On Fri, Aug 23, 2019 at 01:23:45PM +1000, Dave Chinner wrote:

quoted

But the fact that RDMA, and potentially others, can "pass the
pins" to other processes is something I spent a lot of time trying to work out.

There's nothing in file layout lease architecture that says you
can't "pass the pins" to another process.  All the file layout lease
requirements say is that if you are going to pass a resource for
which the layout lease guarantees access for to another process,
then the destination process already have a valid, active layout
lease that covers the range of the pins being passed to it via the
RDMA handle.

How would the kernel detect and enforce this? There are many ways to
pass a FD.

IMHO it is wrong to try and create a model where the file lease exists
independently from the kernel object relying on it. In other words the
IB MR object itself should hold a reference to the lease it relies
upon to function properly.

Then we don't have to wreck the unix FD model to fit this in.

Jason