Re: [PATCH V7 3/6] mdev: introduce device specific ops

[Alex Williamson]

On Mon,  4 Nov 2019 20:39:49 +0800
Jason Wang <jasowang@xxxxxxxxxx> 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.
> 
> Reviewed-by: Parav Pandit <parav@xxxxxxxxxxxx>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
>  .../driver-api/vfio-mediated-device.rst       | 35 +++++++++----
>  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                 | 25 ++++++++-
>  drivers/vfio/mdev/mdev_private.h              |  5 ++
>  drivers/vfio/mdev/vfio_mdev.c                 | 37 ++++++-------
>  include/linux/mdev.h                          | 43 ++++-----------
>  include/linux/mdev_vfio_ops.h                 | 52 +++++++++++++++++++
>  samples/vfio-mdev/mbochs.c                    | 20 ++++---
>  samples/vfio-mdev/mdpy.c                      | 20 ++++---
>  samples/vfio-mdev/mtty.c                      | 18 ++++---
>  13 files changed, 206 insertions(+), 100 deletions(-)
>  create mode 100644 include/linux/mdev_vfio_ops.h
> 
> diff --git a/Documentation/driver-api/vfio-mediated-device.rst b/Documentation/driver-api/vfio-mediated-device.rst
> index 6709413bee29..e35f1f8f946e 100644
> --- a/Documentation/driver-api/vfio-mediated-device.rst
> +++ b/Documentation/driver-api/vfio-mediated-device.rst
> @@ -152,15 +152,6 @@ 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
> -* read : read emulation callback
> -* write: write emulation callback
> -* mmap: mmap emulation callback
> -
>  A driver should use the mdev_parent_ops structure in the function call to
>  register itself with the mdev core driver::
>  
> @@ -172,10 +163,34 @@ that a driver should use to unregister itself with the mdev core driver::
>  
>  	extern void mdev_unregister_device(struct device *dev);
>  
> -It is also required to specify the class_id in create() callback through::
> +As multiple types of mediated devices may be supported, class id needs
> +to be specified in the create callback(). This could be done
> +explicitly for the device that does not use on mdev bus for its
> +operation through:
>  
>  	int mdev_set_class(struct mdev_device *mdev, u16 id);
>  
> +For the device that uses on the mdev bus for its operation, the class
> +should provide helper function to set class id and device specific
> +ops. E.g for vfio-mdev devices, the function to be called is::
> +
> +	int mdev_set_vfio_ops(struct mdev_device *mdev,
> +                              const struct mdev_vfio_device_ops *vfio_ops);
> +
> +The class id (set by this function to MDEV_CLASS_ID_VFIO) is used to
> +match a device with an mdev driver via its id table. The device
> +specific callbacks (specified in *vfio_ops) are obtainable via
> +mdev_get_vfio_ops() (for use by 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
> +
>  Mediated Device Management Interface Through sysfs
>  ==================================================
>  
> diff --git a/MAINTAINERS b/MAINTAINERS
> index cba1095547fd..f661d13344d6 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17121,6 +17121,7 @@ S:	Maintained
>  F:	Documentation/driver-api/vfio-mediated-device.rst
>  F:	drivers/vfio/mdev/
>  F:	include/linux/mdev.h
> +F:	include/linux/mdev_vfio_ops.h
>  F:	samples/vfio-mdev/
>  
>  VFIO PLATFORM DRIVER
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 6420f0dbd31b..662f3a672372 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -42,6 +42,7 @@
>  #include <linux/kvm_host.h>
>  #include <linux/vfio.h>
>  #include <linux/mdev.h>
> +#include <linux/mdev_vfio_ops.h>
>  #include <linux/debugfs.h>
>  
>  #include <linux/nospec.h>
> @@ -643,6 +644,8 @@ static void kvmgt_put_vfio_device(void *vgpu)
