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Date: Wed, 7 Aug 2002 20:13:01 +0200
To: Gregory Giguashvili <Gregoryg@ParadigmGeo.com>
Cc: "Linux Kernel (E-mail)" <linux-kernel@vger.kernel.org>
Subject: RE: O_SYNC option doesn't work (2.4.18-3)
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From: Trond Myklebust <trond.myklebust@fys.uio.no>
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>>>>> " " == Gregory Giguashvili <Gregoryg@ParadigmGeo.com> writes:

     > Well, this is the way it's been working on all UN*X platforms I
     > know. In fact, we came across this problem with NFS clients
     > being unable to synchronize on Linux.

Sorry. AFAICS O_SYNC only affects writes (just like we do).

As for reads: all commercial NFS clients I know of will check data
cache consistency on open(). They will assume that they can cache
attributes and data as per the documentation in 'man 5 nfs' (although
you can turn this off by using the 'noac' mount option).

Furthermore, even with 'noac' they *all* have problems with races in
the sort of scenario you describe because there is no atomic
GETATTR+READ operation.

Bottom line: If you want the sort of data cache consistency you are
describing, you *have* to use file locking.

Cheers,
 Trond
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