 +0100 Pierre Morel
> <pmorel@xxxxxxxxxxxxx> wrote:
>
> > On 14/02/2019 15:54, Cornelia Huck wrote:
> > > On Thu, 14 Feb 2019 14:51:01 +0100 Pierre Morel
> > > <pmorel@xxxxxxxxxxxxx> wrote:
>
> > > > +++ b/drivers/s390/crypto/vfio_ap_drv.c @@ -24,8 +24,9 @@
> > > > MODULE_LICENSE("GPL v2");
> > > >
> > > > static struct ap_driver vfio_ap_drv;
> > > >
> > > > -static struct device_type vfio_ap_dev_type = { -	.name =
> > > > VFIO_AP_DEV_TYPE_NAME, +struct matrix_driver { +	struct
> > > > device_driver drv; +	int device_count;
> > >
> > > This counter basically ensures that at most one device may bind
> > > with this driver... you'd still have that device on the bus,
> > > though.
> >
> > yes, this is what is wanted: this driver can only support one
> > device. May be another matrix driver can support one or more other
> > devices.
> >
> > I should update comment message my be.
> >
> > > > };
> > > >
> > > > struct ap_matrix_dev *matrix_dev;
> >
> > > > -	matrix_dev->device.type = &vfio_ap_dev_type; 
> > > > dev_set_name(&matrix_dev->device, "%s", VFIO_AP_DEV_NAME); 
> > > > matrix_dev->device.parent = root_device; +
> > > > matrix_dev->device.bus = &matrix_bus; 
> > > > matrix_dev->device.release = vfio_ap_matrix_dev_release; -
> > > > matrix_dev->device.driver = &vfio_ap_drv.driver; +
> > > > matrix_dev->vfio_ap_drv = &vfio_ap_drv;
> > >
> > > Can't you get that structure through matrix_dev->device.driver
> > > instead when you need it in the function below?
> >
> > Not anymore. We have two different drivers and devices matrix_drv
> > <-> matrix_dev and vfio_ap_drv <-> ap_devices
> >
> > The driver behind the matrix_dev->dev->driver is matrix_drv what is
> > needed here is vfio_ap_drv.
>
> Wait, we had tacked a driver for ap devices unto a matrix device,
> which is not on the ap bus?

...yes -(

> Maybe that's what trips libudev? >
> (And reading further in the current code, it seems we clear that 
> structure _after_ the matrix device had been setup, so how can that 
> even work? Where am I confused?)

On device_register there were no bus, so the core just do not look for a 
driver and this field was nor tested nor overwritten.

> > > > ret = device_register(&matrix_dev->device); if (ret) goto
> > > > matrix_reg_err;
> > > >
> > > > +	ret = driver_register(&matrix_driver.drv); +	if (ret) +		goto
> > > > matrix_drv_err; +
> > >
> > > As you already have several structures that can be registered
> > > exactly once (the root device, the bus, the driver, ...), you can
> > > already be sure that there's only one device on the bus, can't
> > > you?
> >
> > hum, no I don't think so, no device can register before this module
> > is loaded, but what does prevent a device to register later from
> > another module?
>
> Not unless you export the interface, I guess.

:) definitively right
thanks, this will simplify the code in the next version.
I will take the patch away from this series to get the way to stable as 
Christian requested.

Regards,
Pierre

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