Subject: Re: [PATCH V4 3/6] mdev: introduce device specific ops

From: Cornelia Huck <[email-masked]>
Date: Thu, 17 Oct 2019 17:07:55 +0200

On Thu, 17 Oct 2019 18:48:33 +0800
Jason Wang <[email-masked]> 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 <[email-masked]>
> ---
>  .../driver-api/vfio-mediated-device.rst       | 25 +++++----
>  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                 | 18 +++++--
>  drivers/vfio/mdev/mdev_private.h              |  1 +
>  drivers/vfio/mdev/vfio_mdev.c                 | 37 ++++++-------
>  include/linux/mdev.h                          | 45 ++++------------
>  include/linux/vfio_mdev.h                     | 52 +++++++++++++++++++
>  samples/vfio-mdev/mbochs.c                    | 20 ++++---
>  samples/vfio-mdev/mdpy.c                      | 20 ++++---
>  samples/vfio-mdev/mtty.c                      | 18 ++++---
>  13 files changed, 184 insertions(+), 103 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 f9a78d75a67a..0cca84d19603 100644
> --- a/Documentation/driver-api/vfio-mediated-device.rst
> +++ b/Documentation/driver-api/vfio-mediated-device.rst
> @@ -152,11 +152,22 @@ 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:
> -
> -* open: open callback of mediated device
> -* close: close callback of mediated device
> -* ioctl: ioctl callback of mediated device
> +As multiple types of mediated devices may be supported, the device
> +must set up the class id and the device specific callbacks in create()

s/in create()/in the create()/

> +callback. E.g for vfio-mdev device it needs to be done through:

"Each class provides a helper function to do so; e.g. for vfio-mdev
devices, the function to be called is:"

?

> +
> +    int mdev_set_vfio_ops(struct mdev_device *mdev,
> +                          const struct vfio_mdev_ops *vfio_ops);
> +
> +The class id (set to MDEV_CLASS_ID_VFIO) is used to match a device

"(set by this helper function to MDEV_CLASS_ID_VFIO)" ?

> +with an mdev driver via its id table. The device specific callbacks
> +(specified in *ops) are obtainable via mdev_get_dev_ops() (for use by

"(specified in *vfio_ops by the caller)" ?

> +the mdev bus driver). A vfio-mdev device (class id MDEV_CLASS_ID_VFIO)
> +uses the following device-specific ops:
> +
> +* 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
> @@ -167,10 +178,6 @@ 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 in create() callback through::
> -
> -	int mdev_set_class(struct mdev_device *mdev, u16 id);
> -

I'm wondering if this patch set should start out with introducing
helper functions already (i.e. don't introduce mdev_set_class(), but
start out with mdev_set_class_vfio() which will gain the *vfio_ops
argument in this patch.)

>  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::
>  

(...)

> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index 3a9c52d71b4e..d0f3113c8071 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -45,15 +45,23 @@ void mdev_set_drvdata(struct mdev_device *mdev, void *data)
>  }
>  EXPORT_SYMBOL(mdev_set_drvdata);
>  
> -/* Specify the class for the mdev device, this must be called during
> - * create() callback.
> +/* Specify the VFIO device ops for the mdev device, this
> + * must be called during create() callback for VFIO mdev device.
>   */

/*
 * Specify the mdev device to be a VFIO mdev device, and set the
 * VFIO devices ops for it. This must be called from the create()
 * callback for VFIO mdev devices.
 */

?

> -void mdev_set_class(struct mdev_device *mdev, u16 id)
> +void mdev_set_vfio_ops(struct mdev_device *mdev,
> +		       const struct vfio_mdev_device_ops *vfio_ops)
>  {
>  	WARN_ON(mdev->class_id);
> -	mdev->class_id = id;
> +	mdev->class_id = MDEV_CLASS_ID_VFIO;
> +	mdev->device_ops = vfio_ops;
>  }
> -EXPORT_SYMBOL(mdev_set_class);
> +EXPORT_SYMBOL(mdev_set_vfio_ops);
> +
> +const void *mdev_get_dev_ops(struct mdev_device *mdev)
> +{
> +	return mdev->device_ops;
> +}
> +EXPORT_SYMBOL(mdev_get_dev_ops);
>  
>  struct device *mdev_dev(struct mdev_device *mdev)
>  {

(...)

The code change looks good to me; I'm just wondering if we should
introduce mdev_set_class() at all (see above).