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Subject: Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the
 vfio_ap bus subsystem
To:     Christian Borntraeger <borntraeger@de.ibm.com>,
        Pierre Morel <pmorel@linux.ibm.com>
Cc:     cohuck@redhat.com, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org, frankja@linux.ibm.com,
        akrowiak@linux.ibm.com, pasic@linux.ibm.com, david@redhat.com,
        schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com
References: <1550513328-12646-1-git-send-email-pmorel@linux.ibm.com>
 <1550513328-12646-2-git-send-email-pmorel@linux.ibm.com>
 <f07b6209-bca2-22fe-310e-1e384c8974d9@linux.ibm.com>
 <3c3a90ca-f7ea-7800-453d-31e6d273e82f@de.ibm.com>
From:   Harald Freudenberger <freude@linux.ibm.com>
Date:   Thu, 21 Feb 2019 09:07:35 +0100
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On 21.02.19 08:37, Christian Borntraeger wrote:
>
> On 20.02.2019 14:12, Harald Freudenberger wrote:
>> 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.
> the kernel rule is pretty simple. If userspace breaks due to a kernel change fix the
> kernel.
>
>> 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.
> The class variant sounds promising. Pierre what do you think?
I checked that. My additional zcrypt devices (you can easily create one
with just echo "blubber" >/sys/class/zcrypt/create) and then have a look
to the new device entry in sysfs at /sys/devices/virtual/zcrypt/blubber).
Maybe you need to alloc device numbers for this - I am not sure if it is
sufficient to device_register() without a device number. However, have
a look into zcrpyt_api.c zcdn_init() and zcdn_create().
With a new class, you can also remove the root device needed as an
anchor for the old and for the bus code.
>> 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
>>