> 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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