Re: [nfsv4] "Courtesy locks"

[Mike Mackovitch <[e-mail]>]

On Mon, Sep 13, 2010 at 07:38:38PM -0400, Rick Macklem wrote:
> > 
> > For the Mac OS X NFSv4 client:
> > 
> > > C1) When you get NFS4ERR_EXPIRED, what happens?
> > >
> > >     a) Assume all locks associated with lease have been released
> > >        that the client needs to create a new clientid?
> > >     b) Assume that it means one or more locks have been lost and
> > >        the client needs to determine what as gone and which are
> > >        still valid.
> > 
> > (b)
> > 
> > Upon receipt of NFS4ERR_EXPIRED the client will enter recovery mode
> > where we will attempt to reclaim all opens, all locks and delegated
> > state (if we didn't have non-delegated state that already covered it)
> > and drop/return any lingering delegations we had.
> 
> The FreeBSD8 server will only allow reclaim Ops during the grace
> period right after a reboot. It will return NFS4ERR_NO_GRACE for
> all reclaim Ops (Open with Claim_previous or Lock with the reclaim
> flag true) received outside of this grace period.
> 
> Do other servers allow this? (I thought the above was required
> behaviour?)

I'm not currently working on any NFSv4 server implementation, so I
can't answer your question.  :-)

But if the server is not allowed to process reclaim ops outside the
grace period then there's no hope of nicely handling the case where
the server's grace period passes before the client gets a chance to
reconnect to the server.

In the context of "courtesy locks" I don't think it makes any sense
for a server to keep the state around if it's going to tell the client
that the state expired but not allow the state to be reclaimed.
(Wasn't the point of the "courtesy" to allow them to be reclaimed if
there hadn't been any contention?)

Anyway, I'm simply coding our client to try to allow it to recover as
much state as the server will allow.

--macko