linux-ext4 - Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal

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Date:   Thu, 13 Jun 2019 09:25:54 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        "Theodore Ts'o" <tytso@....edu>, Jeff Layton <jlayton@...nel.org>,
        Dave Chinner <david@...morbit.com>,
        Matthew Wilcox <willy@...radead.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal

On Thu, Jun 13, 2019 at 8:14 AM Jason Gunthorpe <jgg@...pe.ca> 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.