Re: [PATCH V3 4/7] mdev: introduce device specific ops

[Jason Wang <jasowang@redhat.com>]

On 2019/10/15 下午6:41, Cornelia Huck wrote:
> On Fri, 11 Oct 2019 16:15:54 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
>> Currently, except for the create and remove, the rest of
>> mdev_parent_ops is designed for vfio-mdev driver only and may not help
>> for kernel mdev driver. With the help of class id, this patch
>> introduces device specific callbacks inside mdev_device
>> structure. This allows different set of callback to be used by
>> vfio-mdev and virtio-mdev.
>>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>   .../driver-api/vfio-mediated-device.rst       | 22 +++++---
>>   MAINTAINERS                                   |  1 +
>>   drivers/gpu/drm/i915/gvt/kvmgt.c              | 18 ++++---
>>   drivers/s390/cio/vfio_ccw_ops.c               | 18 ++++---
>>   drivers/s390/crypto/vfio_ap_ops.c             | 14 +++--
>>   drivers/vfio/mdev/mdev_core.c                 |  9 +++-
>>   drivers/vfio/mdev/mdev_private.h              |  1 +
>>   drivers/vfio/mdev/vfio_mdev.c                 | 37 ++++++-------
>>   include/linux/mdev.h                          | 42 +++------------
>>   include/linux/vfio_mdev.h                     | 52 +++++++++++++++++++
>>   samples/vfio-mdev/mbochs.c                    | 20 ++++---
>>   samples/vfio-mdev/mdpy.c                      | 21 +++++---
>>   samples/vfio-mdev/mtty.c                      | 18 ++++---
>>   13 files changed, 177 insertions(+), 96 deletions(-)
>>   create mode 100644 include/linux/vfio_mdev.h
>>
>> diff --git a/Documentation/driver-api/vfio-mediated-device.rst b/Documentation/driver-api/vfio-mediated-device.rst
>> index 2035e48da7b2..553574ebba73 100644
>> --- a/Documentation/driver-api/vfio-mediated-device.rst
>> +++ b/Documentation/driver-api/vfio-mediated-device.rst
>> @@ -152,11 +152,20 @@ callbacks per mdev parent device, per mdev type, or any other categorization.
>>   Vendor drivers are expected to be fully asynchronous in this respect or
>>   provide their own internal resource protection.)
>>   
>> -The callbacks in the mdev_parent_ops structure are as follows:
>> +In order to support multiple types of device/driver, device needs to
>> +provide both class_id and device_ops through:
> "As multiple types of mediated devices may be supported, the device
> needs to set up the class id and the device specific callbacks via:"
>
> ?
>
>>   
>> -* open: open callback of mediated device
>> -* close: close callback of mediated device
>> -* ioctl: ioctl callback of mediated device
>> +    void mdev_set_class(struct mdev_device *mdev, u16 id, const void *ops);
>> +
>> +The class_id is used to be paired with ids in id_table in mdev_driver
>> +structure for probing the correct driver.
> "The class id  (specified in id) is used to match a device with an mdev
> driver via its id table."
>
> ?
>
>> The device_ops is device
>> +specific callbacks which can be get through mdev_get_dev_ops()
>> +function by mdev bus driver.
> "The device specific callbacks (specified in *ops) are obtainable via
> mdev_get_dev_ops() (for use by the mdev bus driver.)"
>
> ?
>
>> For vfio-mdev device, its device specific
>> +ops are as follows:
> "A vfio-mdev device (class id MDEV_ID_VFIO) uses the following
> device-specific ops:"
>
> ?


All you propose is better than what I wrote, will change the docs.


>
>> +
>> +* open: open callback of vfio mediated device
>> +* close: close callback of vfio mediated device
>> +* ioctl: ioctl callback of vfio mediated device
>>   * read : read emulation callback
>>   * write: write emulation callback
>>   * mmap: mmap emulation callback
>> @@ -167,9 +176,10 @@ register itself with the mdev core driver::
>>   	extern int  mdev_register_device(struct device *dev,
>>   	                                 const struct mdev_parent_ops *ops);
>>   
>> -It is also required to specify the class_id through::
>> +It is also required to specify the class_id and device specific ops through::
>>   
>> -	extern int mdev_set_class(struct device *dev, u16 id);
>> +	extern int mdev_set_class(struct device *dev, u16 id,
>> +	                          const void *ops);
> Apologies if that has already been discussed, but do we want a 1:1
> relationship between id and ops, or can different devices with the same
> id register different ops?


I think we have a N:1 mapping between id and ops, e.g we want both 
virtio-mdev and vhost-mdev use a single set of device ops.

Thanks


> If the former, would it make sense to first
> register the ops for an id (once), and then have the ->create callback
> only set the class id (with the core doing the lookup of the ops)?
>
>>   
>>   However, the mdev_parent_ops structure is not required in the function call
>>   that a driver should use to unregister itself with the mdev core driver::
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