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

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Message-ID: <20190613171834.GE22901@ziepe.ca>
Date:   Thu, 13 Jun 2019 14:18:34 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dan Williams <dan.j.williams@...el.com>
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 09:25:54AM -0700, Dan Williams wrote:
> 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. 

In the first paragraph above where Ira is musing about 'close a
specific file', he is talking about the driver-device fd.

Ie unilaterally closing /dev/uverbs as a punishment for an application
that used leases wrong: ie that released its lease with the RDMA is
still ongoing. 

Jason