>  	vfio_device_put(((struct intel_vgpu *)vgpu)->vdev.vfio_device);
>  }
>  
> +static const struct mdev_vfio_device_ops intel_vfio_vgpu_dev_ops;
> +
>  static int intel_vgpu_create(struct kobject *kobj, struct mdev_device *mdev)
>  {
>  	struct intel_vgpu *vgpu = NULL;
> @@ -678,7 +681,7 @@ static int intel_vgpu_create(struct kobject *kobj, struct mdev_device *mdev)
>  		     dev_name(mdev_dev(mdev)));
>  	ret = 0;
>  
> -	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
> +	mdev_set_vfio_ops(mdev, &intel_vfio_vgpu_dev_ops);
>  out:
>  	return ret;
>  }
> @@ -1599,20 +1602,21 @@ static const struct attribute_group *intel_vgpu_groups[] = {
>  	NULL,
>  };
>  
> -static struct mdev_parent_ops intel_vgpu_ops = {
> -	.mdev_attr_groups       = intel_vgpu_groups,
> -	.create			= intel_vgpu_create,
> -	.remove			= intel_vgpu_remove,
> -
> +static const struct mdev_vfio_device_ops intel_vfio_vgpu_dev_ops = {
>  	.open			= intel_vgpu_open,
>  	.release		= intel_vgpu_release,
> -
>  	.read			= intel_vgpu_read,
>  	.write			= intel_vgpu_write,
>  	.mmap			= intel_vgpu_mmap,
>  	.ioctl			= intel_vgpu_ioctl,
>  };
>  
> +static struct mdev_parent_ops intel_vgpu_ops = {
> +	.mdev_attr_groups       = intel_vgpu_groups,
> +	.create			= intel_vgpu_create,
> +	.remove			= intel_vgpu_remove,
> +};
> +
>  static int kvmgt_host_init(struct device *dev, void *gvt, const void *ops)
>  {
>  	struct attribute **kvm_type_attrs;
> diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
> index cf2c013ae32f..fa473ded71c7 100644
> --- a/drivers/s390/cio/vfio_ccw_ops.c
> +++ b/drivers/s390/cio/vfio_ccw_ops.c
> @@ -12,6 +12,7 @@
>  
>  #include <linux/vfio.h>
>  #include <linux/mdev.h>
> +#include <linux/mdev_vfio_ops.h>
>  #include <linux/nospec.h>
>  #include <linux/slab.h>
>  
> @@ -110,6 +111,8 @@ static struct attribute_group *mdev_type_groups[] = {
>  	NULL,
>  };
>  
> +static const struct mdev_vfio_device_ops mdev_vfio_ops;
> +
>  static int vfio_ccw_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
>  {
>  	struct vfio_ccw_private *private =
> @@ -129,7 +132,7 @@ static int vfio_ccw_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
>  			   private->sch->schid.ssid,
>  			   private->sch->schid.sch_no);
>  
> -	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
> +	mdev_set_vfio_ops(mdev, &mdev_vfio_ops);
>  	return 0;
>  }
>  
> @@ -575,11 +578,7 @@ static ssize_t vfio_ccw_mdev_ioctl(struct mdev_device *mdev,
>  	}
>  }
>  
> -static const struct mdev_parent_ops vfio_ccw_mdev_ops = {
> -	.owner			= THIS_MODULE,
> -	.supported_type_groups  = mdev_type_groups,
> -	.create			= vfio_ccw_mdev_create,
> -	.remove			= vfio_ccw_mdev_remove,
> +static const struct mdev_vfio_device_ops mdev_vfio_ops = {
>  	.open			= vfio_ccw_mdev_open,
>  	.release		= vfio_ccw_mdev_release,
>  	.read			= vfio_ccw_mdev_read,
> @@ -587,6 +586,13 @@ static const struct mdev_parent_ops vfio_ccw_mdev_ops = {
>  	.ioctl			= vfio_ccw_mdev_ioctl,
>  };
>  
> +static const struct mdev_parent_ops vfio_ccw_mdev_ops = {
> +	.owner			= THIS_MODULE,
> +	.supported_type_groups  = mdev_type_groups,
> +	.create			= vfio_ccw_mdev_create,
> +	.remove			= vfio_ccw_mdev_remove,
> +};
> +
>  int vfio_ccw_mdev_reg(struct subchannel *sch)
>  {
>  	return mdev_register_device(&sch->dev, &vfio_ccw_mdev_ops);
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index 07c31070afeb..7bdc62393112 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -16,6 +16,7 @@
>  #include <linux/bitops.h>
>  #include <linux/kvm_host.h>
>  #include <linux/module.h>
> +#include <linux/mdev_vfio_ops.h>
>  #include <asm/kvm.h>
>  #include <asm/zcrypt.h>
>  
> @@ -321,6 +322,8 @@ static void vfio_ap_matrix_init(struct ap_config_info *info,
