simplify the mdev interface v6

[Christoph Hellwig]

On Tue, Jul 19, 2022 at 10:41:49PM -0400, Eric Farman wrote:
> I suspect the second item (or something similar) is needed anyway,
> because Alex' tree + this series crashes frequently in (usually)
> mdev_remove. I haven't found an explanation for how we get in this
> state, but admittedly didn't spent a lot of time on them since the
> proposed changes to struct subchannel are a non-starter. The other
> crashes were always in something that's almost certainly a victim of
> something else, like kmalloc-related stuff in net/skbuff.
> 
> With the above, the crashes out of the vfio-ccw stack disappear, and
> things work a bit better. But those random kmalloc-related crashes
> persist. I guess I'll pick those up tomorrow.

Ok, I think I'll just wait for this to fan out, no need to rush in
known broken code.