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Date:   Wed, 7 Oct 2020 11:17:21 -0400
From:   "'J. Bruce Fields'" <bfields@fieldses.org>
To:     Frank Filz <ffilzlnx@mindspring.com>
Cc:     'Kenneth Johansson' <ken@kenjo.org>,
        'Patrick Goetz' <pgoetz@math.utexas.edu>,
        linux-nfs@vger.kernel.org
Subject: Re: nfs home directory and google chrome.
Message-ID: <20201007151721.GD23452@fieldses.org>
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On Wed, Oct 07, 2020 at 07:34:27AM -0700, Frank Filz wrote:
> > -----Original Message----- From: J. Bruce Fields
> > [mailto:bfields@fieldses.org] Maybe I overlooked the obvious: if
> > Chrome holds a lock on that file when you suspend, and if you stay
> > in suspend for longer than the NFSv4 lease time (default 90
> > seconds), then the client will lose its lease, hence any file locks.
> > I think these days the client then returns EIO on any further IO to
> > that file descriptor.
> > 
> > Maybe there's some way to turn off that locking as a workaround.
> > 
> > The simplest thing we can do to help might be implementing
> > "courteous server" behavior: instead of automatically removing locks
> > after a client's lease expires, it can wait until there's an actual
> > lock conflict.  That might be enough for your case.
> > 
> > There's been a little planning done and it's not a big project, but
> > I don't think it's actually at the top of anyone's todo list right
> > now, so I'm not sure when that will get done.
> 
> I've had courtesy locks on my back burner for Ganesha though I hadn't
> thought about that there might actually be an important practical
> issue. Does any other server implement them? If we suggest this as a
> solution to the Chrome suspend issue, it might be good to assure that
> the major server vendors implement this.
> 
> There is a problem with the courtesy locks for this solution though...
> The clientid is still going to be expired, and the locks are
> associated with the clientid, so unless we allow courtesy
> re-instatement of expired clientids, courtesy locks don't actually
> solve the problem...

The server's not required to expire the clientid when the lease expires.
A server that chooses to be "courteous" can let it hang around.

As a first implementation our server would probably wait until there's a
lock conflict, then destroy all the client's state.  But we could also
choose to revoke only those locks we have to.  The client uses
TEST_STATEID, I think, to sort out what's happened in that case.

I believe the Linux client implements all of this.  I'm not sure about
the status of other servers.

--b.