Re: NFS_UNSTABLE vs. FILE and DATA sync.

[Chuck Lever <chuck.lever@oracle.com>]

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Wim Colgate wrote:
> 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?

What behavior did you expect O_DIRECT + O_SYNC to provide?  O_DIRECT 
means "don't cache data" and O_SYNC means "make sure the data is flushed 
to the server's disk before each write() system call returns." 
Technically, you don't need NFS_FILE_SYNC writes to do either of those.

Which kernel are you testing?  The client's use of NFS_FILE_SYNC writes 
changed over time.

> -----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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