Re: [PATCH 2/6] mdev: introduce device specific ops

[Jason Wang]

On 2019/9/24 äå6:59, Parav Pandit wrote:
>
>> -----Original Message-----
>> From: Jason Wang <jasowang@xxxxxxxxxx>
>> Sent: Monday, September 23, 2019 8:03 AM
>> To: kvm@xxxxxxxxxxxxxxx; linux-s390@xxxxxxxxxxxxxxx; linux-
>> kernel@xxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; intel-
>> gfx@xxxxxxxxxxxxxxxxxxxxx; intel-gvt-dev@xxxxxxxxxxxxxxxxxxxxx;
>> kwankhede@xxxxxxxxxx; alex.williamson@xxxxxxxxxx; mst@xxxxxxxxxx;
>> tiwei.bie@xxxxxxxxx
>> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx;
>> cohuck@xxxxxxxxxx; maxime.coquelin@xxxxxxxxxx;
>> cunming.liang@xxxxxxxxx; zhihong.wang@xxxxxxxxx;
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>> lingshan.zhu@xxxxxxxxx; Ido Shamay <idos@xxxxxxxxxxxx>;
>> eperezma@xxxxxxxxxx; lulu@xxxxxxxxxx; Parav Pandit
>> <parav@xxxxxxxxxxxx>; Jason Wang <jasowang@xxxxxxxxxx>
>> Subject: [PATCH 2/6] mdev: introduce device specific ops
>>
>> 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.
>> Follow the class id support by previous patch, this patch introduces device
>> specific ops pointer inside parent ops which points to device specific ops (e.g
>> vfio ops). This allows the future drivers like virtio-mdev to implement its own
>> device specific ops.
>>
>> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
>> ---
>>  .../driver-api/vfio-mediated-device.rst       |  4 +-
>>  MAINTAINERS                                   |  1 +
>>  drivers/gpu/drm/i915/gvt/kvmgt.c              | 15 +++---
>>  drivers/s390/cio/vfio_ccw_ops.c               | 15 ++++--
>>  drivers/s390/crypto/vfio_ap_ops.c             | 11 ++--
>>  drivers/vfio/mdev/vfio_mdev.c                 | 31 ++++++-----
>>  include/linux/mdev.h                          | 36 ++-----------
>>  include/linux/vfio_mdev.h                     | 53 +++++++++++++++++++
>>  samples/vfio-mdev/mbochs.c                    | 17 +++---
>>  samples/vfio-mdev/mdpy.c                      | 17 +++---
>>  samples/vfio-mdev/mtty.c                      | 15 ++++--
>>  11 files changed, 138 insertions(+), 77 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 0e052072e1d8..3ab00e48212f 100644
>> --- a/Documentation/driver-api/vfio-mediated-device.rst
>> +++ b/Documentation/driver-api/vfio-mediated-device.rst
>> @@ -152,7 +152,9 @@ 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:
>> +The device specific callbacks are referred through device_ops pointer
>> +in mdev_parent_ops. For vfio-mdev device, its callbacks in device_ops
>> +are as follows:
>>
>>  * open: open callback of mediated device
>>  * close: close callback of mediated device diff --git a/MAINTAINERS
>> b/MAINTAINERS index b2326dece28e..89832b316500 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -17075,6 +17075,7 @@ S:	Maintained
>>  F:	Documentation/driver-api/vfio-mediated-device.rst
>>  F:	drivers/vfio/mdev/
>>  F:	include/linux/mdev.h
>> +F:	include/linux/vfio_mdev.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 19d51a35f019..8ea86b1e69f1 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/vfio_mdev.h>
>>  #include <linux/debugfs.h>
>>
>>  #include <linux/nospec.h>
>> @@ -1600,20 +1601,22 @@ 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 struct vfio_mdev_parent_ops intel_vfio_vgpu_ops = {
> Naming it with _dev prefix as intel_vfio_vgpu_dev_ops is better to differentiate with parent_ops.


Ok.


>>  	.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,
>> +	.device_ops	        = &intel_vfio_vgpu_ops,
>> +};
>> +
>>  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 246ff0f80944..02122bbc213e 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/vfio_mdev.h>
>>  #include <linux/nospec.h>
>>  #include <linux/slab.h>
>>
>> @@ -574,11 +575,7 @@ 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 vfio_mdev_parent_ops vfio_mdev_ops = {
>>  	.open			= vfio_ccw_mdev_open,
>>  	.release		= vfio_ccw_mdev_release,
>>  	.read			= vfio_ccw_mdev_read,
>> @@ -586,6 +583,14 @@ 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,
>> +	.device_ops		= &vfio_mdev_ops,
>> +};
>> +
>>  int vfio_ccw_mdev_reg(struct subchannel *sch)  {
>>  	return mdev_register_vfio_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 7487fc39d2c5..4251becc7a6d 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/vfio_mdev.h>
>>  #include <asm/kvm.h>
>>  #include <asm/zcrypt.h>
>>
>> @@ -1280,15 +1281,19 @@ static ssize_t vfio_ap_mdev_ioctl(struct
>> mdev_device *mdev,
>>  	return ret;
>>  }
>>
>> +static const struct vfio_mdev_parent_ops vfio_mdev_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,
>> +	.device_ops		= &vfio_mdev_ops,
>>  };
>>
>>  int vfio_ap_mdev_register(void)
>> diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c
>> index fd2a4d9a3f26..d23c9f58c84f 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/vfio_mdev.h>
>>
>>  #include "mdev_private.h"
>>
>> @@ -25,15 +26,16 @@ static int vfio_mdev_open(void *device_data)  {
>>  	struct mdev_device *mdev = device_data;
>>  	struct mdev_parent *parent = mdev->parent;
>> +	const struct vfio_mdev_parent_ops *ops = parent->ops->device_ops;
>>  	int ret;
>>
>> -	if (unlikely(!parent->ops->open))
>> +	if (unlikely(!ops->open))
>>  		return -EINVAL;
>>
> device_ops is optional and can be NULL for mdev devices which are not required to be mapped via vfio.
> So please change to,
>
> If (!ops || !ops->open)
> 	return -EINVAL;
>
> and rest of the below places.


