From: Sridhar Samudrala <sri@us.ibm.com>
Subject: Re: NFS file locking for clustered filesystems
Date: Wed, 11 Aug 2004 14:35:44 -0700 (PDT)
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Cc: Olaf Kirch <okir@suse.de>, nfsv4@linux-nfs.org, nfs@lists.sourceforge.net
To: Trond Myklebust <trond.myklebust@fys.uio.no>
In-Reply-To: <1092184994.5857.19.camel@lade.trondhjem.org>
Errors-To: nfs-admin@lists.sourceforge.net

On Tue, 10 Aug 2004, Trond Myklebust wrote:

> P=E5 ty , 10/08/2004 klokka 17:15, skreiv Sridhar Samudrala:
>
> > I gathered the following from your suggestions to make the cluster file=
system
> > process the lock/unlock calls asynchronously,
> >
> > NLM LOCK/UNLOCK Call on a file in a cluster filesystem exported from an=
 NFS
> > server will always respond with NLM LOCK/UNLOCK Reply with NLM_BLOCKED =
as the
> > status.
>
> No. That would break the spec. See:
>    http://www.opengroup.org/onlinepubs/9629799/NLM_LOCK.htm#tagcjh_11_11
>
> NLM_BLOCKED is only a valid response if the client actually asked for
> blocking behaviour.
>
> In the case where the server is not able to reply in a timely fashion (I
> would suggest a short timeout period of a few seconds) it should reply
> with LCK_DENIED. (Note that when I talk about a "short timeout period",
> I do not mean that lockd itself is allowed to block.)

So, in the case of a client which doesn't allow blocking, are you suggestin=
g
that the cluster filesystem to return LCK_BLOCKED immediately and start the
asynchrous call and return LCK_DENIED in a few seconds if it cannot complet=
e
the operation?

But i am not sure if we can handle this easily with the current design of
lockd. As soon as the lock operation returns LCK_BLOCKED, i think svc_send(=
) is
called from svc_process() which will send a reply with NLM_BLOCKED.

Thanks
Sridhar


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