Re: [PATCH 10/10] gfs2: nfs lock support for gfs2

[David Teigland <teigland@redhat.com>]

On Wed, Dec 06, 2006 at 04:23:47PM -0500, J. Bruce Fields wrote:
> On Wed, Dec 06, 2006 at 02:58:22PM -0600, David Teigland wrote:
> > On Wed, Dec 06, 2006 at 02:57:22PM -0500, J. Bruce Fields wrote:
> > > The more annoying problem is the need to cancel the GFS lock when
> > > fl_notify fails; is that something that it's possible for GFS to do?
> > > 
> > > It can fail because lockd has a timeout--it waits a few seconds for the
> > > callback, then gives up and returns a failure to the user.  If that
> > > happens after your userspace posix lock manager acquires the lock (but
> > > before fl_notify is called) then you've got to cancel it somehow.
> > 
> > I'd think we could just send an unlock for it at that point.  Set up an op
> > with GDLM_PLOCK_OP_UNLOCK and the same fields as the lock you're removing
> > and call send_op().  We probably need to flag this internal-unlock op so
> > that when the result arrives, device_write() delists and frees it itself.
> > 
> > (I wouldn't call this "canceling", I think of cancel as trying to force a
> > blocked request to return/fail prematurely.)
> 
> I call it a cancel because it should leave us in the same state we were
> in if we hadn't done the lock.  An unlock doesn't do that, because the
> original lock may have coalesced and/or downgraded existing locks.

Oh yeah, that's painful, I knew it sounded too easy.

Dave