From: Trond Myklebust <trond.myklebust@fys.uio.no>
Subject: Re: mtime not updated in client cache?
Date: Fri, 09 Dec 2005 09:16:23 -0500
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Cc: Vince Busam <vbusam@google.com>, nfs@lists.sourceforge.net
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To: Peter Staubach <staubach@redhat.com>
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On Fri, 2005-12-09 at 09:06 -0500, Peter Staubach wrote:
> Trond Myklebust wrote:
> 
> ><looks at code>
> >
> >Yep. Your code contains a wrong assumption: fflush() is not guaranteed
> >to immediately update mtime/ctime since it does not sync data to disk.
> >The same is true of the posix "write()" function.
> >
> >If you add the line fsync(fileno(fp)) after the call to fflush(), then
> >the mtime will be correctly updated.
> >
> 
> Perhaps I am missing something, but fsync(2) should not cause the 
> mtime/ctime
> to change.  The write(2) call should.  Sequences such as 
> stat(&a)/write()/stat(&b)
> should result b.st_mtime != a.st_mtime.

If you are caching the write on the client, then the server will not
update the mtime on the file.

OTOH, I do not like the idea of updating mtime on the client, since
there is no guarantee that the client and server are synchronised (you
can easily end up with the mtime jumping forwards and backwards).

One alternative would be to flush dirty data to the server on every call
to stat(), but that would slow it down considerably.

Cheers,
 Trond



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