linux-kernel - Re: adding proper O_SYNC/O_DSYNC, was Re: O

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Message-ID: <20090829005921.GE8036@shareable.org>
Date:	Sat, 29 Aug 2009 01:59:21 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: adding proper O_SYNC/O_DSYNC, was Re: O_DIRECT and barriers

Jamie Lokier wrote:
> Ulrich Drepper wrote:
> > >  - O_RSYNC basically means we need to commit atime updates before a
> > >    read returns, right?
> > 
> > No, that's not it.
> > 
> > O_RSYNC on its own just means the data is successfully transferred to 
> > the calling process (always the case).
> > 
> > O_RSYNC|O_DSYNC means that if a read request hits data that is currently 
> > in a cache and not yet on the medium, then the write to medium is 
> > successful before the read succeeds.
> > 
> > O_RSYNC|O_SYNC means the same plus the integrity of file meta 
> > information (access time etc).
> 
> On several unixes, O_RSYNC means it will send the read to the
> hardware, not relying on the cache.  This can be used to verify the
> data which was written earlier, whether by O_DSYNC or fdatasync.

I'm sure I read that in a couple of OS man pages, but I can't find it
again.  Maybe it was something more obscure than the mainstream
unices; maybe I imagined it.  Ho hum.  For now, forget I said anythng.

-- Jamie
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