From: "Wim Colgate" <Wim.Colgate@xensource.com>
Subject: Re: NFS_UNSTABLE vs. FILE and DATA sync.
Date: Mon, 6 Aug 2007 10:40:49 -0700
Message-ID: <A9AD3C3BCF83FD4182B7D4D99E37FAD836BEDD@exchrdm.ad.xensource.com>
References: <46B75B4E.8060000@redhat.com>
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Cc: nfs@lists.sourceforge.net
To: "Peter Staubach" <staubach@redhat.com>, <chuck.lever@oracle.com>
In-Reply-To: <46B75B4E.8060000@redhat.com>
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Interesting information.

Specifically I am trying to inject errors by manually (but politely)
bringing the NFS server down then up, then down (rinse and repeat ...)
while doing IO from a linux client. As mentioned the open file is
O_DIRECT and O_SYNC -- which I thought should mean either the data hits
the server's storage or I should get an error; and I'm more than happy
to deal with an IO error.

I'm confident the writes are less than wsize (4096 bytes to be precise).


Is there a 100% guaranteed method to get the behavior I thought O_DIRECT
and O_SYNC was providing?

Thanks,

Wim


-----Original Message-----
From: Peter Staubach [mailto:staubach@redhat.com] 
Sent: Monday, August 06, 2007 10:33 AM
To: chuck.lever@oracle.com
Cc: Wim Colgate; nfs@lists.sourceforge.net
Subject: Re: [NFS] NFS_UNSTABLE vs. FILE and DATA sync.

Chuck Lever wrote:
> Wim Colgate wrote:
>> If I have a soft mount, and open a file with O_DIRECT and O_SYNC, 
>> should I ever expect a callback (nfs_writeback_done) with a 
>> successful task->tk_status (i.e >= 0) with the committed state 
>> (resp->verf->committed) set to NFS_UNSTABLE?
>
> Yes, this can happen if the server decides to return NFS_UNSTABLE. 
> Rare, but possible.
>
>> A secondary question: if the above is expected, does this occur 
>> because someone is caching the write and is there a mechanism to 
>> disable this effect?
>
> Servers can return NFS_UNSTABLE to any WRITE request, so I can't think

> of a way this might be disabled. 

Actually, it would be a protocol error for a server to return
a commitment level less than was requested by the client.  The
server can return a greater commitment level, but not less than.

       ps

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