>  	matrix->adm_max = info->apxa ? info->Nd : 15;
>  }
>  
> +static const struct mdev_vfio_device_ops mdev_vfio_ops;
> +
>  static int vfio_ap_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
>  {
>  	struct ap_matrix_mdev *matrix_mdev;
> @@ -343,7 +346,7 @@ static int vfio_ap_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
>  	list_add(&matrix_mdev->node, &matrix_dev->mdev_list);
>  	mutex_unlock(&matrix_dev->lock);
>  
> -	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
> +	mdev_set_vfio_ops(mdev, &mdev_vfio_ops);
>  	return 0;
>  }
>  
> @@ -1281,15 +1284,18 @@ static ssize_t vfio_ap_mdev_ioctl(struct mdev_device *mdev,
>  	return ret;
>  }
>  
> +static const struct mdev_vfio_device_ops mdev_vfio_ops = {
> +	.open			= vfio_ap_mdev_open,
> +	.release		= vfio_ap_mdev_release,
> +	.ioctl			= vfio_ap_mdev_ioctl,
> +};
> +
>  static const struct mdev_parent_ops vfio_ap_matrix_ops = {
>  	.owner			= THIS_MODULE,
>  	.supported_type_groups	= vfio_ap_mdev_type_groups,
>  	.mdev_attr_groups	= vfio_ap_mdev_attr_groups,
>  	.create			= vfio_ap_mdev_create,
>  	.remove			= vfio_ap_mdev_remove,
> -	.open			= vfio_ap_mdev_open,
> -	.release		= vfio_ap_mdev_release,
> -	.ioctl			= vfio_ap_mdev_ioctl,
>  };
>  
>  int vfio_ap_mdev_register(void)
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index d23ca39e3be6..8d579d7ed82f 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -45,9 +45,10 @@ void mdev_set_drvdata(struct mdev_device *mdev, void *data)
>  }
>  EXPORT_SYMBOL(mdev_set_drvdata);
>  
> +

Extra whitespace

>  /* Specify the class for the mdev device, this must be called during
> - * create() callback.
> - */
> + * create() callback explicitly or implicity through the helpers

s/implicity/implicitly/

> + * provided by each class. */
>  void mdev_set_class(struct mdev_device *mdev, u16 id)
>  {
>  	WARN_ON(mdev->class_id);
> @@ -55,6 +56,26 @@ void mdev_set_class(struct mdev_device *mdev, u16 id)
>  }
>  EXPORT_SYMBOL(mdev_set_class);
>  
> +/* Specify the mdev device to be a VFIO mdev device, and set VFIO
> + * device ops for it. This must be called from the create() callback
> + * for VFIO mdev device.
> + */

Comment style.  Thanks,

Alex

> +void mdev_set_vfio_ops(struct mdev_device *mdev,
> +		       const struct mdev_vfio_device_ops *vfio_ops)
> +{
> +	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
> +	mdev->vfio_ops = vfio_ops;
> +}
> +EXPORT_SYMBOL(mdev_set_vfio_ops);
> +
> +/* Get the VFIO device ops for the mdev device. */
> +const struct mdev_vfio_device_ops *mdev_get_vfio_ops(struct mdev_device *mdev)
> +{
> +	WARN_ON(mdev->class_id != MDEV_CLASS_ID_VFIO);
> +	return mdev->vfio_ops;
> +}
> +EXPORT_SYMBOL(mdev_get_vfio_ops);
> +
>  struct device *mdev_dev(struct mdev_device *mdev)
>  {
>  	return &mdev->dev;
> diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
> index c65f436c1869..411227373625 100644
> --- a/drivers/vfio/mdev/mdev_private.h
> +++ b/drivers/vfio/mdev/mdev_private.h
> @@ -10,6 +10,8 @@
>  #ifndef MDEV_PRIVATE_H
>  #define MDEV_PRIVATE_H
>  
> +#include <linux/mdev_vfio_ops.h>
> +
>  int  mdev_bus_register(void);
>  void mdev_bus_unregister(void);
>  
> @@ -34,6 +36,9 @@ struct mdev_device {
>  	struct device *iommu_device;
>  	bool active;
>  	u16 class_id;
> +	union {
> +		const struct mdev_vfio_device_ops *vfio_ops;
> +	};
>  };
>  
>  #define to_mdev_device(dev)	container_of(dev, struct mdev_device, dev)
> diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c
> index a6641cd8b5a3..c01e2194e4b3 100644
> --- a/drivers/vfio/mdev/vfio_mdev.c
> +++ b/drivers/vfio/mdev/vfio_mdev.c
> @@ -14,6 +14,7 @@
>  #include <linux/slab.h>
