RE: [RFC 02/20] vfio: Add device class for /dev/vfio/devices

[Tian, Kevin]

> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Wednesday, September 22, 2021 3:56 AM
> 
> On Sun, 19 Sep 2021 14:38:30 +0800
> Liu Yi L <yi.l.liu@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> >  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,
> 

This is also our concern. Thanks for confirming it. Appreciate if you
can help think out some better alternative to deal with it.

Thanks
Kevin