From: Chuck Lever <chuck.lever@oracle.com>
Subject: "sync" mount option semantics
Date: Tue, 4 Mar 2008 18:15:25 -0500
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Cc: NFS list <linux-nfs@vger.kernel.org>
To: Trond Myklebust <trond.myklebust@fys.uio.no>
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Hi Trond-

I have kind of an academic question.

When an NFS file system is mounted with the "sync" option, only  
writes via sys_write appear to be affected.  Writes via mmap or pages  
dirtied via a loopback device are not affected at all.

Similarly, O_SYNC only appears to affect sys_write and not mmap or  
loopback.

Is this the desired behavior?  If so, why not include cached writes?   
Should we document this in nfs(5)?

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com