>  #include <linux/vfio.h>
>  #include <linux/mdev.h>
> +#include <linux/mdev_vfio_ops.h>
>  
>  #include "mdev_private.h"
>  
> @@ -24,16 +25,16 @@
>  static int vfio_mdev_open(void *device_data)
>  {
>  	struct mdev_device *mdev = device_data;
> -	struct mdev_parent *parent = mdev->parent;
> +	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
>  	int ret;
>  
> -	if (unlikely(!parent->ops->open))
> +	if (unlikely(!ops->open))
>  		return -EINVAL;
>  
>  	if (!try_module_get(THIS_MODULE))
>  		return -ENODEV;
>  
> -	ret = parent->ops->open(mdev);
> +	ret = ops->open(mdev);
>  	if (ret)
>  		module_put(THIS_MODULE);
>  
> @@ -43,10 +44,10 @@ static int vfio_mdev_open(void *device_data)
>  static void vfio_mdev_release(void *device_data)
>  {
>  	struct mdev_device *mdev = device_data;
> -	struct mdev_parent *parent = mdev->parent;
> +	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
>  
> -	if (likely(parent->ops->release))
> -		parent->ops->release(mdev);
> +	if (likely(ops->release))
> +		ops->release(mdev);
>  
>  	module_put(THIS_MODULE);
>  }
> @@ -55,47 +56,47 @@ static long vfio_mdev_unlocked_ioctl(void *device_data,
>  				     unsigned int cmd, unsigned long arg)
>  {
>  	struct mdev_device *mdev = device_data;
> -	struct mdev_parent *parent = mdev->parent;
> +	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
>  
> -	if (unlikely(!parent->ops->ioctl))
> +	if (unlikely(!ops->ioctl))
>  		return -EINVAL;
>  
> -	return parent->ops->ioctl(mdev, cmd, arg);
> +	return ops->ioctl(mdev, cmd, arg);
>  }
>  
>  static ssize_t vfio_mdev_read(void *device_data, char __user *buf,
>  			      size_t count, loff_t *ppos)
>  {
>  	struct mdev_device *mdev = device_data;
> -	struct mdev_parent *parent = mdev->parent;
> +	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
>  
> -	if (unlikely(!parent->ops->read))
> +	if (unlikely(!ops->read))
>  		return -EINVAL;
>  
> -	return parent->ops->read(mdev, buf, count, ppos);
> +	return ops->read(mdev, buf, count, ppos);
>  }
>  
>  static ssize_t vfio_mdev_write(void *device_data, const char __user *buf,
>  			       size_t count, loff_t *ppos)
>  {
>  	struct mdev_device *mdev = device_data;
> -	struct mdev_parent *parent = mdev->parent;
> +	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
>  
> -	if (unlikely(!parent->ops->write))
> +	if (unlikely(!ops->write))
>  		return -EINVAL;
>  
> -	return parent->ops->write(mdev, buf, count, ppos);
> +	return ops->write(mdev, buf, count, ppos);
>  }
>  
>  static int vfio_mdev_mmap(void *device_data, struct vm_area_struct *vma)
>  {
>  	struct mdev_device *mdev = device_data;
> -	struct mdev_parent *parent = mdev->parent;
> +	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
>  
> -	if (unlikely(!parent->ops->mmap))
> +	if (unlikely(!ops->mmap))
>  		return -EINVAL;
>  
> -	return parent->ops->mmap(mdev, vma);
> +	return ops->mmap(mdev, vma);
>  }
>  
>  static const struct vfio_device_ops vfio_mdev_dev_ops = {
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index 78b69d09eb54..9e37506d1987 100644
> --- a/include/linux/mdev.h
> +++ b/include/linux/mdev.h
> @@ -10,7 +10,13 @@
>  #ifndef MDEV_H
>  #define MDEV_H
>  
> +#include <linux/types.h>
> +#include <linux/device.h>
> +#include <linux/mdev.h>
> +#include <uapi/linux/uuid.h>
> +
>  struct mdev_device;
> +struct mdev_vfio_device_ops;
>  
>  /*
>   * Called by the parent device driver to set the device which represents
> @@ -48,30 +54,7 @@ struct device *mdev_get_iommu_device(struct device *dev);
>   *			@mdev: mdev_device device structure which is being
>   *			       destroyed
>   *			Returns integer: success (0) or error (< 0)
> - * @open:		Open mediated device.
