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

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Message-ID: <AANLkTi=BW85d6VpGAt0KaGES+4dRQmsvRyFamE=ChEXE@mail.gmail.com>
Date:	Thu, 23 Dec 2010 16:49:53 +0100
From:	Olaf van der Spek <olafvdspek@...il.com>
To:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: Atomic non-durable file write API

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?

Olaf
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