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Date:   Mon, 10 Dec 2018 14:23:10 -0500
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Jeff Layton <jlayton@redhat.com>
Cc:     linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: listing knfsd-held locks and opens
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On Mon, Dec 10, 2018 at 01:12:31PM -0500, Jeff Layton wrote:
> On Mon, 2018-12-10 at 12:47 -0500, J. Bruce Fields wrote:
> > We've got a long-standing complaint that tools like lsof, when run on an
> > NFS server, overlook opens and locks held by NFS clients.
> > 
> > The information's all there, it's just a question of how to expose it.
> > 
> > Easiest might be a single flat file like /proc/locks, but I've always
> > hoped we could do something slightly more structured, using a
> > subdirectory per NFS client.
> > 
> > Jeff Layton looked into this several years ago.  I don't remember if
> > there was some particular issue or if he just got bogged down in VFS
> > details.
> > 
> 
> I think I had a patch that generated a single flat file for locks, but
> you wanted to present a directory or file per-client, and I just never
> got around to reworking the earlier patch.

Oh, OK, makes sense.

> That sounds like a great start. Some ideas:
> 
> The locks file could also list delegations and layouts, but it might be
> good to do them in separate files. That would make it cleaner to display
> info that is only relevant to those types (recall info, in particular).
> 
> You might also consider adding a v4-specific info file. Show things like
> "when was last lease renewal"?

Yes, good ideas.  I hope this could be expandable in such a way that we
don't need all of that at the start.

I also had some idea that we might eventually also benefit from some
two-way communication.  But the only idea I had there was some sort of
"destroy this client now" operation, which is probably less important
for NFSv4 state, since it gets cleaned up automatically on lease expiry.

--b.