> - *			@mdev: mediated device.
> - *			Returns integer: success (0) or error (< 0)
> - * @release:		release mediated device
> - *			@mdev: mediated device.
> - * @read:		Read emulation callback
> - *			@mdev: mediated device structure
> - *			@buf: read buffer
> - *			@count: number of bytes to read
> - *			@ppos: address.
> - *			Retuns number on bytes read on success or error.
> - * @write:		Write emulation callback
> - *			@mdev: mediated device structure
> - *			@buf: write buffer
> - *			@count: number of bytes to be written
> - *			@ppos: address.
> - *			Retuns number on bytes written on success or error.
> - * @ioctl:		IOCTL callback
> - *			@mdev: mediated device structure
> - *			@cmd: ioctl command
> - *			@arg: arguments to ioctl
> - * @mmap:		mmap callback
> - *			@mdev: mediated device structure
> - *			@vma: vma structure
> + *
>   * Parent device that support mediated device should be registered with mdev
>   * module with mdev_parent_ops structure.
>   **/
> @@ -83,15 +66,6 @@ struct mdev_parent_ops {
>  
>  	int     (*create)(struct kobject *kobj, struct mdev_device *mdev);
>  	int     (*remove)(struct mdev_device *mdev);
> -	int     (*open)(struct mdev_device *mdev);
> -	void    (*release)(struct mdev_device *mdev);
> -	ssize_t (*read)(struct mdev_device *mdev, char __user *buf,
> -			size_t count, loff_t *ppos);
> -	ssize_t (*write)(struct mdev_device *mdev, const char __user *buf,
> -			 size_t count, loff_t *ppos);
> -	long	(*ioctl)(struct mdev_device *mdev, unsigned int cmd,
> -			 unsigned long arg);
> -	int	(*mmap)(struct mdev_device *mdev, struct vm_area_struct *vma);
>  };
>  
>  /* interface for exporting mdev supported type attributes */
> @@ -135,6 +109,9 @@ void *mdev_get_drvdata(struct mdev_device *mdev);
>  void mdev_set_drvdata(struct mdev_device *mdev, void *data);
>  const guid_t *mdev_uuid(struct mdev_device *mdev);
>  void mdev_set_class(struct mdev_device *mdev, u16 id);
> +void mdev_set_vfio_ops(struct mdev_device *mdev,
> +		       const struct mdev_vfio_device_ops *vfio_ops);
> +const struct mdev_vfio_device_ops *mdev_get_vfio_ops(struct mdev_device *mdev);
>  
>  extern struct bus_type mdev_bus_type;
>  
> diff --git a/include/linux/mdev_vfio_ops.h b/include/linux/mdev_vfio_ops.h
> new file mode 100644
> index 000000000000..317518f30621
> --- /dev/null
> +++ b/include/linux/mdev_vfio_ops.h
> @@ -0,0 +1,52 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * VFIO Mediated device definition
> + */
> +
> +#ifndef MDEV_VFIO_OPS_H
> +#define MDEV_VFIO_OPS_H
> +
> +#include <linux/mdev.h>
> +
> +/**
> + * struct mdev_vfio_device_ops - Structure to be registered for each
> + * mdev device to register the device to vfio-mdev module.
> + *
> + * @open:		Open mediated device.
> + *			@mdev: mediated device.
> + *			Returns integer: success (0) or error (< 0)
> + * @release:		release mediated device
> + *			@mdev: mediated device.
> + * @read:		Read emulation callback
> + *			@mdev: mediated device structure
> + *			@buf: read buffer
> + *			@count: number of bytes to read
> + *			@ppos: address.
> + *			Retuns number on bytes read on success or error.
