Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the vfio_ap bus subsystem

Harald Freudenberger
2019-02-20T13:12:05Z

On 18.02.19 19:08, Pierre Morel wrote:
> Libudev relies on having a subsystem link for non-root devices. To
> avoid libudev (and potentially other userspace tools) choking on the
> matrix device let us introduce a vfio_ap bus and with that the vfio_ap
> bus subsytem, and make the matrix device reside within it.
>
> Doing this we need to suppress the forced link from the matrix device to
> the vfio_ap driver and we suppress the device_type we do not need
> anymore.
>
> Since the associated matrix driver is not the vfio_ap driver any more,
> we have to change the search for the devices on the vfio_ap driver in
> the function vfio_ap_verify_queue_reserved.
>
> Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
> Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
> drivers/s390/crypto/vfio_ap_drv.c | 48 +++++++++++++++++++++++++++++------
> drivers/s390/crypto/vfio_ap_ops.c | 4 +--
> drivers/s390/crypto/vfio_ap_private.h | 1 +
> 3 files changed, 43 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
> index 31c6c84..8e45559 100644
> --- a/drivers/s390/crypto/vfio_ap_drv.c
> +++ b/drivers/s390/crypto/vfio_ap_drv.c
> @@ -24,10 +24,6 @@ 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 ap_matrix_dev *matrix_dev;
>
> /* Only type 10 adapters (CEX4 and later) are supported
> @@ -62,6 +58,27 @@ static void vfio_ap_matrix_dev_release(struct device *dev)
> kfree(matrix_dev);
> }
>
> +static int matrix_bus_match(struct device *dev, struct device_driver *drv)
> +{
> + return 1;
> +}
> +
> +static struct bus_type matrix_bus = {
> + .name = "vfio_ap",
> + .match = &matrix_bus_match,
> +};
> +
> +static int matrix_probe(struct device *dev)
> +{
> + return 0;
> +}
> +
> +static struct device_driver matrix_driver = {
> + .name = "vfio_ap",
> + .bus = &matrix_bus,
> + .probe = matrix_probe,
> +};
> +
> static int vfio_ap_matrix_dev_create(void)
> {
> int ret;
> @@ -71,6 +88,10 @@ static int vfio_ap_matrix_dev_create(void)
> if (IS_ERR(root_device))
> return PTR_ERR(root_device);
>
> + ret = bus_register(&matrix_bus);
> + if (ret)
> + goto bus_register_err;
> +
> matrix_dev = kzalloc(sizeof(*matrix_dev), GFP_KERNEL);
> if (!matrix_dev) {
> ret = -ENOMEM;
> @@ -87,30 +108,41 @@ static int vfio_ap_matrix_dev_create(void)
> mutex_init(&matrix_dev->lock);
> INIT_LIST_HEAD(&matrix_dev->mdev_list);
>
> - 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;
>
> ret = device_register(&matrix_dev->device);
> if (ret)
> goto matrix_reg_err;
>
> + ret = driver_register(&matrix_driver);
> + if (ret)
> + goto matrix_drv_err;
> +
> return 0;
>
> +matrix_drv_err:
> + device_unregister(&matrix_dev->device);
> matrix_reg_err:
> put_device(&matrix_dev->device);
> matrix_alloc_err:
> + bus_unregister(&matrix_bus);
> +bus_register_err:
> root_device_unregister(root_device);
> -
> return ret;
> }
>
> static void vfio_ap_matrix_dev_destroy(void)
> {
> + struct device *root_device = matrix_dev->device.parent;
> +
> + driver_unregister(&matrix_driver);
> device_unregister(&matrix_dev->device);
> - root_device_unregister(matrix_dev->device.parent);
> + bus_unregister(&matrix_bus);
> + root_device_unregister(root_device);
> }
>
> static int __init vfio_ap_init(void)
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index 272ef42..900b9cf 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -198,8 +198,8 @@ static int vfio_ap_verify_queue_reserved(unsigned long *apid,
> qres.apqi = apqi;
> qres.reserved = false;
>
> - ret = driver_for_each_device(matrix_dev->device.driver, NULL, &qres,
> - vfio_ap_has_queue);
> + ret = driver_for_each_device(&matrix_dev->vfio_ap_drv->driver, NULL,
> + &qres, vfio_ap_has_queue);
> if (ret)
> return ret;
>
> diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
> index 5675492..76b7f98 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -40,6 +40,7 @@ struct ap_matrix_dev {
> struct ap_config_info info;
> struct list_head mdev_list;
> struct mutex lock;
> + struct ap_driver *vfio_ap_drv;
> };
>
> extern struct ap_matrix_dev *matrix_dev;

You are introducing a new bus just for a user space application which is unable
to deal with a device directly attached to the root of devices ? So you are fixing
kernel code because of disability of userspace code. Hm, you are switching
root cause and effect. However, not my job.

Why do you need this dummy bus ? Did you evaluate using a "class" subsystem
instead ? This is very common and my assumption is that libudev is able to handle
this. I am using a "zcrypt" class for providing additional zcrypt device nodes and
this works fine together with udev. I would avoid the introduction and maintenance
of bus code at any cost.

Btw. having a look onto the naming ... the module is named "vfio_ap", the
driver is named "vfio_ap", the bus is named "vfio_ap", the root bus device is
named "vfio_ap" ... a bunch of vfio_aps naming different things.

regards
Harald Freudenberger