Florian Weimer wrote:
quoted text
> * Andrew Morton:
> 
>> I don't think it's a bug.  Sure, O_DIRECT is synchronous, but that's
>> because it is, err, direct.  Not because it provides extra data-integrity
>> guarantees.  If you want those guarantees, use O_SYNC as well.
> 
> This needs to be prominently documented.  Right now, it's far from clear
> that you need both O_DIRECT and O_SYNC.

It's certainly not a requirement for NFS.  O_DIRECT on NFS forces data 
to the server, which always updates a file's metadata on each write, 
including indirect blocks.