> + * @write:		Write emulation callback
> + *			@mdev: mediated device structure
> + *			@buf: write buffer
> + *			@count: number of bytes to be written
> + *			@ppos: address.
> + *			Retuns number on bytes written on success or error.
> + * @ioctl:		IOCTL callback
> + *			@mdev: mediated device structure
> + *			@cmd: ioctl command
> + *			@arg: arguments to ioctl
> + * @mmap:		mmap callback
> + *			@mdev: mediated device structure
> + *			@vma: vma structure
> + */
> +struct mdev_vfio_device_ops {
> +	int     (*open)(struct mdev_device *mdev);
> +	void    (*release)(struct mdev_device *mdev);
> +	ssize_t (*read)(struct mdev_device *mdev, char __user *buf,
> +			size_t count, loff_t *ppos);
> +	ssize_t (*write)(struct mdev_device *mdev, const char __user *buf,
> +			 size_t count, loff_t *ppos);
> +	long	(*ioctl)(struct mdev_device *mdev, unsigned int cmd,
> +			 unsigned long arg);
> +	int	(*mmap)(struct mdev_device *mdev, struct vm_area_struct *vma);
> +};
> +
> +#endif
> diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
> index 115bc5074656..12963767ba37 100644
> --- a/samples/vfio-mdev/mbochs.c
> +++ b/samples/vfio-mdev/mbochs.c
> @@ -30,6 +30,7 @@
>  #include <linux/iommu.h>
>  #include <linux/sysfs.h>
>  #include <linux/mdev.h>
> +#include <linux/mdev_vfio_ops.h>
>  #include <linux/pci.h>
>  #include <linux/dma-buf.h>
>  #include <linux/highmem.h>
> @@ -516,6 +517,8 @@ static int mbochs_reset(struct mdev_device *mdev)
>  	return 0;
>  }
>  
> +static const struct mdev_vfio_device_ops mdev_vfio_ops;
> +
>  static int mbochs_create(struct kobject *kobj, struct mdev_device *mdev)
>  {
>  	const struct mbochs_type *type = mbochs_find_type(kobj);
> @@ -561,7 +564,7 @@ static int mbochs_create(struct kobject *kobj, struct mdev_device *mdev)
>  	mbochs_reset(mdev);
>  
>  	mbochs_used_mbytes += type->mbytes;
> -	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
> +	mdev_set_vfio_ops(mdev, &mdev_vfio_ops);
>  	return 0;
>  
>  err_mem:
> @@ -1419,12 +1422,7 @@ static struct attribute_group *mdev_type_groups[] = {
>  	NULL,
>  };
>  
> -static const struct mdev_parent_ops mdev_fops = {
> -	.owner			= THIS_MODULE,
> -	.mdev_attr_groups	= mdev_dev_groups,
> -	.supported_type_groups	= mdev_type_groups,
> -	.create			= mbochs_create,
> -	.remove			= mbochs_remove,
> +static const struct mdev_vfio_device_ops mdev_vfio_ops = {
>  	.open			= mbochs_open,
>  	.release		= mbochs_close,
>  	.read			= mbochs_read,
> @@ -1433,6 +1431,14 @@ static const struct mdev_parent_ops mdev_fops = {
>  	.mmap			= mbochs_mmap,
>  };
>  
> +static const struct mdev_parent_ops mdev_fops = {
> +	.owner			= THIS_MODULE,
> +	.mdev_attr_groups	= mdev_dev_groups,
> +	.supported_type_groups	= mdev_type_groups,
> +	.create			= mbochs_create,
> +	.remove			= mbochs_remove,
> +};
> +
>  static const struct file_operations vd_fops = {
>  	.owner		= THIS_MODULE,
>  };
> diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c
> index 665614574d50..50ee6c98b2af 100644
> --- a/samples/vfio-mdev/mdpy.c
> +++ b/samples/vfio-mdev/mdpy.c
> @@ -26,6 +26,7 @@
>  #include <linux/iommu.h>
>  #include <linux/sysfs.h>
>  #include <linux/mdev.h>
> +#include <linux/mdev_vfio_ops.h>
>  #include <linux/pci.h>
>  #include <drm/drm_fourcc.h>
>  #include "mdpy-defs.h"
