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SubjectRe: [RFC 02/20] vfio: Add device class for /dev/vfio/devices
On Sun, 19 Sep 2021 14:38:30 +0800
Liu Yi L <yi.l.liu@intel.com> wrote:

> This patch introduces a new interface (/dev/vfio/devices/$DEVICE) for
> userspace to directly open a vfio device w/o relying on container/group
> (/dev/vfio/$GROUP). Anything related to group is now hidden behind
> iommufd (more specifically in iommu core by this RFC) in a device-centric
> manner.
>
> In case a device is exposed in both legacy and new interfaces (see next
> patch for how to decide it), this patch also ensures that when the device
> is already opened via one interface then the other one must be blocked.
>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> ---
> drivers/vfio/vfio.c | 228 +++++++++++++++++++++++++++++++++++++++----
> include/linux/vfio.h | 2 +
> 2 files changed, 213 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 02cc51ce6891..84436d7abedd 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
...
> @@ -2295,6 +2436,52 @@ static struct miscdevice vfio_dev = {
> .mode = S_IRUGO | S_IWUGO,
> };
>
> +static char *vfio_device_devnode(struct device *dev, umode_t *mode)
> +{
> + return kasprintf(GFP_KERNEL, "vfio/devices/%s", dev_name(dev));
> +}

dev_name() doesn't provide us with any uniqueness guarantees, so this
could potentially generate naming conflicts. The similar scheme for
devices within an iommu group appends an instance number if a conflict
occurs, but that solution doesn't work here where the name isn't just a
link to the actual device. Devices within an iommu group are also
likely associated within a bus_type, so the potential for conflict is
pretty negligible, that's not the case as vfio is adopted for new
device types. Thanks,

Alex

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