From: Paul Clements <paul.clements@steeleye.com>
Subject: Re: [PATCH / RFC] nfs-utils: High Availability NFS
Date: Fri, 27 Aug 2004 09:13:06 -0400
Sender: nfs-admin@lists.sourceforge.net
Message-ID: <412F3362.5040707@steeleye.com>
References: <4124DB86.9060505@steeleye.com> <16677.22269.988036.787320@cse.unsw.edu.au> <412E1C10.5020703@steeleye.com> <20040827073049.GA23324@suse.de>
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Cc: Neil Brown <neilb@cse.unsw.edu.au>, nfs@lists.sourceforge.net
To: Olaf Kirch <okir@suse.de>
In-Reply-To: <20040827073049.GA23324@suse.de>
Errors-To: nfs-admin@lists.sourceforge.net

Hi,


Olaf Kirch wrote:

> I'm working on putting statd into the kernel, so I'm necessarily not
> too enthusiastic about adding external callouts to statd :)

With so many things moving out of the kernel to userland, it's 
surprising to see statd moving into the kernel. And it certainly does 
make modifications, such as this, much more difficult.

> On Thu, Aug 26, 2004 at 01:21:20PM -0400, Paul Clements wrote:
> 
>>statd events that trigger a callout:
>>-----------------------------------
>>add client to notify list (SM_MON) - triggers "add-client" callout
>>
>>delete client from notify list (SM_UNMON and SM_UNMONALL) - triggers 
>>"del-client" callout
> 
> 
> I think the same could be achieved by attaching a dnotify handler to
> the directory, and it would be compatible with a kernel level statd.

But the callout happens before statd replies to the client, so there's 
no chance that we lose any clients if there's a failure. If we use 
dnotify then we only find out there's been a change after the change has 
occurred, which means the client may have already gotten a reply saying 
he's been added to the notify list. If we get a failure at this point, 
we've lost a client, and upon failover the client's locks are no longer 
valid.

--
Paul


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