[Intel-gfx] [PATCH v4 15/19] vfio: Add cdev for vfio_device

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu at intel.com>
> Sent: Tuesday, February 21, 2023 11:48 AM
> 
> This allows user to directly open a vfio device w/o using the legacy
> container/group interface, as a prerequisite for supporting new iommu
> features like nested translation.
> 
> The device fd opened in this manner doesn't have the capability to access
> the device as the fops open() doesn't open the device until the successful
> BIND_IOMMUFD which be added in next patch.
> 
> With this patch, devices registered to vfio core have both group and device
> interface created.
> 
> - group interface : /dev/vfio/$groupID
> - device interface: /dev/vfio/devices/vfioX  (X is the minor number and
> 					      is unique across devices)
> 
> Given a vfio device the user can identify the matching vfioX by checking
> the sysfs path of the device. Take PCI device (0000:6a:01.0) for example,
> /sys/bus/pci/devices/0000\:6a\:01.0/vfio-dev/vfio0/dev contains the
> major:minor of the matching vfioX.
> 
> Userspace then opens the /dev/vfio/devices/vfioX and checks with fstat
> that the major:minor matches.
> 
> The vfio_device cdev logic in this patch:
> *) __vfio_register_dev() path ends up doing cdev_device_add() for each
>    vfio_device;
> *) vfio_unregister_group_dev() path does cdev_device_del();
> 
> Signed-off-by: Yi Liu <yi.l.liu at intel.com>

Reviewed-by: Kevin Tian <kevin.tian at intel.com>