Re: [Intel-gfx] [PATCH v3 00/15] Add vfio_device cdev for iommufd support

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 13 Feb 2023 07:13:33 -0800
Yi Liu <yi.l.liu@intel.com> wrote:

> Existing VFIO provides group-centric user APIs for userspace. Userspace
> opens the /dev/vfio/$group_id first before getting device fd and hence
> getting access to device. This is not the desired model for iommufd. Per
> the conclusion of community discussion[1], iommufd provides device-centric
> kAPIs and requires its consumer (like VFIO) to be device-centric user
> APIs. Such user APIs are used to associate device with iommufd and also
> the I/O address spaces managed by the iommufd.
> 
> This series first introduces a per device file structure to be prepared
> for further enhancement and refactors the kvm-vfio code to be prepared
> for accepting device file from userspace. Then refactors the vfio to be
> able to handle iommufd binding. This refactor includes the mechanism of
> blocking device access before iommufd bind, making vfio_device_open() be
> exclusive between the group path and the cdev path. Eventually, adds the
> cdev support for vfio device, and makes group infrastructure optional as
> it is not needed when vfio device cdev is compiled.
> 
> This is also a prerequisite for iommu nesting for vfio device[2].
> 
> The complete code can be found in below branch, simple test done with the
> legacy group path and the cdev path. Draft QEMU branch can be found at[3]
> 
> https://github.com/yiliu1765/iommufd/tree/vfio_device_cdev_v3
> (config CONFIG_IOMMUFD=y CONFIG_VFIO_DEVICE_CDEV=y)

Even using your branch[1], it seems like this has not been tested
except with cdev support enabled:

/home/alwillia/Work/linux.git/drivers/vfio/vfio_main.c: In function ‘vfio_device_add’:
/home/alwillia/Work/linux.git/drivers/vfio/vfio_main.c:253:48: error: ‘struct vfio_device’ has no member named ‘cdev’; did you mean ‘dev’?
  253 |                 ret = cdev_device_add(&device->cdev, &device->device);
      |                                                ^~~~
      |                                                dev
/home/alwillia/Work/linux.git/drivers/vfio/vfio_main.c: In function ‘vfio_device_del’:
/home/alwillia/Work/linux.git/drivers/vfio/vfio_main.c:262:42: error: ‘struct vfio_device’ has no member named ‘cdev’; did you mean ‘dev’?
  262 |                 cdev_device_del(&device->cdev, &device->device);
      |                                          ^~~~
      |                                          dev

Additionally the VFIO_ENABLE_GROUP Kconfig option doesn't make much
sense to me, it seems entirely redundant to VFIO_GROUP.

I think it's too late for v6.3 already, but given this needs at least
one more spin, let's set expectations of this being v6.4 material.  Thanks,

Alex

[1] 98491da60ae1 cover-letter: Add vfio_device cdev for iommufd support