Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal

From: Dan Williams
Date: Thu Jun 13 2019 - 12:31:02 EST

On Thu, Jun 13, 2019 at 8:14 AM Jason Gunthorpe <jgg@xxxxxxxx> wrote:
> On Wed, Jun 12, 2019 at 06:14:46PM -0700, Dan Williams wrote:
> > > Effectively, we would need a way for an admin to close a specific file
> > > descriptor (or set of fds) which point to that file. AFAIK there is no way to
> > > do that at all, is there?
> >
> > Even if there were that gets back to my other question, does RDMA
> > teardown happen at close(fd), or at final fput() of the 'struct
> > file'?
> AFAIK there is no kernel side driver hook for close(fd).
> rdma uses a normal chardev so it's lifetime is linked to the file_ops
> release, which is called on last fput. So all the mmaps, all the dups,
> everything must go before it releases its resources.

Oh, I must have missed where this conversation started talking about
the driver-device fd. I thought we were talking about the close /
release of the target file that is MAP_SHARED for the memory
registration. A release of the driver fd is orthogonal to coordinating
/ signalling actions relative to the leased file.