linux-kernel - Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the vfio

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Message-Id: <c23816b4-e24d-7cf7-8018-a3c085eef9f3@de.ibm.com>
Date:   Tue, 19 Feb 2019 10:44:25 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Pierre Morel <pmorel@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        frankja@...ux.ibm.com, akrowiak@...ux.ibm.com, pasic@...ux.ibm.com,
        david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, freude@...ux.ibm.com
Subject: Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the
 vfio_ap bus subsystem



On 19.02.2019 10:22, Cornelia Huck wrote:
> On Mon, 18 Feb 2019 19:08:48 +0100
> Pierre Morel <pmorel@...ux.ibm.com> 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
> 
> s/suppress/remove/ ?
> 
>> 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@...ux.ibm.com>
>> Reported-by: Christian Borntraeger <borntraeger@...ibm.com>
>> Signed-off-by: Pierre Morel <pmorel@...ux.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(-)
> 
> (...)
> 
>> @@ -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;
>> +}
> 
> I don't think you need this (the important function is the match
> function of the bus).

Yes, with 

diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
index 8e45559795429..8ceec41afe322 100644
--- a/drivers/s390/crypto/vfio_ap_drv.c
+++ b/drivers/s390/crypto/vfio_ap_drv.c
@@ -68,15 +68,9 @@ static struct bus_type matrix_bus = {
        .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)

on top things still look fine.


> 
>> +
>> +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;
> 
> It's a bit annoying that we need to introduce a bus that basically does
> nothing, but I think this looks sane.
> 
> Reviewed-by: Cornelia Huck <cohuck@...hat.com>
>