My understanding is vfio_mdev can not talk to non vfio mdev device with
the help of class id.

Thanks


>
>>  	if (!try_module_get(THIS_MODULE))
>>  		return -ENODEV;
>>
>> -	ret = parent->ops->open(mdev);
>> +	ret = ops->open(mdev);
>>  	if (ret)
>>  		module_put(THIS_MODULE);
>>
>> @@ -44,9 +46,10 @@ static void vfio_mdev_release(void *device_data)  {
>>  	struct mdev_device *mdev = device_data;
>>  	struct mdev_parent *parent = mdev->parent;
>> +	const struct vfio_mdev_parent_ops *ops = parent->ops->device_ops;
>>
>> -	if (likely(parent->ops->release))
>> -		parent->ops->release(mdev);
>> +	if (likely(ops->release))
>> +		ops->release(mdev);
>>
>>  	module_put(THIS_MODULE);
>>  }
>> @@ -56,11 +59,12 @@ static long vfio_mdev_unlocked_ioctl(void
>> *device_data,  {
>>  	struct mdev_device *mdev = device_data;
>>  	struct mdev_parent *parent = mdev->parent;
>> +	const struct vfio_mdev_parent_ops *ops = parent->ops->device_ops;
>>
>> -	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, @@ -68,11
>> +72,12 @@ static ssize_t vfio_mdev_read(void *device_data, char __user *buf,
>> {
>>  	struct mdev_device *mdev = device_data;
>>  	struct mdev_parent *parent = mdev->parent;
>> +	const struct vfio_mdev_parent_ops *ops = parent->ops->device_ops;
>>
>> -	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, @@
>> -80,22 +85,24 @@ static ssize_t vfio_mdev_write(void *device_data, const char
>> __user *buf,  {
>>  	struct mdev_device *mdev = device_data;
>>  	struct mdev_parent *parent = mdev->parent;
>> +	const struct vfio_mdev_parent_ops *ops = parent->ops->device_ops;
>>
>> -	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 vfio_mdev_parent_ops *ops = parent->ops->device_ops;
>>
>> -	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
>> 3ebae310f599..fa167bcb81e1 100644
>> --- a/include/linux/mdev.h
>> +++ b/include/linux/mdev.h
>> @@ -48,30 +48,8 @@ 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
>> + * @device_ops:         Device specific emulation callback.
>> + *
>>   * Parent device that support mediated device should be registered with mdev
>>   * module with mdev_parent_ops structure.
>>   **/
>> @@ -83,15 +61,7 @@ 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);
>> +	const void *device_ops;
>>  };
>>
>>  /* interface for exporting mdev supported type attributes */ diff --git
>> a/include/linux/vfio_mdev.h b/include/linux/vfio_mdev.h new file mode
>> 100644 index 000000000000..0c1b34f98f5d
>> --- /dev/null
>> +++ b/include/linux/vfio_mdev.h
>> @@ -0,0 +1,53 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * VFIO Mediated device definition
>> + */
>> +
>> +#ifndef VFIO_MDEV_H
>> +#define VFIO_MDEV_H
>> +
>> +#include <linux/types.h>
>> +#include <linux/mdev.h>
>> +
>> +/**
>> + * struct vfio_mdev_parent_ops - Structure to be registered for each
>> + * parent 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 vfio_mdev_parent_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
>> 71a4469be85d..107cc30d0f45 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/vfio_mdev.h>
>>  #include <linux/pci.h>
>>  #include <linux/dma-buf.h>
>>  #include <linux/highmem.h>
>> @@ -1418,12 +1419,7 @@ 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 vfio_mdev_parent_ops vfio_mdev_ops = {
>>  	.open			= mbochs_open,
>>  	.release		= mbochs_close,
>>  	.read			= mbochs_read,
>> @@ -1432,6 +1428,15 @@ 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,
>> +	.device_ops		= &vfio_mdev_ops,
>> +};
>> +
>>  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
>> d3029dd27d91..2cd2018a53f9 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/vfio_mdev.h>
>>  #include <linux/pci.h>
>>  #include <drm/drm_fourcc.h>
>>  #include "mdpy-defs.h"
>> @@ -725,12 +726,7 @@ 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 vfio_mdev_parent_ops vfio_mdev_ops = {
>>  	.open			= mdpy_open,
>>  	.release		= mdpy_close,
>>  	.read			= mdpy_read,
>> @@ -739,6 +735,15 @@ 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,
>> +	.device_ops		= &vfio_mdev_ops,
>> +};
>> +
>>  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
>> 744c88a6b22c..e427425b5daf 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/vfio_mdev.h>
>>  #include <linux/pci.h>
>>  #include <linux/serial.h>
>>  #include <uapi/linux/serial_reg.h>
>> @@ -1410,6 +1411,14 @@ static struct attribute_group *mdev_type_groups[]
>> = {
>>  	NULL,
>>  };
>>
>> +static const struct vfio_mdev_parent_ops vfio_mdev_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,
>> @@ -1417,11 +1426,7 @@ 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,
>> +	.device_ops             = &vfio_mdev_ops,
>>  };
>>
>>  static void mtty_device_release(struct device *dev)
>> --
>> 2.19.1