linux-ext4 - Re: Atomic non-durable file write API

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Message-ID: <20101223224309.GH18264@dastard>
Date:	Fri, 24 Dec 2010 09:43:09 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Olaf van der Spek <olafvdspek@...il.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: Atomic non-durable file write API

On Thu, Dec 23, 2010 at 04:49:53PM +0100, Olaf van der Spek wrote:
> On Sun, Dec 19, 2010 at 5:39 PM, Olaf van der Spek <olafvdspek@...il.com> wrote:
> > On Sat, Dec 18, 2010 at 11:15 PM, Calvin Walton <calvin.walton@...il.com> wrote:
> >> Hmm. I’m doing a little interpretation of what Olaf said here; but I
> >> think you may have misunderstood the question?
> >>
> >> He doesn’t care about whether or not the file is securely written to
> >> disk (durable); however he doesn’t want to see any partially written
> >> files. In other words, something like
> >>
> >>     1. Write to temp file
> >>     2. Rename temp file over original file
> >
> > Meta data, including file owner, should be preserved.
> > Ideally, no temp files should be visible either.
> >
> >> Where the rename is only committed to disk once the entire contents of
> >> the file have been written securely – whenever that may eventually
> >> happen.
> >>
> >> He doesn’t want to synchronously wait for the file to be written,
> >> because the new data isn’t particularly important. The only important
> >> thing is that the file either contains the old or new data after a
> >> filesystem crash; not incomplete data. So, it’s more of an ordering
> >> problem, I think? (Analogous to putting some sort of barrier between the
> >> file write/close and the file rename to maintain ordering.)
> >>
> >> Hopefully I’ve interpreted the original question correctly, because this
> >> is something I would find interesting as well.
> >
> > Yes, you did.
> 
> Somebody?

So you are looking for something like:

http://developer.apple.com/library/mac/#DOCUMENTATION/Darwin/Reference/ManPages/man2/exchangedata.2.html

?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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