> @@ -226,6 +227,8 @@ static int mdpy_reset(struct mdev_device *mdev)
>  	return 0;
>  }
>  
> +static const struct mdev_vfio_device_ops mdev_vfio_ops;
> +
>  static int mdpy_create(struct kobject *kobj, struct mdev_device *mdev)
>  {
>  	const struct mdpy_type *type = mdpy_find_type(kobj);
> @@ -269,7 +272,7 @@ static int mdpy_create(struct kobject *kobj, struct mdev_device *mdev)
>  	mdpy_reset(mdev);
>  
>  	mdpy_count++;
> -	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
> +	mdev_set_vfio_ops(mdev, &mdev_vfio_ops);
>  	return 0;
>  }
>  
> @@ -726,12 +729,7 @@ static struct attribute_group *mdev_type_groups[] = {
>  	NULL,
>  };
>  
> -static const struct mdev_parent_ops mdev_fops = {
> -	.owner			= THIS_MODULE,
> -	.mdev_attr_groups	= mdev_dev_groups,
> -	.supported_type_groups	= mdev_type_groups,
> -	.create			= mdpy_create,
> -	.remove			= mdpy_remove,
> +static const struct mdev_vfio_device_ops mdev_vfio_ops = {
>  	.open			= mdpy_open,
>  	.release		= mdpy_close,
>  	.read			= mdpy_read,
> @@ -740,6 +738,14 @@ static const struct mdev_parent_ops mdev_fops = {
>  	.mmap			= mdpy_mmap,
>  };
>  
> +static const struct mdev_parent_ops mdev_fops = {
> +	.owner			= THIS_MODULE,
> +	.mdev_attr_groups	= mdev_dev_groups,
> +	.supported_type_groups	= mdev_type_groups,
> +	.create			= mdpy_create,
> +	.remove			= mdpy_remove,
> +};
> +
>  static const struct file_operations vd_fops = {
>  	.owner		= THIS_MODULE,
>  };
> diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
> index 90da12ff7fd9..be476e7ad1f8 100644
> --- a/samples/vfio-mdev/mtty.c
> +++ b/samples/vfio-mdev/mtty.c
> @@ -27,6 +27,7 @@
>  #include <linux/ctype.h>
>  #include <linux/file.h>
>  #include <linux/mdev.h>
> +#include <linux/mdev_vfio_ops.h>
>  #include <linux/pci.h>
>  #include <linux/serial.h>
>  #include <uapi/linux/serial_reg.h>
> @@ -708,6 +709,8 @@ static ssize_t mdev_access(struct mdev_device *mdev, u8 *buf, size_t count,
>  	return ret;
>  }
>  
> +static const struct mdev_vfio_device_ops vfio_dev_ops;
> +
>  static int mtty_create(struct kobject *kobj, struct mdev_device *mdev)
>  {
>  	struct mdev_state *mdev_state;
> @@ -755,7 +758,7 @@ static int mtty_create(struct kobject *kobj, struct mdev_device *mdev)
>  	list_add(&mdev_state->next, &mdev_devices_list);
>  	mutex_unlock(&mdev_list_lock);
>  
> -	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
> +	mdev_set_vfio_ops(mdev, &vfio_dev_ops);
>  	return 0;
>  }
>  
> @@ -1388,6 +1391,14 @@ static struct attribute_group *mdev_type_groups[] = {
>  	NULL,
>  };
>  
> +static const struct mdev_vfio_device_ops vfio_dev_ops = {
> +	.open		= mtty_open,
> +	.release	= mtty_close,
> +	.read		= mtty_read,
> +	.write		= mtty_write,
> +	.ioctl		= mtty_ioctl,
> +};
> +
>  static const struct mdev_parent_ops mdev_fops = {
>  	.owner                  = THIS_MODULE,
>  	.dev_attr_groups        = mtty_dev_groups,
> @@ -1395,11 +1406,6 @@ static const struct mdev_parent_ops mdev_fops = {
>  	.supported_type_groups  = mdev_type_groups,
>  	.create                 = mtty_create,
>  	.remove			= mtty_remove,
> -	.open                   = mtty_open,
> -	.release                = mtty_close,
> -	.read                   = mtty_read,
> -	.write                  = mtty_write,
> -	.ioctl		        = mtty_ioctl,
>  };
>  
>  static void mtty_device_release(struct device *dev)