You can’t send a notification without having some memory of the fact that a blocking lock was requested. I think the notification is just a hint that the lock might be available, so you could just remember the clients that were looking for the lock and send out notifications and erase their “wait”. The lock would go to whoever asked for it next but the notification can short cut the polling delay the client otherwise has to use. I suppose you don’t have to put any kind of courtesy hold on the lock and just use the notifications. In any case there is still a resource that must be time managed. And it does require at least the lock being held momentarily in the back end unless the backend can also support lock availability notification (GPFS does have a notify upcall but I don’t know if there’s a way to ask GPFS just for a notify instead of a grant).

Frank

From: Malahal Naineni [mailto:malahal@gmail.com]
Sent: Wednesday, July 1, 2020 12:08 PM
To: Frank Filz <ffilzlnx@mindspring.com>
Cc: nfs-ganesha <devel@lists.nfs-ganesha.org>
Subject: Re: [NFS-Ganesha-Devel] Re: Callbacks supported with 4.1

I meant to say "no need to put them in a list in a conflict case" 

On Thu, Jul 2, 2020 at 12:36 AM Malahal Naineni <malahal@gmail.com> wrote:

Since we don't implement callbacks or fairness, we could just drop locks of type STATE_NFSV4_BLOCKING? The current code might be there to implement callback in future though, just trying to understand the code.

Regards, Malahal.

On Thu, Jul 2, 2020 at 12:10 AM Frank Filz <ffilzlnx@mindspring.com> wrote:

Yea, the notify lock callback is not supported, that would take some effort to implement non-blocking locks for NFS v4.1 which is complicated in that I'm not sure if the callback is a guaranteed deal, that the client will send some kind of cancellation if it gives up waiting for a blocked lock, If not, then we need to time out 4.x blocked locks. We also have to make them provisional until the client actually comes back with a new lock request, which means they COULD be handed out to another client in the meantime. This provisional (or courtesy) behavior may be hard to assure in a cluster or even a single node where there are other processes using locking on the same file system (since the courtesy lock would be a normal held lock on the backend - Ganesha can only give a conflicting lock out and cancel the courtesy lock for locks that come through that Ganesha instance).

Frank

> -----Original Message-----
> From: Daniel Gryniewicz [mailto:dang@redhat.com]
> Sent: Wednesday, July 1, 2020 7:21 AM
> To: devel@lists.nfs-ganesha.org
> Subject: [NFS-Ganesha-Devel] Re: Callbacks supported with 4.1
>
> It appears the implemented callbacks are layout recall, device notify, delegation
> recall, and getattr.  You can check the callpoints of
> nfs_rpc_cb_single() to see which callbacks are sent.
>
> Daniel
>
> On 7/1/20 9:13 AM, Trishali Nayar wrote:
> > Hi all,
> >
> > Recently while doing some testing we observed that CB_NOTIFY_LOCK
> > callback does not seem to supported by Ganesha. Is that understanding
> correct?
> >
> > Also, any insights on the 4.1 callbacks that we do support, would be
> > good to know. The RFC mentions quite a few of them.
> >
> > Thanks and regards,
> > Trishali.
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > Trishali Nayar
> > IBM Systems
> > ETZ, Pune.
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> >
> > _______________________________________________
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> >
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